ASHP Energy Usage

[Scots Build]

We moved into a new build last year that has a DAIKIN ERLQ014CAV3 ALTHERMA OUTDOOR UNIT coupled to a 

DAIKIN EHVH16SU26CB6W HYDROBOX/CYLINDER but energy usage seems to be rather high considering it is only being used for DHW for at least 6 months of the year.  The property benefits from large solar gain so no need for the UFH to be on throughout summer.     Does anyone have a similar system and can share roughly how much power it's using and/or the most economical way to set it up?   I've had a read through the manuals but am struggling to know the best way to set it up for lowest running costs.  Is it better to maintain a water temp of say 40degC throughout day then boost to 45 around the time of showers.  Or only have one heating period per day?   There is only 1 person living in the house at the moment and it's using a steady 18kwH per day (in winter with UFH on, its gone over 100kwH/day).   House is modern design and has good airtightness of 1 m3/hr/m2

 

[ProDave]

18kWh per day to heat DHW for 1 is astronomical.  You would be better, at least as a test, to turn the ASHP off completely and just use the immersion heater.

 

What metering do you have to be sure that is the ASHP using that much?

[SteamyTea]

Sounds like it is only using the inbuilt immersion heater to do the work.

9 minutes ago, Scots Build said:

Is it better to maintain a water temp of say 40degC throughout day then boost to 45 around the time of showers. 

Don't boost, it does not work like a gas boiler.  Maybe you should raise the temperature up to 45°C  and just let the ASHP top it up as needed.

 

[Scots Build]

As far as I know, I don't have any control over whether it is the ASHP or the immersion heater that is doing the work.  The controls just allow me to set the temp of the water and at what time it is required.  If I only set one temp/time per day in the clock schedule, say 45 deg @ 12pm, does that then maintain that temp all the time or does it just aim to raise the water temp to that temp at that time and shut off? At moment the schedule is something like this

 

18:00 45 deg

19:00 40 deg

 

which I presumed would maintain 40deg but increase to 45 deg for an hour period.  There is no consistent big spikes in energy usage at 18:00 suggesting immersion is always used, but spikes throughout the day, say every couple of hours

 

I have trialed turning off power to the ASHP for extended periods of time (when house is unoccupied) and background usage for the rest of house is around 4-5kW/d so the ASHP system accounts for the remaining 13-14kW.  I've got a smart meter so can see energy usage in 30min chunks but that's the only metering I have

 

 

[Dave C]

That's an awful lot of energy usage even if it 100% of the DHW heating was on an immersion!

 

Are you sure there's not a dripping tap or leaky pipe somewhere? Few months ago I had my heat pump firing up unexpectedly in the middle of the day, when no large amounts of hot water [should have been] used, and it turned out my daughter had left a hot tap trickling water - over a few hours it drew off enough hot water from the tank that the tank needed topping up again.

[Scots Build]

I'm glad you are agreeing it seems an excessive amount of usage.  I've kinda just accepted that's the way it is as a first time ASHP owner, but it constantly niggles away at me (as well as draining the funds in electric bills) and that's why I turned here in the hope of help to understand what's normal

 

Definitely no leaking tap or shower within the house, and no hot pipes/liquid suggesting a PRV is passing either.  This high usage has been over the last year since we moved in so we'd have noticed any leaks etc

[JohnMo]

Have you read the manual? You should be able to set the DHW production to reheat mode, schedule mode and a combination to the two. 

 

It looks like you are in reheat mode continually, so you throwing heat almost constantly to the cylinder.  You would be better heating the tank once per day to a temperature that is acceptable to your usage.

 

 

 

[joe90]

This thread made me look at my bill / usage which I have not done before. 5kW ASHP, two people, 48’ DHW, (no immersion) ,no heating (summer)  just under 6kwh per day this month.

Edited June 10, 2022 by joe90

[JohnMo]

That what our EPC said we should be using around 5.5kWh.

[SteamyTea]

3 minutes ago, joe90 said:

 just under 6kwh per day this month.

I use kWh/day, or kWh.day^-1, or MJ.d^-1.

