'Energy Doctor' Acrylic Double Glazing

Sounds more like stretching some characteristics and extrapolating them, rather than an unbiased test. Goes to angle of reflection of various frequencies and some creative assumptions as to the statistics of those reflections.

However, that said, I, it may not be a bad thing, for another couple of reasons which have little to do with R/U rating - during my solar engineering and energy efficient engineering days way back in 1985, I put a ten mil acrylic sheet inside the inside panes of what is referred here in Minnesota as "twindow", i.e., an upscale single pane side opening window with a second gasketed removable inside pane. It is my understanding that this type of window was just meant to allow cleaning of the inside of a double pane of glass from inside.

There were a couple reasons for my little experiment.- I had just added on and was fighting an energy code written by people who knew little of the nuances of energy conservation and who wanted to limit windows to 14% of wall - unless the engineer could show, etc., etc.. So I used low-e glass on the new large windows, and made the old windows triple-glazed. (turned out the honest energy package after adding on 800 sq ft of garden great-room was lower than the original wall, without that triple glaze huss) Second, I wanted to limit insolation (solar intake) during the summer months so i didn't have to have a new huge air conditioner, if have one at all. The acrylic is plastic, and thus passes poorly at low angles, which are what one has on the east and west sides of the house relative to late-morning to early afternoon sun.

Third, by keeping the innermost pane warmer on all the windows I have in the older part of the house, the frost owuld be less and just as important, I could use the ASHRAE trick of having a warm surface and feeling warm at lower ambient, thus having my comfort without having the thermostat up five extra degrees. So to do that plus avoid the 1 degree per foot stratification that cause people to feel cold, I turned on the blower 24/7 (costs less in electricity, cleaning bills, and in heat and cool costs) and used "wall washers" (register type) in the winter and "throwers" in the summer, with the acrylic.

Fourth, having kids who played baseball and softball, I didn't have to pick glass out of my carpets/flooring if they hit one into a window (and it happened three times since - but no glass inside)

It all worked great.

And my fuel bills are lower than anyone else around here by 15-20% even though I have more footage, moreso if normalized for adjusting for equal gas appliances, and also consider that after I semi-retired, I don't setback with my super-fancy thermostat at night any more or have the thermostat below 72F heat / 77F AC. (Took a long burn of steady firing to bring the 1 1/2 inch thick plaster walls and stuff up to temp each morning, and so, using the gas meter and checking one mode vs the other for a month of about equal degree days, it looked like what I saved in 5-7 degrees setback was being burned the next morning - And, even if it came up net zero for my particular condition on fuel, it was a net loss energy-wise from the additional thermal stress and extra gas erosion on the heat exchanger standpoint. OK, so that's the trouble with engineers who do big boilers - you start to consider gas erosion :-) ) Electric is lower than many, odd because of the lumens in place, but that may be expected, considering I have mostly low energy bulbs, and I have motion-heat sensors for lights on and off in my bigger rooms, and my same furnace fan has run steady since 1985 (except maybe twenty stops for maintenance of filters and a couple of ignitors, not having that motor inrush needed to start a houseful of air moving and that initial fan-bearing drag over and over.)

hope it helps.....

Mate you should get a job with these guys.. You are good :-)

Bye the bye.. What did they quote you and for how many w>

Acrylic has a lower thermal conductivity value, a lower specific heat, and does not transmit infrared quite as well as most glasses. I believe it also has a smaller emissivity than glass. You can't get the heat *to* it quite as well, so it won't go from there to the glass as easily.

David A. Smith

On Wed, 29 Oct 2003 19:15:08 -0700, " snipped-for-privacy@aol.com \(formerly\)"

Hi David

I'm going to attempt some translation into layman's terms here, so please pull me up if I go wrong.

This means that hot internal room air will not be able to conduct its heat away through the acrylic layer nearly as well as if the inner window was glass (this is good).

