[mikem]

I have a refrigerator in an unheated building. Sometimes, the
temperature in the building drops to 15 deg F. To keep liquids inside
the fridge from freezing, I run a 5W lamp inside the fridge, which adds
just enough heat inside to keep the temp above 35 deg F provided the
outside temp is above 20 deg F.

However, In anticipation of even lower temps, I would like to increase
the wattage of the lamp, and put a thermostat in series with the lamp.

Anybody have a source of a thermostat which operates at 33 to 35 deg F?
Ideally, it should switch 1A. The hysteresis should be ~2 deg F.

MikeM

 

[John Fields]

I have a refrigerator in an unheated building. Sometimes, the
temperature in the building drops to 15 deg F. To keep liquids inside
the fridge from freezing, I run a 5W lamp inside the fridge, which adds
just enough heat inside to keep the temp above 35 deg F provided the
outside temp is above 20 deg F.

However, In anticipation of even lower temps, I would like to increase
the wattage of the lamp, and put a thermostat in series with the lamp.

Anybody have a source of a thermostat which operates at 33 to 35 deg F?
Ideally, it should switch 1A. The hysteresis should be ~2 deg F.

 

[John Popelish]

I have a refrigerator in an unheated building. Sometimes, the
temperature in the building drops to 15 deg F. To keep liquids inside
the fridge from freezing, I run a 5W lamp inside the fridge, which adds
just enough heat inside to keep the temp above 35 deg F provided the
outside temp is above 20 deg F.

However, In anticipation of even lower temps, I would like to increase
the wattage of the lamp, and put a thermostat in series with the lamp.

Anybody have a source of a thermostat which operates at 33 to 35 deg F?
Ideally, it should switch 1A. The hysteresis should be ~2 deg F.

MikeM

These are a bit pricey, but capable:
http://www.westcoastplastics.com/pehtmlpages/fenwal_thermoswitch.html

 

[Fred Bloggs]

I have a refrigerator in an unheated building. Sometimes, the
temperature in the building drops to 15 deg F. To keep liquids inside
the fridge from freezing, I run a 5W lamp inside the fridge, which adds
just enough heat inside to keep the temp above 35 deg F provided the
outside temp is above 20 deg F.

However, In anticipation of even lower temps, I would like to increase
the wattage of the lamp, and put a thermostat in series with the lamp.

Anybody have a source of a thermostat which operates at 33 to 35 deg F?
Ideally, it should switch 1A. The hysteresis should be ~2 deg F.

MikeM

Increase the lamp to 10-15W and wire in parallel with existing
thermostat contacts to compressor. You can add a series switch labeled
"Cold Weather" if you want to get fancy. Unfortunately, conversion to
cold weather operation is usually not this simple, requiring an outside
thermostatically controlled receiver and condenser bypass to effectively
reduce the heat exchanger area and thereby increase sealed system
operating pressures so that liquid refrigerant is prevented from
entering compressor and destroying the valves. Proceed at your own risk.

 

[mikem]

Increase the lamp to 10-15W and wire in parallel with existing
thermostat contacts to compressor.

Good idea. However, I had it in my mind that I wanted a "deadband"
region where neither the heater, nor the compressor would run.
i.e., the heater is <35 deg F, and the compressor only runs
if the temperature in the box is >37 deg F.

You can add a series switch labeled
"Cold Weather" if you want to get fancy.

Or just unscrew the lamp...

Unfortunately, conversion to
cold weather operation is usually not this simple, requiring an outside
thermostatically controlled receiver and condenser bypass to effectively
reduce the heat exchanger area and thereby increase sealed system
operating pressures so that liquid refrigerant is prevented from
entering compressor and destroying the valves. Proceed at your own risk.

Are you saying that the compressor should never be started if the
condensor coils are colder than ~30 deg F? If so, then my "deadband"
scheme should prevent the compressor ever coming on between Nov and
April...

MikeM

 

[Fred Bloggs]

Good idea.

Okay- General Motors, the inventor of modern
mechanical refrigeration, will be happy with your approval of a
technique they used for 50 years.

However, I had it in my mind that I wanted a "deadband" region where
neither the heater, nor the compressor would run. i.e., the heater is
<35 deg F, and the compressor only runs if the temperature in the box
is >37 deg F.

That is an unnecessary add-on, the energy loss due to the bulb is
negligible.

Or just unscrew the lamp...


Are you saying that the compressor should never be started if the
condensor coils are colder than ~30 deg F?

Run it at your own risk- a lot of things can go wrong- it is impossible
to say.

If so, then my "deadband" scheme should prevent the compressor ever
coming on between Nov and April...

-and you will have no freezer either. The outside temperature range is
too large to expect the bulbs not to raise the interior temperature
above 37oF most of the time. The cycle time will depend upon the
insulation heat loss of the box as well as the thermal mass of the
material in the box.

 

[mikem]

mikem wrote:

Run it at your own risk- a lot of things can go wrong- it is impossible
to say.



-and you will have no freezer either.

I dont use the freezer. The fridge is used to store drinking water, soft
drinks, beer, distilled water for batteries and a few cleaning supplies
(the latter two just to keep them from freezing).


The outside temperature range is

too large to expect the bulbs not to raise the interior temperature
above 37oF most of the time. The cycle time will depend upon the
insulation heat loss of the box as well as the thermal mass of the
material in the box.

Thanks for you input...

MikeM