As radiators are fitted in parallel it means that the leaving water temperature does not affect the next radiator along, which in itself is good but even better, you can adjust flow to get the leaving temperature as low as possible. That means that you get the most possible heat out of the water and the return water to your boiler is well down into the condensing range, so getting optimal boiler performance. If you have a heat pump it will also improve your COP, as the nearer the water temperature is to outdoor temperature the less work is required to move the heat across to your water.
Edit: however, low circulating flow temperature to the radiators requires a high flow rate overall.
Returning to my Daikin heat pump, the flow temperature is dictated by the weather compensation curve and as you may have noticed, the weather has been a little chilly recently.
I am pleased to report that the house remains a stable temperature of 20 °C in most rooms. The room that previously only managed 19 °C is still at 19 °C as I had decided that it didn’t need to be warmer, however our dining room temperature has now also dropped to 19 °C.
During the first cool spell after the heat pump was commissioned I went round rebalancing the radiators for the faster flow rate/lower temperature that was the new normal and it seems I wasn’t quite accurate.
The weather compensation has increased flow temperature to 45 °C overnight•, fractionally less during the day. The radiators are noticeably warmer. The power consumption has increased to draw more heat from colder air, peaking at 2.5kW but more often 2kW. In the warmer part of the day it continues to modulate between 500W and zero.
I have a six hour off peak electricity price of 7.5p including VAT. Fortunately I have 25kWh battery storage, increased in early December, to cover most of my heating and other electric usage at other times. Apart from the capital outlay for heat pump and battery the cost of running the heat pump is less than for gas. The heat pump was over half paid for by BUS and I even got a small rebate from Tesla for buying an additional Powerwall. I avoided VAT on the battery by also getting some solar but anyone following in my footsteps would now be able to buy a battery VAT free anyway.
The heating is on 22/7, the other two hours are dedicated to DHW. The lower the heat input the longer the heating needs to run. This is even true in a Passivhaus but less obviously so. The cost is nevertheless lower with the heat pump. Most people set the temperature down slightly at night but as that is my off peak time I take advantage and run at the normal rate.
Sounds good. So the HP can hit a flow-temp of 45deg, when/if required? Do you know what your input-output heat difference is, at a typical radiator - or, presumably you can read-off the return temp (of the total circuit, just before the water goes back out to the HP)?
The HP can achieve over 50°C if needed but I have set a ceiling below that.
I do not have an automated home or loads of sensors. The only heat pump temperature I can see is the “LWT”, Leaving Water Temperature, from the Daikin app. I can read room temperatures off the eTRVs.
'morning Tim. Hope all goes well with the HP. The PPR surveyor who’s writing up the survey he recently did here tells me we’re ok here for a 5kW ASHP, given current conditions - which I’m pleasantly surprised to hear. (83sqm total floor area.) We’re not rushing into anything, just yet, but can I ask who your installer was?
The heat pump is running smoothly thanks. We do have an issue with the Heatmiser thermostat loosing contact with its own base station every time there is a power cut, however short. I have an outstanding complaint with our installer about using a third party thermostat but they are not helpful. That is my only complaint about them. Otherwise they were very good.
My installer was a moderately local company. I’m on the London/Hertfordshire/Essex border and they do Essex. I found them by contacting Daikin sales and asking for approved fitters.
If you have a shortlist of manufacturers you could do similar. In retrospect I would have asked Daikin if they guarantee their fitters’ work. If Daikin had their own fitters then I’m sure they would have used a compatible thermostat from their own range.
I already had a very good idea of what system I wanted, taking not only the heat pump itself into account but also the environmental and labour practices and policies of the manufacturer. A review of manufacturers that I read in Ethical Consumer Magazine praised Daikin for air source heat pumps and Kensa for ground source.
If you still want me to name (and shame?) my supplier after reading this then I will do so.
ok, thanks for that. That’s actually a long way from us, we’re in Manchester…! We had solar PV installed a few years back by a firm just over the Pennines, they also gave a HP quote, might ask them for an up-to-date re-quote, now I know a bit more about it all.
An update on the functioning of my Daikin heat pump.
As you may recall the third party thermostat lost connection while we were away for New Year and the house temperature dropped 5°C over 4 days. I sized my heat pump with a finger in the wind approach and decided on the bare minimum power rating, so although it is good at maintaining house temperature it is not so good at raising it several degrees and it took days to get my high thermal mass home back up to temperature.