My dictionary describes 'specific heat' as 'the amount of heat required to raise the temperature of a unit of mass of a substance by one degree'

So what you are saying here is that an acrylic window will, as previously outlined, take longer to raise to room temperature if the heater inside the house is going full blast. However, once the window

*does* rise in temperature to the inside room temperature, it will have taken less energy overall to bring the acrylic window up to that inside temperature.

If it doesn't transmit infrared light as well, is it correct to say that it doesn't transmit ultra-violet light as well as glass?

As well as being slower to heat up (as described earlier) Acrylic is also slower to cool down

SNOOPY

Dear Snoopy:

But it must then conduct or convect it to the air gap. So this term is, at best, null, and at worst, counterproductive to minimizing the internal surface temperature.

You'd have to look at the absorption spectrum. I know that most acrylics absorb all UV, and this causes premature failure of the acrylic (discoloration or crazing). This is why you use the acrylic on the inside, to extend the life.

The emissivity means that it does not radiate its heat out as fast, correct. Convection to air touching its sides will not be affected by this parameter.

David A. Smith

Hi Hob

Thanks for your comprehensive reply.

BRANZ (Building Research New Zealand) are not in the pockets of individual businesses, so I doubt that the test results themselves are biased. However, I fully accept that the company promoting the test results may be comparing two completely separate tests in such a way that overemphasises the efficiency of glass/acrylic double glazing to glass/glass double glazing.

What you are suggesting here (I think?) is that as the sun moves across the sky then the angle that the rays come into the windows will change. With the midday sun streaming straight into the window, there may be little difference between Acrylic and Glass. But near the start and close of the day there might be a large difference between the two materials

With any house window, most of the sunlight 'gets through', but some is reflected back. The more shallow the angle of the sun, and the consequent greater effective thickness of window material it must pass through, the greater the percentage of light that is liable to be reflected back. By changing the incident angle of the light across a directional spectrum, and by putting a different relative weighting on different 'sun in the sky to house' angles, then you can fiddle the results when producing your 'average' 'R' (Resistance to Heat Loss Coefficient) value test result.

If that 10mil means 10mm, that is one mighty thick slab of Acrylic! Why so thick? The acrylic I was shown by 'The Energy Doctor' was about 6mm thick I think.

Installing Acrylic 'inside' the 'inside window panes' means you have going from outside to inside:

Glass/Air gap/Glass/Air gap/Acrylic

So being an engineer you took up the challenge :-).

Is 'low-e' (low emissivity) glass still pure glass? Or does it have some kind of plastic layer coating it?

Triple glazed (to me) implies two air gaps. I imagine the 'twindow' that you refer to was not designed with that in mind. So how did you mount the acrylic sheet on the inside of your existing 'twindow'?

Another benefit would be minimising solar damage to interior furnishings. If I read between the lines correctly it sounds like you do have an air conditioner though. Did all that acrylic window insulation actually mean that you were able to install a smaller a/c unit than your floor footage would suggest?

Ah, here is some of the critical information I am after. You have confirmed that most of the advantage of acrylic is there when the sun is at low angles.

This is somewhat contrary to the hypothetical ideal material which would let the sun in early in the morning, and then let less of the sun in as the the sun got more square on to the windows, and those afternoon temperatures peaked.

I sincerely doubt that my hypothetical 'ideal material' exists. But could some sort of window tinting produce this 'ideal material' effect? Or perhaps the best solution to avoid furnishing sun damage is to put up an external awning?

The American Society of Heating and Refrigeration Engineers trick?

You are referring here to the idea whereby a 'test' person goes into two equal rooms, each room at an equal temperature, and they will feel equally comfortable in each room. But if internal acrylic double glazing is installed into one of the rooms, that will mean a person in that room will 'feel' warmer, simply because the internal surface temperature of the acrylic window is warmer (because it doesn't lose heat to the outside as fast as glass). What is the reason for that phenomenon?

Is it because there is a greater underlying convection current in a room with 'cold' windows? And that humans can feel the associated air flow as a light 'wind chill'?

