Help design my new system please

[buffalobillpatrick]

If I put a ball valve in parallel across TXV why couldn't I vacuum complete system from 1 port & add refergerant from 1 port ?

BBP

[NiHaoMike]

A ball valve rated for refrigerant use is going to be fairly expensive, certainly much more so than another 1/4" service port and a few couplers.

[buffalobillpatrick]

NiHao Mike, I agree.

I suspected that TXV being closed was dividing system into 2 halves.

There are lots of things that I don't know.

I found this today: "Always charge liquid into suction line while compressor is running. Just be careful and meter refrigerant with your gauges."

Is this done while there is still high vacuum in system?

I read on one of the papers that I should only need about 16 oz. of propane for 2 Ton ?

BBP

[NiHaoMike]

That's for mixtures that might become uneven when charged as gas. (That's the case for R4xx series refrigerants like R410a and R433b, but not pure R290 if that's what you're using.) For a pure refrigerant, it's OK to charge as gas all the way, though it would take a while on a large system. For a system your size, you'll actually be better off charging gas as you'll have an easier time tuning it.

You'll probably want to jumper out the low pressure control while charging. Don't forget to remove the jumper afterwards as it protects the evaporator from freezing.

The TXV will actually open wide when you're pulling a vacuum, but it would still be too restrictive. A set of valve core removers might be a good idea as well, though you can get away without them by just waiting a little longer. Get it down to 500 microns on the third pass (verified with the pump temporarily blanked off) and you're good to go. Keeping the whole system in a warm location while pulling the vacuum helps to speed things up.

[buffalobillpatrick]

NiHao Mike, I was writing this while you posted. When do you sleep?

I have read that I want maximum performance at minimum amps draw.

I can measure the amps into the compressor. I will monitor pressure and temp. between the 4 major components.

What do I look to maximize & minimize?

I know I want maximum heat flow out of the condenser vs. the heat flow into evaporator. I have 1 water flow meter, which is not very accurate.

Do I need to setup a test with 2 x 55gal drums of water to know how much propane to charge?

BBP

[NiHaoMike]

I'm in the CST time zone. I just added my location.

Assuming you can keep evaporating and condensing temperatures constant (should be pretty easy with water), first charge until you can read a meaningful subcooling, maybe 5F differential or so. Then adjust the TXV (if the TXV is nonadjustable, disregard) so the superheat is as low as you can get without the valve hunting or until the superheat gets down to 5F differential. (You can do that with two accurate thermal sensors, one on the line entering the evaporator and the other on the line leaving the evaporator.) Then get the subcooling to somewhere between 10-25F or until the high side pressure starts rising a little. Adjust the charge slowly as it doesn't take much to change things.

You'll be best off tuning it in its actual application.

[buffalobillpatrick]

As suggested earlier in thread, I will limit evaporator input from solar tank with TMV.
100* was suggested as max. Minimum will be 35*

Condenser target output is 145* I want to maintain thermal accumulator > 130*

NiHaoMike, your: "Assuming you can keep evaporating and condensing temperatures constant"
is in conflict with above???

Subcool, measured at input to TXV, (after SLHX) Maximize is goal.
measure input temp. & pressure, convert pressure to Saturation Temp.
Saturation Temp. - input temp. = Subcool (shoot for 13*K delta or more if possible)

Superheat, measured at input to compressor, (after SLHX)
measure input temp. & pressure, convert pressure to Saturation Temp.
Input temp. - Saturation Temp. = Superheat

Is above correct?????

TXV is adjustable. I have read in many references that Superheat should be 20-35*K delta with propane.

BBP

[AC_Hacker]

Originally Posted by buffalobillpatrick

...I have read in many references that Superheat should be 20-35*K with propane.

Do you really mean "K"?

-AC

[buffalobillpatrick]

Yes, as in K* Delta, from the formulas.

That is how it's described in the white papers that I've read. I'm use to using F* but can convert easy.

K* is same as size as C* only start at different 0* points on scale.

0* K + 273.15 = 0* C

(I'm not talking to you A/C as I know that you know this)

BBP

[NiHaoMike]

Delta C and delta K are exactly the same.

By "constant", I mean constant for the duration of the test. Water has such a high thermal inertia that it's going to change temperature rather slowly.