Quote Originally Posted by ck10 View Post
Dear all,

Much appreciation for the responses and advice and please accept my apologies if I've caused any confusion with my lack of information.

In brief, scope of interest is to evaluate the operating COP of existing compressors using ammonia as refrigerant. Parameters measured were the suction and discharge pressures of each individual compressor. Power consumed by each compressor was also measured.

Ideally, as suggested by mad fridgie, is to install a flowmeter to measure mass flow of the ammonia from the common line. However, the intention is to have measurements over a few weeks period and the flowmeter would not be a permanent installation. Of course benefits from having accurate measurements would outweigh the cost of the flowmeter itself, but i'm afraid currently there's no provison for a flowmeter.

I've explored using the tech specifications from the manufacturer as well, which is basically a catalog showing condensing temp @35deg C and evap temp @ -5 , -10, -15 and -20. Current operating pressures are close to design, however I'm unsure if the compressor is operating at full load. If I could address this concern then I would probably be able to compare the actual power consumed vs the design power to evaluate the performance of the compressors.

Thus, it boils down to how I could estimate the refrigeration capacity without the use of flowmeter (hope I'm not asking for the impossible ). Would I be able to make assumptions on the mass flow derived from full load conditions (i.e. how mass flow varies with power, etc). Understand there's a lot of factors involved such as pressure drop losses, heat ingress, superheat, subcool, motor efficiency, age, wear and tear, volumetric efficiency), but I'm wondering if there's general rule of thumb or assumptions which would allow for a broader picture at a macro level for preliminary evaluation?

Once again much appreciation for the advice and for taking your precious time.


Thanks and best regards,
CK
Compressor capacity you can get only from flow meters or from compressor manufacturer. What is the goal of your evaluation? You've got COP 3. Is it good or bad? COP will be diffferent at different operating conditions.