A friend has asked my advice on heating his newly installed outdoor pool. It came as a pre-fabbed product that was hoisted into position over his house, using a large crane (the video of this happening was pretty impressive).
Now it's in situ and the pipes and manifold have been run to a shed next to his house, he's asked me about fitting a gas boiler into his shed to heat the pool's water.
The pool company have suggested a combi boiler of 80,000btu output (to heat the
20,000 litre capacity pool). This would mean using only the CH side of the boiler and dismissing the water-on-demand, HW functions of the boiler. (not too sure what repercussions this might have or even how to facilitate such use).
I'd be interested in your opinions, advice, recommendations as to a sensible solution, even if involving alternative heating methods, as long as they were comparable to installing an additional gas (combi boiler), in terms of cost, timescale and feasability. i.e. realistic and not "in an ideal world" type solution. He is interested in cost, time, ease of maintenance and future servicing.
I've read a bit about solar heating (even if combined with part fuel supply for the winter months) but I don't want to overcomplicate something he wants to embark upon in the very near future.
In a nutshell, his pool supplier suggested a combi and I need a very good reason to suggest otherwise to him.
But how big are such panels? How many are needed? and what sort of siting do they need? The garden is to be landscaped and the pool is not covered, except for a temporary plastic tent type thing that can be opened over the top of it, like a section of a tyre (with side walls).
Just for comparison, take a look at the Thermalec site
formatting link
've used Thermalec heaters with pools at 2 properties now, and I see little point in changing. I reckon to get something like 20 weeks or so with the pool around 28 - 30 C for about £500 per annum - it used to be much less, but energy prices creep up relentlessly!
The most important thing for your friend is to buy a solar blanket for the pool if it wasn't supplied with one. It reduces heat loss when the pool isn't in use, and there's actually a quite significant passive solar gain using a blanket - the top 6" or so of water is usually noticeably warmer when the cover comes off. To maximise the solar gain, he needs to pump whenever the sun is out, to circulate any heat gain through the pool. My pool will peak at about 33 C at the height of summer.
You'll see plenty who'll advocate solar panels, but remember there are other considerations. I had solar panels at my present place, installed by a previous owner. I removed them, as they covered a significant corner of the poolside area and the area underneath was gloomy and dank.
If there's a corner of the garden where they could be installed without a problem, then solar is worth considering if you can pump the pool water directly through them, but forget it if space is a problem. Solar panels any height above the pool will almost certainly require a change in pump size to lift the water. Commercial systems will probably use a separate heating circuit with heat exchanger for the pool water.
Solar pool heating is somewhat of a no-brainer as the low temperature rise needed makes solar very effective. Partly the pool can be heated and insulated by getting a suitable cover which maximises insulation and solar gain - something like those described in
(That site has a lot more information on heating pools)
The greatest loss of heat from a pool occurs from its surface because of evaporation, the cover eliminates this loss when the pool is not in use.
Swimming pool take huge amounts of energy to heat them and solar alone will usually not be sufficient to heat the pool in the UK unless the collectors are of very large size. However it makes a useful contribution and is the only solar heating energy system with a payback time significantly less than its lifetime.
For solar heating you don't even need solar panels - a black pipe collection system works well as the low temperature means low heat losses. A matt black pipe (or pipes) (hosepipe really) placed around the landscaping can be both unobtrusive and effective. More efficient in that it gathers more heat for a smaller area is the black polypropylene plastic collector - basically a semi flexible plastic sheet. Front glazing as used on conventional hot water panels is not essential as the temperature is so low so they go well on the roof of sheds, garages etc. Using higher performance panels such as the Navitron makes the installation smaller. Two panels each of 2.25m2 would make a very significant contribution to the pool heating needs (Navitron say it would suffice on its own for an 11m2 pool)
formatting link
gas as suggested as the other source of heating makes sense. I presume some sort of stainless steel heat exchanger is included in the proposal?
Electric heating is the worst possible way to go. Although it may be the cheapest to install the running costs are by far the highest and quickly wipe out the savings on installation.
formatting link
links to a lot of information on solar pool heating.
formatting link
is one way of integrating the heating with the structure.
It would have been much better, and would lend some credence to your argument, if you supplied references (applicable to the UK, for instance using E7 night-time units, and not nice warm sunny, southern US states) to substantiate your claim. As it stands, it appears to be no more than prejudice.
OK - depending upon where you are in the UK electricity (off peak) is somewhere between 3.5 - 7p a unit. Using your figure of a cost of about GBP500 per annum that comes out at roughly 16,600 kWh at the lower price or 8,300kWh at the higher one.
Using the expensive option of 4 Navitron panels (costing GBP1,600) plus a few bits and pieces the solar installation would cost about GBP2,000 (with DIY fitting). That would provide about 5,000 kWh per season (probably somewhat more as the only information I have to hand is for hot water systems and the solar panel efficiency is better at the much lower pool temperatures) or just under one third of the requirement and save you about GBP150 per year at the lower boundary of the current electricity price or GBP300 at the higher one. Taking a very simplistic calculation and assuming that interest rates and fuel price rises will broadly cancel each other out that gives a payback of 13 years at the lower price or half that at the higher.
