Demand cooling in operating continuously

[rackrookie]

I have three 27HP Discus compressors operating most of the time in Demand Cooling mode. Condensing pressures don´t look bad: 180 - 200 psi. I suspected suction filters cartridges plugged, remove them, and there was no change of behavior. I checked the handbook and noted that these compressors are not built with suction inlet mesh screens, so that an obstructed screen is not an issue. Now I am wondering if there could an internal problem within the compressor that might be allowing discharge gas into the suction side, so that the discharge temperatures are higher than expected. What do you think ?

[dirtyboy103us]

what is the temp of the suction lines coming into your header
there is where you will find the answer you seek

superheat will make your demand cools stay on plus we are in the middle of summer suction lines with poor insulation will hurt also

also have found some that were jumped out to run always
sounds like your having fun now

do you have a sub cooler on this rack and is it working

there are a host of things that could be driving up your suction gas temp
so keep looking for them all and good hunting

what is your rack set to run also, could be its running to low, on an ice cream rack i would run from 7-11psi any lower and not reaching temp and i am looking for a reason

[Airmechanical]

I have three 27HP Discus compressors operating most of the time in Demand Cooling mode. Condensing pressures don´t look bad: 180 - 200 psi. I suspected suction filters cartridges plugged, remove them, and there was no change of behavior. I checked the handbook and noted that these compressors are not built with suction inlet mesh screens, so that an obstructed screen is not an issue. Now I am wondering if there could an internal problem within the compressor that might be allowing discharge gas into the suction side, so that the discharge temperatures are higher than expected. What do you think ?

it would be a craps shot without much more info! (need more information)



.

[jwc64]

Check your discharge line temp. You may find out that you have a faulty sensor or module.

[markettech]

what is the temp of the suction lines coming into your header
there is where you will find the answer you seek

Wise words - Not much more to add here.

[dirtyboy103us]

Wise words - Not much more to add here.

bullshiet





you could add to it if you wanted to, i know it, now your holding back,
you got way to many miles on you to lay low and its killing the young guys

guys like you, jwc,dow and ice and a whole host of guys here love to teach and work on the side of young guys and see the lights turn on as they learn



i had my grandson on a winn dixie roof when he was three so i know where your at, hang in there , and he loved it also

[basser]

One simple question here, "Do you have frost on your suction line?" If your suction line is not frosted your suction line superheat is too high. Answer this if you can and I'll try to get back and explain when I get more time.

[icemeister]

Copeland's Application Enginnering Bulletin AE-1287 tells you all about Demand Cooling. Pay particular attention to Fig.2 which gives you a rough idea of where it's needed with respect to your evaporating temp, condensing temp and return gas temp.

[gas_n_go]

Wise words - Not much more to add here.

As painful as this is to me to admitt I also agree with dirtyboys post
mark the date and time because we dont agree often
except about the importance of regularly scheduled safety meetings

[thegoodhumorman]

You need to check your discharge temperatures of your compressors- this is what your Demand Cooling module is attempting to correct. If you are running a high compressor suction temperature "superheat" your discharge temp will also tend to be higher. I have also seen poor oil viscosity influence this although I think the thin oil is more a product of the extreme conditions rather than the cause. You may need to open some TX valves to get a cooler temp to your comps- check the superheat! 20*f is noted as flooding, and 65*f is pushing too high ( as measured on comp. suction line- 6 " from comp)-
the more saturated your return gas is the more efficient your comp will run - generally speaking.
Run a bench test on them per Copeland but if they are all feeding sounds like a system issue to me.