Radiant Barrier

Squares attached to dome. Covering the inside roof areas is under way.

I have been running about a year now with the two air conditioners. In the beginning this worked very well, but now the air conditioners are struggling. It seems that after a year they do not cool as well. I hate to think I have to buy a new AC every year:(

Previously we had insulated the walls of the observatory with fiberglass batting and drywall. The dome itself continues to get very hot, perhaps 116 degrees as measured by the IR gun.

So, I am implementing two more temperature control measures.

Phase 1: Radiant Barrier

In this first phase I am attaching radiant barrier material to the inside of the dome. I am using simple perforated barrier, not the kind with “bubble wrap” in between. The company says it needs a 3/4 inch gap between the barrier and the roof to work correctly.

Notice the shutter; lower shutter is covered, one piece on the upper shutter.

The material comes in a roll, 24 inches wide. I cut a 24″x24″ rough square from the roll and attach it to the dome with aluminum tape. Pieces are attached to the dome when possible, to other squares otherwise. I overlapped the pieces several inches at least; I am putting square pieces on a round dome, so things don’t line up neatly. The tape is kind of dangerous – I got a number of “paper cuts” on my finger before I realized what was happening. I figured the tape would attach well to the barrier, but I was concerned that it might not stick well to the dome. It turns out the reverse seems to be true;. It sticks very well to the dome, but may develop a problem with un-sticking from the barrier. Time will tell.

I covered the dome, the lower shutter, and under the flat portion of the roof around the dome. I tried one piece on the upper shutter, and it seems to be OK. I worry that it will catch on something when the shutter opens. In addition, it is very difficult to get to the zenith of the dome, so I did not put barrier on the rest of the upper shutter.

The observatory is noticeably cooler now. The IT gun shows temperatures around 90-93 degrees. The AC is still struggling, but not as much as before. We will see if the barrier will stay attached.

Phase 2: Reflective Coating

There are a number of reflective coatings out there that are supposed to reflect the sunlight, or prevent “heat loading”, using nano particles of some sort. Some are Sunshield (Home Depot), Tex-cote, Kool-seal, ThermoSeal, and SureCoat.

I have selected a product from APOC. They make a standard product APOC 247 White for this purpose. In addition, they have a special version APOC 248 – Arizona White which is supposed to be better formulated for the Arizona heat and UV. It is certainly true that the Arizona sun is very high in UV and is extremely destructive, so I elected to try this one.

I have a guy coming in later this week to clean the dome and apply the coating. It looks straightforward, but at my age I am too nervous to climb around up there.


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