The Homemade Heat Pump Manifesto

[stevehull]

Mike,

I see a 3.5 ton coax coil for $113 on Surplus City. Do you feel increasing to that size is worth the small extra cost?

Steve

[NiHaoMike]

How big is the A/C unit you're planning to modify? At some point like 1.5x-2x the rating, it gets to the point of diminishing returns. It certainly won't hurt except for making the unit bigger and heavier.

[BeerGrylls]

Hi All,
first off, thanks for sharing your knowledge in here, had a long read but the info is very valuable. I might need a bit of help or opinions needed for my project, just in case I am missing some obvious things. What is going on:
I live on a small boat, 27ft sailboat, it's getting freaking cold out here on the Danube, I'm not paying for electricity but I am environmentally conscious and want to be self sufficient if possible, resistive heating is just ridiculous. I have been looking at various ways to heat a small boat and I dislike the majority of them, so I ended up with a plan:
-buy one of the highest efficiency ASHP and convert it to WSHP. I bought a Midea MSX07HRNF1QE4 heatpump (8000btu on heating) with a COP of 5.56 or something like that.
-I figured I will install it myself this winter and run it as ASHP simply because it is getting too cold to diy now and I don't have all the tools required to deal with refrigerant lines.
-when spring comes I plan to swap the outside air coil with a water to refrigerant HX, open loop, add an efficient pump for the loop.
-keep all electronics and everything else intact, hopefully everything just works with the coil swap. And voila, happiness...

Well, what I have to figure out is - what HX to get, capacity of HX, what pumping volume and how to fill in refrigerant after the swap (quantity). The Danube gets close to 0 degrees in winter (mostly around 4degC), but outside air can get to -15 -20, I understand that occasionally this harbour can freeze sometimes (once a couple years).

I looked at my heatpump and made a few observations: it seems everything is as big as the 1 ton units in the same series of the product, the higher btu series seem to have identical hardware but their COPs go from 5.56(8000btu) to about 4.2 (12000btu). I believe but not yet confirmed even the dc compressor is the same in all units from 8000 to 12000btu. The compressor I have is DA110S1C-30FZ, the unit has a cap tube setup, no txv, not sure if I should be sad about it, as I read the TXV's are better as they offer adjustments.

I would be curious on your opinions on the HX and if in general my idea is not completely bonkers. It seems like the unit is pretty much the 1 ton unit, but "underclocked" for a higher COP, the label even says it goes from 2600-12500BTU in heating. So should I get a 1 ton HX or lower ? Also it is a R410A unit, not planning in changing refrg. type.

Before spring comes I assume I will have time to collect some tools to do the hacking, and more knowledge hopefully. I'm thinking of going with BPHE just because they are getting so cheap, and flush out the foulants every once in a while, and provide a decent filter on the river water inlet. Have no idea though what pumping capacity should I push through the loop. Ideally I will be running it on solar power once I finish making my panels, the dc compressor looks to draw very little after start. The interior volume is also very low, but the boat is old and there's not much hope to add more insulation now. I have added mineral wool blankets on the deck and some polysterene boards where possible. Also - an important factor is humidity, gets pretty humid inside, hope the interior unit can get rid of the humidity, it seems to have a separate dehumidification program.

It looks to be hard to get a coax HX around here, but BPHX pretty easy, I know they can foul quicker, but also read cleaning instructions from some manufacturers and they don't seem to really turn into hopeless junk that you can't do anything with if your water source is not clean enough, they can be flushed with some cleaning agents etc. Do you think I should avoid BPHX at all costs ? Also - now I'm on the Danube, but I might get into salt water at some point.

Look forward to hear some feedback on my hacking intentions.
Cheers from the cold-ish boat !
Florin

[stevehull]

Florin,

All good ideas. I bet 1 ton (12,000 BTU) would be sufficient heat so long as you can blow warm air around the inside of the boat.

The gallons per minute is not large ~ 2 (or about 8 liters/min) of water flow will be sufficient. That said, you don't need a large pump as the only thing you have to overcome is the pipe resistance. A small 12 V DC water pump should work very well.

Freezing water is not a big issue as you can put overboard a hose that goes about a yard (meter) underneath the ice where the water is not freezing. The COP will get hit as it is hard to extract a lot of heat without freezing the outlet line.

I use an open loop water based heat pumps here and I have about a 10 degree F difference from inlet to outlet. Obviously, if your inlet water is 35 F then a 10 degree drop will not work (as in freezing the outlet line with open loop).

It is important to note that the water flow may have to be higher than stated above to deep your outlet line from freezing.

All that said, I would consider using a large truck radiator as a submerged river water heat exchanger and then use an antifreeze mixture in a closed loop configuration. First, a used large truck radiator is cheap and it has a LOT of surface area. Does the channel where you are have any water flow current? That will also help.

