Radiant panels

[Nick1c]

Anyone come across them? They are effectively in-ceiling radiators that can be used for both heating & cooling. Zehnder do them, they require a minimum ceiling height of 2.2m &, subject to cost seem as if they could offer a good solution to temperature control on a first floor. I am waiting for more info, but would love to hear from anyone with experience of them. The web page is below:

 

https://www.zehnder.co.uk/products-and-systems/heating-and-cooling-ceiling-systems/zehnder-nestsystems-radiant-conditioning

[Jeremy Harris]

Yes, a friend had electric radiant ceiling heating in his house in Penryn, which worked in very much the same way. 

 

Not a great solution, IMHO, as it tended to result in your head being warm and your feet cold.  Not sure what advantage putting heat into the bit of the room that's likely to be the warmest area is, TBH.  It seems a lot more sensible to put the heat in the floor, where it is likely to result in a more even spread of temperature in the room.

 

For cooling, ceiling panels work very well.  We had them in the office I last worked in, fed with chilled water in summer.  Generally very effective, with no noise.

[Dan F]

@Nick1c Went to visit Zehnder this morning, and they showed me this system working and suggested considering it.  Please update this thread with any further information, especially if you end up using them.

 

Thanks!

[Nick1c]

@Dan Feist Being at the end of the country I haven’t seen them - what were your impressions?

[Dan F]

On 09/08/2019 at 15:44, Nick1c said:

@Dan Feist Being at the end of the country I haven’t seen them - what were your impressions?

 

Saw then working, but really hard to tell how effective they are without having them installed at home.  The theory is interesting, about how you save on heating because you don't need to heat the air temperature so much!  That said we weren't keen on the need for expansion gaps at the edge of cieling.

[Temp]

I used a radiant gas heater to keep me warm in a workshop. One side of you felt warm and the other cold...until the air warmed up. 

 

Guide here..

https://www.infraredheatersdirect.co.uk/news/radiant-heat-panels-demystified-fact-vs-fiction/

 

Suggests they are essentially "line of sight"...

 When placing infrared panels, it’s best to think in terms of line-of-sight. Sit in the spot you want heated and think “can I see the panel from here?” – if you can’t, it needs to be move

 

What if you want everywhere heated?

 

 

[Dan F]

This is the Zehnder explanation. 

https://www.zehnder.co.uk/products-and-systems/heating-and-cooling-ceiling-systems/benefits/system-comparison

[Jeremy Harris]

 

8 hours ago, Dan Feist said:

This is the Zehnder explanation. 

https://www.zehnder.co.uk/products-and-systems/heating-and-cooling-ceiling-systems/benefits/system-comparison

 

 

This really needs thinking through carefully, to unravel the inherently flawed logic in their explanation.  If you take the case of a room with a very high heat loss rate, then what they say sort of makes sense a bit.  However, if looking at a reasonably well insulated house, then the explanation only makes sense for a few minutes after the heating has been turned on in a cold house.  After that, the radiant heaters will have warmed up the floor, walls and all internal stuff and they in turn will have warmed up the air, so in reality all that's happened is that the air has reached a warm temperature, such that when the heating has been on long enough for the thermostat to cut off the whole room will be warm.

 

In essence this is identical to UFH, but with the disadvantage that a warm floor is generally perceived as being more comfortable than a cold floor and a warm ceiling.  I've spent lots of time working in hangars that have radiant ceiling heaters that work just like these, and the combination of cold feet and a warm upper body isn't a pleasant one (it is probably the only way to make an inherently cold space workable, though).  UFH delivers most of its heat by radiating it into the room, exactly like these panels.  The radiated heat warms the other surfaces in the room in the same way (but from the opposite direction), plus there is some direct air heating, as well as the indirect air heating from the warmed surfaces.  The same thing applies after the heating has been on for a time, the air gets up to an equilibrium temperature.

 

 

[SteamyTea]

What amazes me, is that after 60 odd years of centrally heating homes (on a mass scale, I know the Romans had a go at it), radiant heating has never taken off.

Not as if we have not been able to manufacture electrical radiant systems until recently.

