Projected energy usage and HERS rating for our green house in Houston
Amidst all the selections, pricing estimates and getting final decisions made in many areas, we are also getting some very exciting projections related to the energy efficiency of the house.
As background, our choice to go with regular stick-and-frame construction, as compared to SIPs or even concrete shells, was driven by budget. In Houston, stick-and-frame is remarkably affordable, making it hard to go another route, when you are trying to get to around $150/sq ft. The major concern was that stick-and-frame would limit how much can be achieved in energy efficiency. Current projections suggest that you can still get a pretty good HERS rating, and low energy costs with our approach.
To offset the choice of construction, we opted for a simple rectangular house shape, which gives you a good ration of volume to shell, making it inherently energy efficient. Then we positioned the windows out of the direct sunlight, and shaded them where possible. Add a metal roof, some good insulation, a sealed attic and you can get pretty far.
The HERS Index rates your house, just like Energy Star rates your appliances. You can read about HERS Index here. In summary, a HERS rating of 100 is the standard new home, in terms of energy consumption. A rating of 0 would be off the grid - a house that consumes no energy, by producing its own. Most existing homes are above a 100. Our '50s bungalow, with $500+/month a/c bills in the heat of the Houston summer is probably well above 100. Right now our estimate is below 60!!
This is very exciting, and will also result in additional LEED points. When doing LEED scoring, in the energy efficiency category, you can use HERS ratings to get a simple LEED point number. Our original estimates was at HERS 77, giving us 8.5 LEED points. Now we may gain more than twice that. Hmmm... This puts LEED Silver in the bag, and has been an impetus to look to see whether we can go further.
In dollars and cents, this also has an impact. We got a first estimate of the energy costs of our house - see below - and it is below $2,200 for the year. This is electricity only, which is heating and cooling and appliances. (Water heating, cooking and the dryer will all be gas.) This year, to date, we have already paid over $3,000 with one more month to go. And the projections are at 16 cents/KwH while we are paying around 13.5 cents for our renewable energy plan. So, taking that into account we could get as low as $1,850. So, our 3,200 sq ft new house might have 60% of the electricity cost of our 1,900 sq ft '50s scape off.
Posted
by Oliver Bogler
