Slash your Air Conditioning bills this summer....

Today’s post: Weds, 4-9-2008

How does cutting your bill to zero or by 70 % sound?

Hot weather is coming soon to where you live & work this year.

(In our area, in the Silicon Valley, after below average temps recently, our first hot weather of this year is literally predicted to start tomorrow.)

Unfortunately, in many homes & buildings a huge amount of money & energy is spent on air conditioning to pump heat out of buildings it could easily never have gotten into to begin with.

For many buildings & most homes moderately inexpensive fixes can keep enough heat from getting in to cut well over 50% from air conditioning costs & energy use or even eliminate them totally & do it each summer after they are installed.

In addition, the more people do this, the less new electric generating capacity has to be built to manage peak demand for electricity which is now driven by afternoon air conditioning use on the hottest days.

In climates where the temperature falls enough at night, you can let in cool night air to remove any left over heat from the day before by opening the windows &/or by using fans to pull in air from outside & push out the inside air. Often, if you have things well set up to prevent heat from getting in &/or have ceiling fans to lower the perceived temperature a few degrees, from 76 actual to 72 perceived, for example, on most days you then will need NO air conditioning use at all.

In climates where it is much hotter or only falls to a level where you still need to run the air conditioning, if you have things well set up to prevent heat from getting in &/or have ceiling fans to lower the perceived temperature a few degrees, you can get a triple play. You only will need to run your air conditioner at night on most days. That means you can get maximum efficiency per unit of energy as the AC works better with cooler temps to dump the excess heat into so your bill is less. And, you use the electricity at night when it often costs less per kilowatt than at peak times in the afternoon. Lastly, you no longer need to add a lot of load in the afternoon to overstress your local power grid. The idea is to have the house at or office at 68 degrees F or even a bit less in the early morning when it’s coolest outside & have it not set to turn back on until the inside gets to 76 degrees (or perhaps 72 if you don’t have ceiling fans yet.) Then, if your heat proofing is good enough, your AC will rarely need to come back on. And, if it does, it will need to run a LOT less.

Well insulated buildings with a lot of thermal mass, ideally with few windows or with double pane windows, that also have good passive design to prevent heat from entering do this very well.

New buildings with part underground or with thick walls made of rammed earth or adobe or straw or well insulated concrete block & heat resistant roofs do this well.

But in most homes today & some commercial buildings, the main problem is in the roof crawl space.

Usually there is no insulation between the roof & the crawl space -- & in some areas not much below it. In addition, the crawl space has almost no ventilation. As a result, instead of the under the roof temperature being only slightly above the outside air, it can be as much as 70 or 80 degrees hotter. Then this trapped heat re-radiates into the rooms beneath acting as a solar heater all afternoon. Even worse, this heat continues to radiate well into the night making the people inside miserable or running up their AC bills like crazy.

My wife & I had a house like that which was also badly insulated and had no air conditioning. On sunny days much above 79 degrees for a high, it was often well over 80 or even 90 until about the time the next morning we had to get up to go to work. This was NOT fun. And, if we had decent air conditioning then, we would have run it a LOT.

We then discovered & installed a system that uses NO OUTSIDE ENERGY AT ALL which prevented this under the roof heat build up. And, we installed ceiling fans.

We didn’t even get to upgrading the insulation and got this result.:

After doing this, we experienced a day well into the high 90’s outside. It would have been over 100 inside from 3 PM to midnight before. After installing this system & adding ceiling fans, it only got up to about 75 inside & then only from about 3 to 6 PM – AND the 75 felt Ok with just the ceiling fans alone. It was in the high 90’s outside and we needed NO air conditioning at all. And, remember that was before we upgraded our ceiling insulation to R19 or better.

Here is the magic trick we used that I cannot recommend more highly after this experience.:

Hot air rises. So, what we did is to install several very well screened air intake vents around the perimeter of our roof’s crawl space that were under the shade of the roof & we had a competent workman also install several convection powered turbines in the roof near its peak. Then we added ceiling fans to our bedrooms & living room. The entire project cost less than $1,000. And, this was a one time fee.

The very same hot air that was giving us such grief before now happily spun the turbines as it rose & drew the much less hot outside air in behind it. This was all solar powered. We needed no outside energy at all to run it.

If we had more money at the time, I would have liked to add the extra ceiling insulation & a radiant heat barrier in our attic and installed wood frame double pane windows.

Even better would have been to add a decent heat pump system to deliver efficient air conditioning if we ever needed it for days above 100 degrees & install enough solar panels to run it all. And, added window shading on the west & south sides of the house would have also helped.

But, much to my delight, we got close to 100 % of the cooling we needed from this single inexpensive fix that still needs no energy bills at all to operate these several years later.

So, if you have a roof that traps heat the way our roof then did, you can add all sorts of useful extras as I would have liked to do. But for about $2500 or less you can heat proof your house better than you might imagine with this simple system.

(In our area we bought the convection powered turbines & ceiling fans at Home Depot.)