HVAC and Building Enclosure

8/14/2019 HVAC and Building Enclosure

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Overview

Misc. CHPS CriteriaThermal Loads in SchoolsGood Envelope DesignVentilation: Natural & MechanicalHVAC System Selection & DesignDisplacement Ventilation

HVAC andBuilding Enclosure

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Training Objectives

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

Based on understanding of: 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

Misc. CHPS

Criteria

HVAC andBuilding Envelope

4CHPS Criteria

2.1. Reduce the use of municipally provided potable water for building sewage conveyance by a minimum of 50% through theutilization of water-efficient fixtures and/or using municipallysupplied 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 (notincluding irrigation) after meeting the Energy Policy Act of 1992sfixture performance requirements.OR2.3. Exceed the potable water use reduction by 30% beyond thebaseline.

1 point

2 points

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

5

Energy Efficiency

Energy Prerequisite 1: Minimum Energy Performance.

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

Energy Credit 2: Natural Ventilation. HVAC interconnect with windows and doors. 90% of classrooms without AC.

Energy Credit 3: Renewable Energy and Distributed Generation.

Energy Prerequisite 2: Fundamental Building Systems Testing andTraining.

Energy Credit 4: Commissioning.

Energy Credit 5: Energy Management Systems.

CHPS Criteria 6

Prescriptive Approach for Energy Efficiency

Energy Prerequisite 1 (10% Savings) Lighting power no greater than 0.95 W/ft 2 (motion sensor credit allowed) Economizer

Energy Credit 1 (20%, 4 points) Daylighting and dimming controls on at least 40% of lighting Radiant barrier in attic.

CHPS Criteria

October 2003


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Commissioning

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.

Energy Prerequisite 2: Testing and Training.

Energy Credit 4: Commissioning.

CHPS Criteria

ThermalLoads inSchools


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Why Talk About Thermal Loads?

An understanding of loads helps when setting envelope designpriorities

Minimizing loads can have many benefits Better comfort Smaller HVAC equipment Lower operating cost CHPS energy efficiency points!

Thermal Loads in School 10

Whats a BTU?

Btu = British Thermal Unit

The heat generated by theburning of one match(approximately).

1 Btu = Energy required to raisethe temperature of 1 pound of water (about 1 pint) by 1 degreeFahrenheit.

Thermal Loads in School

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Heat Gains (independent of outside temperature)

12,800 Btu/hTotal

up to 3,000 Btu/hFairly small with correct orientationand shading

Solar

1,500 Btu/hThree computers(About 150 watts each)

Plugs

3,300 Btu/h1 watt per square foot(1 watt = 3.413 Btu/hr)

Lights

5,000 Btu/h24-30 kids(@ 200 Btu/hr)

People


Heat Losses/Gains(dependent on outside air temperature)

Window conduction

Walls, roofs and floors

Infiltration

Outside air ventilation (a system load r ather than a space load)



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Balance Point Temperature

-25,000

-20,000

-15,000

-10,000

-5,000

0

5,000

10,000

15,000

20,000

25,000

0 10 20 30 40 50 60 70 80 90 100 110 120

Outdoor Air Temperature

C l a s s r o o m

L o a d s

( B t u / h o u r )

Cooling Required

Heating Required

Wall & Roof


Balance Point Temperature (contd)

-25,000

-20,000

-15,000

-10,000

-5,000

0

5,000

10,000

15,000

20,000

25,000

0 10 20 30 40 50 60 70 80 90 100 110 120


C l a s s r o o m

L o a d s

( B t u / h o u r )

Cooling Required

Heating Required

+ Window


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-25,000-20,000

-15,000

-10,000

-5,000

0

5,000

10,000

15,000

20,000

25,000

0 10 20 30 40 50 60 70 80 90 100 110 120


C l a s s r o o m

L o a

d s

( B t u / h o u r )

Cooling Required

Heating Required

+ Occupants



-25,000-20,000

-15,000

-10,000

-5,000

0

5,000

10,000

15,000

20,000

25,000

0 10 20 30 40 50 60 70 80 90 100 110 120


C l a s s r o o m

L o a

d s

( B t u / h o u r )

Cooling Required

Heating Required

+ Lights


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-25,000

-20,000

-15,000

-10,000

-5,000

0

5,000

10,000

15,000

20,000

25,000

0 10 20 30 40 50 60 70 80 90 100 110 120


C l a s s r o o m

L o a

d s

( B t u / h o u r )

Cooling Required

Heating Required

+ Plugs

Balance PointTemperature


GoodEnvelopeDesign



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Control Thermal Loads

Its pretty easy!

