size of heat dump ?

[BLOD]

Does anyone have a formula for calculating the size of heat dump rad (rads?) that might be needed on a solar hot water system ?

thanks

 

[markfxy]

On a correctly sized solar install you don't need a heat dump

 

[BLOD]

Thanks for the reply markfxy,
I'd like to oversize my collectors a bit to get more solar gain in the winter months, hence the need for a heat dump.
I asked the question because I can't decide wether to wire the boiler via a relay and use the ch/hw system & pump as the dump, or to make up a dump circuit using old rads.

 

[markfxy]

have you thought about using a drainback system you can oversize as much as you want without worrying about stagnation

 

[BLOD]

I'd like to use evacuated tubes to help with the solar gain in the winter, and didn't think these worked too well with drainback systems although I could be wrong ?
I'm still thinking that oversizing, along with a decent heat dump could work well.

 

[Wet Bandit]

Hi BLOD,

You're right, drainback's not an option with evacuated tubes, so pressurised only. You can either use a high temp glycol such has Tyfocor LS. This is better at handling higher stagnation temperatures and won't sludge up or degrade as easily.

Also, activate the recooling/holiday option on your controller during Spring/Summer months to minimise stagnation.

Also, when filling the system, consider pressurising a bit higher as this will raise the boiling point. Remember to adjust the expansion vessel precharge accordingly and note the 6 bar rating on your PRV! All this depends on the manufacturers recommendations of course.

Back to the radiator size, you could stick the biggest double in you can fit (in loft maybe?) and divert with something like a Resol VA300 valve.

Cheers,

Matt

 

[Toddyplumb]

Evacuated Tube Heatpipe , they dont stagnate as they are self limiting. Its what I spec all the time

 

[markfxy]

Evacuated tubes are fine for drainbacks we've never had a problem but the thermal shock can be can be a bit noisy. Its best to keep it simple a diverter valve is just something else that can and will go wrong and as glycol is so expensive any savings through the use of thermal will be wiped out if you have to change it.

 

[BLOD]

Thanks for the advice guys.
Have any of you come across a non electrical temperature activated mid pos valve before?
I saw one a few years ago but didn't make a note of who made it.
cheers