Heating-ventilation-air-conditioning Facility Mgnt.pdf

PRIYA KANWAR; VARINDER TAPRIAL

HEATING, VENTILATION & AIR-CONDITIONING Facility Management



VARINDER TAPRIAL, PRIYA KANWAR

HEATING, VENTILATION & AIR-CONDITIONING FACILITY MANAGEMENT

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Heating, Ventilation & Air-Conditioning: Facility Management 1st edition © 2018 Varinder Taprial, Priya Kanwar & bookboon.com ISBN 978-87-403-2537-9

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HEATING, VENTILATION & AIR-CONDITIONING: FACILITY MANAGEMENT

Contents

CONTENTS

About the Authors

6

1 Introduction

8

2 Fundamentals of HVAC Systems

10

2.1

Sources of Heat Gain

10

2.2

Sources of Humidity

11

2.3

Sources of Impurities

11

2.4

The Concept of Heat Exchange

12

2.5

Types of HVAC Systems

13

3

Heating Systems

16

3.1

Furnace Based Heating Systems

16

3.2

Boiler Based Heating Systems

20

3.3

Heat Pump

24

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HEATING, VENTILATION & AIR-CONDITIONING: FACILITY MANAGEMENT

Contents

4

Ventilation Systems

29

4.1

Air Handling Unit (AHU)

29

4.2

Fan Coil Units (FCU)

33

4.3

Variable Air Volume (VAV) Systems

35

4.4

Chilled Beams

36

4.5

Ventilation Scrubbers

38

4.6

Exhaust Fans

38

4.7

Jet Fans

39

4.8

Maintenance of Ventilation Systems

40

5

Air-Conditioning Systems

41

5.1

Types of Cooling

41

5.2

Operating Principle of AC Systems

43

5.3

Components of Air-Conditioning System

46

5.4

Types of Air-Conditioning Units

49

6 Chillers

55

6.1 Chiller

56

6.2

Chilled Water Systems (CWS)

58

6.3

Cooling Towers

60

6.4

Maintenance of Chillers

62

7 Conclusion

63

8

65

Common Terminology

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HEATING, VENTILATION & AIR-CONDITIONING: FACILITY MANAGEMENT

About the Authors

ABOUT THE AUTHORS Varinder Taprial is an Electrical Engineer, graduated from the Naval College of Engineering. He served in the Indian Navy for 22 years wherein he gained vast experience in operations and maintenance management including related functions like procurement, finance, budgeting etc. it was during this time that he started dabbling in writing and ran his own blog covering a variety of topics. The writing bug had bitten him and in 2009 towards the end of his time with the Navy, he published a fiction book, “Enemy in the Ranks.” He then went on to share his knowledge and understanding of the Internet by publishing a book on Search Engine Optimization and another one on blogging. After seeking voluntary discharge from the Navy, Varinder spent the next couple of years working first with a construction company and then a wind energy company. During this time, the opportunity for writing for Bookboon came knocking and the result was three books published in the period 2011-12, all related to Internet and Social Media. Varinder then joined the Facilities Management vertical with an MNC which is one of the largest IPCs in the world. This seemed like a natural progression for him since just like a ship which is self-sustaining a building or a campus also needs to have the capability of sustaining by itself and provide a healthy, safe and secure environment to the occupants. During his association with the Facilities Management function, having handled large accounts and being the Engineering head for India, Varinder has picked up tremendous experience and developed expertise in all aspects of the function. Priya Kanwar graduated as a dentist from Goa University in 1991, and then worked as a Research Fellow for 2 years at the Post Graduate Institute of Medical Education & Research (PGIMER), Chandigarh; followed by 6 months as a Junior Resident. After her marriage to Varinder, who was in a transferrable job, she could not pursue her dentistry full time but kept herself occupied with jobs like a teacher in a primary school, as a sales executive for Citi bank Credit Cards, and also in a Family Clinic in different places across the country, gaining varied experience in multiple fields. During this time, she also pursued a writing course through Writing Bureau, London. From then on, her life turned to the path of a writing career. By 2006, Google had already established itself as the best search engine and the early social media sites were evolving. Taking advantage of the opportunity, Priya started contributing content to the various user generated content sites as well as started her own blog, Reading Café. By signing up with the Google Adsense program, she started generating revenue from her contributions.

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HEATING, VENTILATION & AIR-CONDITIONING: FACILITY MANAGEMENT

About the Authors

Having gained tremendous experience on the various platforms in the five active years of contributing content to various platforms online, she then decided to move on to sharing her knowledge and co-authored two books, namely “Beginner’s Guide to Blogging & Making Money Online” & “Search Engine Optimization – Handbook of Easy Tips Tools & Techniques” in the print format published by Pustak Mahal. Subsequently, she co-authored three more e-books, published by Bookboon in 2012, with her husband Varinder Taprial, namely: 1. Google Beyond Google 2. Business Blogs – The Best Social Media Tool for Businesses (Now 2nd Edition) 3. Understanding Social Media (Now 2nd Edition) Soon after the book on social media was published by Bookboon, they received an invitation from the Information & Broadcasting Ministry of India to contribute an article on Social Media for their quarterly magazine “Yojana.” Her article “Social Media - a Double-edged Sword” was selected & published in the May 2013 edition. Over the last year and few months, she was involved in the creation of an e-learning course in Facilities Management and created/finalized the content required for the same. Do check out our latest e-book published on this topic by Bookboon: 1. Technical Services in Facility Management Join us - Facebook Author Page Write to us – [email protected]

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HEATING, VENTILATION & AIR-CONDITIONING: FACILITY MANAGEMENT

Introduction

1 INTRODUCTION In our earlier book, “Technical Services in Facility Management” we covered the various aspects of management of Technical Services in facilities including the typical equipment fit and we explained that there is a plethora of civil, electrical and mechanical elements which need to be operated and maintained for the facility to serve its intended function. In this book, we will cover one of the most critical equipment in a facility i.e. Heating, Ventilation and Air-Conditioning (HVAC). Heating, Ventilation and Air-Conditioning or HVAC is a set of equipment designed to control and provide a consistent, conditioned indoor ambient environment viz temperature, humidity and air quality, in a facility to ensure comfort of the occupants as also for optimal performance of some equipment which may be sensitive to temperature. The quest for controlling the immediate environment for specific purposes including human comfort, which required certain conditions of temperature, humidity and contents of air, led to the birth of modern day air-conditioning as we know it. Varied temperatures due to geographical locations and during different seasons has been a challenge that mankind has been living with. The impact of extreme temperatures on human bodies is well known; frost bites, sun-strokes, dehydration, hypothermia, etc. are conditions we have all heard of and we also know that certain environmental conditions promote proliferation of disease causing pathogens (bacteria, fungi, mold/mildew, virus etc.). Hence, the correlation between the survivability of the human body to the temperature is well established. It stands to reason therefore that there are certain conditions which are predicated for higher efficiencies, aka productivity, of the human body. At the very essence of it, an HVAC system will comprise of a means to cool/heat a medium, allow for heat transfer to take place between the medium and air to be conditioned, and then throw the conditioned air into the target space. It is obvious that for the environment to be controlled and for the HVAC system to perform optimally, the conditioned air cannot be allowed to indiscriminately mix with the outside air and hence the space being conditioned will need to be enclosed. However, when we do that the indoor air will soon become cooler/warmer, contaminated and stale because of the following: 1. CO2 being released by the occupants and the odor caused by various activities inside the space. 2. Heat generated by occupants and other equipment like lighting, computers etc. 3. Heating/cooling of building envelope by the heat/cold outside. 4. Occupants bringing in dust, dirt and grime with shoes, sweat, etc. as also some disease carrying germs.

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Introduction

Now, in order to ensure that the quality of the indoor environment remains good, the HVAC systems will need to run continuously to maintain the temperature as well as keeping the air clean, uncontaminated and available in sufficient quantities. For this reason, it is required that fresh air is regularly introduced into the system to maintain the oxygen levels and remove the stale air, thereby providing proper ventilation. Additionally, the conditioned air would also need to be distributed proportionally across the space so that there are no hot/cold pockets, which requires what is known as “Air Balancing” to be done on the entire distribution system. Thus, a typical HVAC system will heat or cool the air as required, filter it, distribute it to the conditioned space, introduce fresh air inside the building, remove odor, CO2, and maintain temperature/humidity inside the facility. In modern day facilities which are completely air-conditioned, HVAC systems become a vital system since it can directly impact the quality of air that the occupants breathe and hence can have adverse effects on their health and productivity. In other words, an illmaintained or incorrectly operated system can cause sickness as well as facilitate spread of infectious diseases. Sick Building Syndrome (SBS) is a condition now widely accepted as an illness and is symptomized by headaches, nausea, irritation of skin/eyes and other respiratory problems. Poor ventilation, presence of chemical and biological contaminants are the main contributing factors for this illness. The HVAC system is spread across the entire facility and consumes a huge amount of utility power to function. In fact, for most office buildings the HVAC consumes 3540% of the total power consumed in the facility. The impact on occupant satisfaction is also evident from the recorded helpdesk data which shows that almost 50% of the total requests/complaints received from occupants pertain to temperature. Therefore, it is of paramount importance for the Facilities Managers to ensure that the HVAC system is always performing optimally. This not only reduces the spend on the utility bills but also ensures higher occupant satisfaction. HVAC systems come in various shapes, sizes and configurations starting from a simple window air conditioner to large centralized district heating/cooling systems. However, irrespective of the size and the type of air-conditioning, the basic principle of operation remains the same for all. In the following chapters of this book, we will understand the fundamental principle of operation of heating, cooling and ventilation systems, the types of systems and their utilization, maintenance aspects and the impact that the HVAC systems can have on a business.

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Fundamentals of HVAC Systems

2 FUNDAMENTALS OF HVAC SYSTEMS Heating, Ventilation and Air-Conditioning (HVAC, sometimes pronounced as ‘ech-vak’) system comprises of all electromechanical and passive systems that are used to maintain the thermal comfort and air quality in a building/facility. The primary objectives of the HVAC systems are as follows: 1. Control 2. Control 3. Control 4. Control

air temperature. humidity in air. the quality of air. movement and distribution of air.

