New GSHP Efficiency? 13 January at 1:42PM in Energy 33 replies 1.3K views

kwoodberry

Hi there

We finished a self-build last year. We fitted a Kensa Evo 13KW Ground Sourced Heat Pump (GSHP).

We moved-in in June so only started using the GSHP and UFH at the end of October.

The house is large (~4000 sq ft) with UFH across the ground and the first floor.

Now I know we're in the middle of an energy crisis but I'm surprised to find we are using between 60-70 kWh per day. Nearer 80kWh in December.

We have the Omnie UFH stats set at ~18*c permanently, which bring the rooms up to a comfortable 20*c.

I understand we've got lots of in-ceiling spotlights, but they are all ultra-low energy LED bulbs, and we are very conscious about leaving the lights on unnecessarily.

Does this sound right to you? Is anyone else out there with a GSHP using anywhere near this amount?

The reason for installing a GSHP was for their efficiencies... Our electricity bills are coming in over £700/month   

My gut says the DHW side of the heat pump is working too hard. We never run out of hot water (surprisingly with 2 daughters  ) so perhaps this isn't set up correctly. I am going to speak to Kensa about this.

Just wondered if this sounded reasonable to any other GSHP owners, or am I just being a tight a**?

Thanks!

MattMattMattUK

That usage would appear high, but have you looked at the data directly from the system, running times, flow temperatures , temperature of hot water, etc.?

Also, what is the ground source, borehole, channel, shallow burial?

matelodave

There's an art in optimising how to use a heatpump to maximise its efficiency and minimise its running costs and you need to learn how to do it.

There will probably a few things that you could do to tweak the system - check stuff like the flow and return temperatures on the heating side. What temperature do you have the hot water tank and how often do you heat it it. What controls have you got, have you got weather compensation set up and tuned to your house. Ideally you need to get the flow temperature as low as you can which means running the system longer

Most heatpumps whether Ground or Air Source will be set up to default settings but then need to be tweaked and tuned to suit your premises and lifestyle and that could take you a whole winter before you get it sorted out.

Making adjustments (only one thing at a time), recording what you did and what effect it had and most of all giving a chance to settle down before twiddling something else. You wont know what is happening unless you monitor and record what is going on.

Likewise do an energy audit of other stuff that is being used to isolate the consumption of the heatpump from everything else like the washing machine, dryer, dishwasher TV, hairdryers etc etc,.

4000 square feet is quite a large house and I wouldn't be surprised that you are going to use a fair amount of energy, especially when it gets very cold outside - even though heatpumps (GS orAS) may be efficient, insofar as you get 300-400% more energy out than you put in. However when that energy costs 300-400% more than gas or oil then it doesn't make them cheap to run especially if you try to run them like a conventional boiler/heating system. Dont get hung-up on the energy consumption fo a few days in the middle of winter when really cold outside and the heating is flogging its heart out

A quick shufti at the spec for the 13kw heatpump shows that its SCOP drops from over 4 with a flow temp of 35 degrees to 3.25 when you increase the flow temp to 55.

I've got an air source heatpump with underfloor heating and it cooks away quite nicely with a flow temp of between 28-40 degrees depending on the outside temperature. The room tempeartures are mainly controlled by the varying flow temperature under control of the weather compensation rather than the room stats. Also we dont heat our hot water above 45 degrees except for one hour a week for legionella sterilisation.

We are using around the same amount of energy as you , but for a bungalow thats a 1/3rd of the size of yours - our worst day was 13th December when we chewed through 69kwh of leccy. Our overall consumption for December was 1149kwh which is ana average of 37kwh (but thats everything, heating, hot water, lighting, cooking, washing etc)

Astria

If you are running the system permanently, I guess you are using a low flow temperature about 15 - 20c above what you want the room at, so about 35 - 40c ? Or do you have weather compensation? How is that setup?

An incorrectly configured heat pump can be very expensive to run, and a lot of installers seem to install them to keep customers happy and off their backs rather than in the more efficient way possible. If you try and treat it like a normal boiler then your bills will be very high.

kwoodberry

Hi All. 

Thanks for your contributions. Great response so far!

MattMattMattUK the pipes were installed as slinkys. To you and me a 'slinky' is simply a coiled pipe acting as a heat collector laid in an array of 4no. 1m deep trenches x 60m long.

We did have problems with one of the upstairs bedrooms not heating up enough and Kensa advised we upped the flow temps. So they're now sitting at 43.7*c flow and 42.2*c return.

matelodave Interesting that you questioned the Weather Compensation, as that was never fitted. Our installer said they never fit these for the 1st year and only fit them later if required. I was a little dubious then as I could see the logic in having the Weather Compensation Thermometer fitted externally, especially when we've been getting extreme cold snaps as we did in mid-December.

> Our overall consumption for December was 1149kwh which is ana average of 37kwh (but thats everything, heating, hot water, lighting, cooking, washing etc)

Should have mentioned this. Everything runs off electric here!

One thing we do have which I'm sure doesn't help is a Plug and Glow heater which is wired up to a secondary return. This heater is wired to a timer and Grundfos pump to provide almost instant hot water at the taps during certain hours (7-8am and 5:30-7:30pm). The plumber suggested this as some of the pipe runs were fairly long and we'd find ourselves waiting for 2 minutes for hot water to come out of the hot taps (1st world problem, right!?  ).

In my mind this heater is no different to a kettle boiling away for 3hrs per day. I will switch this off and see if we can live with the HW delay.

Sorry for sounding a bit green on this next point but how could I monitor what's using the lion's share of the leccy? The big items are wired into fused spurs so it's not like I could plug the GSHP or the induction hob into a plug-in energy monitor.

