UFH performance

[Jamesessex]

Hi, apologies if this topics has been posted previously but would be very interested in views. 

 

I’m living in a new build house with underfloor heating and an air source heat pump both of which I’m new too and appreciate I need to get used to them. 

 

Downstairs is underfloor heating with radiators upstairs. 

 

The products are all Vaillant with Heatmiser thermostats in the rooms. 

 

There are so many different settings and features and I’m keen to keep things simple. 

 

The upstairs radiators work well and I’m happy. 

 

It’s the downstairs. 

 

I have the underfloor heating set for 22 degrees at 6am reverting to 21 at 9am back to 22 at 4pm changing to 20 at 9pm. All thermostats have a 1 degree variance setting. 

 

The house is very well insulated and so the temperature between 9pm and 6am drops by just 2 degrees to 20 (with outside temp of 2-4 degrees) and therefore the heat required is 2 degree increase with 3 hours power time between 6am and 9am. 

 

What I’m noticing though is the upstairs radiators make the increase in temperature within about 90 minutes of kicking in at 6am but the underfloor heating struggles. 

 

Typically the lounge will increase from 0.7 degrees in 3 hours (switches off at 9am before even reaching 22), the hallway increases 2 degrees in about 3 hours and the kitchen areas about 1.2 degrees in 3 hours. 

 

I’ve had an engineer visit twice. 

 

The first time he told me to put the underfloor heating on a temperature of 24 degrees and hold permanently for 2 days to heat the floors up. 

 

I did as he suggested and found that the kitchen made it on the second day but the floor heating was very patchy in the living room and hall. Only half the floor was warm. 

 

He came back a second time and adjusted the flow level from 1 litre per minute to 2 litres per minute. This has definitely resolved the patchy heat problem and improved the heating up times (it was something like 6-12 hours before for 2 degrees increase) 

 

I’ve contacted the firm again and they said in an email that I need to make sure the hot water isn’t heating at the same time as the general heating ideally a couple of hours after (it is already set up so both run at different times) and that 21 degrees is probably the most I can hope for. 

 

I was a little disappointed with their response and before I pay for another engineer to visit I thought I would share here for any advice. 

 

What I’m looking for is the downstairs to heat each morning from 20 degrees to 22 degrees in 3 hours or less. 

 

Is that possible with an ASHW and underfloor heating? 

 

I’m satisfied from testing the thermostats all work. The ASHW has a min temperature flow of 25 degrees and max of 45 degrees, the curve is set to 1.7. 

 

Thank you for any advice 

[ProDave]

A few points and questions.

 

Generally an ASHP will not heat the UFH at the same time as it is heating DHW. Because they are generally lower power than say a gas boiler they stop doing space heating to put all their energy into DHW.  So No 1 make sure you are not asking the DHW to heat up at the same time, set that for different times.

 

Next have a look at the UFH manifold.  There should be a temperature gauge on that and a blending valve to set the temperature of the water going into the floor pipes.  You might need to adjust that to put more heat into the floors.

 

I still don't think the installers have "finished" because the point of adjusting the flow rate to each of the floor loops is to balance the system so all rooms heat up at the same time.  If one room heats up very quickly, reduce the flow rate the the loops in that room. If another room is particularly slow, increase the flow rate to that rooms pipes.

[Jamesessex]

On 03/12/2020 at 13:00, ProDave said:

A few points and questions.

 

Generally an ASHP will not heat the UFH at the same time as it is heating DHW. Because they are generally lower power than say a gas boiler they stop doing space heating to put all their energy into DHW.  So No 1 make sure you are not asking the DHW to heat up at the same time, set that for different times.

 

Next have a look at the UFH manifold.  There should be a temperature gauge on that and a blending valve to set the temperature of the water going into the floor pipes.  You might need to adjust that to put more heat into the floors.

 

I still don't think the installers have "finished" because the point of adjusting the flow rate to each of the floor loops is to balance the system so all rooms heat up at the same time.  If one room heats up very quickly, reduce the flow rate the the loops in that room. If another room is particularly slow, increase the flow rate to that rooms pipes.

Thank you. I have chased the plumbers a few times but suspect they won’t call back. I’ve located the flow rates but cannot see the temperature gauge, would that be via the pump settings? Many thanks 

 

[ProDave]

A lot of what I would call sub standard UFH setups seem to be popping up here.

 

This is another one that is missing a temperature blending valve so the HW flowing through the pipes is at whatever temperature the boiler or other heat source provides with no means to adjust it.

 

Can you feel heat in the pipes?  Where is it fed from is there some temperature control upstream?

[PeterW]

That is just shocking install ..!! They appear to be using T&E cable as flex between  the isolator and the controls, and 3 loops for the whole of the ground floor ..??

 

Can you take a photo of the valves near the hot water tank as I expect there is another set and it wouldn’t surprise me if the rads and UFH are fighting for the same heat and only when the rads are satisfied is the UFH getting the flow. 

