High Efficiency Evaporator Coils for Medium Temperature Cases
Dustin Bailey, Engineer
PECI
Jan 5, 2010
Acknowledgements
We would like to thank the following utilities for support• BPA• PSE• AVISTA
Purpose• Deemed measure approval for upgrading
evaporator coils from standard to high efficiency in new MT cases.
• Upgrading the coils provides savings independent of other component measures.
• Energy savings should be deemed based off total case load going to compressor system, independent of climate zones.
AgendaBackground
Description of Measure
Compressor System Interaction
Auxiliary Load Sensitivity
Energy SavingsAdjustments for Energy Savings
Unitized Energy Savings
Floating Suction Interactivity
Energy Savings and Payback
Measure Life
Terms and Conditions
Conclusion
Background - Measure Description
• Current measures are for complete case replacement. This causes the following problems:
◦ only one baseline condition can get savings as defined as a “standard case”
◦ efficient evaporator coil savings are often ignored • Proposing measure for high efficiency evaporator coils for the
critical case independent of other case component measures• Modeled in eQUEST using the PECI GrocerSmart model as the
template
Background - Efficient Coil
Description of Proposed Scenario• An efficient coil has more area than a standard coil
allowing for the same heat transfer with a lower ΔT ◦ Q=U*A*ΔT
• An efficient coil allows the suction group temp of the compressor rack to rise 3 deg F
• Depending on the type of product in the case, efficient coils allow for varying increases of saturated suction temperature (SST).
• 3 deg F is the smallest average increase and was chosen to be conservative.
Compressor Discharge
Compressor Suction
Background - Compressor System Energy Gap
By allowing the SST of the compressor to rise, the power the compressor must exert is reduced.
Energy savings is calculated for a multiplex system as shown below:
)( eebase kWhkWhkWh
Background - MT Refrigeration System
Background - Model DataDescription of Pre and Post Scenario
Savings = 13,000 kWh
Case Data for
Baseline Case Type
SST at Evap, deg F
Coil Inlet Delta T (SST Supply TD),
deg F
Case Data for
Proposed Case Type
SST at Evap, deg F
Coil Inlet Delta T (SST Supply TD),
deg F
MT_Produce Multi-deck 28 12 MT_Produce Multi-deck 28 12
MT_Dairy2 Multi-deck 24 7 MT_Dairy2 Multi-deck 24 7
MT_Dairy1 Multi-deck 24 7 MT_Dairy1 Multi-deck 24 7
MT_Melon Bakery Multi-deck 21 10
MT_Melon Bakery Multi-deck 21 10
MT_Deli Pasta Multi-deck 21 10
MT_Deli Pasta Multi-deck 21 10
MT_Meat2 Multi-deck 20 11 MT_Meat2 Multi-deck 20 11
MT_Meat3 Multi-deck 20 11 MT_Meat3 Multi-deck 20 11
MT_Serv Deli Multi-deck 20 10
MT_Serv Deli Multi-deck 20 10
MT_Meat1 Single-deck 20 11 MT_Meat1 Single-deck 20 11
MT_Fish Multi-deck 16 11Critical Case MT_Fish Multi-deck 19 8
Compressors 14 964,000 kWh Compressors 17 951,000 kWh
Background - Auxiliary SensitivityDescription of Baseline
• Different baselines with different auxiliary loads:
◦ Lamp (T12, T8, LED)◦ Doors (Door, No Door, Efficient
Door (no/low ASH))◦ Evaporator Motors (SP, ECM,
PSC)• Conclusion: Since savings was
independent of different baselines, T8 ND-ECM was chosen to be the representative case as it is a common retrofit case
Base Line Savings
LED D ECM 12,792
LED D PSC 12,811
LED D SP 12,813
LED ED ECM 12,790
LED ND ECM 13,068
T8 D ECM 12,928
T8 D PSC 12,970
T8 D SP 12,975
T8 ED ECM 12,922
T8 ND ECM 13,148
T12 D ECM 12,965
T12 D PSC 12,990
T12 D SP 13,002
T12 ED ECM 12,966
T12 ND ECM 13,224
Average Motor Effect
Average Door Effect
Average Lighting Effect
LED D LED ECM D ECM
0.28% 1.92% 1.37%
Adjustments for Energy Savings
• By increasing the SST of the critical load, the power of the compressor will decrease resulting in system energy savings.
