Hvac And Building Enclosure

October 2003 Training Objectives

HVAC and Building Enclosure

„ Design priorities – – – –

Overview Misc. CHPS Criteria

Building enclosure design priorities (for efficiency and comfort) Ventilation (mechanical vs. natural) HVAC system selection Displacement ventilation design

„ Based on understanding of:

Thermal Loads in Schools Good Envelope Design Ventilation: Natural & Mechanical HVAC System Selection & Design Displacement Ventilation

– Thermal comfort (covered previously) – Indoor air quality (covered previously) – Thermal loads

„ And at the same time… – Introduction to relevant CHPS criteria and BPM guideline contents

Overview

2

Water Credit 2: Water Use Reduction (1 to 3 points)

HVAC and Building Envelope

1 point

2.1. Reduce the use of municipally provided potable water for building sewage conveyance by a minimum of 50% through the utilization of water-efficient fixtures and/or using municipally supplied reclaimed water systems.

1 point

2.2. Employ strategies that, in aggregate, reduce potable water use by 20% beyond the baseline calculated for the building (not including irrigation) after meeting the Energy Policy Act of 1992’s fixture performance requirements. OR 2 points 2.3. Exceed the potable water use reduction by 30% beyond the baseline.

Misc. CHPS Criteria

CHPS Criteria

Energy Efficiency

4

Prescriptive Approach for Energy Efficiency

„ Energy Prerequisite 1: Minimum Energy Performance.

„ Energy Prerequisite 1 (10% Savings)

„ Energy Credit 1: Superior Energy Performance (prescriptive option).

– Lighting power no greater than 0.95 W/ft2 (motion sensor credit allowed) – Economizer

„ Energy Credit 2: Natural Ventilation.

„ Energy Credit 1 (20%, 4 points)

– HVAC interconnect with windows and doors. – 90% of classrooms without AC.

– Daylighting and dimming controls on at least 40% of lighting – Radiant barrier in attic.

„ Energy Credit 3: Renewable Energy and Distributed Generation. „ Energy Prerequisite 2: Fundamental Building Systems Testing and Training. „ Energy Credit 4: Commissioning. „ Energy Credit 5: Energy Management Systems.

CHPS Criteria

5

CHPS Criteria

6

1

Commissioning

HVAC and Building Envelope

„ Typical commissioning process. – – – – – – –

Commissioning plan development. Documentation of design intent. Design review. Submittals review. Inspections and system functional testing. Enhanced operating and maintenance documentation. Post-occupancy testing.

Thermal Loads in Schools

„ Energy Prerequisite 2: Testing and Training. „ Energy Credit 4: Commissioning.

CHPS Criteria

7

Why Talk About Thermal Loads?

What’s a BTU?

„ An understanding of loads helps when setting envelope design priorities

„ Btu = British Thermal Unit

„ Minimizing loads can have many benefits – – – –

Better comfort Smaller HVAC equipment Lower operating cost CHPS energy efficiency points!

„ 1 Btu = Energy required to raise the temperature of 1 pound of water (about 1 pint) by 1 degree Fahrenheit.

„ The heat generated by the burning of one match (approximately).

Thermal Loads in School

Thermal Loads in School

9

Heat Gains (independent of outside temperature)

10

Heat Losses/Gains (dependent on outside air temperature)

People

24-30 kids (@ 200 Btu/hr)

5,000 Btu/h

Lights

1 watt per square foot (1 watt = 3.413 Btu/hr)

3,300 Btu/h

Plugs

Three computers (About 150 watts each)

1,500 Btu/h

Solar

Fairly small with correct orientation and shading

up to 3,000 Btu/h

Total

„ Window conduction „ Walls, roofs and floors „ Infiltration „ Outside air ventilation (a “system” load rather than a “space” load)

12,800 Btu/h

Thermal Loads in School

11

Thermal Loads in School

12

2

Balance Point Temperature

Balance Point Temperature (cont’d)

25,000

25,000 Cooling Required 20,000

15,000

15,000 Classroom Loads (Btu/hour)

Classroom Loads (Btu/hour)

