The Revised Method of Test for

Residential Water Heating and Its

Impact on Incentive Programs

Paul Glanville

ACEEE Hot Water Forum

Tuesday, February 24th, 2015

Nashville, TN

22

>How Water Heaters are Rated Today

>Changes in the MOT

>Test Plan

>Test Results

>Market Implications

Overview

33

Known Drawbacks of the Current Method of

Test/ASHRAE 118.2:

• Daily hot water draw volumes vary significantly and, on

average are lower – recent meta-analysis of 10 U.S.

studies shows average is 50.6 gal/day.

• Too few hot water draws favor low storage volumes, same

analysis shows median daily draw count is 62 draws/day

versus six in the current MOT.

• Thermostat setting of 135°F is too high, majority of units

shipped have out-of-box setting of ≤125°F.

• Limited coverage of MOT leaves out many products

known to be used in residential applications.

How Water Heaters are Rated Today

44

Changes in the MOT

Legislation puts changes on fast track:

The new Federal MOT includes major changes to a

procedure largely unchanged for over 25 years:

• Categorized by output capacity into one of four

groups: Very Small, Low, Medium, or High

Usage, each with unique draw pattern.

• The four draw patterns applied are distributed,

more realistic, unlike the current MOT.

• Products are included that were not previously

given an “Energy Factor (EF)”, thus were

exempt from Energy Star, including hybrid and

light commercial products.

55

Impact: Categorization

Water Heater Type

Draw Pattern NameDaily Hot Water

Draw (Gal.)First Hour

Rating/Max. GPM

Definition

Volume Input

Storage

Very Small Usage 10 0 ≤ FHR < 18

2 < Gal. < 120

< 75,000 Btu/hr or < 12 kW

Low Usage 38 18 ≤ FHR < 51

Medium Usage 55 51 ≤ FHR < 75

High Usage 84 75 ≤ FHR

Tankless

Very Small Usage 10 0 ≤ GPM < 1.7

Gal. < 2< 200,000 Btu/hr or < 12 kW

Low Usage 38 1.7 ≤ GPM < 2.8

Medium Usage 55 2.8 ≤ GPM < 4.0

High Usage 84 4.0 ≤ GPM

• Current MOT rates all products with 64 gal/day

draw pattern

• New MOT (below) has criteria for 4 categories

66

Impact: Categorization

Delivered Efficiency, is

strong function of daily hot

water draw -> Lower

capacity WHs will have

lower rated EFs.

Previously uncategorized

products will go from

Thermal Efficiency (TE) to

EF, recent data show that a

95% TE condensing storage

WH receives a 0.78 EF with

the current MOT

Delivered Efficiency versus Daily Heat Output (Btus)

Kosar, D. et al. “Residential Water Heating Program - Facilitating the Market Transformation to Higher Efficiency Gas-Fired Water Heating - Final Project Report”. CEC Contract CEC-500-2013-060. (2013).

77

Impact: Draw Patterns

Current MOT Draw

Pattern, for all

WHs, is known to

over-estimate the

efficiency of

no/low-storage

equipment.

Distributed draw

patterns in the new

MOT may result in

rated changes of

value between

EF/UEF

0

2

4

6

8

10

12

Ho

t W

ater

Dra

w (

gallo

ns)

Current

MOT: 64

gal/day

New MOT

“Medium”

Category:

55 gal/day

0

2

4

6

8

10

12

14

16

Ho

t W

ater

Dra

w (

gallo

ns) 1.7 GPM

1.0 GPM

88

Other Impacts

• Reduction of thermostat setting to 125°F

• Broadening scope, to include:

• Storage equipment with 2-20 gallons, covering

a previously existing gap for these “hybrids”.

• “Residential-duty commercial” products,

essentially products not covered currently but:

use single phase power, do not produce water >

180°F, and do not require ASME

Boiler/Pressure Vessel certification.

99

Test Plan

• Seven representative WHs tested to current and new MOT.

• Quantify difference in results for EF/UEF (and other parameters) and

their impact on projected energy savings.

