solar tube temperatures

i think for a 300L tank the minimum amount of tubes is 40..... i want to get an extra 10 tubes to make mine 50..
sounds to me thats all you need .those are not bad temps you are getting and the 10 tubes would make a difference...
 
thanks tick tock. But the thing is thats as good as its been getting all year 32-35 in the cylinder. So do you think I would get 65 degrees with another 10-20 tubes?? My system must have been sized incorrectly so
 
we've 60 tubes facing west/north-west and we're getting average temperatures of around 55-65 degrees by sunset.
Heating has not been on in weeks!
 
yes i think you should get 20 more...and yes you were undersized...but im no expert. i believe it is easy to add on extra tubes..go for it
 
cunninghams said:
thanks tick tock. But the thing is thats as good as its been getting all year 32-35 in the cylinder. So do you think I would get 65 degrees with another 10-20 tubes?? My system must have been sized incorrectly so
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From my understanding of solar(from a solar course i did last year and talking to manufactures), a panel has a maximum output which can be achieved when the sun is at it's hottest, the cylinder coil rating shouldn't be smaller than the combined panels output, so you can have as many panels as the cylinder coil can take, you want the cylinder to absorb the heat and the solar pump to keep running, the solar panel should not to get so hot that it shuts down, i would contact the suppliers http://www.precisionheating.ie/ who supply all things Viessman and ask them to confirm panels are the correct size for your cylinder and if so see if they have a engineer to advise you on the best setup, setting for your system and if it's fitted properly, Gary
(No connection with Viessman)
 
some excellent stuff here. I've been planning on switching to a thermal store and tubes for a while. Is nice to get some real world stats.

I'm thinking of about 40-50 tubes (to start with) south westerly facing east coast location, with a 270 litre thermal store, with less than 4 meters between tank and tubes. I'm thinking thermal store rather than twin coil hot water tank, as I can harness the solar better, plus other sources too, eg wood burning stove, PV panels, and standard boilers. I can also run rads and underfloor as well as mains pressure (potable too) hot water, quite something these thermal stores! www.heatweb.com has some fantastic tools and design tips.

Anyone using a thermal store with tubes and boiler to heat a house (3 bed smallish house)? whats it like? do you have to rely on boiler much? how long does your tank stay hot? how many degrees an hour drop? ie. If its sunny, will there be enough energy the next morning to have a bath/warm the house? any figures on temp drop over time (with no output load) would be appreicated if anyone has them (think heatwebs stores have about 50mm insulation), as the mornings are usually the main time for hot water consumption and heating for my house.
 
see if they have a engineer to advise you on the best setup
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Have to agree with what gary said above. It's hard to give proper advice based on "number of tubes".

E.g.:

Some collectors have a reflector which means they need less tubes
Some collectors have larger diameter tubes
Some have smaller
Optical efficiency and zero loss coefficients also determine the output of the collector (e.g. some collectors are good at collecting and retaining energy, others are poor)
Thermal store size also affects system efficiency

The only way to get you system sized properly is to talk to your supplier and make sure they know what they are doing - If you can talk to their engineer and ask them why they sized your system the way they did.

Advice based on "Number of tubes" is not always a good sign!!!

Cheers

Des

(PS - if you are interested have a look at http://www.estif.org/solarkeymark/collector-theory.php - it gives a good overview of the solar efficiency equation!)
 
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This is a fascinating thread which only serves to pique my interest and underline the depth of my ignorance. Can anyone point me towards a basic book/website to commence my education on this subject?

Slim
 
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if i was to do it all again i would have 60 X 70mm tubes and a buffer tank....my tubes now are 40mm.
i didnt know any different last year but i believe 70mm are the way to go.
 
The SEI website is usefull for information on solar water heating and has many relative links.
Coming from a background in lecturing in the plumbing/heating/solar industry and being a time served plumber I would recommend
1. Insulating your home to it's limits
2. Install solar panels/tubes to heat domestic hot water alone (tubes are slightly more efficient, panels look better)
3. Install gas/oil fired condensing boiler to heat radiators
If you ask most plumbing contrators they will recommend solar for hot water and condensing boilers for space heating... end of story!!

Solar heated buffer tanks are suitable for larger installations or one off builds. These cylinders/tanks are huge when fitted into a three bed semi and are very heavy 1 litre = 1 kilo
Radiators used on solar/buffer need to have larger surface areas and can be quite expensive. I would not recommend using standard off the shelf convetor radiators on a solar/buffer system.
 
in my opinion yes. much better to run ufh from a buffer than to run radiators from same. provided each individual underfloor heated area/room has it's own independant control.
 
under floor heating (UFH) runs at i think 45c and that temperature is achievable even in december with the solar tubes so if you are going to do solar do it with a buffer tank and good big tubes!!!!!
 
Hi, can I ask, before I ring our heating engineer, when I go home in the evening, this is for the last few weeks, (we have the usual evacuated tube, south facing panels), when I turn on the tap, it is cold but not really cold but you couldn't use it for anything, we always have to turn on our condensing boiler to heat it up, we have never been able to use it as is, I find the whole thing useless or is there a problem? Do you think I should ring the engineer? My husband says it has been very cloudy but it isn't just sun, it is light??
 

Ring your engineer - sounds like there's something seriously wrong!

The solar should be able to bring your tank should be up at near or above 60 degrees every day for the rest of the summer. The panels don't need direct sunlight as they still collect the diffuse radiation that comes through the clouds.
 
9th May, 16:57 hours, 3 south facing flat panels, (7.5m2 total), 1000l buffer tank. Water temp off the panels : 78.7deg C, water temp in the tank: too hot to touch !
 
Reading through the threads most people appear to opt for solar tubes rather than flat panels.

Does anybody know how more efficient tubes are over panels. I assume this is why the choice of tubes as they are more obtrusive and expensive that the panels.

Another query how realistic is it to use solar panels for UFH say for a 3500ft house
 
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