hi guys, I was sent a brochure from a company called the glass radiator company. they supply a double glazed heated unit to act as both your window and the primary source of heating for your room.... think they can vary the heat output from 30w-250w..my questions is, will this be efficient and has anyone had any dealings with this sort of product. any answers will be greatfully received....link is here: http://www.glassradiators.co.uk/?page_id=54 Cheers

It's about as efficient as any resistive-element heating, probably less efficient in practice than electric-radiant flooring. Their claims for efficiency are predicated on 1-2C lower operating temperature for equivalent comfort (see http://www.glassradiators.co.uk/?page_id=838 ). Just about any low-E window and a radiant floor/ceiling would run at the same comfort level without the higher losses of placing the radiating element within arguably the least-well insulated portion of the wall (the window.)

They don't really give a U-value to the window itself, do they? It would have to be an ultra-high performer to not see substantial losses due to the the hottest point being the exterior-side surface of the interior pane of the window itself.

Claims of efficiency need data, not a fuzzy theory on how they might be used. More efficient than an electric fireplace in a house with no curtains and single-pane windows mayhaps, but the stackup itself doesn't scream "efficiency"- it screams something more like "lossy" to me. (Now if it were triple-pane gas filled or used an inch of aerogel or something, it might actually be pretty good, if a bit hazy due to the aerogel. :-) )

And a heat-pump will blow the socks off any resistive-radiant for efficiency (although it won't not be as cushy-comfy when it's really cold out.)

I am working with a guy that has developed a window that has thermal mass in it to capture and store the suns energy. I recently installed one of his prototypes in a house here in MA and the results were phenominal. This system had 3,000 lbs of water contained on 150 sq/ft of south facing glazing. It also incorporated special exterior glazing a couple of layers of low-E film placed on specific surfaces. Placing electric heat in your window doesn't make sense to me, especially if you can capture the free heat from the sun. Here is a link to a video I did on this window, showing the window heating up to 112F on a cold winters day.
http://www.youtube.com/watch?v=mVHv8lMlNcQ&feature=channel_page
I did a couple of other videos that give a better explaination of the window and they are located on my video link on my website. www.eebt.org
While these windows were just prototypes he is making great progress on making this window commercially available and should be ready within the year. The newest ones are using a different median for storing the energy but the concept is the same. His previous versions did include and aerogel insulation but you couldn't see through the windows at all and there were other issues that made this impractical.

Tom Pittsley
[email protected]
www.eebt.org

I have viewed your videos.  Please let me know when the windows with thermal mass are available to the public.  I seem to always have some clients willing to try almost anything that promises to be energy efficient.  My contact info is below in my signature block. 

You mentioned that the newest windows are using a different median (sic) than water.  What medium would that be?

Alton,
All I can say is that it is a jel. While I am not the invertor of this window, I am working closely with him and have access to his latest developments. He just notified me the other day that his latest development should be ready some time in January 2010 and he is looking for test sites. Unfortuntely I cannot disclose much about the windows without his consent due to a non-disclosure agreement with him. But what I can tell you is that his goal is to provide an integrated thermal mass window and shade system that will be fairly easy to install and his price goal is $100 sq/ft. While these may not be suited for warmer climates the new system will allow for different depths of mass, 1", 2" or 3" . 3 seems to be the number that works best here on NE. the 1" ones heat up really fast but do not retain the heat like the 3" ones. The exterior solar shades he developed to compliment the windows have much broader appeal for anyone experiencing overheating in heat dominated climates on any window. While I do not find the look appealing from the outside, the interior is very nice looking. They function so that the sun never hits your window stopping the solar gains before it gets to your window or mass, while letting in some light and allowing for decent visibility as well. Here is a link to a picture of this shading system. They roll up and will eventually be controlled electrically in conjuntion with an interior thermostat. http://picasaweb.google.com/TomPittsley/ThermalMassWindowsAndShades#5358548641718470146

These shades can be utilized on any south facing window to help eliminate the solar gains. Exterior window shades are used widely in Europe but we in USA take 10-15 years to catch up. They stop about 70% of the heat gains, while they are developing a method to measure this accurately this is based on data from other sources. He actually met with the guys at Oak Ridge laboratory to help develope a method of testing for window shades. What I can tell you that over the last week with temperatures reaching into the upper 80's to lower 90"s the windows have remained cool. I have some data loggers placed throughout the house monitoring it, one is placed directly on the interior side of the thermals mass windows. The inside measured on average 72F, ( range 70-74F) while remaining on degree below the interior room temperature. Much better than I had hoped for. I will continue to post more about these as they develop, hopefully soon.

Tom Pittsley
[email protected]
www.eebt.org