I think the UFH would have been the norm, even though it is not the most efficient, if we had not had a vast stock of housing to retrofit in the late 60's and during the 70's.

Retrofitting, along with a relatively cheap gas supply, was the only economical option for home owners then.

I don't know how much our 'too cheap to meter' nuclear program cost us in the early days, but I suspect the government of the day spent more on gas installations. I can remember the gas man coming around our house and changing the jets because of the swap from town gas to natural gas.

I also think that the selling of radiant heating systems relies on the general public's lack of knowledge.  How often do we hear it being compared to an open fire or the sun.  While the effect is similar, the temperatures involved are very different i.e sun is about 6000°C, a fire is about 600°C.

But what really amazes me is that we are now, in effect, fitting two heating systems to new builds.

We have an UFH, radiator or forced air radiator system, then we add on heat recovery and ventilation.  Some even put a duct heater in for heating and cooling into the MVHR.

Why are we not combine the two from the start?

We have had hot air heating systems for decades, and though there have been problems with them in the past, mainly noise and burning dust, I am sure these can be over come with better design and modern control systems.

Yes you would need bigger ducts, but if you double the diameter of a standard MVHR pipe, you can quadruple the mass air flow rate for the same air speed.

Has anyone ever worked out what size ducting and air flow rates would be needed for a modern, relatively low energy house?

Probably not as large or complicated as people think.

Edited August 13, 2019 by SteamyTea

[Gone West]

31 minutes ago, SteamyTea said:

We have had hot air heating systems for decades, and though there have been problems with them in the past, mainly noise and burning dust, I am sure these can be over come with better design and modern control systems.

Yes you would need bigger ducts, but if you double the diameter of a standard MVHR pipe, you can quadruple the mass air flow rate for the same air speed.

Has anyone ever worked out what size ducting and air flow rates would be needed for a modern, relatively low energy house?

Probably not as large or complicated as people think.

The reason for the noise and smell from hot air systems is because they were 'hot'. If they were 'warm' air systems then the volume and temperature would be reduced and I don'r know why they wouldn't work in a modern house built to current standards (if built correctly). I know my house has a very low heating requirement but I have 125mm ducting and an EASHP which supplies most of my heating.

[Jeremy Harris]

39 minutes ago, SteamyTea said:

 

Not as if we have not been able to manufacture electrical radiant systems until recently.

 

 

I had a summer job before uni working on an assembly line for Gallenkamp, a lab equipment manufacturer, in Chalfont St Peter.  The factory was uninsulated and draughty, but had "black heaters" in the roof, which were just radiant panel heaters.  That was around 50 years ago.  Likewise, practically every big airfield I've ever to has had radiant heaters fitted in the roof space of maintenance hangars.  Often these were steam heated at military airfields, run from the station steam supply.

 

All these heaters had the same problem, the heat conducted out to the floor from the soles of your feet exceeded the ability of your body to warm your feet.  Ask anyone who's worked in a place with radiant heating how their feet felt and they will tell you much the same thing.

[SteamyTea]

1 minute ago, JSHarris said:

All these heaters had the same problem

Our garage workshop was the same.

But hangers and old, leaky, workshops are special cases.

For a house, even built to minimum regs, it should be possible to heat the air directly and just let the rest come up to temperature naturally.

If I had more time, I would have a stab at working out the duct sizes, but down in St. Ives all morning 'gripping and grinning'.  Something I hate doing.

[Ed Davies]

53 minutes ago, SteamyTea said:

I think the UFH would have been the norm, even though it is not the most efficient, if we had not had a vast stock of housing to retrofit in the late 60's and during the 70's.

 

It's not just the cost/disruption of retrofitting. Some old houses did have UFH fitted and were horribly uncomfortable as a result. This was because they didn't have insulation (other than bricks, etc) so needed a high heat input which meant the floor had to be very warm which was quite uncomfortable in much the way that ceiling radiant heaters in a workshop or hangar would be but from the opposite end. This gave UFH a bad reputation.

