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Hot Water Heating: Technologies and Use
Skip HaydenIntegrated Energy Systems
CanmetENERGYBetter Buildings by Design 2010
Burlington VermontFebruary 2010
Natural ResourcesCanada
Ressources naturellesCanada
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Objectives
• Appreciate the differences in various water heating technologies
• See why some systems are less efficient than they are “labelled”
• See how hot water is really used, and how that affects different technologies
• Be better able to choose an efficient water heating technology
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What are youlooking for
??
?? ?
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Residential Energy Use
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In Canada, residentially, hot water being supplied to the tap must be below 120F, to prevent scalding.
This can be achieved by:• Setting the tank themostat to 120F• Adding a mixing valve at the exit of the water
heater, blending cold mains water with the hot water leaving the heater proper
• Both, to counteract “stacking”
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Water Heating Technologies
Tank- Based
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Electric Resistance Water Heater
Who has an electric water heater ?
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Natural Draft Gas Water Heater
• Naturally aspirating• Requires a chimney • Continuous pilot (energy
waste)• Draft hood (extra heated air
loss)• Highly susceptible to
spillage• Large off-cycle loss• Low seasonal efficiency
(.6 EF)• Should be an “antique” !
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Power-Vented Gas Water Heater
• Many do not have Pilot light• Powerful ID fan pulls large
amounts of house air thru draft hood (DH) to cool flue gases, to allow plastic pipe and sidewall venting, resulting in …
• High on-cycle house heat loss• Sig. off-cycle losses thru DH• High resistance to
depressurization• Only marginal efficiency
improvement over conventional natural draft water heater
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Balanced-Flue Gas Water Heater
• May or may not have Pilot light• Typically no ID fan • May have co-axial or co-linear
venting (discuss later)• Uses outside air for
combustion• No draft hood so no dilution air• Depressurization should have
no effect on operation• Most have only marginal
efficiency improvement over conventional natural draft water heater (~0.6 EF)
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3a. Sealed Power-Vented Sidewall with Blended Exhaust
(Plastic Vent)
The unit pulls in cold outside air, brings some down to the burner for sealed combustion, and blends the rest with the hot flue gas
The diluted flue gas is now cool enough that plastic pipe can be used, and the combustion products vented out the side wall.
No house air is required.
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4. Condensing Tank Water Heater
• Sealed combustion and power vent,
• 90% efficient, as mains water provides driving force for condensing flue gas and recovering latent heat
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Now, we are starting to see a range of different technologies to heat water
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Tankless Gas-Fired Water Heaters
Wide range of technologies and potential efficiencies
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“Low Tech” Tankless Water Heater
• Natural draft• Pilot light• Draft hood• Prone to spillage• Inefficient (0.6 EF)• Relatively cheap• Don’t use !
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“Mid-Efficiency” Tankless Water Heater
• Sealed Combustion (Direct Vent DV)
• No pilot light• Wide firing range• Induced draft fan (should
modulate with firing rate)• May have system to
prevent freezing• May have strategy to
ensure no cold “slug”• EF ~ 0.8
Co-Linear Venting
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“Mid-Efficiency” Tankless Water Heater
• Sealed Combustion (Direct Vent DV)
• No pilot light• Wide firing range• Induced draft fan (should
modulate with firing rate)• May have system to
prevent freezing• May have strategy to
ensure no cold “slug”• EF ~ 0.8
Co-Axial Venting
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High-Efficiency CondensingTankless Water Heater
• Sealed Combustion (Direct Vent DV)
• No pilot light• Wide firing range• Induced draft fan (should
modulate with firing rate)• May have system to
prevent freezing• May have strategy to
ensure no cold “slug”• Additional stainless steel
condensing heat exchanger
• EF ~ 0.9
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Concern about co-axial venting in cold climates
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However, this does not mean:“Combo” Conventional Tank Water
Heater with Fan Coil• Relatively cheap• High flue gas
temperature• Reduced life• Inefficient • Much lower AFUE
than furnaces, because standard does not apply
• Not recommended !
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Efficient Low Mass Condensing Boilers with Segregated Tap water
and Highly-Modulating Burners
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External tank must have good heat transfer and very low heat loss
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CommercialService Water
Heating
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Conventional Gas-Fired Water Heater
• Naturally aspirating• Low pressure drop (& ht exch)• Draft hood (extra heated air loss)• Requires chimney• Highly susceptible to spillage• Large off-cycle loss• Low overall efficiency
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Power Vented Water Heaters
• Draft hood• Can be side-walled with plastic
pipe• May reduce off-cycle vent loss• Heat still lost to room thru draft
hood• Large heated air loss to vent
when firing• Minimal efficiency gain
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Efficient, sealed combustion (non-condensing) boiler as segregated heat source with large
external tank for service hot water
External tank works against condensing system !!
