Solar heaters flow rate and temperature rise

[JohnRoss]

Having looked at a lot of solar heater for swimming pools sites  I am getting mixed messages about ideal flow rates versus temperature rise. I would be grateful for typical flow rates and temperature rise obtained for comparison purposes. Litres/minute and degrees Celsius would be good but I can convert degrees Fahrenheit and gallons but please specify US or UK gallons. I understand that the time of year will also affect performance so if you have data about this that would be great too!..........Many thanks..............JR

PS has anyone come across hot air solar heaters for unenclosed swimming pools?

[Théière]

[quote user="JohnRoss"]

PS has anyone come across hot air solar heaters for unenclosed swimming pools?

[/quote]

Air source heat pumps?

[JohnRoss]

Ok no not heat pumps just hot air produced by solar heater and passed through a heat exchanger in the pool water. There is an American site suggesting this for sucking hot air out of an attic and passing the heat into the  pool water though not something that would work with our house though might work in Southern American states with the type of construction they have. See: http://www.ecosmartinc.com/catsolar2.php .......JR

[Théière]

That is something I would like to see! and its American so probably not that efficient then.

Probably using hot air to sell it and sucking the money out of your wallet!

Once the m3 area of your loft has had the heat sucked out what then?

Please send me the link.

[Kitty]

I would like to know this as well.  I'm just getting a price for a swimming pool and am unsure about benefits of solar heating.

[JohnRoss]

The most common ones here seem to be solar mats with pool water passing through and the more expensive racks of heat pipes with a separate pump and heat exchanger. The figures for flow rate and temperature rise are the all important ones that would be good to know so comparisons can be made......................JR

[JohnRoss]

Teapot I guess the radiation falling on the roof would renew the hot air inside the roof during the day. See link above. Not effective with the type of house roof we have here in France I think..........JR

[Poolguy]

[quote user="JohnRoss"]The most common ones here seem to be solar mats with pool water passing through and the more expensive racks of heat pipes with a separate pump and heat exchanger. The figures for flow rate and temperature rise are the all important ones that would be good to know so comparisons can be made......................JR[/quote]

John Ross

Not exactly sure what you mean about the cost. Is it cost per m3, cost/Kwh, or just....? What exactly.

I can tell you that based on the purchase price/heat output (theoretical)/ life span of the various options, evacuated tubes are about €0,04/kwh, Glass panels vary around €0.14kwh and the EPDM mats are about €0.35- €0.50/kwhr, is that the type of comparison you mean?

To me the comparison is quite simple, vis: How much do I have to spend to heat my pool in (say) May from 19°c to 25°c and then keep it there for as long as possible?

Well if you've got a 10 x 5 pool then using EPDM mat, you'll need about 60% of your surface are (at least if not a little more) which is 30m2 at about €130/m2 plus installation, SAY €4,000. Now for that you will have to keep the system free of air locks, put up with a reduction in the circulation rate of your pool and drain the system in winter, as well as find somewhere that has a large area that you can cover with a very large black thing that doesn't bring down the aesthetic of the whole area. It only works when it sunny so don't expect too much by way of heat gain unless you can also see the sun. June to August - not much of a problem, May....? HHHHmmmm

The same pool with Evacuated Tube Solar system you'll need 9m2, it can go out of the way a little more, not so sensitive to orientation (SE- SW), will work so long as there is UV radiation around even on cloudy days, it will work right through the winter, you do not have to drain the system, and will certainly give you the temperature you want in May-October (I have seen systems raise the pool temps 5°C in one day) and (guess what) the price..... is about €4,000 plus installation.

Does that answer your question?

What is it you want to know about flow rates.... the slower the better n'est pas

PM me if you want more information

Andrew

[JohnRoss]

I was hoping for some hard figures about flow rate and temperature rise, cost is another issue but not what I was asking about ................................JR

[chem geek]

John,

Typical specifications for a good quality solar system (in North America) for heating pool water are shown [url=http://www.fafco.com/SolarPoolHeater/06359G_SunSaver_Spec.pdf]here[/url] for an in-ground pool with solar panels typically mounted on a roof vs. an above-ground solar system typically mounted on a rack near the ground shown [url=http://www.fafco.com/SolarPoolHeater/06963B_Solar_Bear_AGP_Spec.pdf]here[/url].  The site I am referring to for these solar panels is FAFCO [url=http://www.fafco.com/SolarPoolHeater/Solar-Energy-Benefits.html]here[/url].

