Domestic Hot Water Research
Research conducted by Bill Rittelmann
Presented by Duncan Prahl
Partners for High Performance Homes Meeting
Westminster, CO, June 23, 2005
© Copyright 2003 IBACOS, Inc. All rights reserved.
DHW Systems: Current Technologies
© Copyright 2003 IBACOS, Inc. All rights reserved.
DHW Systems: Current Technologies
2004
0.82
0.98
© Copyright 2003 IBACOS, Inc. All rights reserved.
0.96
1.00
DHW Systems: Current Technologies
Residential Domestic Water Heating Systems
$7,000
Installed Cost - (USD)
$6,000
Gas Storage
Electric Storage
Heat pump
Gas tankless
Electric tankless
Electric POU (cold water)
Electric POU (warm water)
Gas POU
$5,000
$4,000
$3,000
$2,000
$1,000
$0
0%
20%
40%
60%
80%
Source Energy Efficiency
© Copyright 2003 IBACOS, Inc. All rights reserved.
100%
Efficiency vs Inlet Water Temp
© Copyright 2003 IBACOS, Inc. All rights reserved.
DHW Systems: Sizing Methods
3
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60
DHW Systems: Event-Based Sizing
Key Concepts
•Temperature-dependent flow
The hot water flow rate depends on the
temperature of the cold and hot water. This
includes showers, baths, some clothes washers,
hand washing, etc.
•Temperature-independent flow
The hot water flow is constant regardless of cold
and hot water temperatures. This is
characteristic of most clothes washers &
dishwashers
© Copyright 2003 IBACOS, Inc. All rights reserved.
DHW Systems: Event-Based Sizing
Key Concepts
•Energy Factor is not a constant
The DOE Energy Factor is calculated under one
set of laboratory conditions and does not
account for different climates and usage.
•Inlet water temperature is not a constant
Minimum annual inlet water temperatures vary
more than 40°F across the country.
© Copyright 2003 IBACOS, Inc. All rights reserved.
DHW Systems: Event-Based Sizing
Key Concepts
•“Event-based” method is more universal
The same event descriptions can be used to
accurately size a water heater in Miami or
Minneapolis. Although the resulting hot water
demand will be quite different, the margin of
error in the estimation is greatly reduced
compared to “demand estimation” methods that
use the same values regardless of water
temperatures and end-use fixture descriptions.
© Copyright 2003 IBACOS, Inc. All rights reserved.
DHW Systems: Event-Based Sizing
80
Mid-August
Temperature - (degrees F)
70
60
50
NREL (daily)
NREL (monthly)
1985 ASHRAE (2 ft)
1985 ASHRAE (4 ft)
40
Mid-February
30
20
1
31
61
91
121
151
181
211
241
271
301
Time - (Julian Days)
Inlet (mains) Water Temperature
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331
361
DHW Systems: Event-Based Sizing
20
Inlet Water Temp.
(degrees F)
18
Hot Water Volume (gallons)
16
50%
40
50
60
70
80
90
14
12
10
8
6
Total flow = 2.5 gpm
Duration = 8 minutes
Total volume = 20 gallons
Shower temp = 105 F
4
2
0
110
115
120
125
130
135
140
145
Tank Temperature (degrees F)
Temperature-Dependent Flow
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150
DHW Systems: Event-Based Sizing
Fe
b
M
ar
Ap
r
M
ay
Ju
n
Ja
Ju
l
Au
g
Se
p
O
ct
N
ov
D
ec
45
40
35
30
25
20
15
10
5
0
n
Average Hot Water Use (GPD/occupant)
Monthly per Capita Hot Water Use
DOE standard usage rate = 28GPD
© Copyright 2003 IBACOS, Inc. All rights reserved.
DHW Systems: Event-Based Sizing
Use TRNSYS program to simulate DWH system
Detailed Temperature Profile and Hot Water Flow Rate
© Copyright 2003 IBACOS, Inc. All rights reserved.
DHW Systems: Event-Based Sizing
Electric Water Heater
Inlet Water Temp. 45 F, Tank Volume 50 Gallon
© Copyright 2003 IBACOS, Inc. All rights reserved.
DHW Systems: Event-Based Sizing
Electric Water Heater
Inlet Water Temp. 45 F, Tank Volume 40 Gallon
© Copyright 2003 IBACOS, Inc. All rights reserved.
