But that makes the room colder at night. How do we keep the fridge a constant 40 F and the freezer frozen in a 40 F room?
If the freezer stays 0 F in a 60 F room while the 40 F fridge box is gaining Q Btu/h from the room, cooling the room to 50 will reduce the fridge gain to Q/2, so the compressor will run half the time.
But the required freezer run time will only go down by 50/60, so we need to add enough heat to the fridge box (vs the thermostat box) to raise the run time back up to 50/60 of the 60 F room run time, no?
The fridge box won't absorb any heat at all from a 40 F room, but the freezer still needs 40/60 of the 60 F room run time to stay 0 F.
It's easy to do with the kitchen off the back of my house. With 2' stone walls (C ~ 50 Btu/F-ft^2) inside R10 insulation and RC = 500 hours, the kitchen temp changes slowly.
Starting at 36 F, it would cool to 30+(36-30)e^-(24h/500h) = 35.7 over an average 30 F January day. Leaving the kitchen door to the rest of the house open for a few minutes a day makes up for that cooling.
Right, but then spring happens. Maybe the freezer needs a thermostat that turns on a 15 watt bulb in the fridge box when the freezer temp rises to 10 F. Where can I find one of those?
The way the closed loop control works on modern frig's is working against you. You need a little redesign.
Given:
the freezer, goal=0F, always needs cool in your ambient temp range, 40F to 80?F.
the coldbox (frig - i hate these terms), goal=36F, needs cool on hot days and maybe none on cold days.
Plan:
freezer, meet the demand first, put the thermostat for the freezer IN THE FREEZER, where the coils are to begin with. Closed the loop on the freezer, it will take care of itself.
Coldbox. Block the existing air path between the freezer and the coldbox below. Control that airflow with a moving vane and and fan connected to a thermostat in the coldbox to cool the coldbox with cold air from the freezer to the target temp 40F.
Cheap way of doing the coldbox control is a bimetalic strip in the coldbox that pushes the vane open as the temperature exceeds 40F. A small microswitch could switch on the fan as long as it detects the vane is open.
Just about everything you need is already in the frig. Take up the baseplate in the freezer, you will see the cooling coils, the air path, with vane, to the coldbox, and a fan near the back, that circulates cool in the freezer and coldbox. Plus a big heater to thaw the coils. There is a schematic in an envelop near the compressor or defrost tray.
I don't know how this will affect defrost cycle.
second thought, close off the kitchen and roll the frig to the living room... You can't be married... ;-)
-- larry/dallas
btw, the resistor/timer will work if you invert the function, resistor on for less heating, resistor off for less cooling.
It's all about cost. The commercial refrigeration systems I install/build/repair usually work well regardless of the ambient temperature. I'm about to move two walk in coolers and reinstall them where the condensing units will be in a back room rather than two stories up on a roof. The units will work without a problem because of their more sophisticated control system than a home refrigerator. The control systems use not only thermostats but pressure and fan controls to maintain the temperature. I've worked on Sub-Zero brand refrigerators made for home use that were built like commercial coolers with semi-hermetic compressors and commercial controls but GOLLY! those damn things are expensive. They will work in just about any ambient temperature but the cost is out of my range. I could always take a standard home refrigerator and modify it for a lot less money.
Being able to do it is not beyond my comprehension. Why anyone would really want to do it is beyond my comprehension. I want every room in my house to be at a comfortable temperature at all times. I would find it inconvenient and uncomfortable to have to wait for it to warm up enough for the kitchen to be useful.
You are not saving siginficant energy, since to be able to use the kitchen you're robbing other parts of the house of its heat which has to be compensated for each time you do it.
Well, yes, spring happens. As to where to find what you're looking for, I have no idea.
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