Probably rather more savings, because solar power will be greatest during the day when the pool is most likely to be in use and when the ambient temp is higher.
Off-peak electricity will be heating the pool at night, when the ambient temperature is at its lowest, and the pool is (working on the storage heater principle) likely to be at its hottest at 7 am. It's most likely to be used in the afternoons and evenings, by which time a lot of the stored heat will have been lost.
But why would anyone spend that on pool panels. Pool heating uses very low temp rise, so the simplest of panels will work nicely. Dark coloured hosepipe and polythene film work just fine, anything better is mainly for cosmetic reasons. Simple black panels with neat glass covers dont cost anywhere near 2k.
Pool heating can be set up for =A3200 if electricity is already available for the pump. That gives ROI in the region of 50-100% pa, depending on other heating method options. Glass covered panels will add to the cost, but its still very cheap compared to gas or oil..
Re calculations, I'd suggest asking advice in alt.solar.thermal. Or crossposting this thread to there. How much of the year solar will heat for you depends on your panel area and design, whether youve got electronic pump control or something basic, whether you have a pool cover and so on. I woudl suggest doing all you can to make good use of solar before adding fuel heating on, as its a much better option and if designed ok can heat the pool for as long as people are likely to want to use it outdoors.
Panels can go at ground level, on rooftops, under glass roofing, pipes can be embedded in dark coloured hard surfacing, fencing can be made from or covered with solar panelling, and so on. And at its simplest you can even run a dark hosepipe along the front of your flower borders, where it wll see the sun. In most properties big enough to have a pool, that gives quite a lot of heating area.
You can have a pump on a plug in timer initially, just to see some result. Adding a thermostat set to 30C onto the panels and a 2nd pool stat set to your desired temp limit will get max result from min pumping cost. A differential stat will give you a bit more output still.
I agree, I was simply using the most expensive option to show that even then there are obvious advantages. As you say effective systems can be made for far less.
Warning... long post follows. Sorry, but this is unchartered waters for me, I love a challange and with access to the amassed knowledge and experience, and the kind help, of the many who frequent this ng, I'm completely confident I can deliver on this project. If you have the time, please read on...
Peter Parry wrote:
Thanks Peter, some great and very concise info there, and with links for me to do some further reading.
My friend tells me that everything 'for the pool' was supplied and installed by the pool company and, when asked what else was needed, their response was "you only need a boiler, to connect up to the system we have installed. This can be either a combi boiler or a standard boiler (with a pump) and it needs to be able to have an output of
80,000btu to cope with the 20,000 litre capacity of the pool".
I assume that they don't get too involved in that side of the installation and stick to just supplying the pool and directly associated components. Their advice to him about heating the pool was probably just relaying what most of their existing clients had done to heat pools they've supplied.
Knowing my pal, this was very much a leap before you look purchase (he has the resources to be able to do that, bless him) and his reason for getting me involved was because he knew I'd do the homework before spending his money. I've been tasked with installing the necessary for him (not for free I might add, but it'll still be at mate's rates) because he knows I'll do a thorough job and won't rip him off.
Straight off the bat, I have called for some time out before turning up in the van, with tools on board, in order for me to do some research on a suitable solution for both the short and long term usage of the pool.
The pool being currently in situ and full of water, he is under some pressure from his 9 and 5 year old (and therefore his wife) to get it useable ASAP. However, the garden landscaping will not be completed for quite some time and all is still at the groundworks stage, as his garden was quite high up from the house and a lot of muck has been, and is being, removed.
So, his thinking is to cordon off the pool area so that the kids can use it, and I was wondering what I could do temporarily to get some heat into the pool. I've had a quote for a combi boiler and also for a system boiler... the combi is a lot cheaper than the system boiler, they sell more I suppose, hence the lower price. Both are about
24-25kw, which will give the 80kbtu. Obviously the combi is the cheaper option, but I'm not sure what, if anything, needs to be done to decommission the HW side of the unit. Do I just leave it unconnected or install capped feed and return pipes?
Also, would it be reasonable to assume that I could run the boiler by tapping into the nearest source of gas and electricity for now with the intent to reconfigure at a later date? To explain, the shed which will house the boiler, consumer unit and pool systems is at the side of the house. I can get gas from a 15mm copper pipe that supplies a gas fire on the other side of the wall, and for the electricity, I can run a spur from the outside security lights, as they are on their own circuit straight from the main domestic consumer unit, although this is likely a radial circuit rather than ring main. Would there be enough gas pressure and electrical power from these sources to run the boiler for a few weeks without causing problems?
Eventually, my pal wants to run all sorts of lighting, power outlets, internet access points and speaker setups in the completed garden, he's also considering mains supplied patio heaters, barbeque and (get this) 'fire features' as well as water features. I am unable to devise a system for this right now, as his designers have not yet put forward their proposal for these installations, so I don't know what products will be used nor how many and what are their requirements.
