ASHP & UFH in these freezing temps

[ashthekid]

We have a recently converted old building with plenty of insulation (albeit with some gaps around the oak trusses that provide what feels like ice cold air con at times). We have a new ASHP and UFH setup which has been working fine but definitely pricier that expected which has disappointed me. 
 

My question is, and I knew to not expect great efficiency of the ASHP during anything colder than -2 like it has been the last two nights but my UFH has totally stopped heating up despite us still getting hot water through the taps. The system was suggesting the ambient outdoor temp was -11 last night. The hot water cylinder seems to heat up without any issues but the manifolds that provide the UFH are cold to touch and I’m sure they used to be very warm. 
 

With the hot water cylinder am I correct to assume the target temp is topped up by a backup immersion heater element and that’s maybe why that keeps warm. But what about the UFH. If the ASHP is struggling to get to the desired temp is there some sort of backup immersion heater for UFH that or is that just wishful thinking?

 

What do people recommend I do as otherwise I feel like we are going to struggle to heat our use in winter. This is our first winter in the property so I just want to be prepared or add on some sort of backup system to help. 
we have no gas in our village and it’s too late to add an oil or LPG tank etc so it needs to be relatively small electric backup system in our plant room which is pretty cramped as it is. 
Or should my ASHP be doing better to achieve what it’s designed for? I’m struggling to work out if it’s actually potentially broken or not. 

[mike2016]

Give the installer a call, any alarms on the control display of the ashp? Defrost cycle should kick in to handle the cold. Look at a Willis heater as a backup for next year? 

[sharpener]

5 hours ago, ashthekid said:

 

My question is, and I knew to not expect great efficiency of the ASHP during anything colder than -2 like it has been the last two nights but my UFH has totally stopped heating up despite us still getting hot water through the taps. The system was suggesting the ambient outdoor temp was -11 last night. The hot water cylinder seems to heat up without any issues but the manifolds that provide the UFH are cold to touch and I’m sure they used to be very warm. 
 

With the hot water cylinder am I correct to assume the target temp is topped up by a backup immersion heater element and that’s maybe why that keeps warm. But what about the UFH. If the ASHP is struggling to get to the desired temp is there some sort of backup immersion heater for UFH that or is that just wishful thinking?

 

Sounds like your system is stuck in DHW mode, this will take priority over any heating. If there are backup heaters these should be fairly obvious both physically and from the setup screens.

 

Suggest you set DHW to come on only 0500 to 0700 (or whatever suits your off-peak tariff) and see if things improve. If you need more HW than that provides, divide it up or find the lockout setting which should stop HW production after e.g. 30 or 60 mins to allow UFH to have its turn.

 

Lots of help available here but need to post details of system, make and size of HP, size of HW tank, sq m of house, # of occupants etc

[ashthekid]

To be honest the UFH has been working well and noticeably hot to touch when on and this has been in unison with the hot water cylinder as well. I didn’t think there was a priority feature when timings and things were setup - I assumed you could heat both at the same time or whoever you like. It hasn’t been an issue up until last weekend when we noticed the floor was stone cold. It obviously felt a lot worse when the cold snap happened and really made me realise something was wrong. 
 

I haven’t changed any settings to make this happen so I can only assume something like an actuator valve(or Hitachi flow switch controller) has gone as I can see the manifolds demanding heat(from the lights on), I can see the thermostats are calling for it too but where the hot pipe comes out of the air source(split system) indoor unit it splits and the hot pipe continues one way to the cylinder but notice it does not go the other direction where I assume the control switch is. I can see on the Home Screen that the UFH(labelled Circuit 1 in the photo) is “off” but I couldn’t find anywhere obvious in the settings to switch it on. DHW is showing as on which would explain why our hot water supply is working fine. 
Long shot but I must have switched it off somehow by accident but I honestly don’t know how. I’m one of those guys who doesn’t really like to fiddle around with settings too much in case something like this has happened. 
 

@sharpener I have had the UFH coming on at 4am for months and DHW at 5am so the UFH should have received priority already. 
 

I have a 16kW Hitachi Yutaki S split ASHP system with a 400l hot water cylinder.

Outdoor unit: RAS-6WHVNPE

Indoor unit: 
It covers approx 385sqm through 4 manifolds(2x on each floor).

Occupancy 3-5(this varies as we have people stay a lot).

[ashthekid]

[ashthekid]

It’s constantly saying Demand Off for some reason. 

[ashthekid]

[ashthekid]

[sharpener]

2 hours ago, ashthekid said:

I have had the UFH coming on at 4am for months and DHW at 5am so the UFH should have received priority already.

 

Yes but when does the HW go off? Until that time it will inhibit the operation of the UFH (unless the HW demand is satisfied first, by the tank being up to temperature). You say

 

2 hours ago, ashthekid said:

where the hot pipe comes out of the air source(split system) indoor unit it splits and the hot pipe continues one way to the cylinder but notice it does not go the other direction

 

can you see the three-port valve at the point the circuits diverge and can you do anything that moves the valve actuator?

 

Also in the pix above are the displayed values the setpoints or the actual temperatures?

[PhilT]

All the Youtube videos I can find about the Hitachi Yutaki show this control interface, featuring a big green button which is used to switch the heating or DHW on/off. Yours looks quite different but you should be able to switch your heating ON by simply pressing your on/off button while your screen is highlighting circuit one (47) (third screen above).

[ashthekid]

@PhilT I believe it’s the new LCD controller on the Yatuki S model which also includes the integration with the Hi-Kumo app to control the system via WiFi. 
Well it turns out the reason why the UFH was off was this app had somehow switched it off and I bizarrely could not override it on the controller itself until I went back to this app. It’s a terrible app anyway with it being so basic you literally can only switch the system on or off. 
Since switching it back on I have UFH back. 

