Equipment List

• 2 HOBO XT Temperature Data Loggers
• 1 HOBO to Serial Port Cable
• 1 Refrigerator
• Onset systems Boxcar 4.0 Software
• Microsoft Excel
• Enough jugs to fill a refrigerator

Steps

With EMPTY refrigerator:

1. Activate temperature data loggers with Boxcar software to log temperature every 5 minutes.
2. Tape (1) temperature data logger thermistor to out-flowing compressor coil, and place (1) temperature data logger on first shelf of refrigerator door.
   
3. Leave temperature data loggers in place for at least 48 hours.
4. Download data from temperature data loggers with Boxcar software and import to Excel for data analysis.
   
   
5. FILL refrigerator with water filled gallon jugs (the refrigerator used in this study held 23 gallons of water) and repeat steps 1-4.

Notes

We found placing a HOBO XT thermistor directly on the compressor coils was the best method for determining when the compressor was active. The coils act to bleed heat rapidly from the refrigeration loop. When the compressor turns on, the heat in the coils rises suddenly and rapidly from room temperature (70º F) to approximately 100º F and is equally fast in dropping when the compressor turns off.

We tried other less successful methods before developing our latest methodology, namely using HOBO vibration sensors, AC field sensors, and temperature sensors on the compressor itself.

Our use of water in the refrigerator presupposes thermal mass as one of the leading contributors to improved efficiency. Water has a markedly higher thermal capacity than air. The use of water in the experiment also approximates what the true contents of a refrigerator might be since the nature of "perishability" is tied to the water content of food.