Priorities:1. Pay attention to the orientation of glazing.2. Provide adequate insulation.3. Specify window shading and/or high performance windows.

4. Control roof heat gain through cool roofs and radiant barriers.

Pay attention to details

Good Envelope Design 20

Fenestration Orientation

Orient windows north/south.

Good Envelope Design

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How About Passive Solar?

Heat typically needed in early morning; not a good match.

Direct solar is a source of glare.

Possible applications in corridors and transitional areas.

Might be appropriate for mountain climates.

Good Envelope Design 22

Recommendation:Recommendation:

Guideline IN1Wall Insulation

Vol. II -page 268 Good Envelope Design

Interior or exterior insulation

Provide wallshading

Mass

Foam board sheathing +cavity insulation

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

Steel frame

2x6 with R-192x4 with R-13 or 2x6 with R-19

Wood frame

Central ValleyDesertMountain

South CoastNorth Coast

Wall type

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Fenestration Performance Characteristics

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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Transmission of Common Glazing Materials


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Window Construction

Choose high performancewindows. VLT > 0.65 SHGC < 0.40

Higher SHGC ok for completely

shaded windows.

Single pane glazing may be okin warm coastal areas.

See also Guideline DL1: ViewWindows for VLTrecommendations.


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

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R-38 blown in atticR-38 batt in framed

R-30 blown in atticR-30 batt in framed

Wood-framed, atticand other

R-14 foam boardR-7 foam boardInsulation above deck

Central ValleyDesertMountain

South CoastNorth Coast

Roof type


Guideline IN2Roof Insulation

Vol. II -page 271


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Typically white color.

Single ply: EPDM. CPE. CPSE. TPO.

Liquid applied: Elastomeric. Acrylic. Polyurethane.

White coated metal.


Guideline IN3Cool Roofs

Vol. II - page 273


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Reflective foil sheet.

Cuts radiant heat transfer.

Reduces cooling energy.

Especially beneficial if ducts are in attic space


Guideline IN4Radiant Barriers

Vol. II -page 277


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Georgina BlachMiddle School,Los Altos, CA

GelfandRNP Architects Photo: Andrew Davis, AIA


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Photo: Andrew Davis, AIA

Gym, view from north east

Photo: Ken Rackow

View from southwest

Photo: Andrew Davis, AIA34

Cesar Chavez Elementary School, Oakland

VPN Architects

Ventilation:Natural andMechanical


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What is Ventilation?

The process of supplying and removing air by natural or

mechanical means to and from any space. Such air mayor may not be conditioned.

(ASHRAE Standard 62-1999)

Ventilation


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Why Ventilate?

Comfort dilute odors

Health dilute carbon dioxide and other pollutants

Title 24 says we must

Its a CHPS prerequisite (P1.1 & P1.2)

Ventilation 38

How?

Naturally

Mechanically

Mixed mode (i.e. both)

Ventilation

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Natural Ventilation

Energy efficient ventilation potential.

Traditional in California.

Still appropriate strategy in much of state.

Design for security.

Ventilation 40

When is Natural Ventilation Feasible?

Appropriate climate

Acceptable outdoor noise level

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

Design meets Title 24 ventilation requirements

Ventilation

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Title 24 and Natural Ventilation

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 ft (30 ft x 32 ft) classroom, At least 48 ft opening area. Openings on two sides of the room.

