Heating an outdoor pool

For those interested, here's an update...

After exploring the various options kindly suggested here and elsewhere, and after meeting with a Corgi engineer/inspector/trainer on site, the following solution was adopted for this project.

I worked under the supervision of the CORGI man and will be undertaking full training with him, so that I can get qualified myself. After inspecting the existing gas meter, it became apparent that this would not be sufficient to supply an additional shed boiler as well as the current domestic system boiler, for the house.

The decision was made to remove the current boiler and replace it with a Keston C55. The old boiler (Ideal brand) was rated at 25kw and the pool needed a heating source in the region of 23.5kw (80,000btu), thus a boiler with a total output power of about 48.5-50kw was the ideal, while 40kw would probably suffice. Concerned that my client's expectations should be met (preferably exceeded), and with a good price quoted for the C55, I chose that model as a suitable replacement for the 10 year old 'Ideal' model.

The C55 has a variable output, ranging from 14-55kw, depending on demand, and could easily cope with the additional requirements of the pool's Heat Exchanger, as well as the current domestic HW and CH, with output power to spare. There are also the obvious economy benefits to be gained from the variable output when the demand is less, plus the energy savings that come with a condensing boiler such as the C55.

To incorporate the pool zone onto the primary system, I branched off from the flow and return ports of the C55, to serve the new loop, as well as reconnecting to the existing primaries of the domestic system. To allow isolation of either the house primary or the pool primary, avoiding unnecessary water circulation, I fitted actuating 2-port MVs on both branches of the flow primaries, one on the house side and one on the pool side. Likewise, I fitted gate valves on the returns.

Other changes made to the existing domestic system included: removal of the, now-redundant, circulation pump, located in the airing cupboard... the C55 has an integral pump that has the oomph to push water round the house and pool loop combined. To avoid the C55's pump discharging water into the CH expansion tank, via the vent pipe, in the loft, the system has been converted over to a pressurised one, incorporating a suitably sized pressure vessel.

I had a great time measuring the volume of water in the system, by draining it into a 3 gallon bucket and counting the number of times I had to empty it! Adding to this the volume of water held within 50m of

22mm barrier pipe and contained within the C55 (when full) gave me the total volume of the new system (in gallons), and enabled me to select a vessel of the appropriate size, with a bit extra for good measure... in this case, an 8 gallon vessel was required and a 12 gallon was selected.

The new loop for supplying heated water to the pool's heat exchanger, in the shed, and back, was run using 22mm HEP barrier pipe. This was sheathed in consecutive lengths of foam insulation and then wrapped with 4" Denso tape along the full extent of the run. The 2 pipes were then buried in an 18" deep trench, backfilled with pea shingle and will eventually be patio'd over.

With most of the project now completed, I do have some uncertainty on the configuration of the electrical wiring of the additional system. The pool's thermostat will need to call for heat via the MV on the pool branch of the flow primaries. If the pool's programmer (which I have purchased but have yet to install) confirms that this call occurs within an "on" period, the boiler will fire and heating commences. Exactly as would happen if a call for HW and/or CH came through to the domestic programmer, during an "on" period. However, the domestic MV needs to be closed if pool-only heating is called and the pool MV has to be closed if domestic-only heat is called. If calls are made to both zones, during coinciding "on" periods, they both need to be open! As these valves are "normally closed", it follows that either will only be 'open' during an 'on' period, as allowed by their respective programmers. That's all fine, but what about the need for an "open system" to facilitate pump-overrun of the boiler's integrated pump? If both circuits have switched off, following a heating period, then both MVs will close and water cannot be pumped around the primary to cool down! How can I get round this? I am wondering if this is accounted for within the boiler itself, as the C55's manual states that all system wiring is external to the boiler, with only L,N,E and switched L needed internally.

Cheers deano.

Reply to
deano
Loading thread data ...

Increase in efficiency is your only gain afaics. It might be worth it, I dont know, but it appears your old boiler would have done the job quite satisfactrily.

House heating requirement varies, but a few kW averaged through the heating time is normal enough. IOW a 23.5kW boiler would normally only need to feed the house a very small percentage of the time to heat it. So all you needed do was give the house priority over the pool, the boiler gives you the required output for the pool then, and house heat is not sacrificed at all. However you friend will be guzzling so much gas the change to a higher efficiency model might be worthwhile. But according to your figs above there was no need for a 50kW unit.

