I have a sense of deja-vu...

Read the 'Kevin's top tips' bit at the end of this and then come back and have another go at him!

http://www.telegraph.co.uk/property/luxuryhomes/3361079/Grand-Designs-Kevin-McClouds-trade-secrets.html

Anything there you won't find pushed on here?

^Joiner

Not really changed my mind.

All I really have to say about Kevin is..... "you forgot the door handles?"

Hi Jeremy,

I understand and agree with you. But I try to keep an open mind about new ideas and products [not suggesting you don't]

Several years ago I thermally modelled a large dwelling with more than the 25% glazing allowed under the building regulations. In order to demonstrate compliance, the Client had to massively insulate the other elements of fabric to compensate for the high heat losses through the glazing. I also had to demonstrate that there would be no summer overheating. Since then the regulations have been tightened further.

Its hard to see therefore how the grand designs house can possibly comply given the very large glazing areas and apparent lack of insulation elsewhere. How then has it complied with Part L?

The only unknown aspect is the so called heated glass, [which i'm also very cynical about] Hence my interest.

My guess is that they probably "cheated" with regard to BRs, by ignoring the temperature of the heated glass. If they just assumed the room temperature as the differential across the glass, then the loss would be around half of the true loss and more than good enough to get through.

BR's aren't formulated for the high energy loss across the glass when the heating is on, so it won't have been an issue and the folks in the show are probably deluding themselves that they have chosen their heating wisely. My guess is that they succumbed to bullshit from the manufacturer and didn't do a "common sense check" on the true heat loss via the windows with the heating on.

They cannot cheat the 25% rule as far as I'm aware. There are also minimum back stop u-values which again, they cannot overcome. Basically you have to hit all the targets [which they haven't] or demonstrate compliance using a whole house SAP calculation or other approved software.

I'm no expert at SAP but my understanding is that it is not intricate enough in order to fudge tempertaure differentials accross glass.

The modelling I have done is using TAS, which is infinitely more accurate than SAP but again - there is no capability within the software to cheat in the way you suggest.

Another thing. every product used in the UK requires a BBA or other such Certification. Getting 3rd party approval is notoriously difficult for novel products which rely on unproven methods.

Just look at multifoil - the manufactureres have spent many years trying to convince us all about the imprortance of radiant heat losses.

At one stage they had TRADA certification - but no more. They have been seeking European Certification for several years now. Again, to no avail.

So how on earth did heated glazing get such certification - or doesn't it have any. And if it doesn't, why was it approved for use in the UK.

Grrrr

Interesting. Is SAP really that bad that it can be loopholed in this way?

The glazed area is closer to 50%. And I cannot see the walls being anywhere near 0.1W/m2K as they are simple timber sandwich panels externally cladded. No insulation at all.

I hadn't heard of heated glass until this thread, and it sounds ridiculously stupid for all the reasons that have been given above.
But I've been thinking a bit harder about it and maybe there's no difference between heating the glazing and heating radiators inside the room.

The Glas Ceyssens product that Mike links to above is triple glazing, of which the inner pane is heated.

If the heating element keeps the temperature of the inner pane at the same temp as the air in the room, there will be no heat loss from the room via the glazing.

There will be heat loss from the heated pane to the middle pane (and so on to the outside), but the rate of heat loss won't be any greater than it would be with conventional triple glazing.

So, instead of heating up radiators to to replace the energy that's lost via conventional glazing, this system heats up the glass. The end result is the same rate of heat loss.

Or am I missing something?

Edit: the above assumes that the inside of the house is already warm. Using the heated glass to raise the internal temp would be a lot less effective than radiators.

"But I've been thinking a bit harder about it and maybe there's no difference between heating the glazing and heating radiators inside the room."

My thinking exactly, and I'm still prepared to accept the idea regardless.

Have any of you guys actually visited their site or looked at sites that reference their systems?

No?

Try it.

Do you really believe that a company that makes a 2g system with a Ug value of 0.6 would be so bloody stupid as to make units that most architects and regulatory authorities wouldn't allow to see the light of day - pun intended, because if I didn't laugh about all of this I'd be crying my frigging heart out.

Likewise BC over here - regardless of the involvement of Grand Designs - as other episodes have shown, and as KM himself frequently reminds programme participants, the Regs are there to be followed and you're a rare bird indeed if you can skirt them.

