Just returned from a spell in France which exposed a few weaknesses in Apple Technology. Don't get me wrong, modern technology is great, and I just luurve my i-Phone. However, when it goes wonky it doesn't just drive me crazy, the lost time and wasted effort in finding (and sometimes failing to find) a fix negates so much of the benefit it bought in the first place.
If you haven't got one, the beauty of the i-Phone is its almost permanent connection to the internet, with instant results from on-line searches without having to lug around a laptop and boot it up every time one thinks of something. So taking it to France and using my family's Wi-Fi was a no-brainer. Except that the i-Phone doesn't appear to be able to deal with hexadecimal password encryption, so three days were wasted for several people trawling the internet for an answer. (At least it proves that hexaD really IS effective, I suppose!) It seems we were not alone, and no answer was found. How did Mr Apple miss that one?
So for ten days I felt as if I had had an arm cut off. Never mind, it WAS supposed to be a holiday.
To really put the lid on it, on my return, it dropped the phone connection, and after two days of tearing my hair out, the problem was only solved by swapping the phone (on guarantee) for a new one. Have you ever tried to back-up to i-Tunes then re-load to a new phone...?
Phew! Five or six wasted days in all. I need another holiday....
Friday, July 30, 2010
Friday, July 23, 2010
Yet More Basics....
The third big factor in DGU thermal performance is the coating (if any) on the glass. Put simply, thin coatings act like a see-through mirror, letting visible light through but reflecting selected long-wave radiation (heat) back into the room (or out again if you live in Dubai and want to keep the heat OUT).
There are two main classes of coating: Hard-coat and soft coat. Hard coat films are 'baked on' during the process. The hard-coat film is less efficient in keeping heat in than soft-coat, and also suffers from a reputation of leaving the glass with a dirty appearance in certain lighting conditions. It has a major advantage for small manufacturers in that it requires no special handling techniques in the construction of sealed units. So it's often pushed, not because its the best, but because its cheap and easy to use. Buyer beware! (It IS more effective at GATHERING heat from outside - the so-called solar gain. In the UK winter this is hardly likely to be a reason to use it, and in the summer it's likely to be a real pain.)
Soft coat films are becoming very sophisticated. A still-developing technology, they are capable of being 'tuned' to maximise their performance. Early issues with tinting and colour changes upon toughening are a thing of the past, and generally I consider them far superior to the hard coat films. As much as anything because I hate arguments, and will not take the risk of supplying my customers with what appears to be 'dirty glass' even if it isn't.
Soft coat films require special handing during the manufacture of DGUs, so they tend to be more expensive and are rarely available from the back-street fabricator. However, used in conjunction with warm-edge spacer separating the two sheets of glass, it is difficult to conceive a more efficient and cost-effective way of providing insulating glass.
Next I'll discuss the fine tuning with gas-filling: Another hornet's nest.
There are two main classes of coating: Hard-coat and soft coat. Hard coat films are 'baked on' during the process. The hard-coat film is less efficient in keeping heat in than soft-coat, and also suffers from a reputation of leaving the glass with a dirty appearance in certain lighting conditions. It has a major advantage for small manufacturers in that it requires no special handling techniques in the construction of sealed units. So it's often pushed, not because its the best, but because its cheap and easy to use. Buyer beware! (It IS more effective at GATHERING heat from outside - the so-called solar gain. In the UK winter this is hardly likely to be a reason to use it, and in the summer it's likely to be a real pain.)
Soft coat films are becoming very sophisticated. A still-developing technology, they are capable of being 'tuned' to maximise their performance. Early issues with tinting and colour changes upon toughening are a thing of the past, and generally I consider them far superior to the hard coat films. As much as anything because I hate arguments, and will not take the risk of supplying my customers with what appears to be 'dirty glass' even if it isn't.
Soft coat films require special handing during the manufacture of DGUs, so they tend to be more expensive and are rarely available from the back-street fabricator. However, used in conjunction with warm-edge spacer separating the two sheets of glass, it is difficult to conceive a more efficient and cost-effective way of providing insulating glass.
Next I'll discuss the fine tuning with gas-filling: Another hornet's nest.
