Small heat pump water heater and floor heat - Ram Promaster Forum
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post #1 of 15 Old 05-23-2019, 09:04 AM Thread Starter
epicsurf
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Small heat pump water heater and floor heat

Im really interested in finding a small air to water heat pump to heat water for showers and also use for hydronic floor heating. Does anyone know if this even exists? It would also need a small tank. This in my view would be the most ideal setup since it would be very efficient, serve two purposes, would not use any fuel, and would provide the best type of heat (floor heat) in a high altitude environment. It would require a large battery and solar system and possibly a portable backup generator for emergencies. Thoughts?
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post #2 of 15 Old 05-23-2019, 03:07 PM
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https://www.alibaba.com/products/hea...chScene=cpsp4p

A quick check revealed some 600, 700 watt input models.. unknown is how they deal w/ endless loop small-volume recirculating circuits...

A few of them claim switching over to water-chiller functions...


Maybe a neat idea for my Airstream rehab

================

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post #3 of 15 Old 05-23-2019, 07:44 PM
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I have seen systems that will loop into the coolant system in the car but installation is complex and costly so I never really looked into it.

Current caretaker of the Backroader 159" wb
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post #4 of 15 Old 05-24-2019, 07:48 AM
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I know you don’t want this system but a diesel or gasoline hydronic heater would do both the radiant heat and the tank heat. With a high altitude kit it has a service interval of something like 3000 hours. Really small heat pumps will eventually come but even with a high EER they are going to require an electrical system more expensive than the fuel heaters total installed cost.

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post #5 of 15 Old 05-24-2019, 02:52 PM
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Quote:
Originally Posted by RDinNHandAZ View Post
I know you dont want this system but a diesel or gasoline hydronic heater would do both the radiant heat and the tank heat. With a high altitude kit it has a service interval of something like 3000 hours. Really small heat pumps will eventually come but even with a high EER they are going to require an electrical system more expensive than the fuel heaters total installed cost.
About how much is that?

The simplest and least-cost heating system Im aware of is electric resistance, but that assumes we have where to plug in. If we have to power from batteries that are charged from solar or alternator, then the cost obviously goes way up.

Im curious where the cost of diesel or propane heaters fall in comparison. On principle Id like to go all electric, but battery cost can get high quickly.
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post #6 of 15 Old 05-24-2019, 04:19 PM
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The Espar is available for about $995 from:
https://www.lubricationspecialist.co...y-start-timer/
or $1150 from UK shipped free:
https://www.ebay.com/itm/ESPAR-D5W-S...wAAOSwkjtbIR4e

This is just $200 more than one Lithium Battleborn! Installed it will be much cheaper than electric and can radiant heat through PEX, heat a tank, etc. Electric resistance would require you to plug in.

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post #7 of 15 Old 05-24-2019, 07:30 PM
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,

Hi,

Some thoughts on using a small air to water heat pump to heat the van...


I looked around for something that might work, but could not find anything small enough for what you want -- does not mean there is not one out there.
Daikin has some for houses, but even the smallest one is pretty large for an RV (19000BTU/hr).


If you could find one with a typcal COP (basically efficieny) of 3.5 of the right size, this is an estimate of how much it might pull out of your battery on a cold night. I recorded propane use on a winter trip, and with an outside temp of about 24F, the propane use for my 78% efficient furnace average 0.58 gallons, or 54,000 BTU. At 100% efficieny, this would have been 42,000 BTU or 12,300 watt-hrs.

With the 350% efficiency of your heat pump, it would be 12300/3.5 = 3500 Watt-hrs. This would be about (3500 watt-hr)/(12volts) = 292 amp-hrs from the battery for an overnight of heating, but with a 90% efficient inverter, it would be more like 325 amp-hrs.


So, 325 amp-hrs to provide heat overnight in a pretty well insulated van at 24F outside.



Heating water would add to this. Roughy, heating 5 gallons from 60F to 110F with the same 3.5 COP would be another about 55 amp-hrs.



I think in the end you might need something like 500 amp-hrs of Li batteries, or quite a bit more in lead acid batteries.
This assumes you do a good job of insulating and have thermal window covers -- if you did a really really reallt good job of insulating, you might cut the battery drain in half.


If you use tubing in the floor to heat, then you want to make sure you have lots of insulation under the tubes to prevent a lot of heat loss out the bottom of the van. Maybe a couple inches of polyiso. This and the tubes will make be floor thicker -- maybe about 3 inches thick? This thick floor will effect your headroom.


If you want to use this setup for cooling as well as heating....
The amount of cooling you can get with cold water through floor tubes is limited because if you go too low in temperature with the floor tube water, you will get condensation on the floor. This will limit your cooling capacity unless you add something like a fan coil unit inside for cooling.

And, during summer, the heat pump will have to run one way to heat your water, and the opposite way to provide cooling -- this complicates things. I think that the Daikin units have worked out a way to do this, but I'm guessing it involves several elecrically actuated valves.


