Aircon Best Practice

Home Performance with ENERGY STAR®

Air Conditioner Best Practice Guidelines Training Manual

March 17, 2003

Home Performance with ENERGY STAR® Table of Contents Overview ______________________________________________________________ 1 Requirements for best practices _______________________________________________ 1 Not grossly oversized______________________________________________________________ 1 Ensure adequate airflow____________________________________________________________ 2 Proper refrigerant charge ___________________________________________________________ 2

Training Requirements ______________________________________________________ 2

Sizing & Equipment Selection_____________________________________________ 3 Pay More for Capacity Costs _________________________________________________ 3 Why Size & Select Equipment ________________________________________________ 4

Airflow _______________________________________________________________ 5 Why Adequate Airflow ______________________________________________________ 5 Latent Capacity is Relative to the Need _________________________________________ 7 May not be adequate for airflow_______________________________________________ 8 Airflow specifications at 0.5 inches ___________________________________________________ 8 Filters __________________________________________________________________________ 8 Temperature rise method inaccuracies_________________________________________________ 9 Misleading equipment specifications__________________________________________________ 9 More power not always an answer___________________________________________________ 10

Refrigerant Charge ____________________________________________________ 10 Why Refrigerant Charge____________________________________________________ 11 Fixed orifice____________________________________________________________________ 11 TXV refrigerant control ___________________________________________________________ 12

Best Practice Forms & Instructions _______________________________________ 12

Home Performance with ENERGY STAR® Overview The following manual provides information on best practice for air conditioner installation and startup. For ease of use and quick reference, each section begins with a summary list of important information contained in the section. First, the reasons for each best practice are discussed along with the reasons certain practices are not adequate. Many contractors may already understand how do some of the best practices like refrigerant charge. But it is also important that the contractor understand why each best practice is important. Second, step-by-step directions are provided on completing best practices including filling out the form for the Cash-back reward. Best practices are being developed in collaboration with the HVAC industry in Wisconsin. The best practices described below are expected to become standard practices. Best practices are expected to evolve as the Efficient Heating and Cooling Initiative and the HVAC industry develop and demonstrate even better ways of being of value to the customer. Requirements for best practices ƒ$50 Cash-Back Reward to Contractor ƒAir conditioner should not be grossly oversized (Bigger is not always better) ƒDemonstrate airflow with pressure drop across coil or temperature split using the wet-bulb temperature ƒDemonstrate refrigerant charge by superheat for fixed orifice and subcool for TXV ƒTraining is mandatory for Cash-Back Reward on best practices A $50 Cash-Back Reward will be paid to the installing contractor for completing the best practice requirements described below on equipment qualified for a Cash-Back Reward (i.e. SEER 12 or SEER 13 air conditioners). While the practices are called “best practices,” they should become standard practices for installation of all air conditioners. Best practices will be optional through March 31, 2004. It is expected that best practices will be required for a customer to receive Cash-Back Rewards beginning April 1, 2004. An overview of the requirements for best practices follows: Not grossly oversized The contractor is responsible to ensure that the air conditioner is not grossly oversized. It is recommended, but not required, that the air conditioner size be selected using a load calculation such as Manual J by ACCA. As a minimum, the contractor must compare the size of the air conditioner installed to a typical size based on square feet per ton. If the installed air conditioner is larger than typical, the contractor must provide the reasons why a larger size is being installed.

