As mentioned previously, according to the 2006 DOE energy end-use study, 8% of a residential building‟s total energy consumption was used for refrigeration purposes. This test home operates a 1998 Whirlpool (Maytag) MSD2756AEW side by side, 2-door,
26.5 ft3, refrigerator-freezer combination machine. The power consumption of this home‟s refrigerator was listed in the power consumption measurements shown in Table 7.8 as 0.117 kWh/Hr. This was determined from power measurements made over a 24 hour period (March 14th 2011) which showed the refrigerator consumed a total of 2.81 kWh of electricity. Since the refrigerator operates 24 hours a day for the entire year (8,760 hours), the annual total energy consumption was determined to be 1,024.92 kWh which would cost the home owner about $92.24 each year. The validity of this
estimation will be discussed momentarily. The maximum amperage was listed as 7.2 Amps and the voltage was listed as 115 Volts on the interior of the refrigerator door. Multiplying these two values gives a possible max power usage of 828 Watts, but during normal operation power readings did not reach this maximum value. When in standard operation, this refrigerator cycles between a “cooling” and “dormant” phase. During the cooling phase the refrigerator is removing heat from inside the refrigeration compartment and the power fluctuates between 185 Watts and 160 Watts. The length of the cooling phase depends on factors such was how much warm air entered the cooling space in the previous few minutes. The cooling cycle ranged anywhere from 35 to 10 minutes over the 24 hours of observation. The refrigerator dormant phase showed little power
fluctuation drawing a constant 2 Watts of power between cooling cycles. The refrigerator was also consuming different amounts of power to perform tasks such as indoor lighting when the doors were open and ice/water dispensing through the door. The average power being drawn by the refrigerator over the 24 hours of observation was determined to be 112 Watts based on hourly power measurements. The average measured hourly power being drawn by the refrigerator over the 24 hour measurement period is shown in Figure 7.1 and the total power consumption (kWh) of the refrigerator for that same time period is shown in Figure 7.2. Figure 7.1 shows the fluctuation of power during each hourly measurement of the refrigerator. The data points in this figure are the average instantaneous powers being drawn over the time interval (1 hour). The figure shows a large increase in the power requirement immediately following high use times such as 8:00am – 10:00am (breakfast) and 7:00pn – 9:00pm (dinner). According to Figure 7.2
despite these “short-lived” power increases, the rate of total energy consumption does not vary much over the course of the day.
Refrigerator Hourly Average Power
0 50 100 150 200 250 0 5 10 15 20 25 Time of Day A v e ra g e Po w e r (W a tt)
Refrigerator Average Power
Figure 7.1: Average Measured Hourly 26.5 ft3 Refrigerator Power Usage
Refrigerator Power Consumption
0.00 0.50 1.00 1.50 2.00 2.50 3.00 0 5 10 15 20 25 Time of Day k W h E le c tr ic it y C o n s u m e d Total kWh Consumed
The total annual power consumption value (estimated in Table 7.8 as 1,024.92 kWh a year) is a low estimation of the annual refrigerator energy use. This is because the power requirements of a refrigerator are not constant throughout a typical year. According to the “Geoexchange Project” the energy consumption of a residential refrigerator is much greater in the warm summer months than in the cold and moderate winter, spring, and fall months because the warm air that infiltrates the refrigeration space is warmer in the summer months [33]. This was determined during a similar measurement procedure using a simple power meter to determine the energy savings associated with the installation of a new, energy efficient refrigerator at the Geoexchange project site. The results of this study are shown below in Figure 7.3. Ignoring the
difference between the new and old refrigerators, the trend shows a large increase in power consumption (kWh) from June to August. The exact data values were not given for this figure, but just by reading the plot, the power consumption in July is about 55% higher than the power consumption in March. March 14th is when the power
measurements were made for this test house refrigerator. It is difficult to quantifiably determine the expected increase in power consumption of the test home‟s refrigerator that would occur during the summer time, but the trend is clear, the annual refrigerator power consumption will be much greater than the estimated value seen in the above tables.
Figure 7.3: Geoexchange Graph of Power Consumption (kWh) Old and New Refrigerator [33]
Using an online calculator provided by EnergyStar®, the annual power consumption of a 1998, side-by-side, 25+ cubic foot, comparable refrigerator was estimated to be 1,252 kWh. This is a 227.08 kWh increase from the estimation made from the March 14th measurements. This increase seems very reasonable following the trend seen in the Geoexchange Project results figure. The EnergyStar® online calculator also provides a comparison for a new, energy efficient refrigerator of comparable size. According to the calculator, a comparable EnergyStar® refrigerator would only consume around 600 kWh a year, which is an annual reduction of 652 kWh (47.9%) to the current model. This would save the home owner around $59 a year (annual payment drops from $112 to $54) in electricity expenditures. The cost for an EnergyStar® refrigerator of comparable size and features at local distributors ranges from $700 – $2,000. This would give a simple payback period based on energy savings alone from 11 – 33 years.