NT

Reply to
meow2222

Thanks for that.

You could have probably got away with less power - since you won't be sinking the full output into the house for long durations. Still it should give nice snappy heating times for the house and HW.

The variable output in this case is not modulating that low - so you can still expect cycling in all but the very coldest of weather (unless the house is very poorly insulated).

yup

Not really - given the power of the boiler there is no need to make them exclusive, it should eb able to feed both zones at once if required.

You need some form of bypass[1]... This can take the form of a pipe connecting flow to return via a automatic bypass valve. This pipe needs ot be connected before the zone valves obviously. During normal operation the valve will stay shut and the bypass does nothing. However when the pump is pumping against an otherwise closed system during overrun, the auto valve should open with the pressure (most can be tweaked to see the pressure) and allow some flow. The other option would be to provide some other form of bypass like a small radiator or towel rail that you want heated any time the boiler runs.

Some boilers do include an automatic bypass, however if the manual does not specify it as a feature, the chances are you don't have it.

[1] Previously the bypass would normally have been provided by a rad without a TRV - usually situated in the same room and the main room stat. Now you have added the two port valve, you can no longer rely on this since the path through the whole domestic loop could be blocked by the new valve.
Reply to
John Rumm

Essentially, you have implemented something quite close to my workshop heating project.

The difference is that you presumably have the pool water on the secondary side of the heat exchanger whereas I have a second heating circuit, sealed and pressurised running to radiators in the workshop.

I dealt with most of the issues you mention, so a few comments:

I felt that it was important to protect the integrity of the house primary circuit in the event that the secondary circuit isn't used for a period of time. I wanted to avoid the case of freezing of the water in the underground pipes or the workshop causing loss of the primary heating water and hence the loss of CH and HW in the house. To that end, I fitted the heat exchanger inside the house, where there is no need to protect it from freezing - just insulate to avoid unwanted heat loss. The secondary circuit runs between the house and the workshop and the water is dosed with an inhibitor with antifreeze (Fernox Alphi

11). Obviously you wouldn't do this with the secondary being pool water, but I just wonder whether it might not be better to site the heat exchanger inside the house so that at least the integrity of the main CH/HW primary circuit is protected.

Alternatively, it would be a very good idea to implement a frost protection thermostat so that water could be circulated for short periods in the external heating pipework when it gets really cold.

For this aspect, I wrapped the pipes in foam insulation and ran them in some 150mm underground soil pipe for protection. This was a recommendation in a document that I found, originating from the Building Research Establishment in connection with how to connect a boiler in a remote boiler room to the house. It included how to run the pipes into the house and so on. I suppose that buryoing the pipes in pea shingle affords some protection...

This is the other challenge to deal with - how to do the signalling and control.

I decided that I didn't want to run control signalling by cable between the house and the workshop. The workshop is wired with its own circuit directly from the CU and with local earthing and is hence a TT system for electrical purposes. This is deemed safer than exporting the house earth to the external building.

I'd strongly recommend that you read through the relevant sections of BS7671, because a pool is considered to be a special installation (meaning some specific potential hazards) and there are some particular wiring requirements. In order to avoid possible future liability, I think that this is one case where it would also make good sense to involve a qualified (and insured) electrician with appropriate experience in this area and to make sure that there is a paper trail that the installation has been inspected and signed off properly.

That said.... In order to do the controls at the far end and signalling to the boiler, I did the following arrangement:

- At the workshop end, there is an optimising CH controller with thermostat, time control etc because I want different heating profiles on different days, temperature set back etc. This operates a pump in the workshop which is in the secondary circuit, so water flows when there is a heat requirement.

- At the house end, there is a flow switch in the secondary circuit and the contacts for that close when said water flows. This switch is treated as a zone thermostat for the purposes of the boiler and controls in the house. So there is a motorised valve controlled by the flow switch, opening for heat demand and allowing system primary water to flow through the heat exchanger.

- The auxilliary contacts of the motorised valve are connected in parallel with those of the valves of the CH and HW valves and effectively form 'OR' logic to turn on the boiler - i.e. if any of the contacts close, boiler fires. If you look at the Honeywell web site and search for S-plan plus, you will find the needed wiring diagram.