It is important to understand that the temperature in a space can be controlled by either adding heat to or removing heat from the space. The local climatic conditions and the season will dictate whether heating, cooling or both are required. Now, as we have seen above, temperature is not the only parameter that impacts the thermal comfort of an individual, the humidity (moisture content) in the air also affects the perception of temperature and therefore it is necessary to control the humidity as well i.e. add moisture into the air (Humidification) or remove moisture from the air (De-humidification). It should be noted however, that it cannot be a one-time activity since in addition to the heat gain from external conditions, there are sources internally which continually add heat, moisture to the indoor air. Therefore, the process of conditioning air needs to be continuous. Moreover, since contaminants from external and internal sources can and do mix with the air, it is only deemed logical that the recirculated or fresh air is filtered and cleaned. The conditioned and cleaned air then needs to be delivered to various areas in specific volumes and at specific speeds to ensure mixing and even distribution without creating a high draft. This is achieved through a network of ducting with dampers and diffusers/grills. Let us now look at the sources of heat gain, humidity and impurities in a facility.

2.1 SOURCES OF HEAT GAIN While for heated buildings the internal heat loads actually do not have much impact on the temperature as they are actually helping heat the building, on the other hand, for the building that requires cooling, both the external and the internal heat sources put a higher load on the cooling requirements. The sources of heat can be:

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Fundamentals of HVAC Systems

• External – Heat transfer from Sun’s radiant heat or outdoors through the building structure, doors, roof etc. and glass windows/façade and infiltration of outdoor hot air to indoor space. • Internal – Heat generated by occupants, lighting loads, equipment and appliances like kitchen equipment, computers, printers, etc. The need for adding fresh air to maintain the air quality also brings in air at a higher ambient which needs to be cooled more than the recirculated internal air.

2.2 SOURCES OF HUMIDITY Air usually carries water vapor, the amount being dependent on the temperature of the air. The warmer the air, the more its capacity to hold water vapor. Too high or too low humidity can cause adverse effects on human comfort. Damp air, i.e. high humidity can cause conditions conducive to growth of fungi, bacteria and dust mites as also result in condensation which can potentially damage materials, equipment and promote bad odor. Very dry air also causes discomfort by causing dryness and itchiness in nose /skin and may cause static in the equipment/surfaces in addition to having potentially harmful impact on electronic/IT equipment. While the moisture in the outdoor air will depend on the outdoor atmosphere, the humidity in the indoor space is impacted by internal sources as well. These could be: 1. Water vapor exhaled by human occupants 2. Cooking and washing activities 3. Water seepages through building envelope 4. Plumbing leaks 5. Poor ventilation

2.3 SOURCES OF IMPURITIES 1. External - The quality of indoor air can get affected by the contaminants that can enter from outside the building in the form of: -- Industrial Pollutants (Emissions from nearby sources/buildings/industries) -- Vehicle exhaust -- Pollen, dust, fungal spores, pesticides used for pest control -- Contaminants from previous uses of the site or nearby locales (e.g. landfills)

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Fundamentals of HVAC Systems

2. Internal - Apart from the external factors that contribute to poor quality of air, there are several factors inside the building itself, that can contribute towards poor quality, which are as follows: -- Housekeeping chemicals and pesticides used inside the facility, -- Dust, grime from outside brought inside by occupant movements -- Dust or dirt in ductwork or other components left over from project stage, ineffective filtration, poor filter maintenance -- Smoking, cooking, improper venting of combustion products -- Body odor, cosmetic odor -- Microbiological growth in drip pans, humidifiers, ductwork, coils, soiled furnishings, carpets etc. -- CO2 exhaled by occupants SOURCES OF INDOOR POLLUTANTS Outdoor Air Pollutants Chemicals Released from Modern Building & Furnishing Materials

Molds & Bacteria

Chemicals from Cleaning Products

Cumbustion Gases from Fireplaces & Woodburning Stoves

Cigarette Smoke contains some 4,000 Chemicals Animal Hair & Dander

Chemical Fumes from Paints & Solvents

Carbon Monoxide Fumes from attached garage

Gases including Radon seeping through foundation Figure 2.1: Sources of Pollutants in a Building

2.4 THE CONCEPT OF HEAT EXCHANGE As we have learnt earlier, the maintenance of temperature in a space will require either removal or addition of heat from the space being conditioned. The same is achieved by what is known as heat transfer and the equipment used for such heat transfer is called a Heat Exchanger. When an object comes in contact with another object or surroundings which are at a different temperature, heat will flow so that the objects or their surroundings achieve the same temperature (thermal equilibrium). The heat always flows from the warmer object to the cooler object.

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Fundamentals of HVAC Systems

It is therefore clear, that if we were to pass air over a set of pipes containing hot fluid, the air will gain heat i.e. become hot and likewise if the pipes contained a cold fluid, the air would lose heat, i.e. become cold. In both case heat transfer is taking place. At the heart of the HVAC systems, it is this concept which is used to condition the air in both Heating and Air-Conditioning. For heating, the common medium used in the pipes is Water or Steam and for Air-Conditioning (Cooling), it could be water, glycol or a refrigerant (Refer Chapter 5 – What is a Refrigerant?).

Air Flow Concept of Heat Transfer

Hot Air Heat Gain

Pipes Containing Hot Fluid Warm Object

Cool Object Pipes Containing Cold Fluid

Heat always Flows from Hot to Cold

Heat Loss Air Flow

Cold Air

Figure 2.2: Concept of Heat Transfer

Systems in which the refrigerant picks up heat directly from the air to be cooled are known as Direct Expansion (DX) systems. However, if the refrigerant is used to cool another fluid, which is then used to gain heat from the air in the space to be cooled, then the cooling systems are called Chillers.

2.5 TYPES OF HVAC SYSTEMS Now that we have understood the basic concept of HVAC systems, it becomes easier to appreciate that the types of systems required in a particular facility will depend upon various factors like area to be conditioned (small/big, single room/floor, multiple floors/ rooms), end purpose (heating/cooling/ventilation), placement of different components etc. The type of units or systems used in smaller spaces would be Local Systems requiring maybe individual units which could be placed inside or close to the space being conditioned, whereas a larger space spread across multiple floors/rooms would require a Large Central System with elaborate network of piping and ducting system to distribute the conditioned air in all areas as per requirement.

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Fundamentals of HVAC Systems

HVAC systems can also be classified as per the construction or configuration, namely Package Systems and Split Systems. As the names suggest, Split units will have the components spilt into two units (indoor and outdoor) whereas a package unit will have all the components housed in a single unit. In the split units, the indoor unit and outdoor unit are connected through tubing through which the hot water or refrigerant flows. There is, however a restriction on the length of the tubing that can be used for the unit to be efficient. In a split unit, since the air handling components are in the indoor unit normally no ducting will be required. A package unit can be placed outside and since the air handler is also in the same unit ducts are required to distribute air within the spaces to be cooled.

2.5.1 LOCAL SYSTEMS

A local HVAC system is deployed to serve a single space and will usually be placed within the space itself or at the boundary between the space and external environment. These systems are standalone i.e. independent of each other and will usually be relatively smaller in size and ratings. The local systems mostly house the cooling/heating mechanism, filtration and distribution within the same unit. A window air-conditioner or a room electric heater are examples of local systems.

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There are certain advantages of local systems because of which they might be preferred for certain applications. They are easier to control since only one space is being managed and hence there is only one point of control. There is a reduced risk to operations since failure of one unit impacts only a single location while others can continue to work normally. For the same reason, scheduling the maintenance is easier since the systems can be shut off when the spaces are not occupied. Because of their smaller size, common housing and less complexity local systems are easy to maintain and replace. However, there are associated disadvantages as well. For a larger building and the same cooling load requirement, the combined initial cost of local systems will be higher compared to a central system. Local systems cannot take over additional load (of adjacent space), if required. Smaller units are less efficient and have a lower Coefficient of Performance (COP). At times the architecture of the building (like glass façade) may not allow installation of the local unit. This can be overcome by use of split systems wherein, part of the equipment is placed as an outdoor unit installed on a ledge, ground or rooftop and the other part being the indoor unit placed inside the space to be conditioned. Another aspect is that due to the installation of local units, the aesthetics of the building may get affected (think AC units jutting out of windows or outdoor units placed on ledges)

2.5.2 CENTRAL SYSTEMS

Central systems are designed to condition multiple spaces/zones with each zone having its own controls. These systems are larger in size and rating. Most of the electromechanical components are placed in a central isolated location like a machine room and the distribution systems are placed across the conditioned spaces. The central systems can take advantage of economies of scale, reduce noise and the impact on aesthetics, are more efficient and provide the option of moving the conditioned cooling/ heating medium between spaces as required. Hence return on initial costs and savings in energy costs can be derived from effective use of the systems. However, they do have the disadvantage of a single equipment failure impacting the complete building. Redundancies need to be built to overcome such issues. Moreover, the systems are generally more complex and will have more maintenance requirements and that too from Original Equipment Manufacturers (OEMs) or specialist contractors.

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Heating Systems

3 HEATING SYSTEMS The H in HVAC stands for Heating Systems which are used extensively in places with cold temperatures and climate. The heating systems are also of two types, as mentioned in the last chapter, Local systems and the Central Heating Systems. The local heating systems are the smaller individual units in various forms that are used to provide heat in smaller areas for e.g. portable electric heaters, wood stove and fire places etc. that are used commonly in most homes or even small offices/shops. However, as pointed out, all these systems are only suitable for smaller spaces like individual rooms. Larger spaces or commercial facilities like office spaces, hospitals, educational buildings, malls etc. require a larger heating system, which is provided by the central heating plant. At some places, the local systems may also be used to complement a central heating system. As explained earlier, the heating process comprises of generation of heat, heat exchange with the air to be conditioned and distribution of the conditioned air in the facility. Thus, a typical central heating system will have three basic parts: the heating plant itself where fuel is converted into useful heat, a distribution system comprising of network of pipes/ ducts to deliver heat to various spaces and controls to regulate the system. In a central heating system, heat source used may be a Furnace, a Boiler or a Heat Pump. Let’s look at each of these in detail.

