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Energy Use and Sales Productivity of
Doored and Open Vertical Refrigerated
Display Cases
Brian A. Fricke, Ph.D.
Bryan R. Becker, Ph.D., P.E.
University of Missouri – Kansas City
Objective
• Compare a typical new open refrigerated display case line-up to a typical new glass-doored refrigerated display case line-up
• Quantify and compare the following:
– The overall energy consumption for each case type
– The impact on food product sales for each case type
Synopsis
• Test Plan
• Supermarket Descriptions and Display
Cases Studied
• Display Case Electrical Energy
Consumption
• Product Sales
• Conclusions
General Test Plan
• Identify two similar supermarkets to participate in study
• “Before and after” comparison of selected product sales– Identify existing display case line-up in each store
→ collect sales data of the products for two months
– Replace existing display case line-ups with new display case line-ups
→ collect sales data of the products for two months
– Compare sales data “before and after” installation of the new display case line-ups to determine the effect that new case line-ups had on product sales
General Test Plan
• The products studied in the two
supermarkets were different
– Sales data for the test products were
collected from both supermarkets
– Sales data from one supermarket was used
as a control to adjust the sales data of
products studied in the other supermarket
(and vice versa)
General Test Plan
• The energy usage of each new display case line-up was monitored
– Compare energy usage of a new open display case line-up versus that of a new doored display case line-up
• Energy consumption of the HVAC systems were not monitored and no modifications were made to the HVAC systems
Test Plan Outline
• For Store #1:
– Old open case was replaced with new glass-doored
case
– New case was in the same location as old case
– New case was stocked with the same product as old
case
– Sales of the product were studied before and after the
case was replaced
– Energy usage of new glass-doored display case line-
up was monitored
Test Plan Outline
• For Store #2:
– Old open case was replaced with new open case
– New case was in the same location as old case
– New case was stocked with the same product as old
case
– Sales of the product were studied before and after the
case was replaced
– Energy usage of new open display case line-up was
monitored
Instrumentation
• Refrigerant mass flow through display case measured with coriolis mass flow meter
• Refrigerant temperature and pressure entering display case measured
• Refrigerant temperature and pressure exiting display case measured
• One minute sampling rate
Instrumentation
• Electrical energy consumption of display case auxiliaries individually measured– Fans
– Lights
– Anti-sweat heaters
• Indoor ambient temperature and relative humidity at each store measured
• Outdoor ambient temperature and relative humidity at each store measured
• One minute sampling rate
Store #1 Info
• Located in Osawatomie, KS, a community
of 4,600 people
– Approximately 50 miles south west of Kansas
City, MO
• Average retail sales of $80,000 per week
• Store size is 23,000 ft2
Store #1
• Dairy products, including yogurt, prepackaged cheese, butter, and sour cream, were studied in this store
• Dairy products initially resided in a 44 foot open, multi-deck case line-up
• This case was replaced with a new, medium temperature, 20-doored case line-up, nominally 48 feet in length– Fluorescent lighting
– Anti-sweat heaters with no controls (always on)
– Standard efficiency evaporator fan motors
• Energy consumption of only 10 door portion of case (24 feet) measured
Store #1: Old Open Case Line-Up
Store #1: New Doored Case Line-Up
Store #2 Info
• Located in Wamego, KS, a community of
approximately 4000 people
– Approximately 100 miles west of Kansas City,
MO
• Average retail sales of $140,000 per week
• Store size is 30,200 ft2
Store #2
• Beer and various alcoholic beverages (wine coolers, hard lemonade, etc.) were studied in this store
• Products initially resided in an open, multi-deck case line-up, 24 feet in length
• This open case line-up was then replaced with a new, medium temperature, open, multi-deck case line-up, 24 feet in length– Fluorescent lighting
– Standard efficiency evaporator fan motors
Store #2: Old Open Case Line-Up
Store #2: New Open Case Line-Up
Serendipity
• Owner of Store #1 (new doored diary case) also
replaced 12 feet of open beer case with a 6-
doored case, nominally 12 feet in length
• Allowed comparison of:
– New doored case beer sales to old open case beer
sales in Store #1
– New open case beer sales to old open case beer
sales in Store #2
– New doored case beer sales (Store #1) to new open
case beer sales (Store #2)
Sample Energy Related Data
Suction Temperature and Pressure
Liquid Temperature and Pressure
Suction Temperature and Pressure
– New Open Case Line-Up – – New Doored Case Line-Up –
Liquid Temperature and Pressure
0
10
20
30
40
50
60
70
80
5/25/2009
0:00
5/25/2009
4:48
5/25/2009
9:36
5/25/2009
14:24
5/25/2009
19:12
5/26/2009
0:00
Time
Tem
pera
tatu
re (
F)…
20
25
30
35
40
45
Pre
ssu
re (
psig
)..
