Help design my new system please

[buffalobillpatrick]

I have sold all 3 of the flat plate HX that I was going to use, at a profit.

Am now going with 4 Ton coax HX's. One for each, evaporator and condenser.

I have researched TXV requirement & found this statement:

If refrigerant pressure drop in evaporator exceeds 2# then TXV needs to be External Compensated.

Is this true & how would I know?

Also found this:

Q: When should I use an externally equalized TXV?
1. On any large system, generally over 1 ton capacity
2. On any system utilizing a distributor

Note: For field replacement you can always replace an internally equalized valve with an externally equalized type; however, you should never replace an externally equalized valve with an internal type.

[AC_Hacker]

BBP,

I came across this illustration,
Which reminded me of your consternation,
Compared to you mechanicals, PassiveHouse ain't near as manical,
You just gotta be super-serious about insulation.

Best,

-AC

[NiHaoMike]

Originally Posted by buffalobillpatrick

I have sold all 3 of the flat plate HX that I was going to use, at a profit.

Am now going with 4 Ton coax HX's. One for each, evaporator and condenser.

I have researched TXV requirement & found this statement:

If refrigerant pressure drop in evaporator exceeds 2# then TXV needs to be External Compensated.

Is this true & how would I know?

Also found this:

Q: When should I use an externally equalized TXV?
1. On any large system, generally over 1 ton capacity
2. On any system utilizing a distributor

Note: For field replacement you can always replace an internally equalized valve with an externally equalized type; however, you should never replace an externally equalized valve with an internal type.

Both the plate exchangers and (especially) the coax coils are going to have negligible pressure drop across them.

[buffalobillpatrick]

From pics. on internet the coax HX can be mounted horizontal or vertical?

Oil return is no problem?

[NiHaoMike]

It should be horizontal with the liquid end facing down for the condenser and the vapor end facing up for the evaporator.

[jeff5may]

Since you have a straight shot through of turbulent flow, orientation is not as critical as with plate hx's. If you have a certain limitation with space, the coax hx will do OK either way.

That being said, what Ni~ke said is the choice Mr. Spock would make.

[buffalobillpatrick]

Here are pics. of a copper HX that I made about 10 years ago.

1" reverse flow manifolds connects to 4 equal length 90' loops of 1/2"

I let it freeze some water inside & will have to solder up about 8 splits.

I will fix it for use in top of 1,000 gal. Solar storage tank to source HP instead of the 500' of O2 barrier PEX, which I will now use in radiant slab,
closer PEX loops in slab = lower supply temp. water = higher COP HP.

[buffalobillpatrick]

I bought these 2 copper HX for $47 ea. off Ebay.

My hidden agenda is that I was afraid of screwing-up the brazing of those expensive stainless steel flat plate HX's.

Larger is 7.5 Hp x 2,544 = 19,080 btu/h ?
Is this correct conversion?

DSH (Desuperheater), input is cool water from bottom of 40 gal DHW tank, heated water back to top of DHW tank.
The DSH effectively increases the size of HP condenser, right?

I have decided to not use HP condenser to heat DHW due to lower Eff. with higher compressor discharge pressure.
I went with jeff5may on this.

The tipping point, where the NG 88% Eff. boiler is cost effective vs. HP, seems to be around COP = 3

For DHW, I will use DSH when HP is heating ST120 radiant floor buffer tank, OR Solar (if solar storage tank is hot enough), OR boiler as last resort.

DHW takes priority over radiant floor buffer tank.

Smaller is 2 Hp x 2,544 = 5,088 btu/h ?

I will use this for IHX / SLHX.
(Internal HX / Suction Line HX, I have found 8 different names for this part)

It may improve COP a bit and it will increase DSH output.

From a post by Mikesolar:
"It would seem that the biggest problem with R290 (55C) is that its condensing temp is much lower than R410A (R71C) in a DX system running with a Te of -10C. That's is not bad for space heating but doesn't leave much room for DHW. This coolpack run was without a SLHX.

With a SLHX, the condensing temp on R290 increases to 65C and for R410 it goes up to 85C but the pressure is quite high. Under the same conditions the COP of R290 seems to be a bit higher."

[NiHaoMike]

If you use a heat exchanger to directly supply DHW, you can keep the temperature much lower.

[buffalobillpatrick]

Yes, but with hot water recirculation, wouldn't the required flow sensor on the load side of DHW HX tell the pump on the tank side to run all the time?

I have a iron Taco 008 delta-T pump 2 sensors, possibly that would automatically pump hot water from DHW tank to HX as required, and elemonate the flow sensor issue?