AGP in the UK & considering a bioheater diesel/propane based heater - anyone any experience with please?

Jump to latest Follow Reply
M

mister_rossi_x

Member
Apr 10, 2024
16
Leicestershire
Hi all

Looking for some help and advice on my possible pool set up please. I'm looking at a 2.4m X 3.9m above ground pool (8150 Litres, 1795 US Gallons) - or similar - and the best way to heat & insulate in the UK (East Midlands) weather, to preferably get 9 months usage (25C/77F min for "energetic exercising" - there will be a counter current system - but be nice to be closer to 27C/81F for the missus and kids).

I've been considering a Rexener bioheater or similar diesel/propane based heater, especially after my positive experiences with a Chinese Diesel Heater (CDH) I use in my campervan. These seem to be a very efficient, cheap & quick way to heat a pool or spa, yet I can't seem to find any info about them on here... lots about heat pumps (wary of after a bad experience 10 years ago; they may have improved!?), gas heaters (expensive/tricky to fit in my scenario), standard electric heaters and solar heating - anyone have any experience please with a bioheater / CDH type heater?

The website selling one of the pools I'm considering suggests a 17kw electric heater for that pool for 9 months of the year. This gives out 58,000 BTU.

By my calculations (I can share but didn't want to get too technical on my 1st post - plus they may be horribly wrong!) the Rexener Bioheater I saw is 20kw (68,240 BTU) and would raise that volume of water by 4.6C per hour (minus heat loss - pool would be covered/enclosed somehow to avoid evaporation which I believe is the largest heat loss). Let's say just under 4C per hour.

In terms of keeping the pool up to temp, estimating heat loss overnight (down to 10C) and comparing to my 2kw electric heated hot tub (1190l / 314 US Gal), I'd run it approx. 5 hours a day (ignoring the initial heating); that's 5 times less a day than the hot tub (24hr) but 8.5 times more power so 1.7 times more "expensive", roughly - if it were electricity. But it's not, it's diesel/propane based, so will be much cheaper - no idea how to work that out yet!! I think I'll drop Rexener an email and see if I can get some litre per hour figures from them.

Does this all sound about right?? Am I missing anything obvious?? I'd love to bury the pool to help insulation but that will be very difficult/expensive in my situation and from what I understand, heat loss from the sides/bottom is minimal - need to ensure the pool is covered as much as possible to avoid heat loss from evaporation. Considering some form of polytunnel / acrylic cover to add a little from solar energy (south facing garden... but... UK midlands, so not much sun!!).

Many thanks all in advance!
Ross
 
Hi everyone

I'm planning on fitting an above ground pool in the UK, and I have some questions about heating and heat loss calcs.

I've posted separately in the AGP section for advice on a bioheater; doesn't seem to be a common thing in the US so forgetting that point for a moment (although the following questions matter as I have to think about how much diesel I have to use!!), I've got some queries on a heater (regardless of the type, but lets say it's 100% efficient for the sake of the math) that provides 20kw / 68,240 BTU.

I'm looking at a 2.4m X 3.9m AGP (8150 Litres, 1795 US Gallons) in the UK (East Midlands) weather, to preferably get 9 months usage (25C/77F min for "energetic exercising" - there will be a counter current system - but be nice to be closer to 27C/81F for the missus and kids). Based on the formula (UK numbers - TR temp rise in C, V volume in l, P power in BTU):

TR = P / 4V

The 68k BTU heater will raise my temp by around 2C an hour.

So let's imagine some temperature scenarios:

Cold days - to heat from 10C to 27C will require just over 8hrs running
Slightly milder days - 15C to 27C will require around 6hrs
Warmer days - 18C to 27C will require just over 4hrs

My question is: how much heat loss is realistic to expect overnight, when I've got a covered (probably a telescopic type plastic/acrylic semi circle polytunnel enclosure) AGP, in the UK?

Say it's a spring day, getting to 18C (air temp, in the shade) in the day, but drops to 10C (air temp) overnight. I heat the pool water during the day to 27C. How much will the pool water be first thing in the morning? Will it have dropped to 10C, or will it be more like, say, 15C? Any way to "roughly" calculate?

I know water will eventually reach the same temp as the air, but it takes a long time to do that.... but how long, for that volume of water?! For example, my Lay-Z-Spa hot tub, if off for 8 hours on a cool day (15C air temp) will drop from 40C to about 32C. Is there a way to extrapolate that heat loss - i.e. that's 1C an hour. Can I expect the same for the pool or is it 5 times more heat loss (pool is approx. 5 times larger)??