Water Heater Type Rated FHR/Max. GPM* Revised SUT Daily Volume

Non-condensing Storage (NCS) 75 gal. > FHR > 51 gal.Medium

(Derate for Low Usage Too)

Condensing Storage – Residential (CS-L)

> 75 gal. High

Condensing Storage – Res. Duty Commercial (CS-H)

> 75 gal. High

Non-condensing Tankless (NCT) > 4.0 gpm High

Condensing Tankless (CT) > 4.0 gpm High

Hybrid (H) > 75 gal. High

Electric Heat Pump Storage (EHP) 75 gal. > FHR > 51 gal. Medium

* Note FHRs/Max. GPM determined at new reduced thermostat setting

1010

Test Results

75%

80%

85%

90%

95%

100%

105%

110%

115%

120%

125%

0 0.5 1 1.5 2 2.5

Ch

ange

in U

EF a

s P

erce

nta

ge o

f EF

Tested EF of Water Heater

C/NCT

NCS

H

CS

EHP

Tankless Heaters*

Storage Heaters*

Data show range of +/-20% change in

UEF/EF, on par with what US DOE

published previously.

• Impact of daily volume draw

• Standby recovery bias

*Water Heater Test Procedure Rulemaking: Development Testing Preliminary Report – Energy Conservation Program for Consumer Products and Certain Industrial Equipment: Residential and Light Commercial Water Heaters , US DOE (2013)

1111

Test Results

0

2

4

6

8

10

12

14

0.40

0.50

0.60

0.70

0.80

0.90

1.00

NCT CT NCS-M NCS-L H CS-L CS-H EHP

UA

(B

tu/h

r-F)

UEF

/EF

and

Rec

ove

ry E

ffic

ien

cy

EF - Current MOT

UEF - New MOT

nr - Current MOT

nr - New MOT

UA - Current MOT

UA - New MOT

1.00

1.50

2.00

2.50

3.00

3.50

EHP

“nr” is ηR , the recovery efficiency as calculated by the procedures

1212

Test Results

Why is UEF > EF except for NCS?

• Higher daily draw volumes increase impact of SS

efficiency versus standby losses

• First draw volume of 15/27 gallons larger and, for

Low/Medium Usage patterns, at 1.7 gpm, yielding higher

recovery efficiency.

• Recovery efficiency also higher for units with slower

recoveries (heat pumps), which can fully recover prior to

end of hot water draws.

• Outlet temperature variation can bias UEF/EF.

• Both units not currently rated with “EF” experienced a

standby recovery, biasing EFs lower

1313

Test Results – Delivered Temperature

-4.0%

-2.0%

0.0%

2.0%

4.0%

6.0%

8.0%

10.0%

12.0%

14.0%

NCT CT NCS-M NCS-L H CS-L CS-H EHP

Pe

rce

nta

ge A

dju

stm

en

ts in

DH

W E

ne

rgy

to

De

live

red

Te

mp

era

ture

Tar

get

New MOT

Current MOT

• Both MOTs adjust

DHW output energy for

delivered temperatures

off-target.

• Like other adjustments

(e.g. ambient

conditions), the smaller

it is (total and for each

draw event), the more

repeatable and

accurate the results.

1414

Test Results – Delivered Temperature

105

110

115

120

125

130

135

140

145

1 2 3 4 5 6Ave

rage

Del

iver

ed T

emp

erat

ure

(F

)

Draw Number

NCT

CT

NCS

H

CS-L

CS-H

EHP

105

110

115

120

125

130

135

140

145

1 2 3 4 5 6 7 8 9 10 11 12 13 14

Ave

rage

Del

iver

ed

Tem

per

atu

re (

F)

Draw Number

NCT

CT

NCS-M

NCS-L

H

CS-L

CS-H

EHP

Current MOT

New MOT

1515

Test Results – Draw Pattern

y = 1.0429x - 0.0264R² = 0.9846

0.4

0.5

0.6

0.7

0.8

0.9

1

0.4 0.5 0.6 0.7 0.8 0.9 1

Sim

ple

Del

iver

ed E

ffic

ien

cy

Tested UEF of Water Heater

• Overall test UEF and

simple delivered

efficiency show high

degree of linearity.

