Heat Pumps and Zones (or not?)

drives said:

The concept of employing buffer tanks to try and make microzoning work with a heat pump seems nonsensical to me

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Me too, and I gave up on my microzoning. I can see how someone might want a room to be warmer than others, and I'd probably look to do that with adjusting flow rates on the manifold rather than a bucketload of thermostats and zone valves. Works well albeit accidentally for our WC; the flow rate is set too high for the length of loop and I've never corrected it because everyone appreciates the room being a bit warmer it seems

drives said:

what other family members think of having to close doors all the time

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Other family members think in the most incredible peck, as the nagging to turn lights off, flush toilets, put crap away etc is constant

If I was into microzoning I'd just fit decent door closers like barymatic damped jamb ones and have one less thing to bark about

drives said:

keeping heat pumps running continuously

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As in tweaking flow rates so it runs all the time, at a level that replaces heat lost from the house? I wonder if that leads to more frequent defrost needs, versus being able to run at times of day when defrosting is unnecessary

drives said:

and actually the cheapest way of running one, is for it to be turned off

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Agree, and our place seems to have a low enough heat loss that it running occasionally to bring the slab up a few degrees works well. Most the time our heat pump isn't running

drives said:

In October for example I'll use a home assistant automation to turn it off when the indoor temp reaches a certain level

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Our heating is generally active Dec to Feb, cooling occasionally active in summer, but it's not very effective to cool a slab, and the ceilings are full of acoustic wool so the fairly useless spreader plates are even more so for cooling

drives said:

Between Mid Nov and Feb/March though ours is running pretty much all of the time

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Somewhere I've got a year's data logged from a ct clamp on the Hp supply, I should dig it out.. I expect it fires up for a few hours a day. I look at the HP display every time I pass it (in the hall) and anecdotally it is seldom showing the "heat pump on" symbol. It also displays the return temp, and for a flow of 26, that is usually around 21 to 24, which gives me an idea of when it's due to knock off

drives said:

albeit it will cycle roughly once an hour in slightly milder weather

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Don't forget, in unfavourable conditions (humid, and between 0 and 7 degrees or so) some of that running may just be a defrost

robinbanks said:

Somewhere I've got a year's data logged from a ct clamp on the Hp supply, I should dig it out.. I expect it fires up for a few hours a day. I look at the HP display every time I pass it (in the hall) and anecdotally it is seldom showing the "heat pump on" symbol. It also displays the return temp, and for a flow of 26, that is usually around 21 to 24, which gives me an idea of when it's due to knock off

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Yes, it is probably misleading to refer to a heat pump always running and heating. Our's is alway in heating mode but it will cycle throughout the day and will oscillate around the set weather compensation curve point (with one defrost cycle shown below as you mention above). When OAT drops to around 5-7 degrees C that it when it tends to start running at a consistent outlet flow temp for a longer period of time as obviously then the heat loss of the house is greater to sustain it.

I think the main point is without weather comp, an on off thermostat and higher set flow temp (perhaps 65 to 70 for a boiler), occupants will tend to find a pattern of overshooting the set point and then fall back before it clicks back on again. Weather comp results in a much steadier indoor air temp, and thus more comfort.

I should add again that our house is totally bog standard when it comes to insulation. 1970 build, suspended floor no insulation. 100mm loft insulation. Crap dormer insulation upstairs. Not saying our heating is cheap but it wasn't with a gas boiler. We were paying around 200pcm (160m2 floorspace) combined gas and electric. It would be very similar montly cost now, but we reduce this with a storage battery to take advantage of cheap octopus cosy rates. The current electricity versus gas unit cost ratio makes ashps a harder sell as even a SCOP of close to 4 isn't going to save money.

drives said:

I think you'd be surprised if you removed all your microzoning controls, TRVs or whatever you have and just ran weather comp- just how stable you could get the IAT of all rooms.

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Unless doing so changes the laws of physics, then I know exactly what I'd get :
No room would have a stable temperature, for the previously mentioned reasons.

Shut the dining room door, dining room gets over warm and upstairs rooms go cold. Open that door, dining room goes cold, upstairs rooms go warmer.
Weather comp alone simply cannot maintain a stable room temp in the presence of disturbing factors like variable heat losses and variable other heat inputs.
As above, open the dining room door and heat losses massively increase. To put some scale on it, most of the year I run the CH at 40°C*, but for 2-3 months I need to increase it just for the dining room (pop off the actuator on the blending valve*, screw on a cap to force it to full heat*) so the heating runs at whatever the store temp is at the CH tap-off (generally around 50°C). Door open, it still struggles to keep the room warm; door shut, I know it can comfortably do it at the lower temp and will fairly quickly start cycling the rad valve.

So please explain how you would maintain stable room temp on weather comp alone in a room that could overheat at 40°C flow or be cold at 50°C+ flow depending on factors the system has no knowledge of ?

* The system is designed for intelligent flow temp control. Eventually the intention is to vary the temp according to demand so one rad stays open all the time and the others cycle as required. Then control the boiler to maintain only the minimum store temperature to provide that or DHW (whichever has the higher demand).
But that involves more development work than I have time for - so in the meantime it's a bit of a makeshift setup with a simple electronic thermostat and fixed flow temp. I have just ordered a cheap digital stat module to make it easier to change the temp as required.

SimonH2 said:

Unless doing so changes the laws of physics, then I know exactly what I'd get :
No room would have a stable temperature, for the previously mentioned reasons.

Shut the dining room door, dining room gets over warm and upstairs rooms go cold. Open that door, dining room goes cold, upstairs rooms go warmer.
Weather comp alone simply cannot maintain a stable room temp in the presence of disturbing factors like variable heat losses and variable other heat inputs.
As above, open the dining room door and heat losses massively increase. To put some scale on it, most of the year I run the CH at 40°C*, but for 2-3 months I need to increase it just for the dining room (pop off the actuator on the blending valve*, screw on a cap to force it to full heat*) so the heating runs at whatever the store temp is at the CH tap-off (generally around 50°C). Door open, it still struggles to keep the room warm; door shut, I know it can comfortably do it at the lower temp and will fairly quickly start cycling the rad valve.

So please explain how you would maintain stable room temp on weather comp alone in a room that could overheat at 40°C flow or be cold at 50°C+ flow depending on factors the system has no knowledge of ?

* The system is designed for intelligent flow temp control. Eventually the intention is to vary the temp according to demand so one rad stays open all the time and the others cycle as required. Then control the boiler to maintain only the minimum store temperature to provide that or DHW (whichever has the higher demand).
But that involves more development work than I have time for - so in the meantime it's a bit of a makeshift setup with a simple electronic thermostat and fixed flow temp. I have just ordered a cheap digital stat module to make it easier to change the temp as required.

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All I can say is how does it work fine in our house then with relatively stable temperatures across all rooms. I've put a graph on the above post which evidences it. I can post more if you like of loads of temp sensors I have dotted around the house. If I put a temp sensor right by the oven perhaps the graph might look slightly different but in reality it is a minor localised short term fluctuation in IAT.

That said our hallway sensor plotted above is about 2.5 metres away from our oven, with the door always open to the kitchen.