For the arrangement that you have at the moment, you can't do exactly what I did, but you could if the heat exchanger were in the house. The pump in the outbuilding would be controlled by thermostat and you could have a flow switch in the house.

As it is now, you will need to run control wiring between the outbuilding and the house or implement some other method of signalling. It would be a good idea (may be a requirement) to isolate the house and outbuilding electrical earthing at least. One way to achieve that would be to put a small isolating transformer to effectively separate them. The controls in the outbuilding would power the transformer when heat is required and then the motorised valve at the house end would be run from the secondary side. Even better would be to run the wiring between the two in 24v (i.e. step down transformer at the outbuilding end) and then a relay in the house controlling the MV.

>
Reply to
Andy Hall

Efficiency AND 'performance'! The old boiler was an "ideal" model, rated at 27kw. The house (value: =A30.9-1.0m)) is only about 10-12 years old and is part of an estate of executive mansions, all built at the same time... nice houses, but still built to developer specs on previous agricultural land. Developer's Time and budget constraints would have meant tight control over all aspects of initial build, including boiler spec. There are 18 radiators in the house and the HW is stored in a constant pressure water cylinder (not a Mega-flow, but a Watermill product with a pressurised supply off the mains).

On the basis that the developers had fitted a 27kw boiler for good reason, without going overboard (perhaps allowing for the addition of an extra rad or two); plus the fact that the homeowners are mid thirties, have three kids, regularly entertain both personal and business acquaintances, and both drive Range Rover Sports'... I thought it best to avoid risking a lag in the performance of the domestic heating system, to which they are accustomed.

that adding 23.5kw (for the pool) to the 27kw (output of the old domestic boiler) equaled 50.5kw. In his mind, choosing a boiler with a max output of 55kw, gave a 4.5kw comfort zone (akin to how we feel about a 200mph(+) performance car, while knowing we can never (legally) drive it at that speed).

I've no doubt that there are numerous other solutions to this project, far more economical and efficient than the one I have installed. However, having done a fair amount of research, on this, my most challenging project to date, I am confident that the system will give the performance that is expected of it (and more) and that's more important than overall cost when my relationship with my friend is at stake... after all, he was aware of my lack of experience in this area, before asking me to get involved, and yet, still gave me the go-ahead when I put forward my proposal.

There's more to a job than just tools and parts don't you think?

cheers, deano.

Reply to
deano

~ Welcome... share the knowledge and all that.

~ How much less power? I can't see how the existing unit would have been up to the task, so a replacement was always on the cards. With the likelihood that, at some point in the future, there will be an instance when the CH, HW and pool will all demand maximum output from the boiler, at the same time, doesn't it follow that a replacement boiler should have a max output equal to the sum of the output from the current domestic boiler, plus the extra 23.5kw required by the pool? As for giving snappy heating times, I think that is important to the homeowner... we all like to hand check the rads on a cold day, shortly after firing up the heating, and I would certainly have got some negative comments from the lady of the house if the rads took longer to get warm than before before hooking up to the HE for the pool.

~ Not sure I follow! Will the boiler always give a burn at the same output rate? I know it adjusts itself automatically and heat is controlled by the speed of the fan, but does this mean that the boiler sets itself to the system just once, to calibrate itself, and then remains at that setting until there is a significant change in the system demands?

~ So, should I then remove the MV and gate valve that I have installed in the flow and return pipes that go off to the domestic system? Is there no benefit to having these as part of the system? I suppose that water to heat the pool during an 'off period' for the domestic heating would only have to travel a short loop round the house primary, so no real heat loss incurred there. Then again, having this zone isolated during pool/jaccuzzi heating would prevent the slight heating that the primary loop would give off in that part of the house, which may be a good thing during a hot period in the summer?

~ The length of system pipework between these two MV (with the boiler half way along) is quite short... only about 8' of flow and 8' of return. Would a by-pass valve still be able to cope with this and allow the short-circuited water to cool sufficiently?

~ Agreed, I had a good read through the vey thick manual and don't recall a reference to such a device being fitted. There is an air-pressure release valve mounted on the flow pipe, just before it enters the HE on the boiler, but this is obviously not the same as a by-pass valve to allow bridging of the closed-off primary circuit.

