Monday, September 10, 2012

Getting it right

One of the reasons I know there are no easy ways to energy efficiency is because I know how much work it is to pull off.  My brother has been trying to get his arms around the problems of how to make a dwelling provide shelter with the least amount of energy inputs since at least the 1980s.  Last week, he got the news that a project he's been involved with was named the first Department of Energy Challenge Home in the country.

Legitimate questions could be asked as to why it took until 2012 for DOE to finally find a way to honor such efforts.  It could also be asked just how relevant a 4500 square foot home is to the need for building a nation filled with energy-efficient homes.  I won't even speculate on why DOE has been sleeping at the switch, but I have NO problem with letting rich folks pay to prove new technologies.

Here's how he explained this project to me.

The Dept. of Energy has had a program that had several versions of what is, or was, called Builders Challenge. It is very simply a different version of the EPA’s Energy Star program, although Energy Star gets more involved with certifying appliances, windows, individual components, etc., than whole house verification.

Energy Star does have a whole house program, but their main deal is components. Builders Challenge is what it sounds like, challenging builders to build more energy efficiency into their products, using Energy Star products to achieve that rating.  So Builders Challenge was a part of DOE’s impetus to ‘compete’ with LEED, National Association of Home Builders (NAHB), Green Globes, Florida Green Building Coalition, and many more. Well, in an effort to keep up, they are always lowering the bar, so to speak, trying to have the program that is the most efficient, all the while trying to also be cost effective. There is a point where being efficient crosses the line from being cost effective to being ridiculous. Spending thousands to be so efficient that there is such a long return time on investment that it is not practical is foolish to a certain extent. So the balancing act has become a vital part of all of this. So, the latest, greatest version of Builders Challenge went into effect Sept 1, 2012. To avoid confusion, they renamed it DOE Challenge Home.

So when the time came to submit the home we are currently certifying to the DOE, they asked if we would like to be their ‘guinea pig’ and try to get our home certified under the new program’s protocol. Heck yes, was my answer. So I spent about 2 hours on the phone with the programs software writers, another 2 on the phone with their Building Science guys, and together we walked this very cool home we are certifying through their system, worked out a few ‘bugs’, and came out with a very prestigious rating, a great marketing opportunity (the builder has already posted it twice on his Facebook page), we all learned how their system is going to work, and we all won. Being 1st with a certification in the US is a pretty neat deal.

This house we are working on has been a real handful getting certified. It is a 2 story Autoclaved Concrete structure that has a LOT of very cool features to save water, electricity & resources that ended up with a HERS Rating of –7. Autoclaved Aerated Concrete (AAC) is a very interesting product, and building a 4305 sq. ft. home out of it proved to be a very interesting project.

Since you are probably not familiar with this product, here is the link to the website for the main structural product in the home we are certifying: This is the first time I have come across it and I found it a very cool product. It is so light, an 8” x '8” x 32” block of it will float in water, It provides a ‘R’ value of 24 verses 4 for normal concrete block, offers a 130+ mph wind certification, 0 thermal bridging, needs no added insulation, so there is no drywall required. To run electric and plumbing, you cut a trough, run your utility, and simply patch the hole with a glue like plaster that bonds permanently in about 12 hours, then sanded like drywall mud, and an 1/8“ of plaster finishes the wall with a perfectly slick finish that looks like a drywall wall. You can then leave it slick or texture it, then paint it. On the outside, a plaster finish is all that is required there too. So, you have a very beautiful, solid concrete wall that has no mold producing tendencies, great insulating values, wind protection, nothing to burn, a renewable product that is very sustainable, and by the time you are done, no more cost that a concrete block wall. That is how a sustainable wall would be best described.

We have certified it LEED Platinum, NAHB Emerald, FGBC Platinum, Energy Star, DOE Challenge Home, Florida’s Water Star Gold, and all with a HERS Rating of –7. All of the wood flooring was salvaged from a couple of 1950’s local homes, and all of the plants are drought tolerant and will require little or no irrigation. 70% of the run-off from the roof is captured in a 7000 gal cistern to flush the toilets, the 2 urinals and any irrigation needed on any plants. There is a 6500 gal salt water lagoon just outside the front door that will be maintained with captured rainwater, as well as 3 large saltwater aquariums in a special room visible from the living area but separate from the living space’s environment. And the back porch roof is a 14 KW PV array, that is waterproof and also allows about 10% of the sunlight that hits it through the panels to light the porch during the day, and that light also produces electricity because the panels are bifacial. All the lighting in the home is either LED or Low voltage (12v).
Like I said, it is a very cool house.
The main reason this house has won so many awards is that it has a HERS rating of -7.  On a scale where lower is better, the typical existing home comes in around 140 and a well-built new home ranges from 85-100.  This home is VERY energy efficient plus has around 15 KW of solar panels so it actually captures more energy than it consumes—hence the negative rating.

How Is a Home’s HERS Index Calculated?

It’s time to pull back the curtain to look at the algorithms used to come up with a HERS Index score

It's like golf — the lower the score, the better.

Anyone involved with the Energy Star Homes program has probably heard of the HERS Index, a method of scoring the energy efficiency of a new or existing home. A Web page maintained by the state of Arkansas, for example, explains that the “EPA requires a house qualifying for Energy Star to be built with best practices, tight ducts, and at least 15% more energy efficient than code as shown by a HERS Index score of 85 or less as determined by a HERS Rater.”