The maximum daily output of these typical solar panels is around 1000 BTU per square foot (3.15 KWh per square meter).  HOWEVER, that is measured in Florida in the summer with the panels pointed towards the sun at noon -- in other words, ideal conditions so this is an absolute maximum power output, though this 1000 BTU number is the output for the entire day so takes into account the sun not being overhead the entire time.  The sun's energy is around 1000 Watts per square meter at peak.  The solar panels are around 80% efficient at recommended flow rates (more on that below) in converting solar energy to a temperature rise of the water.  So the peak output is 800 Watts per square meter (about 254 BTU/hr per square foot).

To figure out the temperature rise, we need to make some assumptions about the area of panels relative to the area of the pool and the average pool depth.  For simplicity, let's assume the area of panels is equal to the area of the pool since that will be easy to scale and let's assume an average pool depth of 1.4 meters.  800 Watts = 191 calories per second and 1.4 cubic meters is 1400 liters so that's 3600*191/1400/1000 = 0.5C per hour for a solar panel area equal to the pool surface area assuming 1.4 meter average depth.  That actually sounds about right since in my own pool I get a peak heating of a little less than 1F or roughly 0.5C per hour and I have close to (a little less) than my pool's surface area in solar panels.  So I think you can use this as a rough maximum since France is at higher latitude so even angling your panels to point towards the sun the sun's rays are going through more atmosphere.  The best site I could find to calculate what would happen in France over a day is [url=http://sunbird.jrc.it/pvgis/apps/radmonth.php?lang=en&map=europe]here[/url].  I don't know where you live, but if I use Paris, then I get about 1000 Watts per square meter in July at noon for a "clear" sky, but a "real" sky (which I assume is more typical) is 600 Watts so would be 60% the rate of heating I gave you (i.e. 60% of 0.5C per hour for solar panels equal in area to pool surface area).

As for REAL rates of heating, take a look at those first links I gave and look at the four graphs in either of those PDF files.  Note the "Measured Efficiency" graph and see that the scale has a "(Ti-Ta)" factor.  This is the temperature difference between the air temperature and the panel temperature.  Basically, this says that the colder the air temperature, the more heat loss from the panels so the efficiency will drop.  If there is more wind, then this loss can be pretty large making the panels very inefficient.  The graph shows that the efficiency drops to around 50% with at 15C temperature difference between the panels (close to pool water temperature) and the air (with a 3.9 km/hr wind).  Now note the "Pressure vs. Flow" graph which basically shows the square relationship between flow rate and pressure -- a doubling of flow rate increases the "head" or pressure resistance by a factor of 4.  Now note the "Efficiency vs. Flow" graph and see that faster flow rates are more efficient.  This is counterintuitive at first so let me explain this since a lot of people get this wrong and think that a slower flow rate is better since the temperature rise would be greater in the panel.

It is true that a slower flow rate will result in a greater temperature rise of the water in the panel, but this does not mean that the pool water overall will get a faster temperature rise.  For example, say that a certain flow rate has the temperature in the panel rise by 1C and let's say that this flow rate takes 2 hours for one turnover of the water.  This means that after 2 hours the entire body of pool water will rise in temperature by 1C.  Now cut this flow rate in half.  The temperature rise in the panel will now be 2C (ignoring efficiency differences) but the slower flow rate means it will now take 4 hours for this 2C temperature rise in the entire body of pool water.  Note that a 2C rise every 4 hours is the same as a 1C rise every 2 hours.  Were it not for efficiency differences, the flow rate would not make any difference at all in the rate of temperature rise in the pool.  Basically, the amount of heat transferred per time is the same in both cases -- it is the product of the temperature delta with flow rate that determines the amount of heat transfer.

Now, back to the efficiency loss at lower flow rate.  Basically, at lower flow rate you have a greater temperature rise in the panel, but remember that "Measured Efficiency" graph and the fact that a greater temperature difference between the panel and the air temperature results in more radiated or convected heat loss.  So you don't really want the temperature of the panel to get very hot so the most efficient would be a very high flow rate that keeps the panel as cool as possible (i.e. the smallest temperature rise).  In my pool, the peak outlet temp with the solar on is around 2.7C higher than the pool temp.  However, you see in the "Pressure vs. Flow" graph that higher flow rates mean more head (that is, pressure resistance) and that means more pump power is needed.  Roughly speaking, the power varies as the cube of the flow rate.  A doubling of the flow rate requires nerarly 8 times the power.  So for energy efficiency (but not heating efficiency) you want a slower flow rate.  A reasonable balance between these two is at the recommended flow rate of the panels resulting in 80% efficiency though obviously this is a personal choice between pump electricity savings vs. the rate of heating and number of required panels.  In my own pool, I run at 4 GPM per panel for 12 panels so 48 GPM and I really wouldn't want to run any faster as the power consumption rises rapidly but I also don't want to run much slower as we need fairly fast heating (i.e. need good efficiency) so I can avoid using the much more expensive (and wasteful) gas heater.