Temperature
Pressure
0
10
20
30
40
50
60
70
80
90
5/25/2009
0:00
5/25/2009
4:48
5/25/2009
9:36
5/25/2009
14:24
5/25/2009
19:12
5/26/2009
0:00
Time
Tem
pera
ture
(F
)...
60
80
100
120
140
160
180
200
Pre
ssu
re (
psig
)..
Temperature
Pressure
30
35
40
45
50
55
60
5/25/2009
0:00
5/25/2009
4:48
5/25/2009
9:36
5/25/2009
14:24
5/25/2009
19:12
5/26/2009
0:00
Time
Tem
pera
ture
(F
)...
30
35
40
45
50
55
60
Pre
ssu
re (
psig
)..
Temperature
Pressure
0
20
40
60
80
100
120
5/25/2009
0:00
5/25/2009
4:48
5/25/2009
9:36
5/25/2009
14:24
5/25/2009
19:12
5/26/2009
0:00
Time
Tem
pera
ture
(F
)...
60
110
160
210
260
310
360
Pre
ssu
re (
psig
)..
Temperature
Pressure
Sample Energy Related Data
Refrigerant Flow Rate Refrigerant Flow Rate
Display Case Temperatures
– New Open Case Line-Up – – New Doored Case Line-Up –
Display Case Temperatures
0
2
4
6
8
10
12
14
16
18
20
5/25/2009
0:00
5/25/2009
4:48
5/25/2009
9:36
5/25/2009
14:24
5/25/2009
19:12
5/26/2009
0:00
Time
Flo
w R
ate
(lb
/min
)…..
0
10
20
30
40
50
60
5/25/2009
0:00
5/25/2009
4:48
5/25/2009
9:36
5/25/2009
14:24
5/25/2009
19:12
5/26/2009
0:00
Time
Tem
pera
ture
(F
)...
Air Discharge
Air Return
Evaporator U-Bend
0
0.5
1
1.5
2
2.5
3
5/25/2009
0:00
5/25/2009
4:48
5/25/2009
9:36
5/25/2009
14:24
5/25/2009
19:12
5/26/2009
0:00
Time
Flo
w R
ate
(lb
/min
)….,
10
15
20
25
30
35
40
45
50
5/25/2009
0:00
5/25/2009
4:48
5/25/2009
9:36
5/25/2009
14:24
5/25/2009
19:12
5/26/2009
0:00
Time
Tem
pera
ture
(F
)...
Air Discharge
Air Return
Evaporator U-Bend
Air Temperature within Cases
• Smaller temperature difference between discharge and return air temperatures in doored case vs. open case
• Advantage of doored case:
– Less product temperature variation due to variation in location within case
– Less product temperature variation due to variation in store ambient conditions
– Increased food safety
Sample Energy Related Data– New Open Case Line-Up – – New Doored Case Line-Up –
Auxiliary Electrical Power Auxiliary Electrical Power
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
0.4
5/25/2009
0:00
5/25/2009
4:48
5/25/2009
9:36
5/25/2009
14:24
5/25/2009
19:12
5/26/2009
0:00
Time
Po
wer
(kW
)..
Lights
Fans
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
5/25/2009
0:00
5/25/2009
4:48
5/25/2009
9:36
5/25/2009
14:24
5/25/2009
19:12
5/26/2009
0:00
Time
Po
wer
(kW
)..
Lights
Fans
Anti-Sweat
Electrical Energy Consumption
Mean Electrical Energy Consumption of the Open and Doored Display Case Line-Ups Calculated using
ARI/ANSI Standard 1200-2006.
