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