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22-11-2011, 08:24 PM #1
Understanding the trade-off between compressor work and condenser work
Hi everyone,
I hope you guys don't mind me posting a question but I've been reading articles on the forum for a while and am still struggling with this issue.
Our system:
The compressor (twin screw ammonia) suction pressure is determined by the efficiency of the evaporator, but the the discharge pressure is mainly controlled by the evaporative condensers.
For a given heat load (in our system, approximately 2MW), increasing the fan speed on the evaporative condensers reduces the discharge pressure and therefore the required compressor power. WHY?
Or perhaps a better question; If an evaporative condenser has a given heat dissipation value for a constant wet bulb temperature, what does the extra fan energy achieve? Is it increasing the amount of sub-cooling in the ammonia?
I hope this isn't too much of a stupid question. I understand the rest of the system, but this bit still causes me problems.
Thank you very much in advance!
Kind regards,
Simon