IEA HPP Annex 41 Cold Climate Heat Pumps: Improving ...web.ornl.gov/~jacksonwl/hpdm/Annex 41 - 2015...
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Transcript of IEA HPP Annex 41 Cold Climate Heat Pumps: Improving ...web.ornl.gov/~jacksonwl/hpdm/Annex 41 - 2015...
ORNL is managed by UT-Battelle
for the US Department of Energy
IEA HPP Annex 41 –
Cold Climate Heat
Pumps: Improving
Low Ambient
Temperature
Performance of Air-
Source Heat Pumps
Tandem, single-speed compressor air-source heat pump system laboratory and preliminary field test results
Bo Shen, Keith Rice, Omar Abdelaziz
Oak Ridge National Laboratory
August 19, 2015
2 Presentation_name
Contents
1. Background
2. Lab Testing
3. Field investigation
4. Summary
Target Market: Replace electric resistance heat in cold climates.
3 Presentation_name
1.1 Background
Problem Statement: • Typical ASHPs don’t work
well at low ambient temps due to very high discharge temp and pressure ratio
• Single-speed ASHP heating capacity not sufficient to match building load
• COP degrades significantly with ambient temperature
Technical Goals (Project outputs): Develop a CCHP to minimize resistance heating • COP@ 8.3°C > 4.0; HP capacity@ -25°C > 75% of rated capacity@
8.3°C. • Maximize COPs at -8.3°C and -25°C with acceptable payback period.
0%
20%
40%
60%
80%
100%
120%
-23 -13 -3 7 17 27 37 47 57 67 77 87 97 107
Bu
ild
ing
Lo
ad
Lin
e a
nd
He
ati
ng
Ca
pa
cit
y o
f T
yp
ica
l A
SH
P a
nd
Ta
rge
t C
CH
P
Ambient Temperature [F]
Target CCHP Capacity Goals
Typical ASHP (HSPF=7.5)
Building Heating Load Line, Region V, Well-Insulated Home
Building Cooling Load Line, Region V, Well-Insulated Home
-40
-30
-20
-10
0
10
20
30
40
50
-30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35
Ax
is T
itle
Ambient Temperature [C]
Chart Title
Series1
4 Presentation_name
1.2 Extensive System Configurations
ORNL to assist in modeling, analysis,
component sizing, and performance
verification testing
Condenser
Evaporator
Fla
sh
Ta
nk
Scro
ll M
ulti-S
tag
e
Co
mp
resso
r
Vapor injection
with flash tank
Vapor injection
with economizer
Condenser
Evaporator
Eco
no
miz
er
HX
Scro
ll M
ulti-S
tag
e
Co
mp
resso
r
Ejector cycle
Condenser
Evaporator
Tandem
Compressors
Tandem (parallel) and multi-
capacity compressor(s)
Single-stage compression concepts:
Condenser
Evaporator
Ejector
Co
mp
resso
r
Fla
sh
Ta
nk
Condenser
Evaporator
Eco
no
miz
er
HX
High Stage VS
Compressor
Low Stage
Compressor
Two-stage (series)
compression w/
inter-stage
economizing
5 Presentation_name
1.3 Compare Different Design Options
Over-capacity is the key to meet the 75% capacity goal, i.e. using tandem compressors. Vapor injection boosts HP COP at -25°C.
20%
30%
40%
50%
60%
70%
80%
90%
100%
Performance Ratio @ -13F versus Nominal @ 47F
Capacity
Integrated COP
6 Presentation_name
2.1 ‘More Cost Effective’ Configuration
Condenser
Evaporator
EXV
TXV
Filter/Dryer
Fan
Fan
4-W
ay
Valv
e
Suction Line Accumulator
Tandem
Compressors
For space
cooling
For space
heating
• Use two identical, single-speed compressors, specially optimized for heating mode , tolerate up to 138°C discharge temperature.
• Use a single compressor to match cooling load, and heating load at moderately cold temperatures, turn on both compressors at low ambient temperatures when needed.