There are special, but much more expensive, types of solar panels that are glazed (usually black-painted metal tubes enclosed in glass, like a greenhouse effect) that significantly reduce the problems shown in the "Measured Efficiency" graph since they insulate the collectors from wind and both radiation and convection of heat.  These sorts of panels are typically used for domestic hot water heating since the hot water is obviously a lot hotter than the air temperature.  Such systems are also sold for pools but are VERY expensive compared to unglazed (i.e. plastic tube panels).  They are often called Gobi collectors.

The attic heat exchanger gives a BTU rating at a certain temperature difference with a hot attic, but in reality once the system gets going and removes heat from the attic then its heat output is much lower.  As was pointed out by teapot, this won't be nearly as efficient as solar panels on the roof.  The heat output after the attic temperature is cooled will mostly be dependent on the rate of heat transfer from the sun through the roof into the attic -- that's where most of the loss comes from (i.e. heat reflected or re-radiated or convected rather than transferring into the attic).  Interestingly, the solar panels on my roof also act to cool the house and presumably the attic.  We recently added one panel over our bedroom and it has made a HUGE difference, but it's limited to when the solar is running so on really hot days the solar system shuts off so the cooling benefit is limited (unless we wanted our pool to get well over 32C!).

As for how much of a net temperature rise your pool can retain relative to not using solar panels, this is very much a function of how you insulate your pool.  If you have a very good solar cover, then this helps reduce the heat loss at night which is when most heat loss occurs (it can occur during the day as well if there is less sun and more wind with cool air).  As a rough rule of thumb, a bubble-type solar cover will reduce an overnight heat (and therefore temperature) loss by around 75%.  This roughly means it can keep the overnight loss to 1C if the pool is 15C warmer than the night air.  However, such pool covers can be a bit of a pain to take on and off.  An electric cover is easier, but not as well insulating only reducing overnight heat/temp loss by around 50%.  These numbers assume an in-ground plaster pool since gunite is fairly insulating.  I suspect that an above-ground vinyl pool will not see as much benefit with a solar cover as some heat is lost through the sides, but I'm sure it's a lot better than not using a cover (a total guess would be that a bubble-type solar cover reduces heat loss in an above ground pool by 50-60%).  I have an opaque electric safety cover over an in-ground plaster pool and lose around 2C at night, but the water temp is around 31.5C (my wife uses the pool as a therapy pool almost every day) and the night air average low temperature is around 12.5C (daytime average high temp is around 27C in the summer).

I hope the above makes sense and answers some of your questions.  If not, please let me know what I can clarify.

Richard

[Théière]

Chemgeek, could, or do you use the spare capacity in your panels above the bedroom to heat your domestic water supply when not heating your pool? As that would keep the room cooler and reduce your energy bill further.

Can you tell us the temprature reduction in the bedroom since having the panel fitted?

Just one last question, when you got married and the official said "do you take this women............" How long was your answer [:D]

[chem geek]

The panel over the bedroom is of the type used to heat a pool -- black plastic tubes -- so it does not heat the domestic water supply (and can't -- you need special Gobi-like glazed panels to heat a small volume of water to hot temperatures).  We were most concerned with maximizing the pool temp over as long a season as possible since the gas heat for the pool is expensive (about $1.56 per 1C rise in temperature) and of course uses a non-renewable resource (natural gas).  We wanted to minimize the amount of time my wife needed to use the community center indoor pool in the winter season.  We are considering adding a solar domestic hot water system, but have run out of "prime" roof space so we'll see if it will still work well at a less optimal angle (i.e. not south facing).

I would guess that the temperature reduction in the bedroom by late afternoon on the hottest days (32C) is around 4C compared to when we didn't have the panel.  If we ran the panel all day even on hot days, I'd guess that we'd have a 6C reduction in temp in the bedroom.  It's very noticeable -- we used to have to run a room air conditioner on hotter than average days and we hardly ever have to do that now.  This is with a well insulated roof as we had rebuilt the house around 6 years ago though that one room gets sun over a 3-sided hip roof all day long.

The answer was "I do." [:D]  My thanking the guests after acknowledgments, on the other hand, ... [:$]

[Théière]

The panel over the bedroom is of the type used to heat a pool -- black plastic tubes -- so it does not heat the domestic water supply (and can't

Not even with a diverter valve and heat exchanger? or secondary heating coil?

I am not familiar with the the heating systems in the U.S. do you have a storage tank?