Cooling Required 20,000

10,000 5,000 0 -5,000

0

10

20

30

40

50

60

70

80

90

100

110

120

-10,000 Wall & Roof -15,000

10,000 5,000 0 -5,000

0

10

20

30

40

90

100

110

120

Heating Required Outdoor Air Temperature

Thermal Loads in School

Thermal Loads in School

13

Balance Point Temperature (cont’d)

14

Balance Point Temperature (cont’d)

25,000

25,000 Cooling Required

Cooling Required

20,000

20,000 + Occupants

+ Lights

15,000 Classroom Loads (Btu/hour)

15,000 Classroom Loads (Btu/hour)

80

-25,000 Outdoor Air Temperature

10,000 5,000 0 -5,000

70

+ Window

-20,000

Heating Required

-25,000

60

-10,000 -15,000

-20,000

50

0

10

20

30

40

50

60

70

80

90

100

110

120

-10,000 -15,000

10,000 5,000 0 -5,000

0

10

20

30

40

50

60

70

80

90

100

110

120

-10,000 -15,000

-20,000

-20,000

Heating Required

-25,000

Heating Required

-25,000 Outdoor Air Temperature

Outdoor Air Temperature

Thermal Loads in School

Thermal Loads in School

15

16

Balance Point Temperature (cont’d) 25,000 Cooling Required

HVAC and Building Envelope

20,000 + Plugs

Classroom Loads (Btu/hour)

15,000

Balance Point Temperature

10,000 5,000 0 -5,000

0

10

20

30

40

50

60

70

80

90

100

110

Good Envelope Design

120

-10,000 -15,000 -20,000

Heating Required

-25,000 Outdoor Air Temperature

Thermal Loads in School

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3

Control Thermal Loads

Fenestration Orientation

„ It’s pretty easy!

„ Orient windows north/south.

„ Priorities: 1. 2. 3. 4.

Pay attention to the orientation of glazing. Provide adequate insulation. Specify window shading and/or high performance windows. Control roof heat gain through cool roofs and radiant barriers.

„ Pay attention to details

Good Envelope Design

Good Envelope Design

19

How About Passive Solar?

20

Guideline IN1 Wall Insulation

„ Heat typically needed in early morning; not a good match. „ Direct solar is a source of glare. Recommendation:

„ Possible applications in corridors and transitional areas. „ Might be appropriate for mountain climates.

Good Envelope Design

21

Fenestration Performance Characteristics

Wall type

South Coast North Coast

Central Valley Desert Mountain

Wood frame

2x4 with R-13 or 2x6 with R-19

2x6 with R-19

Steel frame

2x4 with R-13 or 2x6 with R-19

Foam board sheathing + cavity insulation

Mass

Provide wall shading

Interior or exterior insulation

Vol. II - page 268

Good Envelope Design

22

Transmission of Common Glazing Materials

„ Visible light transmittance (VLT). „ Solar heat gain coefficient (SHGC). – Used to be shading coefficient.

„ U-factor. „ Diffusion and Transparency. – a key issue for skylights.

„ Durability. – breakage, scratch resistance, UV resistance, first cost v. replacement cost.

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24

4

Window Construction

Guideline IN2 Roof Insulation

„ Choose high performance windows. – VLT > 0.65 – SHGC < 0.40

Recommendation:

„ Higher SHGC ok for completely shaded windows. „ Single pane glazing may be ok in warm coastal areas. „ See also Guideline DL1: View Windows for VLT recommendations.

Roof type

South Coast North Coast

Central Valley Desert Mountain

Insulation above deck

R-7 foam board

R-14 foam board

Wood-framed, attic and other

R-30 blown in attic R-30 batt in framed

R-38 blown in attic R-38 batt in framed

http://www.denison.edu/enviro/ barney/envtech.html

Good Envelope Design

25

Vol. II - page 271

Guideline IN3 Cool Roofs

Guideline IN4 Radiant Barriers

Recommendation: „ Typically white color.

„ Reflective foil sheet.

26

Good Envelope Design

28

Recommendation:

„ Single ply: – – – –

Good Envelope Design

„ Cuts radiant heat transfer.

EPDM. CPE. CPSE. TPO.

