zoning and avoiding ASHP short cycling

[Tom]

Hi All - our UFH is set up at the moment such that we have one very large zone (abouth 1km of pipe), and then lots of smaller zones (80-90m of pipe)- bedrooms, en suite etc. I want to run the ASHP at it's most efficient so I'm concerned that these small zones, if allowed free reign, would result in short cycling. Would it be possible/feasible to set up the ASHP controller (Mitsubishi) so that a small-zone thermostat can only successfully call for heat IF the large zone is also calling for heat? The small zone can then switch off when needed, or continue to call for heat even if the large zone has subsequently stopped. I've asked the ASHP installer but have yet to receive a reply, would be great to see if any one here thinks this worthwhile or a waste of time or just not possible.

Thanks all

[JohnMo]

11 minutes ago, Tom said:

one very large zone

 

11 minutes ago, Tom said:

concerned that these small zones, if allowed free reign, would result in short cycling

You either have one zone or many, you seem to claim both? If you want efficiency dump all the thermostats, maybe keep one (the one in your controller)

 

One zone is best, but lots of loops, all on or all off. But no real need to stop. Low and slow weather comparison is the most efficient generally.

 

If you want efficiency 

 

1. No mixers, buffers, thermostats no actuators on manifold needed. 2. Balance the loops to get the room temps right.

3. You need floor temp as close to room temp as practical, then if the room heats from the sun that area of the floor stops giving off heat, so heat pump modulates down to compensate.

 

Just spent the last couple of days optimising mine. Low flow temp required 11 degs outside, set flow temp target to 26 degs. The start and stop delta to start and stop the ASHP compressor are key. Ours stopped heating at lunch time today with no intervention from me or any thermostat - just because the sun came out, house got to 21.5.

 

Keep as simple as possible for efficiency.

[Tom]

Thanks @JohnMo, seems like I've been oversold a load of thermostats and actuators by Wunda...! I certainly prefer the idea of keeping it all simpler as you suggest. I have a floor probe in the concrete of the large zone, so that could be retained - though as you indicate above, perhaps I don't even need that if the ASHP would modulate itself down to zero. Would the bedrooms be a bit too warm though, if I rely on a "one flow-temp fits all" approach? I could just suck it and see, can always add back in thermostats and actuators as we learn to live with it.

[JohnMo]

1 hour ago, Tom said:

Would the bedrooms be a bit too warm though

You can turn the flow rate to this loops down to get less heat transfer.

1 hour ago, Tom said:

have a floor probe in the concrete of the large zone, so that could be retained

You could use it for monitoring, but really not needed.

 

1 hour ago, Tom said:

seems like I've been oversold a load of thermostats and actuators by Wunda

Ours started with a thermostat in every room. Had loads of issues, with short cycling - they got deleted down to one. Also had a mixer and pump on UFH that didn't help either, so deleted them also. People will say you need a mixer to protect the floor, when you change over from DHW heating, as you will get a slug of hot water going into the floor. But it is a couple of liters and the heat quickly dispersed.

Think I can actually manage with zero thermostats and just leave the heat pump to get on with it. Will leave the one I have in place for now, but overridden.

 

Tuning the system and getting your head round all the parameters you can change and what to ignore is the most difficult bit. Dread to think how many times I have read the manual.