[chem geek]

We have a natural gas hot water heater (storage tank with 252 liters), but you can't make already pretty hot water hotter from a cooler source without applying energy, as with a heat pump.  That is, you can't use the pool water to heat the water in the domestic hot water heater.  You also can't divert the domestic hot water to the pool solar panel or else it will lose most of its heat to the air faster than it will get heat from the sun.  You either have to use a special panel that will be able to add heat from the sun more than it would lose heat from the tubes OR you can use a photovoltaic (PV) system to generate electricity to operate a heat pump (or to use direct electric heating, but that is inefficient).

I suppose we COULD use the pool solar system in a diverter mode to preheat the cold water input to the hot water heater (with yet another input tank) since we should be able to heat it to somewhere above the pool temperature, perhaps up to 38C, but that would only help when the hot water was being used.  Since we have a hot water recirculation pump for faster hot water, what is really needed is something to give a small boost to the hot water throughout the day in addition to a longer larger heating when we actually use hot water so I think a standard domestic hot water solar panel would be the way to go.  At night, the recirculation pump turns off and the hot water in the tank stays hot (it's VERY well insulated).

[JohnRoss]

Well many thanks Richard for a very full reply to my question. The graphs and panel performance figures were interesting. I have been getting 6 to 7 degrees Celsius rise in water temperature returning from the solar heater in late Spring when the pool temperature was in the low 20's, 5 to 6 degrees in late July when the pool was in the high 20's and 4 to 5 degrees rise now with the pool at about 22 degrees. Flow rate of 36 litres/min.

Night time temperatures here have been as low as 5 degrees of late with, despite a floating bubble cover, a large part of the daytime gains lost overnight. The Summer this year near Niort in 79 has not been good with many days of cloud and little sun resulting in gains of three or four days of sun being lost in the following three or four days of cloud and rain. I take the point about flow rate and have looked at the flow rate/temperature rise product at 22, 30 and 36 litres/min. I had assumed that the highest product indicated the best flow rate for a particular system which in my system seems to be somewhere between 30 and 36 litres/min. I can increase the flow to a maximum of 40 litre/min but I suspect this would be of no benefit if my assumption is correct, your confirmation or otherwise would be helpful on this point. The pool holds a just tad under 75,000 litres and is 5 x 10 metres. The average depth can be taken as about 1.5 metres and the area of solar panel is a bit on the low side being about 18.5 square metres. I intend to increase this to at least half the pool surface area next year.

The point of my post was to see how these figures compared with other people's systems be they plastic solar mats or heat pipe types. I think comparison in terms of flow rate and temperature rise is something most of us can understand although one accepts the concept may be overly simplistic!..................................JR  

[chem geek]

You got it right.  The product of temperature rise and flow rate gives you some sense for the efficiency so lets you trade off the greater efficiency vs. the higher pump electricity cost at the higher flow rates.  The additional heating you are seeing in your pool probably comes from the sun directly hitting the pool.  Even without a solar system, pools with solar covers have warmer water than those without covers.  Clear covers let some sun through while keeping heat in.  [EDIT] The covers mostly prevent heat loss at night; removing the cover during the day can be better for heating the pool from direct sunlight if there is little wind. [END-EDIT]

With 75,000 liters and a flow rate through the solar panels of 36 liters/minute, that's a turnover of nearly 35 hours so I presume that you have a bypass and only a portion of your water flow is going through your panels.  For a larger system, the normal situation is to pipe the solar panels in parallel, not in series, so you can get more of the flow through the panels (though as you've figured out, you are just having lower flow at higher temperature rise in the panel).  In my pool, I have no bypass and the entire flow goes through the panels.  Anyway, your solar system is (18.5/50)*0.5 = 0.185C per hour maximum.  This is consistent with 6.5C over 35 hours or a 6.5C temperature rise out of the panels (at a flow rate that gives 80% efficiency).

Too bad your nights are so cool and that you get strings of cloudy / low sun days.  That's a killer (in a bad way) combination and will have the pool temperatures drop pretty quickly.  A larger [EDIT] flat-mat unglazed [END-EDIT] solar panel only helps when the sun shines. [:)]  In the outskirts of our swim season, the solar just barely keeps up with the overnight heat loss and, of course, eventually we need to use the gas heater until that gets pretty ridiculous (and it gets cold outside even during the day).  This "balance" seems to happen when the overnight lows are around 8C and the sun is far lower in the sky -- April/May and October/November.  We usually stop our season around mid-November, but that's with gas assist.  However, we keep our pool very warm.

Your best bet is to see how other people are doing with solar systems in roughly your same area with similar weather.  You can then somewhat scale according to their solar panel area to pool area, etc.

[Théière]

So that's pretty well it for the old style of black water fed matt.