Ventilation 42

Natural Ventilation Potential, South Coast(Long Beach)

Ventilation


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

1 point

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

3 points

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

Ventilation 50

Natural Ventilation Examples

No air conditioning Cesar Chavez Elementary, Oakland Ross School, Ross, Marin County

San Diego USD Policy No AC unless indoor T > 78F for >10% of

school hours

Ventilation

Ross School Cesar Chavez

HVACSystem

Selectionand Design


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HVAC System Selection Decision Tree

Can natural ventilation meetoutdoor air ventilation

requirement?

Heating only hydronicsystems

Heating only air systems

Radiant floor Baseboard

or

Gas furnaceUnit ventilator

Heating onlyair systems

Heating onlyhydronic +separate air ventilation system

Gas furnaceUnit ventilator

or

Radiant floor Baseboard

Can evaporative coolingmeet cooling requirements?

Is natural ventilationaccessible and beneficialfor a significant portion of

the school year?

Evaporativecooling systemIndirectDirectIndirect/Direct

Mixed mode HVAC system(allow simple occupant controlof HVAC and operableopenin gs)- Packaged rooftop- Gas/electric split- Ductlesssplit- Ceiling panel- Unit ventilator (2-pipe or 4-pipe)- Air or water cooled chiller (if appl.)

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

YesNo

No

No

No

Yes

Yes

Yes

HEATING ONLY

HEATING AND COOLING

Can natural ventilation meet all cooling needs?

HVAC System Design

See Page 298Volume II

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Which is Best? (Hint: its not always clear)

Packaged RooftopPackaged Rooftop

Packaged Split SystemPackaged Split System

Packaged Variable Air VolumeAir-cooledEvap.-cooled


2-pipe fan coils2-pipe fan coils


Variable Air VolumeSingle ductDual duct


Water-Source Heat PumpsCooling tower Ground loop

Water-Source Heat PumpsCooling tower Ground loop Central plant options

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Which is Best? (continued)

Can run individualsystems for after-hour activities






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Compressor failureaffects only a singleclassroom

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Packaged Variable Air Volume

Air-cooledEvap.-cooled




Greater comfort potential dueto more steady temperaturecontrol

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Central plant options

Fewer compressors tomaintain

Potential for lower maintenance cost

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Water-Source Heat PumpsCooling tower Ground loop Central plant options

Potential for lower operating cost

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System Selection Considerations

Initial cost

Noise and vibrationThermal comfort performance

Operating costs and energy efficiency

Maintenance costs and needs

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

Set up a scoring matrixto compare system

alternatives(Its worth spending a fewhours early in the design

process)

Set up a scoring matrixto compare system

alternatives(Its worth spending a fewhours early in the design

process)

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The Good News

Any of these system types can be designed

to be relatively efficient given careful attention tospecifications and design details

(and usually with a little extra up front investment)

HVAC System Design


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HVAC Guidelines

TC1: Cross Ventilation

TC2: Stack Ventilation

TC3: Ceiling Fans

TC4: Gas/Electric Split System

TC5: Packaged Rooftop System

TC6: Displacement VentilationSystem

TC7: Hydronic Ceiling PanelSystem

TC8: Unit Ventilator System

TC9: Ductless Split System

TC10: Evaporative Cooling System

TC11: VAV Reheat System

TC12: Radiant Slab System

TC13: Baseboard Heating System

TC14: Gas-Fired Radiant HeatingSystem

TC15: Ground Source Heat PumpSystem

TC16: Evaporatively PrecooledCondenser

HVAC System Design 62

HVAC Guidelines (contd)

TC17: Dedicated Outside Air Systems

TC18: Economizers

TC19: Air Distribution DesignGuidelines

TC20: Duct Sealing and Insulation

TC21: Hydronic Distribution

TC21: Chilled Water Plants

TC23: Hot Water Supply

TC24: Adjustable Thermostats

TC25: EMS/DDC

TC26: Demand Controlled

VentilationTC27: CO Sensors for GarageExhaust Fans

HVAC System Design

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Design Case: Packaged Rooftop System

Minimize cooling loads (envelope and lighting)

Avoid conservative load calculations (and dont 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


Impact of Cooling Compressor Cycling

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

HVAC System Design

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Impact of Cycling on Efficiency



Equipment Sizing

Bigger is not always better! Avoid oversizing for:

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

Sometimes bigger is better! Ducts. Fans (if they have speed control). Cooling towers. Pipes.

