Theoretical opinion not science -
- You have a half full fridge - It makes sense to only want to cool half the volume regardless of what is in it or not in it.
- The energy equation is a mass equation - i.e. 3 kilos of chicken and 3 kilos of "air" probably take similar energy to cool - you just can't fit 3 kilos of (uncompressed) air in your box. Opening an empty reefer and spilling some cold air is a big deal because whatever volume it is you are immediately replacing 2 DEGC air with 28DEGC air and it has to be cooled. Chicken is a good heat sink. In this case the chicken warms slowly so the same volume full of chicken (full reefer volume) is not a big deal when you open the door because you don't transfer much heat from the chicken during the relatively short time the door is open. But imagine if every time you opened the reefer you took out 1 kilo of cold chicken and put in 1 kilo of warm chicken. Not good.
- The warm air that enters doesn't care where it gets it's energy deficiency from - it will take it from the evaporator coils or from the Chicken as it seeks equilibrium with the rest of the reefer contents - i.e. ice will melt and the chicken will start to thaw.
- Heat rises - we know that so a top loading reefer makes sense because less cool air volume is spilled when the lid is opened.
- Heat transfer takes place on the surfaces. Block ice is better than cube is better than crushed ice when trying to keep ice from melting. When trying to cool a fruity boat drink the opposite is true. Therefore a whole chicken is better than chicken parts
is better than diced chicken when trying to keep it cold. And - OK - 24 oz beers are better than 16 oz beers are better than 8 oz beers.
- And finally what transfers the energy from the coils to the chicken? Right - the air.
So adding all this theory up means - We don't want an empty or half empty reefer. Air spills and needs to be cooled. Air is what cools the items so the items need circulation room when cooling but once cool if we could reduce their surface area they would stay cold longer. It all seems to make sense that we need to reduce the interior
volume of the reefer.
- Construction of the box makes a difference - how is the evaporator coil arrayed? If it's along one wall of the box you do not want to isolate that wall from the groceries or the air.
Assume a top loader with the evaporator coils on the back wall. You want to reduce the volume starting from the front wall. I would reduce the volume with some sort of heat sink like an aluminum
block. It would not lose much heat when the door is open and would facilitate cooling the air quickly when the lid is closed.
If the coils are in the bottom of the box I think the solution is tougher. In this case I think I would still use the heat sink but It would have to be stood off the floor and sides of the box so the air can circulate around the heat sink from the coils to the top of the box.
Look at the freezer
section of the grocery store. Most of the items are in hanging baskets so the air can circulate.
An finally the door of the reefer needs to be as small as possible. Remember ice cream trucks? They had a big door - for loading - but built into the big door was a small door that the guy used to get the ice cream from. And it goes without saying the seals
on the door must be as good as you can get.