Italian pool heating ?s

[RogerT]

Hi, we live in the hills behind Sanremo in NW Italy and have an in-ground pool of 10m x 5m x 1.4M. This was usable last year from beginning June to end Sept just relaying on the sun to heat the water directly and with a bubble cover put on overnight to retain the heat.
We would like to extend the season by a month at each end if possible by setting up a temporary solar panel heating system.
I envisage using a 20 tube panel with a solar-pv panel driving a pump which will pass swimming pool water through the panel (via a stainless steel heat exchanger I think as the pool is chlorinated). What size pump/PV panel will I need for this - is the well-pump advertised on Navitron's website OK, too big/small ?  Where do I buy a SS heat-exchanger ?
Does anyone see any problems with this, or have any suggestions ?
Will this system provide sufficient heating if we start it going say beginning April ? Pool temp at beginning of May was about 17C, so we need to raise that by at least 5 degrees (I started going in at end of May when only 21C, but that was chilly !).

During the winter we intend to move this panel to a South-East facing sloped roof and connect it to a tank which will then feed our gas heater, so that we have pre-warmed water for our underfloor heating and hot water. During summer months the panel will be put away so no problems with over-heating/venting etc. The panel will be on a permanent tiled roof which covers a "conservatory" (well, a room with 3 detachable glass-panel walls on the end of the house), and the tank will be housed under the floor of the conservatory and hopefully provide a little overnight heat to the glasshouse as well.

We want to keep all these systems as simple and cheap as possible, any advice and/or assistance from anyone in the area would be welcome.

Thanks  in advance   Roger

[KenB]

Roger,

From the pool dimensions you gave it could hold up to 70 cubic metres of water.

To raise 70 m3 of water by 5 degrees C, you will need 70,000 x 4190 x 5 joules  or about  407kWh.

If the 20 tube panel has a maximum output of 2kW, you will need over 200 hours of good sunshine to achieve this heat output.

These figures are only ball park, and intended to give some idea of the scale of the heating required.  No  consideration is given to heat losses from the pool, which in colder weather could be quite significant.

It might be worth considering multiple solar heating panels,  but I would consider that any standard Grundfos type circulation pump would be suitable for handling these sorts of volumes - given the time available.

SS heat exchangers are used on combination boilers and can be purchased from any boiler sevicing company. They are normally rated at around 20KW so no problems with your poolheater.

Alternatively have someone weld you a few lengths of SS dairy tube into a big loop or coil, which can be lowered into the pool during the chilly months.


Ken

[Ivan]

We generally work on 25% of the surface area for the 47mm tubes - ie 1x20tube panel will heat 11m2 of pool....in the UK. You can probably adjust accordingly in relation to the Italian sunshine - you will have more days per year of sunshine, and at a slightly higher level. Because of this, you tend to have a greater window for heating the pool by comparison with the UK. In the UK, you would expect to get good heat into the pool for the period April - September.

In the UK, I would recommend 4panels to give plenty of heat for the summer, but you would certainly take the chill of the pool with only 2 panels.

For this size pool, Navitron would sell 170 000BTU heat exchangers for pools- £330

[RogerT]

Ken,  thanks for the calculation.
From what I've seen the last couple of years we get clear skies in the morning at least 80% of the days from April on. Afternoons it tends to cloud over a bit, and as we are on a NE facing slope we lose the sun earlier than if we were on a flat plain. So 200 hours of sunshine should be easily possible in the month of April, and the same again if not more in May, so we should reach a swimmable temperature early-mid May instead of end May.
The pool is not emptied in the winter, but has a thick, dark-green cover on that keeps leaves and other foreign objects out. I think that with this being dark it also adds to the heating significantly. Once this cover is taken off in the spring there is a light bubble-wrap style cover on a roller that can be taken on/off easily. I envisage leaving the cover on for the first few weeks that the solar heater is running.

