Subcooling circuit.

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Subcooling circuit.

Ok .... but why

Whats the benefit

They have worked forever without them

Does it stop the bubbles when the fan kick on and off ? I did notice there werent any bubbles ....

 

Yep

 

, why didnt they use a headmaster ? l.

its an option, whom ever bought it, opted out

and chose fancycling instead

you should have chose a P66. variable speed controller instead IMHO

 

That P66 is a little pricey ..

The fan motor didnt even say where it was made

Part number on fan is 11623E

Im not sure if that motor would like a variable speed ... but then again Im not sure which is worse , variable , or turning on and off a bunch

 

the fan will be fine

used them on many applications, just find the right capacitor is the thing

fan motor cycling is far worse than variable speed for the motor, IMHO

 

I’ve never seen a subcooling circuit on something that small.

 

Russell and heatcraft are using them now on their 1 thru 6HP units.

Small subcooling circuit in the condenser

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Those bullet style fan switches ALWAYS go bad..
Either erratic or dont work at all. Cheap crappy materials.



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Where did you mount the control ?

 

Ha ... you cant see it apparently

The suction insulation is so massive , like 4 inches wide , that it hides it below , its mounted under that suction pipe

 

Got a comp MN#? I thought all Cope comp's w/ a SST below 0*F required air impingement on the comp body during run cycle.

 

I stand corrected on the need for air impingement on freezer comps that utilize "liquid injection" to cool off the comp. The Liquid Injector is more than adequate.

 

ICM control will work with that motor.

 

Which one do you prefer?

 

Txv must have a pure liquid entering with a minimum amount of subcooling to prevent valve hunting and maintain ssh setpoint.
It ca be achieved in different ways.

 

A receiver sucks away most of the subcooling. You can't get it back by simply using a larger condenser or by adding more refrigerant, like you can with systems that don't have a receiver. There are 2 ways to increase subcooling. One way is with the condenser subcooling loop like we have in this example, the other way is with a heat exchanger between the suction line and liquid line. The heat exchanger method seems to be most popular, especially on small cap-tube coolers where the cap tube and suction line are often soldered together. The problem is that this raises superheat, which usually isn't a good thing.

While I'm here I'll point out that I think PHM made a little typo on his advice. He's got 2 cut-in settings, and no cut-out, LOL. His advice is very good though. I think most people who set up fan cycling pressure switches try to set them up with too narrow of a band. His advice is to make it as wide as possible. He's also saying that most expansion valves are designed to work with a minimum 100psi differential between their inlet and outlet. I don't think a lot of people know this about expansion valves. So anyways, you use the normal suction pressure plus 100 psi to figure out where to set the fan cut-out, and about 130° (converted to pressure) to figure out where the cut-in should be.

 

I'm not so sure about that minimum of 100psi PD across the TXV, @ a 40*F Evap Temp. The point of 100psi PD across a R22 TXV is the "rating point" of the TXV. Such as a r22 1 ton TXV is actually .93T @ a 100psi PD across the TXV. And that same TXV is rated as a .73T txv at a minimum shown press drop of 60psi, as shown in the "Extended Capacity Tables". And the max PD is 175psi (1.23T)PD for that same TXV, again in the Extended Capacity Tables. I think.

 

Txv’s nominal sizing based on 100 psid, condenser approach typical 25-35 *f/ 95*f ambient. 130*f sat typical operating design.

 

A R12 and replacement's TXV is "Nominal Rated" at a 60psi PD. As in a 1T R12 TXV is just a 0.79 T TXV w/ a 60psi PD and that same 1T rated(0.79t) r12 TXV is a 1.35t TXV w/ a max shown PD of 175psi.

 

It doesn't allow receiver pressure fluctuation.
Which is what happens in the condenser with fan cycling.

 

Happen to have a part# w/ that pressure anti- gravity, backflow anti-hammering device?

 

.

 

There was a discharge superheat thread somewhere that was really good too.

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That check valve also prevents migration.

 

Hey Terry!

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I wonder who figured out the check valve thing. Can they get away with less total charge that way or is it about the same?

 

I would say this style of x-tra SC'ing cond unit thing needs a little x-tra freon for the slightly x-tra liquid line length.

 

Thats just what we need .... more crap that can go bad

 

Can't argue with that!🙂

 

I've always added a check valve when adding a HPC valve.
I believe it's in a Sporlan bulletin as well.
As for the migration I've never added a heat tape to a condenser but I have on a receiver.

 

Interesting. Thanks for posting that icy78. But why would we care if refrigerant migrates from the "warm receiver to the cold condenser" during the off cycle? I suppose it's so you don't have a few seconds with a flashing sight glass upon startup again? Doesn't seem like a big deal to me. Am I missing anything?

I'm guessing the scroll compressor has a check valve built into it as well, correct?

 

They have a hard time starting back up when it cold out.

 

I may be wrong here but here's what I think they are trying to accomplish.

We often install outdoor units with heated and insulated recievers around here for extreme cold conditions. Its necessary to keep receiver pressures high enough to come out of pumpdown after long off periods when it's -20F or colder outside. A unit with an HPR or "headmaster" acts as a quasi-check valve since it closes to the condenser when the receiver pressure drops, thus helping prevent (but not necessarily eliminating) migration back into the condenser which would happen readily when its cold outside since the condenser is obviously designed for heat rejection. Since this unit has only fan cycling they may have added it to discourage migration and low head pressure when it comes out of pumpdown. I have seen several of these units however that work just fine in pretty cold weather without the check valve. I think it also serves the purpose of preventing flashing due to the fan cycling as mentioned too.

 

Would there be a different best practice for charging this unit in regards to this design?
Not sure if there would be any idiosyncrasies

 

Normal charging when warm outside but extra refrigerant is needed for the flooded condenser. Its in the IOM.

 

The need for a receiver heater is based on 0*F and colder and a few other reasons.