Post on 09-May-2015
description
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
Page 2
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
Page 3
How Do Water Heaters Work?
Page 4
StWH NTWH
Page 5
CTWH CTWH1
Page 6
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
• 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
Page 8
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
Page 9
Storage Water HeaterNon-Condensing TanklessCondensing Tankless
Page 10
Delayed Delivery Time
Efficiency and Savings
Page 12
Page 13
DOE Energy Factor Rating
Page 14
EF Rating vs Measures Efficiencies
Page 15
Estimated Simple Payback
15
Cheapest retrofitnew constructionPower Vent req.
Hot Water Use
Page 17
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
Page 18
Project Average: 36 GPD, 26 Draws/day
Test Method Volume
Page 19
Page 20
Single End Use Draws by Fixture
*Only averaged over the 4 sites that had dishwashers
*
Impact on Gas Distribution
Page 22
Page 23
Community Gas Profiles
One min. gas input rates at 5 homes on a 0 deg day
Page 24
Questions?
Full report: http://mncee.org/twh
Ben Schoenbauerbschoenbauer@mncee.org
This project was funded by Minnesota Department of Commerce – Office of Energy Security
Minnesota Statutes § 216B.241, subd. 1eand
Center for Energy and Environment