[Jamesessex]

23 minutes ago, ProDave said:

A lot of what I would call sub standard UFH setups seem to be popping up here.

 

This is another one that is missing a temperature blending valve so the HW flowing through the pipes is at whatever temperature the boiler or other heat source provides with no means to adjust it.

 

Can you feel heat in the pipes?  Where is it fed from is there some temperature control upstream?

Thanks, it’s fed from a vaillant boiler which uses a valiant air source heat pump. On the system control for the boiler it is showing as the heat pump having a flow temperature of 42 degrees c. When touching the pipe it feels barely warm at all. 

[Jamesessex]

8 minutes ago, PeterW said:

That is just shocking install ..!! They appear to be using T&E cable as flex between  the isolator and the controls, and 3 loops for the whole of the ground floor ..??

 

Can you take a photo of the valves near the hot water tank as I expect there is another set and it wouldn’t surprise me if the rads and UFH are fighting for the same heat and only when the rads are satisfied is the UFH getting the flow. 

Thanks for your note. Here are a couple of photos of the hot water tank area upstairs 

[PeterW]

7 minutes ago, Jamesessex said:

Thanks, it’s fed from a vaillant boiler which uses a valiant air source heat pump

 Is this one of their hybrid heat pumps that works with a gas boiler ..?

 

And all that pipe should be insulated - Building Regs !! Is it brand new ..??

 

Is there an internal Vaillant unit or just the cylinder..?

 

And finally ... any more pumps ..??

 

[PeterW]

@ProDave... Wago’s hanging in mid air ..!!

 

 

Isn’t that against regs ..??

[Jamesessex]

2 minutes ago, PeterW said:

 Is this one of their hybrid heat pumps that works with a gas boiler ..?

 

And all that pipe should be insulated - Building Regs !! Is it brand new ..??

 

Is there an internal Vaillant unit or just the cylinder..?

 

And finally ... any more pumps ..??

 

Hi, no gas on the development just an air source heat pump in the garden. The house is 2 years old, I’ve recently moved in. There is the cylinder and then another vaillant unit which has a sticker on it which says SM 1 inhibitor. No more pumps from what I can see. Thank you 

[PeterW]

No model number or plate on the internal box ..?? 
 

If there are no more pumps then I expect that the issue is the heating system is expecting the rads and the UFH to work at the same time and that is asking for trouble. The rads will suck the heat from the system - I expect it has a circulation pump in the main unit that it is using here - and the UFH is being starved of heat. I would try the following : 

 

- set the hot water to come on between 04:00 and 06:00, which means it will be satisfied before the heating is needed 

- set the UFH flow valves to maximum, don’t turn them too much as they can come off in your hand ....

- set the UFH room stats to come on at 06:00 for heating, and the rads at 06:30

 

A rad flow temperature of 42°C may not feel that warm as your hand will be 38°C anyway. Unfortunately as they haven’t put a blending valve on the UFH, there is no way of turning this up as you will have issues with overheating the floor. 
 

Out of interest, what are the floor coverings in each of the rooms heated with UFH..?

 

 

[Jamesessex]

10 minutes ago, PeterW said:

No model number or plate on the internal box ..?? 
 

If there are no more pumps then I expect that the issue is the heating system is expecting the rads and the UFH to work at the same time and that is asking for trouble. The rads will suck the heat from the system - I expect it has a circulation pump in the main unit that it is using here - and the UFH is being starved of heat. I would try the following : 

 

- set the hot water to come on between 04:00 and 06:00, which means it will be satisfied before the heating is needed 

- set the UFH flow valves to maximum, don’t turn them too much as they can come off in your hand ....

- set the UFH room stats to come on at 06:00 for heating, and the rads at 06:30

 

A rad flow temperature of 42°C may not feel that warm as your hand will be 38°C anyway. Unfortunately as they haven’t put a blending valve on the UFH, there is no way of turning this up as you will have issues with overheating the floor. 
 

Out of interest, what are the floor coverings in each of the rooms heated with UFH..?

 

 

Ah yeah the model number is VWZMWT150. The DMH hot already comes on at 2am for 2 hours when the radiators and underfloor heating is off. The DHW and heating are never on at the same time.  The UFH comes on at 5 am and the rads upstairs at 7 am. After 3 hours the UFH had still not brought the temperature downstairs from 19.5c to 21 degrees hitting only around 20.5. The rads upstairs do this in 90-120 mins. 
 

the maximum the flows go to is 5, they are on 3 at the moment. Is there is any risk attached to increasing them to 5? Not so worried about energy costs just needing the heat. 
 

most of the floors are laminate with the living room being a thin pile carpet. 
 

just spoken to Vaillant from the checks done over the phone they don’t think one of their engineers can help as the air source heat pump appears to be working fine. They suggested increasing the system max temp to 50 degrees c. Spoken to the house builder this morning and they said they would just refer to the installer who has already been twice and doesn’t seem to know what to do. Sounds like I need to find a specialist UFH engineer to come out and inspect it all and see. Maybe the installer has spotted the problem and doesn’t want to say in the hope I will just go away  

[ProDave]

42 degrees won't feel much more than "warm"  The body is a poor thermometer, anything 37 degrees or less (less than body temperature) feels "cold"

 

Usually there is a thermometer of often two on a UFH manifold, obviously an "expense too far" for this job.

