Destratification Pump

[tom1]

Hi all, I have a horizontal cylinder, the stat takes a long time to kick in, I spoke to telford who said a destrat pump would improve performance as the bottom of the tank does not heat up as well as the top. its never been a problem, as programmer brings it  on for 30 mins. but I would like the cylinder to get to temp and stat to open.

would it be best to wire the pump to come on with the stat, that way when the whole tank hits 65 the stat turns the de strat pump and valve off

thanks

 

[kerching]

Never fitted one, so i will be of little use, but

Does the pump need to be on ALL the time the cylinder is calling for heat? Or just in short bursts to whizz the water up a bit?

Just wondering

 

[tom1]

not sure think they wiz the water up to stop legionella as some level of the tank  will be at the right temp. for me though its about getting the bottem of the tank hot as the coil only seems to heat the top, unless my stat is carp, its done it from new, its a dry pocket stat on an unvented system 

 

[Andy™]

where is the stat on the tank?

 

[tom1]

at bottem

 

[roys]

Thought have stratification layers in a cylinder was a good thing as it meant that the hot water draw of the cylinder is nice and hot without having to use lots of energy heating the whole cylinder.

I presumed and maybe wrongly that a destrat pump was used when a lot of cheap energy was available for example solar power systems and so it makes the most of the available energy.

It is a good question as I have never thought it through so if will be good to see what conclusions the forum may come up with.

Just out of interest why is the cylinder horizontal? I have no idea how this changes things.

 

[tom1]

space reasons fits in the eaves. apparently they don't work as well as the vertical ones

 

[roys]

space reasons fits in the eaves. apparently they don't work as well as the vertical ones

So where does the feed and expansion tank go or is it a pressurised system?

 

[Rob_the_rich]

does your telford horizontal unvented cylinder have two immersion heaters? apparently, talking to telford, if both are used, then the cylinder does not stratify and heat is distributed evenly.

But it sounds like it is an indirect system fed from the boiler, so it is likely to need pumping.

if a pump has to be fitted, it is connected between water inlet and outlet, must be a gold pump, and should be on continuously during daylight hours (hours of possible use), but if you put it on its own timer you can experiment with the timings to cut down on energy usage.

 

[tom1]

its unvented with one immersion, indirect.

wilo bronzed pump , is what they recommend.because its potable

would rather not have it on all day if a can be avoided, its just annoying that the stat does nothing, I guess the boiler stat will kick in as hot water keeps returning back.

 

[Rob_the_rich]

Remember to fit the pump so that it pumps upwards to avoid cavitation. but I guess the flow should be from hot water outlet, through pump to cold inlet (else when a tap is on, you get mains hot plus pumped cold) so you should run the pipework in a lazy S shape.

You could wire the pump from the stat switched live and see how it goes, shouldn't be too difficult to put a timer on it if it proves necessary.

Does the stat switch off at its lowest setting?

 

[Rob_the_rich]

Also, check the boiler flow temperature is set higher than the set temperature of the cylinder stat. That would make it never switch off.

 

[Rob_the_rich]

Another thing, if possible, check the temperature of the primary flow at the cylinder. if the boiler is remote from the loft, there might be serious heat losses.

 

[tom1]

the stat turns off on lower setting if its left running long enough, tank is close to boiler all pipe insulated flow and return run hot