„ Reduces cooling energy. „ Especially beneficial if ducts are in attic space

„ Liquid applied: – Elastomeric. – Acrylic. – Polyurethane.

„ White coated metal.

Good Envelope Design

Vol. II - page 273

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Vol. II - page 277

Georgina Blach Middle School, Los Altos, CA

GelfandRNP Architects 29

Photo: Andrew Davis, AIA

5

Gym, view from north east

Photo: Andrew Davis, AIA

View from southwest

Photo: Andrew Davis, AIA

Photo: Ken Rackow

Cesar Chavez Elementary School, Oakland

VPN Architects 34

What is Ventilation?

HVAC and Building Envelope

“The process of supplying and removing air by natural or mechanical means to and from any space. Such air may or may not be conditioned.” (ASHRAE Standard 62-1999)

Ventilation: Natural and Mechanical Ventilation

36

6

Why Ventilate?

How?

„ Comfort Î dilute odors

„ Naturally

„ Health Î dilute carbon dioxide and other pollutants

„ Mechanically

„ Title 24 says we must

„ Mixed mode (i.e. both)

„ It’s a CHPS prerequisite (P1.1 & P1.2)

Ventilation

Ventilation

37

Natural Ventilation

When is Natural Ventilation Feasible?

„ Energy efficient ventilation potential.

„ Appropriate climate

„ Traditional in California.

„ Acceptable outdoor noise level

„ Still appropriate strategy in much of state.

„ Acceptable outdoor air quality (e.g. dust, odors)

„ Design for security.

„ Design meets Title 24 ventilation requirements

Ventilation

Ventilation

39

Title 24 and Natural Ventilation

38

40

Natural Ventilation Potential, South Coast (Long Beach)

„ Title 24 Compliance using natural ventilation permitted if: – All spaces within 20 ft of operable opening. – Total opening area > 5% of floor area.

„ For a typical 960 ft² (30 ft x 32 ft) classroom, – At least 48 ft² opening area. – Openings on two sides of the room.

Ventilation

41

Ventilation

42

7

Natural Ventilation Potential, North Coast

Natural Ventilation Potential, Central Valley

(San Francisco)

(Sacramento)

Ventilation

Ventilation

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Natural Ventilation Potential, Desert

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Guidelines Related to Natural Ventilation

(Daggett) „ TC1: Cross ventilation „ TC2: Stack ventilation „ TC3: Ceiling fans

Ventilation

45

Title 24 and Mechanical Ventilation

– E.g. 30 people per classroom

46

„ Often a good choice in California

Default occupant density

„ Opportunities

– Look up in Title 24 – Divide by two

OR

Ventilation

Mixed Mode Ventilation

Two options for calculating minimum ventilation rate Actual number of occupants:

Vol. II - page 301

– Avoid air conditioning in spring and fall – Save fan energy – Potential psychological benefits

For 960 ft² classroom: – 20 ft²/person for classroom – 960/20 = 48 people. – 48/2 = 24 people.

„ Challenges – Avoid increase in heating or cooling loads – Providing ventilation whenever occupants are present

15 cfm per person minimum for classroom 15 cfm/person X 30 people = 450 cfm

15 cfm/person X 24 people = 360 cfm

Ventilation

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Ventilation

48

8

Energy Credit 2: Natural Ventilation (1 to 4 points) 1 point

Natural Ventilation Examples „ No air conditioning

2.1. Install HVAC interlocks to turn off HVAC systems if operable windows or doors are opened.

– Cesar Chavez Elementary, Oakland – Ross School, Ross, Marin County

„ San Diego USD Policy

3 points 2.2. Design 90% of permanent classrooms without air conditioning.

– No AC unless indoor T > 78°F for >10% of school hours

Ross School

Ventilation

Cesar Chavez

Ventilation

49

50

HVAC System Selection Decision Tree Can natural ventilation meet all cooling needs? No

Yes

HVAC and Building Envelope

Can natural ventilation meet outdoor air ventilation requirement? No

No

Heating only hydronic systems Radiant floor Baseboard or Heating only air systems Gas furnace Unit ventilator

HVAC System Selection and Design

See Page 298 Volume II

Can evaporative cooling meet cooling requirements?