Many thanks
Ross
 
Hi Ross,

I had a similar sized pool AGP (but round) setup in Kent, UK in 2021, I did not have any form of heating. Here's some of the numbers from back then that I'd recorded in the PoolMath app that might give you an idea of what to expect as a baseline without heating.

I've added the weather that was recorded by the app as well to give some context. Your fill water will likely be around 11C but once it we get into summer it's not likely to drop below 18C as a baseline. Definitely get a solar cover to keep the heat in, I'd keep the cover on whenever I wasn't using it.

Date​
Temp​
Weather Temp​
Weather​
2021-08-12 22:22:38​
21.8​
22​
cloudy​
2021-08-10 13:04:05​
20.3​
20​
sunny​
2021-08-09 12:42:55​
19.1​
18​
mostly cloudy​
2021-08-08 10:34:43​
19.3​
19​
cloudy​
2021-08-05 15:43:50​
21.5​
21​
sunny​
2021-08-04 11:00:12​
18.9​
19​
sunny​
2021-08-03 17:32:48​
20.9​
19​
sunny​
2021-08-03 13:31:24​
20.2​
19​
sunny​
2021-07-31 09:06:18​
19.5​
16​
sunny​
2021-07-29 19:36:46​
23.3​
18​
sunny​
2021-07-29 17:11:56​
23.6​
20​
sunny​
2021-07-29 15:23:56​
23.5​
20​
sunny​
2021-07-29 12:56:28​
22.5​
20​
sunny​
2021-07-27 11:25:50​
21.5​
18​
cloudy​
Click to expand...

I sold that pool to a friend in 2022 who added 4 intex solar heater mats and was regularly hitting 28-29C on sunny days, they seemed to be very effective but obviously only work on those sunny days.
 
  • Like
Reactions: mister_rossi_x
If you like data and graphs I've got a lot more for my 25,000 litre in-ground pool that is enclosed in a conservatory (also in Kent).

1712938310990.png

Here's the last year of temperature and heating data: Grafana . The resolution is somewhat reduced for the raintank upload but I can give you more detailed data if you have a use for it.

Last year I used the pool between mid-April and late-September, so about 6 months, this is somewhat driven by the cost of heating but also the weather and outdoor temperature.

The pool is heated by a 7kW heatpump however my measured effective heat output sits around 4.3kW (based on a ~420% efficiency). My measured effective output is just a simple calculation based on rise in temperature for ~8 hours of heatpump running for 25,000 litres. That doesn't take into account any heatloss during the daytime heating so the output/efficient probably is a bit higher.

So far this year I have used 70kWh heating the pool from ~10C on the 6th March to ~22C today. The heatloss obviously increases as the water temperature rises and currently I am losing around 0.7C overnight.
 
  • Like
Reactions: mister_rossi_x
Hi Jake. I've been studying your data - it's very interesting. I guess your heat pump is more or less constantly on...? Your pool temp hardly goes down overnight... I've been trying to estimate how much my pool temp would drop with no heating (i.e. using the bio heater or perhaps a gas based boiler just a few hours each day to bring back to temp) and a polytunnel / greenhouse type insulation. Hard to do... it sounds like, worst case, in the summer months it wouldn't drop below 18 as you've mentioned, and perhaps stay warmer than that...but what about when the day time temp is only 15C, and it drops to 12C, or 10C overnight... would it drop from 27C to 12C, or stay more around 15, 16C etc... I've been trying to put together an excel sheet with estimate values so I can work out how much it would cost with the bio heater / gas options to re-heat in different months. Tricky!!

I figured I could see how much a bucket of water in a greenhouse lost overnight and try and extrapolate based on volume and surface area, but not sure that's possible!! I've even posted on Chat GPT to try and get the AI to work it out, but it got very complicated, what with heat loss coefficients and various formulae. It couldn't work it out in one so had to ask multiple questions and plug things back in and calculate myself, and the answers don't sound right at all... oh well. I'm just going to make some educated guesses of best and worst case scenarios and see how many hours heating / what sort of costs we're looking at!