Enter the evacuated glass solar array that Poolguy sells. massively more efficient and do not require the sun to shine only daylght. It is a different system and requires different maths i.e. it works better with lower flow rates therefore cheaper in electrical terms.

You cannot touch the solar collector on this type of of design as you will burn your hand badly. Can also be used easily to feed your hot water tank when the pool is done.

Do you see what I did there chemgeek.

[chem geek]

It does not require different math.  A glazed (glass-enclosed) solar panel will still be more efficient at higher flow rates since there is still loss from a "hot" panel.  The lower flow rates save on electrical energy but are less heat efficient.  The same principles apply.  Such systems are much more expensive than the black plastic mats and in warmer climates are not an economical solution for pool water heating, though are absolutely the right choice for domestic hot water heating.  As for whether such a system makes sense for John, you would need to give him a Measured Efficiency graph or some real data from systems in the same area with real results in addition to pricing.

If the enclosed panels are hot on the outside, then they aren't being run efficiently and are re-radiating (or convecting with wind) heat back out into the air, especially if used for heating pool water (for domestic hot water, the water is hotter so the panel will be hotter, though if run efficiently only the collector will be somewhat above water heater temp -- somewhere around 60C).  This may be a conscious trade-off for electrical pump energy efficiency but to say that slower flow rates is more heat efficient (i.e. raises temperature faster in the bulk pool water) would still be incorrect.

For example, the Gobi collectors shown [url=http://www.solardirect.com/swh/active/collectors/gobi.htm]here[/url] have specifications [url=http://shop.solardirect.com/pdf/water-heaters/solar-hot-water/active-solar/collectors/gobi-specifications.pdf]here[/url] have an efficiency equation (graph) with a 74% efficiency maximum and a slope of around 0.8 BTU per hour per square foot per ºF which is basically a slope that is 1/4th as steep as the Fafco panel.  Another design encloses each tube as shown [url=http://www.smartenergyne.com/tubecollectors.htm#SPECIFICATIONS]here[/url] where you can see the efficiency graph where the greatest efficiency is with the lowest temperature difference between the manifold and the ambient air.  This occurs at higher flow rates since that carries away the heat faster keeping the panels cooler.  The Navitron SFB panel that PoolGuy sells has efficiency information shown in [url=http://www.navitron.org.uk/download_request.php?id=44]this specifications document[/url].  In Table 2.7 you can see how the power output drops when the difference in collector and ambient (air) temperature gets larger.  Note in 2.3.1 the efficiency equation shows that the efficiency is lowered at a higher temperature difference between the average collector temperature and the ambient air temperature.  It is more efficient in terms of collecting the most solar energy to run at a lower collector temperature and this is at higher flow rates; again, this costs more in electrical energy so there is a tradeoff.  By the way, don't be fooled by Table 2.7 into thinking the collectors are 657/700 = 94% efficient -- they are not.  The 700 number is per square meter while the 657 number is per collector.  The actual efficiency is shown in the 2.3.2.1 diagram where it's a maximum of 41% over the gross panel area.  On a sunny warm day, this is half as efficient as a black mat panel (at 80% efficiency).  Basically, you waste area around the sides of the tube.  The Gobi collectors, on the other hand, are 74% maximum efficiency (as I noted above).

I think that [url=http://shop.solardirect.com/pdf/water-heaters/solar-hot-water/active-solar/collectors/gobi-performance.pdf]this document[/url] best explains the concepts and principles.  Note that a Gobi collector outperforms evacuated tubes in sunny weather while the opposite is true in cloudy weather, but even Gobi collectors from Heliodyne are still a lot more expensive than black flat mat panels though may be less expensive than evacuated tube collectors.  This is why you don't generally see them in the U.S. except in the northernmost climates as you get closer to Canada and even then, it's mostly commercial where they can afford the larger capital expenditure.  Of course, France is at a northern latitude as noted with John's data.  It's a cost/performance tradeoff.

These panels are not "massively more efficient" under sunny warm air or calm conditions.  They are only more efficient when the air temperature is cooler (especially if there is wind).  That's what I said in my post.  As for such panels not needing direct sunlight and still operating with just daylight implying that this is not true with black mat panels, that is not accurate.  The Gobi-style or evacuated tube panels are not better on cloudy days at the same air temperature near the water temperature than black mat panels; the difference is that if the day is cooler, especially with wind, then the Gobi-style and evacuated tube panels are more efficient.  Basically, the Gobi-style has roughly the same efficiency as a black mat panel when the temperature difference between the water and the air is 4 times larger for the Gobi panel than the black mat panel.  I have had my Fafco black-mat-style panels turn on during cloudy days when the water and air temperature were close with the air only around 3C cooler (or perhaps more during spring startup) than the water on a calm day.