Yes

Yes

Evaporative cooling system Indirect Direct Indirect/Direct

Is natural ventilation accessible and beneficial for a significant portion of the school year?

Heating only air systems Gas furnace Unit ventilator or Heating only hydronic + separate air ventilation system Radiant floor Baseboard

No

Yes Mixed mode HVAC system (allow simple occupant control of HVAC and operable openings) - Packaged rooftop - Gas/electric split - Ductless split - Ceiling panel - Unit ventilator (2-pipe or 4-pipe) - Air or water cooled chiller (if appl.)

HEATING ONLY

Cooling and heating system (Ensure efficient duct and fan design) - VAV reheat - Packaged rooftop - Gas/electric split - Unit ventilator (2-pipe or 4-pipe) - Air or water cooled chiller (if appl.)

HEATING AND COOLING

HVAC System Design

Which is Best? (Hint: it’s not always clear)

Which is Best? (continued)

Packaged PackagedRooftop Rooftop Packaged PackagedSplit SplitSystem System Packaged PackagedVariable VariableAir AirVolume Volume •Air-cooled •Air-cooled •Evap.-cooled •Evap.-cooled

Water-Source Water-SourceHeat HeatPumps Pumps •Cooling •Coolingtower tower •Ground •Groundloop loop

52

Packaged PackagedRooftop Rooftop Packaged PackagedSplit SplitSystem System

2-pipe 2-pipefan fancoils coils

„ Can run individual systems for afterhour activities

Packaged PackagedVariable VariableAir AirVolume Volume •Air-cooled •Air-cooled •Evap.-cooled •Evap.-cooled

4-pipe 4-pipefan fancoils coils Variable VariableAir AirVolume Volume •Single •Singleduct duct •Dual •Dualduct duct Central plant options 53

54

9

Which is Best? (continued)

Which is Best? (continued)

Packaged PackagedRooftop Rooftop

„ Greater comfort potential due to more steady temperature control

Packaged PackagedSplit SplitSystem System „ Compressor failure affects only a single classroom

Packaged PackagedVariable VariableAir AirVolume Volume •Air-cooled •Air-cooled •Evap.-cooled •Evap.-cooled

4-pipe 4-pipefan fancoils coils Variable VariableAir AirVolume Volume •Single •Singleduct duct •Dual duct •Dual duct

Water-Source Water-SourceHeat HeatPumps Pumps •Cooling •Coolingtower tower •Ground •Groundloop loop 55

Which is Best? (continued)

„ Fewer compressors to maintain

56

Which is Best? (continued)

2-pipe 2-pipefan fancoils coils

2-pipe 2-pipefan fancoils coils „ Potential for lower operating cost

4-pipe 4-pipefan fancoils coils

„ Potential for lower maintenance cost

Variable VariableAir AirVolume Volume •Single •Singleduct duct •Dual •Dualduct duct

Water-Source Water-SourceHeat HeatPumps Pumps •Cooling •Coolingtower tower •Ground •Groundloop loop

Central plant options…

4-pipe 4-pipefan fancoils coils Variable VariableAir AirVolume Volume •Single •Singleduct duct •Dual •Dualduct duct Central plant options…

57

System Selection Considerations „ Initial cost „ Noise and vibration „ Thermal comfort performance „ Operating costs and energy efficiency „ Maintenance costs and needs

58

The Good News…

Set Setup upaascoring scoringmatrix matrix to tocompare comparesystem system alternatives alternatives (It’s (It’sworth worthspending spendingaafew few hours hoursearly earlyin inthe thedesign design process) process)

Any of these system types can be designed to be relatively efficient given careful attention to specifications and design details (and usually with a little extra up front investment)

„ Space requirements (in the classroom, on the roof or in mechanical rooms) „ Electrical service requirements „ Gas service requirements „ Durability and longevity „ Indoor air quality ventilation performance „ The ability to provide individual control for classrooms and other spaces „ The type of refrigerant used and its ozone-depleting potential

