Home Innovation Insights

Craig Drumheller
November 22, 2012

'Tis the Season for (Percent Energy) Savings

While we're all in the holiday spirit of shopping for savings, let's take a look at savings as they pertain to energy codes. Similar to the appeal of advertisements for 50% off that cool winter coat you've had your eye on, energy savings have a very tangible appeal to consumers as well. But like all the fine print in the Sunday circulars, it's important to know all the factors at work when calculating percent energy savings so everyone knows what they're really saving or striving to achieve.

Over the past six years there's been a big push to increase the stringency of the model energy codes. It's come from many directions including energy advocates, ASHRAE, and the Department of Energy. The effort has gained a tremendous amount of traction; although no laws have been passed, even Congress has sponsored a couple bills mandating building code energy efficiency improvements. This has resulted in unprecedented energy savings in the nation’s model energy codes.

Along with this push comes a desire to set savings targets and measure the energy savings — some frequently mentioned targets include 15%, 30%, and 50%. But what exactly so these targets mean? Every time I hear a “percent savings” goal, my immediate response is “percent of what?” There are a number of ways a percent energy savings can be, and are, calculated. The many assumptions necessary to perform an energy savings calculation are neither obvious nor trivial.

In my experience, when a typical consumer is asked what a 50% increase in the energy code would mean to them, the response is that their monthly energy bill would be cut in half. This is consistent with the Energy Star HERS Index which is based on whole house energy use. However, while the now-expired Federal 45L tax credit provided consumers up to $2,000 if they were able to reduce their energy by 50%, it was only pegged to heating and cooling costs. When looking at energy savings from a builder’s perspective, it's difficult to put the burden of energy savings on items that builders cannot control such as miscellaneous electric loads (e.g., plugged-in loads such as TVs, microwaves, etc.). The scope of the International Energy Conservation Code (IECC) in 2006 included heating, cooling, and water heating costs. The 2009 IECC added hard-wired lighting to the scope.

According to the Energy Information Administration's 2005 RECS, the national average breakdown for an annual residential energy bill is:

  • Heating - 28%
  • Miscellaneous Loads - 24%
  • Water Heating - 16%
  • Cooling - 12%
  • Refrigerator - 8%
  • Major Appliances - 6%
  • Lighting - 6%

Given these averages, heating and cooling combined represent 40% of the total energy cost; adding water heating to the mix increases the percentage to 56%.

The table below illustrates the significance of the different interpretations in calculating percent energy savings. It shows that a 30% targeted energy savings could be interpreted as 30% of just Heating Cooling and Water Heating, which would be a 17% energy reduction for the whole house (total energy bill). Conversely, if the assumption is based on a 30% whole house savings goal, this would result in a 54% reduction in Heating, Cooling and Water Heating.

Baseline 30% Heating,
Cooling and
Water Heating
30% Total
50% Total
Heating, Cooling Only 42% 75% Not Possible
Heating, Cooling and Water Heating 30% 54% 89%
Heating, Cooling, Water Heating and Lighting 26% 47% 78%
Total Energy Use 17% 30% 50%

In addition to determining what energy consumption loads are included in the calculation, it is critical that a clear baseline is established with percent energy savings. Frequently the 2006 IECC is established as the base code. But, many specifications are not defined in a code, so it is necessary to define all parameters that affect energy use, especially the items that become new requirements in subsequent codes. Examples include duct tightness, building tightness, and lighting energy.

After the release of the 2009 and 2012 IECC, there were a lot of questions as to how much energy was being saved, but there was no defined methodology. The Home Innovation Research Labs developed a methodology to consistently calculate energy savings. Every parameter used in the energy calculation was defined in the methodology allowing a skilled energy modeler to repeat the energy savings calculations. The Home Innovation used the 2006 IECC and the scope of the 2006 code (heating, cooling, and water heating energy). We also applied the methodology to the 2009 IECC showing an average percent energy cost savings of 13.9%, and the 2012 IECC showing a 37.9% energy cost savings over the 2006 IECC reference code.

So, while there is still work to be done, a big chunk of residential energy use and percent energy savings can now be clarified and referenced consistently as a result of this methodology. Something for which those of us in the residential code area can be thankful.

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