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Heating (and "free" aircon!) for electric boat


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Looking at heating solutions for the electric narrowboat I'll be getting built next year, I've been trying to find alternatives to the Eberspacher-type diesel heater -- because having gone to all the cost of electric drive to reduce diesel use and allow solar and shoreline power to be used as power sources as well (and charging points, whenever they happen...) it seems wrong to not do the same for heating. There are heat pumps available, albeit a bit big and expensive and not really the right size (3kW too small, 6kW too large):

 

https://www.kensaheatpumps.com/shoebox-ground-source-heat-pump/

 

While following up the recent "isn't it hot?" thread, in an idle moment I did a serach for marine aircon, and found that there might be a solution to both problems:

 

https://www.frigomar.com/en/products/self-contained-unit-inverter-bldc/

 

The biggest unit is rated at 16000BTU/h maximum which is 4.7kW -- perfect for a narrowboat -- and is capable of delivering this for both heating and cooling while drawing 1050W from 230Vac. This sounds a lot, but compared to driving an electric boat (3kW cruising, 15kW maximum) and all the other domestic electrical loads it's actually quite small -- especially since it can be throttled all the way down to 4000BTU (1.2kW) at which point it only consumes 200W. At a typical 2.5kW it consumes 450W to output 8500BTU/2.5kW.

 

It's designed for yachts so normally used with a freshwater inlet, but I don't see why it couldn't use a keel cooler just like the generator. The air would have to be ducted along the boat, there's space to do that either at floor level or under the gunwale.

 

CoP is 4.5 at full power and 5.9 at minimum power, 5.5 at 2.5kW typical. So even if all the power comes from the generator it'll use considerably less fuel than an Eberspacher, with a generator efficiency of 25% and 90% for the inverter (LiFePO4 charge+discharge at 95% each) the "efficiency" at 2.5kW is 125%  -- yes I know that's more than 100%, that's heat pumps for you. With an 8KW generator, 1 hour running would power the heater for 16 hours at 2.5kW output, so much lower power use than propulsion. In comparison, a 5kW Eberspacher (can throttle down to 1.5kW) is 70% efficient in terms of heat into the water compared to calorific value of the fuel (from the data sheet numbers).

 

With all power from the generator this is a 45% fuel/CO2 saving, a bit bigger than the 40% I estimated for propulsion. If some power comes from solar or shoreline this saviong will be even bigger, just like for propulsion -- could even be 100% (no diesel use at all) in summer with a lot of solar if the boat doesn't move too much.

 

And the huge "free" (see below...) bonus -- given what's been happening to our climate recently, and will happen more in the future -- is air conditioning throughout the boat. No more sweltering nights... 🙂

 

The downside is of course cost (about £5000?), just like electric drive and a generator -- but then the cost of this is several times higher still and I'm willing to pay that in exchange for the benefits. These types of systems are common in the yachting world and people seem happy with them, but they're notoriously willing to spend more money in exchange for comfort than most narrowboaters 😉

 

I'm sure some people will say this is technology gone mad, it'll all go wrong, why don't you use a wood stove/drip stove (because I don't want one...), what do you do if it breaks down (use a fan heater...), but to me it seems like a way to do the same for heating as the electric drive does for propulsion -- a clean quiet solution with lower emissions, and the potential in the future (with charging points...) to use no diesel at all.

 

I'd value some genuine comments about whether people think this could work in a narrowboat, and whether I've missed any obvious killer problems. I know I'll be a guinea-pig if this hasn't been tried before, but it's a risk I'm willing to take...

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33 minutes ago, IanD said:

These types of systems are common in the yachting world and people seem happy with them, but they're notoriously willing to spend more money in exchange for comfort than most narrowboaters 😉

 

 

They are widely used but not in the 'yachting' (rag & stick) world, where the hoarding of electricity is even more vital than it is on a NB.

Large Motor Yachts are regularly found with them, but they have either the engine running 24/7 or a generator.

 

We did look at them for the Cat when Med-cruising, but unable to find any way of powering it reliably.

Air-Con would have been welcomed when we chartered a yacht in Cambodia, the sea temperature was in the high 20s degrees and the skipper was extremely concerned that should it reach 30 it could spark off tornados and other unpleasent conditions. It was an Aluminium boat and it is the only time I have actually found it uncomfortable to sit on deck, or get into the water - I ended up sleeping on the sail spread out in the scuppers.

 

We spoke with (I think it was) Dometic and they said that the system would actual work in the North Sea temperatures, up to about level with Newcastle, as above there the temperature became too low, so there should be no problem with canal water temperatures.