Touching on the gas boiler topic, that looks a brilliantly cheap and quick way to heat a pool - run cost wise. It seems installation could be incredibly expensive though - current supply (I have gas central heating) may not be enough, plus the pool would be approx. 10m from the back of the house so would have to dig / run / install a new gas line... sounding technically difficult and potentially costing a fortune.
 
My heatpump has primarily been running during the day taking advantage of free electricity during Octopus Power Ups (Octopus Power-ups | Free green electricity in East England). I definitely could have achieved a faster heat up time if I left it running 24 hours a day. I've so far used 187kWh of electricity since I opened the pool for the year to get it up to ~25C from ~10C. From last year I expect the number of daily hours to maintain that temperature to reduce quite a lot as the outdoor temperature increases, and to potentially put the heatpump into cooling mode during the peak of summer to keep the water under 30C.

I expect your heating profile would be a different to mine as you'd have a much larger heat output and spend less time fighting heat-loss.

I've attached a snapshop below of the last 30 days of just the temperature and heatpump running (on the right y axis). Any time the blue heatpump line is above zero it's heating and you can see the temperature is increasing.

1713196402052.png

Your post did make me wonder about the actual rate of heating so at the weekend I added a rate of change calculation. I've not got much data yet but you can see I get around 0.2 degrees per hour increase when the heatpump is running and up to 0.1 degrees per hour of heat loss overnight with an average 7C outdoor night time temperature. Based on this to maintain 25C water temperature I would expect ~10 hours each night losing heat (say 1C), then ~5 hours each day running the heat pump to bring it back up to 25C.

1713196831534.png

I did actually make an attempt to model the heat loss but found it quite challenging. I made some assumptions about the conductive thermal losses based on surface area and readily available R/U values.
1713197229074.png

Having the pool enclosed in a conservatory massively complicated things as it seemed to have a big contribution to heating/maintaining water temperature so I didn't put much more effort into it.

1713197258394.png

My prediction laid on top of past data did however suggest I wasn't too far off however I did have to fiddle some of the insulation values to get closer.

1713197391062.png
 
More excellent data, awesome! The heat loss rate when your heat pump is off too is really interesting & useful... my water volume will be much smaller but less well insulated so I'll try and make some "intelligent" estimates based off this... my excel sheet so far pales in comparison to your efforts! Thanks once again :)
 
I don't fully trust the temperature when the pump is off. There is some combination of stratification of water, and solar heating of the water near the surface that causes it to be warmer than the rest of the water. Once the pump turns on and starts circulating I often see an additional temperature drop of up to 0.5C.

I've attached a copy of my spreadsheet if you want to get an idea of how I did the calculations. It's not very organised though as it was really just a proof of concept.
 

Attachments

  • Pool Heat Loss and Gain.zip
    35 KB · Views: 1

Enjoying this content?

Support TFP with a donation.

Give Support
I guess the largest "pro" you have with your set up is the temperature of your conservatory. You loose very little heat overnight; my planned polytunnel is going to cool down rapidly at night. Therefore, I think the water temp is going to drop significantly and I'm going to have to put a lot of heat back into it the next day. I've made some "worse case" and "best case" guestimates and put this together:

heatloss_predictions.PNG
 
From this, it looks like the run cost for gas vs the Rexener bioheater (that runs off diesel or even better, cheap red diesel at approx. 83p a litre!) is similar and the Rexener stacks up brilliantly in terms of original purchase cost plus no installation cost - just hook up and go - whereas the gas boiler is going to cost more to buy, I'll need a gas certified installer and possibly a new gas line / supply etc etc - going to contact my suppliers to try and find out what's involved.

Why not just opt for the Rexener?? Well, in the UK the largest legal "jerry can" you can fill at a petrol station is a 20 litre metal one. I'm going to be using that up very quickly... I'd have to be doing constant trips. I'd have to go further for red diesel too. I can't see it being at all practical!!

Maybe I should consider heat pumps again too...

Of course, these calcs could be rubbish and I lose a lot less heat and don't need need to heat it up that much, hence the Rexener might be a good option after all...?!?!
 
Hi guys

Pool enclosures seem to be a great idea, especially in cooler environments (I'm in the UK, East Midlands!) and where you can make use of the sun (Northern hemisphere & I've got a south facing garden... although it's still the UK so limited sun!!). However, the "nicer" ones - i.e. telescopic opening ones - seem to cost £££ (or should I say $$$ on here?!).

