More on U-values

I haven't yet started to plot any results, but some early observations appear: Outside, the surface temperatures are always higher than the OAT. The insulated panel is performing best - by far - and the glass is just a tad colder than the solid wood. The glass margin is almost a degree warmer than centre pane, even with Super Spacer. Inside, the glass feels much colder to the touch than either the insulated wood panel and the solid wood rail. This may be a Thermal Capacity issue, but the effect does not change with prolonged touch. The glass always feels colder than the wood. The dawn OAT has been steadily declining for the past week (3 degrees now) so the temperature gradients are becoming significant.

Annoyed with myself today to learn that I had missed the ST advertising deadline for this week. Time then, perhaps, to revise the ad. for the following weekend. It's interesting swinging the changes and watching the changing response in the website analysis. Not enough data yet to make firm conclusions, but enough to consider some changes, perhaps.

Good news, though, on the refurb market front, with a new prospect in view for a big breakthrough. We'll see. On the one hand we have the GREEN agenda: On the other, the economy. Personally, I think the refurb market will benefit, and that brings us full circle, with the windows system designed for just that market in the first place.

The first interesting observation arrived within five minutes of the arrival of the thermometers. With a mild 10 degrees outside and a cool 18 degrees inside, the wood was one degree colder than the inside surface of the glass, but the wood was warmer to the touch. Perhaps I am seeing the difference in thermal capacity. Glass takes heat from the hand more rapidly than from the wood, and the effect of the air in the sealed unit as an insulator is not immediately apparent. I could observe no difference between solid wood and insulated wood panel. With the arctic blast expected tomorrow, and forecast to last for a few days, I should have better numbers to work on.

( PS. I didn't like the small font, so let's try this one)

More on U-values

Infra-red thermometer now ordered, hopefully it will arrive just in time for the coming cold spell forecast for this weekend. A few days of low temperatures outside should give time for temperature gradients to stabilise. Must pop down to Wilco and look for a couple of cheap thermometers to measure inside and outside air temperatures.

The more I think about this, the more I believe I might be on to something. Coated glass may well reflect energy back into the room, but if the internal surface of the glass is colder than the air in the room, (it is) the air in contact with the glass will be cooled by contact, and advect. (Opposite of convect - means cooling by contact with cold surface, and flowing downwards under its own weight. Cold air is heavier than warm, and sinks to the floor, leading to cold feet despite heating set high. It also might properly be described as a katabatic flow - cold air flowing from the hilltops and filling the valleys overnight). Is this loss properly accounted for in the calculation?

Coated glass undoubtedly reduces the energy loss through the glass, but I will still be surprised if more energy is lost directly through the adjacent wood frame which is warmer to touch than the glass.

Franchise enquiries still flowing in. Website analysis shows a growing number of visitors to the site.

More on U values

It's just dawned on me that I already have a 'hot-box': My own home will work perfectly for the purpose. Both front door and back door have almost equal areas of Low-E Superspacer double glazing, insulated wood panels, and solid wood stiles and rails. Daily observations of inside and outside air and surface temperatures should build up a useful database of thermal gradients from which to calculate some correlations (not absolute, but indicative, nevertheless). Not exactly laboratory conditions, but the facility of being able to take multiple frequent observations is a great benefit. I am starting from the assumption that the temperature gradient is directly related to the thermal conductivity of the material or assembly. The steeper the gradient, the lower the conductivity (ie the better the insulation value). This morning, the empirical measurements (the only ones I have until my IR thermometer arrives) tells me that the steepest gradient is in the wood. Am I wrong? We shall see! If I am, then at least I will have a better understanding of the issue if I can see the figures.

RE: Relative thermal properties (November 14, 2008, 06:42:51 PM)

I have a CD with the BFRC prgram on it, but I simply can't be bothered to gather the obscure data needed to fill all the boxes. These estimation programs were supposed to replace the hot box method, which really needs months of painstaking work to build tables from different samples. I suspect your technique would require a grid to sample many points from which your calculation would produce an average. The relative proportion of frame/glass is a hellish complication, which is why I use the BRE calculator. I might suspect its accuracy (I think it's pessimistic) but it does deal with the frame issues.I have found several sites offering hand-held laser/IR gauges for under £30 with claimed accuracy of 2%. Should be good enough for my purposes. I think I will build a box around a redundant doorway in my workshop and use it this winter to run my own experiments. Steady-state temperature measurements with a small lightbulb in the box should produce useful data over a few months. I am only interested in the fundamental (probably gross) difference between a Low E sealed unit and a solid or insulated wood panel using the same glazing method. Should be interesting.

Part of correspondence with Philip Rougier of Fenestration Associates: Follow the whole thing in The windowman forum http://www.double-glazing-web.info/

Progress! The ST ad is bringing in a satisfying number of enquiries to the landing page at www.wvnet.co.uk. in its first week. We already have viable applicant for the Master Fabricator Franchise for Northern Ireland. Early days, of course but heading in the right direction.

I have also started a correspondence with Terry the Windowman's forum about the U-values of timber-framed windows. I find it difficult to believe that wood is a worse insulator than a double glazed unit. My early enquiries appear to show that I might be on to something. I shall dig deeper.

picking up the thread

How did that happen? What happened to September and October?

The Hargould exhibition at Derby was worth a visit for the seminars on 'Green Building'. The commitment of this government to reduce the carbonfootprint of the building industry was made clear, but not how it was to be achieved.
Switching back from pvc to wood wherever possible is likely to become a 'must'. I bet the pvc brigade will do their best to see that it doesn't happen.

I suppose taking a few weeks off saw a good deal of October pass by, and the rest of it was spent with a customer who was one of my first almost 25 years ago. Two failed units and the need for a complete new window in the bathroom gave a good reason to re-glaze the whole front of the house with the latest in Low-E softcoat / Warm-edge units plus new handles to freshen the old windows up and match the new. After all those years, even I was impressed with how easy it went. The Mk I frames came out without too much of a struggle. The glass likewise, after cutting the gunned silicone with a Stanley blade. New sealed units fitted like a glove using the latest SupaKlip locators and knock-in wedge instead of gunned sealant. A fresh coat of Venetian Red to match the new frame in the bathroom, and the front of the house looks like new, at a fraction of the cost of all-new windows.

Onwards and upwards. The next item out of the workshop will be a mix of casement and rising sashes in SupaWOOD, painted white. I can't wait!