A7 AirTap install (ASHP hot water heater)

[Patrick]

Originally Posted by Vlad

Probable the reason they want you to disconnect other heat source because what if your thermostat fails? HWT can reach over 100 C (boiling water + pressure). You have their refrigeration lines (full of liquid refrigerant) inside this super hot water. Think what is going to happen next???

The TPV will open and vent the hot water.

[Xringer]

The hybrid units likely have an HX with refrigerant too. I wonder how they would deal with 100C?

I've been thinking about this problem for a while. It seems like any system without
a double-wall/(middle wall vented) using refrigerant to heat water, could fail
and inject high pressure gas into your storage tank and/or your house water lines..
I hope my 100 PSI T&P valve will do the job for R22..

If I used the elements in my tank, I would not run them at 3.5kw.
But, even at 1,000 watts. Overheating might be a problem.



So, if I decide to hookup power (even my 800w of PV), I'll do some testing
to see if it's possible to over-heat my 40 gallons of water (using low power)..
If it is, I'll follow the AirTap no extra power rule..

With the limited amount of solar (5 hours a day max), PV might be a safe bet.

[Vlad]

Originally Posted by Patrick

The TPV will open and vent the hot water.

When I checked my PT valve it was seized because I have en expansion tank so it never opens.

But even working TP valve is set @ 210F and 150PSI. Your unit has designed pressure that is printed somewhere. Usually for R22 unit it is in 400psi range. R22 @ 210F will have 600-700psi or even higher (most pt charts are only up to 150F). This is much more than designed pressure.

This unit is meant to be installed on somebody's HWT. They don't know anything about it.
Everything can fail and nobody wants to be responsible for somebody's faults....

Now when you design complete unit from scratch you can add extra safety locks to make sure temperature in HWT NEVER goes above let's say 145F. Is it possible? Yes. This is why complete unit (HWT + refrigeration unit) have "hybrid" mode.

Xringer, if you ever want to add "hybrid" feature to your HWT you can do it but you have to make sure you have extra safety controls. You can add another thermostat or even 2 in series. This thermostat will be set higher than regular but bellow design pressure (just check PT chart). If temperature for whatever reason rises above it's settings it will disconnect or even lock out your elements.

Here is online PT calculator. Very basic but easy.

http://fridgetech.com/calculators/

[Xringer]

Not thinking about the "hybrid" feature now..

But, it looks like it wouldn't be too hard to put the two built-in Tstats in series.
If either one opened, it could shut off the power.

It would be pretty be simple to design a dual safety circuit.
(A redundant backup system that would work in parallel).
So, you would have to have dual failures to get over-heating..

But, nothing electronic is ever 100% reliable. (due to lightning storms).

[Vlad]

Originally Posted by Xringer

Not thinking about the "hybrid" feature now..

But, it looks like it wouldn't be too hard to put the two built-in Tstats in series.
If either one opened, it could shut off the power.

It would be pretty be simple to design a dual safety circuit.
(A redundant backup system that would work in parallel).
So, you would have to have dual failures to get over-heating..

But, nothing electronic is ever 100% reliable. (due to lightning storms).

I agree with you about electronics but go the other way. Just put contactor that closes your main line (L1 L2) and connect its coil(line voltage or 24V in series with fusible switch). Fusible switch will melt inside at set temperature and lock out the contactor. If you want you can put 2 fusible switches in series or 3 or..... They are precisely calibrated and you can choose them with 3-5 degree difference. One of them will work 100%

I am sure the capacity of this heater is not going to be enough. It is just a matter of time when you start cursing in the shower...... and add "hybrid" mode.....

It really sucks to think about if you have enough hot water in your tank. Life is too short to think about things like this. Just do it right and forget.....

[Xringer]

I wanted to do an Anode inspection, mostly just to see if it was going to be possible to remove it.

First, I had to return the 1" socket for a 1" 1/16" socket.
(I found out the hard way, instead of looking it up on the web)
http://waterheatertimer.org/images/A...-image-530.jpg
Notice the Cheater pipe..

Then, I had to use the extension pipes again. Only this time it was a lot harder.
That Anode was super tight. These old arms are hurtin! I'll be lucky if I can go knock down some Candle-pins this week!





It looks like a solid aluminum rod.. But, magnesium looks the same to me..
The rod had two different layers of gunk on it (black & green).
I cleaned it up and re-installed using Teflon tape & silicon oil.
It went in nicely and felt like it cranked right to the bottom.

Did some reading on the web and found Teflon tape is okay to use on anodes.
I checked with my ohm meter and the cap is a dead short to the AC ground.

~~~
I'm getting this done very slowly.. And now it's going to be even slower!
Due to unforeseen problems, my DIY time is going to be cut way back for a few weeks.

[berniebenz]

Can’t get the 20’ cu tubing evaporator snake in my HWH so am going to use this external HX as the evap. I already have a HW circulation loop with pump for my in floor heating system. My $20. offer was accepted. The stainless tubing on this 10 plate HX is standard ½” tubing OD, 0.630” so various fittings can be silver soldered or brazed to the cut off tubing, AR.

Stainless Steel Brazed Plate Heat Exchanger 8x3x1.5 In | eBay

[Old-arky]

Just found this site and hope it adds some much appreciated thoughts and designs to my Feeble brain . I'm interested in a small geo unit for a garage . Today it is 107 on the thermometer outside and 99 in the garage . I will enjoy looking at all the posts and great wealth of info already shared on this site . Thanks to all and have a blessed day.

[berniebenz]

Originally Posted by Old-arky

Just found this site and hope it adds some much appreciated thoughts and designs to my Feeble brain . I'm interested in a small geo unit for a garage . Today it is 107 on the thermometer outside and 99 in the garage . I will enjoy looking at all the posts and great wealth of info already shared on this site . Thanks to all and have a blessed day.

If your HWH is in the garage, consider this A7 ASHPWH, currently at a good closeout price on eBay.

[Xringer]

If it's 99F in the garage, I'm sure the A7 could make abundant hot water..
Plus, it should cool down the garage a bit too. (Until the storage tank got hot)..

If you wanted to work in the garage, I would consider insulation and buying an
inverter mini-spit AC (or AC+Heat model).