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HVAC and the Envelope
Towards to New Rules of Thumb Steve Kemp | April 2015
What climate are these building experiencing?
Denver
Honolulu
Los Angeles
Edmonton
Toronto
From Envelope is King, to it’s the HVAC stupid and back again
My early career • It’s all about the envelope
• Heating and cooling loads are imposed primarily by the envelope, so let’s start there!
It didn’t take me long to find… • HVAC design and specifications are terrible
• Fix the stupid things that we’re doing!
Today… Great envelopes enables great HVAC
Typical Characteristics of High Performance HVAC
• Separates ventilation from temperature control • Humidity control through ventilation, local heating /
cooling
• Simple local controls • Amendable to low temperature heating, higher
temperature cooling • Increases efficiency of primary equipment • Increases opportunity for using waste/free energy
sources/sinks
Equitable (now Commonwealth) Building in Portland
• Modern Prototype of fully air-conditioned building
• Architectural Forum: • “crystal and metal tower” • spectacular for “its huge areas of
sea green glass”
• A/C Installed to counteract the glazing
• It worked! • Maybe not the best precedent
1950s-1960s Constant Air Volume and Perimeter Induction
• Buildings created with large interior spaces • needed year-round cooling
• Perimeter needs both heating and cooling
• Ventilation needed everywhere
• Ventilation air rate typically less than required for cooling
6
Interior: Constant Air Volume
7
Perimeter: Constant Air Volume outdoor air only with Induction Heating/Cooling
Induction Units
Induction Unit
1950s-1960s Constant Air Volume and Perimeter Induction
• Heating and Cooling by air • Economizer (free cooling) for
interior during winter
Then….
• Construction costs increased • Value Engineering! • Induction units and perimeter
air handler deleted to save first costs
Which gave us CAV with Re-Heat
Re-heat
1970s until today: Variable Air Volume Systems
Perimeter heating (and re-heat) provided by baseboards or heating coil in fan-powered VAV box
Re-heat
VAV Systems
• Single air handler for both internal and perimeter spaces
• Air handler and duct work designed for max cooling condition • Low pressure drop
(resistance) at most operating conditions
Significant Fan Power Savings over CAV
with variable speed drives fan power is proportional to cube of air flow
1970s until today: Variable Air Volume Systems
Re-heat
Dedicated Outdoor Air Systems (DOAS)
Provide ventilation air independent of heating and cooling requirements ► optionally dehumidify for improved comfort
Excellent exhaust air heat recovery performance No reheat! 2-pipe and 4-pipe fan coils Radiant heating/cooling Distributed heat pumps Even and VAV-DOAS option Etc… No outdoor air economizer (free cooling) ► operable windows or cooling tower based economizer
How does an HVAC Designer Look at a Floorplan?
Open office area: 8474 ft²
Enc. Office area: 257 ft²
Mee
ting
room
ar
ea: 9
42 ft
²
Storage room area: 1070 ft²
W. r
oom
ar
ea: 2
14 ft
² (ea
ch)
Cor
ridor
ar
ea: 3
21 ft
² K
itche
n / b
reak
room
ar
ea: 5
35 ft
² Boardroom area: 1070 ft²
Enclosed offices (11 of them) area: 170 ft² (each)
30 BTU/ft2 cooling 15 BTU/ft2 heating
20 B
TU/ft
2 co
olin
g 15
BTU
/ft2
heat
ing
10 BTU/ft2 cooling 0 BTU/ft2 heating
20 B
TU/ft
2 co
olin
g 15
BTU
/ft2
heat
ing
Perimeter Spaces Significantly Affected by Envelope
Boardroom area: 1070 ft²
Internal Gains • Lights • Receptacles • People
Solar Gains Winter Heat Loss
Cooling Loads: Lights, Receptacles, People
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
Typical Design Very EfficientDesign
Des
ign
Coo
ling
Dem
and
(BTU
/hr-
ft2)
People
Receptacles
Lights
Cooling Loads: Lights, Receptacles, People, Solar
50% WWR and solar control low-e clear window
0.0
5.0
10.0
15.0
20.0
25.0
30.0
Typical Design Very EfficientDesignD
esig
n C
oolin
g D
eman
d (B
TU/h
r-ft2
) Solar Gains
People
Receptacles
Lights
Interaction with HVAC
0
5
10
15
20
25
30
35
40
45
50
0 0.05 0.1 0.15 0.2 0.25 0.3
Peak
Coo
ling
Req
uire
d (B
TU/h
r-ft2
)
Window + Wall SHGC
Corner Office
Side Office
Typ. Limit of Radiant Cooling
Typ. Limit of Chilled Beam
80% WWR 0.35 SHGC
35% WWR 0.27 SHGC
ASHRAE 90.1-2013
40% WWW 0.40 SHGC
Typ. Limit of Chilled Beam (badly designed)
Typ. All VAV system and Fan Coils (can always push more air!)
Heating Loads: Kansas City
0
10
20
30
40
50
60
2.0 4.0 6.0 8.0 10.0 12.0 14.0
Peak
Hea
ting
Req
uire
d (B
TU/h
r-ft2
)
R-Value of Window + Wall
Corner Office
Side OfficeTyp. Limit of Infloor Radiant
Typ. Cost Effective VRF Heat Pumps
ASHRAE 90.1-2013
40% WWW 0.40 SHGC
Typ. Limit of 180F Baseboard
Toronto Office Tower R-6 spandrel,
60% WWR of U-0.25
What I want R-20 Walls, 35% WWR of U-0.15
Great envelopes enables great HVAC
• Language matters: Are whole Wall + Window usefull?
• for determining relevant heating/cooling system… YES
• Many low energy heating/cooling design have output limitations
• Architects and Engineers don’t have a common language / tool set to identify synergy performance goals
130 kWh/m2-an (42 kBTU/ft2-an)
69 kWh/m2-an (22 kBTU/ft2-an)
MMM Group Limited 100 Commerce Valley Drive West Thornhill, ON Canada L3T 0A1 t: 905.882.1100 | f: 905.882.0055 e: mmm@mmm.ca
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