How high do energy bills have to go before you take action? Countless people still pay 20% or more than they have to, when they could save by just changing billing agents, called “providers” with a few minute phone call.
After arranging for the lowest possible electricity cost, it is time to take some physical actions to improve your system efficiency and cut waste. You can follow the big advertisers and spend thousands in efforts that will save some energy but nothing near what is claimed. Often, those changes do not make much of a dent in the energy bill. What is going on?
Some real solutions may be easier and less expensive than you think. It is always more cost effective to deal with the largest cost factors first.
The sun delivers 1,000 watts per square meter of heat energy to every Texas roof, creating a 150 F furnace built into every asphalt shingled attic. To make things even worse, most AC systems in our area are located right in the middle of that inferno, and with little insulation to boot, hence wasting a lot of your energy budget just fighting that attic oven.
Moving the AC system into conditioned space would help, but is not economically feasible for most houses. There are other options.
Some common choices
Attic vents lead the way for cost effective benefits. This is usually simple, read cheap, and lets some of the hot air out of the attic. Unfortunately, the benefit is generally limited to an attic temperature reduction of a few degrees. This will reduce your electric bill, but only by a small percentage.
Most houses older than 10 years have little or no insulation in the attic. Adding insulation has very rapid cost payback, up to about 6 inches. More helps but drops in cost effectiveness and does nothing to cool the attic.
A radiant barrier in the attic might save as much as 10% of the AC bill, but with the AC portion of electric costs running about 50%, this means only 5% of the total, at best. Government data suggest radiant barriers in the attic have at least a 25 year payback. While a radiant barrier reduces the heat energy radiated from the roof deck inside the attic, it does nothing for the bulk of the heat incursion which is transferred through conduction to the attic air space.
Shade screens only reduce sunlight heat that is directly radiated into the windows. There is no benefit for North or South facing windows. Shade screens do nothing for conductive heat transfer from the hot air outside.
Window replacement can definitely reduce energy costs, but at $400 a pop typically have payback periods of well over 20 years.
AC systems, as typically installed, are usually gross wasters of energy. Most systems work significantly below their potential with leaky/open ducts, inadequate insulation, inefficient units, etc. Thus, an important step is to fix your AC system. Unfortunately, most people, including some AC technicians, seem to think that if cold air blows out of the vents, it is fine. Very few installations would not benefit from careful examination and simple improvements.
The essence of the problem
Although somewhat helpful, all of this is a bunch of band-aids on a gushing energy hemorrhage. Surely we can do better than that. Let’s look at the basics. AC is the largest home energy cost in the South TX area, so this is where we need to concentrate our efforts.
Heat comes into our houses from three sources:
1. Heat generated in the house – incandescent lights, appliances, heaters, and people [each person radiates over 300 watts just being present]. Anything that can be done to reduce heat generating usage saves some energy.
2. Heat comes in through the building envelope due to elevated outside temperature – with an indoor temperature of 78F and an outside temperature of 100 F, the temperature differential [heat driving force] is only 22 F. The bulk of the associated energy loss is easily contained with three inches of insulation. Even single pane windows provide some significant blocking of heat transfer. A few air leaks have little noticeable effect either. Pier and beam houses are usually not insulated underneath, so that can generate a big additional cost, but can be fixed with insulation.
3. Here is the real biggie – The sun gives us direct heat radiation of about 1,000 watts per square meter. Asphalt shingles absorb well over 80% of this heat and convert the roof deck into a 150 F furnace. So our ceiling temperature differential runs more than twice as much as the walls.
But that is not good enough. Let’s put the AC system and ducts in the attic too, with little to no insulation. Now we have a temperature differential between all of the coldest air in the AC system and the highest house temperature in the attic of over 110 F! That is a real energy driving force.
It would be very expensive and difficult to bring those AC systems back into conditioned space for most houses. Even those houses with the AC system in conditioned space are losing gobs of energy just from hot attics, even with good insulation.
The real solution
It is almost amazingly simple: Put the radiant barrier outside, on the roof, and reflect as much as 95% of that 1,000 watts/sq. meter – problem solved! Once the attic is no longer grossly overheated by the sun, it only conducts a similar amount of energy as the walls. The AC systems work less, last longer, and thinner insulation is far more effective.
Actual cost savings on my house dropped the AC costs by 61%, on 100F days, and my AC is in conditioned space!
That is not all, the reflective roof coating also extends the life of my roof by at least 10 years, and it reduces the potential for storm damage in the process. The cost is about 2/3 the cost of a new roof covering, with a fast payback period.
Reprinted by Permission. Stephen Ruback is a licensed Professional Inspector; member of TAREI, and HAR; approved by TREC as a Professional Home Inspection Instructor. In addition, he has earned a BS in engineering from Trinity University, is an author of several books and teaches a variety of self-empowerment courses. For more information, call 832-489-1071, visit www.sruback.com or email firstname.lastname@example.org
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