3.1 FURNACE BASED HEATING SYSTEMS A Furnace is a device to generate heat and comprises of an enclosed structure in which fuel is burned to generate very high temperatures. The fuel that is used can be in the form of natural gas, propane and fuel oil or even electricity can be used to produce heat. The heat that is produced thus is transferred to air in a heat exchanger. The air is pushed through the heat exchanger using a fan and then circulated/distributed via ducts to provide warm air to the spaces served through registers/grills. The cooler air from the space is sucked in back to the furnace system via the return air ducts for reheating. It should be noted here that in the earlier days gravity systems were in vogue wherein the warm air used to rise up the building naturally due to convection and replace the heavier cold air. However, forced air systems are used with most furnaces these days. The by-products of combustion are taken out to the outdoors via a flue pipe.

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Heating Systems

Figure 3.1: Heating Systems

A furnace is ideally suitable for residential use and small office spaces and typically not used for larger spaces. However, the system is simple and does a sufficiently effective job of heating the spaces. The operation is controlled through thermostats, relays and valves. When the temperature of the conditioned space falls below a set level, the thermostat sends a signal to a relay which operates the valve to allow fuel into the furnace to start the heat generation process. Similarly, once the temperature is achieved the fuel supply to the furnace is shut down.

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Heating Systems

Modern high-efficiency furnaces can be 98% efficient and operate without a chimney. The small amount of waste gas and heat produced are mechanically ventilated using PVC/Metal pipes through the side wall or roof of the building. The Fuel Efficiency in a gas furnace is measured in AFUE (Annual Fuel Utilization Efficiency). AFUE is the ratio of annual heat output of the furnace compared to the total annual fossil fuel energy consumed by a furnace or boiler. An AFUE of 90% means that 90% of the energy in the fuel becomes heat and the rest 10% escapes up the chimney and elsewhere. AFUE doesn’t include the heat losses of the duct system or piping, which can be as much as 35%.

3.1.1 COMPONENTS OF A FURNACE

For ease of convenience, we will discuss a Gas based furnace since it is most prevalent one in use. A furnace will typically comprise of the following major components:

Figure 3.2: Components of Gas Furnace

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Heating Systems

• Thermostat: A thermostat is a device or component which can detect temperature in a room and send signals to control other devices. In air-conditioned spaces, a thermostat recognizes when a particular temperature set point has been reached and will send a signal for the furnace to shut off or start. • Heat Exchanger: A heat exchanger consists of a set of coils or tubes that are looped inside the furnace. The heat exchanger in a furnace serves two purposes; this is where the gas or fuel combusts thereby creating the heat and the air which passes around it gets heated up. A blower motor is used to push the air over the heat exchanger and the into the ductwork for transportation to the conditioned spaces. • Igniter: A furnace requires fire/heat to ignite the gases when it is switched on. The older furnaces used a pilot light, which was a small fire continuously burning inside the burner that would ignite the gas as soon as it entered the chamber. Nowadays, a hot surface igniter is used that is heated up by electricity making it red hot to light up the gas. • Burners: The fuel comes out of the burner and mixes with the air to burn and produce the flame. • Gas Valve: The gas valve is electrically operated to control the gas going into a furnace and also to shut off the gas, when a safety switch fails. • Blower Fan: The blower fan is used to suck in the air returning from the conditioned space, as well as fresh air and blow it over the hot heat exchanger. The conditioned air is then circulated throughout space to be conditioned via ductwork. The ductwork has grilles and registers on the other end, viz the rooms to be conditioned, through which the hot air enters the rooms. A fan limit switch ensures that the fan operates only when a set temperature is reached, thus preventing cold air from being circulated and also shuts off the furnace, if the temperature becomes too high. Some furnace models offer a blower fan that can run at variable speeds to improve efficiency. • Flue: A flue or chimney acts as an exhaust for gaseous by-products of combustion used to create heat. • Return Air Filter: A filter is fitted at the entry point of return air to the furnace to prevent any material, debris, dust etc from going inside the furnace. • Draft Inducer Fan: The draft induced creates a vacuum in the exhaust pipe to ensure a safe path for the exhaust gases to go out. It also helps in drawing air into the burner assembly. • Flame Sensor: A Flame sensor is used to detect presence of heat and to shut off the gas in case the there is no flame. • Furnace Limit Switch: When the furnace becomes too hot, a limit switch will turn the furnace (gas supply) off to prevent any damage to the furnace • Safeties: There are additional safety features installed on a furnace like blower door open limit switch, electric motor overload trip, flue gas spill switch etc.

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Heating Systems

Furnaces are available in various sizes that can be used to heat an area quickly, i.e. faster than a boiler-based system. It also costs lesser to install a furnace system compared to a boiler-based system. Condensing furnaces are now available which recover heat from the exhaust gases using a secondary heat exchanger, which is used for pre-heating the return air thus enabling higher efficiencies. Since furnaces use a ductwork to circulate hot air, the same ductwork can be used with an integrated cooling system as well, where required.

3.1.2 MAINTENANCE OF FURNACE BASED HEATING SYSTEMS

Routine maintenance on the furnace will involve the following: 1. The furnace and the area around it should be kept clean since the air movement may get obstructed if it is not clean. 2. The filters get choked/caked while in operation and need to be changed regularly since a poorly working filter can reduce efficiencies, cause unnecessary load on the system and also result in higher utility bills. Blowers, blower motor, pulleys etc should also be inspected and cleaned, belts should be inspected and replaced as required. 3. Inspection of the complete system is required to be undertaken to check for leaks in the ducting system, gas line and flue system. While a leak in the gas line can be a fire hazard, a leak in the combustion chamber or flue system can expose occupants to waste gases like carbon monoxide. Heat exchangers need to be checked for cracks. Electrical connections should be checked and tightened if required. 4. Calibration of thermostats and any measuring instruments/gauges need to be done, replace batteries where required. 5. Annual inspections by a specialist vendor needs to be conducted and the same will include a thorough inspection of the complete system; including burners, flame properties, gas line pressures, ignition systems, safety systems and checking performance of individual components.

3.2 BOILER BASED HEATING SYSTEMS The second type of heating systems are called Boilers that uses hot water or steam for providing heat to the spaces inside a facility. The hot water or steam is circulated via a piping network to delivery devices placed in the spaces to be conditioned. Theses delivery devices are essentially heat exchangers and could be in the form of radiators, air handlers or convectors. The hot water/steam transfers its heat to the air blowing over the delivery device and becomes cooler. In a steam system, the steam condenses into water. The cooler water returns to the boiler for reheating. Besides the specific purpose of conditioning air,

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Heating Systems

boilers and furnaces may be used for other industrial applications requiring hot water, steam and manufacturing as well. Just like furnaces, boilers can be operated on natural gas, LPG, solid fuels, electricity and fuel oil. Again, gas-based boilers are more prevalent and therefore we shall discuss only those for understanding the complete system.

3.2.1 OPERATION OF GAS BASED BOILER

A gas-based boiler, as the name suggests, uses natural gas or LPG as fuel to heat the water. There are essentially two types as mentioned above, the steam boiler and the hot-water boiler. It is important to note that while a steam boiler actually boils water to produce steam, the hot-water boiler does not necessarily boil water, and only heats it to 50-800 C. A continuous supply of natural gas stream is made available to the boiler through a pipe that is supplied from the gas mains. The burner sprays the gas into the combustion chamber and ignites it. The flames are directed onto pipes containing water which gets heated up. The water pipes run through the space to be heated and is connected to delivery devices (radiators) fitted in the space to be heated. A pump is used to push the hot water through the distribution network of pipes. As the hot water passes through the radiators it loses heat to the room air thus warming it in the process. The cooler water is then returned to the boiler to be heated again. In this manner, the process continues to maintain the temperature in the conditioned space. A thermostat in the conditioned space will switch on/off the boiler when the set temperatures are reached. Waste gases from the boiler are exhausted through a flue system.

Figure 3.3: Boiler System

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Heating Systems

3.2.2 COMPONENTS OF GAS BASED BOILER

Apart from the boiler, the heating system will also have following components: • Heat Emitters/Delivery Devices: These are essentially heat exchangers where the heat from hot water is transmitted to the medium for heating air. These can be in form of radiators which heat the air in the room as it passes over the radiator surface or they can be radiant heating system i.e. a network of pipes distributing the hot water, that run through the floor slab/walls to heat it up which in turn heats the air in contact. The warm air then moves up pushing the cooler air to come down and get heated or there could be fan heaters, which use a fan to blow the cool air over the radiator pipes to heat it. • Piping Network: A continuous piping network is created to deliver the hot water to the emitters and then return it to the boiler. • Pump: An electric pump is used to pump the water through the pipe network. • Expansion Tank: The volume of water changes with temperature and the change in volume needs to be catered for, else the pressure may become too high. The expansion tank provides the space for the extra water to move when hot and move back into the network as it cools. • The Feed Tank or the Makeup Tank: This tank stores feed water for the boiler to make up for losses of water and tops up the quantity when required as per the design Vent (chimney) Pressure Reducing Valve Water Feed Valve

Pressure Relief Valve

Air Vent

Aquastat Flow Control Valve

RETURN

SUPPLY

Pressure/ Temp Gauge

Expansion Tank

Burners Drain Valve

Circulator(s) (pump) Gas Valve

GAS FIRED HOT WATER BOILER Figure 3.4: Components of Boiler

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• Thermostats: There are two types, one is the boiler thermostat which controls the temperature of the water in the boiler and the other is the room thermostat which controls switching ON/OFF of boiler basis the room temperature. • Thermostatic Radiator Valves: These valves facilitate setting of different temperatures in different spaces by regulating the flow of hot water through the radiator. • Pressure Relief Valve: If the system pressure becomes too high the relief valve comes into action and releases the pressure to prevent bursting of pipes. • Motorised valves: If the boiler system is also being used to provide hot water for domestic purposes a motorised valve is used to direct the flow of water to the respective system. • Boiler Controls: The hot water or steam needs to be produced in a regulated, efficient, and safe manner. Combustion and operating controls regulate the rate of fuel use to meet the demand. The main operating control monitors hot water temperature or steam pressure and sends a signal to control the firing rate, i.e. the rate at which fuel and air enters the burner. Multiple sensors may be available and include, flue gas CO2 levels, flue gas temperature, stack smoke density, steam/ water flow, oil/gas consumption, etc. The boiler controls are very finely tuned and any disturbance can result in efficiencies going down, and improper combustion. • Safeties: A boiler is a pressurised vessel and hence there is always a risk of pressure becoming too high. It is therefore necessary to have adequate safety systems built in. The safety systems include cut-outs for high pressure and temperature, high and low gas/oil pressure, high and low water level and flame safeguard. These controls break the electrical circuit to prevent firing of the boiler if any of the parameter goes beyond the set limits. Flame detectors monitor the flame condition and deactivate the burner in the event of a non-ignition or other unsafe condition. • Condensing Boilers: Just like a condensing furnace, the exhaust gases from the boiler are at a high temperature and carry a lot of heat which is wasted. In a condensing boiler the exhaust gases are used to pre-heat the cooler water that is returned from the radiators/heat emitters thereby reducing the work that boiler has to do to get the water heated to the desired temperature. This improves the efficiency of the entire system.

