The difference between an EPR valve and a CPR valve?

[kengineering]

I am trying to put together a system for a cafeteria countertop which contains an fan coil air pan and a static coil cold pan. BTU requirements are 8700 @ 20*f for the air pan and 2000 @-10*f for the cold pan. A single 404A condensing unit has been requested. Solenoid valves with a pumpdown cycle controlled with Carel T-stats was the plan. Because of the temperature difference I have concerns of system balance when the larger load ,the air pan, is satisfied and the smaller coil is still calling and being overpowered by the condensing unit.
This is what lead me to the EPR / CPR question. As I read about the use of each of these valves it seems they are nearly the same. I believe I should use an EPR on the smaller coil because the back pressure of the condensing unit will be so overpowering. Does that sound right? Obviously I have never used these valves so I have no experience to draw from.
Also... Am I going about this the right way or does someone have a better way to accomplish this.
And Also...is it possible to run another air pan of the same size in this same system. Yes I do know I will have to beef up the compressor which would create an even greater difference in system balance. Ken

[chemi-cool]

EPR:
http://www.danfoss.com/businessareas...e502a4f50.html
CPR:
http://www.danfoss.com/businessareas...48a22d072.html

[wrench]

The theory is correct that using a epr on the low side to maintain a raised suction pressure should the main counter achieve temperature but you should be careful. If the main counter cuts out and the epr on the small coil has to shut down to increase the coil pressure there is a danger that the unit could cycle on LP switch (depending on the size of the unit), also you have to make sure that there is enough gas coming back to cool the compressor.

[jana]

The cpr will regulate back pressure to the comp, if either of the solenoids has closed off, the comp will still be ok. the lp will shut down the system when temperature is achieved. Wire in a pump out circuit to prevent the lp cycling due to pressure rise.

[oldesky]

The difference between the two valves is the EPR valve controls the pressure at the valve inlet and the CPR valve controls the pressure at the valve outlet.

[Gary]

I am trying to put together a system for a cafeteria countertop which contains an fan coil air pan and a static coil cold pan. BTU requirements are 8700 @ 20*f for the air pan and 2000 @-10*f for the cold pan. A single 404A condensing unit has been requested. Solenoid valves with a pumpdown cycle controlled with Carel T-stats was the plan. Because of the temperature difference I have concerns of system balance when the larger load ,the air pan, is satisfied and the smaller coil is still calling and being overpowered by the condensing unit.
This is what lead me to the EPR / CPR question. As I read about the use of each of these valves it seems they are nearly the same. I believe I should use an EPR on the smaller coil because the back pressure of the condensing unit will be so overpowering. Does that sound right?

No... the EPR would go on the warmer coil.

[lawrence1]

kengineering

Rule of thumb i was taught was to have the low temp load at least 60% and medium temp load at 40% of the condensing unit capacity,even 50/50 was hit and miss.
i would use 2 units if i was doing it.
Regards

[mbc]

EPR / CPR valves

EPR = back pressure valve = controlling Evaporator pressure

CPR = outlet pressure vale = controlling crank case pressure



but it not same totally different

If you have two systems with two diffrent temrature (Delta T in Evaporator is important to you ) with one compressor

You should put EPR in Evaporators is working in high pressure
(Room temperature is high) and adjust EPR with this temperature.
EPR is controlling and adjusting delta T of Evaporator
So compressor suction pressure does not affect that if your pressure in suction goes down it goes to close but if your pressure is higher than EPR adjust it is open completely

CPR should adjust with maximum suction pressure load compressor can carry – safety load (about %5 to %10)
If your pressure goes high CPR goes to close inlet gas flow to compressor
Meanly it is for protecting compressor from over loading and ofcourse
It protect over heating of condenser in this case and discharge pressure if your designing load in condenser is close to compressor load .