Transcript DUCT EFFICIENCY AND HEAT PUMP PERFORMANCE Paul Francisco David Baylon Ecotope, Inc. House Assumptions • House over crawl space – 1350 square feet – 3.5 ton heat.

DUCT EFFICIENCY AND
HEAT PUMP PERFORMANCE
Paul Francisco
David Baylon
Ecotope, Inc.
House Assumptions
• House over crawl space
– 1350 square feet
– 3.5 ton heat pump or electric furnace
– 10% leakage on both supply and return sides
• House with half basement
– Approx. 2200 square feet
– 3.5 ton heat pump or electric furnace
– 5% supply leakage, no return leakage
Equipment Assumptions
• 3.5 ton heat pump is rated at HSPF of 8.2,
SEER of 14
• For heating, resistance added to meet load,
compressor used as much as possible
• Electric resistance furnace sized to meet
load
• Some prototypes use different heat pumps,
both bigger and smaller
Effect of Ducts
• Duct losses add to the load that must be met
by the heat pump or furnace
– supply leakage and conduction result in
capacity that does not make it to the house
– return leakage and conduction result in changed
entering conditions at the equipment
Effect of Ducts
• Ducts in buffer spaces see different ambient
conditions than the house
– in heating season, crawl space often warmer
than outside but colder than house
– in cooling season, crawl space often cooler than
house or outdoors
– in cooling season, attic often hotter than house
or outdoors
Savings from added insulation Portland electric furnace
Heating - 1350 ft^2 house - EFA
Pre-1980
Uninsulated ducts
-31.2%
Add R-4 Supply
6.0%
Add R-11 Supply
10.3%
Add R-4 Return
0.5%
Add R-11 Return
0.8%
R-4 to R-11 Supply
R-4 to R-11 Return
4.6%
0.3%
Heating - half-basement house - EFA
Pre-1980
Uninsulated ducts
-12.6%
Add R-4 Supply
3.2%
Add R-11 Supply
5.5%
Add R-4 Return
0.0%
Add R-11 Return
0.0%
R-4 to R-11 Supply
R-4 to R-11 Return
2.4%
0.0%
1980-1993
-33.8%
6.4%
11.0%
0.5%
0.9%
Post-1993
-33.8%
6.4%
11.0%
0.5%
0.9%
5.0%
0.4%
5.0%
0.4%
1980-1993
-13.8%
3.4%
6.0%
0.0%
0.0%
Post-1993
-13.8%
3.4%
6.0%
0.0%
0.0%
2.6%
0.0%
2.6%
0.0%
Duct Loss for Electric Furnace
50
Crawl Space House
Half Basement House
Uninsulated Ducts
With R-11 added to Supply
30
20
10
Location
ou
la
Mi
ss
ne
Sp
ok
a
Bo
ise
nd
Po
rtla
le
Se
att
ou
la
Mi
ss
ne
Sp
ok
a
Bo
ise
nd
Po
rtla
le
0
Se
att
Loss due to Ducts, %
40
Duct Loss for Cooling
30
Crawl Space House
Half Basement House
Uninsulated Ducts
With R-11 added to Supply
20
15
10
5
Location
Sp
ok
an
e
Mi
ss
ou
la
Bo
ise
Po
rtla
nd
Se
att
le
Sp
ok
an
e
Mi
ss
ou
la
Bo
ise
Po
rtla
nd
0
Se
att
le
Loss due to Ducts, %
25
Duct Loss for Heating
(Heat Pumps)
120
Crawl Space House
Half Basement House
Uninsulated Ducts
With R-11 added to Supply
80
60
40
20
Location
la
Mi
ss
ou
ka
ne
Sp
o
Bo
ise
lan
d
Po
rt
ttle
Se
a
la
Mi
ss
ou
ka
ne
Sp
o
Bo
ise
lan
d
Po
rt
ttle
0
Se
a
Loss due to Ducts, %
100
Summary of Duct Effects
• Duct insulation can account for up to about 1/3 of duct
losses at these levels of leakage
• Return insulation has little impact
• Ducts have little impact in prototype with half basement
• Duct efficiency changes between heating and cooling, with
cooling being higher
• Largest impact of duct loss is for heating with heat pump
due to greater use of resistance at warmer temperatures this effect very large in colder climates (more than doubles
energy use in Missoula if ducts are uninsulated)
• Duct efficiency and percentage savings not heavily
dependent on house vintage
Heat Pump Performance
• Heating performance dependent on outdoor
temperature.
– Heating capacity of compressor reduces 30% between
47oF and 30oF
o
– Air delivery temperature is reduced by 10 F to less than
85oF resulting in severe comfort problems
– Electric resistance is brought on to increase heating
capacity and delivery air temperature
– To control these effects the manufactures recommend a
“Low Ambient Cutout” control set to about 30oF that
transfers turns off the compressor and uses the elements
only.