Move forward to this last week and half term (where we are anyway). We went away again, for 5 days. Given the struggle to increase temperatures after New Year I decided not to set back the heat pump but checking while we were away I saw that the temperature dropped 2°C and stayed there. When we returned the temperature started rising again. The system does not have any built in presence/absence detection.
So how can this be explained? I think I have an answer but feel free to suggest others.
All household thermostats are set high, and function to prevent severe overheating and to report temperatures back to the hub. (I use Homekit.) so the radiators did not drop the temperature. Internal temperature is supported by weather compensation and the resultant flow temperature.
However, the heat pump is not the only heat source in the house. There are body heat, cooking, heat from use of DHW (which had been off), the children’s games machines and assorted other sources. I had also been actively opening and closing curtains to take advantage of solar gain and minimise radiative loss.
I believe that with the house being empty, I have accidentally found the value of my internal gains. 2°C.
P.S. I had also left the MVHR running as normal, which was an oversight as had intended to reduce airflow while the house was unoccupied.
On the subject of weather compensation and flow temperature via an ASHP here is the data for our system. NB these are average daily values (while running) and peak flow temps do push a bit higher than these average (up to 45C typically when sub zero outside).
Here it is. The best fit line may actually be a curve, but I am showing the best fit straight line here. Our set up isn’t fully optimised, eg we still have a lot of 10mm micro-bore pipework and rads are mostly the originals from 1997ish (when we had the gas heating put in).
Thanks @zapaman, those look quite useful, although I realise each setup is unique.
Earlier today I wrote to Customer Support at Daikin asking where I could see output and/or COP. I also complained that the latest version of their app no longer shows external temperature, making it more difficult for me to look into efficiency.
Like you, I intend to enhance my emitters, but in my case the ones I have are actually quite good. Some time ago I managed to get some matching aluminium radiators that I intend to add into the system to distribute heat more evenly and of course increase surface area.
Hey @Tim_Gilbert ,
Glad your having such success with your heat pump. We are working on a project to roll out DSR heating controls in social housing and they have Daikin monoblock heat pumps very similar to yours. There has been a bit of tangled history with Daikin control, with the phasing out of the local API and then throttling of the cloud API but last month they quietly launched the Daikin Europe developers platform (I presume in response to the new EU regulations on end user access to device data). While at present it has less data points available than the old API, at least it’s a official route forward and more data is promised over time.
I don’t know if you’re a home assistant user, but there is a very active new daikin integration for monitoring and control using the new API connection made available via the official ‘Onecta’ app.
If you’re interested in helping us test it, let me know and I’ll send you over a box.
Many thanks,
Matt
Thanks for the offer. The project does look very interesting but I’m an install and forget type of person. As I understand it HA is more a “constantly tinkering” system. I would be happy to learn differently.
The closest I get to integrated home control is Apple’s Homekit, otherwise I just use the manufacturers’ apps. I would be happy to use an app that integrated Daikin HP with Zehnder MVHR. Heating and ventilation seem an obvious area for integration. It can get a bit frustrating at times with so many apps, including the ones for car and charger.
I’m very happy with the overview and control from my Zehnder app, and to be honest most of the time it just runs at the settings that were configured for Passivhaus, not that my house is very near that (yet?). It just seemed logical to control heating and ventilation from one app.
The Daikin Onecta app on the other hand leaves much to be desired.
I see the link is to Home Assistant, so no use to me!
Hi Tim,
Apologies for the overly hasty previous response, to clarify I linked the Zehnder Home Assistant integration as I thought you were suggesting you might be interested in HA if it were able to integrate both your heating and ventilation systems.
DSR = Demand Side Response, the ability to alter your demand in response to grid conditions - these might be in response to signals about price, carbon intensity or grid congestion.
Hope that all makes sense.
Matt
Ah yes, with context I have seen DSR before. As in Octopus Agile and I am now a user of “Intelligent Octopus Go” for EV charging. I have also taken part in every grid “Demand Flexibility Service” session since they started in late autumn’22.
I thought my heat pump came with capability but it turns out it was an optional extra which will be very expensive to retrofit.
I have at last received an answer. You can’t see COP. However on the control panel it is possible to see energy used and energy output, they claim to 20% accuracy, so it can be worked out.
The question about the outside temperature not being displayed any more was not answered.