Wednesday, July 21, 2010
More Basics
The next big factor is the air (or gas) space. Air is a great insulator, but is prone to transfer heat by convection. Remember, hot air rises, so, if there is room for convection currents to develop, heat is transferred from the warm inner pane to the cold outer pane. If the airspace is kept below about 18mm, the viscosity of the air tends to limit this convection, so the insulation improvement to a sealed unit increases with the airgap to around 18mm, after which it falls off. In reality, the curve is very flat from 12mm to 20mm, so the improvement beyond a 12mm airgap is pretty small. 16mm is probably the peak in insulation terms, beyond which any improvement is doubltful or unlikely. To complicate matters further, the failure mode of sealed units is generally via moisture permeation (at molecular level) through the edge sealant, and the wider the airgap, the shorter the life of the DGU.
So sealed unit design, as with almost everything else in life, involves a compromise. In my considered opinion (borne out now by some thirty years of experience) a 12mm gas-gap is a good balance of the factors involved, and for timber windows a 20mm DGU (4/12/4) allows an economy of framing material while still achieving the desired insulation values and long unit life.
On the face of, the 4mm airgap (gas-gap) of Slimline units - with its reduced insulation value - might be offset by a reduced expectation of moisture permeation, and a thus enhanced unit life.
Regrettably, it's not as simple as that.
More next time.
So sealed unit design, as with almost everything else in life, involves a compromise. In my considered opinion (borne out now by some thirty years of experience) a 12mm gas-gap is a good balance of the factors involved, and for timber windows a 20mm DGU (4/12/4) allows an economy of framing material while still achieving the desired insulation values and long unit life.
On the face of, the 4mm airgap (gas-gap) of Slimline units - with its reduced insulation value - might be offset by a reduced expectation of moisture permeation, and a thus enhanced unit life.
Regrettably, it's not as simple as that.
More next time.
Friday, July 16, 2010
Back to basics.
The idea of slim DGUs is - on the face of it - very attractive. The day someone invents a single sheet of transparent material to replace existing double-glazing will signal the end of a massive industry. However, until that day, double-glazing is a developed technology that looks simple but has a great deal of Technical Know-How behind it to make it work. Getting it wrong leads to tears, and there are more than fifty years of often-painful experience to look back on.
Let's start at the beginning:
The most important (and effective) bit of double-glazing is - by far - the second sheet of glass. Obvious enough, but the problems arise in keeping those two panes clean and dry for twenty- five years or more. Glass is not cheap, nor is the labour involved in fitting them, so prematurely failed DGUs are a disaster in every sense: For the customer: For the installer who has to replace them at his own expense, and may even be chased through the courts: For the reputation of the industry, which has a poor reputation at the best of times: and - not least - for mankind, now that the sheer COST of energy is understood. Glass is expensive stuff, made from molten sand, and perhaps coated with exotic and complex films. DON'T WASTE IT!
Let's start at the beginning:
The most important (and effective) bit of double-glazing is - by far - the second sheet of glass. Obvious enough, but the problems arise in keeping those two panes clean and dry for twenty- five years or more. Glass is not cheap, nor is the labour involved in fitting them, so prematurely failed DGUs are a disaster in every sense: For the customer: For the installer who has to replace them at his own expense, and may even be chased through the courts: For the reputation of the industry, which has a poor reputation at the best of times: and - not least - for mankind, now that the sheer COST of energy is understood. Glass is expensive stuff, made from molten sand, and perhaps coated with exotic and complex films. DON'T WASTE IT!
Thursday, July 15, 2010
Back to the Future
It's almost surreal... After thirty years of proving that draining and venting is the ONLY sure way of preventing premature sealed unit failure, we seem to be faced with a resurgence of the very cause of the problem - solid-bedding in oil-based putty. (And/Or NO drain and vent plus insufficient sealant and edgecover, all of which will almost GUARANTEE early failure.
It all stems from this new love-affair with so-called Slimlite double-glazed sealed units, characterised by the use of a 4mm gas space (rather than 12mm or 16mm). The logic sounds OK but is deeply flawed on several counts. I'll develop the theme over the next few weeks, but I predict a return to screaming headlines of the 1980's - "DOUBLE GLAZING = TROUBLE GLAZING" (Sunday Mercury 198?) once the complaints start to flood in (as they will).
It all stems from this new love-affair with so-called Slimlite double-glazed sealed units, characterised by the use of a 4mm gas space (rather than 12mm or 16mm). The logic sounds OK but is deeply flawed on several counts. I'll develop the theme over the next few weeks, but I predict a return to screaming headlines of the 1980's - "DOUBLE GLAZING = TROUBLE GLAZING" (Sunday Mercury 198?) once the complaints start to flood in (as they will).
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