I'm not doing the footwork for you. Innovation comes about because someone has seen the 'possible' in 'impossible'. No wonder the UK is now dragging so far behind the rest of the world!

And units blow. It's the nature of the beast, regardless of glazing manufacturer's guarantees.

Heat MIRROR glazing!

We want to see actual energy use figures

<blockquote><cite>Posted By: Joiner</cite>Heat MIRROR glazing!</blockquote>

Except you can't change the laws of physics when it comes the U value, which is about the rate of conduction of heat through the material under given surface convective conditions.

The key issue here is that no matter what reflective coatings or whatever fancy stuff you do to the surface of the glazing, you cannot do much to stop heat being conducted through the glass and air/gas filled gap that hasn't already been done with high performance glazing. This is the key issue here.

It's clever salesmanship and it takes advantage of the internationally used U value measurement method of only stipulating a 24 deg C temperature differential for test purposes. As rate of heat flow through the glass and gaps will be proportional to (but not linearly so) the temperature differential the manufacturers can neatly get around having to give the true U value with the heating element turned on.

The bottom line is that if the inner pane of glass gets hotter than the room (which it must in order to transfer heat to it) then it will also be pumping heat straight through the window to the outside, via conduction through the glazing.

I think qeipl is right, if the surface temp of the glass is held at the internal air temp, then no heat transfer will occur between the inside of the house and the glass. All the heat lost will be made up by the heat put into the glass, so won't won't get down drafts of cold spots.

Imagine two rooms each with a double (or triple) glazed glass wall on one side.
Both have the remaining walls highly insulated so there is negligible heat loss.
Both are at 20C and the outside is at 0C
The area of the windows is 10m2 and the U values is 1 (all for simple calcs)
So the loss through the window is 200w

Room A has an electric space heater in the middle putting out 200w. There will be a temerateure gradient between the heater and the window. As the window surface will be cooler than the air you will get downdrafts.

Room B has the funny electric window heaters which hold the inside face of the glass at exactly 20C. This means that there is no temp gradient between the glass and the air, so no downdrafts etc.

I think the idea is that these windows have the same (or similar) heat loss as normal windows, but without the cold surface, so no condensation, no downdrafts, no cold spots etc.

Don't forget the standard place to put a radiator is under a window!

On a related note, I'm pretty sure that the argument about the heat loss being higher than expected if the building element is used as a heater (i.e. is warmer than the room) should be used for underfloor heating.

<blockquote><cite>Posted By: beelbeebub</cite>I think qeipl is right, if the surface temp of the glass is held at the internal air temp, then no heat transfer will occur between the inside of the house and the glass. All the heat lost will be made up by the heat put into the glass, so won't won't get down drafts of cold spots.

Imagine two rooms each with a double (or triple) glazed glass wall on one side.
Both have the remaining walls highly insulated so there is negligible heat loss.
Both are at 20C and the outside is at 0C
The area of the windows is 10m2 and the U values is 1 (all for simple calcs)
So the loss through the window is 200w

Room A has an electric space heater in the middle putting out 200w. There will be a temerateure gradient between the heater and the window. As the window surface will be cooler than the air you will get downdrafts.

Room B has the funny electric window heaters which hold the inside face of the glass at exactly 20C. This means that there is no temp gradient between the glass and the air, so no downdrafts etc.

I think the idea is that these windows have the same (or similar) heat loss as normal windows, but without the cold surface, so no condensation, no downdrafts, no cold spots etc.

Don't forget the standard place to put a radiator is under a window!

On a related note, I'm pretty sure that the argument about the heat loss being higher than expected if the building element is used as a heater (i.e. is warmer than the room) should be used for underfloor heating.</blockquote>

For heat transfer to occur the glass has to be hotter than the room. The idea that keeping the glass at 20 deg C will keep the room at 20 deg C isn't correct, as in order to transfer heat there has to be a temperature differential. The greater the heated area the lower this differential can be, but it has to be there all the same.

The point about loss from underfloor heating is valid, except that the only heat transport mechanism in that case is conduction to the soil beneath the house. There is no radiative of convective loss to the ground normally. The temperature differential is also lower, as the ground rarely goes below about 5 deg C under a house. This makes it easier to provide a high thermal resistance under the slab to reduce losses.