Originally Posted by tomkatb
I am curious about adding insulation around a residential fridge.
I am pretty sure they are designed to be free standing. Requiring an air space surrounding the box(installation instructions). Or, they get hot and require more energy.
Yes, battery and solar!!! Though for a residential fridge, you might pay enough for the extra battery and solar to cover a 12V Danfoss/Secor compressor fridge. I don't know how large the 12V fridges come. Mine is 9.1 cu ft of which 2.5 is in the freezer. It takes less than 45 AH in 24 hours with powerful CA sun beating down on the back and top and temp 90-96 inside during day time. BUT, I have insulated it heavily with 2" Poly iso board (R13.1). The one I have does not have coils up the back, so I was able to insulate the back as well.
As for heat flow, considering heat to flow from hot to cold, the problem is keeping heat out of the fridge wherever possible. The sides of a fridge have maybe 2" of poly iso or similar insulation in them. If you could double that to 4", the heat gain would be greatly reduced and the running time reduced.
The residential fridge is no different. But, I think you are looking at a residential fridge with coils running up the back. This is very common. If you push this type of fridge into a cavity between cupboards in a kitchen, those coils will be starved of cooling air unless there is a gap under the fridge and/or along the sides of the fridge .... and on top of the fridge. In that case, YES, one must leave room for air to flow into the space behind the fridge and upward and escape someplace, probably forward over the top of the fridge. This is very inefficient since a natural chimney effect on the back is very limited and the coils will run hot. And, some warm air from the coils is flowing right over the top surface of the fridge where some of it flows through the insulation into the refrigerator. Air flowing along the sides similarly "convection warms" the side walls of the fridge albeit with ambient air. In summary, in this situation you have to live with inefficiency from 1) lack of cooling air on the condenser coils on the back, and 2) ambient air flowing along the sides of the fridge and hot air coming forward over the top.
The instructions you are thinking of surely are there to address this situation. I'd guess it's not common, but has to be covered.
If a residential fridge is truly free-standing, i.e., no air flow encumbrances around it, then adding insulation to the sides and top (and door if you can stand it) will reduce energy usage.
Earlier I specifically mentioned ensuring plenty of air flow over the coils. If I had the above situation I'd put muffin fans somewhere to force room air upward over the coils. This would worsen the "warming" of the fridge by convection on the walls, but at least the fridge would probably cycle off once in a while.
The ideal situation for any fridge, 12V RV or residential is to have unencumbered air flow over the coils and increased insulation anywhere that it will not limit the coil air flow
. If the coils are on the back, and have their own air supply like RV propane and some RV 12V fridges do, then insulation on the top and sides will reduce heat flow into the fridge. Here I'm thinking of the typical outside air inlet near the bottom of the fridge and a chimney effect up the back leading to a roof vent. In this situation one can add insulation to the sides and top of the fridge to limit heat flow into the fridge without restricting air flow upward over the coils in the back.
If I had a rear-coil residential fridge in an RV and it did not have ample air flow from an inlet near the bottom rear and a vent at the top, I would install those.
My own 12V fridge has the condenser coils under the fridge and a fan circulates RV interior air over the coils. As such I was able to heavily insulate the sides, back, and top of the fridge. Image below. The result is just over 40 AH on a 90F day, with massive direct sun on the rear wall behind the fridge, and 60F lows at night. The RV interior runs 90-96F. The manufacturer suggested about 60 AH in a 70F ambient.
The downside of this design is that the fridge dumps warm air into the living space instead of outdoors (i.e., from coils up the back). It's also a bit noisier than one with the compressor in the lower rear. Though the fans on the coils of my propane fridge were quite audible.
The compressor on my 12V fridge came set at 3500 RPM. I'm running it at 2000 RPM even when it's in the 90's ...... though it rarely cycles off during the warm hours. That's fine though since the compressor is considerably more efficient running at 2000 RPM. I'm thinking of adding a time clock that will switch the compressor to 2500 RPM during the day and 2000 RPM at night.
I apologize for the sideways photos .......