Lastly, your area gets wicked hot and steamy in the summer and you can easily have a reversing value in the heat pump guts to allow summer AC to get rid of the humidity you spoke of.

The salty water will eventually corrode the old radiator, so you may want to think of a large coil of HDPE pipe, but I do know that the radiator idea works. Just don't put it flat on the river bottom . . . . best if it can be put down there "upright" so that water can flow around it.

Another thought is to use isopropyl alcohol (10-15%) in the closed loop as this is "less" toxic when (not if) there are coolant leaks. Many in the EC get very fastidious about certain chemicals being dumped into rivers (the Danube formally being one of the most polluted rivers in the world . . . ). But I understand that fish are coming back (but would you eat them?)!

If $ is little object, you can buy open loop geothermal heater/AC for boats and they are not very big.

Keep us posted and we look forward to this interesting problem and how you solve it.


Steve

[BeerGrylls]

Steve,
many thanks for the ideas. $ is an issue, I also want to keep the hack as simple as possible. Regarding low temps - I am thinking of having a split in my river water intake system, with routing valves, very easy to make in HDPE. The reasons is that in the winter I want to draw water from the bottom of the river, as it is warmer there, for that I will simply use an insulated hose with a strainer at the end, just drop it on the bottom (about 3m deep water in the harbour). Also in the winter I don't move the boat so I don't care about a hose going overboard, however in the summer I will take water from the through hull fitting, but I would avoid that in winter as water at the surface is colder than the bottom.
The large radiator idea is interesting, are you saying the radiator is submerged outside the hull and is a antifreeze/refrg HX ? Or it is a primary HX with river<>antifreeze and then an antifreeze<>refrg. HX inside the boat ? I assume the latter. I will avoid this kind of setup due to complexity, more pumps, more controls, more worries etc. Initially was thinking to have a closed loop system running antifreeze in a bunch of hose rolls dumped on the bottom of the river (under the boat) , but again, this is not a very elegant setup.

I assume, in order to avoid the above, the only thing remaining is to closely monitor the river temp and water coming out of the HX and oversize the pump capacity to avoid freezing the HX. But the pump capacity would have to be guesstimated somehow.

The heatpump comes with a reversing valve from factory, so it works both ways (cooling).

Fish are coming back, but I am vegan... This area is particularly clean, I sailed the whole Danube from end to start and I've seen some really nasty polluted areas. Here it is pretty good, there is fish and the Otters are my night neighbours which I love, great area.

I have looked a the marine units too. The option was discarded because: too expensive, low COP's (1.8-2.8). Normally they are really compact so there is little performance to squeeze out of them, sure there are better ones but the prices are ridiculous.

I bought this ASHP unit because I figured it will be an easy hack to WSHP (remains to be seen) and it is really high performance, and I actually bought it as it was on a ridiculous sale, the reason probably being the size. It is about 50kg for 8000btu, the marine units weigh less than half for that capacity.

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

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 ?

Cheers,
F

[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

[waterdigger2]

BeerGryllis. Dont know how much budget you have If you are like me at the moment without a job . You can get a few pieces of wood build a partial box kinda like a solar pannel put in some garbage bags in with some clear food wrapping paper . Doesnt look great . But does keep things a little warmer and also wont break the bank or turn the electric meter into a extremely fast merry go round.

[michael]

I thought this was an interesting site dealing with heat pumps, alternative energy inputs and heat distribution. The site, which is pushing products, has some good design information, but the installation manual seems like a gem to me.

Website:

Cylinder & Thermal Store supplier for air source heat pump, installer, distributor

Installation manual:

http://www.ecoairpump.co.uk/air-sour...rmal-Store.pdf

[AC_Hacker]

Originally Posted by michael

I thought this was an interesting site dealing with heat pumps, alternative energy inputs and heat distribution...

I agree, the install manual is definitely a keeper (I saved a copy into my Alternative Energy trove).

Looks like the heart of the system is a very high performance thermal storage tank like these:

(From THIS PAGE)


Adn also...

(From THIS PAGE)


And also...

(From THIS PAGE)


These tanks are really very well designed, superb insulation, and great care given to the coils that are inside the tanks.

I bought a similar tank from a guy down the street (stainless steel, $20), but it is smallish (40 gal), was for natural gas, and not designed for low temperature heating, so the coils inside the tank are too big and too few to do me much good... I am considering cutting it open and installing some coils (smaller diameter, and more turns) that would be better suited for low Delta-T. It is worth noting how aware these designs are of temperature stratification, and how to use it to maximum advantage.

* * *

Acuario, were the tanks you used, specifically meant for thermal storage? Do they seem to have enough storage volume for your needs?

Best,

-AC

[Acuario]

Very much like my 'Combined solar plus heatpump' heating system..
http://ecorenovator.org/forum/solar-...l-heating.html