www.windowrefrigerator.com

 

Energy Savings

Window vs. Indoor Refrigerator/Freezer (R/F)

 

NOTE:  These calculated energy savings do not include the additional energy savings due to:

1. Freezing water at night (when it is cooler than in the day time) behind the R/F and letting the ice melt during the day (when it is hotter than at night) to keep the R/F cool. These energy savings are due to the enthalpy of fusion of water. It also reduces the electricity demand on the city's electric grid during the peak usage times during the summer.  

2.  Letting the cold outdoor air into the R/F during the winter (or cold nights) to cool it for free without electricity.

 

7red.jpg

 

For more accurate vapor compression cycle calculations, please see the notes written by Mr.  Pei-feng Hsu, Ph.D. Professor & Department Head, Mechanical & Aerospace Engineering Department, Florida Inst. of Technology.

 

Let's assume that the indoor temperature is 750 Fahrenheit (F), the outdoor is 400 F, and we want the inside of the freezer to be - 50 F (it's presently at + 50 F). The indoor freezer uses electricity to transfer heat from its inside + 50 F to its outside 750 F (75 - 5  = 700 F difference). Similarly, the window freezer uses electricity to transfer heat from its inside + 50 F to its outside that is 400 F (40  - 5  = 350 F difference).  Obviously the window freezer has less work to do than the Indoor freezer.  Based on the calculations below, the energy savings rate is 75 %.  It's more than 50% because as the outdoor temperature drops, the window R/F's efficiency increases. 

 

Assumptions

To ensure an accurate comparison, it is assumed that both R/Fs (window and indoor) have exact same power, motor, compressor, cubic volume, and component efficiencies.  All external environmental variables are likewise assumed the same, such as the inside temperature of R/Fs, room temperature, type and amount of refrigerant, number of times the R/Fs' door is opened and closed, etc.

 

In column G and H of the following tables the energy (electricity) savings % for various cities are calculated.  It is assumed that columns G and H (energy savings %) are never greater than 95% because the window R/F always uses some electricity to run its electronic components. 

 

Definition of Columns in the table:   

 

B = Average Outdoor Temperature.  If the outdoor temperature is greater than 70 F, then they both consume the same amount of electricity unless the A/C is on. 

        

C = Average Indoor (Kitchen) temperature (70 F or higher in the summer without A/C).

D = Average temperature inside the R/F (set constant at 29 F).

 

Ti = C - D = Temperature difference between the Indoor R/F's evaporator and condenser.

Tw = B - D = Temperature difference between the Window R/F's evaporator and condenser.  Assuming that the outdoor heat exchanger is covered by a plastic shield to protect against snow, rain, wind or direct sunlight. 

 

G = Energy Savings % assuming that both R/Fs have the same COP (efficiency). 

G = (Ti - Tw) / Ti     This is a simple calculation.  Unlike Column H, it does not take into account (ignores or excludes) the higher efficiency of the window R/F when the outdoor temperature is colder. 

 

H = Energy Savings % taking into account the higher COP (efficiency) of the window R/F.

H = 1 - (Tw / Ti )2   This is more accurate than column G, because it includes the higher efficiency of the window R/F in colder climates.

 

Please see physical tests that supports this equation.

 

Month for NYC

B

C

D

Ti

Tw

G

H

January

31

70

29

41

2

95%

95%

February

34

70

29

41

5

88%

95%

March

42

70

29

41

13

68%

90%

April

53

70

29

41

24

41%

66%

May

63

70

29

41

34

17%

31%

June

72

72

29

43

43

0%

0%

July

77

77

29

48

48

0%

0%

August

76

76

29

47

47

0%

0%

September

68

70

29

41

39

5%

10%

October

58

70

29

41

29

29%

50%

November

48

70

29

41

19

54%

79%

December

37

70

29

41

8

80%

95%

Avg. Min. Energy (electricity) Savings %

 

 

 

 

 

40%

51%

 

Therefore, excluding summer, a window R/F in NYC on average consumes at least 40% less electricity (or 51% less, when the COP calculations are included) than an indoor R/F.  For example, in January and February the average outdoor temperature is 31 F and 34 F, which is very close to the inside temperature of the R/F (29 F).  During these cold months only a small amount of electricity is used to run the window R/F.  Obviously if you add the summer energy savings, the savings rate will be even higher. 

          

According to Energy Information Administration's 2001 official energy statistics table, refrigerators consumed 14% (11.3 billion kWh), freezers 5.2%, lighting 8.6% and TV 2.8%.   A 50% cut in the electricity consumed by the refrigerator (7%) is 81% (7 / 8.6) of the electricity consumption for lighting and more than double the amount used by TVs.  These calculations do not include summer energy savings.

  

To see other cities' energy/electricity savings %'s, click on one of the links below.  The calculations are identical to the above table, except that the average monthly temperatures are different.  

         

*Note:  The following calculated energy savings do not include the additional energy savings due to:

1.  freezing water at night (when it is cooler than in the day) behind the R/F and letting the ice melt during the day (when it is warmer than at night) to keep the R/F cool. This energy savings is due to the enthalpy of fusion of water. It also reduces the electricity demand on the city's electric grid during the peak usage on hot days in the summer. 

2.  Letting the cold outdoor air into the R/F during the winter (or cold nights) to cool it for free without electricity.

 

 

Anchorage        Beijing        Bombay        Buenos Aires        Chicago        Dallas        Denver        Gweru

 

Hamburg        Istanbul        Kabul        London        Los Angeles        Miami        Montreal        Moscow

 

New York City        Seoul City        Shanghai        Tehran        Tel Aviv        Tokyo        Toronto

 

    

www.windowrefrigerator.com

PATENT PENDING