3.2.3 MAINTENANCE OF GAS BASED BOILERS

A boiler, like any other equipment, also needs regular maintenance for it to continue functioning in a safe and efficient manner.

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Conducting Regular Maintenance helps to reduce the boiler operating and energy costs, improves safety, and extends the life of the boiler. Maintenance tasks will typically involve following: 1. Ensure that the area around the boiler is clean and no combustible materials are available. Check the floor under and around the boiler for leaking water. Check for any unusual noise/vibration. 2. Check pressure and/or temperature readings and the display panel for any service codes or errors. 3. Check the combustion air opening for any obstructions. 4. Ensure the vent termination is not blocked with snow, ice, or debris. Visually check the flue gas vent piping and combustion air piping for any signs of blockage, leakage or deterioration. 5. Check for sweating/leakage on the boiler relief valve and the relief valve discharge pipe. 6. Check the water pipe network completely for leaks. 7. Inspection of burners and state of ignition system components. 8. Check filters and replace, if required. Annual Maintenance includes: 1. Thorough inspection and cleaning of heating system, burner assemblies and heat exchangers. 2. Check all wiring and connections. 3. Checking of water PH levels. 4. Inspect condensate system and clean and flush as necessary. 5. Inspect venting system, air inlet and vent terminations for blockage, corrosion or deterioration and ensure all joint and pipe connections are tight. 6. Check systems operating settings and test safety controls. 7. Check for proper operation after it has been cleaned and inspected.

3.3 HEAT PUMP The third type of heating system is called a Heat Pump, which is a device that moves heat energy from one place to the other. It is very much like an air conditioner (discussed in a later chapter) with the advantage that it can reverse direction of flow thus enabling it to condition air on both cold and warm days. In cooler days it removes heat from outside and transfers it inside and vice versa on warmer days. It is also feasible to use heat pumps simultaneously for heating and cooling operation. A heat pump can draw/give away heat from/to multiple sources, i.e. environment air, water and even ground.

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Heating Systems

heat exchanger

soil

soil

aquifer

aquifer

heat storage

heat storage

Summer cooling

Winter heating

360° thinking

Figure 3.5: Heat and Cold Storage with Heat Pump

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For climates with moderate heating and cooling needs, heat pumps offer an energy-efficient alternative to furnaces and air conditioners.

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360° thinking

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Figure 3.6: Heat Pump

Heat pumps can be classified based on the medium used as the source/sink for heat. There are three types of heat pumps: 1. Air-Source Heat Pumps use the outside air as the heat source in winter and heat sink in summer. 2. Water-Source Heat Pumps use water bodies as the heat source/sink. This is not very popular due to its dependence on availability of water body nearby. 3. Ground-Source (also called geothermal, GeoExchange, or GX) Heat Pumps which get their heat from the ground. Both Water and Ground-Source heat pumps take advantage of the fact that temperatures beyond a certain depth in water and ground respectively are nearly constant all through the year i.e. it will be warmer than outdoor air temperatures in winters and cooler than outdoor air temperatures in summers. Air-Source heat pumps are cheaper and easier to install and hence more common. GroundSource heat pumps, though higher in cost, are more efficient. While an air-source heat pump is installed much like a central air conditioner, groundsource heat pumps require that a “loop” of piping be buried in the ground, usually in long,

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shallow (3–6’ deep) trenches or in one or more vertical boreholes. Similarly, water source heat pumps will need to have a loop in touch with a water body like a lake, ocean etc. The method used will depend on the location, the size of the facility and the subsoil. In a direct exchange system, the ground loop contains the refrigerant that traverses through the length of pipe to exchange heat with the soil. In indirect exchange systems water is used to transfer the heat from the refrigerant to the ground. The refrigerant gains/loses heat to water in the water heat exchanger section and the water runs through the ground loop to exchange the heat with the soil. The image (Figure 3.7) below shows the layout of the ground loop and the heat exchange process.

Figure 3.7: Ground-Source Heat Pump

Since heat pump only moves heat rather than generate it, Heat pumps are more efficient than other heating systems using furnaces and boilers and are also much more safer and easier to maintain. The Coefficient of Performance (COP) of heat pumps can have values ranging from 1.75 to 6.

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We will understand more on the Air-Conditioning cycle in Chapter 5 (Air-Conditioning Systems) and the concept or the operation of heat pump will become clearer. Since the components of a heat pump are similar to the Air-Conditioning system, the maintenance needs of a heat pump will also be similar to an Air-Conditioning system besides the reversing valve and the refrigerant / water loop.

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Ventilation Systems

4 VENTILATION SYSTEMS Ventilation (V of HVAC) is an important aspect of the HVAC systems. It is the process of exchanging, replacing or recirculating air in any space with the objective of maintaining the Indoor Air Quality (IAQ) and thus contribute towards the health and comfort of the occupants. Ventilation introduces outside air into the building thus replenishing oxygen and recirculating indoor air to prevent stagnation. This results in removal of unpleasant smells, excessive moisture, heat, dust, bacteria and gases like carbon monoxide and carbon dioxide from the atmosphere inside a facility. Though natural ventilation is a component of the larger scheme, we will cover forced or mechanical ventilation in this chapter. All the equipment in a facility which handle/process air can be deemed to be part of the ventilation system. These, as explained earlier, could be standalone units or work in conjunction with other equipment. Heat exchangers, filtration units, supply and exhaust fans, humidifiers/dehumidifiers, the ductwork for carrying the air for distribution and delivery devices are all part of the building ventilation systems.

4.1 AIR HANDLING UNIT (AHU) As the name suggests, an Air Handling Unit (AHU) handles air. The basic function of the AHU is to circulate indoor air, add fresh air to it and condition it to the right temperature and humidity before delivering it back to the conditioned spaces through ductwork. To serve this function, the AHU has filters for cleaning the air, humidifiers and dehumidifiers for humidity control, a heat exchanger which cools/heats the air and a fixed/variable speed fan to move the air to/from the conditioned space. Ducting is used to carry the air to the conditioned spaces and the same is insulated to suppress the sound of the running AHU motor and that of movement of air. Please note that while a central system usually uses a separate AHU, package systems have the air handler installed in the same unit, however the function remains the same.

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Figure 4.1: Air Handling Unit with Labeled Parts 1 - Supply duct; 2 - Fan compartment; 3 - Flexible connection; 4 - Heating and/or cooling coil;5 - Filter compartment; 6 - Return and fresh air duct

4.1.1 OPERATING PRINCIPLE OF AHU

The AHU is an enclosed equipment with a fan, filter, heat exchanger, humidifier/dehumidifier connected to ductwork. There are two sets of ducts, the supply air ducts which take the air from the AHU to the conditioned space and the return side ducts which carry air from the conditioned space to the AHU. When the fan runs, it pushes the air out through the supply side ducts which creates a vacuum in the plenum (empty space provided for mixing) and pulls the used air from the conditioned space through the return air ducts. The fan also pulls in some fresh air from outside environment. The air is mixed in the plenum and passed through a filter for cleaning and then over a heat exchanger which either heats or cools the air. Thereafter, the air is passed through the humidifiers or dehumidifiers and into the ductwork. This cycle continues. The flow through the supply duct and the return duct should be almost same in order to maintain the pressure in the conditioned space.

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Figure 4.2: Working of AHU (Image sourced from MDPI; Shah, A.; Huang, D.; Chen, Y.; Kang, X.; Qin, N. Robust Sliding Mode Control of Air Handling Unit for Energy Efficiency Enhancement. Energies 2017, 10, 1815. Creative commons attribution license)

The entry of fresh air serves the purpose of maintaining the quality of air and also to replace air lost through openings and exhausts in the floor (exfiltration), thus maintaining the pressure inside the building to prevent untreated air to come into the building (infiltration). If the exfiltration is not sufficient to remove excess air dedicated fans, or exhaust fans in toilets and kitchens can be used to remove the excess air.

4.1.2 COMPONENTS OF AN AHU

An AHU will typically have the following common components: • Housing: The housing that contains all the other components of an AHU, comprising of a metal base frame held together by an extruded aluminium framework. The panels are made of galvanised steel sheets injected with environment friendly PUF (Polyurethane foam, an insulator) of uniform density. The insulated panels are fixed to the frame work using self-drilling & tapping screws. A drain pan is also provided to drain the water in the event of condensation of water. • Air Mixing Section: Fresh air & return air are mixed at the desired rate with dampers that are specially designed for maximum air efficiency. • Blower Section: The blower (motor-fan) helps to recycle the air present in the buildings. Large AHUs can have multiple blowers and fans. When the blower runs it pushes the air over the heating/cooling coils and in the process a vacuum is created behind the blower which pulls in the air from the conditioned space through the return air ducts in the building. The fan & motor is normally mounted on a common channel fitted with anti-vibration isolators to avoid the vibration transfer to main casing.