So, it seems like a feasible approach (if you can find the heat pump), but pretty challenging, and probably pretty expensive.


Gary

136 WB PM, high roof, 1500, gasser, 2014.
SW Montana
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Last edited by GaryBIS; 05-24-2019 at 10:59 PM.
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post #8 of 15 Old 05-24-2019, 10:11 PM
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Quote:
Originally Posted by GaryBIS View Post

......cut.....

If you could find one with a typcal COP (basically efficieny) of 3.5 of the right size, this is an estimate of how much it might pull out of your battery on a cold night. I recorded propane use on a winter trip, and with an outside temp of about 24F, the propane use for my 78% efficient furnace average 0.58 gallons, or 54,000 BTU. At 100% efficieny, this would have been 42,000 BTU or 12,300 watt-hrs.

With the 350% efficiency of your heat pump, it would be 12300/3.5 = 3500 Watt-hrs. This would be about (3500 watt-hr)/(12volts) = 292 amp-hrs from the battery for an overnight of heating, but with a 90% efficient inverter, it would be more like 325 amp-hrs.


So, 325 amp-hrs to provide heat overnight in a pretty well insulated van at 24F outside.


.....cut.....
Gary, thanks for estimates.

Your 12,300 Watt-hours seems mostly consistent with us being able to heat our uninsulated window van with 1500-Watt heater. We rarely use the 1500 Watt setting because 1000 Watts is normally enough. However, at 24 F we would need to run it on high, or 1500 Watts. With good insulation Id guess cutting that in half is very doable. Ive thought a 750/500 Watt heater would heat a well insulated van enough to get by.

Anyway, the one comment I wanted to make is that 24 F is tough duty for a heat pump. Heat pump performance starts to drop off at colder temperatures, and can become ineffective in cold humid environment because of icing up. My question is whether you guessed at COP of 3.5 at 24F, or did you base that on an actual heat pump?
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post #9 of 15 Old 05-24-2019, 10:55 PM
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Hi Chance,
Good point -- I just got the 3.5 off the specs for a couple of heat pumps I took a look at. I'd guess they pick a pretty favorable set of conditions to determine the COP, so probably optimistic for more challenging conditions.


I know minisplit style heat pumps have a cutoff temperature below which they shut down and make no heat at all. I guess some sort of backup resistance heater would be needed if operating in really cold weather, but battery drain would be high.



Gary

136 WB PM, high roof, 1500, gasser, 2014.
SW Montana
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post #10 of 15 Old 05-27-2019, 10:43 PM Thread Starter
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Quote:
Originally Posted by GaryBIS View Post
Hi,

Some thoughts on using a small air to water heat pump to heat the van...


I looked around for something that might work, but could not find anything small enough for what you want -- does not mean there is not one out there.
Daikin has some for houses, but even the smallest one is pretty large for an RV (19000BTU/hr).


If you could find one with a typcal COP (basically efficieny) of 3.5 of the right size, this is an estimate of how much it might pull out of your battery on a cold night. I recorded propane use on a winter trip, and with an outside temp of about 24F, the propane use for my 78% efficient furnace average 0.58 gallons, or 54,000 BTU. At 100% efficieny, this would have been 42,000 BTU or 12,300 watt-hrs.

With the 350% efficiency of your heat pump, it would be 12300/3.5 = 3500 Watt-hrs. This would be about (3500 watt-hr)/(12volts) = 292 amp-hrs from the battery for an overnight of heating, but with a 90% efficient inverter, it would be more like 325 amp-hrs.


So, 325 amp-hrs to provide heat overnight in a pretty well insulated van at 24F outside.



Heating water would add to this. Roughy, heating 5 gallons from 60F to 110F with the same 3.5 COP would be another about 55 amp-hrs.



I think in the end you might need something like 500 amp-hrs of Li batteries, or quite a bit more in lead acid batteries.
This assumes you do a good job of insulating and have thermal window covers -- if you did a really really reallt good job of insulating, you might cut the battery drain in half.


If you use tubing in the floor to heat, then you want to make sure you have lots of insulation under the tubes to prevent a lot of heat loss out the bottom of the van. Maybe a couple inches of polyiso. This and the tubes will make be floor thicker -- maybe about 3 inches thick? This thick floor will effect your headroom.


If you want to use this setup for cooling as well as heating....
The amount of cooling you can get with cold water through floor tubes is limited because if you go too low in temperature with the floor tube water, you will get condensation on the floor. This will limit your cooling capacity unless you add something like a fan coil unit inside for cooling.

And, during summer, the heat pump will have to run one way to heat your water, and the opposite way to provide cooling -- this complicates things. I think that the Daikin units have worked out a way to do this, but I'm guessing it involves several elecrically actuated valves.


So, it seems like a feasible approach (if you can find the heat pump), but pretty challenging, and probably pretty expensive.


Gary
Thanks for helping me figure out if it will be feasible and based on this I'm back to a fuel heater. Running all the pex tubing through the floor would be tricky too. Bummer.
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