• (Suction line accumulator+ EXV discharge temperature control) facilitates charge optimization in a wide ambient temperature range. using TXV and optimizing charge for heating mode is an alternative.
7 Presentation_name
2.2 ‘Premium’ Configuration
• Equal Tandem, Vapor Injection Compressors + Inter-stage Flash Tank + EXV Discharge Temperature Control .
Condenser
Evaporator
Fixed
orifice
TXV
Filter/Dryer
Compressor Unit
Fan
Fan
Fla
sh
Ta
nk
Sight Glass
Oil Separator
Oil
Filt
er
4-W
ay V
alv
e
Liquid Receiver
Hand Valve
Sight Glass
P T
P T
P T
P T
EXV
8 Presentation_name
2.3 Lab Measured Heating Capacities
0
10
20
30
40
50
60
70
80
-23 -13 -3 7 17 27 37 47 57 67
HP
Air
Sid
e H
eat
ing
Cap
acit
y [k
Btu
/h]
Outdoor Air Temperature [F]
2 Comps-VI
2 Comps-1 Speed
1 Comp-VI
1 Comp-1 Speed
Load_DHRmax_V
Load_DHRmin_V
0
5
10
15
20
25
-30 -20 -10 0 10 20
Hea
ting
Cap
acit
y [k
W]
Ambient Temperature [C]
Series1
0
5
10
15
20
25
-30 -20 -10 0 10 20
He
atin
g C
ap
acit
y [
kW
]
Ambient Temperature [C]
Series1
Eliminate Strip Heat in Well-Insulated Homes, Region V
9 Presentation_name
2.4 Lab Measured Heating COPs
• The ‘premium’ system with tandem VI compressors achieved 5% better COPs than the ‘more cost-effective’ single-speed compressor version at various ambients.
1.5
2.0
2.5
3.0
3.5
4.0
4.5
5.0
-23 -13 -3 7 17 27 37 47 57 67
HP
Air
Sid
e C
OP
[W
/W]
Outdoor Air Temperature [F]
Heating COP vs. OD Temp
1 Comp-VI
1 Comp-1 Speed
2 Comps-VI
2 Comps-1 Speed
-30
-20
-10
0
10
20
30
40
50
60
70
80
-30 -25 -20 -15 -10 -5 0 5 10 15 20
Ax
is T
itle
Ambient Temperature [C]
Chart Title
Series1
10 Presentation_name
2.5 HSPF (DHRmin = 11.7kW) – AHRI
210/240
Heating Season Ratings, Region: IV [HSPF in W/W; OD design
temperature -15°C]
‘More Cost-Effective’ ‘Premium’ Case
3.29 3.47 Based on DHRmin
3.21 3.46 Based on DHRmax
Heating Season Ratings, Region: V [HSPF in W/W; OD design temperature
-23.3°C]
‘More Cost-Effective’ ‘Premium’ Case
2.94 3.13 Based on DHRmin
2.81 2.96 Based on DHRmax
11 Presentation_name
3.1 Field Testing of a ‘More Cost-
Effective’ System
Field testing in OH-outdoor unit, at a
residential home having a design
cooling load of 3-ton (10.6 kW)
-Indoor Unit and Data Acquisition,
record data point every half minute.
Insulated compressors’ shell
12 Presentation_name
3.2 Parameters of Field Testing Unit
Parameters (heating mode)
Indoor Fin-&-Tube Coil Outdoor Fin-&-Tube Coil
Face area, ft2 (m2) 3.30 (0.307) 22.3 (2.07)
Total Tube Number 84 64
Number of rows 3 (cross counter-flow) 2 (cross counter-flow)
Number of parallel circs 9 6
Fin density, fins/ft (fins/m)
168 (551) 264 (866)
Indoor Blower (High/Low1) Outdoor Fan
Flow Rate, cfm (m3/s) 1500/1250 (0.708/0.590) 3500 (1.652)
Power [W] 322/203 300
-the indoor and outdoor heat exchangers originally used for a 5-ton (17.7 kW) heat
pump, i.e. oversized for single-compressor operation (3-ton/10.6 kW).
