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