Our contractor used our house as an opportunity to apply for status as an Energy Star builder. It worked. He’s now an Energy Star approved builder, and we have a 5+ star Energy Star home. In the process we discovered a big difference in the projected energy usage by our Energy Star certified rater using REM/Rate and our certified PassivHaus consultants who used the PassivHaus spreadsheet.
First a bit of background. At the beginning of this project we briefly considered certifying the house under one or more of the prevailing certification programs, PassivHaus, The Thousand Home Challenge (THC), LEED and Energy Star. (At the time there was no Net Zero certification.) In the end we decided it was not really worth the cost or effort for PassivHaus or LEED. Most of these certifications have little to offer the homeowner besides bragging rights. We felt that a verifiable record of the performance of the house over time would be enough bragging rights for us. (We’re still considering trying for the THC, but the spreadsheet leaves us a bit bewildered).
We did hire a certified PassivHaus energy consultant (DEAP Energy Group) to run the numbers on our proposed design to estimate our required heating loads, energy usage and required PV array to get to net zero. After all our research, I felt the PassivHaus spreadsheet offered the most accurate projection of energy usage and the associated training for certification promised that there was some intelligence applied to using the spreadsheet. We were very happy with the analysis and feel confident that the results will be confirmed after our first year in operation. We’ve purchased energy and temperature monitors to provide some data for analysis at the end of the year.
Although we had opted out of the certification programs, our contractor, Warren, decided that this project was an excellent opportunity to apply for status as an Energy Star builder, which would grant the house an Energy Star rating if it met all the conditions. (For a house to be certified as an Energy Star home, it has to be built by an Energy Star certified builder. The general process is described on the Energy Star site, How New Homes Earn the Energy Star.) Energy Star represents the lowest hurdle out of the other certification programs, but is also the most widely used. There are several versions of certification available, from 2.0 (now unavailable in 2012) to 2.5 and 3.0. Each version is more stringent than the previous. These versions are timed to replace the prior versions over time. After reading through the high-level requirements, we thought we’d be able to easily qualify under the 3.0 version.
However, because we were already many months into the build before we engaged the energy star certified rater, Newport Ventures, we missed the opportunity to be certified under the newer 2.5 or 3.0 standard. Our choice of HVAC contractor also contributed to this problem, as they were not certified under Energy Star requirements. If we had done our homework earlier, we might have been able to certify under one of the higher standards. So although the house is more efficient and built to more stringent standards than even the 3.0 version, we were only able to qualify under the 2.0 version.
One of the steps in the Energy Start certification process is to rate the efficiency of the house. The result is a HERS (Home Energy Rating System) index value. It is an index value (percentage) because it compares the efficiency of a specific house (ours in this case) with a reference model home that is based on the 2006 International Energy Conservation Code (new house efficiency / model house efficiency = HERS index). The lower the value the better the efficiency. For an excellent review of HERS, see Martin Holladay’s article on GreenBuildingAdvisor, How Is a Home’s HERS Index Calculated? He also describes the various pros and cons of using HERS.
To qualify as an Energy Star home, the house must earn a HERS index value of 85 or better. The lower the value the more efficient the home.
Warren got the final report (Home Energy Rating Certificate) a few days ago. Our HERS index, as rated by Newport Ventures, is 22 which equates to a 5 1/2 star Energy Star rating. We should have been happy, right? We were, except for one thing, we were expecting it to be zero or negative. One of the hallmarks of HERS is that a Net Zero house should get a zero index value or lower.
Unfortunately the certificate itself is quite vague. It doesn’t make it clear whether the power generation capability was included in the score or not, although it appears to be included. It projects our heat load to be half what the PassivHaus spreadsheet indicated (6.9 vs 12.4 MBTU/yr.) and it projects our lighting and appliance load to be much higher. HERS projects our total energy usage to be 42.4 MBTU/yr., DEAP projected 20.4 MBTU/yr. The HERS heating estimate alone makes me suspicious.
We’re going to try to get a bit more clarification from Newport Ventures in the coming weeks. We didn’t expect the numbers to match up exactly, but we did expect them to be in the same ballpark. We will report back when we learn more.