On-Demand Water Heaters

Transcription

On-Demand Water
Heaters
Tom Barrett
Vice President
RHA Inc.
Energy Out West 2008
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On-Demand Water Heaters
• Call them:
– On-Demand
– Demand
– Tankless
• But don’t call them
instantaneous!!!
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Water Heating % of Energy Use
Residential Total Energy End Uses
Adjustment
4%
Space
Heating
35%
Appliances
27%
Lighting
10%
Space
Cooling
11%
Water
Heating
13%
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Residential Natural Gas End
Uses
Water
Heating
23%
Cooking 4%
Laundry/Dish
Washers 1%
Space
Heating 71%
Other 1%
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Residential Electrical End Uses
Water Heating
9.0%
Space Cooling
18.1%
Space Heating
10.6%
Adjustment
6.9%
Lighting
16.2%
Other
4.1%
Computers
1.7%
Wet Clean
6.6%
Cooking
5.0%
Electronics
10.8%
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Refrigeration
11.1%
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Water/Energy Consumption
• Average residential hot water consumption:
– 20 gallons/person/day
– 7,300 gallons/person/year
• Energy (3-person household)
– 275 therms/year ($275 @ $1.00/therm)
– 5,250 kWhs/year ($525 @ $0.10/kWh)
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Average Daily Household Hot
Water Use
Table 1 − Average Daily Household Hot Water Use
End Use
Average Daily Household Hot Water Use
(gallons/day)
Bathing & Showering
10.5 per occupant
Clothes Washing
7.5 (if clothes washer is present)
Dishwashing
6.4 (if dishwasher is present)
2.6 (if dishwasher is present)
Faucets
6.3 (if no dishwasher is present)
Sources:
1) Koomey, Jonathan G., Camilla Dunham, and James D. Lutz. 1994. The Effect of Efficiency Standards on Water Use and Water Heating Energy Use in the
U.S.: A Detailed End-use Treatment. Lawrence Berkeley National Laboratory (LBL-35475).
2) Lowenstein, Andrew, and Carl C. Hiller. 1998. Disaggregating Residential Hot Water Use-Part II. ASHRAE Transactions 104(1).
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Water Heating Energy
• Five Places to Save Energy with Water
Heating Systems
– Water Heater
– Piping
– Fixtures
– Behavior
– Water down the drain
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Water Heater Types
ACEEE
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Energy Star Water Heaters
• Energy Factor (EF) – the ratio of useful energy
output from the water heater to the totally
amount of energy delivered to the water heater.
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Energy Star Water Heaters
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Tankless vs Tank Water Heaters
• Storage tank
– Little burner (30,000 –
50,000 BTUH)
– Big tank (40 - 50
gallons)
• Tankless
– Big burner (30,000 –
195,000 BTUH)
– Little tank (< 1 gallon)
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Tankless Water Heater Systems
• Purpose
– Heat water only when
needed.
– Provide endless supply of
hot water.
– Back-up for solar system.
– Save energy???
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• Whole house
• Point-of-use water heating
– Under sink units
– Small electric water heaters
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• Gas
– Natural Gas
– Propane
• Electric
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Gas-Fired Tankless
• Models
– 0.5 to 7.0 gallons per
minute
– 10,000 BTU/hr to 200,000
BTU/hr
– Indoor and outdoor
– Horizontal and vertical
venting
– Direct and standard
venting
– Pilot and pilotless
– Self-generating pilot and
electronic ignition
– Whole house
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Gas-Fired Tankless
• Types
– Fuel
• Natural Gas
• Propane
– Location
• Indoor
• Outdoor
– Pilot Lights
• Pilotless
• Piloted
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Gas-Fired Tankless
• Types
– Venting
• Direct Venting
• Wall Vented
• Roof Vented
– Power Requirements
• Self-powered
• Electricity required
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Electric Tankless
• Whole house
• Point of use
Stiebel Eltron electric water heater
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Considerations
• How much hot water is used?
– Number of bathrooms
– Number of showers
– Number of occupants
• Location
– Venting
• Problems with hot water delivery?
• Pipe sizing
– Gas (3/4” pipe)
– Water (3/4” pipe)
• Power requirements
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Gas Pipe Supply Sizing
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Side-By-Side Study
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Side-By-Side Study
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Side-By-Side Study
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Side-By-Side – 24 hrs
200
180
160
Tank Flu
140
T-less Flu
120
100
80
60
40
20
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2321
2225
2129
2033
1937
1841
1745
1649
1553
1457
1401
1305
1209
1113
1017
921
825
729
633
537
441
345
249
153
57
1
0
30
Side-By-Side Study
140
130
120
110
100
90
80
Tank Flue Temp
70
60
50
40
Time (minutes)
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2130
2100
2030
2000
1930
1900
1830
1730
1700
1630
1600
1530
1500
1430
1400
1330
1300
1230
1200
1130
1100
1030
1000
930
900
830
800
730
700
630
T-less Flue Temp
1800