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• Filter Section: A Filter section is fitted in all the air handling units which help to filter the impure air i.e. remove dust and other foreign particles. Filters are rated by their MERV (Minimum Efficiency Reporting Value) and the selection will depend on the level of cleaning required. In some AHUs, UV filtration may also be implemented for getting rid of bacteria. Filters may be of different types like Plate Filters, Bag Filters, Compact Filters, EPA Filters, HEPA Filters, ULPA Filters, Carbon Filters etc. • Heat Exchanger Section - Cooling/Heating Coils: The Heat exchanger section comprises of the cooling or heating coil to cool/heat air. The coils are arranged in rows with different fin spacing. Aluminium fins and copper tubes are used in the design of the coils. The coils could carry the refrigerant or water/glycol as per the system. • Heat Recovery Systems: Heat recovery systems may be used in AHUs to reduce energy costs by extracting heat from the facility’s exhaust air stream before it is vented outside. • Humidifiers (Adiabatic/Evaporative Pad, Non-Pressurized Steam, Pressurized Steam): The humidifiers are used to increase the humidity of the air, when required. The same is achieved by adding moisture, water vapour into the air. • Dehumidifiers: Normally, the cooling of air takes away some of the moisture but in places with high humidity some additional measures may be required. Excess moisture is removed by condensation or absorption. • Dampers: Dampers are devices which regulate the air flow by modifying the resistance to the air flow including shutting it off completely. The dampers are at times also connected to the Fire Alarm panel to automatically shut off in case of fire and thus stop the flow of air into the conditioned space. • Ductwork: Ducts are used to carry air to/ from the source (AHU) to the conditioned space. Two duct paths are made one for supply and the other for return. The return is required to recirculate as much indoor air as possible since it is already treated to some level and hence is more economical to re-treat. Ducts are made of galvanized sheets and the supply ducts are insulated while return ducts are not. • Ducting Accessories: The delivery components in a ducting network are components placed in the conditioned space to deliver/retrieve the air. These could be registers, diffusers or grilles and are available in different shapes and sizes.

4.1.3 CLASSIFICATION AND TYPES OF AHUS

AHUs can be broadly classified based on how they are mounted, i.e. Horizontal Floor Mounted, Vertical Floor Mounted or Ceiling Suspended. Another way to classify them is based on where the fan is located with respect to the cooling coils and filter as:

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1. Draw-Through Type: Here the fan is located towards the discharge side and pulls the air through the filters and cooling coil before discharging it from the fan outlet to the ducting network. 2. Blow-Through  Type: Here the fan blows the air through the filters and cooling coil before discharging them to the ducting system. Discharge plenum

Filter Coil Fan

Supply Air

Return Air

(a) Draw-Through Type

Filter

Coil

Discharge plenum

Fan Return Air

Supply Air

(b) Blow-Through Type Figures 4.3 (a) & (b): Diagrammatic representation of Draw-Through & Blow-Through type of AHUs

4.2 FAN COIL UNITS (FCU) A fan coil unit is a terminal unit for air-conditioning system and works more or less in the same way as an AHU. It facilitates a versatile way of providing conditioned air into a space. It is small in size and capacity, has greater controllability and can be mated with a whole variety of grilles and diffusers to match the vision of the architect or interior designer. If required, it also allows the conditioned air to be spread around the served room via discharge ducts, to allow a single unit to distribute conditioned air to a large area. A fan coil unit (FCU) is a very simple device consisting of a heating or cooling/heating coils and fan. The coils could carry refrigerant (in case of DX units) or water (in case of use in conjunction with a chilled water system). Fan coil units can be wall-mounted, freestanding or ceiling-mounted and may be concealed in ceiling voids. A fan coil unit

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(FCU) receives chilled water from a chiller line or hot water from a boiler and circulates that through the heat exchanger. The fan draws the room air blows it over the cooling or heating coil in the heat exchanger. The air comes out of the FCU either cooler or hotter than before. Temperature control can be achieved either by controlling the flow of water/ refrigerant to the unit or by controlling the flow of air through the FCU, thus achieving a wide range of temperatures. A thermostat integrated with the unit can be used to signal the demand to FCU.

Figure 4.4: Fan Coil Unit

Fan coil units can be either 2 pipe units or 4 pipe units, the difference being that 2 pipe systems can either cool or heat at one time (either chilled water or hot water is flowing through one set of pipes), whereas 4 pipe systems has two independent sets of pipes; one each for hot water and chilled water and can heat and cool at the same time. This means the 4 pipe units are not system dependent i.e. they are not dependent on the mode of temperature control of the building

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4.3 VARIABLE AIR VOLUME (VAV) SYSTEMS An AHU will usually consider the entire conditioned space as one zone and supply air at a constant air flow at a particular temperature to all the outlets in the network i.e. temperature can be controlled by changing the set point at AHU only. These systems are called Constant Volume Systems. While some amount of uniformity in temperature can be achieved by air balancing, individual control at the outlet is not feasible. Variable Air Volume systems (VAV’s) can be used to control temperature in a space (cabin or meeting room) by modulation of the amount of air at a constant temperature that serves the particular space. However, it should be kept in mind that since the VAV’s control the flow of volume of air, it is important that the AHU motor is also of variable speed in order to maintain the pressures in different zones. A simple VAV system can be considered to be a box that controls air from a single supply duct and varies the airflow to each space based upon the temperature in that space. From a control perspective, such a system would consist of a temperature sensor, an air flow sensor, a controller, an actuator and a damper.

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The volume of the air flowing into the space is controlled by a motorized damper which is actuated by a thermostat positioned within the condition space. The damper opens and closes depending on the temperature in the room thus varying the amount of cool air going into the conditioned space. VAVs are supplied air by an AHU and hence in the presence of multiple VAVs operating independently the AHU must be capable of handling the fluctuating load. Variable speed motors in the AHU facilitate this need, wherein the speed of the AHU blower goes up or down depending on the demand.

4.4 CHILLED BEAMS A chilled beam is a terminal unit that uses convection for heating or cooling large spaces. Technically, they are heat exchangers in a casing, mounted on or suspended from the ceiling, using chilled water for cooling air by convection. The beams are distributed across the ceiling. Chilled beams may be Passive or Active. • A Passive Chilled Beam completely relies on the air being drawn into the heat exchanger by convection. Chilled water is passed through pipes in a heat exchanger (Beam) either suspended from the ceiling or integrated into the false ceiling systems. The air around the heat exchanger gets cooled and the cooler, denser air falls to the ground causing a pressure drop in the beam that draws in warmer air into the beam. This causes a continuous convective flow to be established thus cooling the entire space. A passive chilled beam does not have any ducts or fans and hence recirculates only the indoor air. Additional arrangements will have to be made for fresh air entry and humidification. It is obvious that the concept will not work efficiently for heating systems since warmer air will continue to be higher up near the ceiling. • Active Chilled Beams have a primary air system i.e. air is supplied to the beam in certain quantity, through ductwork. The primary air pressurises the plenum and then the air is discharged through nozzles which induce air from the conditioned space to pass through the cooling coils. The primary air mixes with the cooled air before being introduced into the conditioned space through nozzles or slots in the beam. The main air handling unit supplies primary air to the chilled beam.

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Figure 4.5: Active Chilled Beam

Active beams are recommended for spaces like classrooms, private and public office buildings, meeting facilities, health care facilities, where the sensible cooling and ventilation air are required.

Active chilled beam for exposed installation

Active chilled beam for suspended installation

Mixed Air

Induction Air Primary air supply, typically through a piece of duct approximately 5" in diameter

Figure 4.6: Active Chilled Beams: Source Gibson, Thomas, and Mindy Espinosa. “Chilled Beams: What They Are, Why You Should Use Them.” The NEWS Magazine, 20 May 2013. Web. 16 Jan. 2017. (Creative Commons license)

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Figure 4.7: Active and Passive Chilled Beams

4.5 VENTILATION SCRUBBERS A scrubber is used to remove particulates/contaminates from the air. The ventilation scrubbers for HVAC application clean the fresh outside air before it is fed into the indoor HVAC system. A pre-filter removes dirt and dust contaminants and a special activated media captures the gaseous contaminants using adsorption. Air scrubbers are commonly used in facilities where the outdoor air quality is not good. In such areas, it becomes necessary to clean the fresh air before being introduced into the building.

4.6 EXHAUST FANS Exhaust fans are used to remove the adulterated/stale air from places like wash rooms and live kitchens. These are regular fans but placed in a manner so as to suck air from the inside and throw it outside. For obvious reasons, the exhaust fans would be installed on the wall with a boundary to the outside environment. Under normal conditions the action of the exhaust fans would create a partial vacuum in the room and hence it is desirable that a grille or louver is built into the door of the room to facilitate replacement of air inside the room. In such a case not only will the fan have to work harder to move the air but the higher pressure will create a draft of air whenever the door is opened.

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4.7 JET FANS Jet Fans are used to ventilate enclosed / underground car parks and basements. Since there is no natural ventilation and due to the large area, the air may become stagnant in certain pockets. The parking spaces, unless properly ventilated, may accumulate Carbon Monoxide and Carbon Dioxide emitted along with the vehicle exhausts. In order to prevent higher concentrations of these gases and avoid a fire risk, jet fans are used to systematically remove these gases out of the spaces by directing the same at high speeds. Multiple jet fans positioned appropriately and directing the air out can take out the contaminating gases efficiently out of the parking lots. Jet Fans do not need any ducts resulting in tremendous cost savings, power savings and increased installation efficiency. Jet Fans can be used for normal ventilation and also for smoke extract in case of a fire. CO/CO2 sensors may be installed and integrated with jet fans to automatically start the fans whenever the concentration of the gas goes beyond the set level.

Figure 4.8: Jet Fans

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4.8 MAINTENANCE OF VENTILATION SYSTEMS All components of the ventilation systems require maintenance for better efficiency, effectiveness and longevity of the equipment. Before maintaining any equipment, it is important that the supply should be switched off. AHUs may at times be considered as confined space (depending on where they are fitted) and due care (Work Permit) needs to be taken while working on these. The heating/cooling coils in the AHU need to be cleaned regularly to maintain heat transfer efficiency. The motors of blower/ fans need to be checked for proper functioning, tightness of connection, currents drawn. Belts if available need to be checked for tension and replaced when required. Filters need to be cleaned and replaced as required. Condensation is a frequent issue in AHUs and needs correction since it adds to humidity and also can promote biological growth, mold etc. Areas need to be kept clean at all times. Variable speed drives will also need maintenance removing dust, dirt, moisture, tightening connections, checking capacitors etc. Sensors and thermostats should be checked for proper operation. The ducting needs to be inspected regularly for leakages. Accumulation of dirt inside the ducting is not good for health and also increases friction for the air. Duct cleaning may be needed when the ducts become overly dirty. Dampers need to be checked for proper operation.