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Tankless Wall-Mount Water Heaters
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Condensing Tank Water Heater
> 90% efficient, as mains water
provides driving force for
condensing
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Condensing Tank Water Heater
If an external tank is used to augment capacity, and is kept above 60C, condensing may only occur infrequently, if at all and efficiency will be at least 10% lower than expected
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Oil-Fired Water Heaters
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Tankless Coil Boiler or Tank-within-Tank Boilers
• Very inefficient summer and overall operation
• Large number of cycles with inherent inefficiency and sooting
• Not recommended !!
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Efficient Oil-Fired Space/Water Heating
Systems
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What about wood?
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• Typically there is a flame over some but not all of the wood.
• Remote from the flame, the volatiles are “boiled”out of the wood and leave the primary combustion zone as “smoke” without getting completely burned.
• If there is no hot secondary ignition source + O2 to ignite them, the result is high emissions and creosote.
How Wood Burns
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Could I put a water coil in an EPA-approved stove?
Any coil installed in an advanced combustion EPA woodstove would likely disrupt the combustion, chill the flame and result in a dramatic increase in emissions.
Don’t do it !
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What about hot water from a wood boiler?
Well, maybe …
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Solar-Augmented Water Heating
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Heat Pump-Augmented Water Heaters
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Nominal “Efficiencies” of Water Heating Technologies
TYPE “Nom” Efficiency Range (%)
Gas Storage 50 – 65
Condensing Gas Storage 76 – 86
Tankless 65 – 85
Condensing Tankless* 90 – 98
Electric Storage 90 – 96
Heat Pump Water Heater* 150 – 200
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Do these numbers reflect the way hot water is really used ?
To answer that question we conducted a significant hot water-use field trial
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Field Test Results• Number of draws much
greater and shorter than present test standard
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 to 1
5 s15
to 3
0 s30
to 4
5 s45
to 6
0 s60
to 7
5 s75
to 9
0 s
90 to
105
s
105
to 120
s
120
to 180
s
180
to 240
s
240
to 300
s
300
to 360
s
360
to 420
s
420
to 480
s
480
to 540
s
540
to 600
s
600
to 660
s
660
to 720
s
720
to 780
s
780
to 840
s
840
to 900
s
900
to 960
s
960
to 102
0 s
1020
to 1
080 s
1080
to 1
140 s
1140
to 1
200 s
1200
to 2
400 s
Duration of Draw (s)
Num
ber o
f Dra
ws
92% of Draws Made < 1 Minute
Accounts for 30% of Daily Volume
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 to 1
5 s15
to 3
0 s30
to 4
5 s45
to 6
0 s60
to 7
5 s75
to 9
0 s
90 to
105
s
105
to 120
s
120
to 180
s
180
to 240
s
240
to 300
s
300
to 360
s
360
to 420
s
420
to 480
s
480
to 540
s
540
to 600
s
600
to 660
s
660
to 720
s
720
to 780
s
780
to 840
s
840
to 900
s
900
to 960
s
960
to 102
0 s
1020
to 1
080 s
1080
to 1
140 s
1140
to 1
200 s
1200
to 2
400 s
Duration of Draw (s)
Num
ber o
f Dra
ws
92% of Draws Made < 1 Minute
Accounts for 30% of Daily Volume
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Detailed Trial ResultsFraction of Daily Volume Drawn vs. Duration
0%
5%
10%
15%
20%
25%
30%
0 to 1
515
to 3
030
to 4
545
to 6
060
to 7
575
to 9
090
to 1
0510
5 to 1
2012
0 to 1
8018
0 to 2
4024
0 to 3
0030
0 to 3
6036
0 to 4
2042
0 to 4
8048
0 to 5
4054
0 to 6
0060
0 to 6
6066
0 to 7
2072
0 to 7
8078
0 to 8
4084
0 to 9
0090
0 to 9
60
960
to 102
0
1020
to 1
080
1080
to 1
140
1140
to 1
200
1200
to 2
400
Duration of Draw (s)
Frac
tion
of D
aily
Vol
ume
Dra
wn
. 30 % 18 % 12 %33 %7 %
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Field Test Results
Average Daily Hot Water Use – 1/3 less than standard
0
50
100
150
200
250
300
350
400
01 02 03 04 05 06 08 13 14 15 17 18 22 24 27 28 31 32 33 35 36 38 39 40 41 4848
-148
-2 50 51 52 53 54 55 56 57 58 59
Test Site #
Ave
rage
Dai
ly D
raw
(Li
tres
)
Study Average = 163 Litres = 43.1 US Gallons
CSA P.3 & US DOE = 243.4 Litres = 64.3 US Gallons
43 gal
64 gal
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Effects of Draws on Water Heater Efficiencies
• The efficiency of a storage water heater decreases as the daily hot water use is reduced.