Also, our leccy meter is in a green kiosk around 150m from the house. It's here where the smart meter is for remote readings and the wifi range on the smart meters is only 50ft so we can't have the plug-in energy monitor up at the house to view usage.

Thanks all, keep the comments coming

Astria

Typically GS/ASHPs have a buffer tank and/or hot water tank, and these need sterilizing every so often and typically use what is basically an immersion heater to get the water upto at least 60c either once a day, week or month depending on configuration. I'd check this as well as if it runs too often it will sky rocket your bills.

You could have a meter connected to your HP to check on usage, but a lecky would typically have to do this, I wouldn't mess with high power devices.

Do you have access to any large single core cables like the ones going to your consumer unit? You could fit an energy monitor onto these no problem via a CT clip. Something like this: https://geotogether.com/product/minim/

The blue connectors below are CT clips around the typical wires I mean:

Strummer22

Ours is an EcoForest 5-22k. It's got a display that tells me electricity consumption, heat production and COP, both instantaneously and over each month/year of operation. As such, it's quite easy for me to make tweaks and see the effect. Does yours have a similar display? That would allow you to see how much of your usage is due to the heat pump.

Here's some things I've done to keep costs down:
1. heat the house to 17.5 - 18 C (no brainer to turn down the thermostat but you need to choose the minimum temp that is comfy for you).
2. turn down the temperature of DWH to 45C and lower the heating circuit temp by 2C from the installer settings (weather compensation was set up by the installer).
3. Limit the compressor to 50% of max, effectively turning it into an 11kW heat pump. It's coped with this except during the very cold weather in December where I set it to run higher. Inverter-driven pumps like that are more efficient at about 50% load than at full load. Does yours have an inverter? (The alternative is that it is either off or running at 100%). Note that limiting the compressor this way will only really help if you think your heat pump is over-sized and doesn't need to run flat-out. I've decided that ours is, as the heat loss from our EPC appears to be dramatically over-estimated.

Let us know how you get on!

Spoonie_Turtle

kwoodberry said:

Sorry for sounding a bit green on this next point but how could I monitor what's using the lion's share of the leccy? The big items are wired into fused spurs so it's not like I could plug the GSHP or the induction hob into a plug-in energy monitor.

Also, our leccy meter is in a green kiosk around 150m from the house. It's here where the smart meter is for remote readings and the wifi range on the smart meters is only 50ft so we can't have the plug-in energy monitor up at the house to view usage.

Thanks all, keep the comments coming

Our water cylinder (ASHP) has the controller on it which has usage and output data if you find the right screen. 

To sort of solve the lack of IHD you could try one of the apps, Bright is very often recommended on here.

Mstty

Before you blame the GHSP for high usage best to take stock of other things.

Your house is about 2.5 X the size of a decent 4 bedroom house so you must expect hefty bills for heating.

How many people living in the property? So they all do their own thing like cook at different times, watch different TVs etc, work from home.and what do they use when working at home.

Is there an electric car?
With a house that size is there a swimming pool/pond with pump/hot tub etc?

Reed_Richards

kwoodberry said:

Hi there

We finished a self-build last year. We fitted a Kensa Evo 13KW Ground Sourced Heat Pump (GSHP).....The house is large (~4000 sq ft) r.

You surely must have made some assessment of how much energy the house would use?  It would not have been a bad idea to put an electricity meter on the circuit that runs your heat pump.  Electricity meters are surprisingly cheap and it was mandatory to have one as part of my heat pump installation.

kwoodberry said:

Interesting that you questioned the Weather Compensation, as that was never fitted. Our installer said they never fit these for the 1st year and only fit them later if required. I was a little dubious then as I could see the logic in having the Weather Compensation Thermometer fitted externally, especially when we've been getting extreme cold snaps as we did in mid-December.

Actually extreme cold snaps are the times when you don't need weather compensation.  The purpose of weather compensation is to reduce the water temperature when it's milder outside so your heat pump can work more efficiently.  I'm amazed that your installer did not install that facility.

kwoodberry said:

One thing we do have which I'm sure doesn't help is a Plug and Glow heater which is wired up to a secondary return. This heater is wired to a timer and Grundfos pump to provide almost instant hot water at the taps during certain hours (7-8am and 5:30-7:30pm). The plumber suggested this as some of the pipe runs were fairly long and we'd find ourselves waiting for 2 minutes for hot water to come out of the hot taps (1st world problem, right!?  ).

I have a long bungalow and I use a hot water return loop to ensure that hot water comes rapidly out of the taps.  But this just takes water out of the cylinder and returns it via the secondary return.  I use a pump which runs for 5 minutes every hour between 7 am and 11pm.  This gives me water out of the taps that is either hot or warm enough.  A Plug and Glow heater as well seems like a belt and braces solution and your plumber must have thought you were made of money.  Can you turn off the heater and just keep the pump running?  My system is certainly a bit of a luxury because the water in the pipes will cool so my heat pump has to work harder keeping the tank at temperature.  At least I have made sure all the pipes on the hot water return loop have the best insulation I can find.  
 

  

IanIanIanIanIan

Also a new build needs to dry out, there are many tonnes of water tied up in its construction. Ours took some 20% extra energy in the first few months but the fabric was noticeably a much better insulator and heat store after the first year.

Ours is an ASHP feeding UFH in a bungalow and easily runs on the minimum 25°C flow temperature except in below 5°Cish when the weather compensation kicks in when it will reap up to 40°C at -5°C (the lowest we have seen here.)