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Home Performance with ENERGY STAR® Ensure adequate airflow There must be adequate airflow for the air conditioner to function efficiently. Adequate airflow must be ensured by either: a) using the static pressure drop across the new coil and coil specifications or b) by the temperature split method done in conjunction with refrigerant charging verification (superheat or subcool). Proper refrigerant charge The way proper refrigerant charge must be ensured depends on whether refrigerant flow is controlled by a fixed orifice (capillary tube or piston) or a TXV (Thermostatic Expansion Valve). Superheat measurement is required for fixed orifice. Subcool is required for TXV. Training Requirements The Efficient Heating and Cooling Initiative is promoting best practices for airflow and refrigerant charge to achieve energy conservation goals. To become eligible for best practices, each contractor must have at least one experienced person attend who will be responsible for providing training and guidance to other contractor staff. This person must be management, lead worker, or a job assignment that includes routinely providing direction to contractor staff on the work to be performed. If a contractor does not have such a person, then each staff performing the best practices must attend. Each HVAC contractor who participates in the Efficient Heating and Cooling Initiative is required to have at least one regular employee attend at a minimum 8 hours of training by December 31, 2003. Training on best practices will count four hours towards the training requirement. The remaining four hours can be taken on any course of their choice from among the following topics: A. Proper central air conditioner refrigerant charging and maintenance B. Improving airflow and the effect on equipment performance C. Duct testing, design and improvement D. Ensuring healthy indoor air quality E. Proper sizing and installation of furnaces and central air conditioning systems F. Principles of Building Performance Science G. Combustion safety The HVAC industry has a variety of existing training (e.g., training provided by HVAC equipment distributors), competent trainers and tests such as NATE to test technician competence. This existing training capability can meet the eight-hour basic training requirement for contractors to continue to participate in the Efficient Heating and Cooling Initiative. Contractors must not only understand how to physically perform best practices but also understand the importance and consequences of best practices compared to doing something else. The following section discusses the importance of best practices so that

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Home Performance with ENERGY STAR® each HVAC contractor will not only understand how to perform best practices but also will believe in and perform best practices.

Sizing & Equipment Selection ƒ2.5 ton = 3 kW of Electric Capacity ƒHidden capacity costs ƒSave $255 to $505 hidden costs Pay More for Capacity Costs At times there have been television commercials saying “pay me now or pay me more later.” The following discusses how electric capacity costs (i.e., the cost to build new generating plants) result in customers paying more costs later. This electric capacity costs prominently caused by air conditioners and lack of best practices are not obvious to customers and are called hidden costs below. The selection of efficient equipment of proper size and installation may be discouraged because all of the costs of using air conditioners are not obvious. The energy costs of using air conditioners may appear low enough that residential customers don’t see a need to install properly sized efficient equipment. However, the cost of using an inefficient or oversized air conditioning only seems low because residential customers pay an average energy charge per kWh of energy used. Air conditioners cause capacity related costs in addition to energy cost. The costs of a utility providing electric generation and transmission capacity are real costs that must be paid for by customers. These additional capacity costs can easily exceed the amount charged for air conditioning use, even without considering the energy costs. The result is higher costs for all energy consumed to make up for the amount not charged just for the air conditioner energy use. In fact, capacity costs from some utilities may be more than two-thirds of the average energy charge for all energy used. The result is that everyone’s utility bills go up when utilities have to install capacity to provide service to inefficient or over sized air conditioners. A 2.5-ton SEER 10 air conditioner requires 3 kW of generation capability. Depending on the type of electric generation plant, it could cost $1,500 or more to provide 3 kW of electric generation capacity. A high efficiency unit installed properly can avoid creating the need for this expensive, additional capacity cost. A higher SEER air conditioner might save 17 to 23% of $1500 or $255 to $345 of generation capacity costs in addition to the energy savings. Proper sizing might save another 10% or $150.