 

First week of this month has been a total of 22.4 kWh, Day usage is 4.9 kWh and Night usage is 17.5 kWh.

So for just me, that is 3.2 kWh.day^-1, So similar to your usage.

78% of it is at the Night rate.

[joe90]

13 minutes ago, SteamyTea said:

So similar to your usage.

That’s good to hear ,!,! If I do manage to get PV installed I could reduce this a fair bit I guess.

Edited June 10, 2022 by joe90

[SteamyTea]

7 minutes ago, joe90 said:

That’s good to hear ,!,! If I do manage to get PV installed I could reduce this a fair bit I guess.

On a pro-rata basis it is similar.  I do just have resistance heating and I cook on electric.

 

You could get loads of PV on your roof, and at different angles.  This time of year you could rent your drive out for EV charging at 25p/kWh.

For a real laugh, you could convert your kit car to an EV.  Two advantages of that, it would cost nothing to run, and it would run.

[ProDave]

So 18kWh total per day, less 5kWh other use means the ASHP is using 13kWh per day, so in round figures that is like a continuous load of 0.5kW 24 / 7

 

Something is not right here.  It should be easy to tell when an ASHP is running, you will hear the compressor going, and the big fan on the outside unit.  Do you observe the ASHP running nearly all the time? or do you notice it turn on say once an hour for a period?  If you don't know that yet, then I would watch it like a hawk on your next day off and find that out.

 

We use roughly 25kWh per WEEK heating DWH for 3, less in the summer because solar PV heats a lot of the hot water needs.

 

Just the simple laws of physics begs the question where is all this energy going?  13kWh into an ASHP each day will be at least 26kWh of heat coming out of it.  You can't lose 26kWh of heat without warming something up, so either your cylinder will get very hot, or all that heat will be going into your house into perhaps unlagged pipework?

 

[joe90]

8 minutes ago, SteamyTea said:

For a real laugh, you could convert your kit car to an EV.  Two advantages of that, it would cost nothing to run, and it would run.

I have priced EV conversion and it’s astronomical, besides it would not sound right (I love the six cylinder triumph engine).

9 minutes ago, SteamyTea said:

You could get loads of PV on your roof, and at different angles. 

A 4Kw set fit perfectly on my garage roof, not the ideal angle for winter but hey!. A timer on the ASHP from 11 am to 3pm 👍

@Scots Buildyours is using way too much, especially for one person 🤷‍♂️

[Scots Build]

Thanks for sharing your usage and pointers everyone

 

The system is definitely in schedule only mode. 

 

 

On 10/06/2022 at 06:46, JohnMo said:

It looks like you are in reheat mode continually, so you throwing heat almost constantly to the cylinder.  You would be better heating the tank once per day to a temperature that is acceptable to your usage.

 

 

 

 

Can anyone help me understand how the schedule works, i.e. I presume if I set it for 45 deg @ 18:00, the system turns on at this time until the required temp is reached in the tank? I had it setup like this before but found the external fans on at random times throughout the day

 

If only heating once per day, is it better to have this time set during the afternoon when the air temp is at its warmest or through the night like the manual suggests (to avoid conflicting with UFH, which is irrelevant throughout summer anyway)

Edited June 11, 2022 by Scots Build
spelling mistake

[PhilT]

On 09/06/2022 at 21:55, Scots Build said:

We moved into a new build last year that has a DAIKIN ERLQ014CAV3 ALTHERMA OUTDOOR UNIT coupled to a 

DAIKIN EHVH16SU26CB6W HYDROBOX/CYLINDER but energy usage seems to be rather high considering it is only being used for DHW for at least 6 months of the year.  The property benefits from large solar gain so no need for the UFH to be on throughout summer.     Does anyone have a similar system and can share roughly how much power it's using and/or the most economical way to set it up?   I've had a read through the manuals but am struggling to know the best way to set it up for lowest running costs.  Is it better to maintain a water temp of say 40degC throughout day then boost to 45 around the time of showers.  Or only have one heating period per day?   There is only 1 person living in the house at the moment and it's using a steady 18kwH per day (in winter with UFH on, its gone over 100kwH/day).   House is modern design and has good airtightness of 1 m3/hr/m2

