The Homemade Heat Pump Manifesto

[AC_Hacker]

Originally Posted by BeerGrylls

BTW - AC hacker, was thinking of how you brazed the copper tubing to the BPHE, the wet rag - why not submerging the BPHE in water instead (in a shallow bucket etc), of course lower than the inlet. Would that work ?

The water submersion method would be a very good way to do it. I hadn't heard of it at the time, though. The method I used is how people in the trade do it, when they're on a job.

Originally Posted by BeerGrylls

The large radiator idea is interesting...

I would NOT suggest using a submerged radiator, as it will quickly become a magnet for fouling due to all the stuff that is in the water. The people who suggest submerging radiators (they're everywhere) haven't had enough first-hand experience with a water heat exchanger, and do not realize that the required heat exchange area in water is drastically smaller than that required in air. If you were in a do-or-die McGeiver type of situation, or if you are on a reality TV show, then sure, it might be better than being thrown off the island... but you'd loose style points. It sounds like you have reasonable solutions available.

The freezing point of water is an issue, but if your pump velocity is high enough, the water will not dwell in the exchanger long enough to freeze. So you should count on much higher than normal flow rate/Ton.

Originally Posted by BeerGrylls

Anyone has experience with BPHE cleaning of performance decrease in open loops?

Yes, their passages are very tiny and will become hopelessly fouled very quickly. Do not use BPHE in open loop, unless you have a large and thorough filtering system.

Stick with some kind of tube-in-tube HX. If you have tools, you should be able to make one. Only the refrigerant tube needs to be copper. Make sure that the passages are large enough to allow debris to flow in, and right on out.

Originally Posted by BeerGrylls

So the current plan is - 1 ton water to refrg HX (coax or BP), variable speed water pump (capacity to be determined, the air coil fan is rated 30W, would be nice if the pump is the same power rating because I could even use motor wiring for the pump, fan is BLDC) and to figure out refrg. filling after the hack is mechanically done.

Your two big enemies are fouling and freezing.

I love BPHEs but stay away from BPHE because of fouling for river water.

You are going to need a robust pump to get your flow velocity up high enough to avoid freezing. Like maybe 2X or 4X what would be normal flow. You should be able to use the power to the fan to power a relay that would control higher current to your pump. Your COP will be so high, that extra power for a pump is not so important. River water, even when near freezing, contains a lot of heat. An ASHP on a day that is about 0 degrees F, will be happily providing you with warmth... same with water.

Before you start hacking your equipment and hurling truck radiators in to your lovely river, you should become acquainted with some of your fellow River Rats, and see if any of them have done, or if they know anyone else who has done what you are attempting... you might be surprised. River Rats are a crafty lot, and from my experience, a friendly lot, too.

I did talk to a boat-dweller the other day. He didn't have a heat pump, but there were people around him that did. He talked about the constant stream of water going into the river, next to his boat... he said it made him have to go to the bathroom all the time. I bet you never considered that part of the situation, did you? Anyway, even that could be resolved by having the discharge tube below the surface of the water.

He said that there was a boat in his moorage that had 4 or 5 units, each dribbling into the river. At that rate, it's a wonder he didn't wet his bed.

You're the first poster who has wanted to hack their sailboat!

Welcome aboard.

-AC