Electrical Energy Consumption Open Display Case
Line-Up
Doored Display Case
Line-Up
Compressors (kWh/day) 42.20 11.70
Lights (kWh/day) 5.18 11.93
Fans (kWh/day) 5.69 4.58
Anti-Sweat Heaters (kWh/day) -- 15.50
Total (kWh/day) 53.07 43.72
Total (kWh/day per ft) 2.21 1.71
• Per unit length of case, the open display case
line-up consumed approximately 1.3 times more
energy than the doored display case line-up
Open Case Line-Up Electrical
Energy Consumption
0
10
20
30
40
50
60
70
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 41
Day
Ele
ctr
ica
l E
ne
rgy
Co
ns
um
pti
on
(k
Wh
/da
y)
Fans
Lights
Compressors
Compressors: 79% of the total daily electrical energy consumption
Fans: 11% of the total
Lighting: 10% of the total
Open Case: Energy Consumption
vs Indoor Ambient Conditions
• Energy consumption closely follows indoor ambient humidity
30.0
35.0
40.0
45.0
50.0
55.0
60.0
65.0
70.0
75.0
80.0
0 7 14 21 28 35 42
Day
Te
mp
era
ture
(F
)
En
erg
y C
on
su
mp
tio
n (
kW
h/d
ay
)
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
Re
lati
ve
Hu
mid
ity
(%
)
Indoor Temperature
kWh/day
Indoor RH
Doored Case Line-Up Electrical
Energy Consumption
0
5
10
15
20
25
30
35
40
45
50
1 4 7 10 13 16 19 22 25 28 31 34 37 40
Day
Ele
ctr
ica
l E
ne
rgy
Co
ns
um
pti
on
(k
Wh
/da
y)
Fans
Anti-Sweat Heaters
Lights
Compressor
Anti-sweat heaters: 36% of the total daily electrical energy use
Compressors: 27% of the total
Lights: 27% of the total
Fans: 10% of the total
Doored Case: Energy Consumption vs
Indoor Ambient Conditions
• Energy consumption independent of indoor ambient conditions
30.0
35.0
40.0
45.0
50.0
55.0
60.0
65.0
70.0
75.0
80.0
0 7 14 21 28 35 42
Day
Tem
pera
ture
(F
)
En
erg
y C
on
su
mp
tio
n (
kW
h/d
ay)
0.0
5.0
10.0
15.0
20.0
25.0
30.0
35.0
40.0
45.0
50.0
Rela
tive H
um
idit
y (
%)
Indoor Temperature
kWh/day
Indoor RH
Electrical Energy Consumption vs.
Indoor Relative Humidity
• Open case line-up: Consumed 1.25 times as much energy when the indoor relative humidity was 45% as compared to when the mean indoor relative humidity was 20%
• Doored display case line-up: Electrical energy consumption remained relatively constant with increasing mean indoor relative humidity
30
35
40
45
50
55
60
20 25 30 35 40 45 50
Mean Indoor Relative Humidity (%)
Ele
ctr
ica
l E
ne
rgy
Co
ns
um
pti
on
(k
Wh
/da
y)
Open Line-Up
Doored Line-Up
Energy Efficiency Improvements for
Doored Display Case
• Significant anti-sweat heater energy usage
with doored case
– Anti-sweat heaters were on continuously
• Energy use could be drastically reduced
by using:
– Anti-sweat heater controls or “no heat” doors
– LED lighting
Energy Efficiency Improvements for
Doored Display Case
• For 10 doored case line-up, assume:
– Zero energy consumption for “no heat” doors
– 265 watts energy consumption for LED lighting
• Estimated energy consumption:
– 20.5 kWh/day
– 0.802 kWh/day per foot
• 53% energy savings compared to new doored display case
line-up tested in this study
• 64% energy savings compared to new open display case
line-up tested in this study
Weekly Beer Sales: Store #1
(Control and Serendipity)
0
20
40
60
80
100
120
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Week
Qu
an
tity
So
ld Pre
Post
Weekly Beer Sales Data from the Old Open and New
Doored Display Case Line-Ups for the Period 4 January
2009 through 6 June 2009
Weekly Beer Sales: Store #2
0
50
100
150
200
250
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Week
Qu
an
tity
So
ld
Pre
Post
Weekly Beer Sales from the Old Open and New Open
Display Case Line-Ups for the Period 4 January 2009
through 6 June 2009
Summary of Weekly Beer Sales
• Two-sample, unequal-variance t-test:
– Increases in sales were significant at the 0.05 level
• Rate of increase in beer sales was essentially the same for both the new open and new doored display case line-ups:
– „Doored versus open‟ had no effect on product sales
Beer Sales Statistics Open Display Case
Line-Up
Doored Display Case
Line-Up
Mean Weekly Quantity Sold, Pre-
Installation 104.4 55.4
Standard Deviation of Weekly
Quantity Sold, Pre-Installation 9.26 10.6
Mean Weekly Quantity Sold, Post-
Installation 134.6 70.5
Standard Deviation of Weekly