[ProDave]

2 hours ago, PeterW said:

@ProDave... Wago’s hanging in mid air ..!!

 

 

Isn’t that against regs ..??

Confirmation of it being a "qwality job"

[Dave Jones]

you cant really treat UFH like a rad, trying to tweak the temps throughout the day. It wont work, it heats up the screed which takes time. 

 

If you have no immersion, then the heat pump can either heat up the UFH or your hot water not both at the same time.

 

Dont worry about blending valves they are not fitted on new ones they can program the heat pump/cylinder to send the correct temp to the UFH without it.

 

As you have found out while being efficient they are crap in comparison to a combi.

 

limited hot water, cant have heat/hot water whn you want it etc.

[Dave Jones]

there is a nice in the market here I think, builds requiring effectively combi like performance (or dual combi's for larger houses) out of a heat pump system. 

 

Designing the  multitude of tanks, pumps, controllers to make a workable system for a family. Rather than a single tank pensioner setup.

[ProDave]

13 hours ago, Dave Jones said:

Dont worry about blending valves they are not fitted on new ones they can program the heat pump/cylinder to send the correct temp to the UFH without it.

I would disagree with that.

 

So my HP has just finished heating my DHW to 48 degrees, and that means the water circulating out of the heat pump is perhaps 56 degrees.  The motorised valves change over and that 56 degrees water still in the pipes is now heading for the UFH.  Thankfully the blending valve will take care of that and it won't just sent that very hot water down the UFH pipes.  But it would without a blending valve.

[PeterW]

32 minutes ago, ProDave said:

I would disagree with that.

 

So my HP has just finished heating my DHW to 48 degrees, and that means the water circulating out of the heat pump is perhaps 56 degrees.  The motorised valves change over and that 56 degrees water still in the pipes is now heading for the UFH.  Thankfully the blending valve will take care of that and it won't just sent that very hot water down the UFH pipes.  But it would without a blending valve.

Even more important is that as they get closer to the target temperature the water returning from the floor is warmer - the delta reduces so the heat input required is modulated down to hit the target flow temperature. The issue is that a heat pump has a minimum flow and minimum water heat input, go below either of these and it will shut down so blending valves allow for longer gaps in the shut down (less short cycling) and less impact on the ASHP. 
 

1 hour ago, Dave Jones said:

there is a nice in the market here I think, builds requiring effectively combi like performance (or dual combi's for larger houses) out of a heat pump system. 

 

Designing the  multitude of tanks, pumps, controllers to make a workable system for a family. Rather than a single tank pensioner setup.

 

It’s called basic system design. It is the review of the requirements such as combined flow rates, number of concurrent showers, peak flow demand etc, and the space heat requirements of the build to get to an optimum target design.
 

There is however a common myth that combi boilers give “mains pressure hot water” and that equates to a high flow of hot water. I can assure you they can give mains pressure but they can’t give “mains flow” as they all have flow restrictors so that you can have 3 Bar of pressure but only 12 litres per minute - and flow is what customers want for showers.
 

Couple that with the issues of requiring low energy houses, PV to meet SAP scores with no FiT so looking at self consumption, and you’re into a realm of big stores of hot water (welcome back to the 1970’s of hot water designs..!!) with low density heat input sources ..! It is a minefield and it’s no wonder that it is badly executed - combi type performance from a heat pump without resistance heating to boost flows is the holy grail !!

[Dave Jones]

i agree its not a good step forward. A lot of people moving into heat pump driven homes will feel conned i think when they realise they are back into the 70's of waiting for an immersion to get the tank up to heat before they can have a quick shower while everyone else has to share a bath as the hot water has ran out.

 

Without massive expense it's really not workable.

 

 

[Alex Carr]

Hello Jamesessex - I'm not going to blind you with ashp science as I'm no expert in this area, but I want to say one general thing. We have a Vaillant ashp powering ufh in a basement floor and vertical rads upstairs plus heating for hot water. The rads heat up quickly and we are happy with their performance, but the ufh is by its nature slow and takes near half a day to entirely heat up our spacious basement (heatmiser thermostats in each basement room) - everything I've read says low and slow if you don't want to get nutted with heating bills. That appears to be how it is with ufh, low and slow but ultimately effective. I will add that our property is 200 years old and we did an extensive retro-fit with regard to insulation, so there is relatively little heat loss. The minutae of running an ashp economically and effectively is, in my humble opinion, a steep learning curve which requires expectations to be re-tailored.

Edited October 28 by Alex Carr