DHW Systems: Event-Based Sizing
Electric Water Heater
Inlet Water Temp. 75 F, Tank Volume 30 Gallon
© Copyright 2003 IBACOS, Inc. All rights reserved.
DHW Systems: Event-Based Sizing
Electric Water Heater
Inlet Water Temp. 75 F, Tank Volume 20 Gallon
© Copyright 2003 IBACOS, Inc. All rights reserved.
DHW Systems: Event-Based Sizing
•
•
T_inlet=60 F
V = 30 gallon
T_inlet=45 F
V = 40 gallon
T_inlet=36 F
V = 50 gallon
Summary of the Tank Size vs. Inlet Water Temp. (Electric)
© Copyright 2003 IBACOS, Inc. All rights reserved.
Temperature Variance
Temperature in different US cities
City
Yearly Average
Temp. (ºF)
T_min
T_max
Fairbanks, AK
26.9
11.80
51.00
Anchorage, AK
35.9
28.66
52.15
Duluth, MN
38.5
27.04
58.96
Juneau, AK
40.6
36.51
53.69
Fargo, ND
41
27.90
63.10
Saint Cloud, MN
41.5
29.26
62.74
Glasgow, MT
42.4
30.65
63.15
Green Bay, WI
43.8
33.34
63.26
Missoula, MT
44.3
36.89
60.71
Burlington, VT
44.6
34.47
63.73
Great Falls, MT
44.8
36.61
61.99
Minneapolis - St. Paul, MN
44.9
32.71
66.09
Casper, WY
45.1
36.53
62.67
Concord, NH
45.1
35.86
63.34
Madison, WI
45.2
34.85
64.55
© Copyright 2003 IBACOS, Inc. All rights reserved.
DHW Systems: Event-Based Sizing
City
Yearly Average
Temp. (ºF)
T_min
T_max
Corpus Christi, TX
71.6
68.24
83.96
Orlando, FL
72.3
70.64
82.96
Tampa, FL
72.3
70.73
82.88
Vero Beach, FL
72.4
71.58
82.22
Phoenix, AZ
72.6
66.33
87.87
Yuma, AZ
74.2
68.63
88.77
Fort Myers, FL
74.4
73.72
84.08
West Palm Beach, FL
74.7
74.50
83.90
Miami, FL
75.9
76.19
84.61
Honolulu, HI
77.2
79.41
84.00
Key West, FL
77.8
78.39
86.22
•
© Copyright 2003 IBACOS, Inc. All rights reserved.
Temperature in different US cities
DHW Systems: Event-Based Sizing
Preliminary conclusions from TRNSYS analysis:
•
The size of the water heater is closely related to the
cold water inlet temperature. Therefore, the sizing
method should include climate zone consideration.
•
The water usage pattern will influence the size of the
water heater. The water schedule profile should be
part of the sizing consideration.
© Copyright 2003 IBACOS, Inc. All rights reserved.
DHW Systems: Piping losses
Domestic Hot Water Piping
"Stranded" heat loss, 30 feet of pipe
50%
Energy Lost In Pipe / Energy Consumed
1 inch pipe
45%
0.75 inch pipe
40%
0.5 inch pipe
0.375 inch pipe
35%
30%
25%
20%
15%
10%
5%
0%
2.5
5.0
7.5
10.0
12.5
Draw Size (Gallon)
© Copyright 2003 IBACOS, Inc. All rights reserved.
15.0
17.5
20.0
Efficient DHW Systems
• Factors that Impact Water Heater
Energy Efficiency
• Fuel Conversion Efficiency
• Inlet (mains) Water Temperature
•• Daily
HotLosses
Water Volume
Standby
(Storage Volume)
•• Tank
Inlet (mains)
Water
Temperature
Set Point
Temperature
••
••
Tank
SetAir
Point
Temperature
Ambient
Temperature
Occupant
behaviorEfficiency Standards
NAECA Minimum
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Efficient DHW Systems
DOE Test Procedure First Hour Rating
© Copyright 2003 IBACOS, Inc. All rights reserved.
Efficient DHW Systems
Water Heater
Performance
90
Volume (Gal.)
80
70
60
57
50
Inlet Water
Temperatures
40
30
20
105
110
115
120
125
130
135
140
35 F
55 F
75 F
58 F
145
150
155
Setpoint Temperature (degrees F)
• 50-Gallon Electric Water Heater
• Conventional Controls
© Copyright 2003 IBACOS, Inc. All rights reserved.
