Heat Pumps

There is plenty of heat in 40F sea water for a rev cycle machine to extract. The problem is if ice starts to form in the heat exchanger. A bit of ice forms and this reduces flow, which allows more ice to form. Then the problem literally "snowballs" til flow is choked off.

This problem is way worse if water flow is low. With four units on one pump the OP probably has a lot of plumbing, and some units might get plenty of flow, some might be on the low side.

Also some units are better at cold operation than others.

Just an idea that popped in my head (not super well thought through) is to have two pumps in parallel, with the second pump left off unless in cold temps, then switch to both on to increase flow. Just thinking aloud.

FF did you need fans to move the air around? What kind of boat where you living on?

Anyone here have experience with Reflecks diesel heaters?

catalinajack said:

So, is it safe to conclude that the more raw water one can push through the units, the better cooling/heating? For example, Oberdorfer makes an AC pump that puts out 1,440 GPH. My pump puts out 900 GPH.

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Oscar, increasing flow as CJ posts only works to a point.

Increasing water flow with a larger pump assumes your suction and discharge piping is upsized as well to keep friction losses in check. The same holds true for the heat pump unit itself. They are sized for flow too.

Have you considered a passive diesel fired unit like Dickenson? Relatively inexpensive and lots of them out there.

How,does the Dickerson compare with other brands. Specifically Reflecks. See more Reflecks on voyaging sailboats and high lat craft. why?

Hippocampus said:

How,does the Dickerson compare with other brands. Specifically Reflecks. See more Reflecks on voyaging sailboats and high lat craft. why?

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Sure, either would work. So would a few well placed electric heaters. There are several cost effective many options for heating a vessel for those periods when water temps are marginal for reverse cycle.

We have four heat sources. Diesel hydronic, engine heat, reverse cycle and electric spot heaters.

"FF did you need fans to move the air around? What kind of boat where you living on?"

Fans were not needed the heating unit was in the main aft cabin, galley and dining with Concordia bunks .


The hull and deck is Airex , s slight insulation.


A single 4 ft section of heat tubing warmed the the pilot house ,return was in engine space and the fwd cabin had a 6ft and and an 8 ft section of finned tubing ft .
The fwd return tube was thru the hanging locker so there was no problem with uniforms etc.

There are fans that work on a hot surface , I have seen them used with 40ft sail boats to move the heat in a cabin.

Has anyone thought about using a hot water heater on board to heat hydronic baseboard or the like? Obviously need 120 volts. I have a friend who heated a 3,000 sq foot barn with a domestic hot water heater and a radiant floor

Cigatoo said:

Has anyone thought about using a hot water heater on board to heat hydronic baseboard or the like? Obviously need 120 volts. I have a friend who heated a 3,000 sq foot barn with a domestic hot water heater and a radiant floor

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Given a big enough water heater, it'll work. But it's no better in terms of power in vs heat out than just using space heaters.

Great responses . Thanks all.

Cigatoo said:

Has anyone thought about using a hot water heater on board to heat hydronic baseboard or the like? Obviously need 120 volts. I have a friend who heated a 3,000 sq foot barn with a domestic hot water heater and a radiant floor

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A standard boat water heater would not cut it.. 1500W element will give you the same heat as a 1500w plug in heater.


HOLLYWOOD

Cigatoo said:

Has anyone thought about using a hot water heater on board to heat hydronic baseboard or the like? Obviously need 120 volts. I have a friend who heated a 3,000 sq foot barn with a domestic hot water heater and a radiant floor

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Your friend's results need to be put in context. I suspect he did not make that work in Fairbanks AK.

Like someone said, a 1500W water heater will give you the same heat as a 1500W space heater. That said, floor heat does better than baseboard in perceived efficiency as the heat is on your feet and not going up the wall to the ceiling.

I have a 1000 square foot work shop in Eastern PA. Winter temps mostly around freezing with regular excursions into the 20's and occasionally into the teens.

I have PEX in the floor and circulate anti freeze through a domestic water heater. It's 240V and hooked up to a 30A breaker..... Roughly 5500W. It keeps it around 45 degrees.

oscar said:

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Your friend's results need to be put in context. I suspect he did not make that work in Fairbanks AK.

Like someone said, a 1500W water heater will give you the same heat as a 1500W space heater. That said, floor heat does better than baseboard in perceived efficiency as the heat is on your feet and not going up the wall to the ceiling.