Ivan, thanks for your input also.
I had seen the calculation of 25% of pool surface area on the website, but assumed that was for a UK pool, enclosed, used year round, which is not my situation, but maybe I should consider a 30 tube panel instad of 20.
As I also want to be able to pre-heat water going into my combi boiler in the winter, I want something that is easily moved from one location to another. What are the relative weights of the 20 and 30 tube panels, and assuming the plumbing is setup to make it possible, how practical will it be to move the panel every spring/autumn ?

Thanks again for your help...   Roger

[KenB]

Roger, Ivan,

My calculation was purely from the point of view of how much heat needed to get the pool warm, whilst the 25% area rule of thumb, will likely be the amount of heat needed to keep it warm - in the UK.

I am sure that there will be a way of mounting perhaps a 30 tube or 2 x 20 tube panels on a trolley so that they can be faced south and easily manoeuvred.  However, I am guessing that a more permanent installation that provides a combi -preheat and any excess heat going to the pool might be more appropriate.

Ken



 

[robertsathome]

Hi All,

my name is Chris Roberts and a newbie.

I want to buy a Navitron solar thermal system.

I have a 5 bed house with DHW, 3 showers and a hot tub that I would like to heat with your system. The hot tub is 1200 liters at 40c-currently heated by a 1.5kW electric tube heater that runs approx. 75% in winter and about 30% in summer. I propose to have the hot tub linked in series (to keep it simple) after the hot water cylinder, using a simple copper tube as a heat exchanger(preferably finned). I wondered if the 30 tube unit would be sufficient or whether I need 2 x 20 tube units. Also can you provide a finned U tube for my hot tub or one of your finned coils from a cylinder, perhaps. I would welcome any suggestions you/forum may have on the overall set-up and hot tub heat exchanger options.

I also need an accredited installer in my area (Melton Mowbray).

Regards,

Chris

[Ivan]

Roger, Ken's point is quite an important one - it will take a lot more heat to heat the pool up initially, than it will to maintain temperature. So the solar system may appear to struggle to begin with, but once up to temperature, it will not need to work as hard to keep the pool warm.

The 20tube panel weighs just under 50kg with the tubes installed. A 30tube panel is just under 75kg. It is feasible to move them around. You would need two people at least, or do as Ken suggested and install wheels. Normally, most people regard the solar system as a static device, as plumbing it in and out of various setups could be quite time-consuming. To preheat the combi, you would also need a store of some kind - either a pressurised cylinder or a thermal store. Remember the sun is not an on-demand heat source. Hence the need to buffer the heat until it is required.

------------------------

Chris,  The DHW requirement is quite straightforward. Rule of thumb in the UK is 6.5 - 8.5litres of cylinder volume per 47mm tube - A 20tube panel is ideal for cylinder volumes between 130 and 170litres. If you use a lot of water, then I would suggest 170 - 210litres with a 30tube panel. The hot tub is a little more difficult, as I have not had too much experience with these. I am not sure whether you mean the hottub heater is heating the water for 75% of the time in winter, or whether you mean that it is turned on for 75% of the time, but operating on a thermostat (obviously, this would mean it uses rather less energy than if it was heating for 75% of the time). Hot tubs do indeed consume copious amounts of energy, and we have supplied a few panels for this purpose. Previous customers have gone for 30tube panels, but I don't remember how their hot tub sizes compare with yours. Hot tubs may not all be the same, insulation-wise - which will also make a difference. Do you have chlorine or bromine (or similar chemicals) in the water? If so, you will need a stainless steel heat exchanger. If the water is purified with ozone or UV filters, then you can use a copper loop as suggested. Yes, we can supply this, if required.

Navitron is situated at Oakham, a short distance from Melton Mowbray, so we should be able to find a guy to sort out your installation.


Ivan

[Bargeman]

Hello Roger,

Personally I find the 25% 'rule of thumb' a bit hit and miss/overly simplistic. In the RETScreen software there a spreadsheet based model that allows you to calcuate heat losses for an outdoor swimming pool. It takes into account climate (wind, sunshine, temperature and humidity) and various types of characteristic heat loss (evapourative, radiative, convective etc). The climate data can be sourced from the NASA website if you know the latitude and longitude of your site.

