Heat Loss - Pen & Paper Check

[dilalio]

Government are finally starting to understand that banning gas for existing dwellings is a long way off, but you can bet that they will increase it's cost and most likely transfer the current levy on electricity to it in the not too distant future!

 

[dilalio]

Size the radiators for a DT30 rather than DT50

Replacing all rads or installing new system then they have to be sized for low temperature heating to meet building regs.

Max flow temp of 55°C

It is also a buildings regs compliance issue.

 

[Diggory]

Firstly, thank you for advice and your generosity of time; it’s very much appreciated.
There’s still lots I don’t know but I’m much better informed now, than when I started.

To recap -
- I didn’t get on with on-line heat loss apps
- I calculated manually heat loss by room using areas / U values / ACH / etc.
- Using Watts for each room, I was sizing my rads against DT50 lists.
- Advice explained the derivation of DT50 and encouraged DT30 sizing.
- A reference to building regs ‘55deg C flow’ was kindly provided.

I now understand - lower temp flow/return will make my boiler condense and run more efficiently (up to maybe 10%). And the consequence is that I’d need significantly larger (approx double size) rads to achieve the same output at the lower flow temperature. I’ve looked at the building reg reference kindly provided and noted the 55°C flow temperature; I was pleased to note a pragmatic acknowledgment that achieving the 55°C may not always be possible in older buildings with constraints on rad sizing. In these cases, it suggests that the system should be designed to operate at the lowest possible temperature while still meeting heating needs of the dwelling.

I will spec this up and see if DT30 sizing is physically possible (I would very much like to achieve this).
I am however mindful of the significant challenge in a very old and small property with quirky room layouts and high U values.

Best D

 

[endecotp]

Say you sized your radiators to need 80/60 flow/return temperatures when the outside temperature is -5. OK, so what happens when the outside temperature is actually +10, as it is for much of the year? Either: (1) the boiler continues to produce water at 80, inefficiently, heating the room up quickly and then turning off, or (2) the boiler produces water at 55, and the room heats up more slowly but more efficiently.

More sophisticated boilers / controls will do the right thing, e.g. using “weather compensation”. What yours does, I don’t know.

 

[Diggory]

Thank you @endecotp - that’s a very valid point.
I don’t think my boiler is sophisticated enough to have weather compensation.
I guess my only option would be to manually adjust flow temp in summer months.

I can 100% see the merit in the recommended DT30.
What I’m grappling with is the logistics of old house Vs modern requirements.
And as it’s a flow/return criteria - it’s a whole system challenge.

Best D

 

[dilalio]

approx double size

Not really double.
There's a factoring equation and a lot of rad manufacturers now provide a range of flow temps with their rad specs, so you only need to know your flow temp (TRT/MWT)

Heat pumps with low flow temps (below 55°C) have been successfully installed in properties with high heat loss... System design and execution is key.

Check out the following...

Urban Plumbers

This YouTube channel is about super-efficient heating solutions for residential and commercial properties. This channel will show you how to design, install, and commission modern and ultra efficient heating systems using weather-compensated gas boilers, domestic hot water priority set ups, and...

youtube.com

Heat Geek

A network of the the most efficient heating installers in the world, with GUARANTEED heat pump installations. Upgrade your home with an air source heat pump, and save money every month. Get a FREE instant estimate at heatgeek.com

youtube.com

And for heat loss calcs (pay the £10 for the advanced one)...

https://heat-engineer.com/en/

 

[dilalio]

Remember... ANY heat source will perform better with low flow temps.

Gas boilers also perform well on efficient systems and the price of gas is only going to rise!

 

[Diggory]

And for heat loss calcs (pay the £10 for the advanced one)...

Thanks - I don’t mind paying for an app
I just couldn’t find one - please send me a link to the one you are referring to

Thanks D

 

[dilalio]

Thanks - I don’t mind paying for an app
I just couldn’t find one - please send me a link to the one you are referring to

Thanks D

Not an app.
I sent you a link above.

 

[Diggory]

I sent you a link above.

Thx - I’ll have a read
D

 

[dilalio]

Thx - I’ll have a read
D

Heat engineer website.

 

[Diggory]

Hi again everyone -

I’ve had a good look at my sizing now.
Alas, I simply do not have wall space for the larger DT30 rads.
I can however (just about) accommodate the DT40 sized rads.
If I understand correctly, that will give me a flow / return of 70degC / 50degC ?
And I’d be just below the condensing threshold (<55 deg C) so still a useful strategy ?

Thanks D

 

[dilalio]

K33 rads.

 

[Diggory]

K33 rads.

Thanks reply and pointer; I have been looking at these.

Eg….,window cill at 600mm.
The two outgoing rads were 300h
k3 at 300h x 1000 and 2000 are 1349W and 2698W respectively
I’d need one of each (2x 2000mm would block off the 13A mains socket)
That gives me 4,047W - I’m looking for 5,500W so I’d need a third rad.
Stelrad don’t do a K3 in a 450mm.
I’m also concerned about wall fixing K3s.
Walls are very old - I’m unable to add feet.
The practicalities in an old house are very real.

Set in context of ‘designed to operate at the lowest possible temperature while still meeting heating needs of the dwelling’.
Albeit not ideal, the DT40 sized rads are looking more viable.

D

 

[dilalio]

Thanks reply and pointer; I have been looking at these.

Eg….,window cill at 600mm.
The two outgoing rads were 300h
k3 at 300h x 1000 and 2000 are 1349W and 2698W respectively
I’d need one of each (2x 2000mm would block off the 13A mains socket)
That gives me 4,047W - I’m looking for 5,500W so I’d need a third rad.
Stelrad don’t do a K3 in a 450mm.
I’m also concerned about wall fixing K3s.
Walls are very old - I’m unable to add feet.
The practicalities in an old house are very real.

Set in context of ‘designed to operate at the lowest possible temperature while still meeting heating needs of the dwelling’.
Albeit not ideal, the DT40 sized rads are looking more viable.

D

Heat loss is heat loss.
Low temp heating will be enforced one way or another.

Physics and regulations care not how old your walls are

At the end of the day, it's your decision but if BC are involved, they won't have it.

Otherwise, crack on.