~ It has been and all the new system components have been installed around the boiler, in the utility room at the back of the house. The roomstat is located in the entrance hall. If, however, (as mentioned above) there is no real need for the MV and gate valve I have installed on the house primary, these can be removed and the pump-overrun can use the full length of the domestic primary, uninterrupted.

Many thanks, deano.

Reply to
deano

Youre not understanding something here. Briefly, the addition of the pool heating loop to the old boiler would have made _no_ difference whatever to the house heating performance - assuming it was wired up competently of course.

NT

Reply to
meow2222

I agree that the existing boiler was certainly on the small size. Certainly if you had used it then you would have to have given the house heating priority over the pool to maintain short heat up times in the house. However once the house was up to temperature there probably would be a fair amount of spare capacity to heat the pool - but perhaps not enough to heat it at the maximum rate supported by its heat exchanger.

With boilers in the 30 - 35kW range you would have had a bit more choice of models and would probably also be able to find a boiler with a wider modulation range, which will offer better comfort and economy for the house heating. The house is unlikely to require more than say 8kW continous demand for space heating once up to temperature, so there would then been adequate power to drive the pool at full rate and the house.

Well given that the heat up time of the pool is going to be many hours regardless of how much boiler power you have available to throw at it, delaying the pool from reaching its target temperature for an hour or so in unlikely to be a problem.

No the boiler will change its rate based on the temperature of the return water. As this gets hotter it ought to reduce its burn rate. This has the effect of matching the boilers output to the actual load, and also in the case of a condensing boiler, helping to increase the efficency of the boiler.

Ideally (for house heating) it is better to have a continous burn matching the heat loss of the house, rather than intermittent burns that overshoot the set point of the house and then require the boiler to cycle on an off too often. So a boiler with a wide modulation range (i.e. can go down to 5kW or lower) is good in this respect. If the minimum burn rate on the boiler is significantly higher than the heat loos rate of the house then you are back to situation similar to using a smaller fixed rate boiler.

No, it should be a continous closed loop control system.

Ideally you need a S Plan system where the boiler and the house are each on independaent zone. So the pool or the house or the domestic hot water can call for heat, and the zone valves enable or disable the zone as appropriate. Since you have the power available with the big boiler you also have the option of running the heating and fast recovery domestic hot water concurrently (you could divert the pool heating zone to the DHW and have no impact on the house).

Since you have to allow for the possibility that none of the zones will be open, you would still need the bypass.

(I presume the pools heating circuit is designed to limit its maximum rate of absorption to something reasonable (say 25kW))

The main requirement for the bypass it to avoid obstructing the pump. A small amount of heat loss is handy to dissapate heat out of the primary heat exchanger, but since this is probably a lightweight construction on a modern boiler this won't be that great.

Since you have plenty of power to play with I suppose the ideal zoning would something like house heating split into however many are required to adequately partition the house, with pool heating and domestic hot water sharing another. You could then have the water heating zone itself partitioned as a W plan setup with priority given to the DHW using a fast recover cylinder. That way when someone runs a bath, the hot water can be given 20kW of heat input to recover, and unlike a typical domestic setup there would be no need to prioritise this over the house heating. (it would be prioritised over the pool, however that is not going to notice the 15 min interruption to restore the cylinder).

Reply to
John Rumm

Hi Andy,

Thanks for your reply. I did read it so> Essentially, you have implemented something quite close to my workshop

You're right there and, as it happens, I have studied all the posts on the thread you initiated, regarding your workshop... somebody here referred me to it, only for me to discover that I had read it before, as part of the research I did, some months ago, when constructing my own garden workshop, and looking at various ways to heat it. Furthermore, as a result of replacing the boiler on this pool project, I am in possession of the old boiler that I removed, and I'm considering re-installing this into my workshop, to provide the heat source needed there!

YES! The additional zone that I have installed, branches off the primary flow and return, from the boiler. It runs externally, to the shed, and is connected up to a heat exchanger. On the other 'side' of the HE is the pool loop which is an 'in-direct' secondary circuit, getting its heat from the transfer provided by the HE.