A comparison of panel efficiencies (using gross area, since that is relevant regarding roof or ground space) is as follows at different temperature deltas between the collector and the ambient air.  You can assume that the average collector temperature will be somewhat higher than the pool temperature (2-4C) [EDIT] except for the evacuated tube that runs hotter at lower flow rate; figure 8-16C [END-EDIT].  These are all at 800 Watts per square meter sunlight (so 80% of peak sunlight) and at low wind (3.9 km/hr).

deltaT(ºC)    flat black    Gobi glazed    evacuated tube

    0                 80%            74%               41%

    5                 68%            71%               40%

  10                 55%            68%               40%

  15                 43%            65%               39%

  20                 30%            63%               38%

  25                 18%            60%               37%

  30                   5%            57%               36%

  40                 N/A             51%               35%

  50                 N/A             46%               33%

Though an evacuated tube will do better at lower sunlight levels, such as on a cloudy day, the total power output is far less.  Maximum power from light on a cloudy [EDIT] overcast [END-EDIT] day can be only 1/3rd so around 300-350 Watts per square meter instead of 1000.  The fact that an evacuated tube has a higher efficiency than Gobi glazed at lower power isn't that big a deal since total power is so much less.  I suppose if one lived in an area that was very cloudy or very cold most of the time, then an evacuated tube's higher efficiency in such conditions would be more valuable.  At 300 Watts per square meter, the evacuated tube at 30C temperature difference has an efficiency of 28% while the Gobi glazed panel has an efficiency of 29%.  Only for even darker days or greater temperature differences does the evacuated tube become more efficient than the Gobi glazed.  Since hot water heater applications have a bigger temperature difference, I'd expect evacuated tubes to perform better than Gobi for that application than for pool heating.  [EDIT] With a 40C temperature difference, then at 300 Watts per square meter (overcast day), the evacuated tube has an efficiency of 24% while the Gobi glazed panel has an efficiency of 13%.  With a 50C temperature difference, the evacuated tube is 19% efficient while the Gobi glazed panel produces no output. [END-EDIT]

I am NOT recommending one panel over another.  I gave information in my original post in this thread, including writing about the glazed panels noting their greater efficiency in cooler weather and their higher price.  I did not refer explicitly to evacuated tube panels but the point of remaining reasonably efficient when the temperature difference is greater (i.e. higher flow rates) is the same.

Your summary was short, but gave no information on what the original poster was asking regarding specifics of flow rate vs. temperature rise nor how the product of the two is a rough proxy for heating efficiency.  Not everyone wants detailed information, but some people do.

[JohnRoss]

Thanks again Richard and yes the flow through the solar heating system is only a proportion of the total flow through the pump and at a guess I would say less than 25% of the total flow. The pool is by DESJOYAUX and everything is contained in a block which hangs on the side of the pool therefore no long pipe runs, no sand filter, uses a 6 micron mesh bag filter but no possiblity of reverse flow to give heating from the bottom, as suggested in one of your links, though the main output nozzle can be angled down and to the side to stir up the bottom and give a rotation to the water in the pool. The side nozzle is what I use to feed the solar heating system.

Your best bet is to see how other people are doing with solar systems in roughly your same area with similar weather.  You can then somewhat scale according to their solar panel area to pool area, etc.

Indeed so come on folks it is your flow rate and temperature rise data I am after.....................................JR

[Théière]

Richard,

Your gobi flate plate collectors are behind the times, more efficient evacuated tube arrays are available.  http://www.heatmyhome.co.uk/index.php is just one example out of many.

These do not rely on direct sunshine but on light so are great in the northern hemisphere i.e. UK (where the low output flat panels are poor in performance) or in spring and autumn (fall). which is normally when you want to extend your swimming season, yes?

JohnRoss, Desjoyaux? therefore no long pipe runs, and no flow at the top end of your pool either. Contact the manufacturers of the evacuated solar arrays, they will have all the information you require.

I see you added a link to your post for the loft heater. It is an air source heat pump mounted in the loft space instead of outside, they are a very efficient means of heating, not necessarily that model as I am very very dubious of ECOsmarte, they make lots of claims about their Ionizers that do not stack up or make for good pool chemistry.

Reading your post above it sounds as if you already have a system installed so why are you asking.

There are plenty of previous posts on this subject, suggest you read some.

Post edited by the moderators. Users must not post messages which are insulting, abusive,

racist, sexist, or derogatory in any way to others.

[chem geek]

[quote user="teapot"]

Richard,

Your gobi flate plate collectors are behind the times, more efficient evacuated tube arrays are available.  http://www.heatmyhome.co.uk/index.php is just one example out of many.

