I run our Daikin 8 kW/h monobloc 24/7 and have 2 x Tesla Powerwalls, i.e., 27 kW/h capacity. We effectively go ‘off-grid’ outside the 6 hours of Cosy cheapest rate periods; I have not detected any demand from the whole house consumption that requires any resorting to grid, maybe fractions of seconds on peaks would not register, I don’t really know. Regards, Toodles.

Just a message for Transparent; I saw your message (which then vanished and hasn’t been seen since) I replied to a posting and did not set or change the attributions in any way. I’m sorry for implicating you in any way but I know not why this should have happened. Regards, Toodles.

@robl Interesting. I'd appreciate details of the 2.5KW heat pump. Seems very low but if it works for you....

thanks

@transparent   "you'll now appreciate why this forum is a good site to learn about such issues!"
Indeed!
Carbon Tracer App looks interesting but Google Play says my Android phone (an up to date model)  is not compatible. Pity.

I haven't tried to use the Carbon Tracer App @geo3geo
I use it on a web browser because I pull in data across some 20 or so National Grid tabs which are kept open!

Your electricity supply is managed from the National Grid offices in Worcester.
There is a dedicated manager for the Kidderminster area, and a number of staff members who handle G99 application enquiries.

Beware if you try searching for National Grid Worcester to obtain contact details.
You will most likely end up with phone numbers and addresses for National Grid at Worcester, Massachusets!

In the UK, use the generic contact options, and identify that you're in the Kidderminster area.
That will enable an email to be forwarded to the relevant team.

Posted by: @geo3geo

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@robl Interesting. I'd appreciate details of the 2.5KW heat pump. Seems very low but if it works for you....

thanks

I'm glad you asked!  It is very low, but it does work for us.  The heatpump is diy - I guess I started building it with cheap parts for interest, thinking I could always give up and buy a kensa shoebox or similar.  It's an R290 (propane) system, with 200m of glycol filled pipe wiggling under the back garden picking up heat.  The heatpump itself lives outside but is wrapped with insulation and thermally linked to the house, giving it a stable operating temperature, yet keeping the 300g of propane outside.  It's very simple, as low power gshp system usually are - just on or off - it's generally not worth using variable speed control at this power level.  This made the design a lot simpler - so electrically there is a 600W (fridge type) compressor and two 40W pumps, switched on and off by relays from the original hysteresis thermostat in the house.  The compressor is by danfoss, and they handily give away design software for free.

In reality though, it's the huge amount of insulation that we've installed that makes it possible.  We have a 4 bed 1963 house wrapped in 150mm of external insulation, and in loads more places too, lots of effort making airtight and adding MVHR, so pretty much any heat source would find our home easy to heat.  That 2.5kW of heat has a flow and return of 32C and 25C, through the original 1963 radiators, original pipework.  We use 1MWh/year of elec into the heatpump to heat the house and the same again for hot water.  It can heat the hot water up to 50C, but does takes hours to do as it's low power.  If anything takes away any heat, then it cannot achieve that 50C.  In contrast, the gas boiler we used to use (we disconnected from gas last year), could heat the house and the hot water at the same time, no bother.

Posted by: @robl

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Posted by: @geo3geo

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@robl Interesting. I'd appreciate details of the 2.5KW heat pump. Seems very low but if it works for you....

thanks

I'm glad you asked!  It is very low, but it does work for us.  The heatpump is diy - I guess I started building it with cheap parts for interest, thinking I could always give up and buy a kensa shoebox or similar.  It's an R290 (propane) system, with 200m of glycol filled pipe wiggling under the back garden picking up heat.  The heatpump itself lives outside but is wrapped with insulation and thermally linked to the house, giving it a stable operating temperature, yet keeping the 300g of propane outside.  It's very simple, as low power gshp system usually are - just on or off - it's generally not worth using variable speed control at this power level.  This made the design a lot simpler - so electrically there is a 600W (fridge type) compressor and two 40W pumps, switched on and off by relays from the original hysteresis thermostat in the house.  The compressor is by danfoss, and they handily give away design software for free.

