Evaluating Small-Diameter Ductwork in High-Performance Homes

Pennsylvania Housing Research Center

Residential Building Design & Construction Conference

March 2016Andrew Poerschke

Agenda

Townhouse Small-Diameter Case Study• Overview• Comfort• System Run

Home-Run Manifold System• Design Approach• Lab Results• Field Results

25/13/2016

How We Think About Comfort

ACCA Manual RS

ASHRAE Standard 55

35/13/2016

Walls – R-23Ceiling – R-38Ducts – R-4Slab Edge – R-10Exposed Floor –

R-50

Ductwork in conditioned space

45/13/2016

Denver, CO homebuilder: Testing a small-diameter duct system for 3-story townhomes

• Reduce floor-to-floor stratification

• Improve comfort• Improve energy

efficiency• Ductwork in

conditioned space

Case Study

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A1 A2 A3 B1 B2 B3Design Cooling Load (kBtu/h) 16 13 18 16 13 18

Air Conditioner Rated Capacity

(kBtu/h)24 24 36 24 18 24

Outdoor Unit Model IS24G065 IS24G065 IS36G110 CA13NA24 CA13NA18 CA13NA24

Air Handling Unit Model M2430BL1-EA2 M2430BL1-EA2 IS12MPA 59SC2C040S17 59SC2C040S17 59SC2C040S17

Ductwork Location

Conditioned space

Conditioned space

Conditioned space

Conditioned space

Conditioned space

Conditioned space

Air Handling Unit Location Second floor Second floor High wall fan

coil First floor First floor First floor

Building Measured

Air Leakage (ACH 50)

2.97 3.49 3.98 2.15 2.73 3.18

Ductwork Measured Air

Leakage (CFM @ 25 Pa)

54 47 N/A 5 5 -

Floor Area 1,300 ft2 1,100 ft2 1,600 ft2 1,300 ft2 1,100 ft2 1,600 ft2

ControlExperiment

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Small-Diameter Duct System

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Small-Diameter Duct System

Small Bulkhead

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Summer

Winter

Room-to-Room Uniformity

Small-Diameter MSHP Standard

95/13/2016

Summer

Winter

A1 A2 A3 B1 B2 B3Average Room-to-Room ΔT (°F) 2.4 2.1 6.4 2.6 4.8 6.6

105/13/2016

System RuntimeSummer

Winter

Plug-n-Play Duct System

• Home-run duct design method• Each runout ~20 CFM• Total system capacity 250–350 CFM

115/13/2016

Lab Data

125/13/2016

Verify predictability of airflow

Input curves for simulations

Straight DuctSingle ElbowTwo Elbows

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0

10

20

30

40

50

60

0 10 20 30 40 50 60

ΔP (P

a / m

)

Aiflow (CFM)

e=0.0001 e=0.0 Measured Data

Lab DataDarcy–Weisbach vs. Measurements

25 Pa = 0.1 in. H20

Field Data

145/13/2016

Walls – R40Attic – R60Slab – R10

0.7 ACH50

Plenum Static Pressure

155/13/201625 Pa = 0.1 in. H20

0

0.05

0.1

0.15

0.2

0.25

0.3

0.35

0

10

20

30

40

50

60

70

80

90

2/11/2016 2/12/2016 2/13/2016 2/14/2016 2/15/2016 2/16/2016

Pres

sure

(In.

H20

)

Pres

sure

(Pa)

𝛥𝛥𝛥𝛥 = 𝑓𝑓ℓ𝜌𝜌(𝑄𝑄)2

4𝜋𝜋2𝒓𝒓𝟓𝟓

165/13/2016

66.567

67.568

68.569

69.570

70.5

0:00 6:00 12:00 18:00 0:00

Roo

m T

empe

ratu

re (F

)

Bedroom 2 (Open) Bedroom 2 (Closed)

-7-6-5-4-3-2-1012

0:00 6:00 12:00 18:00 0:00

Roo

m to

The

rmos

tat (

F)

Room to Thermostat (Open) Room to Thermostat (Closed)

Bedroom Temperature

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Duct Supply Temperature

02468

10

2/10/2016 2/11/2016 2/12/2016 2/13/2016 2/14/2016

Bedr

om2

vs.

Bedr

oom

3 S

uppl

y Te

mpe

ratu

re

Diff

eren

ce (F

)

60657075808590

2/10/2016 2/11/2016 2/12/2016 2/13/2016 2/14/2016

Roo

m S

uppl

y Te

mpe

ratu

re (F

)

Bedroom 2 Outlet Bedroom 3 Outlet

0

10

20

30

40

50

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Plen

um v

s. R

oom

Te

mpe

ratu

re Δ

(F)

Bedroom 2 Outlet Bedroom 3 Outlet

~ 2x BTU

R-3 added

0

10

20

30

40

50

60

-10 0 10 20 30 40 50

Duc

t Tem

pera

ture

(C)

Time since start of cycle (min)

Supply Plenum (Steel) Foyer Supply (Steel)

Living Supply (Steel) Supply Plenum (Unico)

Master Bedroom Supply (Unico) Bedroom 2 Supply (Unico)

Plenum Sup (PVC) Bedroom 2 Outlet (PVC)

Hall Outlet (PVC Ins.)

185/13/2016Compared to town house with similar duct lengths Δ10°C = Δ 18°F

Duct Supply Temperature

20°C

10°C

Where Are We Going?

Current effort runs through mid-2016• Design Methodology• Cost and Labor• Simulations• Cooling Field Data

195/13/2016

Questions and Discussion

205/13/2016