ASHP & UFH setup

[richo106]

Hi All

 

Our renovation project has enabled us to build a well insulated and hopefully quite air tight house (not tested) we have opted for an ASHP that is used for our DHW (300L tank set at 52 degrees) and also UFH both upstairs and downstairs ( 1 manifold upstairs and 1 manifold downstairs) I have set my buffer tank/thermal store to 35 degrees. Each room has its own thermostat which controls an actuator loop.

 

I have never had an ASHP/ UFH before so I have been trying to look at the best way to set this for the winter months

 

My question is how do people who have lived with a setup like this set it up? Speaking to my installer he recommends setting all thermostats to the required / same temp (I.e 20/21) and ignore any time controls and just keep the house at constant temperature at all times? He feels you use a lot of energy warming up the house from cold and better to leave ticking over

 

My wife works from home most days

 

I would love to hear peoples opinions and experiences on this?

 

Many Thanks 

 

[nod]

He’s right We are on a HP with UFH and gas with UFH last time 

The UFH is so slow to heat up and down that timers are not really practical We have the same temperature set throughout the year 

[JohnMo]

33 minutes ago, richo106 said:

have set my buffer tank/thermal store to 35 degrees. Each room has its own thermostat which controls an actuator loop.

For me that's a similar setup as I originally had with a gas boiler. But way off what I now have with the heat pump. If it wasn't needed it got deleted.

 

Anything that adds to flow temp required, adds to the running costs. An UFH manifold with mixer, will always mix around 5 degs of return water in to the hot in flow water. A buffer unless huge has a degree of mixing especially when different circuits of the heating system opens and closes.

 

Bouncing off thermostats results in higher running costs - why because have to run too hot a flow and that hits CoP hard. 

 

Two floors of UFH is already a huge buffer and thermal store. You really don't need another. You also don't want to be running lots of thermostats. If you have them operate as limit stops, not controllers. So if you want 21 degrees in room set the thermostat to 22/23 and fine tune weather compensation curve to suit. Balance room loops to get individual room at the correct temperature.

 

A simple weather compensation curve, is all you need. Run 24/7.

[IanR]

1 hour ago, richo106 said:

I have set my buffer tank/thermal store to 35 degrees.

 

Hopefully that was installed with the ASHP and not a hang-over from a previous system, so is probably a buffer rather than a TS. TS are unsuitable for ASHP.

 

You say the buffer is set to 35°C, do you actually have a thermostat on the buffer or a temp sensor connected to the ASHP controller?   It could run a little more efficiently if controlled it via the flow temp or return temp, especially if you add a Weather Compensation curve so in mild weather the flow temp is lower and therefore more efficient, and in cold weather it raises it up. Hopefully your installer gave you a design flow temp - that will be for the coldest day, so gives you a good place to start from when creating the WC curve.

 

1 hour ago, richo106 said:

Speaking to my installer he recommends setting all thermostats to the required / same temp (I.e 20/21) and ignore any time controls and just keep the house at constant temperature at all times?

 

That's pretty much how I run mine. I do have rooms set to slightly different temperatures and I leave the ASHP to run when it needs to through most of the day. I do block it from running between 22:00 and 06:00, but that's a personal choice and my HP can comfortable generate in 16 hours all the heat my house would need.

 

Edited September 13 by IanR

[Beelbeebub]

From an UFH perspective I originally had several zones each with a time controlled thermostat. It wasn't very satisfactory. 

 

Different rooms at different temperatures doesn't seem to work. The heat always leaks in between rooms faster than your floor can put it in. We were ending up with the system trying to heat the entire house from just one floor zone, which ended up very warm. 

 

I eventually ditched all of them for a single zone and no timer. Just a simple thermostat. Balancing by room was done by tweaking the flow rates and the flow temp was adjusted as low as possible - abkut 28C from memory. 

[Andehh]

Sign up to octopus cosy as a tariff (I can PM a referral for mutual credit for us both if you're interested?) it gives you three super cheap rates spread over the day for people with an ASHP. Then have your ASHP, via the controller timed so that it hits a default temperature you like during those cheap slots (21 degs etc), and leave it as that.

 

We have our DHW via 300L rank timed to come on for an hour morning cheap slot and again afternoon cheap slot...

 

All works very well, and very reasonably priced.

[richo106]

Thank you everyone for all the comments regarding this, very much appreciated. Some of it certainly went over my head though!