These do not rely on direct sunshine but on light so are great in the northern hemisphere i.e. UK (where the low output flat panels are poor in performance) or in spring and autumn (fall). which is normally when you want to extend your swimming season, yes?[/quote]

The efficiency charts or formula coefficients don't lie.  Look at my post again as I've added some more data in table form to show the differences, at least for the Navitron brand.  When there are claims of being more efficient, they may be talking about efficiency relative to the area of the small collector inside the tube, but that's pretty much irrelevant and what needs to be looked at is the efficiency over the total area (i.e. the "gross" area) consumed by the panel installation including the space required for the evacuated tube.  After all, that's what takes up the roof space.  Even if one had a small 100% efficient unit inside a larger unit, the 100% number would be irrelevant.  When they quote 40% more efficient, they are comparing against their own brand (more on that below).

I can't find a spec sheet with efficiency graphs or coefficients for the evacuated tube link you gave -- if you can find that for me, then I can run some numbers and compare it both to Navitron evacuated tube and to Heliodyne Gobi.  I do see that they talk about flat panels (mostly for domestic hot water) as using a special fluid, but that isn't necessary in the Heliodyne Gobi collector as they can accept water directly to/from the hot water heater tank avoiding the losses associated with an additional heat exchanger (assuming the climate is non-freezing and the water is not very hard).  When a manufacturer compares a new technology of theirs against their own older technology, that doesn't mean their older technology was being done efficiently; in this case with the link you gave, it wasn't.  Again, please note that they are talking about hot water heater applications and that makes evacuated tubes more likely to be better due to the larger temperature differences; application is everything and pool water at 27C to 31C is a lower temperature so a smaller temperature difference compared to the air vs. 50C to 60C for domestic hot water temperature.  Pool water vs. air temp differences are from zero to around 25C while domestic hot water vs. air is from 20C to 55C.

As for relying on light and not sunshine, again please read my updated comments in my post (that I was revising as you wrote yours).  The Heliodyne Gobi does very well except in the most extreme conditions of very low light or very large temperature differences.  I can see the latter for hot water heating, but not for pool heating except under very extreme conditions (and then wouldn't be very efficient when the sun did shine or when temperature differences were smaller).  I totally agree that the less expensive unglazed flat panels for pool heating, such as what I have, do not do well when the temps get cooler -- it really has nothing to do with cloudy conditions directly since they work fine in lower light; it's the lower temperatures (and wind) that kills them.

I totally agree with you regarding EcoSmarte in general.

[JohnRoss]

There are plenty of previous posts on this subject, suggest you read some. If you can point me at the posts that contain the specific information I am seeking I will be most grateful though I don't remember seeing quotes of flow rates versus temperature rise, maybe you have seen something I have missed.

The water in my pool seems to rotate at all levels, one only has to watch the odd leaf moving on the surface, half way down and on the bottom if that was what you were referring to in your comment about Desjoyaux pools. I am satisfied there is no stagnant water and that sufficient mixing of water at different levels is taking place provided the output nozzle is set at a reasonable angle.

Reading your post above it sounds as if you already have a system installed so why are you asking. Clearly because I wish to compare the performance of my system against other systems so that extensions/modifications can be made if necessary.

Having read again the info given on the site that the link I gave refers to I note that they do not use any form of heat pump, just a fan and heat exchanger. One might speculate that some sort of greenhouse construction with a fan and heat exchanger might be worth considering if the idea had some merit. A variation, if you will, on the Trombe wall with a much lower thermal mass absorber as you would not want too slow a response of course! Further you will note that I was not suggesting it was a system that would work well with the type of house roof construction that most of us have here! I have not read many of your posts so forgive me if I ask if you have some commercial interest in pool equipment, like Andrew, which might colour your opinion?......................................JR

   

[chem geek]

[quote user="Poolguy"]

Well if you've got a 10 x 5 pool then using EPDM mat, you'll need about 60% of your surface are (at least if not a little more) which is 30m2 at about €130/m2 plus installation, SAY €4,000. Now for that you will have to keep the system free of air locks, put up with a reduction in the circulation rate of your pool and drain the system in winter, as well as find somewhere that has a large area that you can cover with a very large black thing that doesn't bring down the aesthetic of the whole area. It only works when it sunny so don't expect too much by way of heat gain unless you can also see the sun. June to August - not much of a problem, May....? HHHHmmmm

The same pool with Evacuated Tube Solar system you'll need 9m2, it can go out of the way a little more, not so sensitive to orientation (SE- SW), will work so long as there is UV radiation around even on cloudy days, it will work right through the winter, you do not have to drain the system, and will certainly give you the temperature you want in May-October (I have seen systems raise the pool temps 5°C in one day) and (guess what) the price..... is about €4,000 plus installation.

