Air Source Heat pump schedule

Baronoli

Hello all,

We've just moved into a new build with a ASHP and the developer wasn't very clear on its functions.

The unit is a Mistibishu Ecodan, which is connected to underfloor heating and a Heatmiser 8 zone thermostat system.

The controls were set to a target flow temperature of 60c, but is this the best option? It also has target room temperature and "compensation curve"

I've read a few posts on it and people suggest it should be on almost all the time. I currently have it to come on at 05:00am and turn off at 09:00. Then back on again at 17:00 and then off at 10(house empty all day).

I only have 3 zones requesting heat in the morning and 1 requesting heat at 18:00 until 10.

Should I be extending the air source heat pumps schedule settings to be on even if I'm not having a zone request heat ?

Thank you all and apologies if this is in the wrong place.

Thank you

matelodave

An ASHP running at a target flow of 60c is going to be very expensive to run.
The optimum efficiency for most ASHP is quoted at around 35c and it reckoned that it'll cost an extra 2.5% for every degree above that.

Additionally most ASHPs wont raise the water temp much above 50-55c so will use a backup or boost immersion heater to attain higher temperatures which will have a fairly dramatic effect on your leccy bill.

Mines not an Ecodan, its a Daikin and I've got the weather compensation adjusted to run at a nominal 35 degrees at around 5 degrees outside, 40 degrees when it's zero outside and about 25 degrees when its 15 degrees outside and it runs when it want to - sometimes all night and all day.
My hot water is set to 45 degrees with a weekly one hour boost to 60 to sterilise the tank. I have the backup/booster heater switched OFF although there is a 3kw immersion in the hot water tank which activates during the boost period to raise the temp to 60.

I dont switch the heating off but I've got programmable thermostats in each room (8 zones) which control the times and temperatures appropriate to their use.
The minimum temperature is set to 17 degrees (otherwise it takes a very long time to reheat the bungalow) The temps are then raised during the times that we are using the rooms - bathroom & bedrooms 7am to 9am and then around 9:30 to 11pm.

The lounge is up to 19 all day (7am to 10pm), the study 0800 to 5pm.

Underfloor heating is quite slow to respond - it acts like a storage heater so you need it on early to warm up the slab and off early to get the benefit of the stored heat - only you can assess when the appropriate times are.

It took me a whole winter to get mine optimised but I understand how it works. Running it like a conventional boiler at the temperatures you are using will cost you a lot of money.

I would be checking and recording my leccy meter every day to get a pattern of usage and to be able to monitor the effect any tweaks or adjustments.

The consumption will vary a great deal at this time of the year - we get through over 1000kwh a month in Dec through to Feb/March then it tails off to around 250-300kwh in the summer.

have a look here at my real time energy consumption and you see that the machine runs when it needs to, all day and all night if necessary https://www.energyhive.com/dashboard/dave. You can also look at some of the history to see how it varies - this Feb has been quite warm so we've used less than normal

Baronoli

Wow thanks for your reply! Very helpful!

I'll definitely look at the compensation curve.

Sorry if I still sound a bit dim here: if I switch my heating schedule to be constantly on and only had 4 out of my 8 zones requesting heat at intervals when there's someone in and my target flow temperature set to 35 I wouldn't be out of pocket? There's only two of us and we're out of the house from 07:00-18:00 we only really need heat at 05:00-07:00 and 18:00 - 22:00. I'm just so used to a combi boiler it's alien to think leaving it on all day isn't going to cost more than 2 cycles of timings !

Thank you so much

matelodave

You do need to see how your energy consumption varies with different settings.

I dont know anything about the Ecodan set up but a lot of people seem to be unhappy with the cost of running them and it's usually because they are running it like a conventional boiler and they've got the boost/back up heaters keeping the flow temperatures high. The lower the flow temperature the lower your running cost will be. The boost heater is usually rated at around 6kwh so you want to try and avoid using it as much as possible.

Another thing that I've seen with Ecodan (we had the same when we had our quotes) is that they seem to undersize them so they are flogging their hearts out. My heating requirements are around 10kw and we were quoted for 8 or even 5kw Ecodans. My Daikin is 11kw. If the unit is too small then it has to rely on the boost heater to make up the shortfall

It's trial an error I'm afraid, but it does help if you can monitor your energy consumption - it might be worth getting something like an Owl or similar (unless you've got a smart meter) so you can see what is going on.

What sort of tariff are you on - I'm on the cheapest a single rate tariff I can find because most of my heating is during the day and evenings so wouldn't use much during off-peak hours. We are at home all day.

Don't forget that you don't have radiators that get red hot and heat the place quickly, a heat pump and under floor heating tend to maintain a gentle heat for longer so they have a very slow response time.

If I shut mine off it can take 24 hours or more to reheat the place, so try turning it down by a 2-3 degrees during the day and overnight rather than letting the pace get stone cold and increasing the temps in the rooms when it's required. as in all things make sure your insulation is as good as you can get it.

look at my graph and you can see that it needs to get quite cold overnight before the system kicks in and the average consumption is only around a kwh a hour when it is on. The horrible peaking at around 7-9am is when the machine is heating the water and I make the morning coffee.

Jonesya

You'll be using a lot of electricity, so find out what tariff you are on and if it is a multi-rate tariff with different charges according to the time of day, then find out what the switching times are. Because then you'll want to set the times according to the tariff rates to minimise the cost.

Once you know a bit more about the system and how quickly it heats the house up, and how quickly it cools down again, you might want to look at some of the time of use tariffs if you're not already on one - the latest ones which use smart meters to give more flexibility over the time bands tend to have lower prices during the day and overnight, but high prices during the evening peak between 4-7PM, so depends on how much heat the house retains over that period and if you can heat up the house before 4PM, then shut the system off for 3 hours over the peak before putting it on again at 7PM..

Bulb offer one in their Bulb Labs section, Octopus have an Agile one with variable pricing but with a similar structure. And there's the regular Economy 7, or rarer Economy 10 (hours over-night and in afternoon and evening).but those last two are probably more suitable for storage heating.

If you can avoid that peak period, the Bulb one might be interesting:
https://bulb.co.uk/smart/

Baronoli

Thanks Both:

We're still waiting on the developer to sort out the meter readings, so I haven't found a tarriff yet.


I played with the settings last night and set the bedroom, en-suite, main bathroom and living room to 21C. From what I can see from the heatmsier graphs our rooms don't even drop below that hardly!:

From 00:00 - 09:00AM this morning the living room went only as low as 23.3C at 05:00

From 00:00 - 0900AM this morning the Main bathroom only went as low as 20.3C at 06:00

From 00:00 - 09:00AM this morning the Main Bedroom only went as low as 20.3 at 03:00

From 00:00 - 09:00AM this morning the Ensuite only went as low as 20.5 at 01:00

Should I be increasing the temperature of all these rooms to 22C to save on the system having to heat them all up from cold and keep that as a constant "comfort" temperature? We don't actually feel cold to have them on higher (apart from the main bedroom).

Thanks