Hot Water Heating: Technologies and Use

Transcription

1 Hot Water Heating: Technologies and Use Skip Hayden Integrated Energy Systems CanmetENERGY Better Buildings by Design 2010 Burlington Vermont February 2010 Natural Resources Canada Ressources naturelles Canada

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3 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

4 ?? What are you looking for???

5 Residential Energy Use

6 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

7 Water Heating Technologies Tank- Based

8 Electric Resistance Water Heater Who has an electric water heater?

9 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!

10 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

11 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)

12 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.

13 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

14 Now, we are starting to see a range of different technologies to heat water

15 Tankless Gas-Fired Water Heaters Wide range of technologies and potential efficiencies

16 Low Tech Tankless Water Heater Natural draft Pilot light Draft hood Prone to spillage Inefficient (0.6 EF) Relatively cheap Don t use!

17 Mid-Efficiency Tankless Water Heater Co-Linear Venting 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

18 Mid-Efficiency Tankless Water Heater Co-Axial Venting 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

19 High-Efficiency Condensing 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 Additional stainless steel condensing heat exchanger EF ~ 0.9

20 Concern about co-axial venting in cold climates

21 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!

22 Efficient Low Mass Condensing Boilers with Segregated Tap water and Highly-Modulating Burners

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24 External tank must have good heat transfer and very low heat loss

25 Commercial Service Water Heating

26 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

27 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

28 Efficient, sealed combustion (non-condensing) boiler as segregated heat source with large external tank for service hot water External tank works against condensing system!!

29 Tankless Wall-Mount Water Heaters

30 Condensing Tank Water Heater > 90% efficient, as mains water provides driving force for condensing

31 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

32 Oil-Fired Water Heaters

33 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!!

34 Efficient Oil-Fired Space/Water Heating Systems

35 What about wood?

36 How Wood Burns 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 + O 2 to ignite them, the result is high emissions and creosote.

37 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!

38 What about hot water from a wood boiler? Well, maybe

39 Solar-Augmented Water Heating

40 Heat Pump-Augmented Water Heaters

41 Nominal Efficiencies of Water Heating Technologies TYPE Nom Efficiency Range (%) Gas Storage Condensing Gas Storage Tankless Condensing Tankless* Electric Storage Heat Pump Water Heater*

42 Do these numbers reflect the way hot water is really used? To answer that question we conducted a significant hot wateruse field trial

43 Field Test Results Number of draws much greater and shorter than present test standard 100% 90% 80% 92% of Draws Made < 1 Minute 70% 60% Accounts for 30% of Daily Volume 50% 40% 30% 20% 10% 0% 0 to 15 s 15 to 30 s 30 to 45 s 45 to 60 s 60 to 75 s 75 to 90 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 1020 s 1020 to 1080 s 1080 to 1140 s 1140 to 1200 s 1200 to 2400 s Duration of Draw (s) Number of Draws

44 Detailed Trial Results Fraction of Daily Volume Drawn vs. Duration 30% 25% 20% 15% 10% 5% 30 % 18 % 7 % 33 % 12 % Fraction of Daily Volume Drawn. 0% 0 to to to to to to to to to to to to to to to to to to to to to to to to to to to 2400 Duration of Draw (s)

45 Field Test Results Average Daily Hot Water Use 1/3 less than standard Average Daily Draw (Litres) gal CSA P.3 & US DOE = Litres = 64.3 US Gallons Study Average = 163 Litres = 43.1 US Gallons 43 gal Test Site #

46 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

47 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

48 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

49 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.

50 Changing The Test Standard Current test standard: Storage = 60% Tankless = 80% Realistic test standard results in lower actual efficiencies: Storage = 45% Tankless = 70%

51 Summary Most 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

52 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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54 ekocomfort Advanced Integrated Mechanical Systems A major Canadian initiative to develop and market high efficiency, integrated space-water-ventilating systems

55 Results Average Draw Flow Rate 12.0 Average Volume Flowrate (Litres / Minute) CSA P.3 & US DOE = 11.4 Litres / minute = 3.0 US Gallons / minute Test Site # Study Average = 2.9 Litres / minute = 0.8 US Gallons / minute

56 Detailed Results Number of Draws vs. Draw Duration 100% 90% 80% 92% of Draws Made < 1 Minute 70% 60% 50% 40% 30% Number of Draws 20% 10% 0% 0 to 15 s 15 to 30 s 30 to 45 s 45 to 60 s 60 to 75 s 75 to 90 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 1020 s 1020 to 1080 s 1080 to 1140 s 1140 to 1200 s 1200 to 2400 s Duration of Draw (s)

57 Hot Water Use per Family A = Adult C = Child 2A 3A 2A + 1C 2A + 2C 2A+3C 3A + 2C 4A Test Site # Average Daily Volume Draw (Litres)