NIBE F2040 12kW with SMO S40 controls not following WC?

[glyn.hudson]

Update: Good news! After disabling the BT50 indoor sensor at around midnight last night, the system is now running today with the expected WC flow temp today. It’s maintaining a constant 20.5C, I’m very happy with this so far.

@etchelsa

You mentioned the system was open loop with 2x UFH systems. Do these have a circulation pumps on a manifold, or is it just pumped via the charge pump? If its the latter and you’re running on intermittent setting, it could be you have no flow around the circuits once the degree minutes are satisfied and the compressor turns off. It will then rely on natural heat loss from the location of the BT25 sensor to drop below the target S1 temperature and get the degree minutes to -60 (or whatever is set on the controller). This might explain why you have 8 hour off periods.

That’s a very good point. The system is fully open-loop with just a single circulator, there are no pumps on the manifolds. The BT25 sensor is located just above an insulated volumiser, so once the circulator stops, it will take a long time for the temperature the sensor sees to decay. This would explain why there’s such long gaps in between runtimes, I’ve now set the circulator on ‘Auto’ and set it to run at 10% between cycles. I’ll report back what difference this makes…

@dMb

On cold-but-bright days I get a lot of passive solar gain - enough to raise the whole house by 1C or more and the south-facing ground-floor rooms can get uncomfortably warm. I therefore use BT50 to ‘dial down’ the WC curve when that happens

Are there any settings to set how much influence the BT50 indoor sensor has? It seems in my case it was having too much influence, coupled with the slow response time of UFH.

In my case the BT50 is located in a windowless hallway, so wouldn’t be much use for sensing solar gain, in fact the hallway is a terrible place since it’s adjacent to the front door, so would be getting a cold bast of air every time the front door is opened! I think it’s best I keep it disabled!

@stevedvo

I realised after a long period of data collection that the Agile tariff will actually be much cheaper overall [although with the risk of occasional expensive days] so I switched over to that recently and have been running the ASHP in a more ‘normal’ way without the Cosy boosts.

Interesting, thanks for sharing your findings. I agree, I’m sceptical how much load shifting is possible with a heat pump without a battery being involved. Possibly if a house is very well insulated with a lot of UFH thermal mass it might work, but for most houses I don’t think people will want the temperature to drop and the inefficiency of the HP having to work harder to re-gain the lost degrees.