the revised method of test for residential water heating ......kosar, d. et al. “residential water...
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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
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22
>How Water Heaters are Rated Today
>Changes in the MOT
>Test Plan
>Test Results
>Market Implications
Overview
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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
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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.
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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
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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).
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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
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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.
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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
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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)
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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
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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
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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.
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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
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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.
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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.
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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
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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
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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
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2020
Test Results – Draw Pattern
CT
H
CS-H
CS-L
0 200 400 600 800 1000 1200 1400
EHP
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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
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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?
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23
Questions & Answers
@gastechnology