• Despite range of

delivered efficiencies

for each on-cycle

event.

1616

Test Results – Draw Pattern

0.4

0.5

0.6

0.7

0.8

0.9

1

0 5 10 15 20 25 30

Sim

ple

Del

iver

ed E

ffic

ien

cy o

f Ea

ch O

n-C

ycle

On-Cycle duration (min)

NCT

CT

NCS-M

H

CS-L

CS-H

• The range of delivered

efficiencies for each on-

cycle event is high (without

adjustments for change in

stored energy).

• Impact of using an

assumed constant

recovery efficiency• Impacts Higher UEF

systems. Same magnitude

error in quantifying

recovery heat,

disproportionately affects

UEF of EHP vs. NCS by

order of magnitude.

1717

Test Results – Draw Pattern (Long)

0

2

4

6

8

10

12

50

60

70

80

90

100

110

120

130

12:00:00 AM 12:02:53 AM 12:05:46 AM 12:08:38 AM 12:11:31 AM 12:14:24 AM

Dra

w R

ate

(G

PM

) an

d F

irin

g R

ate

(1

0,0

00

Btu

/hr)

Tem

pe

ratu

re (

F)

TC #1 TC #2 TC #3

TC #4 TC #5 TC #6

Avg Tank Inlet Outlet

Draw Rate Firing Rate

CS-H

1818

Test Results – Draw Pattern (Short)

0

2

4

6

8

10

12

50

60

70

80

90

100

110

120

130

140

4:27:50 PM 4:30:43 PM 4:33:36 PM 4:36:29 PM 4:39:22 PM 4:42:14 PM 4:45:07 PM 4:48:00 PM 4:50:53 PM

Dra

w R

ate

(G

PM

) an

d F

irin

g R

ate

(1

0,0

00

Btu

/hr)

Tem

pe

ratu

re (

F)

TC #1 TC #2TC #3 TC #4TC #5 TC #6Avg Tank InletOutlet Draw RateFiring Rate

CS-H

1919

Test Results – Draw Pattern

115

117.5

120

122.5

125

127.5

130

132.5

135

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

1 2 3 4 5 6 7 8 9 10 11 12

Ave

rage

Tan

k Te

mp

era

ture

(F)

Effi

cie

ncy

Draw Number

Avg. Rec. Eff. Del. Eff. Starting Avg. Tank T

115

117.5

120

122.5

125

127.5

130

132.5

135

0%

10%

20%

30%

40%

50%

60%

70%

80%

90%

100%

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

Ave

rage

Tan

k Te

mp

era

ture

(F)

Effi

cie

ncy

Del. Eff. Avg. Rec. Eff. Starting Avg. Tank T

CS-L

NCS-M

2020

Test Results – Draw Pattern

CT

H

CS-H

CS-L

0 200 400 600 800 1000 1200 1400

EHP

2121

Market Implications

• For these data, where UEF < EF for baseline (NCS) but EF < UEF for all

others, water heaters now may have shorter paybacks.

• Depending on local conditions, incentives for higher efficiency residential

water heaters may make more sense where they may not currently.

• Further Challenge for Utilities: But what is baseline? Is it category

specific or universal?

Water Heater Type NY CA FL

CS-L 42% 43.2% 38%

CS-H 17% 17.6% 16%

NCT 25% 25.4% 24%

CT 9% 9.4% 9%

H 33% 34.6% 28%

Assuming High Usage draw

patterns using measured

EF/UEF values, all product

types show improved

economics with 2013 avg.

utility prices.

Reduction in Payback Period with New MOT

2222

Conclusions – Things to Look For

• Repeatability – How do the distributed draw

patterns impact repeatability of the test? How

well are the short hot water draws

characterized?

• Does the same test within the tolerances, ±

0.1 gal/draw (1 gpm/1 gal. draw), ± 2°F

inlet, etc. yield the same on-cycle pattern?

• What’s the baseline? – With pending

conversions for existing products, do

consumers compare mid to mid usage

products, high to high?

• Most common min. EF will be categorized

as “mid”, most mid/high efficiency will be

categorized as “high”, how to compare?

23

Questions & Answers

@gastechnology