Heat Pumps and Zones (or not?)

[robinbanks]

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

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

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

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

keeping heat pumps running continuously

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

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

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

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

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

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

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

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

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

 

[drives]

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

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.