Temp differences in well insulated fridge

[gauvins]

Wanted to report that I've measured 15c (30F) differences in temperature in my small (a tad over 60L/2cf) and super insulated box. The bottom is close to freezing while the top is barely chilly. I was expecting differences, but certainly not so large. (Temperature monitored with Garmin's Tempe sensor and ambiTemp app; I've moved the sensor inside the fridge)

Cold air drops at the bottom, warmer rises, there's a large thermal mass (water, milk, juice, beer) such that the compressor runs just a few minutes per day. Air at the top gets progressively warmer because the lid has less insulation.

We've ordered a fridge fan.

[GordMay]

Originally Posted by gauvins

Wanted to report that I've measured 15c (30F) differences in temperature in my small (a tad over 60L/2cf) and super insulated box...
... We've ordered a fridge fan.

Good plan!

[john61ct]

Is that within 24 hours of adding warm contents?

Air spaces filled with thermal mass like warer bottles?

In use being opened, or while all closed up?

Sure your envelope is uniformly tight?

That's a big delta. . .

[gauvins]

Well... I am currently alone and open the fridge only a few times a day. 90%+ has been there for more than a week. There's probably 25L of liquid, with 2L added in the mornings. So, essentially static content.

The temperature difference was initially low, but has increased over time.

As I said, it is a small (2cf/60L) box that I placed inside a much larger cavity (9cf?). I've poured polyurethane to fill it, which has added more than 2 feet under the base of my smaller box, and a good 6 inches on the sides.

The evaporator sits on one side, the thermostat on the middle of the adjacent wall, near the bottom per the manufacturer's recommendations

So what happens is that the cold air at the bottom stays cold because the insulation is very high, while near the top, insulation is "normal" (say, 4 inches), so the air gets progressively warmer.

Will update, but several factors will make it difficult to assess the impact of the fan, as I'll get it when wife and kids join me. Content will rotate faster, the fridge will by opened more often and ambient temperature will be higher.

Still. I was indeed surprised by the differential. Surprised as well by the relative absence of material about this phenomenon. Most entries wrt fridge fans talk about muffin fans to assist the compressor. Just a few address the issue of air layers.

My guess is that if insulation is the same on all sides, differences will be less. If, for exemple, bottom insulation were poor, and top insulation were excellent, differences would probably be minimal