• Key assumptions◦ The compressor set point (suction group set point) is 2 deg F
less than needed by the critical case◦ Efficient coils will decrease the TD by 3 degrees (averaged
data from various manufacturers)◦ Floating suction control is present on 26.9% of all refrigeration
systems, and 21% (conservative) of the MT cases have doors (EnergySmart audit data)
◦ Results were modeled using eQUEST with T8 ND ECM on the critical case in the PECI GrocerSmart Model
Unitized Energy Savings Before Floating Suction Interactivity
Reduction of Suction Load (Btu/h)
Reduction Ratio
Reduction of Refrig Mass Flow (lb/hr)
Reduction Ratio
Reduction of Comp Power (kW)
Reduction Ratio
4,046 4.30 56 4.29 0.4 4.28
17,384 3.28 240 3.25 1.7 3.21
57,004 1.37 783 1.37 5.5 1.37
78,149 1,075 7.6
Compressor power scaling with the reduction of suction load
Weather Zone Energy Savings/ Suction Load (kWh/MBH)
Boise, ID 38.41
Pocatello, ID 38.23
Billings, MT 38.67
Portland, OR 39.57
Burns, OR 38.26
Seattle, WA 39.24
Yakima, WA 38.90
Spokane, WA 38.61
Average 38.74
Standard Dev 0.48
% Dev 1.2%
Savings for various weather zones in the PNW without floating suction control
Floating Suction InteractivityFloating suction reduces available energy savings from the efficient coil measure
Base Line
Savings for Systems w/ FS
With Doors 3,664 kWh
No Doors 9,934 kWh
Effect of doors on the evaporator savings for a multiplex system with floating suction control.
kWhkWhkWhkWh
kWhkWh(kWhkWh
kWh
kWh
MBH
kWh
MBH
kWh
DkWhDkWhkWh
FSkWhFS(kWhkWh
kWh
kWh
MBH
kWh
MBH
kWh
FS
FS
FS
Adjusted
Final
NoDoorDoor
GSAdjusted
GS
Adjusted
FSFinal
617,8%)21(*664,3%)211(*934,9
821,11%9.26*617,8%)9.261000,13
000,13
821,11*38.74
)1()(
)1
*
*
**
%%
%%
kWh/MBH35.22
Energy Savings and Payback
•Total system MBH difficult to quantifyQuantify saving per linear foot of total display case associated with compressor group
•Using GrocerSmart model as the prototypical grocery store:T8 ND-ECM model:
– Assuming $0.10 per kWh this results in a savings of $2.75/ln ft of total system case length
•Cost data was collected from a variety of manuf for the coil upgrade and adjusted according to copper commodity prices–The conservative estimate for cost is $42.5/ ln ft
•EnergySmart audit data shows that the median number of cases replaced is 82 ft for a cost of $3,485–Therefore, the typical store’s simple payback period can be calculated:
ft
kWh
MBH
kWh
ft
MBH
ln
47.2722.35*
ln
78.
years
kWhft
ft
kWh
05.3143,1$
485,3$
143,1$10.0$
*416*ln
47.27
Typical Case Replacement Lengths Payback is proportional to the length of case replaced with HE coils and case length can vary from store to store.
Histogram of Case Replacement Lengths
0
5
10
15
20
25
30
35
40
45
3 36 69 102 136 169 202 235 268 301 335 368 401 More
Case Length
Nu
mb
er o
f In
cid
ents
0.0%
10.0%
20.0%
30.0%
40.0%
50.0%
60.0%
70.0%
80.0%
90.0%
100.0%
Measure Life Assumptions
• Measure Life/Effective Useful Life is assumed to be the same as evaporator motors which have a life of 15 years
◦ Southern California Edison1, PG&E2 and BPA3 program all use 15 year measure life for ECMs
» 1Energy Savings Potential for Commercial Refrigeration Equipment. June 1996. U. S. Department of Energy. Arthur D. Little. p 5-51
» 2CALMAC Protocols, Appendix F, Effective Useful Live Values for Major Energy Efficiency Measures, September 2000
» 3Council Plan 1996; 15 year EUL used for all Retrofit HVAC Systems & Controls including motor retrofits
Must replace an existing medium temperature evaporator standard coil with a high efficiency coil on the critical case(s) to result in a compressor suction group saturated suction temperature rise of at least 3 degrees. This is done through case replacement and several cases may need to be replaced to ensure the resulting critical case(s)’ coil(s) are replaced. A design review is required by the program to confirm the which cases must be replaced. The savings of this measure are independent of other case component measures and those measures may be claimed separately. If several suction groups exist this measure may be applied to each individually.
Terms and Conditions
Conclusion
• Measure provides large opportunity for savings through more efficient operation of a refrigeration compressor system
• Efficient evaporators coils must be in the critical case
• The calculated savings is for a multiplex system with a rise of 3 degrees of SST
• Floating suction controls reduce available energy savings efficient evap coils
• factored into the unitized energy savings
• Cost variability—based on the total length of the critical case replaced
• Requesting approval for high efficiency evaporator coils for medium temperature cases as a measure
Unitized or
Modeled Savings
Unit of measure
Energy Savings (kWh)
Measure life
Measure Cost
Lost Opportunity
Measure
Measure Cost
Source
RTF B/C Ratio
High Efficiency Evaporator Coils for Medium Temperature Cases
Unitized ln ft 27.47 15 $42.50/ln ft No Manuf. TBD