Dual Compressor Bank Question

[Stewie007]

So what do you think of using dual compressors? Not a cascade, but a Dual Compressor bank. Hehe

Whaddya Think?

[n00b 0f l337]

Just two in one loop?
It has some fun rammifications, you might get more interest in vapor phase section.
First, if you start them separately then one has to deal with the pressure difference. So you really need to have a valve system in place to isolate the second compressor at static pressures.
Or start them together and hope your power system works. Either way why not use a bigger compressor? Is it for adjustable capacity? Then the refrigerant charge is bonkers when running only one. So then you use a CPEV or TXV, but then the TXV isn't sized right, or your manually adjusting a CPEV and you could do that with one bigger compressor.

What's the point?

[Hondacity]

K.I.S.S. applies

[Stewie007]

Well I doubt I'll really do it, was just brainstorming.

It would be interesting though. I'd have to modify the compressors to install an oil equalizer line in the back end. The receiver would help with the extra refrigerant, but the real issue would be the orifice. With two 3/4 ton compressors in tandem I'd have to have a metering device capable of both 3/4 and 1 1/2 Ton load. I have seen a few with that range but not for 404A/507 in my small amount of research, but definitely doable.

The idea would be to limit the pull down time (temperature wise) by adding a second compressor during the first run and then using the second compressor for maintenance of the desired temperature. It would involve more programmable controls, but not out of the question.

The real problem, though, is it would be ridiculously expensive, but I thought it made a good "Tim the Tool Man" type of idea... hehehe... More power!

[n00b 0f l337]

Why an oil equalizer line? Seems to be over intricate.
Simply each compressor get an oil separator before the lines merge.

[Gray Mole]

Hehe

In the 'Cheap vs Easy' competition, cheap usually wins. It's a bit of a pain to install an oil equalizer line in a pair of rotaries but it's a lot cheaper than a pair of oilseps and valving (if needed).

Interesting idea but much easier to do if you're running both fulltime. Isolating is harder than just running both I guess.

Worth doing when you have a pair of smaller compressors. Load requirements are normally taken care of by twin TEV's.

Easier way though, is to just size a single compressor. Or you could run a pair of HX's, and have a pair of independent systems instead of tying them together. Then you can run the second system when required for load.

Your water can then just run through them in series, activating the second system when the temp goes above your setpoint.


Gray

[n00b 0f l337]

KISS always wins.
Two separate systems or just split a condenser in half (it'd be the same effect as one loop). So really you just add another metering device and evaporator.

[Stewie007]

Oil Equalizer lines are common in multiple compressor units and its not all that hard to implement. It prevents oil starving or over saturation in the event that one compressor is running. Isolating each compressor is as easy as including a check valve at the outlet. So I wouldn't worry there. No need to isolate the suction end as as the running compressor will attract all refrigerant flow.

As far as control I am at odds of how to do it. The main control of the unit is the pressure control. When the temp control trips at the low set point it closes the solenoid and the unit begins to pump down. At a given pressure setting (ideally a slight vacuum) the compressor turns off. When the temp sensor reactivates the solenoid, pressure rises and at the cut in point on goes the compressor. The problem arises in activating the second compressor at start-up, and by load demand. Running them both full time would just waste power. So hmmmmmmmmmmmmm.

[Stewie007]

I just figured out how to do it.

Run a temp sensor off of the pressure sensor and set it above the set point of the temp sensor controlling the solenoid. That way, it can only run when the water is warm enough (i.e. the first time it is activated). It will also kick on if the single compressor can't handle the load and the temp rises far enough to activate it.

Win/Win.