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5 AIR-CONDITIONING SYSTEMS So far, we covered the Heating & Ventilation components of the HVAC system in the previous two chapters, and that brings us to the last component of the acronym, AC i.e. Air-Conditioning systems. The Air-Conditioning traditionally referred to the cooling component of the HVAC systems, but now that we have seen that a heat pump can serve both the purposes of cooling and heating, Air-Conditioning inadvertently becomes the right term to use. In this chapter, we will focus on Air-Conditioning systems that help in cooling the air. Once the concept of cooling is clear, the working of heat pump, discussed earlier (Chapter 3), will also become clearer since it only involves reversal of the flow of gas. Unlike the furnace and the boiler, which actually generate heat, the air-conditioning systems do not generate heat but just move the heat between inside the building and outside using the principles of thermodynamics. We know that heat energy will spontaneously flow from a warmer body/medium to a cooler body/medium. However, in order to make the heat move from a cooler body to a warmer body requires work to be done. This work is performed by the air-conditioning or refrigeration equipment.

5.1 TYPES OF COOLING There are different mechanisms by which cooling can be achieved by the Air-Conditioning systems, of which the following are predominantly used for cooling a facility: 1. Free Cooling: In relatively cooler climates or at night times in certain places, outdoor temperature can be lower than that required inside the facility. The lower external temperatures can be used to chill a coolant which in turn can be used to cool air inside. A pump is used to circulate the coolant, which may be Water or Glycol, to the heat exchangers (AHUs) in the space to be cooled thus removing heat from the air in the area. At times, the chilled coolant may also be stored for later use i.e. to provide cooling on warmer days. The modern day mechanical cooling systems also make use of free cooling in the economizer mode, by allowing a larger amount of the cooler outside air to come in to the facility thus obviating the need to run the cooling system and saving energy. 2. Evaporative Cooling: If hot air is passed through water or a wet pad some of the water will evaporate and provide a cooling effect to the air. This principle is used for cooling in very dry hot climates. A fan located inside an enclosure with wet

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pads on the sides will suck in air from outside through the wet pads. As the air passes through the pads it becomes cooler and moister before being discharged into the room. This helps to maintain the temperature and humidity in the room. It should be noted that these systems will be ineffective where the humidity in outside air is already at high levels. 3. Mechanical Cooling: Mechanical cooling is the lowering of temperature within a space using refrigerant compressors, absorbers or other systems that require energy use and mechanical work to be done in order to condition the space.

5.1.1 WHAT IS A REFRIGERANT?

We know that when ice, a solid, is heated it changes into a liquid form (water) and similarly when water is heated, it changes form into gas (vapour). Similarly, when the vapour is cooled it condenses into liquid and on being cooled further it gets converted to ice. In fact, this is true for all substances. When a substance changes its state of matter, it either gains heat or loses heat. The transition from solid to liquid to gas absorbs heat and the transition from gas to liquid to solid gives up heat. This property of substances is used in Air-Conditioning to absorb heat from the indoor and then give up heat to the outdoor. Certain substances are more amenable to use for this purpose than others depending on their characteristics like vapor density, thermal conductivity, toxicity, cost etc. A refrigerant is a substance, often a fluid, used in a refrigeration cycle to transfer heat from one place to another using the laws of thermodynamics. The refrigerant changes its phase from liquid to gas and back to liquid during each cycle thus enabling the heat transfer which is so important for the refrigeration/ Air-Conditioning purposes. Many refrigerants have been used in the past, the more common ones being Chlorofluorocarbons (CFC) and Hydrochlorofluorocarbons (HCFC) (R-12 & R-22). However, both these types have an ozone depleting potential and hence are being phased out. R-290 (Propane) and R-600A (Iso-Butane) are environment-friendly refrigerants that are completely halogen free, have no ozone depletion potential and are lowest in terms of global warming potential. These are essentially hydrocarbons and have high-energy efficiency but are also highly flammable.

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5.2 OPERATING PRINCIPLE OF AC SYSTEMS So far, we have learnt that Air-Conditioning uses a cyclic process wherein the refrigerant changes its state to absorb and reject heat alternately. There are two basic cycles which are employed in the Air-Conditioning systems, which are: • Vapor Compression Cycle • Vapor Absorption Cycle

5.2.1 VAPOR COMPRESSION CYCLE

In the Vapor Compression Cycle, as shown in Figure 5.1 below, the refrigerant is in a vapor form when it enters the compressor where it is compressed. The high pressure and high temperature vapor from the compressor is let out to a condenser (heat exchanger) where it loses some of its heat to the outside environment and condenses i.e. turns into the liquid state. The low temperature liquid which is still at a high pressure is then sent to an expansion valve, where the pressure decreases abruptly causing evaporation of part of the liquid and in the process cooling it. The expansion valve, also called a metering unit or throttling unit, also regulates the flow of liquid into the evaporator. The mixture of cool liquid and vapor is then sent to the evaporator where the remaining liquid also evaporates absorbing the heat from the warm air around it and thus cooling it in the process. The moisture from the air is also removed as the moisture condenses on the evaporator coil. The water will drip down into the condensate pan located underneath the coil. The water is then discharged to the drain by connecting a hose or piping to the pan. Thereafter, the cycle repeats itself.

Figure 5.1: Refrigeration cycle

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In order for this cycle to be deployed in air-conditioning, the refrigerant in the evaporator interacts with the indoor air and removes heat and the heated refrigerant in the condenser interacts with the outdoors to give away heat. Most Air-Conditioning systems in facilities use the vapor compression cycle for cooling. If the direction of the flow of refrigerant is changed then the condenser and evaporator roles are interchanged (Indoor coil becomes the condenser and outdoor coils become the evaporator) and the same process can be used for heating as well.

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HEATING, VENTILATION & AIR-CONDITIONING: FACILITY MANAGEMENT

Air-Conditioning Systems

Hot Air Discharge

High Pressure Vapor

High Pressure Liquid

Condenser

Outside Ambient Air

Metering Device

Compressor Indoor Ambient Air Air Handler Low Pressure Vapor

Evaporator Coil

Low Pressure Liquid/Vapor

Figure 5.2: Vapor Compression Cycle

5.2.2 VAPOR ABSORPTION CYCLE

Vapor Absorption Machines (VAMs) use the vapor absorption cycle which is similar to the vapor compression cycle, except that instead of the compressor a combination of absorber, pump and a generator is used to achieve the high-pressure gas required for the condenser. The refrigerant (Ammonia or Water) in vapor form, at a relatively higher pressure in the evaporator, moves into the absorber and is absorbed (dissolved) in a suitable liquid (Water for Ammonia and Lithium Bromide for Water). The absorption process reduces the volume of the mixed solution thereby allowing more vapor to move in from the evaporator. A pump is used to raise the pressure of the saturated solution heating it in the process and drives the solution into the generator. The saturated solution is further heated in the generator causing the refrigerant to evaporate and separate from the liquid. The hot refrigerant in vapor form passes through the condenser where it loses its heat and condenses. The refrigerant is then taken through an expansion valve thereby cooling further and then finally into the evaporator where it gains heat and turns back completely into the vapor form. The absorption cycle systems have a very low Coefficient of Performance and are predominantly used only where waste heat is readily available than electricity. Below is a comparison between the two systems. We will discuss only vapor compression systems in this book.

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S.no

Aspect

Air-Conditioning Systems

Vapor Absorption System

Vapor Compression System

1

Energy Input

Vapor absorption system uses waste heat from furnace, exhaust team or solar heat.

Vapor compression system uses electrical or mechanical energy for operation of compressor.

2

Moving parts

Only a small pump is the moving part.

An electrically driven compressor is used.

3

Load variation

Can handle partial loads without much impact on performance

The performance is impacted at partial load.

4

Risk of damage

No risk of equipment being damaged by liquid entry.

Liquid in the compressor can damage the compressor

5

Coefficient of Performance

The COP of the system is poor.

The COP is higher.

Figure 5.3: Comparison between Vapor Absorption & Vapor Compression Systems

5.3 COMPONENTS OF AIR-CONDITIONING SYSTEM Let us now look at the different components of the Air-Conditioning systems. Since vapor compression systems are more prevalent, only those will be discussed here. The Figure 5.4 below shows the components of a simple Window AC.

Figure 5.4: Components of a Simple Window AC

• Compressor: A compressor is a device that compresses a gas thus increasing its pressure by reducing its volume. In an Air-Conditioning system, the compressor draws the low-pressure gas from the evaporator and compresses it to a high temperature - high pressure gas before supplying it to the condenser. Compressors 46

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Air-Conditioning Systems

used in Air-Conditioning may be classified into reciprocating, centrifugal, rotary, screw and scroll compressors. However, in Window and Split ACs we would normally find only reciprocating or rotary types of compressors. • Condensers: A condenser is a device used to convert a substance from its gaseous state to its liquid state. In the process, heat is transferred from the substance to its surrounding medium or a condenser coolant, which may be air or water.

Figure 5.5: Condenser

Air-Cooled Condensers may use natural convection or forced air convection. In both the systems the refrigerant flows inside the condenser tubes and the outside air flows over the condenser tubes cools the refrigerant. In a Water-Cooled Condenser, instead of using air, cold water is used to take away the heat from the refrigerant. The condensers may be of double tube type or shell & tube type. The water-cooled condensers require a cooling tower (described in chapter 6) to take away the heat from the water and then resupply it for condenser cooling. Water-cooled condensers normally require lesser space but are more difficult to maintain. They are used for large conditioning plants serving large cooling loads. There are evaporative condensers also available but not in vogue due to lesser efficiencies. • Expansion Valve: Expansion valves are also called metering devices, allow expansion of the refrigerant from a liquid to a vapor state. While the condenser allows the refrigerant to cool, the pressure remains unchanged. The expansion valves are flow restricting devices which reduce the pressure of the fluid passing through it and allows it to expand. It does so by means of a combination of a movable pin and spring. The temperature at the outlet of evaporator and pressure of the evaporator are used as the controlling factor. Higher temperatures cause more fluid to flow into the evaporator. A constant supply of the refrigerant is also ensured to the evaporator by the expansion valve.

