Heat pump heating

[sgr143]

Pondering the chilliness of my boat at night at this time of year , and thinking in terms of the gradual move away from diesel, I was wondering if heat-pump heating is now, or might be soon be, an option, rather than the diesel-based heaters. . It seems to be what is now done for heating on electric cars , though I think their system voltages are rather higher than a boat's lowly 12V.
I did have a brief look online, but boaty heat-pump stuff seemed to be about air-conditioning rather than heating, and heat-pumps for heating seemed to be all about 240V domestic installations.
Any thoughts?

 

[dunedin]

The energy density of diesel is much greater than batteries - 1L diesel equivalent to 10kWh battery. Away from shore power I doubt electric heating will be very effective.

 

[neil_s]

From what I've read, in a domestic 240v heat pump installation, you get out about three times the heat compared to the electricity used. I guess if you want about 1Kw out, that means you have to put 330w in. To run that heat pump is going to take 28 amps from your battery system. This assumes you have lots of thermal insulation and 1Kw is going to be enough - and that a small heat pump system can match the efficiency of a domestic set up. My battery would keep that going for about two hours. I guess I've got to keep the Valor paraffin for a while, yet!

 

[sgr143]

From what I've read, in a domestic 240v heat pump installation, you get out about three times the heat compared to the electricity used. I guess if you want about 1Kw out, that means you have to put 330w in. To run that heat pump is going to take 28 amps from your battery system. This assumes you have lots of thermal insulation and 1Kw is going to be enough - and that a small heat pump system can match the efficiency of a domestic set up. My battery would keep that going for about two hours. I guess I've got to keep the Valor paraffin for a while, yet!

I reckon you are right - those numbers stack up pretty well. 3:1 is what I've heard, too. Back to the hot water bottle from the gas stove and a good thick sleeping bag for me!

I did meet and had a chat last year at Lymington with a chap whose boat had an absolutely massive solar array - I can't remember the exact number but it made me whistle; batteries to match too. All-electric cooking and other domestic gear for a family liveaboard. I guess when you're talking about electric-car equivalent battery banks it begins to make more sense.

 

[Boater Sam]

Using electricity for heating when you have to recharge batteries is totally useless.

 

[William_H]

If you look at boat airconditioning look for the term "reverse cycle" which here in oz means a heat pump that can switch from cooling to heating. ol'will

 

[Dave 71]

Modern heat pumps can be a lot higher than 3:1 these days, the technology has come on some way, at least for use on land. 3:1 might be a good rule of thumb for an air source heat pump in cold weather, which extracts heat from the air. Water or ground source heat pumps will be higher as the water or ground temperature is higher, so for each kWh of heat provided, less input energy is needed. With a stable source temperature from sea water, 6:1 would be possible, so 2kW of heat would need about 300W input. That's at full output, once up to temperature inside the boat it would back off a bit.
A heat pump is basically an air conditioner (or a 'fridge motor' for that matter) running backwards so can heat or cool. Some boats in warmer climates have air con, so if you can run air con from batteries you can run it in heating mode, the physics dictate that there will always be more output in heating than in cooling mode. I don't know the exact arrangement of a boat's air conditioning, but would imagine they either use (or could be arranged to use) a seawater cooling circuit and heat exchanger in a similar way to a diesel engine or a plate of some kind fixed outside the hull as a heat exchanger rather than extracting heat from the air. That would make them much more efficient. Power draw off of batteries and charging would still be an issue but new battery tech will overcome that and I would think as we move away from fossil fuels it will become the norm, with some sort of cross over tech from the car industry being marinised for use in production boats, I think some high end stuff (say an Oyster or similar) might use semi-bespoke heat pump/air con systems. Their customers probably aren't put off by the cost which is just hidden in the overall price tag. So it would be possible to retro fit, but likely to be expensive and complicated.

