Posted by: @murchison2003

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Hi 

I’ve just found this forum by accident but reading some of the stuff on here already, seems like a good place to be with really helpful comments and help from people. 

I’ve recently replaced my ground source heatpump I’ve had for the past 14 years with a Vaillant Arotherm plus 12 kw as I couldn’t swap the ground source pump due to new regulations ( I would have needed to install a further 300m ground loop to comply) .

I’m finding the running costs a bit higher with the air source but still trying to play with the settings to achieve max efficiency. I have solar generation with 20 kw of battery storage, ev and charge from home almost all of the time. I am on an ev tariff which I am most grateful for as I’d hate to imagine what my bills would be without it. 
Can I ask anyone on here if they too have transitioned from ground to air and have you noticed any difference in any way. 
Thanks in advance. 

ASHP's are not as efficient as GSHP's, because their primary energy supply, from the air rather than the ground, keeps changing, and can go well below the 8C to 10C supplied by the ground loop. An ASHP becomes less and less efficient as the outside air temperature falls.

A further factor is that ASHP's start to require a defrost cycle as the air temperature falls, particularly when the humidity is high.

I am surprised to hear that you could not just replace your GSHP with a direct replacement. What are these new regulations? It seems that 'regulation' has now insisted that you replace an efficient system, with a less efficient one.

Maybe 'regulation' should apply a little common sense, or be replaced with a 'regulation' that has more than two brain cells? 😋 

Derek

Thanks for your reply.

The reason was that my ground source heat pump had an electric immersion as back up if demand from the ground was not enough. Ground source pumps are now built without back up and with any pump now either air or ground must be sufficient to supply all calculated demand for the property.🤷‍♂️

That’s the reason. 

@murchison2003 This is a matter I am taking up with my installer for our proposed Daikin Monobloc unit as due to space not being available for a large tank (of a size required by MCS guidelines for a 3 or 4 bedroom house) we are having a Sunamp Thermino ePV 210 unit for the hot water; this will be powered by our solar PV normally but if this is not providing enough energy, the grid should take over. The Daikin has sufficient capacity to supply the DHW but would not actually be doing so. We wish to avail ourselves of the BUS grant so I have asked the installers for reassurance and clarification on this - rather than the previous ‘should be fine’ we received from them. Regards, Toodles

Posted by: @murchison2003

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Derek

Thanks for your reply.

The reason was that my ground source heat pump had an electric immersion as back up if demand from the ground was not enough. Ground source pumps are now built without back up and with any pump now either air or ground must be sufficient to supply all calculated demand for the property.🤷‍♂️

That’s the reason. 

Just a further example of the  'tail wagging the dog', when it could have been quite feasible to supplement your heat demand with a simple fan heater during the few occasions when the GSHP could not cope. There are some ASHP owners who have to do exactly this, if the outside air temperature falls to -5C or below. 🙄 

During the winter months from the start of December to March, the brine coming into the pump was usually around 1 degree to zero and leaving the unit at -4. Over the 14 years I had the pump, the auxiliary heater had only 454 hrs on it . This is why I wasn’t really overly concerned about the pump working properly. Only difference that I’m noticing is that my ground source I pump ran at 3kw while this one runs at 5kw. It’s only for a couple of months hopefully that it will be having to do a good bit of work then the solar and batteries will compensate for the running costs. 
I’ll be able to fully compare running costs fully over a full year. 

Posted by: @murchison2003

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The reason was that my ground source heat pump had an electric immersion as back up if demand from the ground was not enough. Ground source pumps are now built without back up and with any pump now either air or ground must be sufficient to supply all calculated demand for the property.🤷‍♂️

There’s no shortage of ASHPs mentioned on these forums that don’t satisfy the heating demands of the property they’ve been installed in due to miscalculations and/or misselling. Some of these policies and regulations truly beggar belief. 

Posted by: @murchison2003

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During the winter months from the start of December to March, the brine coming into the pump was usually around 1 degree to zero and leaving the unit at -4. Over the 14 years I had the pump, the auxiliary heater had only 454 hrs on it . This is why I wasn’t really overly concerned about the pump working properly. Only difference that I’m noticing is that my ground source I pump ran at 3kw while this one runs at 5kw. It’s only for a couple of months hopefully that it will be having to do a good bit of work then the solar and batteries will compensate for the running costs. 
I’ll be able to fully compare running costs fully over a full year. 

Has your ASHP been correctly commissioned and optimised, since 5kW seems rather excessive. What are the operating parameters and operating mode? Do you have heat loss calculations for your home?

Yes had the heat loss calculations done and I’m happy with the system installed, I have an A+ house according to my latest EPC which was done 6 weeks ago. 
I can’t check the settings just now as I’m away from home however my installer is aware and are going to come out and check the settings. To be fair, the house runs at 21-22 deg 24/7. 

Groundsource is usually a lot simpler - a lot of them are just simple on/off things just like an old fridge, controlled by relays and thermostats.  There's not a lot of pressure to improve them to inverter designs which are more efficient.  In contrast almost all ashp are inverter units, the R&D budget coming from the enormous volume of air conditioners sold around the world.  Inverter units are quieter that on/off ones, and I think that this is the major attractor to them for A/C and ashp, in order to keep the unit quiet.  In contrast, the gshp is often in a box somewhere, and hopefully can be made quiet that way.

The gshp->ashp differences I would expect are that the (inverter ashp) power level can be increased with little penalty - the only penalty is that weather compensation is now needed to give the best efficiency due to that extra power.  Those old on/off gshp would have been rated closer to the actual demand - if it was over-rated then efficiency would suffer as the radiators would get hotter than needed.

In short - if it's plumbed well(many are not), confirm that weather compensation is on, Ideally find out how to set it yourself.  Modern inverter ashp I think can give similar COP to old clunky on/off gshp.

My original question was regarding the running costs as my pump ran at 5 kw no matter what. 

After a bit of YouTube research combined with a visit from my installers to check the settings, I found that my heat curve was at 1.9, how that happened nobody knows. My efficiency was about 2.6 and was chewing through the kWh. Some parts of my house were cool and knew there wasn’t something just quite right. 
So after some consultation and the installer playing with the settings, I trialled the curve, adaptive curve setting off and running on weather compensator, we starting the heat curve setting at 0.4 for a few days with the pump practically running all the time keeping the flow temp constant around 28-30 deg. Result is there’s a huge difference in the efficiency which is now showing 4.6 on the heating but it is 10 deg today, the temp one night was 2.5 deg where the efficiency fell to 3.7, still ok for an air source pump. The whole house is staying constantly at 22/22.5 deg 24/7 and the electric consumption of the pump apart from when it’s heating the Dhw has been 1-1.5 kWh. 

I’m still trialling the settings, I’ve increased the heat curve today to 0.5 to monitor heat and consumption for a few days but overall I’m a lot happier with the set up now. 

Another thing we have to remember is that electric costs have trebled in the last year. I’m lucky that I installed more Solar pv last year with battery storage which is now starting to reap rewards as the longer days and increased uv is starting to kick in. My initial expectation was to hopefully be virtually off grid between March and September so we’ll see what happens as the year progresses. 

Hi

what do you have your heat curve set at now?