My Unused Solar Air Heater

[richc]

Hi to All,
I recently purchased a 56-year-old home that came with a rooftop solar air heater.
A photo of the heater is attached. I am guessing it was put up in the 70's or 80's and has not been
used for at least 20 years. There is no sign of a control for it in the house anymore, although
the intake and outlet diffusers are still in the ceiling. There is an electrical wire exiting the roof,
so I guess there are are fans or thermostat(s) in the roof unit. I cannot find any diagram or other information
on this type of unit. There are no signs of a rain leak and I am hoping the unit can be made functional again.
I would be grateful if anyone out there can direct me to a diagram or perhaps reason out where the
critical components are and how they work. Thanks in advance,
Richc

[peakbagger]

Hard to see the unit in detail from the photo. There was a lot of "crap" sold in the seventies which isnt worth fixing and some that is. If the glazing on the unit is plastic, its probably not worth fixing. The glazing should be clear, if its milky its probably plastic. Occasionally glass glazed units will get milky from moisture leaking in the unit and fogging the glass, over a period of time, this fog stays and forms a deposit on the interior of the glass. In theory this can be cleaned and the glass resealed but if you break the glass, its not worth replacing. A hot air collector is a great mold generator if it gets damp inside you need to make sure that it is sealed from the outdoors. Take a hose to it and spray it all over with a strong stream and look for leaks.

Heat rises so there has to be a fan somewhere to convey the hot air from up in top of the collector to inside the house. You need to find the fan and see if it works. There is usually a controller that looks at the temperature on the top of the collector and compares it to inside the house, you need to find this and figure out if the temperature sensors are working and the controller is working. In theory whenever the collector is warmer than the house the fan will run. Home Power Magazine in the past has had articles on diagnosing older controllers, it may be worth getting an electronic subscription to get access to their back issues.

The down side with heat rising is that the collector will work quite well at sucking the heat out of your house when the weather is cool or at night as warm air from the ouse will rise up and radiate to the outdoors then sink down into the house. The system should have some flaps or dampers in the ducts that prevent this from happening. They dont need to be powered, usually they are weighed so that with the fan off the damper is closed, with the fan on it lifts the damper open.

New solar air collectors qualify for a 30% federal tax rebate. There is alot to be said to buying a new one rather than spending a lot of money to fix and old one, but thats is up to you.

[richc]

Thanks peakbagger,

I do have a lot of unknowns at this time concerning my solar air unit. My gut feeling is that it is not worth fixing or replacing.

Regarding the glazing, I am a little perplexed. I have attached a photo of the surface and it looks and feels a lot like a thin sheet of fiberglass.
I always thought solar collectors had a clear glazing.

Your statement about it possibly being a mold collector has me concerned, since I certainly would not want that problem.

At this point I am not even sure how to look at the fans or the controller since they are up in the unit (probably) and I do not see any access
except through the sun surface.

Thanks for the tip on the dampers - another item worth checking. Will let the forum know what I decide.

Richc

Hard to see the unit in detail from the photo. There was a lot of "crap" sold in the seventies which isnt worth fixing and some that is. If the glazing on the unit is plastic, its probably not worth fixing. The glazing should be clear, if its milky its probably plastic. Occasionally glass glazed units will get milky from moisture leaking in the unit and fogging the glass, over a period of time, this fog stays and forms a deposit on the interior of the glass. In theory this can be cleaned and the glass resealed but if you break the glass, its not worth replacing. A hot air collector is a great mold generator if it gets damp inside you need to make sure that it is sealed from the outdoors. Take a hose to it and spray it all over with a strong stream and look for leaks.

Heat rises so there has to be a fan somewhere to convey the hot air from up in top of the collector to inside the house. You need to find the fan and see if it works. There is usually a controller that looks at the temperature on the top of the collector and compares it to inside the house, you need to find this and figure out if the temperature sensors are working and the controller is working. In theory whenever the collector is warmer than the house the fan will run. Home Power Magazine in the past has had articles on diagnosing older controllers, it may be worth getting an electronic subscription to get access to their back issues.

The down side with heat rising is that the collector will work quite well at sucking the heat out of your house when the weather is cool or at night as warm air from the ouse will rise up and radiate to the outdoors then sink down into the house. The system should have some flaps or dampers in the ducts that prevent this from happening. They dont need to be powered, usually they are weighed so that with the fan off the damper is closed, with the fan on it lifts the damper open.

New solar air collectors qualify for a 30% federal tax rebate. There is alot to be said to buying a new one rather than spending a lot of money to fix and old one, but thats is up to you.

[peakbagger]

The glazing is supposed to be clear, unfortunately many companies used clear "plastic" as a way of reducing the weight instead of glass. There really wasnt and still isnt a good exterior grade plastic that will hold up to the sun long term and throw in elevated temperature and the stuff degrades even more. If the sun cant get through the glazing, it cant heat the interior and the collector is going to lose efficiency. I do know of several solar hot water systems that uses this type of plastic when they were built in the early eighties, some of them are still running but at a lower efficiency. The owners kids have grown up and moved away so the degraded performance matches the lower need.

Given the degraded glazing, I would consider putting it on craigslist and letting someone take it down for you.

There are several manufacturers of wall mounted solar air heaters that look a lot better and a heck of a lot easier to access than the roof units (if you have sun on your wall). Due to the wall mount location the fan is very small and some dont even use one.

[inetdog]

My gut feeling is that it is not worth fixing or replacing.

Regarding the glazing, I am a little perplexed. I have attached a photo of the surface and it looks and feels a lot like a thin sheet of fiberglass.
I always thought solar collectors had a clear glazing.

Richc

My guess is that at one time that fiberglass was considered "clear", although it may never have been particularly efficient. A homemade system too cheap to use glass or plexiglass as a cover?

Fiberglass that has weathered that much would certainly need replacing, and may be leaking in places right now. Looks like some corrosion around the screw in the picture, so it may not be particularly well built.

[richc]

Thanks inetdog and peakbagger,

I guess the sad state of the glazing says it all: It's time for this unit to come down. I will see if I can find someone to get it down, haul it away, and patch up the roof which is going to look like a piece of Swiss cheese. I'll probably have to get the whole section of roof re-shingled. No wonder I got a good deal on this house.

My guess is that at one time that fiberglass was considered "clear", although it may never have been particularly efficient. A homemade system too cheap to use glass or plexiglass as a cover?

Fiberglass that has weathered that much would certainly need replacing, and may be leaking in places right now. Looks like some corrosion around the screw in the picture, so it may not be particularly well built.

[inetdog]

Thanks inetdog and peakbagger,

I guess the sad state of the glazing says it all: It's time for this unit to come down. I will see if I can find someone to get it down, haul it away, and patch up the roof which is going to look like a piece of Swiss cheese. I'll probably have to get the whole section of roof re-shingled. No wonder I got a good deal on this house.

Hopefully that will be the only surprise you find!

BTW, it is relatively easy to make plastic UV resistant as long as you can make it black. . The problem is in making it clear to visible light and still not have the interior broken down by the UV.

[russ]

Even the plastic coverings used on greenhouses has a life before it starts to yellow - numbers I remember seeing are in the 10 year range for the best coverings

[peakbagger]

Since you probably need to do the roof, a sawzall will most likely cut it up into managable pieces pretty quickly. Give the age of the collector, I would expect the roof is toast.