Extra Large Radiators

Happy_Sloth

Bendy_House said:

Happy_Sloth said:

Ooh good question....  Actually the number i read appears to change so i suspect it's the "Current Heat" rather than the "Setting"

What i can confirm is the radiators even when turned to max are NEVER yelp hot,  i warm my hands on them all the time, they are never uncomfortable to hold.  

Good news - your boiler is running at pretty much its most efficient level.

Bad news - your house is cold as a result... :-)

The solution is larger rads so they'll output 'more' (or the same) but with a lower supply temp. BUT, not worth doing unless you have to anyway - the replacement cost of rads will outweigh any energy savings for a good while.

As and when you do replace them, then go over-sized as FB suggests. 

When you say oversized do you just mean get the biggest we can for the rooms? 

BUFF

Bendy_House said:

Yes, that would seem to be. In which case the flow is at a nice lowish level already, and I would hope the return will therefore be at around 50oC, so a fair amount of condensing taking place.

Can you confirm how you see that 60oC reading? Photo? 

60oC is "I can't keep my hand on this rad for more than a few seconds" hot, and I suspect (pretty sure) that the declared output of these original rads would have been based on a higher supply temp than that, probably more like 80oC. That's YELP!

With a flow temp of 60C hopefully the return is (well) under 50C.

FreeBear said:

Happy_Sloth said:  What i can confirm is the radiators even when turned to max are NEVER yelp hot,  i warm my hands on them all the time, they are never uncomfortable to hold. 

Most radiator specifications are based on a water temperature of 70°C and an assumed room temperature of 20°C - The difference is referred to as the Delta T or Δt - If you are running at a lower Δt, the size of the radiator needs to be increased by some 12-15% for each 5°C drop.

A lot of them these days will also give a Delta T30 figure for output. For those that don't, according to Stelrad:
"For systems not operating at ∆t50 the factors in the table below should be applied. The output of a given radiator can be obtained by multiplying the quoted ∆t50 output by the operating factor. Conversely, to derive a non ∆t50 output, divide the heat output required by the relevant operation factor." The operating factor for Delta T 30 is 0.515.
https://www.stelrad.com/wp-content/uploads/2014/08/stelrad_technical_info.pdf

Bendy_House

Happy_Sloth said:

Bendy_House said:

Happy_Sloth said:

Ooh good question....  Actually the number i read appears to change so i suspect it's the "Current Heat" rather than the "Setting"

What i can confirm is the radiators even when turned to max are NEVER yelp hot,  i warm my hands on them all the time, they are never uncomfortable to hold.  

Good news - your boiler is running at pretty much its most efficient level.

Bad news - your house is cold as a result... :-)

The solution is larger rads so they'll output 'more' (or the same) but with a lower supply temp. BUT, not worth doing unless you have to anyway - the replacement cost of rads will outweigh any energy savings for a good while.

As and when you do replace them, then go over-sized as FB suggests. 

When you say oversized do you just mean get the biggest we can for the rooms? 

Well, with some thought given to it...

There are 'calcs' as FB and BUFF say, but I don't know what they are... :-)

Bendy_House

Listening to R4 today, the guy from Octopus has apparently agreed a deal with a Northern Irish company to produce ASHPs in bulk, with the hope the price will be brought down to be similar to a combi boiler.

As part of the discussions on the suitability and effectiveness of ASHPs, a researcher commented on what we already know - insulation needs to be very good - but also that the rads should be oversized to operate with water at 30oC... Lawdie.

UFH is ideal for this, of course, 'cos it's like a giant radiator!

ComicGeek

Bendy_House said:

Listening to R4 today, the guy from Octopus has apparently agreed a deal with a Northern Irish company to produce ASHPs in bulk, with the hope the price will be brought down to be similar to a combi boiler.

As part of the discussions on the suitability and effectiveness of ASHPs, a researcher commented on what we already know - insulation needs to be very good - but also that the rads should be oversized to operate with water at 30oC... Lawdie.

UFH is ideal for this, of course, 'cos it's like a giant radiator!

I didn't hear what they said, but water at 30 degrees is unnecessarily low. We design high efficiency systems at 35-40 degrees, but heat pump efficiencies are still good up to 50 degrees with this temp reduced as the weather gets warmer - that equates to a delta T of 30 degrees (difference between water temp and room temp) so perhaps that's what they said?

UFH running up to 45 degrees is efficient but not everyone can have or wants UFH - I much prefer the responsiveness of radiators personally.

Bendy_House

ComicGeek said:

I didn't hear what they said, but water at 30 degrees is unnecessarily low. We design high efficiency systems at 35-40 degrees, but heat pump efficiencies are still good up to 50 degrees with this temp reduced as the weather gets warmer - that equates to a delta T of 30 degrees (difference between water temp and room temp) so perhaps that's what they said?

UFH running up to 45 degrees is efficient but not everyone can have or wants UFH - I much prefer the responsiveness of radiators personally.

That is probably what they meant, right enough