Desert Fridge - cold storage

[Qasid]

Dear members,
Please could advice me regarding a project which I am working on which aims to provide a sustainable cold storage solution for farmers in rural Africa. (see overview here (http://dl.dropbox.com/u/10128779/Desert%20Fridge%20Project%20EWB%20research%20conference%202011%20v3%20%281%29.pdf))

Basically we have decided to build a 4.5x4.5x2m cold store (see CAD drawings here (http://dl.dropbox.com/u/10128779/DF%20including%20cut-through%20and%20airlock%20%2808_02_2011%29.pdf)), using a solar powered mechanical vapor compression refrigeration system with phase change material thermal storage to store 1550Kg of vegetables at 8-13oC (max ambient temperature 35oC).

Our initial calculations suggest a space heat gain of around 300w (using 200mm polyurethane foam insulated walls and roof and ground insulation using a hollow concrete block layer) and a further 750w required to remove field heat (maximum expected 300Kg of hot produce entering per day), giving an overall estimated nominal cooling load of around 1050w.

We urgently need to know the following:
Are our cooling loads realistic? - (I wanted to access the ASHRAE tables but couldn't find a free source - so we are currently depending on basic hand calcs)
Is there any off the shelf system we could use (or modify slightly) to meet our specifications? (there is a good supplier of LG products in Gambia...)
Thank you.

Kindly,
Qasid

[frostedflake]

you can try cool pack, it has a cold room calculator that might come in handy.

http://www.et.web.mek.dtu.dk/coolpack/UK/download.html

[arne22]

If you are buliding a "cold room" in a hot country, why should the heat energy radiated from the sun get the chanse of getting absorbed by "the cold room outher wall" at all. Why not remove the radiated heat energy from the sun by building a kind of two "layer wall" with free sirculation of air between ? (So that ehe radiated heat energy from the sun reaches the outher wall, but not the inner wall, that will be in the shaddow.)

Is there any water in the ground ? What will be the temperature of this water ? If that "double pot humid susystem" works for tomatos, why can it not also work in a bit bigger scale, for instanse at the outher surface of the inner wall, that will be in the shaddow, and colled a bit down with evaporating water.

There will still be an amount of heat in the "inner part" of "the cold room" that has to be pumped out using a heat pump, but this amount of energy will be smaller, if there is less heat energy comming into the room.

Just some ideas.

[arne22]

Some more ideas:

We had an interesting discussion about "solar powered aircondition systems" a short while a go. Absorption pumps, among other, were mentined.

http://www.refrigeration-engineer.com/forums/showthread.php?10999-solar-powered-air-conditioning

[Magoo]

Your cooling load requirements are too light, more like 3500watts cooling capacity.
Absorbtion coolers require a cheap heat source that could be acheived with solar water heating panels.

[Tradewinds]

Whatever you decide to use, make sure it is simple in design and has plenty of spare parts. No point in having a fancy fridge if you can't get parts for it.

Being 'Rural Africa/Gambia', do you have a power supply? Is this why you are going for solar panels?

I did some voluntary work in rural Tanzania and the problems we faced were:
Things don't get fixed. They just run until they break down.
No parts or money to fix equipment
No skills to fix equipment

Companies would provide pumps etc for water supplies but as soon as a bearing went or a motor burnt out, it would just sit there broken.


I like the double skinned wall idea mentioned above.