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Home Performance with ENERGY STAR® Why Size & Select Equipment ƒReduce gross over sizing of air conditioners and seek more practical solutions ƒCustomer comfort and satisfaction ƒBest way to ensure adequate airflow and save up to another 10% ƒSave 2 to 10% by reducing cycling losses ƒReduces hidden costs It may be tempting to install a larger air conditioner than necessary to provide quicker cooling or because the “right size” is not known. Time, cost, and information or knowledge are barriers to installing the right size of air conditioner. The Efficient Heating and Cooling Initiative will be researching in conjunction with contractors’ better practical ways of dealing with sizing issues. For now, requirements on sizing are focused on reducing grossly oversized air conditioners. The following are four reasons to not grossly oversize an air conditioner: 1) comfort, 2) ensure adequate airflow, 3) reduce cycling losses, and 4) reduce costs. Less comfort can result from increased cycling caused by oversized air conditioners. Temperature and humidity swings combined with the on and off of airflow can result in dissatisfied customers. Properly sizing an air conditioner can also be the best way to ensure adequate airflow. Modern furnaces in Wisconsin generally are capable of providing adequate airflow. Therefore, adequate airflow can be insured by simply not installing an air conditioner that is larger than the size airflow will efficiently support. By eliminating gross over sizing, the tons installed should be less than the tons that can be supported by the airflow such that: Tons < cfm available /425 cfm/ton (or 400 cfm/ton wet coil) As discussed below, ensuring adequate airflow might save 10% of the energy used by the air conditioner. Even if there is adequate airflow, reducing the size of the air conditioner can reduce the amount of fan energy necessary to blow the air. Installing a smaller air conditioner may also reduce cycling losses. The first few minutes of air conditioner operation is inefficient because much of the cooling is used to simply offset the amount of heat added by the fan to circulate air. When the air conditioner first starts all of cooling is needed to offset the heat from the circulation fan. Even after a couple of minutes, 40% of the cooling energy is used to offset the heat from the circulation fan. Sizing correctly can save 2 to 10% of the air conditioner energy. Reducing the size of the air conditioner saves money. The smaller air conditioner costs less and reduces the costs for the utility (paid by consumers) to have capacity to supply the air conditioner. Installing a 2 ton 12 SEER air conditioner instead of a 2.5-ton air Page 4

Home Performance with ENERGY STAR® conditioner might use 0.5 kW less electric capacity. The following calculation shows a 2.5-ton air conditioner uses 2.5 kW compared to 2.0 kW for a 2.0-ton air conditioner: 2.5 ton *12,000 Btu/ton 12 Btu /watt * 1,000 watt/kw

= 2.5 kW

2.0 ton *12,000 Btu/ton 12 Btu /watt * 1,000 watt/kw

= 2.0 kW

If it costs $500 for each additional kW of capacity, the 0.5 kW difference could be $250 savings. As discussed above, the capacity costs are hidden in average energy charges that the customer may not recognize as being caused by the air conditioner. Of course, the way a customer uses the air conditioner impacts the utility costs. Most customers operate between two extremes of use. First, the customer who waits until it is the hottest outdoor temperature to turn on the air conditioner causes the most costs. This customer may think they are saving money by buying an oversized air conditioner to cool the house down quickly after it is already hot. But because the air conditioner is continuously running when most other air conditioners are running, it causes the highest electric capacity costs that everyone ends up paying. Second, a customer who does not use the air conditioner during the hottest weather would still cause costs for the capacity of transmission and distribution lines to deliver the electricity. But, generation plant capacity costs caused by these customers could be lowest. Some recent news stories have reported the objection of some citizens to the building of new transmission line capacity, which might be needed in part to supply oversized inefficient air conditioners.

Airflow ƒInadequate airflow can waste 10% ƒFreeze-up at 200 cfm/ton ƒLow airflow causes temperature stratification ƒMore fan power is not always the answer ƒSelect equipment based on available airflow (at least 425 cfm/ton dry coil) ƒ400 cfm/ton (wet coil) is needed for superheat refrigerant charge verification ƒSelect equipment based on cfm for next to highest speed in case airflow is less than expected. Why Adequate Airflow This section on airflow discusses cfm measured either with a wet coil (air conditioner operating) or with a dry coil (air conditioner not operating). When there is moisture on