I understand your point completely and keeping all of the main system components in the house makes a lot of sense. However, certain parts of the installation were the responsibility of the pool supplier and they did their bit long before I came on to the job. On the behest of the client (and no doubt, with a bit of persuasion from themselves... to make the installation easier) all of the pool's plant components, including the pump, filter, blower and Heat Exchanger, were located in the shed, down the side of the house, nearest to the pool, as was all pipework connecting the above, to the pool, in 1.5 and 2" plastic with solvent fittings. This had then also been buried underground, as part of the ongoing groundworks. This is where the original brief of putting a boiler in the shed initially came from and, as you know, things have since digressed from that in many ways, due to feasibility issues. Hence, I'm stuck with the HE in the shed.

Affirmative... having put the two tubes in the ground, freezing of the pipes during a non-use period, occurred to me and I have been thinking about fitting a pipe-stat, to monitor the temp in the sub-terranian pipes.

They have also been topped off with soft sand and will have a patio re-instated above them, so I'm not really worried about that aspect of the installation. Point taken for future ref though, about using the 4" pipe... although drainage fittings are very expensive.

I have also installed a CU into the shed, where the pool components are located. This is fed by a 16mm armoured cable, run in the same trench as the heating pipes. However, I have connected this up to a spare "way" on the domestic consumer unit, using a 45a MCB, which is on the "RCD-protected" side of the DIN rail. Contrary to what you learned, I was advised that using the house earth was suitable... but that doesn't mean I disagree with what you did. I also bonded the metal sheathing, of the armoured cable, and the metal components of the pool's plant equipment, to earth, in the shed CU, via suitable banjos, bolts and crimp fittings, using 6mm earth cable.

I have a man that can... my mate's dad does just that! He certifies installations, during the morning, at various commercial properties, in central London. In the afternoons, he looks after his private customers, such as me. I always get him to come and check what I've done, it makes sense to have a fresh pair of eyes check your work, regardless of what is required by law. I'm happy to say that he has yet to find fault with my work, yet he always has useful suggestions on alternatives to certain things I have done, which would have been quicker to implement, while remaining within the guidelines.

My intention is to run a cable from the pool/shed area, to the utility room, in the house... as you have mentioned above. I was going to take power for the circuit from the shed's CU and just use the armoured cable as a control wire, to operate the MV for the pool zone, in the utility room.

However, this would result in a circuit remaining live, even when the main fused switch for the system is switched off, which is not ideal, nor good practise. So, I intend to run a 5-core+earth, armoured cable from the shed, into the utility room. The pool's thermostat will send a 'demand' signal, via this cable, to a separate programmer, located in the utility room. If the programmer is currently in an "on" period, the signal will be passed on to the MV for the pool zone, and this will open, thus allowing flow to begin and the boiler to fire.

I still need to work out whether I need the MV on the house side of the primary circuit, so that this can be closed if no demand is currently coming from the house HW and CH. Or, should I just allow flow around the house primary, when only pool heating is called for? If I am to completely isolate the house primary when 'pool only' heating is called,I need to start thinking about pressure relief and by-pass valves, and also, an additional pressure vessel, located in the shed, to protect the pool circuit, as the house circuit, and its pressure vessel will be cut off from this circuit!

The saga continues....

cheers deano.

Reply to
deano

I think in practice you're unlikely to be bathing outdoors when the temp is sub zero, hence no pool heating would be needed at such times.

NT

Reply to
meow2222

I disagree, on two counts...

Firstly: Having recently spent thousands of pounds on this project, my mate is desperate to take a dip in his new pool (as are his kids) regardless of the time of year and the outside temperature. He has also described to me his vision of sitting in the spa / jacuzzi section of the pool, with his wife, sipping champagne, whilst surrounded by snow-covered ground and steam coming off the water's surface... I'd be exactly the same if it was my pool.

Come this time next year, following extensive use throughout the summer, the novelty may have worn off, amongst the resident family, and there will be less demand for regular 'winter' use of the pool. However, being the party-throwers, for which they are renowned, they will want to keep the pool on standby, so it can be used, at short notice. and as such, are likely to maintain it at a status sufficient for constant use.

Secondly: Should it be necessary for the pool to be shut down for any period of time, water would still remain in the flow and return pipes of the zone loop from the boiler to the shed. This water would be prone to freezing during a cold spell, regardless of being buried in the ground and sheathed with insulation. A pipe stat, connected to the MV, for this zone, would provide protection against freezing by initiating flow and firing the boiler, thus warming and circulating the water in this loop. The water in the pipes on the secondary side of the HE, to and from the pool, is protected from freezing by devices fitted to the pool pump and/or filter.