Efficient DHW Systems
70
65
60
57
Volume (Gallons)
55
50
45
Control Strategy
40
Conventional
35
Energy Smart
30
DOE Test Procedure
25
20
105
110
115
120
125
130
135
140
145
150
155
Setpoint Temperature (degrees F)
• First-Hour Rating – 50-gallon electric
water heater
© Copyright 2003 IBACOS, Inc. All rights reserved.
Efficient DHW Systems
70
Control Strategy
60
Conventional
Volume (Gallons)
Energy Smart
DOE Test Procedure
50
41
40
30
20
105
110
115
120
125
130
135
140
145
150
155
Setpoint Temperature (degrees F)
• 30-Minute Rating – 50-gallon electric
water heater
© Copyright 2003 IBACOS, Inc. All rights reserved.
First Hour Ratings….
• Size Matters
• But Technology Matters More
© Copyright 2003 IBACOS, Inc. All rights reserved.
Breaking the Limits of Efficiency
• Develop a non-solar electric DHW system with
a source energy efficiency greater than 100%.
(site to source multiplier is assumed to be 3.16)
• Identify efficiencies and limitations of earthcoupled heat pump systems adjacent to
foundations.
• Quantify displacement of primary energy use
relative to thermal storage capacity in a high
performance home.
© Copyright 2003 IBACOS, Inc. All rights reserved.
Non-Coincident DHW Heat Recovery
ROOF MOUNTED
HX
WH
Greywater
Tank
Passive Heat Recovery
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Non-Coincident DHW Heat Recovery
Annual Energy Savings
35%
Annual Energy Savings
30%
25%
20%
15%
Mean Annual Mains Temp.(°F)
10%
46
55
64
5%
0%
40
80
120
160
Heat Recovery Tank Size - (gallons)
Passive Heat Recovery
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200
Non-Coincident DHW Heat Recovery
7000
35%
6000
30%
5000
25%
4000
20%
3000
15%
Recovered Energy
WH Energy Use
2000
10%
Savings 80-gallon
1000
5%
0
0%
7.5
15
22.5
30
Heat Exchanger Pipe Length - (meters)
Passive Heat Recovery
© Copyright 2003 IBACOS, Inc. All rights reserved.
37.5
Energy Savings
Energy - (kWh/yr)
Impact of Heat Exchanger Size
Non-Coincident DHW Heat Recovery
ROOF MOUNTED
Source
WH
Outlet
HX
Inlet
Load
Inlet
HP
Outlet
Active Heat Recovery
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HX
Greywater
Tank
Non-Coincident DHW Heat Recovery
Annual Energy Savings vs. MWT and DW Tank Volume
100%
Drain Water Tank Volume - (gallons)
90%
40
80
120
Annual Energy Savings
80%
67%
70%
68%
70%
70%
66%
72%
69%
63%
60%
50%
Annual energy savings increase
as mains water temperatures
increase but drain water tank
volumes beyond 80 gallons
have little impact
40%
30%
20%
10%
HW Tank Volume = 80 gallons
0%
46.4
55.4
64.4
Annual Mean Mains Water Temperature - (°F)
Active Heat Recovery
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72%
Non-Coincident DHW Heat Recovery
Annual Energy Savings vs. MWT and HW Tank Volume
100%
Hot Water Tank Volume - (gallons)
90%
40
80
120
Annual Energy Savings
80%
67%
70%
70%
69%
66%
63%
61%
72%
70%
60%
50%
Annual energy savings
increase as mains water
temperatures increase and
HW tank volume is increased
40%
30%
20%
10%
DW Tank Volume = 80
ll
0%
46.4
55.4
Mean Annual Mains Water Temperature - (°F)
Active Heat Recovery
© Copyright 2003 IBACOS, Inc. All rights reserved.
64.4
71%
Non-Coincident DHW Heat Recovery
System Energy vs. Hot Water Tank Volume
2000
WH Energy
HP Energy
Annual Energy Use - (kWh/yr)
1800
1600
1400
1200
Total system annual energy use
decreases as the volume of the hot
water tank is increased to 80
gallons, but increases beyond that
1000
800
600
Annual Mean MWT = 55.4 °F
DW Tank Volume = 80 gallons
400
200
0
40
80
Hot Water Tank Volume - (gallons)
Active Heat Recovery
© Copyright 2003 IBACOS, Inc. All rights reserved.