On top of this you need to know,

a) target temperature, typically about 27 degs C,
b) surface area of the pool
c) wind shelter,
d) overshading,
e) make up water ratio (5%)
f) number of hours per day covers are in place
g) months during which the pool is in use
h) inlet temperature of water (min 7.7/max 12 degC)

From this the model calculates the heat losses (kWh) every month. If you express this value on a daily basis, you can then calculate the heat output required from the solar collectors. Alternatively you can calculate for each month the average pool temperature you can expect to achieve for a given collector surface area. I tend to find this to be the most meaningful way of sizing the collector area. As stated previously, this applies to maintaining a desired temperature but not the initial build-up of heat.

I find it best to perform this calculation on a month-by-month basis. In Kent in July very little additional heat is required to maintain a 27 degC target temperature. In fact for most pools/collector areas you will need to dissipate heat by leaving off the covers. However to maintain the target temperature in June and August a more substantial input is needed, for which I find the 25% rule understates the collector area requirement. Clearly in a UK climate if you want to be using the pool in May or Sep the collector area needs to increase substantially.

RETScreen uses a simplified model to calculate heat losses, but has shown a good match to more elaborate commercial scale swimming pool modelling software.

regards

[RogerT]

Thanks again for the further replies.

I checked the diary for last year yesterday and discovered my memory was faulty - in fact I first went in at the beginning of May when the water was already at 19C - I was very hot and didn't stay in long !
We took the thick dark winter cover off about 10 days before that and put the summer cover on. I also tried to heat the pool up with about 50M of black tubing and a small pump, but I calculated that the heating contribution was negligible so discontinued it, although it works well for the outside shower in the corner by the gazebo.
So, all I am looking for is something simple that I can start running in April that will add to the temperature so that the pool is warmer earlier in May. I am not too worried about sizing things to meet a specific temperature by a specific date as there are too many other variables such as the weather, and also the system will extend the season adequately as it will be easier to maintain the temperature than heat it up initially.
If you look at the attached picture which is looking to the North West, I wll probably position the panel on the right-hand side of the pool and just trail the pipes into the water over the edge. Not very elegant, but we don't have many visitors that early, so nobody to see it or get scalded. 
Back then to my earlier question: what size pump will I need to move the water through the heat-exchanger/panel given that there will not be much head ?  Will the well-pump advertised on Navitron's website be OK, or too big/small ? 

For pre-heating water next winter, I have not yet decided what to do, if anything. The "conservatory" will be built at the end of the house that you can see in the picture, with the entrance from the shuttered french window that leads off one of the bedrooms, but I now think the roof pitch will be too shallow. It is also a long way from there to the combi boiler which is situated at the far end of the house and it would be hard to run pipes all that way as everything is tiled or covered in stone.
Similarly, plumbing that permanent panel in to heat the pool and/or vent hot water in the summer would be difficult with the changes in level and paved areas that would have to be dug up, so I am reserving judgement on that...

Thanks again   Roger

[RogerT]

Ivan, wife was just in Imperia and passed a Solar Energy shop. They have evacuated tubes which look similar to yours, but she was quoted 80 euros per tube, i.e. over £1000 for a 20 tube panel ! 
They say they get their stocks from "England" (she thinks they said Bangor), so are they supplied by you ?
 
I am planning to go ahead with a very simple system with a 30 tube panel with a closed loop pipe supplying a copper coil submerged in the pool. This will only be used for a month or 2 each year in the spring and autimn, and covered/stored during the height of summer when no heating needed. I'll put a solar powerd pump in the circuit so it will run whenever there's sun to heat the panel. Panel will sit on the side of the pool, just above water level and about a metre away, so no great head or distance to pump.

Questions:
1. How quickly will copper corrode in the pool - we keep the chlorine level as low as legal/possible ?  DO we need to invest in a SS coil at extra expense ?
2. I have a 24 Vac 2.5 amp pump already - will the 60 watt Solar PV panel drive this ? OR
3. Do I need to invest in the Navitron Solar well pump ?  OR
4. Is there some cheaper solar PV/pump solution that I can use ?
 