 

The excess usage is so high there might be a fault with the compressor (is it running most of the time?), or the refrigerant circulation has been compromised somehow. In summer it should only be using a tiny amount for DHW. My 11kW heat pump runs each day for 30min at 3pm (when daily outside temps are at max.) and only uses around 1kW to do so, for 2 people. In summer we get enough hot water for a couple of showers and other domestic chores at a set temperature of only 40degC on ECO mode

[joe90]

I concur, in summer my 4Kw ASHP with two people runs fir about an hour to top the DHW tank up to 48’ and not every day!

[Scots Build]

Something definitely seems to be amiss with it then.  I'm going to call the installers back to check it over

[Marvin]

⁴Hi @Scots Build

What is the floor area?

How many people living in property?

What's the volume of the hot water tank? 

Where is the tank and how long roughly is the pipework between external unit and tank?

 

To compare:

 

We have 100m2

2 people

205 litres, and a very well insulated tank which is inside the most insulated part of the building.

Our one way pipework distance between external unit and tank less than 4 meters. 

 

Doubt if we used 1 kWh a day to heat the water during summer (although we now have a solic 200 installed so now impossible to judge).

 

During summer we heat the water in the afternoons, allowing a 2 hour slot within which to bring the temp up.

 

Something definetly wrong with your system. 

 

Even if you leave the hot water timer on 24 hours a day it would only heat the water in the tank if it became too cold.

 

Good luck

 

M

 

 

 

 

 

 

[Scots Build]

On 13/06/2022 at 06:24, Marvin said:

What is the floor area?

300sqM

 

How many people living in property? 

1 year round, 2 for 5 months/year

 

What's the volume of the hot water tank? 

around 280L

 

Where is the tank and how long roughly is the pipework between external unit and tank?

Within garage, which is fully insulated TF, same spec as house.  Unit and tank are back to back on internal/external wall so minimal pipework

The installer has been back and we had a good chat about the system and he set it up for how we live, rather than how the builder dictated it was setup.

 

It hasn't helped improve the energy usage much though.

 

It is setup now to heat the tank twice a day, morning and night.  It uses about 1.7Kwh in the morning to heat tank to 48degC, then another 1.5Kwh to bring it back to 48degC in the late afternoon

 

It still seems excessive to me but not much more I can do about it it would seem

 

Thanks to all for help and assistance

[JohnMo]

So your usage is down to 3.2kWh per day, from 18kWh per day.  That sounds like a win.  £1600 saved in water heating costs!

[Ralph]

2 hours ago, Scots Build said:

It is setup now to heat the tank twice a day, morning and night.  It uses about 1.7Kwh in the morning to heat tank to 48degC, then another 1.5Kwh to bring it back to 48degC in the late afternoon

We also have a Daikin, I've found that having the temp down to 42decC has knocked quite a bit of our usage and we've not really noticed the drop in temp for showers etc. We're using 3Kwh per day for hot water and that's with two of us, including one who seems to think she's a mermaid given the time she spends in the shower.

[jack]

2 hours ago, Scots Build said:

It is setup now to heat the tank twice a day, morning and night.  It uses about 1.7Kwh in the morning to heat tank to 48degC, then another 1.5Kwh to bring it back to 48degC in the late afternoon

 

That's a 3 kW kettle element for an hour a day, or about £0.30 a day at current rates. Doesn't seem wildly excessive given the volume of water being heated. 

[ProDave]

2 minutes ago, jack said:

 

That's a 3 kW kettle element for an hour a day, or about £0.30 a day at current rates. Doesn't seem wildly excessive given the volume of water being heated. 

Please tell us your electricity supplier, as mine charges me almost £1 for 3kWh

[JohnMo]

3 minutes ago, jack said:

 

That's a 3 kW kettle element for an hour a day, or about £0.30 a day at current rates. Doesn't seem wildly excessive given the volume of water being heated. 

You beat me to it