Anybody created a pre-heat DHW cylinder

This extra electricity comes at times of high sun output, ie when ufh is no t usually being used. So in principle you could add a stat that stops the u fh pump coming on when the cyl is too hot for it. Then you get the benefit of your extra leccy without a bunch of extra costs.

NT

Reply to
tabbypurr
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Strikes me as bad design then. Can't you fit a mixing valve between the flow and return of the floor loop such that the pump circulates via the valve when the temp approaches 60 C.

Reply to
Dave Liquorice

60 seems unusually high for ufh

NT

Reply to
tabbypurr

between

circulates

Only quoting the OP and that's the maximum to avoid damage. What ever, to me not having some regulation of the UFH loop temperature independant of the store temp isn't right. Limiting the store to 60 C reduces the amount of energy it can store by about 30%.

And a store with a 60 C max must struggle to provide a decent quantity of DHW unless the OP has that mixer valve set to the pathtically low "safe" 43 C. Ours is set at 53 C or there abouts, hot as in you can put your hand in it but don't want to keep it there for more than a few tens of seconds hot. The store middle temperature is normally about 70 to 80 C, top can get to 90+ if I miss judge the weather and get a good burn going in the stove without the heating coming on enough. It can deliver a bath of DHW at 53 C and 15 to

20l/min before it starts to run out heat.
Reply to
Dave Liquorice

Agree ... but floor will never get to 60 ... each room has its own zone with digital set back temperature control. The max temp of water in cylinder is 60 .... there is heat exchanger coil, with 28mm feeds to manifolds ... then individual zones .... so too many losses to get as high as 60.

It probably would be nice to have a mixer on heating loop, wasn't in the design ... I could retrofit. Need to check if tank is happy being run hotter - problem will be Nu-Heat state design temp of cylinder in 60 .... they will be unlikely to confirm it can be run hotter - I will ask. Without some statement that tank can be run higher my risk would be too high to just 'chance it'

Reply to
rick

The regulation is done by the stat keeping tank at 60 ........ you may deem that not enough but seems to work fine. Stat is fitted in lower 1/3 of store.

There is never any shortage of hotwater ... this is set to 53 deg ... and runs at full mains pressure ... on 22mm pipes.

You can run it full flow to fill a bath and still running hot when bath is full.

Nu-Heat advise the high efficiency cross flow heat exchanger (rather than a coil)allows this.

Flow is from mains pressure of 3.5bar at 25L/min .. and has never once run out of hotwater when in use.

Reply to
rick

Mine was the earlier double rubber pipe system. (Which apparently they sold briefly after the triple, but before moving to PEX.) Failures of the double and triple systems seem to be similar, and common.

Mostly it's perished near the manifolds, one zone leaked somewhere I couldn't find it, and one zone (the last failure) isn't leaking, but the rubber is gunked up and hardly any water circulates. Possibly because, although it's had inhibitor in it, it's been repeatedly refilled because of all the leaks.

Reply to
Alan Braggins

Some of us like to wash in hot water in the summer, even when the heating is off. Also, not all of the summer is warm enough to swim comfortably in my swimming pool without heating. (It used to be better, but more of it is shaded by trees now.)

Reply to
Alan Braggins

The baffle in the middle of the store for one reason. The other reason I know of is that the DHW take off is from a crossflow plate heat exchanger, to keep up continuous high flow rate of hot water, then need to stir the tank or it quickly would form a cold 'pocket' around itself and flow would cool down

Reply to
rick

They normally use tall cylinders for these applications so that you can rely on stratification to deliver lower temperatures to the UFH using lower tappings on the cylinder. That does not stop you having the upper section hotter than the UFH temperature.

Reply to
John Rumm

That in itself means the upper section of the store will be able to reach a much higher temperature.

You have shown it as a coil in the diagram... normally there would be a circulation pump to drive the primary of the DHW HE - that solves the problem of cold pockets forming in the cylinder - the opt is pumped to the inlet of the PHE primary, and the return from it go back into a lower tapping on the cylinder.

Like:

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(that shows a vented store, but the same principle can apply for unvented)

As long as you have adequate volume of water stored, and the PHE has enough transfer rate, you should be fine. (you will need to shift around

80kW to keep pace with a flow rate of 25 lpm)
Reply to
John Rumm

I'm not seeing how any of that adds up. A crossflow PHE must be external, a nd will run hot from the top, returning it to the bottom. The pumping inher ent in that prevents cold pockets. To get best boiler efficiency & provide a cooler zone for ufh the boiler hot should enter the top of the cylinder.

NT

Reply to
tabbypurr

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