I was planning to come over to the UK and pick up the panel, but have now delayed the trip to April - how much would it cost to ship the panel to me in Ceriana (NW Italy, near Sanremo) ?

I also want to buy a roof mounting kit so I can fit that when the roof of the "conservatory" is being constructed in the next month or two. How much would it cost to ship just that out here on it's own, and how much extra if included with the panel ?

Thanks again for everyone's help and patience...   Roger

[Ivan]

Hi Roger,

No, as far as I know we do not supply them. There are plenty of suppliers in the UK charging rather more than we do, so of course, if they were to put a margin on top...they could easily end up at £1000per panel.

1. The copper will corrode very slowly - I know of one person with pool water going through his flatplate - it took 10years for the flatplate to spring a leak. The leached copper compounds in the water may form a health hazard

2. I would assume that a 60W solar PV would drive your pump (assuming correct voltage)....but a 60W PV will produce 60W in direct bright summer sunshine - in other conditions it will produce less. Oversizing needs to be carefully considered. Open circuit voltage of a '12v' PV is around 21v, so if you oversize, let's say you use 2x55W 12v panels in series, you will get 110W in sunny conditions. This will be more than the 60W pump consumes, so the voltage will rise. You will need to make sure this will not damage the pump, or provide adequate voltage regulation to prevent it exceeding the pump's max voltage tolerance.

3.The solar well pump is designed for pumping small volumes of water many metres vertically. It is only designed for very low flow rate, and it is not designed for closed loop systems.

4. I think there are some 12v circulators on the market at the moment that have built-in inverter. This might be an option

I don't know the shipping costs off hand - if you would like to give the office a call, they can get an actual price. We have to get quotes each and every time for continental shipments.

Ivan

[RogerT]

Ivan, the 30 tube system I bought from you a couple of months back is installed and working brilliantly as previously reported, but I am still not having any luck in finding a way to replace the mains-powered pump. I just noticed someone suggested using your well-pump to lift rain-butt water, so...

3.The solar well pump is designed for pumping small volumes of water many metres vertically. It is only designed for very low flow rate, and it is not designed for closed loop systems.

My system is not completely closed-loop or pressurized, I just pump the pool water into the manifold and let it run out again. I currently have a flow rate of 2L/minute, but that is with the manifold about a 1.5M above the level of the pump. Next time I have some able-bodied men visiting and able to help me, I will be moving the panel to the terrace below the pool such that the manifold will be at about the level of the pool, so the head will be less than .5M.
With this small head, if your pump delivers 80L/hour at 10M, I suspect the flow might be higher than I want for efficient heat transfer.
I know this pump may not be ideal, but if it works that will be good enough as I will be able to use it at other times of the year to lift water from our ancient rainwater collection tank (mentioned elsewhere - should soon be back in action and holding at least 100K litres when full) to a 1000L holding tank on a higher terrace to give better pressure for hoses and automatic watering systems (and an overflow into a water feature ! )

4. I think there are some 12v circulators on the market at the moment that have built-in inverter. This might be an option

If the well pump is really not suitable, could you please give me a link to a supplier of these ?

Thanks again, good luck with the showers in Glastonbury

Rgds  Roger

[Ivan]

Hi Roger,

I Would not think the well pump is your best option - it is quite expensive, for a start.  I would do a search for low voltage pump and see what you find. Danfoss make one, also Laird. Both are pricey, and not particularly good, in my opinion. You could try looking for a phosphor-bronze pump, and I think Grundfos offer a 12v version of their mains circulator pump.


Ivan

[Contadino]

I'd recommend an El SID PV pump, but you'd need to check the throughput figures.  I use mine as a circulating pump from a 10w panel and it's performing perfectly.  I went for a 10w panel on the advise of the manufacturer as it's a glycol loop and apparently the mixture thickens up in the cold weather, so in your situation, maybe a 5w panel would be sufficient.

[RogerT]

> I'd recommend an El SID PV pump...

Sounds ideal - I'd already enquired about this from a supplier in the UK but have had no reply yet. I'll chase them up.

Have you found a supplier in Italy ?

Ciao   Rog