HVAC System Design

59

HVAC System Design

60

10

HVAC Guidelines

HVAC Guidelines (cont’d)

„ TC1: Cross Ventilation

„ TC9: Ductless Split System

„ TC2: Stack Ventilation

„ TC10: Evaporative Cooling System

„ TC3: Ceiling Fans

„ TC11: VAV Reheat System

„ TC4: Gas/Electric Split System

„ TC12: Radiant Slab System

„ TC19: Air Distribution Design Guidelines

„ TC5: Packaged Rooftop System

„ TC13: Baseboard Heating System

„ TC20: Duct Sealing and Insulation

„ TC6: Displacement Ventilation System

„ TC14: Gas-Fired Radiant Heating System

„ TC21: Hydronic Distribution

„ TC7: Hydronic Ceiling Panel System

„ TC15: Ground Source Heat Pump System

„ TC8: Unit Ventilator System

„ TC16: Evaporatively Precooled Condenser

HVAC System Design

„ TC17: Dedicated Outside Air Systems „ TC18: Economizers

„ TC23: Hot Water Supply „ TC24: Adjustable Thermostats „ TC25: EMS/DDC „ TC26: Demand Controlled Ventilation „ TC27: CO Sensors for Garage Exhaust Fans

„ TC21: Chilled Water Plants

HVAC System Design

61

Design Case: Packaged Rooftop System

62

Impact of Cooling Compressor Cycling

„ Minimize cooling loads (envelope and lighting) „ Avoid conservative load calculations (and don’t rely on rules-of-thumb) „ Avoid over sizing (design conditions occur relatively few hours per year) „ Economizer – factory installed and run tested, direct drive preferred „ Thermostatic expansion valve „ High efficiency, SEER 12 or better „ Design ducts for low air velocity

Standard Efficiency

High Efficiency

Image Source: Small HVAC System Design Guide, CEC PIER Program, 2003

HVAC System Design

Source: Small HVAC System Design Guide, CEC PIER Program, 2003

HVAC System Design

63

Impact of Cycling on Efficiency

64

Equipment Sizing „ Bigger is not always better! Avoid oversizing for: – – – –

AC/heat pump compressors. Furnaces. Boilers. Chillers.

„ Sometimes bigger is better! – – – –

Source: Small HVAC System Design Guide, CEC PIER Program, 2003

HVAC System Design

65

Ducts. Fans (if they have speed control). Cooling towers. Pipes.

HVAC System Design

66

11

Economizer Energy Savings

Packaged System Problems Economizers

100.0%

90.0%

Refrigerant charge

80.0%

Low airflow

Annual Energy Savings

70.0%

60.0%

Cycling fans during occupied period

50.0%

40.0%

Fans run during unoccupied period

30.0%

Simultaneous heating and cooling

20.0%

10.0%

No outside air intake at unit

0.0% 1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

Climate Zone Non-integrated Economizer

0

Integrated Economizer

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Problem Frequency

Source: Small HVAC System Design Guide, CEC PIER Program, 2003

HVAC System Design

Source: Small HVAC System Design Guide, CEC PIER Program, 2003

HVAC System Design

67

Economizer Actuator Types

68

Economizer Specifications „ Factory-installed and run-tested economizers „ Direct-drive actuators „ Differential (dual) changeover logic „ Low leakage dampers

Linkage Driven

Drive Drive

Source: Small HVAC System Design Guide, CEC PIER Program, 2003

HVAC System Design

Source: Small HVAC System Design Guide, CEC PIER Program, 2003

HVAC System Design

69

Thermostatic Expansion Valve Impact

70

Design Case: Packaged Rooftop System Costs

1.2

1000 ft2 classroom, 4 ton AC, SEER 10

TXV 100%

Normalized Efficiency Normalized Efficiency

1

0.8

Increase SEER 10 to 12 ($100 per ton)