 

The buffer tank was installed as part of the ASHP install as it was a completely new install, and there is a temp sensor on the buffer tank that feeds back to my ASHP controller

 

After reading these comments my thoughts are now to set all my thermostats in house to the same temperature (20 degrees) and using the Octopus cosy tariff will set up my ASHP the following:

04.00 - 07.00: UFH Buffer tank and & hot water  - ON

07.00 - 13.00: OFF

13.00 - 16.00: UFH Buffer tank and & hot water  - ON

16.00 - 22.00 OFF

22.00 - 00.00: UFH Buffer tank - ON

00.00 - 04.00: OFF

 

Would this seem sensible?

Regarding my thermostats, would you put any time controls on them or is the energy used for the UFH pump negligible?

 

@Andehh Yes please PM regarding octopus, I need to speak to EON first as typically I have just signed up for a year with them so need to talk about leaving etc..

 

As always as comments/advice must appreciated. I just want to try and make sure my system is set up correctly

 

Many Thanks

 

 

[JohnMo]

My thoughts are

 

Really depends on how you sized the heat pump if it's massively over sized it may work, if not you are going to have a cold winter, especially when it gets to sub zero, with those settings.

 

DHW will always have priority, so hot water will take 1 to 1.5 hrs out of a time slot. So you only have 1.5hrs for heating in the buffer DHW time slots.

 

You have 8 hrs of heating on your schedule, less DHW, depending on your cylinder setting that could heat twice so let's say 2.5hrs has gone. So now 5.5hrs max schedule is left. A 6kW heat pump will do 5.5 x 6 so 33kWh aporox. If you have a design heat load of 4, that is 4 x 24, so 96kWh required at say -3. You would have a short fall of 63kWh of heat. So may not be enough heat on a 7 Deg day.

 

I would set to full weather compensation, but set an override thermostat or timer to set back during the really (tea time) expensive period.

 

Not a fan of the Cosy tariff, it really is a battery tariff, being miss sold.

[IGP]

What ASHP do you have? If it’s a Valliant Arotherm Plus or a Viessmann Vitocal 15X you can go on OVOs Heat Pump Plus add on which is 15p/kWh for heat pump usage and that doesn’t have any special times so you can run its low, slow and steady for maximum SCoP and a cheap heat pump tariff to boot.

[ProDave]

8 minutes ago, IGP said:

What ASHP do you have? If it’s a Valliant Arotherm Plus or a Viessmann Vitocal 15X you can go on OVOs Heat Pump Plus add on which is 15p/kWh for heat pump usage and that doesn’t have any special times so you can run its low, slow and steady for maximum SCoP and a cheap heat pump tariff to boot.

How does that work?  Do they fit a separate meter for the heat pump?  It sounds like hark back to the "total control" tariff that gave cheap rate 24/7 for heating appliances but that had it's own meter for that.

[jack]

2 hours ago, richo106 said:

@Andehh Yes please PM regarding octopus, I need to speak to EON first as typically I have just signed up for a year with them so need to talk about leaving etc..

 

If you're able to leave and decide to go with Octopus, please consider using BuildHub's referral code to get the benefit of £100 split between you and the forum.

 

Details are in the link in my signature.

 

Good luck either way.

[IGP]

4 hours ago, ProDave said:

How does that work?  Do they fit a separate meter for the heat pump?  It sounds like hark back to the "total control" tariff that gave cheap rate 24/7 for heating appliances but that had its own meter for that.

Those models have a MID approved meter inbuilt already as I understand it. 
 

https://www.ovoenergy.com/heat-pump-plus

 

[richo106]

12 hours ago, JohnMo said:

My thoughts are

 

Really depends on how you sized the heat pump if it's massively over sized it may work, if not you are going to have a cold winter, especially when it gets to sub zero, with those settings.

 

DHW will always have priority, so hot water will take 1 to 1.5 hrs out of a time slot. So you only have 1.5hrs for heating in the buffer DHW time slots.

 

You have 8 hrs of heating on your schedule, less DHW, depending on your cylinder setting that could heat twice so let's say 2.5hrs has gone. So now 5.5hrs max schedule is left. A 6kW heat pump will do 5.5 x 6 so 33kWh aporox. If you have a design heat load of 4, that is 4 x 24, so 96kWh required at say -3. You would have a short fall of 63kWh of heat. So may not be enough heat on a 7 Deg day.

 

I would set to full weather compensation, but set an override thermostat or timer to set back during the really (tea time) expensive period.

 

Not a fan of the Cosy tariff, it really is a battery tariff, being miss sold.

