Potential problem with solar install

yllw.ldbttr

I had a solar system installed a few weeks back in a house that I purchased end of last year.
Firebird system, 40 tubes.
300 Litre water tank, house contains 2 adults and 2 kids.

Up until now I'd been seeing a modest benefit, need only a top up from oil heating some mornings for showers.
This weekend it has taken off with the good weather but I have what may or may not be a problem...

Today by around 3pm the system shut down stating emergency collector shutdown active, I'd seen this a few times but today I was watching it.
Max store temp was set at 60, factory default.
Once the two sensors in the tank hit that temp the pump stopped and the collector temp quickly went to 200 degrees.

According to the installer this is correct. I used lots of hot water, and then the top sensor in the tank was reading 60 but lower sensor 30, so I assumed the system would start heating the water again. The installer said no, that once the collector goes above 130 it will stay shut down, even if the tank is fully cold...until the collector goes below 130 again (which happen after sunset the last few days)


This makes no sense to me, I'd assumed the system would heat the water in the tank when it's colder than the max temp, if not, it means you effectively get only one tank of hot water per day no matter what.

Does this sound right, am I missing something, and given that this is happening now I'd imagine it will be worse in the summer, is it likely to cause any long term system damage?

Would appreciate any feedback/ advice.

Thanks.

John T Carroll

yllw.ldbttr wrote: »

I had a solar system installed a few weeks back in a house that I purchased end of last year.
Firebird system, 40 tubes.
300 Litre water tank, house contains 2 adults and 2 kids.

Up until now I'd been seeing a modest benefit, need only a top up from oil heating some mornings for showers.
This weekend it has taken off with the good weather but I have what may or may not be a problem...

Today by around 3pm the system shut down stating emergency collector shutdown active, I'd seen this a few times but today I was watching it.
Max store temp was set at 60, factory default.
Once the two sensors in the tank hit that temp the pump stopped and the collector temp quickly went to 200 degrees.

According to the installer this is correct. I used lots of hot water, and then the top sensor in the tank was reading 60 but lower sensor 30, so I assumed the system would start heating the water again. The installer said no, that once the collector goes above 130 it will stay shut down, even if the tank is fully cold...until the collector goes below 130 again (which happen after sunset the last few days)


This makes no sense to me, I'd assumed the system would heat the water in the tank when it's colder than the max temp, if not, it means you effectively get only one tank of hot water per day no matter what.

Does this sound right, am I missing something, and given that this is happening now I'd imagine it will be worse in the summer, is it likely to cause any long term system damage?

Would appreciate any feedback/ advice.

Thanks.

Yes, thats about right and yes, repeated high system temperatures simply is not good for any solar system, I have seen evacuated tube arrays at 240C under stagnation conditions. The collector reset temperature is probably 5C to 10C lower (hysteresis) than the activation temperature of 130C, you can get the circ pump to restart by putting the controller on manual control and starting the pump, however this may not be advisable as the pump has a design operating temperature of 110C to 120C.

Preventing stagnation is the right way to go, this ideally means the installation of a dump radiator and a solar rated three way valve,the controller must also have the necessary logic to enable this. The central heating system can also be utilised to do this but depending on zoning etc it can be a bit messy.

I have a very simple “manual” (central heating dump) set up on my system which I have never had to utilise as I have a flat plate array and my cylinder set point is 80C, I have very soft water here (Cork Northside). This 80C setting would certainly have helped but may not have prevented stagnation on your E.Tube array with yesterdays weather.

I tested the dump yesterday when the cylinder temperature was 73C and it knocked the temperature back to 60C in 10 minutes (mainly due to the primary water being cold). I have no zoning but I have a motorised valve on the cylinder coil, I also have an isolating switch on the supply to the Oil BURNER and I have a radiator without a TRV. To operate the the dump I: (1) Switch off the oil burner,(2) Open the motorized valve with the attached lever. (3) Change the heating controller to “Constant On” and (4) Turn up the room thermostat to start up the system (without the fan/burner). The central heating circ pump will then circulate water through the boiler, the cylinder coil and the radiator.

I also have the cylinder top probe installed adjacent to the midway position of the coil, this gives a true reading of the top half of the cylinder and under normal (oil fired boiler in service) conditions will open the motorised valve well before a top mounted probe would detect it.

PeteHeat

Never manually start the pump when the manifold is reading 200c / stagnation conditions.

Essentially what you have at the manifold is steam which can cause the expansion vessel to explode, I can supply a link to a system where this happened however as I own the web site it's against forum rules to do so.

You need a heat dump installed, depending on the space you have this can be inside your home or even under the soffit on a north facing wall outside.

Some fit them in the attic however with the now more common use of high levels of insulation in attic spaces you need to ensure the heat can dissipate before fitting a radiator up there.
.

John T Carroll

PeteHeat wrote: »

Never manually start the pump when the manifold is reading 200c / stagnation conditions.

Essentially what you have at the manifold is steam which can cause the expansion vessel to explode, I can supply a link to a system where this happened however as I own the web site it's against forum rules to do so.

You need a heat dump installed, depending on the space you have this can be inside your home or even under the soffit on a north facing wall outside.

Some fit them in the attic however with the now more common use of high levels of insulation in attic spaces you need to ensure the heat can dissipate before fitting a radiator up there.
.

Peter, forum rules allowing, can you please PM me that link as its frightening/appalling if this can happen, one would expect that the system safety valve would be sized suitably to prevent such an occurance. The system safety valve on my system is set at 6 Bar.G which corresponds to a saturation (water) temperature of 165C, so if the system liquid contents, for whatever reason, ie mixing with superheated vapour/steam, reached this temperature/pressure then the safety valve should start venting and should be sized to prevent the pressure rising to 110% of the set pressure, theoretically the pressure should not rise above 6.6 Bar.G. Whats even more alarming is the fact that the collector protection temperature is settable, certainly up to 200C and probably even greater. Assuming a max cylinder temperature setting of 60C as in yllw.ldbttr,s case and assuming a collector protection temperature of 200C, then the circ pump will stop at 60C, the collector temperature will start to increase and its quite possible that the circ pump will restart (depending on the hot water draw off) before the collector temperature has reached its limit of 200C or whatever, so as long as the collector protection temperature is user settable then one could be faced with a catastrophic situation or am I talking through my hat (or even worse)??