Tankless Water Heaters: Do They Really Save Energy?
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Transcript of Tankless Water Heaters: Do They Really Save Energy?
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Tankless Water Heaters – Do They Really Save Energy?
Ben Schoenbauer, Research Engineer, Center for Energy and Environment
2012 ACEEE Summer Study on Energy Efficiency in Buildings
Paper #193
August 15, 2012
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Field Study overview
+ Objectives+ To determine installed performance of TWH
+ To monitor hot water consumption behavior
+ Methodology+ 10 sites
+ 25 water heaters
+ 8 Tank Water Heaters (TANK)+ 9 Non-Condensing Tankless Water Heaters
(TWHs)+ 7 Condensing Tankless Water Heaters (CTWHs)
+ 4 week alternating mode test
+ Extensive data logging
+ Homeowner surveys
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How Do Water Heaters Work?
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StWH NTWH
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CTWH CTWH1
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Hot Water MeterWater in from city
or well
Water Heater #1
Water Heater #2
Water Heater #3 - Storage
To hot water end use
Total Gas Meter
Gas into house
To other Gas uses
Outlet RTD
To cold water uses
Total Water Meter
Water Heater Gas Meter
Water Heater shut off and drain kit
Inlet RTD
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• Delayed delivery time• Cold water sandwich• Consistent Supply temperature• Minimum flow rate for firing• Performance for multiple simultaneous uses
Hot Water Quality Issues Facing Tankless Water Heaters
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Issues Facing Tankless Water Heaters
+ Hot water quality+ Delayed delivery time+ Cold water sandwich+ Consistent Supply temperature+ Minimum flow rate for firing+ Performance for multiple simultaneous uses
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Storage Water HeaterNon-Condensing TanklessCondensing Tankless
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Delayed Delivery Time
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Efficiency and Savings
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DOE Energy Factor Rating
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EF Rating vs Measures Efficiencies
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Estimated Simple Payback
15
Cheapest retrofitnew constructionPower Vent req.
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Hot Water Use
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Difference In Hot Water Use
+ 0 of 10 sites in our study – no significant difference in water use between tank and tankless heaters
+ 1 of 10 sites – slight increase in hot water energy demand
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Project Average: 36 GPD, 26 Draws/day
Test Method Volume
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Single End Use Draws by Fixture
*Only averaged over the 4 sites that had dishwashers
*
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Impact on Gas Distribution
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Community Gas Profiles
One min. gas input rates at 5 homes on a 0 deg day
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Questions?
Full report: http://mncee.org/twh
This project was funded by Minnesota Department of Commerce – Office of Energy Security
Minnesota Statutes § 216B.241, subd. 1eand
Center for Energy and Environment