High-albedo roof – DIY
I live near Miami, FL and high electricity bills drive me crazy.
High electricity bill in South Florida means typically one thing only – your cooling is too expensive. And the three largest solar heat gains in old single family houses come from windows, roofs, and ventilation. Windows were tackled by large shades, ventilation virtually eliminated by heavy impact resistant hurricane protected openings, which don’t let much air through, and I was left with roofs, which attics were insulated, and some even had Whirlybird fans, but the AC distribution ducts were placed inside those attics.
Therefore, not surprisingly, I experimented with different DIY methods of cooling my roofs, including adhering polyiso sheets which I salvaged from a dumpster at one construction site (all were eventually blown away by wind) , coating the roofs with the dedicated bituminous aluminum coating sold at a home improvement store (was washed away very quickly), tackling expensive reflective insulation sheets under the deck (no perceiveable difference in ambient temperature inside attics), etc. All to no avail….
While I was doing it, I observed with astonishment the excellent durability of the average latex paint. It seems the formulation used for the average house paint exceeds many other commonly used coatings. Therefore, when I was about to dispose of several pails of old latex paint, I decided to spray it on my roof instead of dumping it in a landfill.
I left an unpainted square for comparison. And when the paint dried, I came back with my infrared camera. The result?
With the cloudy sky, this square was average 20 degrees hotter than the coated roof area….
Next day I noticed my AC is no longer working – it has no reason any more, the temperature inside is 72 degrees.
Stay tuned, I will report on the longevity and energy savings…
Here is the video I took during the operation:
I pulled my datalogger with sensors and run it yesterday evening until batteries run out (after ~3.5 hours) . The AC run only twice per hour for ~10 minutes. I will turn it on today to see how it goes. In the long term, with the AC running that infrequently, I would need to tackle the issue of high interior air humidity. It’s around 50% RH but the air outside is quite dry now, around 60% RH.
Update 3/23/2014. The small experiment becomes interesting. I just got the FPL bill covering the period 2/6-3/6, which shows 20% lower kWh consumption than last year. I coated the roof on 2/28. Unfortunately I have not installed an electric current datalogger on AC wiring, before I coated the roof. Unfortunately, because it would give the best comparison of the energy savings, without the variations caused by multiple other factors. However, the ad-hoc project devoted partially to the disposal of an old paint in ecologically-friendly way was performed in the normal hectic fashion, so even taking the pictures was a challenge.
Update 10/18/2014. The paint holds well onto the asphalt shingle after seven months.
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