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Home Performance with ENERGY STAR® the coil 400 cfm per ton is used and when there is no moisture on the coil 425 cfm is used. Research1 suggests that low evaporator airflow rates (e.g. 300 vs. 400 cfm per ton) could produce a 10% increase in residential cooling energy over what would be expected based on rated performance. Inadequate airflow wastes energy because of the low airflow across the evaporator coil and because of temperature stratification within the house. Low airflow across the inside coil has adverse effects on unit performance. It lowers the evaporator coil temperature, reduces total capacity, increases latent capacity and lowers sensible capacity. If the airflow is as low as 200 cfm/ton, the coil can freeze making the problem even worse. Temperature stratification caused by low airflow also wastes energy. Without adequate velocity from proper airflow, cool 6 air simply stays near the floor with hotter air staying in the top part of the room. The result is 270 cfm/ton uncomfortable people and o F 4 320 cfm/ton inefficient air conditioner operation. The graph to the right 2 shows the degrees of temperature difference between the floor and the thermostat in a Wisconsin 0 house with low airflow. This illustrates it is especially 0 5 10 15 important when there is low Minutes airflow, to have supply registers that produce sufficient throw (or air velocity) to reduce temperature stratification. Air velocity can be increased by reducing the supply register free surface area or by not having turning vanes in the register. Actual airflow can be lower than expected in actual operation and it can be cost prohibitive to make changes to increase airflow after installation. Selecting and installing equipment based on the cfm that can be delivered from the next to highest fan speed is therefore important. The higher speed is available in case airflow in lower than expected. The next section discusses latent capacity relative to airflow. Then some common practices that may not be adequate to ensure adequate airflow are discussed.

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ASHRAE Transactions: Symposia; Impact of Evaporator Coil Airflow in Residential Air-Conditioning Systems – Danny Parker, John Sherwin, Richard Ralustad, and Don Shirey III.

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Home Performance with ENERGY STAR® Latent Capacity is Relative to the Need ƒLatent capacity is not constant. ƒLatent capacity increases with relative humidity ƒLatent capacity increases as the need for latent capacity increases ƒLatent capacity from low airflow decreases as the need increases Latent capacity is the amount of capacity the air conditioner has to remove moisture from air. Latent capacity is not constant. The amount of latent capacity available varies with both the need for moisture removal and the airflow. Relative humidity reflects how much moisture is in the air relative to how much moisture air could hold. The following discusses how latent capacity changes with relative humidity and the amount of airflow.

Latent Capacity

Tons

The latent capacity of an air conditioner depends on the specific models of evaporator and condenser coils installed. To illustrate the relative importance of airflow and relative humidity on latent capacity, the performance specifications of a two-ton (13 SEER) air conditioner is shown in the graph to the right.

1.40 1.20 1.00 0.80 0.60 0.40 0.20 0.00

-100 cfm @ 75 -100 cfm @ 85 Lat @ 75 F

70%

60%

50%

40%

30%

20%

Lat @ 85 F The top two lines on the graph illustrate a substantial increase in latent capacity as relative humidity increases. The top line shows the Relative Humidity latent capacity at 75° F outdoor temperature; and the second line shows the latent capacity at 85° F outdoor temperature. Fortunately, the amount of latent capacity increases substantially as the need for latent capacity increases.

The bottom line2 shows the variation of the tons of latent capacity resulting from a 100 cfm/ton reduction in airflow. While the increased latent capacity from low airflow may be a significant percentage of the total latent capacity for low relative humidity, it is a minor part of latent capacity when relative humidity is high enough to be important. The real problem with humidity control is not the availability of latent capacity when the air conditioner is running. The problem is that when the air conditioner is off and does not provide any latent capacity. An oversized air conditioner may simply cycle off too long to keep proper humidity control. 2

The bottom is actually two nearly identical lines at 75° F and 85° F outdoor temperatures.