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Posted (edited)
11 minutes ago, Alan de Enfield said:

 

 

They are widely used but not in the 'yachting' (rag & stick) world, where the hoarding of electricity is even more vital than it is on a NB.

Large Motor Yachts are regularly found with them, but they have either the engine running 24/7 or a generator.

 

We did look at them for the Cat when Med-cruising, but unable to find any way of powering it reliably.

Air-Con would have been welcomed when we chartered a yacht in Cambodia, the sea temperature was in the high 20s degrees and the skipper was extremely concerned that should it reach 30 it could spark off tornados and other unpleasent conditions. It was an Aluminium boat and it is the only time I have actually found it uncomfortable to sit on deck, or get into the water - I ended up sleeping on the sail spread out in the scuppers.

 

We spoke with (I think it was) Dometic and they said that the system would actual work in the North Sea temperatures, up to about level with Newcastle, as above there the temperature became too low, so there should be no problem with canal water temperatures.

Thanks for the feedback, Alan -- I meant large motor yachts, not sailing yachts, for the reasons you said.

 

The user manual says:

 

8. 0 WORKING LIMITS
The unit operates correctly within the following ranges:
· Summer cooling mode: 15°C < sea water temperature < 40°C
· Winter heating mode: 5°C < sea water temperature < 20°C
Should working conditions be out of these ranges, in your particular application, please contact Frigomar
before installation in order to find a suitable solution.

 

So should be mostly OK for canals, unless they freeze over (water temperature probably 4C at the bottom of the hull). It's not clear what happens outside these ranges, I expect that a keel-cooled closed-circuit filled with water/antifreeze/corrosion inhibitor would work colder but the unit might flag a "too cold" alarm and turn off. I'll ask the suppliers or the manufacturer.

Edited by IanD
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Terry Darlington had a marine air conditioning unit fitted to his narrowboat Phyllis May during his trip down the American East Coast in the book  Narrow Dog to Indian River when the heat became unbearable, although his boat had a conventional diesel propulsion engine.

 

 

Edited by cuthound
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1 hour ago, IanD said:

 

So should be mostly OK for canals, unless they freeze over (water temperature probably 4C at the bottom of the hull). It's not clear what happens outside these ranges, I expect that a keel-cooled closed-circuit filled with water/antifreeze/corrosion inhibitor would work colder but the unit might flag a "too cold" alarm and turn off. I'll ask the suppliers or the manufacturer.

A keel cooler is a second heat exchanger between the heat source (canal water) and the system refrigerant, which will introduce an additional temperature difference compared with a direct freshwater input. So with freshwater you could get the unit to work at a lower temperature. I think that second temperature difference will also reduce the system overall efficiency, which you don't really want. In other words, if the system is designed for fresh (or salt) water circulating through it, you should use it that way.

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Posted (edited)
6 minutes ago, David Mack said:

A keel cooler is a second heat exchanger between the heat source (canal water) and the system refrigerant, which will introduce an additional temperature difference compared with a direct freshwater input. So with freshwater you could get the unit to work at a lower temperature. I think that second temperature difference will also reduce the system overall efficiency, which you don't really want. In other words, if the system is designed for fresh (or salt) water circulating through it, you should use it that way.

I'm aware of all that (thermodynamics as part of engineering degree), but fresh water circulation is not a good idea on canals given the amount of crud (mud, weed, debris) in the water -- even on lumpy water boats, many people have said that intake/filter clogging is by far the biggest problem with this type of system. But with fibreglass hulls a keel cooler isn't a good option, unlike steel narrowboats.

 

I would fit a bigger keel cooler than would normally be used with this amount of heat to reduce any temperature difference and efficiency loss.

Edited by IanD
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33 minutes ago, IanD said:

 But with fibreglass hulls a keel cooler isn't a good option, unlike steel narrowboats.

 

For completeness, but tangentially off-topic.

 

Absolutely nothing wrong with a keel cooler on GRP or Wooden boats.  If you are happy with a dry exhaust, they are far more reliable than direct or indirect fresh water system. Even with a wet exhaust, all you risk with a full or partial failure is the exhaust hose rather than the engine.

 

I tend to agree with your thoughts on preferring a keel cooler solution, especially if it's larger than strictly required.

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Posted (edited)
1 hour ago, Tony Brooks said:

 

For completeness, but tangentially off-topic.

 

Absolutely nothing wrong with a keel cooler on GRP or Wooden boats.  If you are happy with a dry exhaust, they are far more reliable than direct or indirect fresh water system. Even with a wet exhaust, all you risk with a full or partial failure is the exhaust hose rather than the engine.

