Weather Compensation for Radiators only and UFH only

[John Carroll]

Can the same temperature compensation models  be used for the above, ie a house with Radiator heating  only and another house with UFH heating only.

In the attached Vaillant WC Curves, one might use Curve 1.8 with radiator heating where a rad temperature of 70C might be required at -5C but use say Curve 0.6 with UFH heating where a UFH flow temperature of 42C might be required at -5C. Can some one post their UFH WC curves please.

Vaillant Weather Curve.docx

Edited November 18 by John Carroll

[John Carroll]

Came across this sometime/somewhere where some one was (ASHP) running their rads on WC of 43C@-10C & 35C@15C, must have had mighty big rads, if I ever installed a ASHP I reckon if I installed a extra rad in 3 downstairs rooms the I could probably run reasonably comfortably with a more aggressive WC slope.

ASHP WC.xlsx

Edited November 19 by John Carroll

[marshian]

On 18/11/2024 at 08:40, John Carroll said:

Can the same temperature compensation models  be used for the above, ie a house with Radiator heating  only and another house with UFH heating only.

In the attached Vaillant WC Curves, one might use Curve 1.8 with radiator heating where a rad temperature of 70C might be required at -5C but use say Curve 0.6 with UFH heating where a UFH flow temperature of 42C might be required at -5C. Can some one post their UFH WC curves please.

Vaillant Weather Curve.docx 203.76 kB · 3 downloads

 

I would think that the WC curve would be the same for UFH as Rads if the heat loss of the property is the same and the heating is running in the same way

 

The rads are just providing the distribution of the energy same as the UFH to replace the heat lost.

 

I'm running my WC at a curve of 1.3 but I'm gas boiler and scheduled heating rather than 24/7 with setbacks - I'm absolutely sure I could run a lower curve (1.0 or 1.1) if I moved away from scheduled heating (I get to do this at Xmas when I'm home for an extended period).

 

UFH is just a massive great radiator in the floor but it's slower to respond and needs a longer lead in than rads at lower flow temp but once it's up to temp it's just replacing the heat loss

[John Carroll]

15 hours ago, marshian said:

 

I would think that the WC curve would be the same for UFH as Rads if the heat loss of the property is the same and the heating is running in the same way

 

The rads are just providing the distribution of the energy same as the UFH to replace the heat lost.

 

I'm running my WC at a curve of 1.3 but I'm gas boiler and scheduled heating rather than 24/7 with setbacks - I'm absolutely sure I could run a lower curve (1.0 or 1.1) if I moved away from scheduled heating (I get to do this at Xmas when I'm home for an extended period).

 

UFH is just a massive great radiator in the floor but it's slower to respond and needs a longer lead in than rads at lower flow temp but once it's up to temp it's just replacing the heat loss

 

UFH by its very nature has to run with relatively low temperatures to avoid damage to floor surfaces, so is sized accordingly, Rads are sized on a T50 basis so a required room temperature of 20C would require temps, flow/return/dT, of 75C/65C/10C at whatever the lowest OAT they were sized to. Most of my own would just about deal with a OAT of -10C, consequently I would need to oversize by a factor of at least 2 even with at a OAT of 5C or so and by a factor of 2.5 at a OAT of 0C to enable running with lowish  ASHP temps, see attached.

ASHP WC Extract.xlsx

[Lofty718]

 On my Vaillant I run two different flow temperatures/curves for radiators and UFH. But the only way to acheive this is with electronic mixing valves (esbe) and hydrolically seperated pumps for each zone

 

`i wouldn't want to do this with.a heat pump though, I would design UFH and rads to all run at the same flow temp

Edited November 20 by Lofty718

[JohnMo]

On 18/11/2024 at 08:40, John Carroll said:

Can the same temperature compensation models  be used for the above, ie a house with Radiator heating  only and another house with UFH heating only

Yes they can, because they are just flow temp rise influenced by outside temp.  But unlikely a house with UFH would have the same curve as a house with radiators because design flow temps are unlikely to be the same.

[JohnMo]

23 hours ago, John Carroll said:

if I ever installed a ASHP I reckon if I installed a extra rad in 3 downstairs rooms the I could probably run reasonably comfortably with a more aggressive WC slope

If you just installed fan coils you could run a fixed flow temp of 30 to 35, depending size of fan coil.

[marshian]

6 hours ago, John Carroll said:

 

UFH by its very nature has to run with relatively low temperatures to avoid damage to floor surfaces, so is sized accordingly, Rads are sized on a T50 basis so a required room temperature of 20C would require temps, flow/return/dT, of 75C/65C/10C at whatever the lowest OAT they were sized to. Most of my own would just about deal with a OAT of -10C, consequently I would need to oversize by a factor of at least 2 even with at a OAT of 5C or so and by a factor of 2.5 at a OAT of 0C to enable running with lowish  ASHP temps, see attached.

ASHP WC Extract.xlsx 21.76 kB · 3 downloads

 

Can I make a couple of comments

 

1. You make very nice spreadsheets that are really easy to follow and incredibly useful as a resource - thank you

 

2. I'm very sure all of my rads are oversized 😉 but your spreadsheet has made me actually think about how oversized mine are (I did the heat loss calcs a while back and when I've finished my loft insulation project I'll do the whole thing again to correct for the changes). I will probably help my understanding if I go and work it all out room by room.

 

I'm not about to change rads for even bigger ones - that would probably be an expense for little gain (or a stupidly long payback) I'm already operating the boiler on CH in condensing mode all the time the returns on reducing flow temps further might be fairly damn small.