Garage heater kit for fridge?

[nicksanspam]

Frigidaire sells a $29 5303918301 laminated "garage heater kit," with

2 wires that wraps around the cold control of a fridge to allow it to work in to work in a cooler room, down to about 40 F.

It apparently heats the thermostat to fool the compressor into turning on, even if the fridge compartment is cool enough (eg 40 F in a 40 F room. Without this kit, the compressor does not run often enough to keep ice cream from melting.

How does this work, exactly? Is the heater always on? Is it just adding enough heat to the fridge compartment to make the compressor run long enough to keep the freezer compartment frozen? If so, why is it wrapped around the cold control, vs somewhere else in the fridge box?

I just bought an 18.2 CF Hotpoint fridge. I'd like to cover the outside with 2" foamboard and run it in a cool kitchen to reduce the energy used from 480 kWh/year to 240 or so, but Hotpoints don't come with these kits. Would leaving the light on all the time in the fridge compartment do the same thing? Is there a more energy-efficient way to do this? Warming the whole fridge box takes more power than just warming the thermostat.

Nick

[Edwin Pawlowski]

Warming the fridge box is dumb too, as the food will be getting warm along with the thermostat.

[Uncle Monster]

I found some information. I originally thought the heater was a crankcase heater for the compressor but something I read indicates that the heater is for adding heat to the "control compartment" to fool the thermostat into making the compressor run for a longer period of time. It also negates the Energy Star rating of the fridge. I do a lot of commercial refrigeration where pressure controls may be used in lieu of thermostats ie, better temperature control over a wider ambient but much more expensive. I could adapt a home refrigerator to run well in low ambient conditions by adding extra controls and sensors but the control compartment heater is simple and cheap. KISS

[8~{} Uncle Monster

[nicksanspam]

The thermostat would still control the fridge temp. The Hotpoint manual says don't run it in a room cooler than 60 F... 2" of extra foamboard would lower the fridge box conductance to about 2 Btu/h-F and the freezer conductance to about 1, so the freezer would need about 40 Btu/h of cooling at 0 F in a 40 F room, which might come from a 15 watt bulb in a 40 F fridge box that runs whenever the room is less than 60 F.

If the light uses 15 watts and the fridge uses 5, on average, that's 20x24h = 480 Wh/day, ie 175 kWh/year if the room were always 40 F or 26x24h = 624 Wh/day if the room were always 70 F. It would be nice to get this down to

100 Wh, like the Mt. Best chest freezer fridge modification.

With better controls, it might only need 5x23h = 120 Wh/day.

Nick

[ransley]

I would not jump into this without research, my home ac condensor has a heater for the compressor , there are low temp ratings for all compressor equipment I have. My low temp warning is about 50-55f for my sears energy star frige. I would worry about ruining the unit, leaving a light on will just waste energy like opening the door 24hrs a day.

[nicksanspam]

Is the heater always on? Maybe it turns off when the compressor runs? Why heat the control compartment instead of the box?

If the control is heated, the thermostat could still work, but the fridge box would be colder than without the heater, given the same thermostat setting.

Putting a bulb in the box would just increase the run time without affecting the box temp.

This could be more efficient with 2 fans and 2 thermostats and no heater.

Disabling the door heater and auto-defrost could also help.

Nick

[Edwin Pawlowski]

The thermostat unit heats just that tiny portion of the unit to make the freezer be colder. To warm the entire refrigerator box with a 40W bulb is wasteful and will warm the contents a bit. Saving energy at the expense of potential food deterioration or spoilage does not make sense.

[AZ Nomad]

If your fridge/freezer is such a POS that it is too stupid to run the compressor when the freezer is too warm, then you ought to either replace it or get a separate freezer.

[Uncle Monster]

You have to understand that the heater puts out very little heat. The heat is just enough to trick the thermostat, not to warm the refrigerator compartment. Home refrigerators are designed to operate within the typical ambient temperatures found in a living space. The much more expensive commercial refrigeration systems are designed to operate in places that would be quite uncomfortable for me and thee. It's all about cost and affordability. What I've seen of Sub-Zero refrigerators, a line of very expensive refrigerators, looks like commercial equipment to me, I couldn't afford one.

[8~{} Uncle Monster

[nicksanspam]

Or 24h(40F-10F)1Btu/h-F/3.41Btu/h/W/3COP = 70 Wh/day, ie 26 kWh/year worth $2.60 per year at 10 cents/kWh, with a 10 F freezer compartment and a 40 F fridge compartment in a 40 F room.

But the thermostat's in the fridge compartment, no? The fridge wants to be about 34 F...

Who mentioned 40 watts? A bulb in the box would not change the box temp.

Nick

[nicksanspam]

How would that accomplish the goal?

Nick

[Edwin Pawlowski]

If it does not change the box temperature, it is not going to make the thermostat do its thing. 40 watts burning adds heat and while it is mostly overcome by the operation of the compressor, it still has to raise the temperature a bit. How much depends on the differential of the thermostat.

[Wayne Boatwright]

On Sat 27 Sep 2008 01:46:53a, told us...

Maybe you should have bought the Frigidaire. Problem solved.

How cold do you plan on keeping the kitchen? Most refrigerators perform perfectly well down to around 60°F. Unless you're always dressed for winter, anything lower could hardly be considered comfortable. I must say, a refrigerator encased in 2" foamboard sounds really "attractive". Not! Why on earth would you really want to do this? I don't think you'll be saving a thing and you need a different project. :-)

[Uncle Monster]

I haven't see a mechanical drawing or pictures of your particular fridge but I'm guessing that there is a housing in the top of the refrigerator compartment that contains a thermostat, defrost timer and perhaps light bulb. The housing has openings that allow the air to circulate around the thermostat. The slight heat produced by the heater is enough to raise the temperature around the thermostat to trick it into running the compressor for a longer period of time. It's not necessary to increase the temperature of the whole refrigerated box, just the temperature around the thermostat.

[8~{} Uncle Monster

[nicksanspam]

The box temp change would be minimal.

Who mentioned 40 watts?

Nick

[nicksanspam]

I kept it 36 F one year.

Nick

[nicksanspam]

That doesn't make sense to me...

Nick

[Wayne Boatwright]

On Sat 27 Sep 2008 05:18:08p, told us...

That's beyond my comprehension.

At that temperature, you don't even need a refrigerator, just a freezer.

[Edwin Pawlowski]

Typical appliance bulb wattage

[larry]

It's like the timer with a 10K resistor clipped under a regular wall thermostat to do an over-night "setback". Thermostat thinks it's getting warmer and turns off the furnace when the room isn't warmer.

Frig controls are wacky these days, you chill the freezer, themostat the coldbox, and use a fan and vent to regulate the freezer temp.

If the differential is that small, why not use a few "frig" chips (Peltier devices) to do the job in place of the compressor? A single one sq inch chip will cool your six pack in your 12v car cooler in the summer. Or an old Bernz with the Ammonia absorption cooler. I have a 1950's

12v/110v portable that will still develop a 60 degree differential and bust 2 six packs of soda in the basement during the winter ;-)

-- larry / dallas