 

I tend to agree with your thoughts on preferring a keel cooler solution, especially if it's larger than strictly required.

Maybe I should have said "a more difficult option" -- good yes, but much harder to implement (and non-standard) than on a steel narrowboat hull where it's dead easy (and standard).

 

If the heater/aircon unit at full power can push 4.7kW of heat out through the keel cooler, that's probably similar to a diesel of around 6bhp output, for which the rule-of-thumb is that a third of the calorific value of the fuel goes into the exhaust, a third into the cooling system, and a third as useful power. The recommended keel cooler area for this would be about 1.5 square feet in a steel hull (4bhp/ft2), but that's with moving water not still, so I'd aim for at least double that or preferably more. Since the unit would be fitted at the stern, there's plenty of space to fit a keel cooler on the swim next to the electric motor, probably one each side to avoid the possibility of all the heat being dumped on the bank side with restricted water circulation.

 

https://betamarine.co.uk/keel-cooling-calculations/

 

It's all looking feasible... 😉

Edited by IanD
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2 minutes ago, IanD said:

Maybe I should have said "a more difficult option" -- good yes, but much harder to implement (and non-standard) than on a steel narrowboat hull where it's dead easy (and standard).

 

If the heater/aircon unit at full power can push 4.7kW of heat out through the keel cooler, that's probably similar to a diesel of around 6bhp output, for which the rule-of-thumb is that a third of the calorific value of the fuel goes into the exhaust, a third into the cooling system, and a third as useful power. The recommended keel cooler area for this would be about 1.5 square feet in a steel hull (4bhp/ft2), but that's with moving water not still, so I'd aim for at least double that or preferably more. Since the unit would be fitted at the stern, there's plenty of space to fit a keel cooler on the swim next to the electric motor, probably one each side to avoid the possibility of all the heat being dumped on the bank side with restricted water circulation.

 

https://betamarine.co.uk/keel-cooling-calculations/

 

It's all looking feasible... 😉

What about when you form ice on the outside of the hull in winter when the canal water is down to 4°C ?

3 minutes ago, IanD said:

  Since the unit would be fitted at the stern, there's plenty of space to fit a keel cooler on the swim next to the electric motor, probably one each side to avoid the possibility of all the heat being dumped on the bank side with restricted water circulation.

 

Are you having a water cooled motor?

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Posted (edited)
21 minutes ago, ditchcrawler said:

What about when you form ice on the outside of the hull in winter when the canal water is down to 4°C ?

Unlikely given the relatively low heat flux through the keel cooler; water density decreases below 4C so the water cooled below 4C will rise to the surface. I doubt the canal gets this cold much below the top few inches anyway when it's frozen over and water isn't mixing much.

 

But if it does happen then the heater will stop working, which is obviously a PITA. There's plenty of power available (10kW inverter+10kVA generator) to run a portable 3kW fan heater blowing into the ducting if this happens (or maybe a plinth fan heater), at the cost of having to run the genny more -- and I don't intend to liveaboard full time, so the chances of being away on the boat when it's this cold are small.

 

When you've got enough power and battery capacity to run a 15kW drive motor (and a 10kVA onboard generator), there are lots more electrical possibilities than on a normal diesel boat... 😉

Edited by IanD
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I second the points about needing a larger keel cooler.  Moving through the water greatly increases the effectiveness of a skin tank.  My 6 kVA generator, working fairly hard,  has much  the same effect on the skin tank as the 22 HP main engine at Thames speeds.

Heat sourcing and dumping via a skin tank will require careful siting of the unit to get the essential water flow rates and it may need a supplementary circulating pump. Much will depend on the unit's internal pump.

 

The quoted CoP figures look optimistic to me.  Modern refrigerants have generally resulted in worse thermodynamic performance, albeit more ozone friendly.  I would want to look carefully at the evidence to be sure they can be achieved in the real world.  It would not be the first time enthusiasm has triumphed over accuracy in a sales document.

If you do go for it, please keep us posted.

N

 

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43 minutes ago, IanD said:

Unlikely given the relatively low heat flux through the keel cooler; water density decreases below 4C so the water cooled below 4C will rise to the surface. I doubt the canal gets this cold much below the top few inches anyway when it's frozen over and water isn't mixing much.

 

But if it does happen then the heater will stop working, which is obviously a PITA. There's plenty of power available (10kW inverter+10kVA generator) to run a portable 3kW fan heater blowing into the ducting if this happens (or maybe a plinth fan heater), at the cost of having to run the genny more -- and I don't intend to liveaboard full time, so the chances of being away on the boat when it's this cold are small.

