Hot Water Heating: Technologies and Use

Skip HaydenIntegrated Energy Systems

CanmetENERGYBetter Buildings by Design 2010

Burlington VermontFebruary 2010

Natural ResourcesCanada

Ressources naturellesCanada

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

What are youlooking for

??

?? ?

Residential Energy Use

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”

Water Heating Technologies

Tank- Based

Electric Resistance Water Heater

Who has an electric water heater ?

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” !

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

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)

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.

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

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

Tankless Gas-Fired Water Heaters

Wide range of technologies and potential efficiencies

“Low Tech” Tankless Water Heater

• Natural draft• Pilot light• Draft hood• Prone to spillage• Inefficient (0.6 EF)• Relatively cheap• Don’t use !

“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

“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

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

Concern about co-axial venting in cold climates

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 !

Efficient Low Mass Condensing Boilers with Segregated Tap water

and Highly-Modulating Burners

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

CommercialService Water

Heating

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

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

Efficient, sealed combustion (non-condensing) boiler as segregated heat source with large

external tank for service hot water

External tank works against condensing system !!

Tankless Wall-Mount Water Heaters

Condensing Tank Water Heater

> 90% efficient, as mains water

provides driving force for

condensing

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

Oil-Fired Water Heaters

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 !!

Efficient Oil-Fired Space/Water Heating

Systems

What about wood?

• 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

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 !

What about hot water from a wood boiler?

Well, maybe …

Solar-Augmented Water Heating

Heat Pump-Augmented Water Heaters

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

Do these numbers reflect the way hot water is really used ?

To answer that question we conducted a significant hot water-use field trial

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

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 %

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

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

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

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

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.

Changing The Test Standard• Current test standard:

Storage = 60% Tankless = 80%

• Realistic test standard results in lower actual efficiencies:

Storage = 45% Tankless = 70%

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

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

eKOCOMFORTeKOCOMFORTAdvanced IntegratedMechanical Systems

A major Canadian initiativeto develop and market

high efficiency, integratedspace-water-ventilating systems

“www.eKOCOMFORT.com”

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

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

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