Balanced coverage?

[Andy]

I was what sapping a mate today who has a 2 year old house. Quality build and he was saying horrendous amount of power consumed in Winter and said same as stinsy re cost of heating element to top up house heat. I'd love to be convinced and make plans to change out my GCH boiler for a ASHP but it just doesn't seem to be there yet. I also wonder as we are both in NE Scotland if the real temp difference has truly been taken into account for our Northern sites when sizing is taking place? Can these units be overspecced to perform in harsher climes and have an easier run to themselves the other 6 months. Just a thought or 2....

We can easily see 2 months straight with neg temps..I just could not see myself replacing a standalone system that can do the whole job(gch) with a system that needs another source to help it along. I happily await being shot down in flames and told why I should go ashp and part of me wants that.

Hey, we've an old converted smiddy near yourself 600' up a hill. . Its inverter driven so always running. No stop starts generally. With a 12 kw GSHP at -14 ºC we had a COP of 2.69 and no resistive heating. The pump maxed out at 3.68kw. Probably worse than normal as we have a room with no walls/insulation at the moment with renovation. That's the only night the COP dropped below 3 and most of the time it is closer to 4. Shoulder months it is often above 5.

I didn't go near ASHP as the efficiency really drops below freezing with an old house. A friend has quite a sizeable new build and only had a tiny bill running on airsource this winter, but his house will have been built to new insulation regulations and running on underfloor. We have over sized radiators.

Another friend in Torphins got start/stop GSHP for his 1980s bungalow and the had a borehole drilled in the drive next to the house. Its worked out really well also outperforming my calculations for his house.(not an installer, just a geek)

[Andy]

I forgot to mention. In Scotland we get a hefty grant that covers the whole install for GSHP. This will be removed next Feb I believe. I used the £10K interest free loan (scotland only) and remortgaged to get the remainder. This is paid back in 7 years. The benefit of inverter driven is daytime is covered nicely by solar panels come feb/march.

[Joeboy]

I was what sapping a mate today who has a 2 year old house. Quality build and he was saying horrendous amount of power consumed in Winter and said same as stinsy re cost of heating element to top up house heat. I'd love to be convinced and make plans to change out my GCH boiler for a ASHP but it just doesn't seem to be there yet. I also wonder as we are both in NE Scotland if the real temp difference has truly been taken into account for our Northern sites when sizing is taking place? Can these units be overspecced to perform in harsher climes and have an easier run to themselves the other 6 months. Just a thought or 2....

We can easily see 2 months straight with neg temps..I just could not see myself replacing a standalone system that can do the whole job(gch) with a system that needs another source to help it along. I happily await being shot down in flames and told why I should go ashp and part of me wants that.

Hey, we've an old converted smiddy near yourself 600' up a hill. . Its inverter driven so always running. No stop starts generally. With a 12 kw GSHP at -14 ºC we had a COP of 2.69 and no resistive heating. The pump maxed out at 3.68kw. Probably worse than normal as we have a room with no walls/insulation at the moment with renovation. That's the only night the COP dropped below 3 and most of the time it is closer to 4. Shoulder months it is often above 5.

I didn't go near ASHP as the efficiency really drops below freezing with an old house. A friend has quite a sizeable new build and only had a tiny bill running on airsource this winter, but his house will have been built to new insulation regulations and running on underfloor. We have over sized radiators.

Another friend in Torphins got start/stop GSHP for his 1980s bungalow and the had a borehole drilled in the drive next to the house. Its worked out really well also outperforming my calculations for his house.(not an installer, just a geek)

Thanks for both posts Andy and welcome onboard. I'll reference this thread a lot next year so thanks again for the input.

[Andy]

Its good to find the old crowd continuing on It was a shock when it all stopped. If you ever want to see what's involved with the GSHP then ping me a message.

[andygo999]

This may be useful to someone, as it is real world experience, location Yorkshire dales, family of 4. No gas to the house.

We have an ASHP, but also UFH and a thermal store, most of the time the ASHP runs off E7 electricity.

When we were looking for the ASHP we were told on more than one occasion that the temperature which they had to use to calculate heat demand was dependant on location in our case they used a value of -3C iirc. They also based the heat load of the house on the EPC which was probably very pessimistic. We have had no problems with the ASHP producing enough heat even in depths of winter (though we have only had a few coninuous days of sub zero temperature). The ASHP heats a 430L thermal store and the UFH is driven off the TS with individual thermostats in most locations on the ground floor. The first floor only has UFH for the bathrooms. The thermostats are set such that the target temperature drops once the E7 period finishes, so we are using both the TS and the screed (70mm S&C over 125m2) for storing heat.