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Figure 5.6: Expansion Valve

• Evaporator: The final component in the refrigeration cycle is the evaporator, where the cold refrigerant absorbs heat from the air passing over it, thereby cooling the air and in the process changes state from liquid to gaseous form. The air flows directly over the surface and is cooled by the refrigerant passing through the tubes. Plates and fins are added to increase the area of contact. The evaporators in larger systems like those used with chillers are of the shell and tube construction and can be classified as dry expansion (Refrigerant flows on tube side and while the water flows on the shell side) or flooded type (refrigerant level is maintained in the shell and water flows through the tubes).

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Figure 5.7: Evaporator Coil

• Thermostat: A thermostat is used in all the air conditioners for feedback and maintaining the desired temperature in the area to be conditioned. Thermostat senses the temperature and switches on/off the cooling/heating system at previously decided set points. Thermostats may be mechanical (bi-metal), electrical or electronic (thermistors).

5.4 TYPES OF AIR-CONDITIONING UNITS Now that we have learnt the principle of operation of an Air-Conditioning system and the major components, let us look at the various types of systems available.

5.4.1 WINDOW AIR CONDITIONERS

A classic package unit, these are small units that can fit into an opening in the wall/window of a facility. These are limited by capacity and are used for smaller spaces/rooms. All the components are installed within a compact unit and a fan is used to blow air over the evaporator coils and then directly into the room. Filters are added on the return side to prevent dust from entering into the system.

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5.4.2 SPLIT TYPE UNITS

The basic air conditioner is split into two parts, an outdoor unit and an indoor unit. All components except the evaporator are installed in the outdoor unit and the evaporator is placed inside the room to be cooled. The two units are interconnected by copper tubing for the refrigerant flow. The outdoor unit houses the compressor and hence noise and vibration inside the cooled space is reduced to a large extent. These units are suitable for use in smaller rooms and two or more units can be deployed to offer rotation as well as redundancy. In facilities with central cooling, the split ACs can be used as an alternate for off-peak hours when only few critical spaces may need cooling thus conserving energy and reducing utility bills. It should be noted that the distance between the indoor and outdoor units is constrained by the limitation of length of copper tubing (150 feet max) due to pressure drop in the refrigerant over the distance.

Figure 5.8: Types of Air Conditioners

5.4.3 PACKAGED DUCTABLE SYSTEMS

Just like the window air conditioner, in construction a packaged system houses all the components in a single unit. However, these are typically larger and installed outdoors and instead of throwing air directly into the room they use a blower to push the air into the conditioned spaces through ducting installed for the purpose. In cooler environments, a heating system may also be integrated into the package unit, thus obviating the need to

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have a separate heating system in cold weathers. The condenser cooling could be by air or water. These units are used commonly in places that may be large enough to preclude use of split ACs or located away from central areas to justify the extensive ductwork and piping required for a central AC. The window and split air conditioners are usually used for the small Air-Conditioning capacities up to 5 tons. The central Air-Conditioning systems are used for where the cooling loads extend beyond 20 tons. For intermediate cooling capacities the packaged air conditioners may be used. The packaged air conditioners are available in the fixed rated capacities of 3, 5, 7, 10 and 15 tons.

5.4.4 VARIABLE REFRIGERANT FLOW/VOLUME (VRF/VRV)

VRVs are systems used to control the temperature in a conditioned space by varying the flow of refrigerant to the indoor units as per the demand. They are similar to split ACs with the difference that they can serve multiple indoor units of varying capacities in different zones and vary the flow of refrigerant to each as per the demand of the specific indoor unit. The technology offers many advantages like simultaneous cooling, heating in different zones, a tighter control on temperature, higher efficiencies and finally the scalability to add more indoor units if capacity exists in the outdoor unit. The indoor units used could be of any type like FCUs, ceiling mounted cassette, floor standing units, hi-wall units etc.

Daikin, a Japanese company, developed the technology calling it VRV (Variable Air Volume). Daikin registered VRV as a trademark and hence other manufacturers using the similar technology use the term VRF.

Like the systems discussed earlier, VRF systems also operate on the direct expansion (DX) principle meaning the refrigerant is circulated in the heat exchangers in indoor units (evaporators) and directly cools the air. The outdoor unit is connected through piping to multiple indoor units. The refrigerant travels through these pipes to the expansion valves in each branch. Dedicated electronic expansion valves are used to accurately control the flow of refrigerant to each evaporator depending on the feedback received from temperature sensors and hence the flow in each

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evaporator is different basis the requirement. The overall demand or the change in the same is managed by varying the speed of the inverter driven compressor in the outdoor unit. A capacity control ranging from 6% to 100% can be achieved by these compressors. Due to this tighter control the VRF system have higher efficiencies and energy consumption is also substantially reduced. A schematic VRF arrangement is indicated below (Figure 5.9):

Figure 5.9: Typical VRF Layout

The refrigerant pipe-work uses a number of separation tubes and/or headers (refer schematic Figure 5.9). A separation tube has 2 branches whereas a header may have more than 2 branches. Either can be used however, the separation tube is not provided after a header because of air balancing issues.

5.4.5 PRECISION AIR-CONDITIONING UNIT (PAC)

Some mission critical facilities or spaces like data centers, server rooms, laboratories etc. require a very strict control of temperature and humidity as well as have a low level of tolerance to dust. The comfort Air-Conditioning systems are not capable of meeting these needs. The precision air conditioners, also known as a CCU (Close Control Units) or CRAC (Computer Room Air Conditioner) are refrigerating equipment specifically designed to provide precise control of temperature and humidity in all applications which require a very high degree of precision. Precision Air Conditioners (PAC) are designed specifically to meet the following objectives to be achieved with a very high degree of reliability:

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• • • •

Air-Conditioning Systems

Air temperature control (± 1.0°C). Air humidity control (± 7/8%). High airflow rate. Year-round operation (24 hours a day, 365 days a year), without any interruption.

The working principle of PACs is the same as any other AC with the difference being in the components and control systems used for maintaining the air quality to a high degree of precision. The PAC deploys higher capacity components with higher efficiencies like a scroll compressor, electronically commutated fans, electronic expansion valves and solid-state microprocessor-based controls. Redundancy may be built in by having multiple gas circuits in a single unit and also by providing multiple units to cater for the load. PACs may be classified: (a) as per the condenser cooling mechanism i.e. Water Cooled or Air Cooled or (b) according to the manner in which the air is distributed i.e. Under Floor System (air supplied through the openings in raised flooring) as shown in the Figure 5.10 or Overhead System in which the flow is reversed (air is delivered through openings in the ceiling).

Warm Air

Warm Air

Server

PAC

Server

Raised Floor Cool Air Hard Floor Figure 5.10: Under Floor System

5.4.6 CENTRAL PLANTS

All the systems we discussed so far, are direct expansion systems, which means that the refrigerant cools the air directly without any intermediary medium. While a central plant can be a direct expansion, it is not suitable for the modern-day facilities where the cooling load is very high, and such a plant if used would require large amounts of refrigerant to be circulated through a maze of tubes/pipes to cool all the areas/floors of a facility. Such a

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plant, in addition to facing technical complexities, will also bring forth a safety concern of large amounts of refrigerant leaking into the occupied spaces. To overcome this issue, central plants are used to cool water or a water solution which is in turn circulated through pipes and heat exchangers (typically, AHUs/FCUs) on the floors to cool the air. Since the plants chill the water or other solution, these types of central systems are also called Chillers (Refer Chapter 6). The systems require additional equipment on the liquid side, for pumping and recirculating the liquid. Primary and secondary pumps are installed for pumping the liquid in the system and an expansion tank may be added to prevent hammering in the pipes.

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Chillers

6 CHILLERS For deployment of DX systems in larger facilities, like a complete floor of a large building having multiple zones to be cooled or a full hospital building, higher capacity units or more number of units will need to be used to meet the cooling load thereby increasing the capital costs. DX units are constrained by the length of piping that can be used for carrying the refrigerant from condenser to evaporator due to pressure drop and thermal losses over the length of the pipe making it impractical and uneconomical to have a common unit serving multiple indoor units at a large distance. This will also require use of a large quantity of refrigerant, which is not inexpensive by any means. In addition, there is always the risk of a leak in the pipe which may release a large amount of gas in the occupied space. Chilled Water Systems or Chillers provide a solution to cool larger buildings efficiently without suffering from the issues with DX systems as indicated above. The principle of operation of various components remains the same; however, indirect cooling is used for cooling the air in conditioned spaces. The chiller’s refrigerant gas is used to cool water instead of air in the evaporator. This chilled water, which now acts like a secondary refrigerant, is then transported to the heat exchanger of the various air handling units of the facility and cools the air, just like the refrigerant does in the DX system. There are no

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Chillers

issues of pressure loss with water and it can be pumped to any height or distance using pumps. Any water loss in the system can be made up by simply adding more. There is of course an addition of piping and pumps to distribute the cold water through the building and back to the chiller for cooling. However, the total capital and operating cost is much lower than it would be for a DX plant serving a similar area. A typical chilled water central Air-Conditioning system comprises of three major sub-systems: The Chiller, Chilled Water System and Air Distribution System. In case of a water-cooled chiller, another component of condenser cooling system comes into play i.e. the Cooling Tower. We will cover only the water related systems here as the Air Handling Systems was covered in Ventilation Systems (Chapter 4).

6.1 CHILLER A Chiller is a machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle to produce chilled liquid (secondary refrigerant). This chilled liquid flows through pipes in a building and passes through heat exchanger coils in air handlers, fan-coil units, or other systems, thereby cooling and also dehumidifying the air in the building. The liquid used for cooling may be Water, or a Brine with a Salt or Glycol base, or a mix of Glycol & Water. The basic requirement of a secondary refrigerant is that it should be non-corrosive, inexpensive, have high specific heat, have good heat transfer characteristics, should be chemically stable and have a low viscosity. Examples of secondary refrigerants are water, sodium chloride, calcium chloride, ethylene glycol, ethyl alcohol, trichloroethylene etc. For general Air-Conditioning requirements water is preferred due to less cost but some industrial processes may require use of other liquids.

