Do you ever worry what would happen to the contents of your medical fridge if the power went out? Do you have a back-up protection/alarm/annunciation system in place? A common generator for refrigerator is abattery backup generator (aka UPS). However do you know the best size of generator you need for your refrigerator?
To determine the generator size you need for your refrigerator you need to determine the power draw over a reasonable time span, assuming the ambient room temperature is consistent year-round. This can be measured, or the manufacturer can be consulted for the average watts per hour or kilowatts per day.
Once you know the power requirement of the refrigerator and how long a power outage you plan to sustain, a system size can be determined.
Key Things You Need to Know about Refridgerators and Electricity
Refrigerators are not complicated. Refrigerator compressors run on electricity. Electricity is measured in amps or watts which is delivered over time. Power is measured in amp-hours or watt-hours.
The typical 16 cubic foot frost free fridge uses 6 amps per hour of electricity at a voltage of 120 Volts on an average day; equaling 144 amp-hours. The actual amount of power measured in watts per day is usually found by contacting the manufacturer, since it is really the amount of energy loss primarily due to the quality of the insulating materials, and design.
The most common type of fridge is a refrigerant-compressor. A refrigerant, like Freon, is circulated in tubing to remove heat from the interior, cools that location and then is liquefied by the compressor, which heats it and then is circulated in tubing exposed to room temperature. The cooled refrigerant is decompressed, which cools it below room temperature, and then is returned to the internal coils.
The temperature is controlled by a thermostat which controls how often the compressor runs. A typical compressor runs approximately three times an hour for a normal heat load.
Powering a Refrigerator from Stored Energy:
A battery generator consumes little energy, has no moving parts needing lubrication, makes little noise, and doesn’t ‘wear out’. The most important part is the battery. Lead-acid batteries are best for stationary situations, since they cost much less than lightweight lithium, nickel, or cadmium batteries. Battery’s power is measured in ‘amp-hours’, which denotes how much power can be dispensed over a useful time period. It should be noted that a battery rated at 100 amp-hours at 12 volts will produce a nominal 10 amp-hours at 120 volts, less the discharge rate efficiency loss (related to time), less the power conversion efficiency loss from DC to AC. The battery’s capacity must exceed the power demand the refrigerator will require for the duration of the power outage. Think of it as a container.
An electronic power converter must be sized for current larger than the ampere draw the compressor will need to start up. This is also called the ‘Locked Rotor Amp’ rating. This may be more than six times the running amp draw. The electronic power converter converts low voltage battery power to 120 volt alternating current. Another essential part is the transfer switch. This will either direct power from the battery to the power converter and on to the refrigerator, or power from the utility to both the refrigerator and the battery recharger.