freezer efficiency vs ambient temp

[mab]

Hi all,

In theory, the amount of heat that leaks into the freezer decreases with ambient temp and so the run time of the freezer should drop as ambient temp drops.

but I'm sure I read somewhere (here?) that the efficiency of a freezer decreases if the ambient temp falls too far below that which the freezer is designed for. So at some temperature it'll start using more power again? (I tried searching but came up with nada). Is this true or did I imagine it?

My standard chest freezer (which does indeed seem to run for less time as the temp drops) is out in the shed, so I was wondering what the optimum shed temp might be for minimum power consumption. I'm about 12 miles from the coast here in the UK (and about 800ft up), so I don't expect the ambient temp to go more than a few degrees below freezing for any length of time.

basically I'm wondering if I should leave the shed open, or close it up if the weather's going to be cold?

mab

[mab]

having done some searching in the wider world of the WWW, I fine that they are indeed designed for indoor temps and mine with an 'N' class is designed for temps > +16°C, though it seems perfectly happy at + 3°C - and doesn't warm up nearly as fast as it would indoors.

from what I've found the problem with low ambient temp is condensation in the insulation.

[hiker]

i keep my frezzer in a unheated   enteryway...hardly ever comes on when its cold..if ever...........

[Frank S]

i keep my frezzer in a unheated   enteryway...hardly ever comes on when its cold..if ever...........

Sorry Hiker but I've got to do this; The first salesman to sell a freezer to an Eskimo explained it like this your food will be easier to thaw because the freezer will hold  a more consistent temp, remember how hard it is to thaw a fish that is frozen to -50 I think he sold 3 his first day

[mab]

 

well as long as i don't use more power than with the freezer indoors and I don't break the freezer i'm happy.

thx

m

[DamonHD]

In the past some refrigerants would get too viscous at low temperatures and damage the compressor: I'm told that that is generally not a problem any more.

Rgds

Damon

[bart]

   I do mainly commercial HVAC and have been lucky enough to have been able to stay away from the refrigeration side of things, to many after hour service calls.
But the principals involved are the same. Basically cooling/freezing is based on having enough refrigerant pressure to force it through the metering device. When out door temps. get low, so does the refrigerant pressure and thus less cooling/freezing.
With lower pressures, compressor draws less amps and runs longer.
   There are some other bad things that can happen, but if I was to worried about them I would not have my freezer in a unheated garage.
   

[Volvo farmer]

In the past some refrigerants would get too viscous at low temperatures and damage the compressor: I'm told that that is generally not a problem any more.

My understanding is that the oil in the bottom of the compressor is the problem, not the refrigerant itself.  If the oil is too thick due to low temperatures the compressor might draw too much current and trip the internal overload or burn out the windings. This is all hearsay and gossip and word of mouth, but I have heard that older R12 systems had larger, more robust compressors than what is on the market today and that older freezers actually were less prone to having problems being operated in unheated spaces. 

[mab]

well I guess anything old tends to be more robust than it's modern equivalent. 

This 'old' freezer uses R134a whatever that is. I'm not to worried now; if it does get too cold it'll trip the inverters overload before it burns out.

As a separate (but related) question: I don't suppose anyone knows the specific heat capacity of magnetite? I'm struggling to google a definitive answer; the best I've got is 0.935 J/°Cg.

The reason I ask is that I've lined the inside walls of the freezer with storage-heater bricks for thermal mass - I'm sure they're better that ice (2.1 J/°Cg) for thermal mass vs volume, but I'd like to be sure.

thx

m