How to run my ASHP most efficiently?

dllive

Hi,

I had a Mitsubishi Ecodan air source heat pump installed last year. When commissioning the system the installers spent literally 2 minutes going through the settings with me.

A year later, I now feel I would like to optimise the settings so I can get the ASHP working most efficiently. (the installers are now bust so I cant ask them for guidance).

For example, Ive just had a look at the Ecodan and the schedule is set for 24/7:



I only use hot water for doing washing up at 6pm in the evening. Also I have a sporadic shower perhaps twice a week (I shower daily at work!). So it seems a waste to have the hot water on 24/7!?

When I was digging in the settings I found the DHW is set to 'Eco'. What does that mean?



Ive also just found stats for energy CONSUMED and energy DELIVERED. I assume the consumed energy is how energy the system is using to run; and the delivered is how much eergy the system has generated to the house?





I keep weekly meter readings and I cant tally the figures up to what is on the Ecodan. For example, the past 2 months:

2 Nov: 34110 - 154 kw/h
9 Nov: 34236 - 126 kw/h
16 Nov: 34399 - 163 kw/h
23 Nov: 34554 - 155 kw/h
30 Nov: 34658 - 104 kw/h
7 Dev: 34834 - 176 kw/h
14 Dec: 34978 - 144 kw/h
21 Dec: 35134 - 156 kw/h
28 Dec: 35252 - 118 kw/h

The heating is also set to 24/7, however I have a thermostat in the house which Ive programmed to come on for 2 hours in the morning and 2 hours in the evening. Should I set the Ecodan to only turn the heating on 2 hours in the morning and 2 hours in the evening, or does my thermostat override the Ecodan?

Apologies for the long post. TBH I got the ASHP installed becuase I thought it would use a lot less electricity, but its actually consuming about the same if not more! Just looking for guidance on getting it to run cheaper.

Thanks

lovesgshp

The system should be operating 24/7, so if you are shutting it down for most of the day then it has to reheat the house after the off time which can take quite some time.

You cannot use it as a normal type heating system.
Eco on the DHW is ok, it will just try to keep the tank hot for demand.

Andy_WSM

dllive wrote: »

TBH I got the ASHP installed becuase I thought it would use a lot less electricity, but its actually consuming about the same if not more!

According to the annual consumption data you have posted above it is delivering 3 times more heat than it's consuming in energy, so it's definitely NOT costing you more!

If it really has consumed 1,469 kWh this year then it has only consumed approx £200 of energy assuming you are paying a reasonable tariff of around 13p / kWh.

Trying to tie up the data with your houses main meter is futile because you don't know what everything else is consuming!

matelodave

As Andy says you cant equate it with your leccy bill unless you are only measuring the power consumed by the heatpump.

Most people also use leccy for lights, TV, washing cooking and lots of other stuff at the same time so you can't separate out the power specifically used by the HP unless it's on a separately measure circuit.

Ideally you need a programmable thermostat which allows you to reduce the heating temperature by only 2-3 degrees over night and possibly during the day so the house doesn't get stone cold.

Trying to reheat the place from cold just means that the unit flogs it's heart out to try and get the place warm, something it cant do unless you've got a really high flow temperature.

Make sure that you dont set the heating flow or water temperatures so high that the back-up/boost heater activates. Keep it as low as possible, certainly below 50 degrees.

Cardew

I don't understand the 'consumed' and 'delivered' energy displays.


Taking the 2019 figures it shows a delivered 4520kWh for a consumption of 1469kWh giving a very respectable COP of 3.08



However the figures do not add up as it would appear that:


In Oct the Ecodan consumed 300kWh and deliverd 603kWh giving a COP of 2.01


In Nov consumed 511kWh and delivered 870kWh giving a COP of 1.70


In Dec consumed 510kWh and delivered 933kWh giving a COP of 1.83


Thus Oct/Nov/Dec consumed 1321kWh and delivered 2406kWh giving a COP of 1.82


The OP states he has had the system since last year. However in the whole of 2019 it states it has consumed 1469kWh of which 1321kWh were consumed in Oct/Nov/Dec thus only 148kWh consumed in the remainder of 2019.


However it claims to have delivered 4520kWh in the whole of 2019 of which 2406kWh were delivered in Oct/Nov/Dec.



Thus 2114kWh(4520 minus 2406) were apparently delivered in the remainder of 2019 but this was delived on an input of only 148kWh which is clearly not possible. Not the most ardent fan would claim a COP of 14.28!

Something is wrong - anyone an explanation?

dllive

lovesgshp wrote: »

The system should be operating 24/7, so if you are shutting it down for most of the day then it has to reheat the house after the off time which can take quite some time.

OK, so Ill leave the settings on the EcoDan as they are. But I control the heating on this:


I have it set to come on for an hour in the morning and a couple of hours in the evening. Youre saying it will be more economical to leave it on all the time? (perhaps 18 degrees during the day and then a few hours at 20 degrees in the evenings)?

dllive

matelodave wrote: »

As Andy says you cant equate it with your leccy bill unless you are only measuring the power consumed by the heatpump.

Most people also use leccy for lights, TV, washing cooking and lots of other stuff at the same time so you can't separate out the power specifically used by the HP unless it's on a separately measure circuit.

Ah! Ive just looked on the consumer unit and there is a seperate circuit for the immersion and heat pump (I forgot!).





The figures are:
Heat pump: 04297.41
Immersion: 0001740

dllive

matelodave wrote: »

Make sure that you dont set the heating flow or water temperatures so high that the back-up/boost heater activates. Keep it as low as possible, certainly below 50 degrees.

Ive just looked at the Ecodan. The flow temperature is showing as 0 (and always had):




Heres the heat curve (not sure what it does but I remember the engineer said it was important):



So how do I make sure its set below 50 degrees?

matelodave

According to the readings it is set to 50 degrees for hot water and 47 degrees for your heating flow.

The heat curve shows that the flow temp varies to take into account higher outside temperatures. The flow temp is reduced to around 25 degrees when it's +30 outside and increases to a max of 47 degrees as the temp drops down to around +5 degrees.

Dont fiddle with them as they are set about right. The +/- adjustment will probably offset the slope - you could try reducing it by perhaps one or two degrees which should reduce your consumption a bit BUT it might take longer to heat your house. Dont increase it because it will increase your consumption.

Control your house temperature with your programmable thermostat.

We have our hot water set to 45 degrees and heat it for just two hours a day

dllive

Thanks @matelodave . I now understand what the curve is doing! I might offset the slope and see if it makes a difference to cost.

matelodave wrote: »

We have our hot water set to 45 degrees and heat it for just two hours a day

This sounds sensible, but doesnt that mean that each day the tank has to heat up from cold? Does this mean you have to time when you have your showers to avoid havng a cold shower? (As I say, I use the showers at work becuase I cycle in. I only occasionally shower at home sporadically, for example when I have a few days off work). You set that on the Ecodan do you?

lovesgshp

dllive wrote: »

OK, so Ill leave the settings on the EcoDan as they are. But I control the heating on this:


I have it set to come on for an hour in the morning and a couple of hours in the evening. Youre saying it will be more economical to leave it on all the time? (perhaps 18 degrees during the day and then a few hours at 20 degrees in the evenings)?

Yes, I think a drop of 1-2c in the day if ufh, or 2-3 if rads. With your DHW tank, what size is it and drop the temp to 48C. Check the times/days for the legionella heat cycle, as this could be kicking in the electric heater. (It will normally heat the DHW up to around 60/65c).
The heat curve looks ok, so not worth altering.