Figure 6.1: Chiller

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Chillers

The Chiller also comprises of a compressor, condenser, evaporator and expansion valve, there being two main differences; (1) the size of the components is much larger and (2) instead of the refrigerant cooling the air in the evaporator, it is now cooling water. Another component which can be seen in the Figure 6.2 below is that there is a connection going to the cooling tower which means that this diagram represents a water-cooled chiller.

Cooling Tower Water Line

Refrigerant Loop CHILLER UNIT

TEV

Condenser

Compressor

Evaporator

Chilled Water to Living Space

Water Line

Figure 6.2: Chilled Water System

Chillers can be broadly classified into two by the manner in which the condenser is cooled: Air-Cooled or Water-Cooled.

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Chillers

Figure 6.3: Air-Cooled Water Chiller Plant

6.2 CHILLED WATER SYSTEMS (CWS) After the water has been cooled by the chiller, there is a need to transport it to the various end users i.e. the air handling units where the chilled water will cool the air being supplied to the conditioned spaces. The water also needs to be transported back to the chiller for cooling again. The movement of water is achieved through pumps, piping and valves. Technically speaking, at this stage the chilled water can be classified as a secondary refrigerant. The pressure and volume of water changes with temperature and there may be water losses as well. An expansion tank used in the chilled water system facilitates maintenance of pressure and caters for the change in overall volume of the system. There can be multiple configurations of the pumping system deployed in the chilled water system. Two are discussed below for a basic understanding.

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Chillers

6.2.1 DIRECT PRIMARY (CONSTANT FLOW)

In a Primary only system, there is only one set of pumps which is used for distribution of the chilled water to the entire network and bring it back. The distribution is at constant flow irrespective of the load. Valves at the building air handling systems will allow the chilled water to be bypassed under low load conditions so that the total flow through the chiller remains constant. This system is inefficient because of the wastage of energy. The mixing of chilled bypass water with the return water reduces the efficiency of the chillers. Direct Primary

Loads Chiller 1

Chiller 2

Chiller 3

3-Way valves Primary Pumps Balancing Valves Return Figure 6.4: Direct Primary Distribution System

6.2.2 PRIMARY – SECONDARY SYSTEM

In this scheme, the chilled water system is divided into two distinct loops, primary and secondary. This arrangement can supply variable flow through the system while maintaining a constant flow through the chillers. 3-way valves in the secondary loop control the flow of water through the air handlers depending on load, however the overall quantity of water through the system will remain the same.

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Chillers

Primary Loop

Secondary Loop Secondary Pumps Loads

Chiller 1

Chiller 2

Chiller 3 Supply

3-Way valves Primary Pumps Balancing Valves Return Figure 6.5: Primary Secondary Distribution System

6.3 COOLING TOWERS As discussed earlier, for water cooled condensers the cooling water needs to lose the heat gained to the environment. This is done using a Cooling Tower. The tower blows air through a stream of water causing some of it to evaporate, and the evaporation cools the water stream. Some water is lost due to evaporation and also by falling outside the sump, therefore water has to be added regularly to make up for the lost water. Make up water also helps in removing the high concentration of minerals from the water which collect due to evaporation of water. Cooling water in a cooling tower may require chemical treatment or dozing to maintain the quality of water. Warmer temperatures and the deposits like sludge, scale, rust etc in the cooling towers encourage the growth of the bacteria legionella and need to be guarded against. Legionnaire’s disease can be a fatal condition and it is recommended that the cooling tower water be tested for Legionella regularly. Though there may be slight differences in how water and air react inside a cooling tower, the basic principle remains the same. A diagrammatic representation of cooling tower is shown in Figure 6.6 below.

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Chillers

Figure 6.6: Cooling Tower

Figure 6.7: Cooling Tower of Large Office Building

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Chillers

6.4 MAINTENANCE OF CHILLERS • Clean and inspect outdoor coils: Dirty condenser coils reduce the efficiency of the condenser thereby reducing the efficiency of the entire system. Clean condenser fan, coils, comb bent fins, lubricate bearings, inspect belts and drives if available and check all connections, • Inspect the compressor(s). It must be working properly for your system to operate efficiently. Check for leakage and vibration, refrigerant level, oil levels, crankcase heater and check operating temperatures • In the control panel check wiring, switches, and other components. These may have a direct impact on the performance and also includes safeties which prevent damage to the equipment • Inspect the water system for water leaks and repair as required. Check operation of pumps, valves and actuators in the system. Depending on the quality of water in the system, the same may require chemical treatment/dosing • For cooling towers, water testing and treatment with corrosion inhibitors and biocides is required to be done; fans, motors, belts and gears need to be cleaned, adjusted and replaced if worn; electrical components such as wiring and capacitors need to be checked and replaced if needed, inspection and cleaning of basin, louvres, fills, spray nozzles, water and air flow need to be checked.

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Conclusion

7 CONCLUSION Control of the indoor environment has become a necessity in a modern-day facility and rightly so. Most people spend up to 80% of their time indoors. Poor quality of air and thermal conditions in those places can impact their health and also cause illness. While some of these conditions could be short term like itching, nausea, headaches etc., some other long-term effects include respiratory diseases, heart problems and cancer. No one is comfortable in a space which is too hot or too cold, is smelly or damp or where the air feels stale. It is also obvious that since the larger buildings house a greater number of people, the impact is that much greater. For any business, be it a commercial office space, a mall, a hospital, an educational institute etc., the impact of poor indoor environment is detrimental to the overall business. The productivity of employees is affected, illnesses mean more absenteeism, then there is the cost of medical treatment and severe conditions may even lead to employee attrition. For public spaces, the poor indoor environment can cause a direct loss of customers. A well designed and maintained HVAC plant can help maintain a good quality of indoor air and obviates conditions which are contra-indicated for a productive, healthy and safe indoor environment. Regular maintenance and optimized operations can reduce the total cost of ownership as well as the utility bills. We learnt about the various types of equipment used for Heating, Cooling & Ventilation and understood how they work in unison to undertake the task of maintaining temperature and humidity, circulation and filtration of air, addition of fresh air to replenish oxygen and moisture and removal of stale air. In facilities, the ownership of HVAC systems may vary from a single ownership to a distributed ownership. A landlord or building owner will generally cater only for central plants for human comfort, the smaller systems or PACs if required will need to be installed by the occupiers/tenants. For a central plant also, the landlord may provide the complete HVAC system for the building including the chilled water system and the AHUs or provide only the chilled water connection to the floor. The AHUs and the ventilation ducting becomes the responsibility of the tenants. On the other hand, the landlord may not provide the HVAC system at all and will ask the tenant to install their own. The operations and maintenance of the plant becomes the responsibility of the entity that installed the system. There is cost involved in operating and maintaining the HVAC plants. For a single occupancy building, the central plant HVAC costs can directly be billed to the single tenant. However,

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Conclusion

if there are multiple tenants, the billing is done basis the energy consumed by the tenant. This is measured by what is called a BTU meter. BTU meters measure the energy content of liquid flow in British Thermal Units (BTU), a basic measure of thermal energy. The amount of chilled water flowing through the circuit and the temperature differential between the chilled water supply and chilled water return lines are used for this purpose. Irrespective of who maintains and operates the HVAC system, timely and effective maintenance on HVAC systems can not only improve occupant health and safety but can also go a long way towards enhancing the equipment useful life thus obviating or at least delaying high repair/capital costs. Proper scheduling of the equipment and managing the temperature set points basis the occupancy and during different times of the day can result in energy savings of a high order. Lastly, please remember that irrespective of how well you maintain and operate the HVAC equipment, there will still be some occupants who will complain about the thermal comfort. It is because there are a lot of factors which impact an individual’s perception of the temperature including the clothes they are wearing, their metabolism, their gender, size, age, level of activity etc. ASHRAE (American Society for Heating, Refrigerating and Air-Conditioning Engineers) requires that at least 80% of the occupants be satisfied with the indoor thermal conditions. What it means is that, there is no need to go around changing the setting of the HVAC system every time there is a complaint about feeling hot/cold. Though you must investigate the complaint for any local issues, if 80% or more of the occupants are satisfied with the thermal conditions, you can trust the HVAC system to be working just fine.

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Common Terminology

8 COMMON TERMINOLOGY TR – Tons of Refrigerant is a unit used to define the heat extraction capacity of an airconditioning unit. One ton of refrigeration is the amount of cooling obtained by one ton of ice melting in one day. BTU – British Thermal Unit Another measure of heat, a BTU is the amount of heat required to raise the temperature of one pound of water by one-degree Fahrenheit. Number of BTUs per hour define the capacity of a plant. 1 TR = 12000 BTU/hr. KW – At times KW may be used to define the capacity of the plant, 1 TR is equal to 3.517 KW. COP – Coefficient of Performance is the ratio of outpower and input power. Since it is a ratio it is dimensionless. Both output and input power need to be the same unit, i.e. KW. EER – Energy Efficiency Ratio is the ratio of output in BTU and input power energy in KWh used as a measure of energy efficiency of the plant. Therefore, the unit is BTU/ KW/h. the higher the EER, more is the efficiency. CFM – Cubic Feet per Minute is used to define capacity of a fan/ventilation system by the volume of air moved in a minute. iKW/TR – Input Kilowatt per ton is the amount of power required to produce 1TR of heating. The lower the iKW/TR the higher the efficiency. Delta T (ΔT) – It is the difference in temperature for a fluid when it enters a system and when it leaves the system. Plenum – An enclosed space created to facilitate air flow and related to air distribution. AFUE – Annual Fuel Utilization Efficiency is a measurement used to rate furnace efficiencies by dividing the ratio of heat output by heat input. MERV – Minimum Efficiency Reporting Value is a rating system for air filters. Ranging from 1 -20 basis the minimum size of particulate matter that the filter can catch, the higher the rating the more effective is the filter.

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Common Terminology

Condenser Approach - is the difference in temperature of liquid refrigerant in the condenser pipe and the leaving condenser water. Should be less than 3 0C. Evaporator Approach - is the difference in temperature between the refrigerant in the evaporator and the leaving chilled water. Usually between 10 - 14 0C for a single pass evaporator and lesser for a multi-pass evaporator.

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