Thermosiphon Solar Heaters
October 2016 - February 24, 2017
The thermosiphon pictured here is not complete, the panels that separate the heating enclosed area from the cool air enclosed area have been removed. The thermosiphon is 12 feet long and 30 inches wide, and made from three 4 feet long sections.
The major problem was the smell from the discounted and returned Valspar® Cement Sealer (that showed indoor furniture upon the sealer on the label) used to coat the surfaces in flat black so that they would absorb the heat from the sun. I did have that particularly bad smell coming from the sealer that I used, but beyond that there is some smell from almost any paint due to the excessive heat build up in the heater. The solution to this problem, that causes the home to smell noxious, is, as a home heater has to do, to have the air exchanged periodically with fresh air. I do not know any way that eventually the air will not grow stale using a closed system heater. The electric heater in my trailer gets its heating air through a chimney in the roof, and a gas or oil heater must draw air into the home to burn it and in so doing keeps fresh air in the home. Ventilation is certainly necessary, and when paints are used in hot locations with direct sunlight upon them there is a definite need to exchange the air.
Notice the budging of the poly carbonate, transparent panels, especially in the middle panel on the long side where the Duct tape rises. Another problem that arose unexpectedly is the polycarbonate, transparent covers for the thermosiphon being less strong than expected. Originally, I thought fastening the sides alone would be enough, then I thought putting two cross braces across the thermosiphon, one at the top and one at the bottom, would be enough. Now I believe I will need a brace every foot of each 4 feet long panel to prevent bowing that pulls on taped seems necessary to seal the unit.
Note the interface between the thermosiphon and the window. The width of the thermosiphon was originally designed to be large enough to fill the entire windowsill, but it could not simply be placed in the windowsill and then the gaps covered. The interface between the thermosiphon and the window needs to be something that can break away without damaging the window. Although not expected to breakaway, during construction and manipulation of it and during fitting it is advisable to have it independent of the window, plus in a severe storm or an accident it is better to have it be able to breakaway than to take the window with it. This piece requires significant design consideration; during my initial design phase I left this piece un-worked and thought it would be easy to construct. This surely added a larger amount of time to the project than anticipated. The idea of designing the thermosiphon or the window interface to fit commercially made heating vents did cross my mind, but none of those are electronically controllable, or they are too expensive. This is significant when a cloud or clouds move to block the thermosiphon and the air is cooled instead of being heated. In such a situation the vent(s) need to be closed, but some put heat sinks or heat collectors made of metal or some other material to retain the heat during such times. I have yet to completely decide which plan is better, but at the present time I favor vent control. As you can see in the next picture, the inside of the vent has a bottom and top opening. The bottom is where cool air is drawn in and the top is where hot air is expelled through convection (although both are blocked by Styrofoam blocks in the picture).
There is a way to exchange the air, I could bring fresh air into the bottom of the thermosiphon rather than taking it from inside the house. Perhaps constantly exchanging that lower chamber air would ventilate the house. I have not thought about this much, so this simply a note.
I believe I will use a Wifi sensor on the air fan of the trailer heating system, controlled by the thermosiphon controller, to exchange the air as that is necessary to prevent the noxious smell that builds up from the paint used on the thermosiphon. The signal would originate from a temperature controller on the thermosiphon whose work it is to open and close vents according to the inner thermosiphon temperature as needed.