Download - HVAC and Building Enclosure
-
8/14/2019 HVAC and Building Enclosure
1/15
Overview
Misc. CHPS CriteriaThermal Loads in SchoolsGood Envelope DesignVentilation: Natural & MechanicalHVAC System Selection & DesignDisplacement Ventilation
HVAC andBuilding Enclosure
2
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
-
8/14/2019 HVAC and Building Enclosure
2/15
7
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
HVAC andBuilding Envelope
9
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
11
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
Thermal Loads in School 12
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)
Thermal Loads in School
-
8/14/2019 HVAC and Building Enclosure
3/15
13
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
Thermal Loads in School 14
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
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
+ Window
Thermal Loads in School
15
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
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
+ Occupants
Thermal Loads in School 16
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
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
+ Lights
Thermal Loads in School
17
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
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
+ Plugs
Balance PointTemperature
Thermal Loads in School
GoodEnvelopeDesign
HVAC andBuilding Envelope
-
8/14/2019 HVAC and Building Enclosure
4/15
19
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
21
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
23
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.
24
Transmission of Common Glazing Materials
-
8/14/2019 HVAC and Building Enclosure
5/15
25
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.
Good Envelope Design
http://www.denison.edu/enviro/barney/envtech.html
26
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
Good Envelope Design
Guideline IN2Roof Insulation
Vol. II -page 271
Recommendation:Recommendation:
27
Typically white color.
Single ply: EPDM. CPE. CPSE. TPO.
Liquid applied: Elastomeric. Acrylic. Polyurethane.
White coated metal.
Good Envelope Design
Guideline IN3Cool Roofs
Vol. II - page 273
Recommendation:Recommendation:
28
Reflective foil sheet.
Cuts radiant heat transfer.
Reduces cooling energy.
Especially beneficial if ducts are in attic space
Good Envelope Design
Guideline IN4Radiant Barriers
Vol. II -page 277
Recommendation:Recommendation:
29
Georgina BlachMiddle School,Los Altos, CA
GelfandRNP Architects Photo: Andrew Davis, AIA
-
8/14/2019 HVAC and Building Enclosure
6/15
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
HVAC andBuilding Envelope
36
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
-
8/14/2019 HVAC and Building Enclosure
7/15
37
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
39
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
41
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
-
8/14/2019 HVAC and Building Enclosure
8/15
-
8/14/2019 HVAC and Building Enclosure
9/15
49
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
HVAC andBuilding Envelope
52
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
53
Which is Best? (Hint: its not always clear)
Packaged RooftopPackaged Rooftop
Packaged Split SystemPackaged Split System
Packaged Variable Air VolumeAir-cooledEvap.-cooled
Packaged Variable Air VolumeAir-cooledEvap.-cooled
2-pipe fan coils2-pipe fan coils
4-pipe fan coils4-pipe fan coils
Variable Air VolumeSingle ductDual duct
Variable Air VolumeSingle ductDual duct
Water-Source Heat PumpsCooling tower Ground loop
Water-Source Heat PumpsCooling tower Ground loop Central plant options
54
Which is Best? (continued)
Can run individualsystems for after-hour activities
Packaged RooftopPackaged Rooftop
Packaged Split SystemPackaged Split System
Packaged Variable Air VolumeAir-cooledEvap.-cooled
Packaged Variable Air VolumeAir-cooledEvap.-cooled
-
8/14/2019 HVAC and Building Enclosure
10/15
55
Which is Best? (continued)
Packaged RooftopPackaged Rooftop
Packaged Split SystemPackaged Split System
Water-Source Heat PumpsCooling tower Ground loop
Water-Source Heat PumpsCooling tower Ground loop
Compressor failureaffects only a singleclassroom
56
Which is Best? (continued)
Packaged Variable Air VolumeAir-cooledEvap.-cooled
Packaged Variable Air Volume
Air-cooledEvap.-cooled
4-pipe fan coils4-pipe fan coils
Variable Air VolumeSingle ductDual duct
Variable Air VolumeSingle ductDual duct
Greater comfort potential dueto more steady temperaturecontrol
57
Which is Best? (continued)
2-pipe fan coils2-pipe fan coils
4-pipe fan coils4-pipe fan coils
Variable Air VolumeSingle ductDual duct
Variable Air VolumeSingle ductDual duct
Central plant options
Fewer compressors tomaintain
Potential for lower maintenance cost
58
Which is Best? (continued)
2-pipe fan coils2-pipe fan coils
4-pipe fan coils4-pipe fan coils
Variable Air VolumeSingle ductDual duct
Variable Air VolumeSingle ductDual duct
Water-Source Heat PumpsCooling tower Ground loop
Water-Source Heat PumpsCooling tower Ground loop Central plant options
Potential for lower operating cost
59
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)
60
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
-
8/14/2019 HVAC and Building Enclosure
11/15
61
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
63
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
HVAC System Design 64
Impact of Cooling Compressor Cycling
Source: Small HVAC System Design Guide, CEC PIER Program, 2003
HVAC System Design
65
Impact of Cycling on Efficiency
Source: Small HVAC System Design Guide, CEC PIER Program, 2003
HVAC System Design 66
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
-
8/14/2019 HVAC and Building Enclosure
12/15
67
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
Source: Small HVAC System Design Guide, CEC PIER Program, 2003
HVAC System Design 68
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
Source: Small HVAC System Design Guide, CEC PIER Program, 2003
HVAC System Design
69
Economizer Actuator Types
Linkage Driven Drive DriveSource: Small HVAC System Design Guide, CEC PIER Program, 2003
HVAC System Design 70
Economizer Specifications
Factory-installed and run-tested economizers
Direct-drive actuators
Differential (dual) changeover logic
Low leakage dampers
Source: Small HVAC System Design Guide, CEC PIER Program, 2003
HVAC System Design
71
Thermostatic Expansion Valve Impact
Source: Small HVAC System Design Guide, CEC PIER Program, 2003
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
HVAC System Design 72
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)
-
8/14/2019 HVAC and Building Enclosure
13/15
73
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
HVAC andBuilding Envelope
75
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.
Displacement Ventilation
77
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
-
8/14/2019 HVAC and Building Enclosure
14/15
79
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
Displacement Ventilation 80
Providing the Neutral Air
Displacement Ventilation
81
Providing the Neutral Air (contd)
Displacement Ventilation 82
Providing the Neutral Air (contd)
Displacement Ventilation
83
Providing the Neutral Air (contd)
Displacement Ventilation 84
Integrated Thermal Energy Storage
Displacement Ventilation
-
8/14/2019 HVAC and Building Enclosure
15/15
85
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
Displacement Ventilation 86
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.