Do insulated radiator panels save money? - I'm testing them now

masonic

I haven't purchased the paper, but from the abstract the first thing that jumps out at me is why on earth aren't we manufacturing radiators with rough surfaces like this? Since the temperature at the surface of the radiator is hotter than that of the wall (hopefully), this effect would be amplified and would also mean that overall heat transfer to the room would be quicker, allowing the radiator to run at a lower temperature.

grahamc2003

heatman wrote: »

With at least adequate timing, this paper has been published this month.

(search google for "The effect of surface roughness and emissivity on radiator output"). As a new user, I can't put in the link.

This is some lab tests on these exact panels. The reason that they appear to save money, is that by keeping the walls colder they reduce the heat to the room. In return they increase the turbulence in the flow, and hence increase it up to the original output.

By keeping the wall cooler, they can save an amount of heat loss. If you can get them cheaply enough, put them on. However, as has been stated earlier, the aluminised foam or bubble wrap is just as good, and much cheaper.

I too just read the abstract. It doesn't say there that the roughness or anything else under test saves any money. It says the radiator will give out more heat. (Probably a tiny bit more, which of course has to be paid for).

The only cost savings come from the added insulation over a small area of the wall. Other papers by the same authors show the power of the radiator (that is the rate it gives out heat) can be moderated by various means. Putting reflective material begind lowers the heat output (very slightly), painting the wall behind black increases it, the surface roughness also seems to increase it. But all these are really tiny effects to the extent of indignificance imv.

I just wonder if the authors are funded by companies who sell these reflective panels, who can then pick and choose extracts from these reports to support their sales efforts, i.e. 'Such and such report proves our panels increase the heat output of radiators, and lower bills' which, while true, isn't the full story that the effects are almost insignificant.

masonic

grahamc2003 wrote: »

I too just read the abstract. It doesn't say there that the roughness or anything else under test saves any money. It says the radiator will give out more heat. (Probably a tiny bit more, which of course has to be paid for).

...and the way that happens is that the rough surface "causes the surface temperature of the wall to increase", meaning that heat energy lost by conduction through the wall actually increases. You are effectively using the wall as a secondary radiator, and of course some of the heat will go back into the room, while the rest is lost externally.

TomSharpe

as you will all be aware, the more heat that is lost from a radiator into a room, the better, because the room will heat up faster and the room stat will shut the boiler off sooner. the boiler also has its own internal thermostat, which monitors the temperature of the water returning to it from the radiators. if the radiators do not lose their heat quick enough, and the return water going back to the boiler reaches a certain temperature before the room reaches the desired temperature, then the boiler will cycle (turn off and turn back on more frequently) and the room will never reach temperature. this is obviously very inefficient...

so with that in mind, my concern regarding reflective rad panels, is that they will reflect heat back into the radiator, increasing the return temperature and shutting the boiler down before room temperature is reached... (incidentally, this is also why you shouldnt dry clothes or towels on radiators as this increases return temperatures)

im thinkin about getting a pipe stat and testing the return temperatures with and without rad panels in place, but what are everyone else's thoughts...?

LCK73

I'm interested in Tom Sharpe's findings as considering installing these behind my rads but this has cast doubt in my mind....

Cardew

LCK73 wrote: »

I'm interested in Tom Sharpe's findings as considering installing these behind my rads but this has cast doubt in my mind....

You really should read post #119 to see how minimal the savings are - according to the Energy Saving Trust

BlueBook_2

TomSharpe wrote: »

as you will all be aware, the more heat that is lost from a radiator into a room, the better, because the room will heat up faster and the room stat will shut the boiler off sooner. the boiler also has its own internal thermostat, which monitors the temperature of the water returning to it from the radiators. if the radiators do not lose their heat quick enough, and the return water going back to the boiler reaches a certain temperature before the room reaches the desired temperature, then the boiler will cycle (turn off and turn back on more frequently) and the room will never reach temperature. this is obviously very inefficient...

so with that in mind, my concern regarding reflective rad panels, is that they will reflect heat back into the radiator, increasing the return temperature and shutting the boiler down before room temperature is reached... (incidentally, this is also why you shouldnt dry clothes or towels on radiators as this increases return temperatures)

Incorrect. With a higher return temperature, the burner in your boiler will cycle on less frequently, using less fuel. The pump, however, will continue circulating hot water around your radiators until the return temperature drops below the preset level (the burner will cycle on again) or the room thermostat / TRV reaches it's preset.

The reason you shouldn't cover a radiator is that convection is impeded, thus reducing it's efficiency in heating the space.

rogerblack

The above mentioned paper
http://www.sciencedirect.com/science/article/pii/S0378778810003531
is irrelevant to shiny panels. Is it really being cited by makers of them?

It says rough surfaced panels with a high emissivity - which means a low reflectivity - make a moderate difference to the radiator output.

They do this by becoming hot by the radiated energy from the back of the radiator, and effectively providing another radiator surface, as well as encouraging convection because the surface is hotter, with its roughness meaning better mixing occurs.

In short - something like http://www.ebay.co.uk/itm/5-NEW-Polystyrene-Packing-Sheets-600x400x10mm-/290495776291?pt=UK_Packaging_Materials&hash=item43a2e5c623

Rough surface - high emissivity.

Alternatively, a couple of layers of bubble-wrap, with the bubbles towards the radiator.


The paper is somewhat bogus.
The number of construction materials with low emissivity in the thermal IR is essentially zero.
So, it's comparing a rough, painted surface to a radiator placed on unpainted metal.
This is going to be astoundingly uncommon.

The effect is going to be fairly small, though the additional insulation cooling the hot-spot behind the radiator may also be positive.

Cardew

BlueBook wrote: »

Incorrect. With a higher return temperature, the burner in your boiler will cycle on less frequently, using less fuel.

I am not sure of the point you are making.

By definition if the water has a higher return temperature the radiators will have dissipated less heat, therefore the room thermostat will keep the pump running until the room thermostat switches it off.

So if a room requires xxxBTu(or kW) to reach the required temperature it will not use less fuel by having a higher return temperature.

In fact with modern condensing boilers the whole aim is to get the return temperature of water as low as possible so the boiler remains in condensing mode, and hence is more efficient.

BlueBook_2

Cardew wrote: »

I am not sure of the point you are making.

The point is that the less time the burner is on, the less fuel it uses, regardless of whether it's a condensing boiler or not!

Cardew wrote: »

By definition if the water has a higher return temperature the radiators will have dissipated less heat, therefore the room thermostat will keep the pump running until the room thermostat switches it off.

The pump will be running, but the burner will not be operating (not using fuel!), the hot water in the system will be recirculated until the boiler senses the return temperature is below it's preset.

Cardew wrote: »

So if a room requires xxxBTu(or kW) to reach the required temperature it will not use less fuel by having a higher return temperature.

It does use less fuel if you're not wasting the input energy heating the outside atmosphere.

Cardew wrote: »

In fact with modern condensing boilers the whole aim is to get the return temperature of water as low as possible so the boiler remains in condensing mode, and hence is more efficient.

A condensing boiler will always be more efficient in any like-for-like operating condition than a non-condensing boiler, however any boiler not burning fuel is more efficient than a boiler burning fuel, period.