 

When you've got enough power and battery capacity to run a 15kW drive motor (and a 10kVA onboard generator), there are lots more electrical possibilities than on a normal diesel boat... 😉

 

Will you be fitting a secondary source of heating to provide redundancy should one fail?

 

If so what would be the secondary source of heat?

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8 minutes ago, cuthound said:

 

Will you be fitting a secondary source of heating to provide redundancy should one fail?

 

If so what would be the secondary source of heat?

What I said -- backup would be fan heater(s).

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18 minutes ago, IanD said:

What I said -- backup would be fan heater(s).

 

Must have missed that bit. What happens when the genny fails during a cold spell? Surely that is a common point of failure?

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I think the heat exchanger / skin tank idea for heating, is problematic. Bear in mind that heat transfer through a heat exchanger is proportional to the temperature difference. With a conventional Diesel engine dumping maybe 5kw at a typical low engine power for canal use, the temperature difference is perhaps 60C (say 75c engine, 15C water).

 

But if you want to heat from canal water at 5C and pass 5kw and accept say 0C as the circulating temperature (ie 5C temperature difference, you need 12 times the area, which is a lot! Ok you can probably I put more realistic figures into that, but the outcome I suspect will still be a requirement for a huge skin tank to minimise the temperature difference between canal water and circulating water in winter.

 

Perhaps you could use the entire base plate as the heat exchanger? Some kind of metal pipework (thermally) close coupled to the baseplate, or even make the entire baseplate into a skin tank by having a steel layer above, sandwiching in a cavity (with baffles)?

 

But anyway my point is that you need to do the sums to check feasibility.

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Have to agree with the OP. Ive also never been able to understand the point of going to all the trouble and expense of installing electric propulsion when you're probably still burning a lot more fossil fuel, either coal or diesel to heat the boat. In that context, unless perhaps you're doing a lot of cruising, electric propulsion seems like tokenism.

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37 minutes ago, blackrose said:

Have to agree with the OP. Ive also never been able to understand the point of going to all the trouble and expense of installing electric propulsion when you're probably still burning a lot more fossil fuel, either coal or diesel to heat the boat. In that context, unless perhaps you're doing a lot of cruising, electric propulsion seems like tokenism.

Which is why I'm trying to find a better solution for heating. To be honest, for me emissions reduction/running costs is not the reason for going electric, silent cruising is. If every narrowboat in the UK went electric, the CO2 reduction would be 1000x smaller than if all cars switched to BEV. And the fuel savings would take tens of years to pay back the higher cost of installation. 

55 minutes ago, nicknorman said:

I think the heat exchanger / skin tank idea for heating, is problematic. Bear in mind that heat transfer through a heat exchanger is proportional to the temperature difference. With a conventional Diesel engine dumping maybe 5kw at a typical low engine power for canal use, the temperature difference is perhaps 60C (say 75c engine, 15C water).

 

But if you want to heat from canal water at 5C and pass 5kw and accept say 0C as the circulating temperature (ie 5C temperature difference, you need 12 times the area, which is a lot! Ok you can probably I put more realistic figures into that, but the outcome I suspect will still be a requirement for a huge skin tank to minimise the temperature difference between canal water and circulating water in winter.

 

Perhaps you could use the entire base plate as the heat exchanger? Some kind of metal pipework (thermally) close coupled to the baseplate, or even make the entire baseplate into a skin tank by having a steel layer above, sandwiching in a cavity (with baffles)?

 

But anyway my point is that you need to do the sums to check feasibility.

I intend to do just that 😉

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2 hours ago, cuthound said:

 

Must have missed that bit. What happens when the genny fails during a cold spell? Surely that is a common point of failure?

There are always single points of failure in a boat, or anything else. If the hull leaks, you sink. If the engine fails (or you run out of diesel), you can't go anywhere -- and you don't have any lights or power. If the gas runs out (in most boats) you can't cook anything.

 

In a house, if your central heating fails in winter, you get very cold -- and if the mains goes off, nothing works and it gets dark *and* cold. If the water supply goes off you have big problems. If the gas goes off you can't cook or have any heating.

 

A generator failing in a cold spell is no different to any of these, there's no backup except to get it fixed ASAP or go home if you're not a liveaboard. It's not any worse -- or better -- than any of the above cases.

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From personal experience I have fitted two of these systems. The first was using a skin tank, the supplier wanted us to use a water intake but the owner insisted on a skin tank it did not work. 

The systems was totally reinstalled within the year. The second did not use a skin tank worked first time. 

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11 hours ago, IanD said:

There are always single points of failure in a boat, or anything else. If the hull leaks, you sink. If the engine fails (or you run out of diesel), you can't go anywhere -- and you don't have any lights or power. If the gas runs out (in most boats) you can't cook anything.