My other issue is that it's going to be an AGP and unlikely I can "dig down" even a little (due to various boring factors I won't go into here) and that means any enclosure can't be higher than 1m (as there's a legal / planning permission rule over garden / external structures over 2.5m, and the pool is 1.5m high... although I'm trying to seek clarification / confirmation with my local authority), plus, it would need to fit & sit on the AGP pools sides - which are usually thin / not designed to take weight load. However, I might build decking up to/around the pool, to make it look nicer and also provide "seating" for a pool enclosure.

I had another idea though - how about I enclose the entire thing - i.e. the exposed above ground sides of the pool too (which would help with heat loss) - as it will only be 4 x 2 metres in size? I've seen cheap polytunnels (plastic / acrylic greenhouses) that are 6 x 4 m, which would just about fit the space I have available and would also protect the pool equipment from the elements?!

There's a few problems I can see with this. First is the fact these things usually have only one entrance (door at one end), and don't really open up. On a hot day that's not going to be great... some have windows which would open up a little, but it'd be far preferable to be "open to the skies". Again though... I'm in the UK, no that's not going to exactly be a high percentage of days!

Also, if I have a heat pump - would that work well in that humid environment? Actually, it may work better than one fully external, as it should be warmer... although they output cold air, right? So I'd have to vent that out somehow...

An ideal solution would be if there's a polytunnel out there that assembles in pieces, potentially two halves or even 4 quarters, that could quickly and easily be disassembled, and is light enough so that a portion could be physically moved out of the way to open up the pool...?

Not sure if such an option exists or whether I'm living in cuckoo cloud land again, but I'm going to have a long and thorough google research session!

Anyone covered their pool with a greenhouse / polytunnel type solution? I did find one example on YouTube and it sounded good, although there was no way his could be opened up...

Cheers
Ross AKA "the mad inventor"

P.S.

Oh... I saw this !!!

EXIT pool dome 400x200cm - universal | EXIT Toys

EXIT pool dome 400x200cm - universal
www.exittoys.co.uk www.exittoys.co.uk

Yeah. It's probably not great... but could extend the season a bit. You'd have to take it off and put it away though whenever the wind picked up (and I've noticed it's windier in my new house than where I used to live, seems we're on a high-ish point of land) and would definitely have to put away during winter. Although I'd also be concerned a polytunnel may break in winter... if there's heavy snow. Although it seems my spot of east midlands in Leicestershire randomly seems to miss snow as opposed to a few miles up/down the road, so I may get away with that... just needs to be wind proof!
 
The heatpump option is definitely easier. Anything up to ~12kW and you can just plug it in on a 13amp plug. I've got control of everything automated and wouldn't find time to re-fuel regularly. Would be interested to know what brand/model you end up going for.
 
  • Like
Reactions: mister_rossi_x
Here's a discussion.

Anyone Have a Winter Pool Dome - Ameridome or Others?

Hi all. I'm looking for reports of anyone whose had an Ameridome or similar style winter pool enclosure. Pool Domes | Ameri-Dome Inground Swimming Pool Enclosures I have a torn meniscus among other issues that has not healed since June. I've seen a specialist who wants me to keep up my pool...
www.troublefreepool.com www.troublefreepool.com
 
  • Like
Reactions: mister_rossi_x
I'm going to go down the heat pump path, I have made the decision! Just had an electrician come round and quote for a higher ampage outdoor socket.

The pool will be housed in a polycarbonate polytunnel / greenhouse. I believe the heat pump kicks out a lot of cold air out the back, so it would need to be outside... or... does it draw warmth from one side? In which case, would it be better fitted in the wall of the enclosure with the warm air in there being pulled in one end, and the cold air going outside?
 
Thanks for this - great read! Unfortunately though an Ameridome wouldn't work for me (size, layout, visuals etc).

I haven't been able to find a suitable greenhouse / polycarbonate based polytunnel that suits my needs, as they all have doors at the front and usually no other opens - have seen a few greenhouses with one roof panel that opens.

Now thinking about reaching out to builders to either:
(a) build be a bespoke "greenhouse" from scratch
(b) modify an existing one - i.e. remove panels from the side and turn them into double doors / sliding doors, and add more opening roof hatches so can have half the roof open in summer
 

Enjoying this content?

Support TFP with a donation.

Give Support
You must log in or register to reply here.
Top Bottom
Back
Jump to latest Follow Reply