Variable Frequency Drive

[Samarjit Sen]

I would like to maintain a constant Td in Evaporator. Will using a Variable Frequency Drive Help to maintain the same. The Room Temperature has to remain constant. The refrigeration compressors are semi hermetic reciprocating operating with R 22. In addition to this I also propose to use Electronic Expansion Valve and a Evaporator Pressure Regulator.

Are their any documents available with any obe on Variable Frequency Drive system on Refrigeration application.

[Brian_UK]

Here's a starter for you....
http://www.optidyn.com/refrigeration.html

[Samarjit Sen]

Thank you for the link. My intention for using the VFD is to control the suction pressure, which in turn will maintain the Td of the Evaporator at a constant point. I would appreciate if any body could guide me in this respect.

[frank]

Why not use an EPR instead?

[Samarjit Sen]

By using the Epr we shall be maintaining the Constant Evaporator Pressure. The Evaporator Td will be somewhere at 2 or 3oC Due to this the superheat shall also be reduced considerably and the performance of the Compressor shall be effected. Now to attain the low Td at a constant stage, we have to use a number of Controls such as EEV, EPR, Hot Gas By Pass Valves and preferrably a VFD. This will ensure the performance and the efficiency of the plant.

In case I am wrong at any point, please do correct me.

[750 Valve]

I cant really see why you'd want to fit an EPR and a VFD, by using the VFD to control the suction pressure you will not need the EPR. If it is a singe liquid line system steer away from Pulse type EEVs - they will cause liquid hammer - use stepmotor EEVs instead and you will have a VERY stable system.
Just be mindful of the minimum frequency you run.

[Samarjit Sen]

Thank you 750 Valve,

I will do as you suggest. We will not use the EPR, and shall incorporate the VFD. Also instead of EEV we shall use the Step motor EEV.

Our intention of doing all these is to maintain a uniform Low Evaporator Td so as to have a constant 97% RH inside the Rppm with -1oC Room Temperature.

Further suggestion shall be highly appreciated.

[750 Valve]

Further suggestion shall be highly appreciated.

Big coils and lots of airflow, size your evaps for a very low TD, 1 or 2k, circulate the air well within the room. I have found danfoss ets stepper valves to be good, and a cheap reliable controller is an ekc316a but they don't make them in small capacities.
Im not sure what frequency your line supply is but don't forget you can ramp to 60hz with most comps these days - but don't forget to size your condenser for the extra kw if you usually only run to 50hz. Check with your comp manufacturer for both their max and min speeds to be sure though.

[Samarjit Sen]

We have a frequency of 50 Hz in our country. What is your opinion about Sporlanstepper motor EEV.

I would like your suggestion as to will it be better to use blow through Evaporators or Draw through Evaporators. We are maitaining a very high air discharge . At present we have been using Draw through Evaporators and they have given very good results. We are trying to further improve on our design. Your valuied suggestions shall be highly appreciated.

[750 Valve]

Induced draft or "draw thru" evaps will give better uniform airfow across your coil and are easier to clean, I would not recommend forced draft unless space is limited - eg upright cabinet. Sporlan stepper valves are good as well, which control system will run them? What will defrost the coils at -1C room temp, if off cycle then all evaps must defrost at once and the room temp will rise (the RH should stay high tho with re-evaporation) but if elec or hot gas then you can defrost evaps individually and maintain room temp, also how many evaps in the room?

[Samarjit Sen]

As of now we have been using ceiling hanging type Air Cooling Evaporators with draw throgh fans. The defrost system is being done by air.

As we are unable to get the stepper motor EEVs from Danfoss in India, we propose to use the Sporlan make. Each room will have one large unit coolers.

Further suggestions in this respect shall be highly appreciated.

[750 Valve]

Just be aware that the environment WILL change due to the defrost cycles, unless you want to use multiple evaps per room and defrost them individually (which may be an issue with off cycle at -1C).
Other than that go for it and post some photos of the job if once its done.

[Samarjit Sen]

Thank you 750 Valve,

Your suggestions and advices has been very valuable to me. I shall definately get back to you with the results.

[señorfrio]

Hi My friend, I´m new in the forum and I use a drive to have speed control in the fans of my evaporator (at 50 Hz) If you use the drive to energy saving its ok.you need a determinate air flow through the evaporator and that its the reason that its not posible to reduce the speed. at minus frequency you can have pressure troubles in the evaporator (refrigerant phase)

You can use a soft starter only to energy saving its more cheaper than a frecuency drive