What’s the approved method for connecting an appliance (CH pump) to two switched supplies without risk of shorts or unidentified live circuits?

Two independent controllers, either of which could be on or off at any time, or both simultaneously on, which is unlikely, but would need to be protected against.

cheers

bump for the trades in from a days grafting…
anyone?

two pumps!

are you windhager boys made of money? 🙂

Depending on the arrangements on site, I would say via 2 relays contained in 1 box with suitable labelling for ‘ Two separate supplies’.

relays was kind of where I was going, but I’m surprised there is no off the shelf solution. or at least I could do with some help with the search terms

I’ll draw something up tonight and send it too you.

Stu

cheers stu. am actually in plumbing class now and teacher is no help 🙂

I agree. Use 2 relays/contactors. Run the control voltage for each one through a NC contact on the other (electrical interlock)

This way when one is energised, the other cannot be. I’m sure Stu is already one step ahead on this and his drawing will explain better

This is what I mean about having to adapt things etc. If you were doing it for a client then having something that is all intergrated is a real plus.

Anything goes wrong companies will try to wriggle out of it saying not standard etc, also most plumbers etc wouldn’t have a clue and maintaining it could prove difficult.

Might be over west way next few weeks…..

but you know my system is miles away from a client product bear. and for a reason.
I’m off from mid July but do come by if you can

July 13 is my possible date

And yes I realise why you have done it your way, but you are doing a course with the aim of going into a business?

Stoner, what are you trying to do?

A pump on many standard fully pumped systems can have 3 methods of powering it, from Cylinder stat, Motorised head and boiler pump over-run.

He’s probably trying to sneak some of his neighbours heat into his industrial heat store to keep his red at the right temperature…….

out of curiosity, where/what are the switch wires coming from?

Bear – 13th a bit late for us: Le Tour goes past our mate’s place on the 15th and we’ll already be there! Woohoo!
Another time then. (and Im doing the course with the aim of learning stuff. As for pissing around with my home CH system I consider it more of an experimental lab 😉 )

Stu’s been a top bloke and emailed me a circuit diag based around a pair of relays which fills in the hole in my understanding, and is bang on. Im very grateful.

The reason for the switching is that I have a solar thermal system that, like a nuclear reactor, cant be turned off so I need to be able to rig an automatic heat dump for when we go on holiday.

(usually losses and uses are more than sufficient to prevent an overheat, but sustained collection with no emission may be too much for the losses in the system to dissipate)

So I want to link my solar thermal controller (which turns on the solar thermal pump that brings heat from the collector to the thermal store) to ALSO turn on my Underfloor heating. Obviously only when I want it to, by a switch. My 1,500 sq ft stone floor then becomes my heat dump.

This means I have two controllers sending live to the one UFH pump, independently of each other (although obviously extremely unlikely that they do it together). The UFH controller is a timer/thermostatic jobbie with its own switch relay. The solar thermal pump is actuated by the hysteresis between the solar collector and the thermal store.

So with the relay set up, although I have to caution that there are more than one point of isolation, I can use the two relays to switch a spur to the UFH pump.

i.e. when the UFH controller say “yes”, then it’s on and not f***** with the solar controller, and when the Solar Thermal controller say “Si” it’s on too. And indeed both can be on at the same time with no problems.

While not suggesting that the relays are not a good option, what about two pumps in parallel?

£60 on a 15-50 and a load of buggering around with a tight lay out…or £10 of relays and a plastic box? 😉

Stoner, are you not over complicating this?

I can’t envisage your system, but if you want the ufh pump to run at the same time as the solar pump, can’t you just fit a pipe stat with the common being fed from the solar pump live. So in effect you’ll get solar pump kicks in, power to stat, heat in pipe causes stat to make putting 240vac to ufh pump?

You could do the sane but with a permanent live which would keep the ufh pump running even with no demand from the solar controller.

that still gives me two live sources for the UFH pump. Dont forget in normal conditions, the UFH pump is separately controlled and needs to continue to be so.

The switch control is not the problem, its managing the live circuits at the pump that is.

Permanent live to pump rapes the planet! Bad soxo!

So when will there be a second demand on the ufh pump, what causes this? Temperature rise?

Edit: the permanent live was to the pipe stat.

UFH pump is controlled by a stand alone room stat/timer which has its own relay to the fused spur to the UFH pump. Its at this point I want to drop in with a second control circuit.

Its a thermal store system, so heat call etc is managed elsewhere.

£60 on a 15-50 and a load of buggering around with a tight lay out…or £10 of relays and a plastic box?

fair point
😀

Do you want this to be fully automated, so whenever temp rises the heat is dissipated, or do you want this to happen on demand?