@sharpener Those are set temp points on the Home Screen. 

What temp do you suggest I set the UFH set temp too? I have adjusted it to 43 now as I’m noticing our bills are really starting to shoot up now the outdoor temps are dropping. I’ve been hitting £30 a day recently. 
 

And during those really cold nights when the ASHP struggles, is there a backup or addon that could be put in place for me to switch like you would an immersion heater on a hot water cylinder? @mike2016 suggested a Willis heater. This sounds like a good option. 

[sharpener]

11 minutes ago, ashthekid said:

Well it turns out the reason why the UFH was off was this app had somehow switched it off and I bizarrely could not override it on the controller itself until I went back to this app. It’s a terrible app anyway with it being so basic you literally can only switch the system on or off. 
Since switching it back on I have UFH back. 

 

Well what do you know! Every day a school day.

 

11 minutes ago, ashthekid said:

What temp do you suggest I set the UFH set temp too? I have adjusted it to 43 now as I’m noticing our bills are really starting to shoot up now the outdoor temps are dropping. I’ve been hitting £30 a day recently. 

 

43C flow is quite high for UFH. Assuming you are running weather compensation turn the slope down by 0.1 per day until it gets too cold then back a bit. If not then switch it on.

 

11 minutes ago, ashthekid said:

And during those really cold nights when the ASHP struggles, is there a backup or addon that could be put in place for me to switch like you would an immersion heater on a hot water cylinder? @mike2016 suggested a Willis heater. This sounds like a good option. 

 

Well during the daytime a Willis heater will use peak rate electricity with a CoP of 1.0 which is less than ideal. If your tank has an immersion heater then it would be more economical to heat the DHW with it at night-time rate, freeing up some HP capacity if you need it. If not, can you fit one, might be cheaper and less disruptive than a Willis heater.

 

On 03/12/2023 at 20:19, ashthekid said:

I have a 16kW Hitachi Yutaki S split ASHP system with a 400l hot water cylinder.

Outdoor unit: RAS-6WHVNPE

Indoor unit: 
It covers approx 385sqm through 4 manifolds(2x on each floor).

Occupancy 3-5(this varies as we have people stay a lot).

 

So that is 42W per m^2 which is not very generous according to this cheat sheet and might not be enough in a cold snap, air changes per hour are crucial so stop up the draughts you mention in the OP!

[ashthekid]

Yeah the air gaps are definitely annoying and affecting the large open space room which has tall ceilings and the exposed trusses. That's the toughest room to heat by far and you could really feel it again last night with the temps that bit lower again.

[ashthekid]

My logic behind the set point for UFH being 43 was that if the DHW is set to 45 and thats what the ASHP is pushing for then i may well use that similar temp as the same amount of energy is going to be used to reach the higher temp anyway.

Is it not sensible to just have them set at the exact same temp each?

[PhilT]

49 minutes ago, ashthekid said:

Is it not sensible to just have them set at the exact same temp each?

No. DHW at 45 is for the water in the tank, not the heating flow temp - that is determined automatically and would likely exceed 50 to achieve DHW of 45. Regarding space heating the general recommendation is to use "weather compensation" - select "Mode" on your control panel and see what options is displayed - probably fixed flow temp. There is a video featuring a later version here but hopefully the steps will be similar for yours.

 

[JohnMo]

1 hour ago, ashthekid said:

My logic behind the set point for UFH being 43 was that if the DHW is set to 45 and thats what the ASHP is pushing for then i may well use that similar temp as the same amount of energy is going to be used to reach the higher temp anyway.

Is it not sensible to just have them set at the exact same temp each?

 

Your logic is flawed. To achieve the DHW set point your heat pump will run hotter say up to around 50 to 55. Your heat pump will start flowing at a lower temp when it starts to do DHW. Basically it flow at return temp plus dT, as dT decreased it will step up flow temp until it hits set point for the cylinder.

 

DHW is only a small proportion of your total energy use, so get the heating system flowing as low as possible, let the heat pump sort out DHW.

[sharpener]

29 minutes ago, JohnMo said:

DHW is only a small proportion of your total energy use, so get the heating system flowing as low as possible, let the heat pump sort out DHW.

 

To expand on that a bit, the hot water will have priority and so the heating will go off while it is doing it. Hence to get the best efficiency you need to heat the hot water to the lowest acceptable temp and at times when the other demands on the hp are going to be minimal e.g. the last hours of the off-peak window.

 

Heating needs to be on weather comp as others have said, not programmed to a fixed temp. Once you have got that right the HP will automatically run at the lowest temp that will meet the house heat demand and so with the highest possible CoP.

[HughF]

I run my ufh at 29.5… 150 spacing in 125mm concrete. I have a mixture of rads (sized for 45 flow at -4) and ufh, so I have to use a mixing station. If you just have ufh throughout then next summer you should consider throwing the mixers in the bin and running weather comp straight off the heat pump flow/return.

 

[andyj007]

get on an overnight cheap EV =charge rate and run that ASHP full chat charging up your floors during that time ..  then step it back during the day.. this could save you some ££  , you have to look at the whole year costs ..  ASHP are way more £ to run during cold spells to get temoerature up (hence teh overnight chep tariff) compared to oil or gas IMO , but soon pull that back in  late autumn and erly spring so that over the year you should be more economical and cost effect ..

 

 

[George]

£30 a day is a bit bonkers. Our energy use (Inc a 16kW ashp) peaked at £100 in a week but that was for everything including our biggest luxury of an Everhot.

 

No EV charging though

Edited December 9, 2023 by George