heated window question

jp_2

hey Mark,



when you were doing all those window tests, did you ever do a comparison with the power OFF,  comparing to a standard window of the same size & thickness?



as I was looking for reasons for the unglazed collector vs glazed collector differences, I starting wondering , if the heated window conducting film was acting as a IR reflector?  this would explain why so little heat apparently  does not  "go out the window".



i still think the best solution would be to run the windows at the same temp as an inside wall, unless you have free electricity........ 



jp

Mark Eatherton

Of course :-)

Unfortunately, when I attempted to check it with our flux sensor this winter, it was to cold to get a good bond between the sensor and the glass, so I was unable to verify back loss of heated versus unheated glass. Hopefully have definitive answers in the next year.



And yes, I agree with you, the "Thermally opaque" mode is the most efficient. Think of it as variable controlled Resistance Value... If you need cooling (office building) the window is cold. If you need heat, the window is neutral, or heat producing depending upon what is going on within the space.



Thanks for asking.



ME

jp_2

a simpler approach?

why not just build 2 foam boxes, say 2x2x2 ft  with 1 inch thick foam, one 2x2 panel the heated glass, the other box a 2x2 ft  plain glass same thickness as heated glass panel.



put simple tstats in both boxes.  set heated window box at say 80F.   put small appliance light bulb in other normal glass box, set its tstat at 80F too.  don't need to wait til next winter.



use those cheap kilowatt meters and see what happens after 6-8 hrs.   then place a 2x2 foam panel over the glass in both boxes and repeat the experiment.



not total precision here, but if it does whats claimed a rather sizeable difference should be seen, no?



jp



maybe you have done this, I haven;t kept up much in the last couple of year.

jp_2

too simple?????????

that too simple ?   seems after all a insulated shell is just a heat sieve, and measuring wattage in is about as easy as it could be?  though I would make the boxes thicker to greater offset glass losses compared to foam loses.



looks like with the heat flux sensor you need to make many measurements across the glass and do averaging.



how many systems you got out there working?



i saw the pictures of you place, long wall of heated glass, whats the total wattage draw on a 20F day?





jp

Mark Eatherton

How would one recommend simulating design conditions?

What you are describing is similar to a "Hot Box" methodology.



I suppose one could extrapolate whatever conditions they had to a deeper temperature exposure.



One problem I can see is that the simulation would be devoid of internal mass effect, which all buildings have.



Maybe if I get some spare time this summer, I will try it and see what happens.



THanks for the input.



ME

jp_2

Hmm a trick question?

are you saying you factor in weight of a structure when you do a heatloss?



you had me going, I was thinking of a building empty, then one filled with water, how would they react???   but mass internal to the structure should not effect heatloss of the skin.



colder temps would be more interesting.  but a hot box, cold box it should be the same.  don't you still have cold night temps? with no mass, an hour should tell plenty.   face it up and use nighttime cooling   those night time clear sky temperature depressions I measured sure were interesting to see, but now they make prefect sense, thanks for bringing up the topic years ago!



you got me interested, I should go look in the junkyard for old grocery store freezer doors.



jp

jp_2

prefect window project

I do have a customer wanting a bay window in a breakfast nook, the ones where the bay is a seat.  a 3x4 ft heated window there would be the perfect ticket, being this is considered the wintertime breakfast area.......



jp