@clockworks  while your sorting your wireless controller I have time to write a post on your rad capacity and the correct maths for sizing. So maybe look at this later.

I think you stated 5.5 kWh capacity based on DT25 output. And you calculated that using correction X 0.41. So by dividing by 0.41 you get DT50 of 13.41kwh.

So using DT50 data- if your WCcurve was calling for 35c flow temp there is a different correction factor needed. I’ve drawn up the attached factor correction sheet for all lower flow temperatures since the manufactures tables don’t do 2.5c increments. So to arrive at the actual output capacity of your rad system multiply the DT50 rating of all your rads by the correction factor in the chosen flow temperature.

I have then used this sheet to work out the output of 15kwh of radiator capacity. 

so you can see that even a 15kwh rad capacity the output at 35c is still only 2.41kwh. That assumes all rads are fully Open and none are closed.

so you can use this chart to calculate your rad output at different flow temperatures so long as you know your correct DT50 radiator rating.

I use Auto Adapt - I think you’ll find- in your capacity it will just try to run at hotter flow temps to limit cycling because it can’t operate at lower outputs. But it might give you more balanced room temps.

I've got the WC curve set for 49 degrees at zero, 32 degrees at 16 outside.

6 degrees outside today, so it's flowing at 43 degrees.

Rooms are all between 19 and 20.5.

Because of the cycling, the average flow is closer to 42 degrees, and the return is averaging 39 degrees

Say the average temp in the rads is halfway between the averaged flow and averaged return, so 40.5 degrees.

Room average is 19.75.

So, the true delta is 20.75 degrees - correction factor of a smidge over 0.3, giving a 4kW output if all my radiators were open.

In practice,  a couple of the rads are being limited by the TRVs to keep the room temps down, and the one in the main bedroom is completely off.

Yes, I'm below the minimum output of the heatpump even on a relatively cold (for West Cornwall) day in January.

I think I said earlier in the thread that even at zero, the house only needed just over 4kW of heat, averaged over the day, to stay at 19/20 degrees.

I'll try fitting the wireless remote, and running in AA mode. If it runs hotter to reduce the cycling, hopefully it will also go to idle for a decent amount of time. Maybe one hour on, one hour off, would work better - unless it's really cold outside?

To me, the MCS way of working out heatpump sizes seems a bit off, erring on the side of caution to stop customers complaining on the odd really cold day, but running sub-optimally for the rest of the time?

Installers gave no choice but to follow the MCS guidelines, or the grant money won't get paid. 

Using HDD data from a colder area (Plymouth) for a coastal property 80 miles away isn't ideal, and basing hot water consumption on 6 people in a 4 bed house when there's only 2 of us, our showers are electric, and we don't even have a bathtub skews the numbers a fair amount too.

Maybe the real answer would be "stacked" 2kW units, where you could run just one tiny heatpump in milder weather, with more kicking in as required?

My brother lives a couple of miles away, 3 bed detached house. A bit less floor area than mine, but it's mostly 3 foot thick solid granite and "rubble". He's had 2 surveys, both coming in at over 11kW!

Massively over-specced I think, but he's got to go along with it to qualify for the grant. His bottled gas-powered boiler is beyond repair. 

@clockworks I have reverse engineered my heat loss calc now that I have 18 months of actual performance data.  My review is that the heat loss figure was overstated due to:

Solid stone walls performing better than calculated (high thermal mass/inertia)
Overstated ventilation rates (room air-changes)
Solar heat gain and heat gains from body heat and domestic equipment

Outside Design Temperature assumption (too low)
Degree day assumptions (base temperature too high)

If I was to do this again, I would carry out a heat loss 'measurement' (eg: How energy efficient is my home? - Build Test Solutions ), to calibrate/moderate the calculations.  Perhaps a consideration for your brother?  I would be 99% certain that the U values used for his walls will be too high.

Thing is, many people replacing a gas or oil boiler with a heatpump will already know (or be able to easily find out) how many kWH their house needs per year. They just need to understand how to relate it to living with a heatpump.

I knew that, on average, I used about 850 litres of oil a year. I had one delivery each year for 13 years, between 750 and 900 litres. With an oil system boiler, that works out at around 8000kWH in tip-top condition.