I had an attack of cross cultural comprehension syndrome with that last paragraph! I would regard a blower as some kind of fan heater, but I'm not sure that such a meaning makes sense in that context. As for "wall washers" (register type) and "throwers" I have to confess my ignorance and state that I have no idea what you mean. Perhaps some kind person can translate for me :-)?

Ah, I now understand why you went to 10mm thick acrylic! If you did this in 1985, that means these windows have been in place for eighteen years. There has been no discolouration in all that time? If so that is impressively durable. But if the acrylic was installed behind existing double glazed windows I am sure that helps to explain why the acrylic has lasted so well.

This is the problem I alluded to earlier, with my comment on 'ideal window material'. Because your house walls and windows are made out of material that 'holds the heat' (and as a corollorary of that to 'hold the cold'), then consider what will happen if your house really does get cold overnight. It is going to take a lot longer to warm up than a thin walled glass windowed house. It is probably better to keep the house at a constant temperature, even if it seems like you are 'wasting energy' heating it at night when no-one is awake.

Getting a bit off topic here, but I have been told that switching those low energy light bulbs on and off all the time is liable to significantly shorten their life. Either the technology of these bulbs has improved a lot over the last eight years, or you have *very* expensive electric power in Minnesota!

A bit tongue in cheek here? Surely having a daily single on and off start for the electric fan for the gas boiler would not add to your electricity bill in any significant way?

It was an enjoyable and useful ramble to read. Thanks Hob

SNOOPY

Yes, it sounds like the same system, except that the matching steel strip is glued onto the existing window frame in the 'Energy Doctor' product.

I think the quality of the acrylic here is what is critical. How you would tell what is good and what is not is a question I would very much like to know the answer to! The 'Window Doctor' said that they import the acrylic from Asia, but exactly 'from where' over there I do not know.

The Energy Doctor offers a ten year warranty, but there are certain exclusions I think. You aren't allowed to use regular window cleaner on it for a start. A special cleaner is supplied with the windows. Perhaps your window was mistreated by the office window cleaners Tony?

I know that magnets do lose their effectiveness over time, but I was thinking that if the windows are permanently in place that deterioration effect should be lessened. However, that is just supposition on my part. If anyone else has counter experiences that prove me wrong, please speak up!

I am very surprised that an acrylic sheet with any form of natural bow was used in the first place. Perhaps such a bow is inherent in the manufacturing process? I have a couple of floor-to-ceiling windows that will take very large sheets to cover. I wonder if there is a maximum size of window that can practically be covered?

SNOOPY

I can't understand why it is not standard practice to fit double glazing in New Zealand. Not here in Christchurch anyway. I imagine areas further north might not get much of a benefit but I'd say most of the south island would.

About 3 or 4 years ago I was renting and moved house during the winter. I moved from from one rented house to my parents house. Both houses were about the same age (about a year), and seemed to have used the same building materials.

The rented one had double glazing.

The difference in what it took to heat the place was HUGE. The double glazed house kept its heat for much much longer than the single glazed house. I always though that double glazing made a fair difference, but after that experience I would never build a house without double glazing.

I can't see why the companies that supply double glazing aren't advertising like crazy - giving comparisons for electricity savings, heating savings etc. Maybe they're busy enough without advertising.

It should be standard in new houses. I'm replacing the wooden windows here with aluminium in the reasonably near future, and I feel the extra cost of double glazing is well worth it.

- Scott

[snip]

Hah! Any owner of a small business is likely to be the office cleaner as well, and I can say for certain that the 'office window cleaner' did not mistreat the acrylic window. :)

The cloudiness was not a surface effect though, it was within the acrylic itself.

What does the Ten Year Warranty guarantee? Does it guarantee a reasonable transmission of light after 10 years (say 95%)?

10 years is a long time in the d-g industry, is the Warranty insurance-backed, so that you are still covered even if the original supplier has gone out of business? [snip]

There was another secondary double-glazing system around at about the same time. This didn't use that 3M magnetic stripe, the secondary glass was mounted in a hardwood frame, (about 25mm square) and simply clamped to the original window frames. This method would seem more suitable for large-area secondary panes.