 

E.g., when I was staying in the static caravan my landlady's husband said the one regret about their pretty-well-insulated conversion of their house/B&B (they used one or two walls of the old house so it was effectively a new build, slightly older building regulations than current but they'd well exceeded the insulation requirements) was that they hadn't fitted UFH. They'd been put off by his memories of his aunt's old house which had been uncomfortable in this way.

 

This  adds to the warming not to extrapolate from hangars to well-insulated houses for ceiling radiant heaters.

 

1 hour ago, JSHarris said:

UFH delivers most of its heat by radiating it into the room, exactly like these panels.

 

Ceiling panels will deliver a larger proportion of their heat radiatively [¹], rather than by convection.

 

[¹] and conductively, but I think that's pretty much negligible anyway.

[Wil]

Just to do a massive thread revival, I'm considering doing this at home but with a homebrew solution in the upstairs bedrooms where furniture tends to get in the way of the floor.

 

It'd be built down from existing ceiling plasterboard with battens with insulation between, joist spreader plates and a plasterboard finish over. I have the height in existing rooms to drop the ceilings 50-100 needed. I also have 300mm loft wool over the existing plasterboard ceiling.

 

Any reason why this is completely daft if I can vaguely sort airtightness at the same time? Room heat losses at -3.4degC external vary from 1000-1600W. Taking the figures from radiant floor output of 70-100W/m2 can I just expect the same from a ceiling system? So for a room with 1600W of heat loss, I need 16-23m2 of ceiling? 5x5 is a big old space... I guess I could run it a little hotter than UFH... I'm trying to avoid the equivalent radiators at 50degree output need 3892W output!

[SteamyTea]

8 minutes ago, Wil said:

Any reason why this is completely daft if I can vaguely sort airtightness at the same time? Room heat losses at -3.4degC external vary from 1000-1600W. Taking the figures from radiant floor output of 70-100W/m2 can I just expect the same from a ceiling system? So for a room with 1600W of heat loss, I need 16-23m2 of ceiling?

Give it a go and then tell us you you think it is not a good idea.

[Wil]

5 minutes ago, SteamyTea said:

Give it a go and then tell us you you think it is not a good idea.

Tell you why it's not a good idea or tell you  how I get on?

 

It's just a sparkly idea to avoid having 3 radiators in the room at the moment... far from the reality of being installed. Just wanted to know if anyone was using a radiant wall/ ceiling as it seems to be done a bit more on the continent. The fact no-one else is daft enough to do it suggests they know something I don't... perhaps it's better for cooling only.

 

[SteamyTea]

[Wil]

Well, that would do it. So the surface temperature of my roof would need to be 100degC to achieve 800W/m2 if my room surfaces were at freezing?

 

This somewhat belies the fact that my 1800W electric radiant heater used to heat me in my shed pretty happily. Does this mean those units outside pubs are at 200degC on the surface or something?

Edited July 27, 2021 by Wil

[SteamyTea]

9 minutes ago, Wil said:

Does this mean those units outside pubs are at 200degC on the surface or something?

Yes, or hotter. 

If ceiling mounted radiant heating worked, we would all be doing it.

There is also the distance from the radiant source to take into account, though at a couple if metres, this is not generally significant, and the object you are trying to heat, which may have an exposed surface area many times smaller than the emitter.

Also, humans breath, so regardless of the person's surface temperature, if they are breathing in cold air, they will be cooling.

[Wil]

2 minutes ago, SteamyTea said:

Also, humans breath, so regardless of the person's surface temperature, if they are breathing in cold air, they will be cooling.

 

But Humans emit heat? We plan cooling in commercial buildings based on heat load from people and equipment? We tend to heat up again through exothermic muscle usage? 

 

Why does this differ from UFH? In a 'sealed box' without external air transfer, both systems would perform identically. The radiant floor has the advantage of being able to feel it in bare feet, but the time to heat the room would be identical no? Because both systems are effectively heating surfaces which then heat the air? Both systems will induce the cool air to fall past the warmed air giving an overall similar effect? Or would RCH cause some sort of layering of the air in temperature bands so the warmth never got down to the bottom?

 

Are we basically saying cooling from ceiling = good, heating from floor = good because all it's doing is displacing air anyway?