Seattle
80
1600
Total
Integrated
1400
1200
1000
40
800
600
20
400
200
0
-10
0
10
20
30
40
Outdoor Temperature
50
60
0
70
Hours
Capacity, MBtuh
60
Portland
80
1600
Total
Integrated
1400
1200
1000
40
800
600
20
400
200
0
-10
0
10
20
30
40
Outdoor Temperature
50
60
0
70
Hours
Capacity, MBtuh
60
Boise
80
1600
Total
Integrated
1400
1200
1000
40
800
600
20
400
200
0
-10
0
10
20
30
40
Outdoor Temperature
50
60
0
70
Hours
Capacity, MBtuh
60
Spokane
80
1600
Total
Integrated
1400
1200
1000
40
800
600
20
400
200
0
-10
0
10
20
30
40
Outdoor Temperature
50
60
0
70
Hours
Capacity, MBtuh
60
Missoula
80
1600
Total
Integrated
1400
1200
1000
40
800
600
20
400
200
0
-10
0
10
20
30
40
Outdoor Temperature
50
60
0
70
Hours
Capacity, MBtuh
60
Heat Pump Performance
Adjustments
• Heat pump set-up determines the overall
performance
– Improper charge and/or air flow results in a 5-12%
reduction in COP
– Defrost control reduces performance by 2% for demand
defrost and 10-12% for timed defrost
– Crankcase heater can be similar to defrost in cold
climates
– QC protocol necessary to insure that proper installation
and specification are met
Performance Adjustments
Partload adjustments by Climate zone: Heating
PTCS Installation Specs
HSPF
ARI Rating
6.8
7.1
8
8.12
8.3
Portland
Seattle
Boise
Spokane
Missoula
7.4
7.5
6.5
6.5
6.3
8.3
8.4
7.4
7.3
7.1
8.4
8.5
7.5
7.4
7.2
8.6
8.7
7.6
7.6
7.4
7.1
7.1
6.3
6.2
6.1
Climate adjustment
1.04
1.05
0.92
0.91
0.89
No PTCS Installation Specs: Charge & Flow
Portland
Seattle
Boise
Spokane
Missoula
6.7
6.8
5.9
5.9
5.7
7.0
7.1
6.2
6.1
6.0
7.9
8.0
7.0
6.9
6.8
8.0
8.1
7.1
7.0
6.9
8.2
8.3
7.3
7.2
7.0
DF&charge adjustment (Proctor, 91)
0.95
0.95
0.95
0.95
0.95
7.4
7.7
5.3
5.2
4.9
Control adjustment
0.906
0.928
0.728
0.719
0.695
No PTCS Installation Specs: Control with Low Ambient Cutout
Portland
Seattle
Boise
Spokane
Missoula
6.1
6.3
4.3
4.2
4.0
6.4
6.6
4.5
4.4
4.2
7.2
7.4
5.1
5.0
4.7
7.3
7.5
5.2
5.0
4.8
Heat Pump Cooling Performance
• Cooling performance rating uses SEER to indicate
cooling energy requirements
• Actual cooling seasonal COP depends on ambient
humidity and temperature in the climate
• Effective average for seasonal cooling
performance about 65% of the SEER rating
– A SEER of 14.0 is 9.1
– Duct performance can reduce this efficiency by 10-30%
– Not very dependent on Northwest climate
ns
Se
ly
pp
Su
d
Crawl Space
R
-1
1
te
ul
a
d
ly
pp
Su
ns
U
ni
R
-1
1
te
ul
a
e
e
at
lim
C
ns
+
U
ni
ib
le
ed
ns
ib
l
Se
R
at
COP
Seasonal COP & Ducts
Cooling - Spokane
5
Half Basement
4
3
2
1
0
Seasonal COP & Ducts
Cooling - Portland
5
Half Basement
Crawl Space
4
COP
3
2
1
ly
pp
Su
R11
ula
ins
Un
Su
R11
X Data
ted
ly
pp
ted
ula
ins
lim
+C
ibl
e
Se
ns
Un
ate
e
ibl
ns
Se
Ra
ted
0
Duct Efficiency Impact on Heat
Pump Performance
• Duct losses can reduce heat pump
performance to less than half of rated COP
• Much more severe in cold climates
• Overall performance depends on quality
duct installation as much as quality heat
pump installation
Seasonal COP & Ducts
Heating - Spokane
3
Without cutout
With cutout
Crawl Space
Half Basement
COP
2
1
Su
pp
ly
R11
d
lat
e
Un
ins
u
Su
pp
ly
R11
d
lat
e
Un
ins
u
ate
Cli
m
Ra
te
d
0
Seasonal COP & Ducts
Heating - Portland
3
Without cutout
With cutout
Crawl Space
Half Basement
COP
2
1
ly
R11
Su
pp
d
lat
e
su
Un
in
ly
R11
Su
pp
d
lat
e
su
Un
in
ate
Cli
m
Ra
te
d
0
Summary
• Overall system efficiency strongly interactive between
ducts and conditioning system
• Significant duct losses can largely eliminate potential
savings from heat pumps
• Overall system efficiency requires quality control of both
heat pump installation and duct installation
• Heat pump controls crucial to overall performance,
especially in cold climates
• HSPF and SEER rating numbers are poor approximations
of actual performance, even with ideal installation
• Percentage improvement from lower to higher SEER may
be appropriate