Is it possible??? and no corny stuff this isnt Domestic!!!

I want to link two condensing units to one evaporator blower.

Each condensing unit is 7.5 Kw Prestcold Semi Hermetique

Evaporator is rated at 20 Kw.

Room is a freezer room.

I want to run the systems independantly and in turns, occasionally have both condensing units run together during peak periods.

My question is, Is this possible ??

Second question

Should I do it ??

Third.

How ????

:D


Any help appreciated. Im starting the job in another weeks time..........just after I get over the spate of AC orders that filtered in after we had one, just one or couple hot days!!!!

All it took was for the " Sun tablioid" to announce...........that were going to die of heat this year!!!

And for those that havent heard of the Sun..........well they have a delicious Page 3.................

But looking outside right now, its raining.............as usual.
Its grey and..............cold.................ish

Only bright ness was a little earlier.........saw this flight formation of swans or something migratory......... swooping overhead...........

Was awesome!!

Hi abe,

Do you mean that both condensing units will work on the same TEV? i.e. parallel?

Or the evaporator coil is divided into two circuits?

Chemi :)

Considering things like oil return, superheat, capacity control etc, the only possible way to do it is to have a 2 circuit evaporator with interlaced coils. This would allow for "one" evaporator and two condensing units all serving one area.

The control could be via a two stage eliwell or similar.

apart from the obvious mismatch 2 x 7.5kw on a 20kw evap

the most important question is WHY!!?

cheers

richard

This sort of thing has been done for years on medium to large packaged water chillers with multiple compressors. Two or more compressors are attached to a common Evaporator with one TEV.
You will need to be careful with matching your system if you have a variable load.
I presume that you will want to cycle the two units independently? Or run them in tandem?
Either way, you will need to do a few essential things
1. Both compressors MUST be on exactly the same level
2. Link the liquid and suction (obviously)
3. Link the oil lines on the two compressors below the oil level so that there is a common oil level in both sumps. If you don?t the dominant unit will hog all the oil.
4. You will also need to equalise the sump pressure above the oil lines.
5. Keep all common pipework identical in length.
I would strongly recommend oil pressure protection if you can because there is a danger that if only one unit works at 50% capacity, that equals 25% total load ? oil may migrate and not come back.

But again the question.....why?
________
herbalaire

It seems its not as easy as it might have appeared to me..........

I shall explain............to the " why question.

This customer likes to save money. He runs the units at night, and switches them off during the day.

I know thats naughty.............very naughty..........But who am I to tell him how to run his business.

Anyway, up to now the two systems have been running independantly on two seperate systems. Sometimes he switches one on, then another.............

One evaporator required replacing............two fans shot. heaters gone.........one heap of ice.

I tell him he needs a new evap............. Believe me........the whole carcass is scrap and Im not going to replace fan motors or heaters...........the drains leak.............its awful.

So I ring around the wholesalers........I come across one evaporator going cheap. But its a monstor. All I required was one 10Kw evap. This one is 20Kw.

So my little head tells me,. the other evaporator is about shot too.

Why dont I link the 2 condensing units to one evaporator.......one valve but seperate electrics.

That way, customer can run the condensing units either one at a time, or together,however he feels like it.

The reason he switches off complete store during day is because he is getting constant shipments of frozen stuff coming in all day.........

Its frozen already..........So it just sits in the room and is then quickly delivered again the next day........

So he saves on his electric bill running only at night...........

I hope that makes sense.

But upon reading what you fellow professsionals say.........I might get myself into an awful lot of trouble..........

Better to play safe and follow tried and tested procedures........

Well ???

Shall I ???

Mess about ???

:)

It sounds as if your man is intent on spending a fiver to save a quid.

From your point of view you?re right about the risk of selling him a pup. If it doesn?t work you have bought the problem of putting it right, probably at your cost.
Second hand evaporators usually come with residual contamination. You don?t know what?s in it or where it has been.

There are other more serious considerations. The local health inspector may not be very keen on the idea of uncontrolled temperature fluctuations in frozen food; the core temperature may not vary, but the outer limits of the food stack may, even in a sealed insulated room. You are dicing with death if there are any problems with contaminated food. There are very strict rules in the UK about food storage temperatures. Rigidly enforced, too.

Apparent saving may not be as good as it appears because the cost of pull down afterwards on a warmish room.

Why take a commercial risk because of someone else?s greed?
________
Henry Ford II history

Even both compressors running at the same time is a challenge - you might need a common receiver.

Cycling compressors on and off will require precise oil management controls OR get your piping lengths , compressors on identical levels i.e. you want to ensure that that the suction piping to one compressors is EXACTLY the same as to the other. One knock or bend to the tubing in the future can alter the oil balance.

In short, possible but not worth the risk and future hassle !