change R22 DX system to R22 4:1 pump recirculation system

[JERRYCOOL]

Dear all,
i have a storage here with dx type fan cooler. during the recent years, the temperature of the storage is too high since the defrost and the bad the condensing units.
Now, i am going to use big screw compressors to provide low temperature R22 pumped liquid to the evaporator. I think this will make better efficiency to the fan cooler.

My question is that:
1. does any body have similar experience? if does, could you help to tell me what should be considered for the job.
2. what is teh best solution for hot gas defrost.

best regards!!
jerrycooolll!

[JERRYCOOL]

thanks every one advanced.

[US Iceman]

I have done something like this before on an ammonia system. What exactly are you looking for?

[JERRYCOOL]

hello US ICEMAN,
did you have too high the pressure drop across the evaporator?

[JERRYCOOL]

should I size all the control valves(solenoid valves and hand expansion valves) per the actual capacity?teh actual connection size is very small compare to the same capacity recirculated evaporator.

[US Iceman]

did you have too high the pressure drop across the evaporator?

I'm assuming from this comment you forgot to remove the orifice in the distributor. This is where most of the pressure drop comes from. Remove the orifice and TXV, and install a hand expansion valve so you can regulate the liquid flow into the evaporator.

You don't need 4:1 overfeed rate. All you need is enough liquid to fully wet the coil. An overfeed rate of 1.5:1 is more than enough. Those high overfeed rates are essentially safety factors, which are too high in my opinion.

The evaporator capacity will increase about 15% due to the additional liquid wetting the interior of the tube versus the tube surface being used for superheating of the vapor.

This also helps with your valve sizing problem.

If you are looking at using 1 or 2 big screw compressors you will loose any energy efficiency you hope to gain. When the system operates at part load, the efficiency of the screw compressors is terrible. You would be better off using reciprocating compressors and VFD's, but this depends on how big your system capacity is.

[JERRYCOOL]

Hello, US Iceman.
we are starting the building job now. But we still have some doubts about the job since we don't have any information from the manufacturers. I download a manul from the internet. From this drawing, I found that it has a distributor. Do we need to cut it?

[JERRYCOOL]

I can't see the distributor at the moment since all the piping are hidden inside the cooler. I will need to disassemble the cooler to confirm the piping arrangement.

[US Iceman]

Here is a link to a brochure on distributors.
http://www.sporlan.com/20-10.pdf

What I recommended is not described in this paper, but it is based on the same principles.

When you use a refrigerant pump you have less pressure available. The normal situation is where you have the compressor discharge pressure available, so the orifice in the distributor is selected to provide more pressure reduction.

Since the pump provides less pressure than the compressor discharge, by removing the orifice in the distributor you compensate for the lower available pressure.

If you think of the problem like a Cv calculation, you need less pressure to attain a specific flow capacity with a larger orifice. This is in effect what I am doing here.

We are removing some of the restriction by removing the orifice so that it can operate with the lower available pressure (from the pump).

[Peter_1]

What capacity are we talking about?

Can you anyhow use the distributor, fabricated for a DX system with the pump circulation system?
As far as I've seen and heard, pump circulation evaporators are different of DX types, the circuit is different.

JerryCool, don't confuse an orifice with a distributor. The orifice is mounted in the distributor.

The pdf files is like Chines for me

[US Iceman]

Can you anyhow use the Distributor, fabricated for a DX system with the pump circulation system?
As far as I've seen and heard, pump circulation evaporators are different of DX types, the circuit is different.

Hi Peter,

Yes you can use a distributor on a liquid overfeed system. I have done several projects like this and working on another right now. The evaporator manufacturers can do this, but it does cost more than a standard liquid overfeed coil.

You are correct about the differences in the coil circuiting normally used. Imagine a DX coil with the orifice removed from the distributor, and a hand expansion valve replacing the TXV.

Instead of controlling superheat with the TXV, we simply control the hand expansion valve setting to overfeed the coil.

[JERRYCOOL]

Thanks Peter, I confused with orifice and distributor.
I took a picture of the distributor, found that there is no way for me to remove the orifice unless cut the distributor. The problem is that i don't know if i can put them back after i removed the orifice. There are 30 OD6mm tubes for me to put them back.

[TXiceman]

What US Iceman is describing is leave the distributor in place, but remove the orifice from the distributor body. Typically a DX coil application has about 30 PSI drop across the orifice and maybe 5 to 10 psi drop across the actual distributor tubes. You use the hand expansion valve to feed just enough liquid to have a wet return from the coil. Watch the superheat and when it reaches 0 dF, open the HEV (hand expansion valve just about 1/8 more turn and it should work fine.

The orifice is removal in most distributors such as Sporlan. A few will have a welded in-place orifice and you might try drilling it out using magnetic drill to collect the bits.

It will work better if you have 5/16" tubes rather than 1/4" tubes, especially since you are wanting to use hot gas defrost.

Ken

[US Iceman]

Thanks for helping to fill in some of the details Ken. Very few people I have talked to understand how this works.

[JERRYCOOL]

I will try to do it!
Thanks Ken ,Iceman and Peter. We can see how it will work soon.

jerry