View Full Version : building a vfd dehumidifier and have a few??

28-10-2010, 08:00 AM
ok so far i have a copeland 2 ton 3 phase scroll compressor and a standard 3 hp variable frequency drive. i am going to use a standard air handler for the evaporator and then add an extra 2 ton cased coil to the output as a condenser. I am going to use a 3 phase motor with vfd for the blower motor too. I am going to use R22 with a txv rated for 1.5 to 3 tons. I was going to vary the air flow based on evap temp and try and keep it at 35 degs so it wont freeze up but work well at low room temps of down to 55 deg I was going to vary the compressor rpm according to the humidity level with a 4-20 loop and control.

My questions are how much can i throttle down the compressor? I know its not made to work with a vfd but it was so cheap its worth a try. In my experience most regular motors work fine with vfds as long as you don't push it. i read that oiling is a concern with vfds? this compressor is small and will not see very high discharge pressures so i don't think it will make too much difference. my other question is whether or not the txv will work? I havn't ever varied the load or capacity this much before.

any tips or help will be very much appreciated

28-10-2010, 09:50 PM
A Copeland scroll: from 30 to 60 Hz and you can use a TXV
Condenser after the evaporator ;)
I should control the compressor speed according to the suction pressure, much more precise. Most VFD's accept direct a LP transducer.

31-10-2010, 02:44 AM
what range should i use for controlling the suction pressure? thanks for your help

31-10-2010, 03:37 PM
Just above the dewpoint of water