Quantity Sold, Post-Installation 26.7 11.1
Percentage Increase 29% 27%
Weekly Dairy Sales: Store #1
0
100
200
300
400
500
600
700
800
900
1000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Week
Qu
an
tity
So
ld
Pre
Post
Weekly Dairy Sales Data from the Old Open and New
Doored Display Case Line-Up for the Period 4 January
2009 through 6 June 2009
Weekly Dairy Sales: Store #2
(Control)
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22
Week
Qu
an
tity
So
ld
Pre
Post
Weekly Dairy Sales Data from the Open Display Case
Line-Up for the Period 4 January 2009 through 6 June
2009
Summary of Weekly Dairy Sales
• Two-sample, unequal-variance t-test:
– No significant difference (at the 0.05 level) in diary product sales before and after installation of the new doored display case line-up
• Rate of dairy sales remained the essentially the same before and after the installation of the new doored display case line-up:
– „Doored versus open‟ had no effect on product sales
Dairy Sales Statistics Open Display Case
Line-Up
Doored Display Case
Line-Up
Mean Weekly Quantity Sold, Pre-
Installation 3864 639.4
Standard Deviation of Weekly
Quantity Sold, Pre-Installation 403.6 41.3
Mean Weekly Quantity Sold, Post-
Installation 3846 621.5
Standard Deviation of Weekly
Quantity Sold, Post-Installation 464.5 152.2
Percentage Increase -0.47% -2.8%
Conclusions
• Two stores studied:– Store #1
• Replaced old open case with new doored case
• Measured sales of diary products from old open and new doored cases
• Measured energy consumption of new doored case
– Store #2• Replaced old open case with new open case
• Measured sales of beer and alcoholic beverages from old open and new open cases
• Measured energy consumption of new open case
– Serendipity• Replaced old open case with new doored case
• Measured sales of beer and alcoholic beverages from old open and new doored cases
Conclusions
• Total electrical energy consumption– Per unit length of case, open display case line-up consumed
approximately 1.3 times more energy than the doored display case line-up
• Electrical energy consumption of the open display case line-up exhibited significant variation from day-to-day– Mainly attributed to daily variation in compressor energy consumption
• Electrical energy consumption of the doored display case line-up was relatively consistent from day-to-day– All of the components of the electrical load remained fairly constant
• Increasing mean indoor relative humidity:– Electrical energy consumption of the open display case line-up
increased
– Electrical energy consumption of the doored display case line-up remained relatively constant
Conclusions
• Smaller temperature difference between discharge and return air temperatures in doored case vs. open case
• Advantage of doored case:
– Less product temperature variation due to variation in location within case
– Less product temperature variation due to variation in store ambient conditions
– Increased food safety
Conclusions
• Beer sales increased:
– 29% in the new open display case line-up
– 27% in the new doored display case line-up
• These increases in sales were significant at the
0.05 level (two-sample, unequal-variance t-test)
• Rate of increase in beer sales was essentially
the same for both the new open and new doored
display case line-ups:
– „Doored versus open‟ had no effect on product sales
Conclusions
• Dairy products:
– There was no significant difference (at the 0.05 level)
in diary product sales before and after installation of
the new doored display case line-up (two-sample,
unequal-variance t-test)
• Rate of dairy sales remained essentially the
same before and after the installation of the new
doored display case line-up
– „Doored versus open‟ had no effect on product sales
Acknowledgments
• Funding for this project was provided by:
– American Society of Heating, Refrigerating and Air-
Conditioning Engineers (ASHRAE)
– Air-Conditioning and Refrigeration Technology
Institute (ARTI)
• The authors would also like to thank Affiliated
Foods Midwest for facilitating our interaction with
the supermarket owners that participated in this
study
Thank You!
• Questions?