[/quote]

As I noted in an earlier post, with a 1.4 meter pool depth, a 100% pool

area panel coverage with an 80% efficient solar panel would raise the

temperature 0.5C per hour near noontime.  That's based on a solar

insolence of 1000 Watts per square meter which is the peak most

anywhere with panels pointed towards the sun around noon.  The claim is

that 9 square meters, or 9/50 = 18% of the surface area will result in

the same amount of heating as the flat plastic panel.  During the

summer, that is certainly not the case.  9 square meters would result

in at most 0.1C per hour rise and that's assuming 100% efficiency

(whereas actual efficiency from the

[url=http://www.navitron.org.uk/download_request.php?id=44]spec[/url]

is at most 41%).  If the pool was raised by 5C in one day, it wasn't

due to the solar panel but mostly to sunlight hitting the pool directly

(or some other heating source or a more shallow pool than 1.4 meter

average depth or a much smaller pool area than 50 square meters).

If you use [url=http://eosweb.larc.nasa.gov/sse/RETScreen/]this link[/url] you can get the total solar insolence per day for a location and for France near Paris it's 5.63 KWh per square meter per day in July.  That's a horizontal insolence so tilting the panel to point directly at the sun at noon for 47 degrees latitude taking into account the Earth's tilt in summer would be 5.63/cos(47º-23.44º) = 6.14 which is 5,284,689 calories per square meter which would raise 1.4 cubic meters of water 3.77C per day and that's with 100% efficiency with a panel area equal to the pool surface area with 1.4 meter average depth.  There is some benefit with the evacuated tube silvered backing to partially follow the sun, but the 41% efficiency wipes that out (and more).  The 9 square meter panel heating a 50 square meter area, 1.4 meter deep pool could only contribute, at most, 0.7C per day at 100% equivalent efficiency (or sun tracking).

It is physically impossible to get more energy from the sun than what it is delivering over an area.

Now outside the summer or any other time where the temperature of the

air is much cooler than the pool water and especially if there is a

cool wind, it is true that the flat plastic panel won't work while

either the glazed Gobi panel or the evacuated tube panel will.  In an

extreme situation of temperature difference or in the case of domestic

hot water heating, the evacuated tube panel will be more efficient than

the glazed Gobi panel.

If I had more money at the time we were rebuilding the house and

putting in the pool and if I had known more about collector options, I

would have put in the equivalent of the Heliodyne Gobi collector so

that we could extend the swim season further without using gas at least

partly in April/May and October/November.  The gas usage probably costs

us incrementally around $1000 per year, but the panels with sufficient

capacity were nearly 3 times as expensive.  If we had a bubble cover,

we could get away with less panel surface area (perhaps even half as

much) and even without new panels our gas usage would be cut in half,

but we have an opaque electric safety cover instead.  It just goes to show what a big difference a seemingly small thing such as the type of solar cover can make. 

For hot water heating, the evacuated tube panel would probably be the

best to maximize year-round operation so I will look into that as an

option.

It's too bad you don't sell your Chemigem system in the U.S. because it

would be great to recommend a quality reasonably priced chlorine dosing

system.  One can buy a peristaltic pump, but there isn't a full

controller package and pool builders (PBs) and other installers don't

generally install such systems in residential pools (they tend to

promote SWG systems instead).  If that had been available when we put

in our pool, I probably would have bought it and had our PB install it.

Richard

[Théière]

Hi John Ross,

The ecosmarte system is an air source heat pump. You can see the pump compressor on their drawings http://www.eco-smart.org/productdocs/1-saph.pdf

The Company is just not clever enough to invent anything.

Regarding my commercial interests, I do not have any commercial interests except for ioniser systems, which I do sell and install, I try to recommend suitable products for customers needs from the whole market.

Regarding my statement of your pool, as I do not know the dimensions it could be that your system works but on another one 11m x 5m there is virtually no movement of water pased halfway up the pool. Algae grows at this end and when I was asked to sort it out last year it turned out to be a hard task. It is a very easy installation for the company and that's why it's done but it does not make for a good pool. 

[kitty]

We are just about to finish our pool heating system.  It relies on Navitron evacuated tube collectors.  The heat is transferred to the pool via 100m of poly pipe buried in the concrete base of the pool.  We have 25 m2 of collectors.  The pool is constructed of poly blocks filled with concrete and the base of the pool is also insulated with polystyrene.  The pool is covered by a pool Abri.  We hope we can keep the pool warm most of the year.  The house underfloor heating will also come off the same circuit.  Our blog has full details ( http://smartfrance.blogspot.com ).  So we will have performance data soon if anyone is interested look at the blog.