a question for solar installers

[unguided1]

I have been talking to a company that soon intends to start installing solar panels and all the bits that go with it. I have been asked would I like to do their cylinder changes, so potentially it could be a good contract.
my problems arise over the fact that the cylinders they are asking me to install, are open vented. I have no issues installing the cylinders themselves apart from I have recommended that any cylinder installed should be fitted with a solar care mix valve on the hot outlet.
My worry is the fact that the feed and expansion tanks in most houses nowadays are plastic, and potentially if any safety devices on the solar failed, then potentially you could have 100 degree + water coming out of the open vent. There have been reported instances where f and e tanks have failed because of immersions set at the wrong temperature and boilers pumping over.
I have no issues with unvented cylinders.
so what do you guys think or am I worrying unnessacerily

 

[Mike Jackson]

There is no problem as long as the cistern is correctly supported and the holes are drilled through far enough apart. If the citern is not correctly supported you'll need to add on the cost of theremedial works to the cylinder install.

 

[unguided1]

so what you are saying mike is that, there is no chance of the feed and expansion tank being melted from 100 degree + water if the solar safety controls fail.
Regards
Mike

 

[so-solar]

Hi
Every solar install we do has a high limit stat just above the cylinder stat! this is wired through our central controller and a 2 port on the solar flow. If the high limit stat trips then the 2 port loses its power and shuts! the stats are manual reset. I am not sure what other installers are doing but I designed this system myself to combat your exact problem! Remember that all zone valves on a solar install are to be solar rated, And also, No solder on solar!

 

[Mike Jackson]

All the cistern failures reported have been due to incorrect fitting. When heated to 100C the plastic can soften and will slump if inadequately supported. The cistern can need replacing after overheating but shouldn't fail.

 

[unguided1]

cheers for all the advice on this guys, just to let you know I am doing my first install for this company on saturday, which will be in their show room, all I have to do is install the hot water cylinder a plastic roof tank and a basin, their blokes will be installing the solar, on to the cylinder, so on saturday I will be able to find out what sort of controls they are installing on the solar side, I will let you know how it goes.
regards
Mike

 

[unguided1]

well I fitted it all up on saturday morning, the firms installers are fitting up the solar today, so we should have some results in the next couple of days.
regards
Mike

 

[Jimbob]

they do plastic cistern that can take more heat in an event, they hold themselves together bit better. As for solar not sure what everyone else as said but it will be electonically controled with a stat on the solar and stat on the cylinder. when theres a 10deg diff the pump will come on and when the cylinder reaches a designated temp and pump will shut off, easy as that.

A mixing valve should be fitted on the outlet of the cylinder incase of overheating aswell, but notsure if these operate well on a gravity supply. Hope it works out alright for you

 

[so-solar]

so jimbob............. what happens when the solar controller malfunctions and goes into 'hand' mode biringing the pump on continuosly. Therefore all you are relying on is heat transfer into the cylinder. Once the cylinder is to temp the pump keeps going, transferring more heat. This happened with an install we were involved in and ther customer recorded water temps well above 65'c. Hence the reason we designed a system to include a 2 port and a manual reset over heat stat. The stat clicks out killing the power to 2 port which is normally closed. The 2port is located on the solar flow, shuts off the flow and also we wire it through our solar controller in such a way it knocks the pump off! killing the system. A fault code shows up as 'no ciculation' Problem solved

 

[doug]

Personally ive alltered the programming of the solar controller so the btm of the cyl is 70 deg c this means that the top is 80+ this also means with the ammount of cold added we can get 3 baths out of a 210ltr cyl, one after each other, when the suns gone in, and its all free!!. This is only for test purposes you must understand just to see how good solar actually is.

 

[Plucky]

Agreed so solar.

Ive been fitting alot of the worcester Greenskies kits with the Worcester dual coil unvented cylinders and they supply a zone valve to use on the solar return. However I believe certain manufacturers do not specify this.

Blending valve is important on solar cylinders!

 

[Jimbob]

iv never seen a 2 port on a solar system and iv fitted quite a few different systems. Even a greenskies kit, which at the time didnt come with a zone valve, althought i agree its a good idea which id never thought of.

 

[Bob Croft]

As mentioned above, there is definitely an issue with thermal mixing valves on gravity systems due to the head. The ones I looked at needed around 5 Mtr head minimum.

 

[bobpape]

Forgive the question but are not the solar collectors roof mounted and if so how can open vented system work especially as the FE cystern is inside the same roof,(and lower)

 

[unguided1]

Hi bobpage
the solar pipework is a pressurised system, and self contained, heating a solar coil inside the cylinder, the cylinder itself is open vented and totaly seperate system to the solar. The concern i have is if all safety controls failed you would then have an uncontrolable heat source heating the cylinder,
regards
Mike

 

[doug]

This excessive heating would not last for long. if the pump kept running for arguments sake, then the cylinder would be cold again in the morning. Also if the primary temp got that high the pressure would be that great that the Mechanical safety discharge would opperate thus loosing your primary flow mixture. Then the cyl would not heat up at all.

 

[david williams]

you would be lucky if temp got that high