Thank you @JohnMo for this answer very informative/usual. My ASHP is 12kw and truthfully I have no idea what my design heat load is, one guy said he would install an 8kw but guy I went with said he would install a 12kw as he prefers not to run them flat out.

 

I completely understand regarding timings or lack of but currently I pay 20.72p per kWh and the cosy tariff is 10.74p per kWh during the periods stated in my schedule, 21.93p per kWh day rate and then 31.79p per kWh during 16.00- 19.00.  So at the minute I am struggling to see how I wouldn’t save a good amount of money if I switched, as we generally do washing and dishwasher during the cheap periods 

 

as always I come on this forum for a bit of a sense check so appreciate being corrected on this 
 

I really need to read up on weather compensation as this is something I have not heard of until I started this post

 

Many Thanks 

Edited September 16 by richo106

[richo106]

For Info I have 12kw Panosonic Aquarea Monobloc. WH-MXC12J6E5

So any advice regarding weather compensation would be alway welcome 

 

[JohnMo]

7 hours ago, richo106 said:

weather compensation

WC, is matching flow temperature to outside temp. So as it gets colder the flow temperature increases to compensate for the increased heat losses.

 

A curve would normally start at 20 degs outside and the minimum flow temp of the heat pump, which is normally 25. Then the design flow temp of your house. If you don't know this set to 35 at -6 say as a start point.

 

Move all room stat settings to a few degrees warmer than you want the house or room.

 

To fine tune, leave the warm weather setting alone and only adjust the cold weather end and only flow temperature. So if your heating is on, and if it's to hot in the house trim the flow temp down and vise versa if to cold. Only make an adjustment once per day and generally no more than 1 deg initially then parts of a degree after. Once set you are done.

 

If after the above a room is warmer or cooler than you like, you adjust the loop flow on the UFH manifold, increase the flow to make action warmer and decrease to make cooler.

 

Use the thermostats as room limit stops, so set a degree or so warmer than target.

 

It sounds like your heat pump is big for the house, so leave the buffer for now.

 

How you doing the above on your heat pump - not sure

[Andehh]

22 hours ago, richo106 said:

Thank you everyone for all the comments regarding this, very much appreciated. Some of it certainly went over my head though!

 

The buffer tank was installed as part of the ASHP install as it was a completely new install, and there is a temp sensor on the buffer tank that feeds back to my ASHP controller

 

After reading these comments my thoughts are now to set all my thermostats in house to the same temperature (20 degrees) and using the Octopus cosy tariff will set up my ASHP the following:

04.00 - 07.00: UFH Buffer tank and & hot water  - ON

07.00 - 13.00: OFF

13.00 - 16.00: UFH Buffer tank and & hot water  - ON

16.00 - 22.00 OFF

22.00 - 00.00: UFH Buffer tank - ON

00.00 - 04.00: OFF

 

Would this seem sensible?

Regarding my thermostats, would you put any time controls on them or is the energy used for the UFH pump negligible?

 

@Andehh Yes please PM regarding octopus, I need to speak to EON first as typically I have just signed up for a year with them so need to talk about leaving etc..

 

As always as comments/advice must appreciated. I just want to try and make sure my system is set up correctly

 

Many Thanks

 

 

 

Exactly right, that's how we have it.

 

Then if you find during the coldest period mid january it isn't quite keeping up (does with us in January, as we have a 'good' Insulated and 'good' air tightness.... But not class leading) spralling bungalow, high ceilings and lots of glazing just add an hour or so into the night time tariffs, but even then we pay an average of something like 15p/kWh over the year, and we have an electric hob we use during peak tariff periods due to children and diner time falling into it.

 

We also keep our DHW around 52 degrees a day and go through a solid tank a day, so have it heated morning and afternoon.

 

Edit, we have it so the DHW comes on 5.30-6.30am and 2.30 to 3.30pm)...ie mid cheap period so there is already warmth in the pipes dissipating into the floor when the system swaps over... But not at the end of the cycle where the temp in ASHP is 52degrees vs 35 degrees for UFH... Just my engineering OCD wanting to eek out every degree where I can.

Edited September 17 by Andehh

[IGP]

I would do your own heat loss, it's not super difficult but for mental bandwidth reasons, perhaps do it once you’ve done the weather compensation bit as @JohnMo described. 
 

Knowing that is invaluable and you can start to make very informed decisions without relying on variable quality tradesmen. 

Edited September 17 by IGP
Spelling

[Benpointer]

On 16/09/2024 at 11:13, JohnMo said:

My thoughts are

 

Really depends on how you sized the heat pump if it's massively over sized it may work, if not you are going to have a cold winter, especially when it gets to sub zero, with those settings.