If automated, id utilise the central heating off from the clock to put power to a pipe stat, so that the pump will run only if the heating is off at the clock, you could utilise a second pipe stat on the ufh circs to stop the pump again at a certain temperature. This would have the benefit of stopping the pump running if there is no ch demand, and the ufh is already hot.

I don’t see the point of having a heat dump, if it’s not going to be driven by system temperature.

Will you be bypassing the thermal control for the underfloor by doing this, running the risk of overheating the floor?

solar thermal system that, like a nuclear reactor, cant be turned off

Couldn’t you just cover the panels to insulate them from the sun whilst your away?

solar thermal system that, like a nuclear reactor, cant be turned off
Couldn’t you just cover the panels to insulate them from the sun whilst your away?

Beat me to it 🙂

Tin foil?

I’ve used the tarp approach when I’ve been servicing but I don’t trust it to stay in place for weeks on end in all weathers when it’s effectively a 150sq ft sail in the garden 🙂

there is no thermal protection of the floor, only the blending valve.

the risk of overheat is fairly remote.
my array can collect c. 45kWh a day in peak conditions. however the only retains anything like that kind of energy when accumulating from cold. at higher storage temperatures the losses I reckon are substantial (say 50% @ 75degs +)

the floor is designed around IIRC about 100W /sqm, so can absorb/emit about 15kW. my collector is rated at only 5kWp.

so in a worse case scenario of 30 days of peak collection of 5kWp and accumulation;after losses of say 3kWh that’s about 20W/sq m to be sunk,. well within the design parameters of the floor without even calculating air temperature rise and heat and vent loss.

unless you think I have something very wrong?

I can of course also have the ufh controller provide over run function at night to create thermal capacity in the accumulator

dp

Huge thanks to Stuart the Sparkie who kindly emailed me a wiring diagram for the relay actuated two-way.

Fitted it this afternoon, a few head scratchers to remember which wire goes in which one of 8 contacts on each of the two relay bases 😳 , but it all worked first time: solar controller and UFH controller both able to switch on UFH pump.

As you can see, installing a second pump in series would have been a bit of a pain.

paulosoxo – thanks for the posts, but this is a thermal store set up, not a boiler controlled CH one. The heat dump requirement is during holiday when away. Thermostatic control isnt important as the heat dump circuit override will only be turned on as we leave the house to go away, and off on our return.

talk about making things difficult for yourself, intergrated solutions are available………

(you need to be careful you don’t overheat your floor otherwise it can damage floor finishes)

(you need to be careful you don’t overheat your floor otherwise it can damage floor finishes)

I knew you were going to say that. zero risk given the differences in scale ^ see above.

intergrated solutions are available

I knew you were going to say that, too 😉

But humour me, how does windhager deal with solar collection in non-use periods?

As you can see, installing a second pump in series would have been a bit of a pain

Wouldn’t the second pump have been in parallel? I don’t understand this liquids stuff

IIUC, in series one pump can pump through the other if it’s off. If both on then they simply pump together.

with relays…….

Actually honestly I don’t know, think they use big buffer vessels and they have loading pumps which circulate. Am hoping to go on a controls course with them when new training school opens so will find out more.

Overheating shouldn’t occur if the mixing valve works, but could that stop the hot water being sent round the underfloor if water temp is satisfied? Therefore pump will not be circulating the the hot water from the store. I know you talk about scale but it is always theoretical with watts/m2 etc.

how many panels have you got, how big is thermal store?

its always theoretical but you have to look at the potential for energy collection and emission. approx max of 1:3 would, I think, never exceed design specs.

but could that stop the hot water being sent round the underfloor if water temp is satisfied?

Floor temp would need to be 40degs for blender to be wholly closed on the primary side since in any other situation return would be below blender threshold. Beyond impossible.

Actually honestly I don’t know, think they use big buffer vessels

Same thing as me then. All Im doing is pre-empting a failsafe. I actually think that my buffer/collection losses would be enough to maintain a balance (a hot one, but a balance nonetheless) but just in case while Im away for a month at a time I want the comfort of knowing that there’s a heat dump in action.

EDIT: Panels sized at c. 9sqm effective collection @ c.1kW/m then around 45kWh per day.
Ive actually proven that when I drained the thermal store.

I refilled with 700 litres of 11 degree mains cold water, took the tarps off the collectors and five hours of middle-day 100% sunshine (in May, being at about 5kWh a day total per sqm) had raised the water by 30degs. Which is pretty much 25kWh of energy.

BUT that’s from cold. There’s no way I could collect even half of that additional energy while pumping 70deg+ water out to the collectors and back again.