Knowing that the HERS Index measures a home’s energy efficiency is a good starting point. But it’s useful to dive a little deeper, to understand how the Index is calculated and exactly what it measures.

Defining the HERS Index

The HERS (Home Energy Rating System) Index was established in 2006 by the Residential Energy Services Network (RESNET), a California-based national association of home energy raters and energy-efficiency mortgage lenders. The lower a home’s HERS Index, the more efficient the home.

To calculate a home’s HERS Index, a rater uses a computer program — most commonly, REM/Rate. (RESNET has also approved three other software programs for calculating the HERS Index.) After the rater has entered data about the home into the program, REM/Rate compares the home being rated to a “reference home.” The reference home is an imaginary home of the same size and shape as the home being rated. In other words, the size of the reference house is not fixed; when a house is being rated, it is always compared to a reference house of the same size as the rated house.

The reference home does not have the same window area or window orientation as the home being rated; instead, the area of the windows in the reference home is assumed to be 18% of the floor area of the rated home. The windows of the reference home are assumed to be evenly distributed on the four orientations of the home.

The reference home is assumed to barely meet the 2006 International Energy Conservation Code; if the home being rated has thicker insulation or better window glazing than the imaginary reference home, those improved specifications will result in a lower (better) HERS Index.

Lighting and appliances are accounted for

The HERS Index accounts for on-site energy production, if any, and energy used for lighting and appliances. The reference home is assigned a budget for lighting and appliances; if the home being rated includes energy-efficient appliances or lighting fixtures, these items can help lower (improve) the home’s HERS Index.

The imaginary reference home is assigned a HERS Index of 100. Most existing homes have a HERS Index over 100, since most existing homes fall short of the requirements of the 2006 IECC. If a rated home gets a HERS index of 100, it can be expected to use the same amount of energy as a code-minimum home of the same size — a home equipped with “typical” lighting and appliances that are operated according to average American usage patterns.

If a rated home gets a score below 100, it will use less energy than a code-minimum home. A score of 0 corresponds to a net-zero-energy home.

Each 1 point decrease in the HERS Index corresponds to a 1% reduction in energy consumption compared to the imaginary HERS Reference Home. A home with a HERS Index of 70 uses 30% less energy than a code-minimum home of the same size and shape.

“The HERS Index measures the relative performance of your home with respect to a home of equal geometry that is constructed exactly as the HERS reference home is constructed, using a standard set of appliances that are operated according to a standardized set of operating assumptions,” explained Philip Fairey, deputy director of the Florida Solar Energy Center. “The reference house has the characteristics of the energy envelope requirements in the IECC. But the IECC addresses only heating, cooling, and hot water, while the HERS index addresses all energy uses.” more
This building used a lot of great technologies but the most interesting may be the structural concrete so not only is this house energy efficient, but is rated for 130 mph winds.  This is Florida that gets hammered by hurricanes so this is no small matter.
AERCON is not only the name of a company but the name of a product that is changing the future of industrial, commercial and residential development in the United States. Precast Autoclaved Aerated Concrete (PAAC) has been used throughout the world for decades; however, AERCON (PAAC) buildings have been constructed in the United States with minimal national awareness. With an impressive list of benefits that includes superior fire protection, acoustic and thermal insulation, versatility, durability, and light weight along with reduced construction time and labor costs, AERCON offers an innovative building material for the next generation. more
My brother's rating service
The Winter Park builder 


  1. That's congratulations to your brother on such a great achievement.

    I've always maintained that even my 100 year old little house given my spartan homelife and south-facing roof would go negative energy 9 months/year; but given my underwater mortgage and employment situation there is 0% reason/opportunity to make the investment to find out.

    And I'm not alone in that predicament, which is a big reason why the USA expectation for private-only conversion toward green energy means only about 25% of housing is even in play to consider greening up.

    Heck, the USA is so overbuilt in housing stock, I bet 25% of all housing stock is empty...there are more empty houses than homeless people in most towns.

  2. Yes indeed Mike, even though we are finally figuring out how to build these super-efficient homes, the economics of the era will keep them from being built. This home is being built in the Orlando area where the housing market has collapsed. What is so sad about all this is that we just went through a building boom that produced hundreds of thousand new homes—the overwhelming majority probably came in at a HERS of over 100.

  3. It’s too bad that these options weren’t explored or presented to possible homeowners during the building boom. It would have saved them all the effort in trying to make their home as energy-efficient as possible and save on future utilities, as well as enjoy a cozy home.


  4. It’s nice that people are taking the time to do the Builder Challenge, as it provides new concepts on how to make an energy-efficient house without sacrificing aesthetics and appeal, and vice-versa. Hopefully, the output of these challenges would become a standard in home building, or at the very least, part of the catalog for it.

    Rolf Matchen

  5. It's not too late to make your home energy-efficient. Anyone who plans to renovate their roof, windows, and doors might benefit from your story. They must coordinate with their contractors for their energy-efficient homes. It's been a while now, and I hope you'll continue to encourage more homeowners to make their homes energy-efficient. :)

    Vernia Kale @ Muth Roofing