In reality though, it's the huge amount of insulation that we've installed that makes it possible.  We have a 4 bed 1963 house wrapped in 150mm of external insulation, and in loads more places too, lots of effort making airtight and adding MVHR, so pretty much any heat source would find our home easy to heat.  That 2.5kW of heat has a flow and return of 32C and 25C, through the original 1963 radiators, original pipework.  We use 1MWh/year of elec into the heatpump to heat the house and the same again for hot water.  It can heat the hot water up to 50C, but does takes hours to do as it's low power.  If anything takes away any heat, then it cannot achieve that 50C.  In contrast, the gas boiler we used to use (we disconnected from gas last year), could heat the house and the hot water at the same time, no bother.

 

Have you considered adding solar PV, to not only help power your heat pump, but also to help provide hot water for much of the year?

@derek-m I already have PV, only 2.2Kw but enough to feed a heat pump via a battery system. Which is where this thread started!

Any links you can share for DIY heat pump systems? Your GSHP would I guess offer a higher COP than ashp. Also, wouldn't suffer from fan noise. Seems a very sound system.

Posted by: @geo3geo

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@derek-m I already have PV, only 2.2Kw but enough to feed a heat pump via a battery system. Which is where this thread started!

Any links you can share for DIY heat pump systems? Your GSHP would I guess offer a higher COP than ashp. Also, wouldn't suffer from fan noise. Seems a very sound system.

I would always try to encourage anyone to start with improved insulation and draft proofing.

GSHP's should be more efficient than ASHP's, certainly in colder weather conditions, since the temperature below ground is normally a fairly constant 8C to 10C. When the ambient air temperature is 10C and above, then an ASHP will probably be more efficient. As far as I am aware a GSHP should also not require any defrost cycles, though I have not investigated GSHP's in any great detail.

My own heating system incorporates a 2.6kW Air to Air (A2A) ASHP, which I use to supplement our gas boiler when there is sufficient output from our 4kW solar PV system. This also has the added benefit of providing free AC during warmer periods when solar PV generation is plentiful. During Spring through to Autumn most of our hot water is provided by solar PV via a power diverter unit.

A 2.2kW solar PV system, even with a battery storage system, will not be able to provide sufficient electrical energy to run even a small heat pump during the heating season. Battery storage will allow TOU tariffs to help reduce the cost of importing electrical energy to run a heat pump.

At the end of the day it is a matter of deciding if the cost of a battery storage system saves sufficient money from cheaper tariffs to make it cost effective. Battery storage could actually use more overall energy, since such a system is not 100% efficient.

I recently watched a Youtube video detailing how a DIY heat pump was constructed, but unfortunately did not note where I found the video.

@derek-m Yes, i'm thinking of getting an EPC cert to see where I can make improvements. Would need one anyway if I went down the normal ASHP route.

When you refer to DIY, do you mean build a heat pump or buy one and install it yourself?

Attached below is a link to more detail on our gshp system.  It's over at buildhub - the first post there has a 3MB pdf where I left the details of what I did. 

I think most gshp can be very quiet.  Ours uses the parts from a large domestic fridge and sounds like it - then the whole thing is placed in an insulated box, and you'd not know it was on unless you were told.

I'd say the efficiency of gshp and ashp are similar.  The physics predicts a gshp should be higher COP than an ashp due to having a higher temperature source and not requiring defrost cycles, but there are a few confounding factors:  

ASHP need variable speed fans and compressors, otherwise they would be unacceptably noisy - like the old-school air conditioners everybody fears.  This handily also improves the COP, as the fans and compressors are run slightly more efficiently at lower power.  

ASHP benefit from the vast amounts of R&D money and time spent on almost identical air conditioners, which are prevalent around the world.  In contrast I'd guess gshp have 1% of the research spent on them.  

The groundloops or boreholes for gshp are time consuming or costly to drill or dig.  This leads to making them "just big enough", and limiting the COP.

If I was paying for a commercial installer, I would get a monobloc ashp installed.  It's a lot cheaper and simpler, far less chance of them doing it wrong.

https://forum.buildhub.org.uk/topic/27460-diy-gshp/#comment-415637