To cope with this final load, I have suggested that, when the time comes for the patio, adjacent to the back of the house, to be uprooted, we take the opportunity to put in a yellow plastic gas pipe and a suitably sized armoured cable. These will run from the shed to the other side of the house where the main gas supply is located and there is easy access to the domestic consumer unit, meter and tails. When the garden is finished and the various systems have been designed and installed, the boiler and consumer unit connections can then be moved over to the higher capacity gas and power feeds, to cope with the additional loads from the whole garden.
Does this sound like a plan? Is it likely that the temporary gas and electricity supply will be able to cope with the demands from the boiler? Obviously, the greatest draw on the gas and power supplies will be during the initial heating period, up from the ambient temperature to a comfortable bathing level. Some 25hrs or so as indicated by Andy Hall's earlier post to this thread, therefore, during this period, I can ensure that no other gas appliances are used within the house, keeping pressure as high as possible (through routed 15mm copper) for the boiler. As I said above, I'm a bit dubious about the electrical supply, spurred from the exterior security lights, being up to the task. But that's easy enough to find out from the boiler manufacturers.
Appreciative of my efforts and receptive to my advice, my friend will go along with whatever I suggest. However, I'd really like to be able to give him a short-tern fix and get the pool useable, via a temporary connection ASAP, followed by a permanent installation. If this is a bit hair-brained, or fly-by-nightish then I'll tell him to be patient and put it straight to his kids... you know what they're like... pool's coming, pool's coming, pool's here, pool's in, it's in... whoopeee... can't use it!
At least one supplier has much better prices than that on the E7 night rate. Look at the British Gas (YIK) 'Click Energy' tariff: 2.062 -
2.689 p/kWh (inc. VAT) depending on region. The day rate price is high of course, but the tariff could still be a good choice if a substantial fraction of your consumption is at the night rate.
For a quick fix how about adding the pool as an extra zone on the house central heating (hopefully gas). One zone valve, one stat, one plate heat exchanger, a loop of insulated MDPE pipe to the pool and a pump (possibly the pool's existing circulation pump) and you're laughing. That'll give you more time to play with clever solar or mixed systems and certainly less dodgy than the shared 15mm gas connection and locking appliances off ;-). It might even work as a permanent solution if there is the spare capacity in the boiler and in the colder months or after the pool is up to temp the heat exchanger feed could be throttled down to ease the load on the boiler.
Depends a bit on the boiler. Some may have an inhibit on mains water failure.
Assuming you have a supply of mains pressure water available[1] then I would hook it up to the inlet side anyway, and just connect a short pipe to the outlet with a service valve on the end.
[1] Would be handy for filling the sealed system!
Gas would be a concern... lets do some sums:
Lets assume the boilers input energy is 24kW (as opposed to its output, so we can ignore its efficency), 24kW is 24,000 joules / sec or 86.4MJ/hour.
Calorific value for natural gas is about 39 MJ / m^3, so you would need a gas flow rate of say 0.615 l/sec or 0.22 m^3/hour
So if we look at:
formatting link
discharge rate for 15mm pipe at a 1mbar pressure drop is listed as
2.9m^3 for a 3m effective pipe length or 1.9m^3 for a 6m one.
That would suggest a maximum effective pipe length from the meter to the boiler of no more than about 4m (counting each bend as 0.3m or an elbow at 0.5m equivilent)
The electrical load presented by the boiler will be low (under 3A) so is less difficult. However all the normal precautions about running a power supply to outbuildings would apply.
The gas supplier may appreciate it if you draw the gas from your mates side of the meter rather than theirs... (although that would make the pool heating much cheaper!)
I take it he has a gas boiler in the house for the CH etc? If so why not use that as a temporary source of heating?
Have a look at the design that Andy implemented for supplying heat to a outbuilding:
formatting link
way you could implement solar for the pool, with gas boiler for backup / topup. The pool however would remain isolated from the house CH circuit so no chance of compromising that, and also no need to take gas or electrcity out to the shed for a temporary lash up.
A large length of dark flexible hose, preferably large diameter, 1"-2",
100ft or so. Lay it out in a spiral, with very roughly a pipes width of space between each turn. Put sheet polythene on top, weighing it down round the edges. Hook up a 100w pump and run during daylight hours. Cheap basic setups like these will give plenty of heat. Something under it would help a bit more too, even just sheet poly.
Be aware though that whatever the source, 20,000 litres is a huge thermal store, and it will take many days to reach target temp if you only install enough to keep it at target temp. Getting it there fast would require another big spiral of pipe.
If you have a CH pump lying about, that would do to get it running. People tend to install overly large pumps, wasting electricity. CH pump is a bit low power, but the system will still run, still capture the same heat, just lose a little more of it.
no way Jose. 25kW is a serious load. To get it into perspective, a lighting circuit is fused at 1.2kW or thereabouts.
Instead of putting a yellow gas pipe in from the house, you'd be better to put 2 pipes in for warm water. That way if you want more heat, you've got the options of adding panels to the house roof or gas.
You can make fire effects with solar tech too... :)
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.