This wasn't actually that far off the heatloss calcs, probably because my boiler was a lot less efficient than the 90% I'd assumed.

The water demand was massively off by a factor of 5 or more, but there's nothing that can done about that. MCS rules for the size of house.

What I didn't have a clue about was the importance of 24/7 running, the influence of outside air temperature, not "micro-zoning", flow temperatures, HDD numbers, etc.

It's a pretty complex subject, and I'm learning after the fact because I had no idea what I didn't know when I signed up. Even if I had known then what I know now, it probably wouldn't have made a difference. The computer said "6kW", so that's what I had to get to qualify for the grant.

I'm not unhappy with the ASHP, as the house is now much more evenly warm, and the running costs aren't that much higher than oil. - £6 on a cold day, £2 when mild. I am a bit annoyed that I've had to spend hours each day for the past 6 weeks reading up about it and tweaking, and several hundred quid on gadgets to monitor everything.

Luckily I've got the time, I'm willing to learn, and I'm reasonably practical. It's become a project, if not an obsession!

My brother is currently heating just one room at a time with 2 oil-filled radiators. Might struggle with that monitored survey, as most of his house is "freezing" - very little heat to lose in most rooms. Whatever they install will be cheaper to run than oil-filled radiators, or the gas bottles that he used to use.

Posted by: @clockworks

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It's a pretty complex subject, and I'm learning after the fact because I had no idea what I didn't know when I signed up.

Indeed!

This general lack of energy knowledge within the wider UK population has been of concern to Ofgem, the energy-industry regulator.
We are being held back from making technological advances.

It's just too easy for a professional installer to recommend a heat-pump system without the home-owner being able to question what's being proposed.

This knowledge-gap is being discussed amongst us Forum Moderators.
If you think there are ways to better address the situation, then now is the right moment to say so.

Personally, I'm very much in favour of the typical 'conversation in a pub' approach. 🍻

There's a lot which can be usefully discussed within a small group where one or two have already experienced a HP installation.

Heat pumps, electric cars, and climate change seem to be very divisive subjects. I'm not sure there's any way to educate the general population, short of the mass media getting involved. Problem is, the popular press just like sensationalism, not rational and factual content.

"EVs suit some people more than others", or "heatpumps work fine if they are specced and installed properly" doesn't sell papers or generate clicks, and most people wouldn't believe anything the government says nowadays. "Big subsidies, they must be rubbish".

Reasoned discussion down the pub is probably the way forward . It seems to be working for EVs.

Posted by: @clockworks

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Reasoned discussion down the pub is probably the way forward . It seems to be working for EVs.

Spot on @clockworks @transparent - this is exactly why we have organised a local community meeting - this needs local community action, towards households becoming 'informed clients' 

@ajn9000 - Then please post details of that Community Meeting here on the Events Topic...

... and provide a link from here.  🙂 

Whereabouts are you in the country?
and who is your Local Planning Authority?

@transparent - done

https://renewableheatinghub.co.uk/forums/postid/41222

Thanks @ajn9000

I've added some advice for attendees traveling from east of the border. 😉 

Splendid, thank you @transparent 😉 

Finally got time to fit the wireless remote, and try auto adaptation mode this morning.

I left the Evohome boiler relay connected, but I'll have to disconnect it I think, as the heatpump switches off if the boiler relay goes off. Enabling the wireless remote leaves the IN1 input active, and this is how the Evohome was connected.  There's a switch in the Mitsubishi controller to inverter the switching logic of IN1, but nothing to disable it. If I flip switch 2.1 to "off", the heatpump will run with nothing connected to IN1, and be controlled purely by the master remote schedule and the wireless remote temperature sensor.

Next problem is, where to site the wireless remote? I think the inner hallway will be best. It's the most stable for temperature (no external walls or windows), and the radiator is "open".  The hallway drops less than a degree in 4 hours with the heating off.

I'd be interested to know the operating logic behind AA mode -

How much influence do the outside and inside temperature readings have on the flow temperature?

Does AA mode allow extra "overshoot" of the flow temp if the remote stat is set higher above the actual room temperature?

Does the weather compensation curve still play any part in AA mode? If so, is that long-term, or just a starting point for the learning process?

I've left the Evohome TRVs running to act as "limiters" in most rooms for now.