So, as you can see, there is a need for some form of frost protection for this additional zone.

cheerz, deano.

Reply to
deano

Well, its in interesting definition of 'need' :)

NT

Reply to
meow2222

Oh, being *in* a nice warm pool is fine, it's the bit between the pool and a nice warm indoors that's the problem......

My spa is in my conservatory and it don't get used that often in winter!

Unless they have unlimited funds, I suspect the novelty will soon wear off.

I had a heat exchanger from the c/h system to the pool in my last house (oil-fired boiler). It was installed by a previous owner. I hardly ever used it - probably two or three times at most. I found the Thermalec heater was much better for the purpose. The pipes from the boiler (28mm copper) had two gate valves in the pump chamber. These were left more or less permanently shut. The pipes were only just below g/l where they came out of the house, although they did then drop to perhaps 12 to 15 inches below g/l. I never had any problems with the pipes freezing in 13 years. The original pump did, and cracked. It was an elderly cast iron body, so was in need of replacing anyway.

Reply to
The Wanderer

Yeah, I'll give you that.

Every time my mate moans about how much this project is costing him and how he has to keep chasing suppliers and tradesmen for delivery dates and install dates, I have had to bite my tongue on a number of occassions and refrain from saying things like "Oh, I really feel for you mate, having all this aggravation, just so you can have the luxury of a heated swimming pool. All those folk who'll be freezing this winter because they can't afford to heat their homes, really have no idea, do they!" [removes tongue from cheek].

d.

Reply to
deano

Some actions are only ever carried out the once :)

NT

Reply to
meow2222

I do see his point in a way. He is probably also very busy and in general he probably delivers on what he says he will do or puts in the extra effort when needed to meet a commitment. I have a similar approach

It's very irritating when dealing with people who make commitments and don'r keep them, have no sense of urgency in terms of meeting a customer's requirements and have to be constantly pushed in order that they do so.

Paradoxically, if suppliers did have a better customer service ethic and made things happen more quickly, they would have the time to do more business or to have more personal time.

Unfortunately, that requires a change of mindset for most people.

Reply to
Andy Hall

As do I. I take pride in my work, am as thorough as I can be (when compiling my estimates and during the actual works), am concerned for my clients' convenience, their faith in me to deliver, and I try to keep my prices as keen as possible even though I know I am usually competing with other tradesmen, who's standards are below my own. I'm always busy, so I must be doing something right!

My mate is not short of a bob or two and the cost of the high powered boiler has already been forgotten... my labour costs were the same as they would have been for any replacement boiler and I passed all my trade discounts on to him. On the other hand, if I had walked the line when speccing the replacement boiler, and gone for a lower power, cheaper model, I would have risked getting it slightly wrong and if the performance was on the disappointing side... I would have never heard the end of it and putting it right would cost a fortune and mean starting from scratch.

Agreed... it seems to be the general behaviour of most of the big names out there, and its only getting worse. I often spend ages in my local plumbers' merchant chatting and learning no end of new tips from the staff and regulars who are often there. Go to one of the sheds and you're lucky to find someone who even knows where they are!

d.

Reply to
deano

Exactly. It is important to know the customer's expectations. To him, the difference in cost is not a big deal. A disappointing result is.

That's expectation again. I don't really expect a lot of any of these places other than a good price and delivery plus replacement without titting around if something is wrong. It shouldn't be difficult

Reply to
Andy Hall

A LOT of people. I spend sometimes a whole morning or two a week chasing up other firms to get things done. Some of these like telecommunications suppliers have effective monopolies still, so no real chance of going elsewhere either:(

Reply to
tony sayer

Sad isn't it.

I have real difficulty with people and organisations who promise something and then don't deliver, don't bother to let me know in reasonable time so that I have the opportunity to rearrange other things or make other arrangements and then don't seem to appreciate that it's unacceptable.

I suppose that if we have to have monopolies or as you say, effective monopolies, nobody in them would think of the concept of having individual performance targets with money attached to them. It's amazing how that focuses attention.

Reply to
Andy Hall

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.