 

DHW will always have priority, so hot water will take 1 to 1.5 hrs out of a time slot. So you only have 1.5hrs for heating in the buffer DHW time slots.

 

You have 8 hrs of heating on your schedule, less DHW, depending on your cylinder setting that could heat twice so let's say 2.5hrs has gone. So now 5.5hrs max schedule is left. A 6kW heat pump will do 5.5 x 6 so 33kWh aporox. If you have a design heat load of 4, that is 4 x 24, so 96kWh required at say -3. You would have a short fall of 63kWh of heat. So may not be enough heat on a 7 Deg day.

 

I would set to full weather compensation, but set an override thermostat or timer to set back during the really (tea time) expensive period.

 

Not a fan of the Cosy tariff, it really is a battery tariff, being miss sold.

We have been very happy moving to the Cosy tariff for our ASHP/UFH.  We were running it 24x7x52 using the room stats to control demand before we switched to Cosy.  Now we just switch it off for the high rate period (16:00 - 19:00).  We've not noticed any difference in the warmth of the house but I reckon we're saving >£40 pm using Cosy. 

[Dave Jones]

19 hours ago, Benpointer said:

We have been very happy moving to the Cosy tariff for our ASHP/UFH.  We were running it 24x7x52 using the room stats to control demand before we switched to Cosy.  Now we just switch it off for the high rate period (16:00 - 19:00).  We've not noticed any difference in the warmth of the house but I reckon we're saving >£40 pm using Cosy. 

 

you could save double that with the agile tariff and some timeclock programming/automation.

 

We have home assistant control the ASHP, EDDI for tank boost, electric towel rads, battery. Octopus tell you each day at around 4pm what the next day rates are so you can work out cheapest slots to use. The savings are quite amazing, especially with the paid to use sessions where you get £££ for using as much as you can.

[Thorfun]

On 16/09/2024 at 11:13, JohnMo said:

Not a fan of the Cosy tariff, it really is a battery tariff, being miss sold.

I’m on it and use it exactly as a battery tariff! We charge the batteries during the cheap rate and use that power for the rest of the time. Works great for us. What’s even better is also signing up to the 15p/kWh export tariff so we get paid more than it costs us to import. So far in September we’ve run the house and we’re about even. So have run the house for free. 

[mk1_man]

Same here, using batteries on the Cosy tariff. Charge them during the off peak periods and run the house, heat pump etc from the batteries during the other periods.  Works really well.  DIY install of Sunsynk 5kW inverter and two of their batteries.  Just need to get some solar panels now

[richo106]

How much are you looking for a DIY battery install including inverter and batteries? How is the best way to size your batteries? I have a 5 bed house and all electric, i have only just switched and last week averaged 12 - 16kwh per day (no heating on)

 

I am not looking to have solar panels at anytime due to my roof layout and which way my house faces so would the cost of installing a battery set up be worth it? 

 

I have just switched to cosy tariff and last week average £2.50 - £3 a day with no heating

 

Looking forward to hearing some feedback on this as batteries is not something I have considered before as I ruled out solar straight away

 

Many Thanks 

[crispy_wafer]

good question, as there's loads of options out there and for the uninitiated it's a bit of a minefield.

[JohnMo]

57 minutes ago, richo106 said:

How is the best way to size your batteries?

If you can charge a few times a day, you just need to look at the likely usage between changing. Then pull together a spreadsheet to compare running cost to capital cost and do what makes sense for you. Most dominant period is winter.

 

Most simple is AC coupled battery. If you add solar later it all still works.

[sharpener]

 

I think 10kWh is probably the workable min for a 5 bed house cooking by electricity and 15kWh might be more useful.

 

I originally fitted 2 x 3.55kWh Pylontech modules, in the winter it had run out by the time I wanted to cook supper so I added a third.

 

Have now installed an HP as well so in winter I could probably use more but the economics don't really stack up unless you use all the capacity 365 days a year. The 270 litre thermal store can hold a further 10kWh and was cheaper than adding a fourth battery module for the HP.

 

The extra, 3rd cheap window with Cosy will definitely be a help but I expect the next few months will be a voyage of discovery. Ultimately I will see if it is worth using the battery to arbitrage between Cosy tariffs, but the round trip efficiency calculated on the annual totals reported by the Victron inverter is only 70 - 75% so this factor will make quite a dent in the profitability of that.

 

 

 

 

 

Edited September 26 by sharpener