HVAC System Design


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Economizer Energy Savings

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

70.0%

80.0%

90.0%

100.0%

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Climate Zone

A n n u a

l E n e r g y

S a v

i n g s

Non-integrated Economizer Integrated Economizer



Packaged System Problems

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7

No outside air intake atunit

Simultaneous heatingand cooling

Fans run duringunoccupied period

Cycling fans during

occupied period

Low airflow

Refrigerant charge

Economizers

Problem Frequency


HVAC System Design

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Economizer Actuator Types

Linkage Driven Drive DriveSource: Small HVAC System Design Guide, CEC PIER Program, 2003


Economizer Specifications

Factory-installed and run-tested economizers

Direct-drive actuators

Differential (dual) changeover logic

Low leakage dampers


HVAC System Design

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Thermostatic Expansion Valve Impact


0

0.2

0.4

0.6

0.8

1

1.2

50% 60% 70% 80% 90% 100% 110% 120% 130% 140%

% Factory Charge

N o r m a

l i z e

d E f f i c i e n c y

TXVShort orifice

N o r m a

l i z e

d E f f i c i e n c y

% Factory Charge

100%

TXV

Fixed Expansion Device


Design Case: Packaged Rooftop System Costs

$275 ($0.28 per ft 2)Net Cost

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

$775 ($0.78 per ft 2)

$75

$300

$400

Total

Thermostatic expansion valve

Economizer

Increase SEER 10 to 12 ($100 per ton)

1000 ft 2 classroom, 4 ton AC, SEER 10

1.4 years4.1 years

With downsizing creditWithout downsizing credit

Simple payback period$190 per year Savings (~1,600 kWh/yr, @ $0.12/kWh)


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Additional Packaged Rooftop Measures

Higher efficiency, SEER >12 (add $350 per ton for SEER 16)

Multiple compressors or variable speed compressor

Variable speed or multiple speed fan

CO 2 ventilation control

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

Special HVACSystems:DisplacementVentilation


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Displacement Ventilation

Fresh cool air is slowly suppliednear the floor.

Air rises asit warms.

Air is exhausted near theceiling.

Courtesy H. L. Turner Group

Displacement Ventilation 76

Benefits of Displacement Ventilation

Healthier environment; germs are not spread as easily.

100% fresh air vs. recirculation of return air.

Improved acoustics.

Energy efficient system.

Compatible with operable windows and natural ventilation.


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Displacement Ventilation Details

10+8+Ceiling Height

400 600 cfm (100%)400 500 cfm (~30%)Outside air flow

63 68 52 - 55Cooling supply air temperature


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Displacement Ventilation Details (contd)

DisplacementSystem

ConventionalSystem

2.4 kW3.6 kWTotal demand

0.2 kW0.3 kWFan demand

2.2 kW3.3 kWCooling demand

2 tons3 tonsAC size


Providing the Neutral Air


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Providing the Neutral Air (contd)




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Integrated Thermal Energy Storage



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More Information on Displacement Ventilation

Guideline TC6: Displacement Ventilation Systems.

Yuan, Xiaoxiong. Performance Evaluation and DesignGuidelines for Displacement Ventilation . ASHRAETransactions. 1999. V. 105. Pt. 1. www.ashrae.org .

Current research project: CEC PIER Indoor Environmental Quality Study, ThermalDisplacement Ventilation in Classrooms.

Demonstration classrooms to be installed summer 2004


What You Should Remember

Minimize cooling loads through orientation and shading design.

Take advantage of natural ventilation where its feasibleto expand comfort range and save energy.

Perform load calculations and avoid over sizing AC equipment

Consider displacement ventilation for better air quality and energyefficiency.

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