PDA

View Full Version : Small Refrigeration Efficiency







Inalex
08-02-2008, 01:00 PM
I have realised over the course of a recent project that I know next to nothing... so

I am looking for a decent text on the design of the workings of small scale (domestic or small commercial) cabinet coolers and freezers with a strong lean towards energy efficiency. I have the ASHRAE handbooks but they are geared towards the larger end of things. I would like a discussion of the effects of different selection options on energy use.

Any ideas anyone?

The MG Pony
08-02-2008, 07:02 PM
start with insulation and leakage free box design that there will net a good degree of savings of energy then once a box size is selected and insulation figures out figure out heat ingres and cooling demand by the load you'll put into it.

Inalex
09-02-2008, 05:37 PM
I have done the standard calculations, and I have figures for compressors, valves etc. I can, and have, designed very well sealed and insulated boxes. I can run all the standard load calculations; I use the same calculations and tables in the ASHRAE Handbooks.

What I really want to know is what choices I should be making for efficiency, and the tradeoffs that must be made, component lifespan versus energy efficient running. For instance, compressor sizing, whatever calculations are used there is a wide margin for choosing different sizes and specifications of compressor for a given box size. How much energy is saved with hot gas defrost in a small box? How about variable speed compressors allowing a faster pull down and cycling back for efficient running? Air blown over convection driven? Capillery over valve? I even considered two compressors, a smaller one for continuous running and a larger one for pull down, both set up to run at peak efficiency; this seems a sensible idea but in practice it's probably useless, it must have been tried and reported on?

Someone must have written something on the design of the efficient box refrigeration and freezing system?

The MG Pony
09-02-2008, 06:29 PM
Its all a trade of of cost Vs efficiency sadely people want cheap now rather then cheap running cost.

Technicaly a valve is superior over cap tubing and utilizes the evap more theroughly.

Convection is better as no fan but size to get good low head pressur gets big and pricy and requires more maintanance to keep it clean,

a modulated compressor will offer best part load and pull down ability but is costly,

Hot gas is ideal as it does not consume primary energy and is fast but requires an additional solenoid valve and tempriture sensor for termination.

Last time I toyed with the idea of making a super efficient fridge as you are the cost came out around 2,000 Canadian dollars and then some, can it be don? Certainly will it ever sell? Verry unlikely aside from a verry small interest group like remote places of living or a remote comercialy opperated get away that is self powered.

Again general public see as far as their nose in fog! Why spend x,xxx now and save xxx,xxx. later? they want the cheapest thing now sade but thats what I found when I did some local market research.

star882
26-02-2008, 11:13 PM
One of the best ways to save energy is... design it so the door is on top. Doesn't take very much to engineer and very effective.
If the design temperature is above freezing, defrost by just running the evaporator fan.

Then start thinking about the more advanced stuff like inverter drive compressors and such. Interestingly enough, an inverter for a small compressor is only $25 or so of parts.