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Home Performance with ENERGY STAR® May not be adequate for airflow ƒAirflow specifications at 0.5 inches w.c. are not adequate ƒ77% of houses with Static pressure over 0.5 inch w.c. ƒClean filter analysis inadequate ƒTemperature rise method had over 20% error in 50% of houses ƒEquipment specification can be misleading ƒMore fan power not always a solution (70% more hp for 20% more cfm) Airflow specifications at 0.5 inches One approach to checking for adequate airflow is to check whether there is less than 0.5 inches w.c. of external static pressure. Furnace fans are often assumed to be able to provide 400 cfm/ton (wet) airflow at 0.5 inches w.c. of external static pressure. However, a dirty filter alone might have 0.5 inches w.c. pressure drop. In a sample of homes in northern Wisconsin, 77% had total external static pressure exceeding 0.5 inches w.c.. Over 0.5 inches w.c. for just the filter and return was found in 28% of the homes. The combined pressure loss across the evaporator coil, the ducts and the filter can in reality be too much to allow adequate airflow. Filters Dealing with the consequence of air filters is a key to maintaining adequate airflow. Differences between filters and how clean filters are kept can easily turn adequate airflow into inadequate airflow and waste energy. Even two filters that appear the same can have one filter with twice as much static pressure loss as the other filter. While the customer controls the filters used and the maintenance of filters, the contractor should do what they can to ensure filters clean the air while not causing energy waste from low airflow. Increasing the effective surface area of the filter is one way to reduce the pressure loss from the filter. But the increased surface area should not be allowed to become an excuse for poor filter maintenance. Periodic filter maintenance should be stressed to consumers. The Efficient Heating and Cooling Initiative is considering how to promote better practices for filters in the future. For now, it is up to the contractor to communicate with the customer and select equipment that can best deal with the consequences of filters. It is not adequate to measure the external pressure and airflow when the filter is new. The table below (based on the Wisconsin DFD master specification SECTION 15885B) illustrates the initial and final resistance from different types of filters. Combining these filter pressure losses with the pressure drop across the air conditioning coil (e.g., 0.15 inches) could mean inadequate airflow even if there were no pressure loss from supply and return ducts.

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Home Performance with ENERGY STAR® Filter type Panel filter 25-30% (dust spot) Efficient Media filter (2” thick pleated, 90-92% weight arrestance) HEPA filter

Initial resistance Inches w.c. 0.15 0.30

Final resistance Inches w.c. 0.50 0.90

1.00`

2.00

Temperature rise method inaccuracies One approach to measuring airflow is to measure the temperature rise across the furnace. The airflow is calculated using the amount of heat output by the furnace and the amount of temperature rise. Both the amount of heat output and the temperature rise have inherent inaccuracies. Unless one measures the efficiency of the furnace and clocks the gas meter, it is difficult to know the heat output of the furnace. The temperatures measured can vary, depending on where the temperature(s) is measured. This temperature variation is in addition to the need to prevent radiation from affecting the temperature measurement. Research3 presented at the 2000 conference of the American Council for an Energy Efficient Economy reported that the single-point temperature rise method had errors greater than 20% in more than half of the homes tested.

Cfm

Misleading equipment specifications Even the use of equipment specifications can have problems in assuring adequate airflow. Analysis of the fan curve from a case study illustrates some of the difficulties. The top four lines on the graph to the right show the specifications on fan performance at four different speed taps. Since, the product literature shows 1435 2000 cfm fan output at the highest 1800 speed and highest pressure listed 1600 in the literature, one might Low 1400 Low-Med expect the furnace to easily Med 1200 supply at least 1200 cfm needed High Initial cfm 1000 for a three-ton air conditioner. Final cfm 800

But the lower two lines show the measured cfm (before and after cleaning) is much different than expected from the equipment literature. Only 745 cfm was measured before cleaning.

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600 400 200 0

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0.5

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In. W.C.

A New Device for Field Measurement of Air Handler Flows by Larry Palmiter and Paul Francisco

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Home Performance with ENERGY STAR®

cfm

If a curved line is fitted to extend the product literature to the pressures measured (including the coil pressure loss), a better picture of performance is 2000 shown in the graph to the right. 1800 The squares, diamonds, xs, and 1600 triangles are the product 1400 literature points as shown in the Low Lowgraph above. The four 1200 M d Med downward sloping lines are 1000 High curves fitted of the performance initia 800 lfinal data and the measured points at 600 four fan speeds. 400 200 0.1 0

0.2

0.3

0.4

0.5

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0.8

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In, W.C.

