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Im trying to figure out how they calculate the BTU of a unit . IF a system uses 1000kw how do they work out how much output it gives ?
If i was to make a fridge from scratch how do i work out how much BTU output it is .
Not trying to work out the size of unit i need to cool a room .
Old fashioned rule of thumbs gives that for 1kW input you get 2kW cooling capacity and 3kW worth of heat to reject.
Modern systems should be able to beat that.
To properly calculate it you will need to look at each individual part of the refrigeration circuit and get your enthalpy diagram out.
:cool:
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not the enthalpy diagram ! does any one actually use them at work ha ?
So and inefficient system would be like 1.8kw cooling effect for 1kw . What about a 200kw system is it normally just double . 400kw and 600kw heat needed to be rejected .
Rules of Thumb are useful as reminders of which way is uphill. There is no singular relationship between Input and Output of a refrigeration circuit; depends on your refrigerant(s), the condensing temperature, the evaporating temperature, the compression process and how it is cooled, how you handle the liquid expansion process, the suction superheat and so on.
But staying within the lines: www.irc.wisc.edu/file.php?id=113
extracts certain values out of ASHRAE fundamentals and elsewhere to form Table 1; Page 4.
Those are all at same condensing & evaporating conditions and do not account for the deviation of compressors from the ideal (isentropic) process.