Air Conditioner or Refrigerator Start-up and Transient Conditions

[Aero55]

Hello,
I am looking for some information on the start-up and transient condtions of an air conditioning or refrigeration cycle. I know how to calculate the steady state operation of the refrigeration cycle. However, I am unaware on what happens when the AC cycle is started and how long it would take to reach steady-state conditions. Would any of you be able to recommend a good source text or some other source, person, etc. that would be able to point me in the correct direction?

I am interested in using a propane refrigerant cycle, but it will probably be under varying conditions, so this is a critical aspect that I need to know more about.
Thanks in advance

 

[quark]

Just calculate the heat to be removed from the space or material from their initial temperature to the final temperature required(and add steady state heat rate to this). If you already have a capacity in your mind then time requirement to acheive a steady state condition can easily be calculated.

Principles of Refrigeration and Air Conditioning by Roy J Dossat is a good book. Check the ASHRAE handbooks.

PS: I think you should be a bit specific.

Regards,

 

[MintJulep]

Sorry Quark. It's not so easy. System capacity is a function of load, and the load is variying.

Transient analysis of refrigeration systems is a pita.

 

[sterl]

Assuming for a moment that: you have a large enough motor to drive your compressor at full capacity, all anticipated conditions; and that the condenser capacity is such that the change in condensing pressure is not going to be huge as your mass flwo drops, the capacity of the system model at a breadth of pressure rations is failry easy to establish from the compressor modelling mathematics. See COPELAND for data on recips or scrolls. Screws a little mmore complex, but still pretty easy...As someone indicated, however: The real issue is the heat capacitance of what you are cooling...and if its air, its actually much more complicated than the distributed temperature change of the identifiable masses of your confinement.

In effect: If you can get an idea of the real thermal capacitance of the confines you are trying to cool, you can convert it to a tank of vapor at initial (saturation) temperature, then calaculate how fast your compressor could pump it to a second tank at a constant pressure, the pressure of the first tank decaying with respect to time...That's a transfer problem, which for small tanks being pumped into large, the Corken's and Howden's of the world have calculated many times for a variety of gases. Its also been done for large volume pipe lines to establish the frequency of pumping stations and similar.