$400

Economizer

$300

Thermostatic expansion valve

Fixed Expansion Device

Total

TXV Short orifice

0.6

Reduce from 4 tons to 3 tons ($500 per ton) Net Cost

0.4

Savings (~1,600 kWh/yr, @ $0.12/kWh) 0.2

0 50%

$75 $775 ($0.78 per ft2) - $500 $275 ($0.28 per ft2) $190 per year

Simple payback period 60%

70%

80%

90%

100%

110%

120%

130%

With downsizing credit Without downsizing credit

140%

1.4 years 4.1 years

% Factory Charge

% Factory Charge Source: Small HVAC System Design Guide, CEC PIER Program, 2003

HVAC System Design

71

72

12

Additional Packaged Rooftop Measures

HVAC and Building Envelope

„ Higher efficiency, SEER >12 (add $350 per ton for SEER 16) „ Multiple compressors or variable speed compressor „ Variable speed or multiple speed fan „ CO2 ventilation control

Special HVAC Systems: Displacement Ventilation

„ Specify commissioning „ Integration with lighting motion sensor control „ Interlocks on windows and doors „ Increase the air flow to extract extra sensible cooling capacity out of the unit, allowing the selection of a smaller “nominal” unit.

HVAC System Design

73

Displacement Ventilation

Benefits of Displacement Ventilation

„ Fresh cool air is slowly supplied near the floor.

„ Healthier environment; germs are not spread as easily. „ 100% fresh air vs. recirculation of return air.

„ Air rises as it warms.

„ Improved acoustics. „ Energy efficient system.

„ Air is exhausted near the ceiling.

„ Compatible with operable windows and natural ventilation.

Courtesy H. L. Turner Group

Displacement Ventilation

Displacement Ventilation Details Conventional System

76

Displacement Ventilation Details (cont’d) Displacement System

Ceiling Height

8’+

10’+

Supply air flow

1,000 – 1,500 cfm

400 - 600 cfm

Diffuser air velocity

600 – 800 fpm

<100 fpm

Cooling supply air temperature

52° - 55°

63° – 68°

400 – 500 cfm (~30%)

400 – 600 cfm (100%)

Outside air flow

Displacement Ventilation

75

Displacement Ventilation

Cooling load (lights)

77

Conventional System

Displacement System

3,300 Btu/h

x 0.13 = 430 Btu/h

Cooling load (people)

5,000 Btu/h

x 0.30 = 1,500 Btu/h

Cooling load (equip)

1,500 Btu/h

x 0.30 = 450 Btu/h

Cooling load (shell)

0 – 3,000 Btu/h

x 0.19 = 0 – 570 Btu/h

Total space cooling load

9,800 – 12,800 Btu/h

2,380 – 2,960 Btu/h

Ventilation air load (varies by climate)

14,000 Btu/h

14,000 Btu/h

Total cooling load

23,800 – 26,800 Btu/h (2.0 – 2.2 tons)

16,380 – 16,960 Btu/h (1.4 tons)

Displacement Ventilation

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13

Displacement Ventilation Details (cont’d)

AC size

Conventional System

Displacement System

3 tons

2 tons

Cooling demand

3.3 kW

2.2 kW

Fan demand

0.3 kW

0.2 kW

Total demand

3.6 kW

2.4 kW

Displacement Ventilation

Providing the Neutral Air

79

Providing the Neutral Air (cont’d)

Displacement Ventilation

80

Providing the Neutral Air (cont’d)

81

Providing the Neutral Air (cont’d)

Displacement Ventilation

Displacement Ventilation

Displacement Ventilation

82

Integrated Thermal Energy Storage

83

Displacement Ventilation

84

14

More Information on Displacement Ventilation

What You Should Remember

„ Guideline TC6: Displacement Ventilation Systems.

„ Minimize cooling loads through orientation and shading design.

„ Yuan, Xiaoxiong. Performance Evaluation and Design Guidelines for Displacement Ventilation. ASHRAE Transactions. 1999. V. 105. Pt. 1. www.ashrae.org.

„ Take advantage of natural ventilation where it’s feasible to expand comfort range and save energy. „ Perform load calculations and avoid over sizing AC equipment

„ Current research project:

„ Consider displacement ventilation for better air quality and energy efficiency.

– CEC PIER Indoor Environmental Quality Study, Thermal Displacement Ventilation in Classrooms. – Demonstration classrooms to be installed summer 2004

Displacement Ventilation

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86

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