I have a 1000 square foot work shop in Eastern PA. Winter temps mostly around freezing with regular excursions into the 20's and occasionally into the teens.

I have PEX in the floor and circulate anti freeze through a domestic water heater. It's 240V and hooked up to a 30A breaker..... Roughly 5500W. It keeps it around 45 degrees.

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Was in R.I. He used an oil fired water heater. Pex in the floor. Not sure what that equates to in watts. The shop was insulated and always at about 55 degrees. I am quite sure he could have pushed it further but was a comfortable temp when restoring his cars.

GoneFarrell said:

Oscar,
The way I see it: you would be using energy (likely shorepower?) to heat a fluid and then try to suck the heat out of the fluid and move it to air. Every transformation of heat from one medium to another comes at an efficiency cost, pick a number.

Seems to me you would keep the boat toasty using the energy you'd put into the fluid to directly heat the air in the boat, eliminating at least one transformation of heat energy. I can appreciate that you don't want to lay more hoses and bus heaters all over the boat, for example.

If this is for at-anchor then might be different solution path.

Edit: looks like David beat me to the punch with his post#4!

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Bingo!

Hippocampus said:

Anyone here have experience with Reflecks diesel heaters?

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Love my Reflecks, diesel tank on the fly deck feeds it, easy to light, gives of loads of heat, I normally keep it on the lowest setting and keep on all the time when cold, in the UK so not that cold. Only thing is I have a radiator in 1 sleeping cabin and a bus heater in the other, it’s a shame the heater doesn’t feed them.

Hippocampus said:

... Water/antifreeze mix comes out at 55 F all the time. Ambient air temp is irrelevant......

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I have never understood how geothermal heat can warm your house above the 55 degree ground temp ? If its a long explanation, don't bother answering....but I'm quite curious.

It’s just a heat pump. Take out 55 degree water. Return it a bit colder you have heat. Return it a bit warmer you have cooling. So it covers all HVAC needs.

AMG why doesn’t the Reflecks supply the radiator(s)?

Hippocampus said:

AMG why doesn’t the Reflecks supply the radiator(s)?

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It was installed by the previous owner and it's not the model with a boiler, the radiator and bus heater is heated by a Webasto water heater, interestingly I have an AC system which has been decommissioned and it doesn't have a reverse cycle but 2 electric heating elements. I wonder how that will compare to a heat pump.

But it works and you have warm toes.

oscar said:

Don't know the GPH on my pump but it's substantial. It feeds 4 units and in cooling mode they work VERY well. But yes, I'm going to see how low it will go. As mentioned my previous experience was another boat and it may well have had a relatively small pump.....So good point.

One point I disagree with is that your Geo thermal unit works in lower temperatures because there's Glycol in it. It works because it goes far enough into the ground that it reaches the strata where the temperature is 50-ish degrees. Always.

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If you wanted to do the same thing in a boat, make a glycol loop, and run it down to the bottom and back up. It is always warmer in deeper water, even if it freezes over on the surface.
Just make sure you stow the tubing loop before starting the props.

Some guy in Norway (if I remember correctly) had an A/C system using the submerged loop a few years back. Basically, it was a bus heater with a fan and small dc pump.

We have 3 x reverse cycle units in the PacNW. We've not had issues with insufficient heat although we've used some small, quiet, slow fans on a couple occasions to move air around a bit in our 4788 pilothouse. Given that the OPs boat is a "traditional" motor yacht many of the suggestions wouldn't work re the whole boat. Larger pumps might be the answer, but as has been noted, the system will have limits on just how much water can be sucked in and circulated during any given interval - so some attention needs to be paid to intake an hose cross sections, hose paths and sharp turns/tees, etc. to determine the limits of the system re flow and pressure. On our boat we have two pumps, one servicing the salon (16K btu) and one servicing the pilothouse unit and the stateroom unit (12K btu each). In our case both pumps are serviced by the same thru-hull and for which I've had concerns about throughput and flow but it seems to work. In any case, perhaps a second pump would work or perhaps a second pump+thru-hull would work. Another thought on a larger boat is simply - how many zones need to be heated at the same time? Might the whole situation improve with a slightly larger pump and some zone management for those times when the system just can't do all four at once? Anyway - just a few more random thoughts on the subject.