• The efficiency of a tankless water heater decreases as it is used more frequently with short draw times and long standby times.
Short Draw, Short Delay
Short Draw, Long Delay
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Water Use & Tank Water Heater Efficiency
Should we use more hot water to keep the Storage Water Heater efficiency high ?
NO !
We need a high appliance efficiency but we also want reduced energy consumption
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Water Use & Tankless Water Heater Efficiency
Should we run the tankless water heater longer and use more water to keep its efficiency high ?
NO !
Again, we want a high appliance efficiency but we don’t want to waste energy
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Changing the Water Heating Test Standard
• Changing the test method to more closely reflect a “real life” draw pattern will result in a very different efficiency, in all cases.
• A water heater performance test method that reflects real use performance will help the true Energy Savings or Emissions Benefits to be established
• A new test standard would reward manufacturers that make the correct technology choices, that would result in more efficient water heating products.
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Changing The Test Standard• Current test standard:
Storage = 60% Tankless = 80%
• Realistic test standard results in lower actual efficiencies:
Storage = 45% Tankless = 70%
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SummaryMost existing non-condensing tank-based water heaters (both gas and oil) are quite poor performers in terms of energy efficiency
Well-designed, power-vented tankless heaters are sig. more efficient; they still have the potential to improve their real efficiency significantly
The water heater efficiency standard needs to be changed to reflect real life and real technology performance
Look to condensing or near-condensing systems
Combined/Integrated systems offer an attractive pathway to achieving high efficiency water heating while efficiently satisfying other energy demands as well.
Integration with renewables and heat pumping is part of water heating’s future
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Objectives
• Appreciate the differences in various water heating technologies
• See why some systems are less efficient than they are “labelled”
• See how hot water is really used, and how that affects different technologies
• Be better able to choose an efficient water heating technology
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eKOCOMFORTeKOCOMFORTAdvanced IntegratedMechanical Systems
A major Canadian initiativeto develop and market
high efficiency, integratedspace-water-ventilating systems
“www.eKOCOMFORT.com”
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ResultsAverage Draw Flow Rate
0.0
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
9.0
10.0
11.0
12.0
01 02 03 04 05 06 08 13 14 15 17 18 22 24 27 28 31 32 33 35 36 38 39 40 41 48 48-1
48-2 50 51 52 53 54 55 56 57 58 59
Test Site #
Ave
rage
Vol
ume
Flow
rate
(Litr
es /
Min
ute)
Study Average = 2.9 Litres / minute = 0.8 US Gallons / minute
CSA P.3 & US DOE = 11.4 Litres / minute = 3.0 US Gallons / minute
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Detailed ResultsNumber of Draws vs. Draw Duration
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 to 1
5 s15
to 3
0 s30
to 4
5 s45
to 6
0 s60
to 7
5 s75
to 9
0 s
90 to
105
s
105
to 120
s
120
to 180
s
180
to 240
s
240
to 300
s
300
to 360
s
360
to 420
s
420
to 480
s
480
to 540
s
540
to 600
s
600
to 660
s
660
to 720
s
720
to 780
s
780
to 840
s
840
to 900
s
900
to 960
s
960
to 102
0 s
1020
to 1
080 s
1080
to 1
140 s
1140
to 1
200 s
1200
to 2
400 s
Duration of Draw (s)
Num
ber o
f Dra
ws
92% of Draws Made < 1 Minute
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Hot Water Use per Family
0
50
100
150
200
250
300
350
400
01 15 41 47 50 48 48-1 59 18 38 33 02 04 26 35 39 30 14 36 05 06 16 17 28 31 32 40 48-2 54 52 53 03 24 13 51 27
Test Site #
Ave
rage
Dai
ly V
olum
e D
raw
(Li
tres)
2A 3A 2A + 1C 2A + 2C 2A+3C 3A + 2C 4AA = AdultC = Child