 

[Stemar]

Drawing your heat from water at 8 or 9 deg in the southern UK will work better than air at 4 deg, or 4 deg water instead of 0 in the N Sea, but storing enough power to run the system is going to be a significant issue unless you've got a fairly generous mains connection.

Uma has just about everything else electric, but they have a solid fuel stove for heating. I'm sure that if it was doable with current technology, they'd be doing it.

 

[Tintin]

The two guys who started Kensa over 22 years ago got into HP tech while they were working on superyachts as skipper and engineer. Heat pumps have been used in SY's for decades for AC, refrigeration (obvs) and heating.

Kensa is one of the world's leading ground source heat pump companies, manufacturing in Cornwall, part owned now by Legal and General, and now employs over 160 people down here. They also developed and supplied the robust heat pumps for the RNLI Tamar class lifeboats.

My only connection is I know them well, sail with one of them every now and then, and my business is a complementary technology (ufh).

An issue to overcome for low voltage systems is the large start up current for the compressors, but to a certain extent "soft start" tech has helped.

 

[Daverw]

Running off battery for short periods even 500w not a real issue but for a heat pump unlike a fridge will very rarely cycle in use and would be difficult to maintain along with other loads. If you have a gen set no issue and would work but then why would you not use eber etc

 

[geem]

Modern heat pumps can be a lot higher than 3:1 these days, the technology has come on some way, at least for use on land. 3:1 might be a good rule of thumb for an air source heat pump in cold weather, which extracts heat from the air. Water or ground source heat pumps will be higher as the water or ground temperature is higher, so for each kWh of heat provided, less input energy is needed. With a stable source temperature from sea water, 6:1 would be possible, so 2kW of heat would need about 300W input. That's at full output, once up to temperature inside the boat it would back off a bit.
A heat pump is basically an air conditioner (or a 'fridge motor' for that matter) running backwards so can heat or cool. Some boats in warmer climates have air con, so if you can run air con from batteries you can run it in heating mode, the physics dictate that there will always be more output in heating than in cooling mode. I don't know the exact arrangement of a boat's air conditioning, but would imagine they either use (or could be arranged to use) a seawater cooling circuit and heat exchanger in a similar way to a diesel engine or a plate of some kind fixed outside the hull as a heat exchanger rather than extracting heat from the air. That would make them much more efficient. Power draw off of batteries and charging would still be an issue but new battery tech will overcome that and I would think as we move away from fossil fuels it will become the norm, with some sort of cross over tech from the car industry being marinised for use in production boats, I think some high end stuff (say an Oyster or similar) might use semi-bespoke heat pump/air con systems. Their customers probably aren't put off by the cost which is just hidden in the overall price tag. So it would be possible to retro fit, but likely to be expensive and complicated.

Rule of thumb for ASHP efficiency is 2.7:1. GSHP efficiency is 3.5:1. These are seasonly adjusted figures that allow for the sometimes very cold air temperatures as well as milder temperatures where efficiency will increase.
It's not practical to run heat pumps off batteries on small boats even with LifePO4 batteries since you still need to put the energy back in. Not an issue on a large yacht or motor yacht where running generators 24/7 is the norm.
From my understanding of a few Captains on Oysters, they rarely run AC at anchor if ever. They save that for when they are in a marina.

 

[jwilson]

I have never been aboard a boat that could run it's A/C or heating from batteries for more than minutes or at most an hour or so at a time, even with a huge battery bank. Plenty of 'all-electric' boats, but the electricity comes from a genset running on diesel or shorepower.

 

[Zing]

I have an efficient air-con (i.e a heat pump) , which will heat and cool (reverse cycle). 10,000 BTU max and that is achieved at less than 700w including the seawater pump. I run it all night on batteries at very low current draw, about 150w as it modulates down and then lower as it cycles on and off. Heating performance is similar. You need batteries to match or to have constant power available obviously. This type has very low start up peaks and is pretty quiet.

