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.

 

[SimonH2]

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.

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.

 

[drives]

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.

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.

 

[SimonH2]

OK, so it works for you. That doesn't mean it works for everyone - and as I described above, it cannot work for us unless you can change the laws of physics.

 

[Ivor Windybottom]

Digging up my old thread, we've had a heat pump with 4 zones installed for almost a year now.

It's utterly brilliant, don't listen to any of this voodoo rubbish about heat pumps needing one circuit with all the rads open or whatever. Just treat it like a gas boiler, if your rads are big enough then it reacts really quickly despite the lower flow temperature.

Here's my Heatmiser app...

We both work from home, Work is my zone, Study is hers. It will switch from these two zones to Play shortly, then the Rest zone would normally join in at 7pm at 18 degrees but I've put it into standby now as the weather's warming up and it's just not needed.

Obviously there is some heat spreading between rooms where one is heated and the other not. But we've had it at 21 in the lounge all evening while the bedrooms are 12 before their turn for some heat. So it's saving vast amounts of energy that would have been used heating rooms that we're not using.

A plumber did the plumbing, I did the wiring. I added four override buttons to switch the zones on from the cupboard so the plumber can do what he needs without running round the house messing with 4 controllers.

The zone valves and wiring (in a cupboard)...

All zone controllers are Heatmiser hard-wired controllers. So it's basically four separate combined timers and thermostats. Each zone has any temperature as needed at any time. The four are only linked by the app. It's not dependent on any batteries or the internet. The network is only used for the app, and this is just an optional extra - it works perfectly without any network connection at all (obviously minus the app).

Each controller is mains-powered, each feeds back a switched live when it wants heat. This directly powers its zone valve. The switch outputs from all zone valves are wired together and wired to the heat pump - if one or more is on then the heat pump will be on. If the zone valve failed to open then its contacts wouldn't switch and the heat pump wouldn't come on, so it's failsafe.

It has a spring-loaded bypass valve, as the heat pump stays on for a couple of minutes after the valve goes off. This ensures it's not pumping into a dead end.

I've set the 3pm changover between working and lounging so there's an overlap, therefore the heat pump doesn't get told to shut down then told to restart immediately after.

The flow temperature is regulated by the heat pump automatically depending on the outside weather, it works really well.

Obviously there's some "cycling" when the heat pump goes on and off as the controllers tell it to switch on and off. This seems to work just fine. Last time I looked the COP was 3. The controller that's intended to be used with the heat pump senses the room temperature and tells the heat pump to back off before it switches off, which may make it more efficient. But I'm sure this loss I've introduced will be massively outweighed by us not heating the half of the house we're not using at any one time.

 

[richw]

Isn't there idea that a heat pump, with low-temperature radiators (or UFH) should basically be on low all the time? Because if your house goes gold, then you can't whack it on high for 30 minutes like you can with gas. Presuming the heat pump is cheap to run, so why not have the whole house at 21 deg? (or perhaps a max of 18-19 overnight). Is there any financial benefit to zoning?

 

[drives]

@Ivor Windybottom have you tried it without zoning? How do you know that this approach is saving vast amounts of energy out of interest?

Great it works and you are happy with it. That is the main thing obviously.

 

[endecotp]

It's utterly brilliant, don't listen to any of this voodoo rubbish about heat pumps needing one circuit with all the rads open or whatever.

Yes, voodoo rubbish. “How do you know this is cheaper than running it 24/7 and keeping the whole house at 21 degrees constantly?” - because it’s obvious, unless your brain has been fogged by too many borderline-consipracy youtube videos.

 

[SimonH2]

Presuming the heat pump is cheap to run

That's where your premise fails - they are not cheap to run. At a typical CoP of 3, and typical energy costs, they should be similar in cost to a gas boiler - some have found them disappointingly expensive, some have found them cheaper.

so why not have the whole house at 21 deg? (or perhaps a max of 18-19 overnight). Is there any financial benefit to zoning?

To start with, if our bedroom is 18°C at night, SWMBO would be throwing the window open. But apart from that, the higher the temperature gradient between inside & outside, the higher the heat losses.

There is an argument that keeping one room cold can increase running costs while still reducing heat losses. If the system is running by modulating the flow temperature, then the HP might need to increase the temp, reduce it's CoP, and hence use more electricity.
But that's not the case here.