Radiant panel temps Q

[Waramanga]

Hi all,
What temp would be recommended to run radiant hot water panels at? I have seen people mixing feed water to panels to keep them down to to 70 degree supply for safety reasons (school environment) but the panels get rather large at such low temps. Any thoughts on this? Is there any logic to this, that is, 70 is hot and so is 80, just that one will burn you a bit quicker perhaps.
I will be running a condensing boiler so it will be a bit more efficient at 70deg supply temp.
Cheers

 

[IRstuff]

Are we talking fahrenheit or celcius? 70F is not even skin temperature; it's a typical temperature for swimming pools. If celcius, then yes, it's way too high. A 65C bare metal surface will produce burns with only a 1 second contact.

Consult: BS EN 13202:2000 Ergonomics of the thermal environment - Temperatures of touchable hot
surfaces or EN 563: 1994 Safety of machinery - Temperatures of touchable surfaces

TTFN

FAQ731-376

 

[Zesti]

Are these panels the type that hangs overhead, from the ceiling? Then I guess there is no risk of people touching them.

Of course in radiation heattransfer you have "T^4" so a larger temperature-difference bumps up the heattransfer a lot.

If you want to run low temperatures then radiant panels are the wrong choice I guess. I'd say you need "convective panels" if you want to use low water temperatures. This would be panels with ribs, more suited to warm the air directly.

We recently did a large project where the whole building is heated with low-temp panels (wall-mounted) except for one large space where radiation-panels are on the ceiling. There is an extra boiler for these panels to get the higher temperature.


PS: IRstuff, it's "CelSius"...

 

[cdxx139]

Ive used these radiant panels in a school setting (K-8). As IR states, they are high up and installed in the ceiling grid, so no chance in scorching the kids. I used low temp heating system 140 supply down to 105 with OA reset. I remember these panels not getting very good output at all, it barely covered my skin loss, and I used the full 25 feet or so of exterior wall. It did keep the floors clear (fin tube is your alternative) and the client requested them (how can you argue).

 

[Waramanga]

Hmmmm,
well, just for a bit of background, we see these panels in old schools and buildings all the time running 82deg supply temps, however by the time it gets to the panel its obviously a bit down on that. I was wondering what a modern installation may have as a supply temp. I mean, even 70 deg panel is going to burn but the panel is 30% bigger in size with respect to an 80deg panel.
I will investigate the passive wall hung convectors, but they dont have that radiant componenet which gives the panels a significant comfort advantage i think.
cheers

 

[IRstuff]

That's why I usually only use °C, or K. ;-)

You might consider some circulation fans. The only plus in using these panels is presumably that they reusing heat from somewhere else, not requiring new generation of heat. But, the heat is all located at the ceiling, but you want the heat closer to the floor.



TTFN

FAQ731-376

 

[Zesti]

IRstuff wrote:


But, the heat is all located at the ceiling, but you want the heat closer to the floor.


The radiant panels located near te ceiling will of course heat up the air around them directly. But, the idea of radiant panels is that they radiate heat to the floors and walls (and directly to the people on the floor).
This will heat up the walls and floors which will in turn heat up the room-air.

This is why radiant panels can also be used in high warehouses etc.: the heat will radiate down to floorlevel.

If you lower the temperature of the panels the radiation heat transfer will be lower and the relative heat transfer by convection will become much larger. Radiant panels work best, as they were intended, at higher water temperatures.

 

[IRstuff]

Sure, but most radiant heaters that I've seen are electrically or gas driven, to point where something is glowing, which is more like 700°C, not 70°C. That said, a 70°C radiant panel will put out about 400 W/m^2, which is pretty toasty if you're fully illuminated.

However, it's tricky to get proper heat balance, since the "temperature" is subjectively sensed by the individuals in the room, making a full ceiling radiant heater of that type difficult to control.

TTFN

FAQ731-376

 

[ChrisConley]

We typically run radiant ceiling panels with a mean water temperature around 76 deg C to 65 deg C. Burn protection has never been mentioned as an issue, as the devices are in the ceiling. Light bulbs get pretty hot as well.