Degrees F
180
170
160
150
170
160
150
140
130
120
110
100
90
80
70
60
50
40
Tank Flue
T-less Flue
T-less V1
ON
OFF
850
852
854
856
858
900
902
904
906
908
910
912
914
916
918
920
922
924
926
928
930
932
934
936
938
940
942
944
946
948
Degrees F
Tank vs. Tankless
Time (hr:min)
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2130
2125
2120
20
2115
40
2110
60
2105
2100
2055
2050
2045
2040
2035
2030
2025
2020
2015
2010
2005
2000
1955
1950
1945
1940
1935
1930
1925
1920
1915
1910
1905
1900
Degrees F.
Details
180
160
140
120
100
80
Tank Flue
T-less Flue
T-less V1
T-less V2
0
Time (hr:min)
33
Installation
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Installation
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Installation
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Installation
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Installation
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Installation
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Installation
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Installation
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Installation
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Installation
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Installation
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Installation
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Installation
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Installation
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Installation
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Installation
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Installation
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Installation
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Installation
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Tankless Study Results
Natural Gas Usage Summer Months (therms)
2006
2007
Usage
Reduction
Client #2
186
115
71
38.2%
Client #3
91
74
17
18.7%
Client #4
63
106
-43
-68.3%
Client #5
117
116
1
0.9%
Client #6
26
17
9
34.6%
Total
483
428
55
11.4%
Average
96.6
85.6
11.0
11.4%
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% Reduced
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Client #3
Client #3 Natural Gas Consumption (therms)
90
80
2006
70
2007
Therms
60
50
40
30
20
10
0
Feb
March
April
May
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June
July
Aug
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Client #4
Client #4 - Natural Gas Consumption (therms)
70
2006
60
2007
Therms
50
40
30
20
10
0
Feb
March
April
May
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June
July
Aug
Sept
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Client #5
140
2006
120
2007
Therms
100
80
60
40
20
0
Feb
March
April
May
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July
Aug
Sept
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Client #6
70
2006
60
2007
Therms
50
40
30
20
10
0
Feb
March
April
May
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June
July
Aug
Sept
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Water Consumption Results
Water Consumption Pre – Post Installation (CCFs)
2006
2007
Consumption
Increase
Client #2
98
73
-25
-26%
Client #3
30
65
35
117%
Client #4
60
73
13
22%
Client #5
34
32
-2
-6%
Client #6
n/a
n/a
n/a
n/a
Total
222
243
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9.5%
Average
55.5
60.75
5.3
9.5%
Ave/Month
6.2
6.8
0.6
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% Change
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Study Results
• Client Satisfaction
– Very satisfied
– Few problems
• Not enough “hot” water – turn up tank
• Not “instantaneous” – two-minute start time
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Issues
• Gas line size
– A standard water heater burner capacity - 40,000
BTU/hr
– a tankless burners can range from 145,000 BTU/hr
• Gas meter/pressure regulator
– The utility company may have to change out the
meter/pressure regulator to accommodate a tankless
water heater to provide adequate gas supply and
pressure for a tankless system.
• Maintenance issues
– Annual cleaning procedure required
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Issues
• Instant hot water
– Water up to temperature – 1 to 2 minutes
– At 2 gallons/minutes wastes 2 gallons
• Cold water sandwich
• Low-flow showerheads
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Cost Effectiveness
•
•
•
•
•
•
•
Cost = $2,000 per unit installed
Expected savings $40 - $60/year
4 – 5 therms/month/40 – 60 therms/year
Simple payback - 33 – 40 years
Water usage cost - $14 or more annually
Total savings = $25 to $40 a year
Simple payback period of 40 – 50 years
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Nat Gas Tank to Tankless
Water Heater Info Tool
Existing Tank
Tankless
48.1 gpd
48.1 gpd
EF
0.50
0.80
RE
0.68
0.82
40,000 BTUH
165,000 BTUH
0
$2,000
$65 – 83/year
SIR 0.4 – 0.5
Water Usage
Capacity
Installed Cost
Savings
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Other Water Heating Options
• Storage Tank
– Conventional
– Condensing Water
Heater
• Heat Pump Water
Heater
• Indirect Water Heater
• Solar Water Heater
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On-Demand Water Heaters

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