120
Non-Coincident DHW Heat Recovery
C.O.P.s vs. Drain-Water HX Piping Material
5.0
Coefficent Of Performance - (C.O.P.)
Drain-Water HX Piping Material
PEX
Copper
4.0
3.0
The thermal properties of the drainwater HX piping have little impact on
system performance when HW
tanks are 120 gallons or larger
2.0
1.0
Annual Mean MWT = 55.4 °F
DW Tank Volume = 80 gallons
0.0
40
80
Hot Water Tank Volume - (gallons)
Active Heat Recovery
© Copyright 2003 IBACOS, Inc. All rights reserved.
120
Earth-Coupled Heat Pump Water Heater
Hot water load – 72 gpd
4 showers and 1 load of laundry
5141 kWh/yr
Auxiliary Heat
353 kWh/yr
70°F – air
WH
Heat Pump
1620 kWh/yr
ROOF MOUNTED
Outlet
HX
Inlet
Additional Heat Loss
1845 kWh/yr
Load
Inlet
HP
Outlet
69°F – slab surface
R-10
Source
51°F (normally 63°F)
49°F
© Copyright 2003 IBACOS, Inc. All rights reserved.
ECHP Water Heater - Chicago
Sub-Slab Earth-Coupled Heat Pump Water Heater
Chicago, Slab-on-grade, R-10 under slab & vertical at perimeter
Coefficient of Performance - (C.O.P.)
4.5
75
Change in slab temperature
is less than 1 °F
70
4.0
65
3.5
60
3.0
Whole-house C.O.P. increases
when slab heat loss is beneficial
55
2.5
50
Annual whole-house
C.O.P. is 2.32
2.0
45
Heat Pump C.O.P.
1.5
1.0
0.5
Minimum temperature below
slab is well above freezing
Heat Pump & Tank C.O.P
Heat Pump, Tank & Slab C.O.P.
Under slab Temp. with E-C
Under slab Temp. no E-C
Slab surface Temp. with E-C
Slab surface Temp. no E-C
Slab losses during heating season
reduce whole-house C.O.P.
0.0
Jan
Feb
© Copyright 2003 IBACOS, Inc. All rights reserved.
Mar
Apr
May
Jun
Jul
Aug
Sep
40
35
30
49°F
Oct
25
Nov
Dec
Temperature - (°F)
5.0
ECHP Water Heater - Chicago
Remote Earth-Coupled Heat Pump Water Heater
Chicago
5.0
75
Heat Pump C.O.P.
70
Heat Pump & Aux. C.O.P
4.0
Heat Pump, Aux. & Tank C.O.P.
3.5
Temp. - Earth at EC loop
65
60
Annual aggregate
C.O.P. is 2.05
Temp. - Earth surface
3.0
55
2.5
50
2.0
45
1.5
40
1.0
35
Monthly aggregate C.O.P drops
in summer due to unwanted heat
losses from tank
0.5
EC fluid temperature is near
freezing year-round
0.0
Jan
Feb
© Copyright 2003 IBACOS, Inc. All rights reserved.
Mar
Apr
May
Jun
Jul
Aug
Sep
49°F
Oct
30
25
Nov
Dec
Temperature - (°F)
Coefficient of Performance - (C.O.P.)
4.5
ECHP Water Heater - Miami
Sub-Slab Earth-Coupled Heat Pump Water Heater
Miami, Slab-on-grade, R-10 under slab & vertical at perimeter
5.0
Change in slab
temperature is
less than 1 °F
70
4.0
65
Annual whole-house C.O.P. is 3.82
3.5
60
3.0
55
2.5
50
Whole-house C.O.P. soars when
slab heat loss is beneficial
2.0
45
Heat Pump C.O.P.
Heat Pump & Tank C.O.P
Heat Pump, Tank & Slab C.O.P.
1.5
1.0
Slab losses during heating season
reduce whole-house C.O.P.
0.5
40
Under slab Temp. with E-C
Under slab Temp. no E-C
35
Slab surface Temp. with E-C
Slab surface Temp. no E-C
30
0.0
25
Jan
Feb
© Copyright 2003 IBACOS, Inc. All rights reserved.
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
49°F Nov
Dec
Temperature - (°F)
Coefficient of Performance - (C.O.P.)
4.5
75
Domestic Hot Water Systems
And that’s how it
works.
Any Questions?
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