See here, where there are performance curves for various models: Self Contained Unit - Inverter BLDC - FRIGOMAR

 

[geem]

I have an efficient air-con (i.e a heat pump) , which will heat and cool (reverse cycle). 10,000 BTU max and that is achieved at less than 700w including the seawater pump. I run it all night on batteries at very low current draw, about 150w as it modulates down and then lower as it cycles on and off. Heating performance is similar. You need batteries to match or to have constant power available obviously. This type has very low start up peaks and is pretty quiet.

See here, where there are performance curves for various models: Self Contained Unit - Inverter BLDC - FRIGOMAR

I know you are running LifePO4. Sounds like good kit with better than 4:1 COP ?

 

[Zing]

I know you are running LifePO4. Sounds like good kit with better than 4:1 COP ?

Yes, in truth a bit worse than that due to inverter losses (8% from memory) and there is a similar battery charger loss plus some very small peukert loss. So all in, maybe low 3 ish. Actually if you factor in the generator engine and alternator losses it ends up at near to 1. Solar self sufficiency is my ambition.

 

[geem]

Yes, in truth a bit worse than that due to inverter losses (8% from memory) and there is a similar battery charger loss plus some very small peukert loss. So all in, maybe low 3 ish. Actually if you factor in the generator engine and alternator losses it ends up at near to 1. Solar self sufficiency is my ambition.

We are solar self sufficient for all power needs and hot water but not the watermaker. We run the genset for 15 mins a day for our fresh water. We make about 50 litres a day. no Aircon but not something we ever crave apart from when in the boatyard in Curacao.
The genset does less than 100 hrs per year

 

[Zing]

We are solar self sufficient for all power needs and hot water but not the watermaker. We run the genset for 15 mins a day for our fresh water. We make about 50 litres a day. no Aircon but not something we ever crave apart from when in the boatyard in Curacao.
The genset does less than 100 hrs per year

Get a DC energy recovery watermaker. Mine is great (Schenker 30). You can then probably ditch the genset. You will use less than 0.2 kWh per day for your 50 lts.

 

[V1701]

An aside but I was talking to somebody the other day, or rather they accosted me as I was walking back to the boat to ask what I thought of the idea of painting his entire boat black. To my predictable reply that he would cook in there in the summer he said "you're not the first person who's told me that but I'll get a portable air con in there to cool it down". All on a Westerly 25, go figure...

 

[geem]

Get a DC energy recovery watermaker. Mine is great (Schenker 30). You can then probably ditch the genset. You will use less than 0.2 kWh per day for your 50 lts.

I have been the 12v watermaker route previously. It's not for me. Far happier with a 200 l/hr generator run watermaker. Super simple. No energy intensifier pump.
We use our spare solar power to make hot water and we run the ice machine.
I have a 155 ah alternator (@24v) to install. This will mean we will be able to run the watermaker when the main engine is running via the 3kw inverter. It will be our back up system.
We wouldn't want to be without the generator so it's good to use it. We only need to do a single oil change each year and it's very fuel efficient.

 

[Zing]

I have been the 12v watermaker route previously. It's not for me. Far happier with a 200 l/hr generator run watermaker. Super simple. No energy intensifier pump.
We use our spare solar power to make hot water and we run the ice machine.
I have a 155 ah alternator (@24v) to install. This will mean we will be able to run the watermaker when the main engine is running via the 3kw inverter. It will be our back up system.
We wouldn't want to be without the generator so it's good to use it. We only need to do a single oil change each year and it's very fuel efficient.

We are on different paths. There are clearly many ways to skin a cat ( and cat pumps). I’ve switched to the low energy one from the high pressure version. Quiet, cool and low energy. I’m also working up to ditching the genset. Noisy, hot and unreliable.

It sounds like your engine may soon to fulfil the role of genset if you were to ever need one, but I‘d be surprised if you can run your watermaker off your inverter. I can’t run my old one easily off a 5kw inverter (2.5kw motor). Start up loads are on the limit. Have you tried it?