What are you trying to achieve?

My understanding is you’re best not interfering with the HPs controls. 

we’ve just changed ours and ripped out the stats. Although it’s cooler now the pumps are still turning off when the room temp is met but we’re using the Mitsubishi stat rather than a 3rd party. 

Yes I agree that we do not want to interfere with the heat pump controls, more that I want my dumb thermostat to be controlled by my heat pump so that the pumps run when the HP wants them to run.

There is probably a way the electrician can re-integrate the pumps into the ASHP, however I am concerned that the pumps would run the whole time in that case. 

We set out pumps to be controlled by the ASHP rather than the stats and had the same concerns as you. Eg if on WC would the pumps just run 24/7?

but using the Mitsubishi room controller, even on WC it still shuts the pumps down if the room temp is +1c over the target temp 

so rather than over complicate can you get a Nibe room controller?

@luke 

pumps use less than 100w, many as low as 5w..they all are speed variable, so look on the pumps.

in the first best world you wouldn’t need more than one pump for a heat pump up to 14kws, but obviously UFH increases that requirement

We have 4 on ours. 1 on flow, 1 on return (due to long outdoors pipe run they didn’t oversize…)

central heating

UFH

Posted by: @alec-morrow

In the first best world you wouldn’t need more than one pump for a heat pump up to 14kws, but obviously UFH increases that requirement

Does it? Eek! Only one pump in my UFH system ... is that bad?

Actually, that leads me on to another question. My Vaillant system feeds a manifold with valves on each output controlled by thermostats in each room. Currently the (one and only) circulation pump is connected to the SensoComfort unit, so when it decides the room is warm enough it shuts down the whole system. That's not much good if the kitchen (a colder room) is still trying to heat up, the Heatmiser valve opens, but the circulation pump is off so no heat is forthcoming. What I've ended up doing is turning up the heat on the SensoComfort, but it means the pump is running 24/7, which is noisy, uses about 25w of electricity, and will no doubt wear out much sooner than it should.

Looking at it there are a couple of options ...

1. the Heatmiser controller has a Boiler output which can control a relay which sends a trigger to the Vaillant wiring centre to tell it that heat is required, but it looks like a faff to set up. 

2.Alternatively, the Heatmiser has a (currently unused) pump output, so I could connect the circulation pump to that instead. This would be a much easier option, but is there a downside? I'm thinking that fundamentally the ASHP heats the contents of the buffer tank, which then gets sucked through the system by the circulation pump, so I'm wondering if that would be ok?

Posted by: @luke

I think most people here agree that thermostats being used with an ASHP on WC control is a big no!

 

Last winter I simply upped the thermostat temperature to keep the thermostat 'calling for heat' and as such keeping the 2 circulation pumps running.

I would like to smartify this if possible due to shorter demand time in the shoulder seasons.

 

I run some home automation software called Home Assistant. With this I pull in (from the cloud unfortunately) flow temps etc from my Nibe ASHP. (I believe this could also be done by Modbus?)

I'm thinking of using Home Assistant and some form of smart relay to control the main circulation pumps based on parameters I receive from the heat pump.

Does anyone have any better suggestions?

 

 

Hi Luke,

Have a look at the Nibe manual and see it there is a specified electrical output for running external water pumps. If not then look for an output that indicates that the heat pump is running which could be used to power the water pumps directly or via an interposing relay. There will be a signal from your indoor controller to the outside unit, telling it to run or stop. This may be at 240v AC or a lower control voltage. 

@squonk 

It is difficult giving definitive advice without knowing your precise system layout, but it may be that you need to zone the two areas. If you can arrange your system such that either zone, or both, can call for heat and hence start the heat pump. When both zones are up to temperature the heat pump will then be switched off.

Posted by: @derek-m

@squonk 

It is difficult giving definitive advice without knowing your precise system layout, but it may be that you need to zone the two areas. If you can arrange your system such that either zone, or both, can call for heat and hence start the heat pump. When both zones are up to temperature the heat pump will then be switched off.

That sounds like a lot of potential re-plumbing to split the zones, which is outwith my comfort zone. I'm happy enough with the way the rooms are controlled, just need to link the two parts (ASHP and UFH) so that they are working together, currently they are working independently of each other.

@squonk

If you have radiators in the room where your indoor controller is situated then throttle in the valve slightly to reduce the flow rate, and hence the quantity of heat energy being supplied. This will slow down the rate at which the room warms, and hence give the UFH more time to warm the other areas.

@derek-m No radiators anywhere, just UFH.