would this work?
 

Hello everyone! I am trying out a new idea,, as I am new to this. I have an 8000btu air con unit. If I place the evaporator hx in my 250 gallon grey water tank (fed from the 32f to 90f bath water to run the toilets) and place the condenser hx in my water to water hx which loops into my 80 gallon thermal store, can I get usable heat (160f) from this?

Thank you for your time.

Even if you used really good HXs, 130F is getting pretty close to the maximum you can realistically expect.

...that is not to say that a source of cheap 130F heat can't be usable.

-AC_Hacker

You could realistically expect 160 or more out of a de-superheater, however you will really want to be condensing at a much lower temperature otherwise your COP will be terrible (for 32F evaporation temp) and probably just bearable (at 90F).

Now, using an R410 system with a low pressure gas (like R22 or R290) might do what you want, as the condensing pressures at 160F will be much like R410 at ~110F (which is about where you want to be pressure wise). Actually, scrap R22 as at those pressures your discharge temperature will be high enough to cause it to break down on the compressor outlet valves. R290 would work very well however as it has a much lower heat of compression.

If you simply place your unmodified condenser in a bath of water you want to heat to 160F then you'll likely just trip out under HP.

If it's something you are willing to experiment with, there is certainly enough collective wisdom in here to help you out.

Thank you for the quick replies. 110f would be hot enough for normal hot water use, as the tempering valve reduces the faucet temperature to this. I could boost the thermal store temperature once a week by lighting the woodburner to remove any risk of legionella. Would 110f be too much for an unmodified ac unit with the hx's in the water tanks? I am only trying to avoid icing up the evaporator, and make use of an untapped low grade heat source. I can put on all the sensors and electronics to stop it breaking, if I know what temperatures these should be set at.

If you have the skill set to integrate an electronic feed-back system into your project, why would you want to screw around with unmodified refrigerant-to-air HXs?

Bite the bullet and extend your skill set so that you are getting or building good HXs and integrate them into your system.

BredC's advise is good, but you need to get comfortable with breaking into your system to implement any of it.

A whole new world awaits...

-AC_Hacker

With regard to making a bespoke refrigerant to water hx, how do I know how much refrigerant to put in? Does it have to be a certain pressure?

Well, when you change the HX(s), you will change the internal volume of the system, so you can't go by weight anymore.

Your A/C should have pressure info somewhere on the system.

If you're going to use R-22, use the pressure info when you charge.

If you're using R-290, the pressure will be less, somewhere around 50 to 70 pounds low side, 120 to 190 high side.

Your system should make frost at the input to the evaporator.


That should get you started.

-AC_Hacker

For cars, when replacing 134a (or whatever) with propane I just fill it until it blows cold. I'm no expert but I'm not sure how precise you need to be.

A couple of things.

Propane is not a drop in for R134a. It has quite a bit higher pressure and finds weaknesses in systems quite quickly. A 60/40 mix of Propane/Iso-Butane gives about the same pressures as R12 and is a lot safer.

If you have a cycling orifice tube system, then you don't need to be all that precise as there is an accumulator at the output of the evaporator, so a little too much won't hurt really. If it's a capilliary or TXV system, then under low loads a little too much can send liquid back to the compressor and destroy the valves (don't ask me how I know!). TXV systems have a receiver on the high side between the condenser and the evaporator. They are quite a bit more tricky to get right, and it's very easy to overdo it and damage stuff.

Thanks for the replies. I have just managed to get a portable 1 ton ac unit for free. The fan is noisy which is why they stopped using it. I will give it a blow through with the air compressor to clear the dust, then I can make sure it is good to hack. I will get a couple of pressure gauges, so that I can repressurise the new system. I take it that I have to pressurise the low and high side seperately? Or do I put the propane in at 70psi on the low side, and the compressor does the rest?