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Originally Posted by valdelocc

Craig,

Could you explain why a bigger condenser will increase the evaporator TD?
thanks.

A larger condenser by itself, won't.

A larger condensing UNIT, will.

The reasoning should be fairly simple. Larger condensing unit, larger compressor, more pumping capacity.

Originally Posted by craig1

In both the above statements, he's probably talking about the condensing unit, not the condenser coil.

so if you have a 4000 BTU evap and connect a 4000 BTU condensing unit, it will include a 5000 BTU condensing coil or whatever is needed to deal with the total heat. If you increase the BTU rating of the condensing unit without touching the evap, the evaporator will run colder.

Craig,

Could you explain why a bigger condenser will increase the evaporator TD?
thanks.

Originally Posted by valdelocc

Thats a good read! I'm also a little puzzled about it, Dick talks about sizing the condenser to match the evaporator load without taking into consideration the heat of compression, I also dont get why an increase in condenser capacity would also increase the temperature differential in the evaporator.

In both the above statements, he's probably talking about the condensing unit, not the condenser coil.

so if you have a 4000 BTU evap and connect a 4000 BTU condensing unit, it will include a 5000 BTU condensing coil or whatever is needed to deal with the total heat. If you increase the BTU rating of the condensing unit without touching the evap, the evaporator will run colder.

Dick Wirz's book is very well done, and with a down to earth flavor which reflects the experience of a real-life field service technician. I truly do appreciate his writing style as it's a good read that doesn't get bogged down in a bunch of techno-babel and but I also see instances such as the receiver/subcooler statement quoted above which appear to be nothing but a personal observation or assumption with no apparent basis in fact.

So please don't start believing that subcooling is gained in a receiver...or we may have to start a whole new thread on the subject

http://hvac-talk.com/vbb/showthread.php?t=56495

Thats a good read! I'm also a little puzzled about it, Dick talks about sizing the condenser to match the evaporator load without taking into consideration the heat of compression, I also dont get why an increase in condenser capacity would also increase the temperature differential in the evaporator.

Dick Wirz Commercial Refrigeration.

I'll PM ya.

Originally Posted by Phase Loss

I was doing some reading and came across this, Never heard of this, but I guess it makes sense.

"If you cannot measure any subcooling at the
condenser outlet, but you are fairly certain the unit
has enough refrigerant, then check the temperature
of the liquid line leaving the receiver. Some manufacturers
(Heatcraft for one) use the condensing unit
receiver as the subcooler rather than adding tubing to
the condenser coil."

I'm curious as to who wrote this and where he got that statement about Heatcraft using the receiver for subcooling.

Originally Posted by Phase Loss

yeah I've seen that.

but they are talking about using the receiver as a subcooler..in particular, Heat Craft condensing units.

Now condensing units usually have the receiver in the direct air stream off of the condenser.

If they were using the receiver as a subcooler, wouldn't it make more sense to place the receiver in the condensers air intake?

All of my receivers are heat traced and insulated, the machines fail in the winter here if the heater breaks due to loss of pressure after a defrost. I might add that the roof can get down to -10f for a couple months. We would only be able to subcool after the receiver here.

E

This is all very interesting to me. Mcquay AGS screws use a what looks like a radiator that is 3x1x2" as what they call an economizer. It subcooling the liquid from the condenser and injects it back into the compressor to cool the gate. I could see them using a similiar setup but dump it back into the liquid line rather than back into the compressor.

Side note--we have a lot of Heatcraft equipment but havent seen that yet. I'm sure that's the latest thing that's right around the corner for the rest of us.

Originally Posted by Phase Loss

And I've never seen a receiver placed outside the condensing unit in the condensers air intake.

However I have seen plenty of larger remote air cooled condensers with the receivers located under them in the intake air. Never thought about why.

maybe this is why

I kind figured it was because they'd look silly with a big tank sitting on top of all the fans.


Funny you mentioned it, though. That was immediately where my thinking went when you mentioned receiver in the incoming air.

And I've never seen a receiver placed outside the condensing unit in the condensers air intake.

However I have seen plenty of larger remote air cooled condensers with the receivers located under them in the intake air. Never thought about why.

maybe this is why

yeah I've seen that.

but they are talking about using the receiver as a subcooler..in particular, Heat Craft condensing units.

Now condensing units usually have the receiver in the direct air stream off of the condenser.

If they were using the receiver as a subcooler, wouldn't it make more sense to place the receiver in the condensers air intake?

Originally Posted by Phase Loss

But back into the condenser right?

Basically.


The condenser empties into the receiver, then the liquid leaves the condenser, goes through a small coil and out to the equipment.

Hard to see a whole lot of heat transfer from a vessel like a receiver.

But back into the condenser right?

I have seen subcooling coils added to the receiver outlet on some units.

and before everyone rushes to point out that subcooling is not an important measurement when dealing with a receiver...

I know, and that's not the topic.

Receiver/subcooler

I was doing some reading and came across this, Never heard of this, but I guess it makes sense.

"If you cannot measure any subcooling at the
condenser outlet, but you are fairly certain the unit
has enough refrigerant, then check the temperature
of the liquid line leaving the receiver. Some manufacturers
(Heatcraft for one) use the condensing unit
receiver as the subcooler rather than adding tubing to
the condenser coil."