Destratification pump for horizontal cylinder

[xanld]

Hi, if like to add a destratification pump to my Telford invented horizontal cylinder so that I can heat more water using surplus solar with the top mounted immersion heater.

I can fit a tee to the outgoing 22mm hot water with non return valves to the incoming cold supply.

Can anyone recommend a suitable pump?

 

[Johntheo5]

Have you looked at the longest element (of a dual immersion???) that can be installed in this cylinder, you will then know what % of the cylinder that can be heated once the height of the cylinder is known.

I see its a horizontal cylinder so how can it have a top mounted immersion?. and wouldn't think a horizontal cylinder would stratify in the first place.

 

[xanld]

Top = side! It's on the side if the cylinder was vertical, but since it's on it's side, it's on the top. The top according to gravity. On the curvy bit. Am I making this clearer? See attachment the immersion is close to the hot water outlet and thermostat. The cold comes in on the far side with a feed pipe which takes the cold water right to the bottom.

And yes - I contacted the manufacturer's and they said 14" was the longest. I've got one on order and will see. My guess is that this may struggle to heat down the full width (height?!) length of the cylinder - or at least not as quickly as a destrat pumping the hottest water straight to the corner at the furthest end from the immersion and hot water outlet.

And yes - stratification does occur - I've got probes at the top and bottom (by gravity), and when we draw hot water, and cold flows in, the top stays hot whilst the bottom is cold. The manufacturers recommend a destrat pump and the manual has diagrams, but they haven't given advice on any particular model or spec.

 

[Johntheo5]

That's interesting re the thermostat, would normally associate that with a heating coil and would expect the immersion element to have its own rod thermostat, if the rod is the same length as the heating element then the whole cylinder should heat up uniformly from cold but would expect some difference between the stat setpoint and the cut out temperature on partial reheat. On my vertical cylinder with a dual immersion the long element is - 24ins and the short one + rod stat 11ins, on whole cyl cold heat up the cylinder temp is within a deg or two of the setpoint but on partial heat up. I think I've seen around 5/6 deg difference.

The horizontal cylinder is different I suppose in that the hot water will tend not to move horizontally towards either end, surprising maybe that they don't install two immersions.

 

[xanld]

Yes, the immersion has its own rod thermostat. It's a solar tank, and the main coil comes from my Air Source Heat Pump. This heats it uniformly.

The immersion is only a top-up, and because it operates at lower currents, is good for utilising surplus solar.

But the immersion currently only heats the top, and then stops without the bottom being heated. You may be right that this is because the existing immersion is too short - I'm not sure of the size of the existing one. When my 14" turns up, I'll remove the existing one (which isn't working) and see. But the manufacturers only recommended a maximum of 14", and the cylinder diameter is 20" (externally) so I'm guessing 14" is probably max.

Perhaps the 14" immersion will be enough, but my hunch is that a destrat pump would do a better job, and much quicker than relying on convection alone. The horizontal heat transfer without a pump is probably slow over such a long distance too.

 

[Johntheo5]

A 14"element in a 20" cylinder will only heat 70% leaving ~ 90L "cold" in 300L cylinder. I gave some help/advice to someone who installed a external Willis type immersion (with vertical cylinder) for his solar divert, its working quite well but required 22mm piping throughout and a pipe stat set to 70C as the heater stat could only be used in a supervisory capacity as it didn't cut off the power until the heater outlet reached 85C despite being set to 65C, new stat made no difference. Probably not a good choice though with only a 20" high cylinder.
The destrat pump should certainly do the job as you should pick up at least another (when available) 5kwh of diverted power required to heat 90l from say a average mains of 12C to 60C.

 

[xanld]

OK yes - the external diameter is 20", so internally it will be less, but yes, maybe it can fit an 18" rather than 14". I'm just slightly conscious about ignoring the manufacturer's explicit instructions on this...

Certainly I'll see what happens with a longer immersion before looking at the destrat.

My pipes are all 22mm. At the moment, my immersion cuts out at about 60, another reason I'm looking to replace it so that I can go a bit hotter with solar surplus.

Nonetheless, for future reference at least, I'm still interested in what makes a good destrat pump. This: https://www.amazon.co.uk/Trident-Central-Heating-Water-Circulation/dp/B08XMGMW6R/ ?

 

[Johntheo5]

That certainly won't make a good destrat pump as its made of cast iron and will corrode away in no time from all the oxygen rich water passing through it, that pump is for central heating purposes, you need a bronze pump which don't come cheap.

 

[xanld]

OK, how about this: https://www.amazon.co.uk/JASSFERRY-Central-Heating-Automatic-Circulation/dp/B09TNJVKZQ
It doesn't appear to be bronze, but it does say it's suitable for showers (which is the same water as I'd be pumping), as do many of them.

p.s. I've ordered an 18" immersion too to see if this fits. I'm not entirely convinced the hot water will transfer horizontally across the entire length of the cylinder very quickly, and I'm guessing this is why Telford are keen for a destrat pump to be fitted, but this is definitely a simpler option than the destrat pump which I'll consider as a fallback.