 

In a house, if your central heating fails in winter, you get very cold -- and if the mains goes off, nothing works and it gets dark *and* cold. If the water supply goes off you have big problems. If the gas goes off you can't cook or have any heating.

 

A generator failing in a cold spell is no different to any of these, there's no backup except to get it fixed ASAP or go home if you're not a liveaboard. It's not any worse -- or better -- than any of the above cases.

 

Of course there are always single points of failure, however the decision on whether or not to provide redundancy should be dependent upon impact of failure, likelihood of failure and time to repair.

 

The hull is unlikely to fail suddenly, providing it is maintained adequately at a reasonable periodicity.  Most boats have 2 or 3 gas bottles to prevent the hardship caused by thrm running out.

 

I disagree that loss of heating is no different. Loss of heating in winter is likely to result in divorce in my household, so it is something I would try to ensure didn't have a single point of failure. On an all electric boat with a built in generator i i would consider carrying a suitcase generator just to provide heating if the main generator failed.

 

In my experience (48 years boating, including 23 years of shared ownership and 7 of

sole ownership) after water pumps and batteries, engines are most likely to suffer issues.

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1 hour ago, cuthound said:

 

Of course there are always single points of failure, however the decision on whether or not to provide redundancy should be dependent upon impact of failure, likelihood of failure and time to repair.

 

The hull is unlikely to fail suddenly, providing it is maintained adequately at a reasonable periodicity.  Most boats have 2 or 3 gas bottles to prevent the hardship caused by thrm running out.

 

I disagree that loss of heating is no different. Loss of heating in winter is likely to result in divorce in my household, so it is something I would try to ensure didn't have a single point of failure. On an all electric boat with a built in generator i i would consider carrying a suitcase generator just to provide heating if the main generator failed.

 

In my experience (48 years boating, including 23 years of shared ownership and 7 of

sole ownership) after water pumps and batteries, engines are most likely to suffer issues.

That's your point of view as a liveaboard, which I don't disagree with for your case. Mine is different, as I will be a "holiday home" boater. The point about the hull was a joke, in case you hadn't realised 😉

 

Of course you have to consider all the possible failures, just like in a house, but there are always some where there is no backup. The key is to avoid the really obvious and common ones where possible. On an essentially electric boat, unless there's enough solar power (unlikely in winter) the whole system relies on the generator. Maybe a suitcase generator would be an emergency backup, as you suggest.

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2 minutes ago, IanD said:

 

 

Of course you have to consider all the possible failures, just like in a house, but there are always some where there is no backup.  

With most modern houses its electricity, no electricity = no cooking, no hot water, no heating, no communication

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5 hours ago, Keith M said:

From personal experience I have fitted two of these systems. The first was using a skin tank, the supplier wanted us to use a water intake but the owner insisted on a skin tank it did not work. 

The systems was totally reinstalled within the year. The second did not use a skin tank worked first time. 

Thanks Keith for some actual experience. When you say "these systems" do you mean the Frigomar one in particular or something similar? What was the power rating and how big was the skin tank?

 

I'm well aware that this could be an issue, I'm going to do some calculations to try and work out how big a skin tank might be needed to make it work. I think it would be easy to get in 1m2 of tank (the size normally used for a Beta 43) for the 4.7kW Frigomar.

 

If this really is a non-starter then of course I can go back to freshwater cooling as designed, but I'm also aware that people doing this have had many complaints about intake blocking. Maybe what's needed is a grille/mud box with the actual intake inside, to stop it getting blockes so easily compared to a simple pipe surface fitting.

Just now, ditchcrawler said:

With most modern houses its electricity, no electricity = no cooking, no hot water, no heating, no communication

My point precisely.

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2 minutes ago, IanD said:

That's your point of view as a liveaboard, which I don't disagree with for your case. Mine is different, as I will be a "holiday home" boater. The point about the hull was a joke, in case you hadn't realised 😉

 

Of course you have to consider all the possible failures, just like in a house, but there are always some where there is no backup. The key is to avoid the really obvious and common ones where possible. On an essentially electric boat, unless there's enough solar power (unlikely in winter) the whole system relies on the generator. Maybe a suitcase generator would be an emergency backup, as you suggest.

 

I'm not a liveaboard, like you I am a leisure boater! I do however have a canalside house with an end of garden mooring.

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1 minute ago, IanD said:

   Maybe what's needed is a grille/mud box with the actual intake inside, to stop it getting blockes so easily compared to a simple pipe surface fitting.

Something like @Biggles put on his boat

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