There is an 11.2kW Mitsubishi Ecodan which I suspect is probably oversized for the house, however it does not stop and start that often probably due the TS. The house is about 225m2, orginally built 1957, but renovated finishing 2018, so I would suggest well insulated and quite air tight. There is a MVHR system, this is one aspect that I think needs modifying, as when it is 0C outside and 20C inside the supply air to the rooms is only 17C which tends to be very obvious in the bedrooms (no heating) so am looking to put a duct heater run off the ASHP in place this autumn (I started a thread on this recently). The supply air temperture drops as the outside air temperature drops so if 20C difference inside to outside gives roughly 17C supply, if -4 outside the supply drops to 16C etc.

We also have a 3.3kWp PV system and an Eddi, but as yet the Eddi does not turn on the ASHP when there is surplus PV (job for this summer), it does divert to an immersion heater at the top of the TS.

We have no need for any additional heating backup (there is no resistive heater in the ASHP). The only time we have suffered from the ASHP not keeping the house warm was when someone (we never worked out who) presumably accidently turn it off. It took 2 days before we realised we had a real heating problem and about another 2 days before we had thigs back to normal. The UFH runs at about 25C on the ground floor. I believe the ASHP uses 4-5000 Kwh per year (but may be January before I can be sure due to incorrect initial setup - yes 60C output temperature!).

I have heard that ASHPs are popular in Scandinavia where temperatures drop well below what we normally experience (even in Scotland) so strongly suspect that most problems come from incorrect sizing in the first place, exacerbated by lack of understanding on how to get the best out of them (which is not by runing then a gas boiler). It would be interesting to know how much training/explanation of how to use the heat pump is given to those that opt for one without the understanding that most on this forum would have. Turning the ashp to run at 60C output to heat the house up and then off and on at 60C is definitely going to result in excessive electricity usage and high bills.

Hi Countrypaul

I read with interest your post about using an ASHP with a thermal store.
I'm hoping to do something similar but have been getting conflicting advice and wonder if you could give me some real world experience.

Does your ASHP heat the TS hot enough to provide a decent amount of DHW?
If so, how hot do you have to get the store to get usable DHW?

Our home is a small 2up 2down stone cottage (with single storey kitchen extension).
Up to now it's been heated using a solid fuel Rayburn.
The Rayburn is connected to a 277l Gledhill Thermal Store.
The Thermal store heats 26m2 of UFH downstairs and five radiators upstairs.
The Rayburn boiler has rusted through so we need to find another heat source. (I'm also sick of lugging coal around)
I'd hoped to simply swap the Rayburn for a small ASHP - I've been inspired by this guy whose house is a similar age and style to ours https://trystanlea.org.uk/

However I've been getting different opinions on whether or not it will work. Some installers say yes...but at least three have said it won't work because the ASHP won't get the TS hot enough to provide useful DHW. They say the heat losses would be too much. They also point out that to get usable DHW from a TS (say 48 degrees) the water will need to be much hotter (70 - 80) because of the heat losses in the plate exchanger at the top of the store.

Most say we would be better off with a UVC.

I'd be interested in how your store performs with a TS.

Also how is it connected? is there a heat exchanger in the ASHP loop? or does your store have a coil for the heat pump?

Appreciate any help or advice

Andy

[Countrypaul]

Hi Andy,

We have a 430L open vented thermal store which has a coil split into 2 sections to provide DHW. There are 2 TMV (thermostatic mixer valves) one at the top to mix the hot water from the top of the TS with water from the lower TMV. The lower TMV takes water from the middle of the coil (approx middle of the TS) and mixes that with cold water (if the middle is hot rather than warm). The idea is that this preserves the hot water at the top of the TS for as long as possible and limits the likelyhood of a TS full of lukewarm water. The TS also has connectiond for solar thermal (not implemented) and a WBS (also not implemented yet) as well as 3 immersion heaters. The top imersion heater only heats the portion of the thermal store that is used for DHW. his immersion is connected to an Eddi (PV diverter), during winter we end to have the Eddi set to heat the DHW portion on a timer using E7, during summer the Eddi usually provides enough DHW. Because we are using a coil in the TS to provide DHW the DHW is mains pressure but we avoid the annual inspection of an UVC.