-Power source: 240 V, 60 HZ, single-phase.
13 Presentation_name
3.3 Field Testing from February to May,
2015 (half winter)
0%
2%
4%
6%
8%
10%
12%
Heat
Ener
gy De
liver
ed [%
J]
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
Build
ing H
eatin
g Loa
d [W
]
-Field ambient
temperature went
down to -24.4°C
(-12°F).
-Seasonal,
average, heating
COP was 3.16,
i.e. 10.8 HSPF.
-supplemental
resistance energy
use was 1.3% in
total heating
energy.
14 Presentation_name
3.4 Compressor Running Time Fractions
0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
70.0%
80.0%
90.0%
100.0%
Compressor Run Time Fractions
2 Comp Run Time Tot Comp Run Time
-The second compressor
cycled with 80% running
time, even at -25°C (having
room for more capacity).
-The second compressor
was needed at ambient
temperatures below -12°C.
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
Hea
ting
Load
and
Cap
acity
[W]
Heat Load Capacity_1Comp Capacity_2Comp
15 Presentation_name
3.5 Resistance Energy Uses
0.0%
0.5%
1.0%
1.5%
2.0%
2.5%
3.0%
3.5%
Resistance Energy Ratio per Bin
Due to temperature setback schedule
-can be eliminated by changing the control and letting the second compressor run longer to match the temperature setting point.
16 Presentation_name
3.6 Heating COPs
2
2.5
3
3.5
4
4.5
CO
P [
w/w
]
Heat Pump COPs
COP_2Comp COP_1Comp Total COP
-Heat pump COP at 47°F (8.3°C) >3.5. -Heat pump COP at -13°F (-25°C) > 2.0. * Total COP includes resistance heat, cyclic and frost/defrost losses.
17 Presentation_name
3.7 Return and Supply Air Temperatures
15
20
25
30
35
40
45
50
55
">12.8C"
"12.8to 10C"
"10 to7.2C"
"7.2 to4.4C"
"4.4 to1.7C"
"1.7 to-1.1C"
"-1.1 to-3.9C"
"-3.9 to-6.7C"
"-6.7 to-9.4C"
"-9.4 to-12.2C"
"-12.2to -
15C"
"-15 to-17.8C"
"-17.8to -
20.6C"
"-20.6to -
23.3C"
"-23.3to -
26.1C"
Air
Te
mp
era
ture
[C
]
Heat Pump Return and Supply Air Temperatures
Return Air Temp Supply Air Temp
-Maintain 30°C supply air temperature at low ambient temperatures. * Temperature setting at 20°C (68°F) with 1.1K (2R) dead band.
18 Presentation_name
3.8 Defrost Frequency and Energy
0.0%
0.2%
0.4%
0.6%
0.8%
1.0%
1.2%
1.4%
1.6%
1.8%
2.0%
"12.8to 10C"
"10 to7.2C"
"7.2 to4.4C"
"4.4 to1.7C"
"1.7 to-1.1C"
"-1.1 to-3.9C"
"-3.9 to-6.7C"
"-6.7 to-9.4C"
"-9.4 to-12.2C"
"-12.2to -
15C"
"-15 to-17.8C"
"-17.8to -
20.6C"
"-20.6to -
23.3C"
"-23.3to -
26.1C"
Defrost Time Ratio to Bin Run Time
0.0%
0.5%
1.0%
1.5%
2.0%
2.5%
Defrost Load to Bin Heat Energy Delivered
Defrost frequency and energy were minimum for CCHP -With running one compressor, frost formation was slow, due to the oversized outdoor HX. -When the two compressors were needed at low ambients, the ambient humidity level was very low.
19 Presentation_name
4. Summary
• Over-capacity capability in a heat pump is the key to match the 75% capacity goal – tandem or variable-speed compressors are required.
• The tandem single-speed compressors had sufficient capacity to eliminate resistance heat down to -25°C during the field testing in Ohio.
• Proper charge control strategy is necessary to optimize heat pump operations at low ambient temperatures.
• Defrost losses were minimum during the field investigation.