Low temperature flow radiators

waqasahmed

Hi

I saw this 
https://brugman.eu/en-gb/blog/radiators/why-low-temperature-radiators-are-must#:~:text=Low temperature radiators are environmentally,your radiator is significantly improved.

And apparently they're a must if you have HP, but I've no idea why exactly they're a must. Does anyone know why? 

In addition, they say they're more efficient because they run at a lower temperature. I take it that they're getting at the time it takes to heat up the liquid inside? As otherwise, surely radiators are 100% efficient as would any form of space heating 

If the efficiency pov is regarding the time it takes to get to 45C vs 85C, would it be worth buying these? Ie: not in pure green terms but from an economical POV where you don't have a heat pump? 

QrizB

The efficiency of a heat pump depends very much on the difference in temperature between the hot end (the water in the radiators) and the cold end (outdoor air). The closer those temperatures, the more efficient it is.

Most domestic radiators in the UK are designed for a water temperature of 85C, but most heat pumps won't achieve that temperature. You can run the radiators cooler (I ran mine at 50-55C for most of the winter, even with a gas boiler) but their output falls.

If designing a system for a heat pump, you would normally use much larger radiators so you can get as much heat into the house with water at 45C as you would normally do with water at 85C.

waqasahmed

QrizB said:

The efficiency of a heat pump depends very much on the difference in temperature between the hot end (the water in the radiators) and the cold end (outdoor air). The closer those temperatures, the more efficient it is.

Most domestic radiators in the UK are designed for a water temperature of 85C, but most heat pumps won't achieve that temperature. You can run the radiators cooler (I ran mine at 50-55C for most of the winter, even with a gas boiler) but their output falls.

If designing a system for a heat pump, you would normally use much larger radiators so you can get as much heat into the house with water at 45C as you would normally do with water at 85C.

Thanks 

I take it there's not much point having the low temperature flow radiators unless you've got a HP? 

tacpot12

waqasahmed said:

I take it there's not much point having the low temperature flow radiators unless you've got a HP? 

Even with a condensing boiler low temperature radiators will save you money. 

Reed_Richards

A "low temperature radiator" is just an ordinary radiator with a larger surface area then you would need if it were to be operated at a higher flow temperature.  Selling a radiator as a low temperature radiator is just a marketing ploy.  .  

waqasahmed

tacpot12 said:

waqasahmed said:

I take it there's not much point having the low temperature flow radiators unless you've got a HP? 

Even with a condensing boiler low temperature radiators will save you money. 

Could I ask how exactly? I mean they might jab their water boiled at a lower temp, but would there be any real benefit? I can't see anything showing how much they'd save compared to how much they cost too, even if that's in percentage terms. 

theoretica

waqasahmed said:

tacpot12 said:

waqasahmed said:

I take it there's not much point having the low temperature flow radiators unless you've got a HP? 

Even with a condensing boiler low temperature radiators will save you money. 

Could I ask how exactly? I mean they might jab their water boiled at a lower temp, but would there be any real benefit? I can't see anything showing how much they'd save compared to how much they cost too, even if that's in percentage terms. 

see eg https://www.heatgeek.com/wp-content/uploads/2018/11/RWT_v_ECB_Graph_Update_2-1-1024x812-1.jpg from https://www.heatgeek.com/condensing-boilers-efficiency/

waqasahmed

theoretica said:

waqasahmed said:

tacpot12 said:

waqasahmed said:

I take it there's not much point having the low temperature flow radiators unless you've got a HP? 

Even with a condensing boiler low temperature radiators will save you money. 

Could I ask how exactly? I mean they might jab their water boiled at a lower temp, but would there be any real benefit? I can't see anything showing how much they'd save compared to how much they cost too, even if that's in percentage terms. 

see eg https://www.heatgeek.com/wp-content/uploads/2018/11/RWT_v_ECB_Graph_Update_2-1-1024x812-1.jpg from https://www.heatgeek.com/condensing-boilers-efficiency/

Thanks 

So roughly 92% efficient vs 86% efficient

Would I then expect to see a 6% reduction on bills? 

QrizB

waqasahmed said:

So roughly 92% efficient vs 86% efficient
Would I then expect to see a 6% reduction on bills? 

All other things being equal? Yes, as you're recovering energy that would otherwise be lost in the flue gases.
That's why I run my system at 50-55C.

matelodave

The amount of heat a radiator can deliver to a room is determined by the temperature of the water flowing through it, the material its made of (copper is better than aluminium which is better than steel), it's effective surface area and the temperature difference between the room temp and radiator temp (called Delta T)

So to get the same amount of heat from it at a lower flow temperature (ie reduce the Delta T) you have to increase it's surface area, either by adding lots of fins and/or making it a lot bigger, there is no other magic way of doing it.

ABrass

matelodave said:

The amount of heat a radiator can deliver to a room is determined by the temperature of the water flowing through it, the material its made of (copper is better than aluminium which is better than steel), it's effective surface area and the temperature difference between the room temp and radiator temp (called Delta T)

So to get the same amount of heat from it at a lower flow temperature (ie reduce the Delta T) you have to increase it's surface area, either by adding lots of fins and/or making it a lot bigger, there is no other magic way of doing it.

Old fashioned steel radiators are pretty inefficient because of the factors you mention.

Which means you can replace them with an equally sized but much more powerful modern radiator.