I have experimented with various seting on the ASHP, initially it was setup by the installers in hot water only mode and provided a store full of water at about 55C. Whilst this easily provided enough heat for both heating and DHW the COP was not surprisingly attrocious (<2). The ASHP is currently set to provide water at 40C, but is only triggered when the bottom of the TS gets down to 25C using an external thermostat, this achieves a much better COP (around 3) but I want to try reducing that this winter to see if I can get any improvement in the COP. I have recenty wired the ASHP to the EDDI so that it should be triggered when there is sufficient excess PV rather than relying on the immersion only. This is not yet active as I need to check some details with Mitsubishi. I also want to see if I can run the ASHP at the lower temperature but at the higher temperature baased on a timer so as to aovoid the immersion being on a timer.

I have the room stats for the UFH set to a higher value during the E7 period and then fall back to the desired value when the E7 period finishes, this usually means that the TS is heated during the E7 period and needs little additional input from the ASHP unless it is very cold out. The TS was designed to allow the ASHP to directly heat it, however during installation it was spotted that the ASHP needs a higher pressure that we could provide with an open vented system so a FPHE was installed with an additional pump. When the ASHP comes on the additional pump circulates the water in the TS through the FPHE, whilst the normal pump with the ASHP circulates the glycol solution through the FPHE. This does have the disadvantage that some efficiency is lost due to the FPHE and the ASHP temperature needs to be higher that it would if directly connected. When the ASHP was providing 60C output the supply to the TS after the FPHE was about 55C - not sure if this increased at the whole TS heated up though. I cannot see why the TS would need to be at 70-80C to provide 48C DHW but my experience is based on a coil not FPHE for the DHW.

When we had the ASHP providing the water at 55/60C we had no problems with the temperature of the DHW - but all bathroom taps have TMVs and are limited to about 42C. During summer/ early autumn & late spring the Eddi easily manages to provide enough DHW unless everyone has a bath on a dull day. I cannot remember how much of the TS is reserved for DHW.

If doing things again I would consider fitting an inline water electric heater on the DHW supply from the TS just to top up the DHW temperature on demand if the TS supply was not hot enough rather than using an immersion heater on a timer. I have not looked into the how this would work out in practice - that is something that would be very installation dependant (no of people in the house, showers vs baths etc.) but might be appropriate for yourself.

Be careful with your installers, they will always stick with what they have done before and will be fightened of trying anything new especially if they think they will be blamed if things do not perform as well as expected. I had a similar experience to you in that several installers wanted to put i a separate UVC for DHW. I used http://www.tmsthermalstore.com/ in the end and the TS was bespoke made by Newark. The plumber that did a lot of the work had never installed a TS before but followed the design and could see what should be the consequences. The two lower imersions were intially used to provide space heating with the ASHP being added in later (one winter using immersions why still be renovated, and one and most of a second when we moved in).

[AE-NMidlands]

That sounds a clever system, but I guess it would be written off as "too complicated" by most designers, plumbers and users. I am particularly interested in your creative use of a pair of TMVs. Are they adjustable? and if so what make and model please? I have been looking for an adjustable TMV for a while, but with no luck.
A

[Stinsy]

@countrypaul: you certainly didn't get a discount cylinder!

A big and important benefit of mains-pressure DHW heated via a coil is that you don't have to waste energy periodically heating the cylinder to 60℃ to prevent legionnaires.

A lot of people go for a more simple setup where the water in the cylinder is shared between the HP and the Rads/UFH and you have a single coil for the DHW.

[Countrypaul]

That sounds a clever system, but I guess it would be written off as "too complicated" by most designers, plumbers and users. I am particularly interested in your creative use of a pair of TMVs. Are they adjustable? and if so what make and model please? I have been looking for an adjustable TMV for a while, but with no luck.
A

As far as I a aware there is nothing special about the TMVs, will try and find out the make/model - but yes they are adjustable - but so are the ones used on the DHW supply to the baths and basins. The design of this part of the system was done by TMS - there is a video on their website if you wat to check it out.

[Countrypaul]

@countrypaul: you certainly didn't get a discount cylinder!

A big and important benefit of mains-pressure DHW heated via a coil is that you don't have to waste energy periodically heating the cylinder to 60℃ to prevent legionnaires.

A lot of people go for a more simple setup where the water in the cylinder is shared between the HP and the Rads/UFH and you have a single coil for the DHW.

Very true about the lack of need to heat the wholw cylinder to 60C weekly - that seems to be an option on many heat pumps, but they may just use an immersion to do that either internal or external to the HP.

The original design was a simpler setup with the water shared by the HP & UFH, but as I mentioned the requirement to have 1bar pressure for the HP meant we had to implment the FPHE. Also wth 600L+ of water circulating, the HP would require that to contain 25% glycol -£££ ouch).