Single vs double glazed flat panel collectors

Interceptor · May 2011

I'm hoping someone can provide me with some information regarding the benefits of single vs double glazed collectors. At what point (outdoor temp) does the insulating benefit of double glazing typically overcome the reduced light transmission? I have some double glazed collectors that will be used for year-round DHW heating, I'm wondering if it would be beneficial to convert them to single glass. They are low iron glass with black chrome absorbers. The collectors are very old and there is limited information available from the manufacturer.

Kevin_in_Denver_2 · May 2011

Where do you live?

And what's the collector tilt? A high tilt favors keeping the two panes, a low tilt favors removing one pane.

Your climate would be considered a "heating climate" if your heating degree-days (HDD) are greater than 3-4000/yr.

If you're in a warm climate or "cooling climate" you should remove one pane of glass.

Double pane liquid panels are extremely rare, which means the manufacturers typically didn't think the extra cost and added weight were worth the extra energy collected. But it should help performance when the temperatures are lower.

These are just rough guesses. A much more accurate answer could be obtained with an f-chart simulation, but you'd need lab test results for the collector in question. The lab report for a similarly constructed panel might be close enough for a decent simulation.

Interceptor · May 2011

some details

I'm in eastern PA, near Allentown, about 40.5 latitude, 75.5 longitude, 600' above sea level, looks like about 5900 HDD per year. The panels are not installed yet. They will be ground-mounted on a rack at whatever angle we determine to be optimal.

The collectors are Solaron (Chamberlain) 5000 Series, manufactured around 1978. I do have some literature from Solaron, but it does not list the specific model collectors I have.

1/8" thick low iron tempered glass

copper tube on copper sheet with black chrome selective coating

solar absorptivity = .95

infrared emissivity = .075

solar energy transmission single glazed = 90%

solar energy transmission double glazed = 81%

fiberglass insulation = R10

Fr UL = .8 (single glazed)

Fr tau alpha = .73 (single glazed)

I do not have the Fr numbers for double glazed.

hot_rod · May 2011

with the

Y intercept and the slope you can build a graph of your collectors efficiency. Then use the inlet fluid formula to see the efficiency of your collector under different operating conditions. No doubt they will be better at colder ambient conditions, but how much.

The cost and weight was the achilles heel for double glass collectors. But double coverings may be back with a glass outer layer and a polymer film below to create the air space.

This example is a "typical" single glass flat plate. On page 12 of this I-dronics

www.caleffi.us/en_US/caleffi/Details/Magazines/pdf/idronics_3_us.pdf

you will see a pool collector, flat plate and evac tube example, and an explanation on how to use the inlet fluid parameter.

I contacted SRCC to see if they still have a database of early collectors. I have a line on 60 SunCatchers built in the 80's that I would like to see some performance. These are a fin tube absorber.

I believe the Revere Copper collector also used a double glass, built with sliding door glass panels.

F-Chart still has a selection for double glass collectors, as well as pebble bed storage

hr

Kevin_in_Denver_2 · May 2011

Keep them as is

I worked for Solaron in 1982-1983. By then we made our own single glazed liquid panels. Hot air panels usually had double glazing.

Depending on the construction, removing the inner glass panel could be difficult and you might compromise the water tightness. Of course you don't want to remove the outer glass because you'd make a little swimming pool. As Rod indicated, some double glazed panels are built like window glass, and both pieces of glass are hermetically sealed to each other, making removal of one pane nearly impossible.

Assuming a four person family, if you have only two panels, remove a pane and tilt them at latitude. If you have 4 panels, tilt them at latitude plus 15 and keep all the glass. You will get more in the winter but still have plenty in summer. If you have 3 panels, then play with Fchart to decide what to do.

Jack · June 2011

If the glass is still clear

keep it the way it is. As Kevin said, you can screw them up with handling the glass and not getting the seal to "re-seal". What is the likelihood of an old gasket that is being removed and handled of resealing properly. Pretty slim I think. You have an excellent collector for DHW application. Put it in and enjoy.

Interceptor · June 2011

broken

The reason for me considering this is that one of the collectors was damaged in shipping, the outer layer of glass got broken. Insurance paid for it, but if I can seal it back up as a single pane unit I can use it and it's like getting a free collector. But that means also converting another one to make a matching set since one 3x8 is not really enough for even a small system.

My mechanical skills are above average and there is no doubt that I can physically convert them to single pane and make them water tight, that is not an issue. I understand it may be difficult to separate the panes without breaking them. I'll inspect the broken one to see how the panes are attached and see if it's feasible to separate them. I'll most likely just keep the broken one for spare parts, but I would rather use it.

Single vs double glazed flat panel collectors

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