New GSHP Efficiency?

Mstty

IanIanIanIanIan said:

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.)

How's your consumption for heat and hot water going? Size of bungalow etc would be handy and presume recent modern construction? Size of ASHP in kWh output? Make and model would be good too. Nice to see what others are running in the ASHP world.

j2009

COP for a GSHP is usually around 4. At 44p per kWh for electricity then you're paying 11p per unit of heat (ignoring inefficiencies). This is much more than oil (8.5p per kWh) and more than gas (I think). 

So, take off (say) £100 for domestic electricity (tv, fridge etc) and scale down the remaining £600 to allow for the above fact that GSHP are more expensive than traditional heating so maybe gas/oil would have cost about £400-£450p/m. On balance that doesn't sound outrageous bearing in mind it's a big house and you only heat aggressively from Dec-Mar.

However, if you're saying you spend £700p/m in August/September then yes there is a big problem, £700p/m is equivalent to running at 2kW heater 24/7 for the month.

Reed_Richards

j2009 said:

.. At 44p per kWh for electricity...

Fortunately electricity does not cost around 44p per kWh, it costs around 34p per kWh provided you are on the SVT tariff for single ratel electricity.  On an Economy 7 tariff or similar, the day rate will be more.  But @j2009 quotes an inflated price for electricity so their calculations are not valid   .

j2009

Reed_Richards said:

j2009 said:

.. At 44p per kWh for electricity...

Fortunately electricity does not cost around 44p per kWh, it costs around 34p per kWh provided you are on the SVT tariff for single ratel electricity.  On an Economy 7 tariff or similar, the day rate will be more.  But @j2009 quotes an inflated price for electricity so their calculations are not valid   .

Thanks for your contribution, even doing the maths for you and using 34p the point is the kWh/cost isn't a million miles from what I'd expect a large house to cost (bear in mind there's a whole bunch of assumptions so no point in worrying about super accuracy).

Conclusion: c.8.5p per kWH (same as oil) doesn't look unreasonable and suggest a serious problem so and sadly tweaking the GSHP won't make it materially cheaper.

markin

Could you post all the bills and reading, The total and the date you moved in, 2000kwh? 65 kwh average a day for 31 days is a lot, The first 10 days were not that cold where they?

............

If it is 2000kwh at around cop of 3 5500kwh would that be in the range of £550 if a Gas heated home?

Mstty

Time for the OP to return to their thread ideally after lots of people have asked and put forward key questions.

matelodave

for what its worth this is my monthly leccy consumption since 2011 and it goes up and down with the weather, how much I've tweaked (quite a bit in the early days) and even if we are away (see Nov/Dec 2015)

If we turned it down too far, we were cold or it just took too long to get the place back up to temperature. Its about right at the moment and we are toasty warm unless the temperature drops below around -5 when we have to tweak the flow temp up by a couple of degrees.

This is our total electricty consumption, so its not only heating but everything else as well. You can see how the weather does affect it though if you compare our summer (June-Sept consumption) with the colder months

kwoodberry

Hi all,

Wow, what an overwhelming response.

Thanks everyone... and yes, some very valid questions. I will try to answer as many as I think could be relevant.

We moved in at the end of June 2022, but our bills were being estimated up until 2nd September 2022. They had massively underestimated so we had a big bill to clear to get us back on track. However, looking back over those summer months it would appear we were averaging around 32kWh/day.

Here's the meter readings on account over the past few months:

• 12th Aug 2022 - 4614.0
  
• 2nd Sep 2022 - 5755.0
• 11th Oct 2022 - 6914.4
• 11th Nov 2022 - 8039.3
• 11th Dec 2022 - 9828.1
• 11th Jan 2023 - 12003.1
• 16th Jan 2023 - 12352 (manual reading today)

I have been in touch with Kensa, went through some checks and the GSHP is apparently set up correctly. There is no digital display of energy consumption but many diagnostics screens. One screen I found showed an average COP of 3.96.

I had also incorrectly assumed the plug and glow worked continuously during the pre-set times programmed on the timer (as I wrote on the 13th), but this was incorrect. The DHW is drawn off the buffer and only if the temp of this water drops below 48*c does the plug and glow kick in (during those morning and evening hours) to heat the water up to 48*c to ensure instant hot water to the taps.

The EPC states the following:
The primary energy use for this property per year is 54-kilowatt hours per square metre (kWh/m2).

In answer to other questions;

• No swimming pool/pond pumps etc
• There is an outbuilding where I run a home office. I was actually working in here during the cold snap with the AC units running at high temps over 8 hours a day, so expected December to be higher usage than a typical winter month. I've since set up office back in the main house where the rooms are consistently warm (19-20*c).
• No high-load servers or any IT equipment of that nature
• Family of 5, two adults, 3 kids under the age of 13 so no cooking at different times etc.

So, doing the math, this is probably not far off "as expected" usage, if we take 32kWh/day during the summer months into account.

Thanks for all your help and questions on this. If nothing else, it got me digging into the numbers a bit deeper.

markin

32kWh/day is still a little extreme for summer, But the 21 days from the readings below is 54/day, was the A/C running in the house or office?

• 12th Aug 2022 - 4614.0
  
• 2nd Sep 2022 - 5755.0

1141 kwh


Try setting hot water to only 1hr a day.

MikeJXE

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.

I don't know a single thing about heat pumps but I do know about trenches

Is 1m deep enough ?

I have worked in many trenches and you don't get any heat at 1 metre, heck water services have to be 75cm deep or they are liable to freezing 

I would have thought 2m or 2.4m would have been a minimum depth as I know it's much warmer there ?