Need an education on VFD applications for a rotary screw compressor

[Nelson21]

We have many customers in our area that are strictly cold storage. They run a single 200 HP rotary screw on an across the line starter. The compressor is loaded around 40% 9 months out of the year. I believe this is a scenario where a VFD or VSD would be beneficially. Does anyone have experience with energy savings on similar applications?

[Peter_1]

Does the screw doesn't have a unloader slider? We have experience with it but don't go below minimum speed for proper oil lubrication. If it has already a slide valve, only savings you will see is less wear.

[RANGER1]

I would say its a perfect candidate for a VSD as there would be good savings in power. Ideal to keep screw fully loaded as much as possible. All industrial screws usually have minimum speed of 1450 rpm with exception of Frick which can go down to 750rpm (keep loaded though to prevent oil build up in machine with no mass flow through it). Usually motor needs insulated bearing & earth brush on rotor on 150kw motor & above. What types of machines & sizes do you have?

[Peter_1]

http://docs.lib.purdue.edu/cgi/viewcontent.cgi?article=1626&context=icec and http://www.bowmanrefrigeration.com/uploads/2/8/3/8/2838230/v_series_manual.pdf and
https://www.google.be/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&ved=0CFIQFjAE&url=http%3A%2F%2Fwww.irc.wisc.edu%2Ffile.php%3Fid%3D270&ei=VLjiUfqtC4eu0QW5uoCACg&usg=AFQjCNH76zvTrrUEyXll4VP8V5uufO72JA&bvm=bv.48705608,d.d2k

[Josip]

Hi, Nelson21 :)

Welcome to RE forums ...


We have many customers in our area that are strictly cold storage. They run a single 200 HP rotary screw on an across the line starter. The compressor is loaded around 40% 9 months out of the year. I believe this is a scenario where a VFD or VSD would be beneficially. Does anyone have experience with energy savings on similar applications?

Idea to instal VFD is OK ... but I will suggest you to instal a good reciprocating compressor with 50% capacity of your screw compressor .... don't know capacity of screw compressor but I think one with 4 or 6 pistons will be good, depend on fluctuation of load .... not bad idea to have an oil cooler in case when run at small capacity for longer time and with heads cooled with water ...

your customers will be very satisfied with power consumption ... because reciprocating compressor use as much energy as does the work ... furthermore they will have spare compressor when you need to do any maintenance on the screw compressor ...

Believe me, this is a good advice and it is free ;)

Best regards, Josip :)