More power not always an answer One temptation is to simply increase the fan motor power to provide adequate airflow. As shown below, the horsepower to increase airflow in a fixed system is proportionate to the cube of the cfm airflow or to the cube of the fan speed. For instance, a 70% increase in power could be required to increase the cfm by 20%. One should not always simply increase the power (or speed) of the fan to provide adequate airflow. Horsepower new = Horsepower initial * (cfm new / cfm initial)3 Increasing the cfm with more power may simply offset the savings due to improved airflow when the static pressure is already high. This means the fan speed for cooling or heating should not be set higher than necessary for the equipment to function efficiently. The above equation applies to a fixed system and not to changes in the filter or ductwork. It is therefore better to increase cfm through reductions in static pressure loss than through increased power and increased fan speed setting.

Refrigerant Charge ƒCharge refrigerant as accurately as possible for fixed orifice ƒFixed orifices waste 1% for each 1% deviation in charge ƒ57% found not to be within 5% of proper charge ƒTXVs save by adjusting to varying conditions ƒOptimal charge less important for TXV systems

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Home Performance with ENERGY STAR® Why Refrigerant Charge Fixed orifice According to research published in ASHRAE transactions4, over 1% of air conditioning energy is wasted for each 1% error in refrigerant charge in residential air conditioners with fixed orifices. Fixed orifices (capillary or piston) are used to meter refrigerant flow in as much as 90% of residential central air conditioners. Research5 presented at the 2002 American Council for an Energy-Efficient Economy (ACEEE) illustrates the degree of problem with refrigerant charge. Based on 8,873 residential central air conditioners, 57% were identified in need of charge repair to bring the air conditioner within 5% of manufacturer recommended charge. The graph above illustrates the range and degree of charge error found for the air conditioners with improper charge. It is important for contractors to be as accurate as possible with the amount of refrigerant charge on air conditioner systems with fixed orifices. Contractors have an opportunity to receive a reward for demonstrating the proper refrigerant charge through superheat measurement on systems with fixed orifices. It is expected that demonstrating proper refrigerant charge will eventually become mandatory. If contractors don’t properly charge systems with fixed orifices, a TXV may eventually be a requirement for customers to receive a Cash-Back Reward. While contractors should install equipment in accordance with manufacturer recommended specification, a standardized superheat method with airflow measurement will be required for the reward. The standard superheat method contains a target superheat based on the condenser dry bulb temperature and the return air wet bulb temperature. It is generally recognized that measurements of proper superheat require 400 cfm per ton airflow. Also, improper airflow can waste energy, as discussed above. Therefore, demonstration of adequate airflow is also mandatory to receive a reward.

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Influence of the Expansion Device on Air Conditioner System Performance Under a Range of Charging Conditions by M. Farzad and D.L. O’Neal 5 What Can 13,000 Air Conditioners Tell Us by Tom Downey and John Procter, Proctor Engineering Group, Ltd.

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Home Performance with ENERGY STAR® TXV refrigerant control A TXV (thermostatic expansion valve) adjusts flow of refrigerant based on actual operating conditions. This ability to adjust refrigerant flow reduces energy waste due to less than optimal refrigerant charge, airflow, and air conditioner size. The graph to the right (from the ASHRAE research) shows the impact of refrigerant charging for air conditioners with fixed orifices and air conditioners with TXVs. Air conditioners with TXVs instead of fixed orifices do not waste significant amounts of energy from improper charge when charged within –15% to +5% of the proper charge. Manufacturers recommend the subcool method to verify refrigerant charge for air conditioners with a TXV. Proper refrigerant charge is needed to ensure liquid refrigerant does not return to the compressor and cause damage in addition to ensuring the charge is accurate enough to allow the TXV to function properly. The Cash-back reward is available for contractors charging refrigerant according to manufacturer recommendations on subcool.

Best Practice Forms & Instructions The following section provides step-by-step instructions for completing forms required for best practices.

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Home Performance with ENERGY STAR®

Best Practice Forms and Instruction