Energy Efficiency and the Energuide Rating System
Continuing down the path of exploring energy efficiency in houses, my next few blog posts will focus on some of the common energy efficiency standards in the industry, and their connection to the British Columbia Building Code, and each other. The first standard is NRCan’s Energuide Rating System for houses.
It is worth noting that we are currently anticipating the release of the 2012 BC Building Code (BCBC), however, it appears that any changes to Part 10 – Energy and Water Efficiency, will not be released until sometime in 2013.
The current BCBC Part 10 references NRCan’s Energuide Rating System as an alternative compliance path to satisfying the insulation requirements in Part 9 of the BCBC. In 2013, we expect that reference to the Energuide Rating system will no longer be as an alternative compliance method, but rather as a baseline standard not only for Part 9 insulation requirements, but overall energy efficiency for housing and small buildings.
NRCan Energuide Rating System
The basics of the Energuide rating system is a comparison of the overall energy usage of a designed house, versus that of a theoretical baseline reference standard house. Ratings are established between 0 and 100, with 80 being the expected code standard in the 2013 code. Currently 77 is the required rating for alternate compliance.
Energy usage considers the overall energy consumption (electric or fuel) of the house for items such as space heating, lighting and appliances, domestic hot water and ventilation systems, and also considers the overall energy loss through the building envelope, which factors thermal resistance (insulative values) as well as air-tightness.
Determining the Energuide rating starts during the design stage, where the house design is modelled by a Certified Energy Advisor using the simulation software HOT2000, and compared to the reference building. This process facilitates various trade-off and upgrade opportunities with various building components (ie. insulation, windows, mechanical systems, solar panels etc.) to achieve the Energuide rating ‘goal’ of 80 or better. Once the house is constructed, the Advisor is required to verify that as-designed systems are installed, and to perform a blower-door test to confirm the actual air-tightness rating for the house. This verification aims to confirm that the as-built house meets the ‘goal’ established during the pre-construction simulation.
What does Energuide 80 Look Like?
Compared to a house built to the 2006 BC Building Code, a standard house achieving Energuide 80 will generally see greater insulation values in walls and ceilings, additional requirements for basement insulation (walls and slabs), in addition to higher efficiency space heating, ventilation, and domestic hot water systems.
How Effective is the Energuide Rating System
The Energuide standard is one of several standards that are intended to consider the ‘house as a system’ overall evaluation, which is a big step from the basic prescriptive requirements Part 9 of the BC Building Code has always referenced. That being said, it should be understood that Energuide 80 is only a stepping stone to the Energy Efficiency targets we will see in the next decade.
Despite its improvements over the basic code requirements of the past, there are flaws within the system that should be recognized. The most basic flaw is the trade-off system without established minimum standards. Here, excellence in some aspects can overshadow failure or substandard performance elsewhere. Most other energy efficiency standards demand a hard-deck for most items across the board, whereas Energuide aims more for an aggregate evaluation.
The trade-off scenario can best be demonstrated in higher end homes, where there are more ‘toys’. Toys generally refer to things like high-performance, high-efficiency electric or fuel-fired mechanical heating and ventilation systems, solar-power systems and even geothermal heating systems. In a rating system based upon energy consumption, and more accurately ‘purchased’ energy consumption, better ‘toys’ can start to skew the numbers very quickly. For example, consider the hypothetical scenario where an un-insulated, non-airtight home is equipped with a ground-source geothermal heating system and solar power collectors. This house might achieve Energuide 80 or better rating simply because purchased energy consumption is so low regardless of excessive heat loss. While this example represents an unlikely scenario, it exposes the extremes of a trade-off system.
Consider another scenario where a homeowner pays top dollar for a high-efficiency heating and ventilation system, triple-glazed windows, additional insulation in the walls and ceilings, but the house is constructed with extremely high air leakage (5 or 6 ACH – refer to previous blog post “Ventilation and Whole Building Air Tightness” for a thorough explanation of air-leakage and Air Changes per Hour ACH). The Energuide rating can still balance out and achieve a rating of 80 or greater.
The unfortunate truth is the rating system allows an unacceptable air leakage rate to be tolerable. To compensate, the mechanical systems need to run longer and more often, costing the homeowner more money than they should. High efficiency units running longer than needed is counter-productive with respect to saving energy.
One would think this would result in a failure during the blower door test. However, while blower-door testing is a requirement to verify the whole-building air leakage rate of the house, it isn’t a pass-fail criterion as most people would expect. Despite the formality of the test, Energuide actually has no required minimum standard for air-tightness at all. The only requirement is to verify that the as-built air leakage rate isn’t worse than the input value assumed during the simulation.
Furthermore, it isn’t uncommon for energy advisors to seek the desired Energuide rating by assuming a high, or ‘worst-case’ air-tightness rating during the design simulation and then compensating in other areas. This way, there is little chance that the blower-door test will negatively impact the Energuide Rating during the as-built verification stage. If as-built air leakage is less than the modest assumptions; great!
Obviously it can be costly to improve the air tightness of a home once it has reached a stage where verification tests are being performed, but this can be a significant compromise towards being a truly energy efficiency house if as-built air-tightness proves equal to the worst-case assumptions.
Implementing prescriptive air tightness requirements are undoubtedly being considered for upcoming revisions to the Energuide Rating System, however they exist in other house energy efficiency standards such as R2000 and Passive House, which one could argue leaves the Energuide System trailing behind.
It’s easy to poke holes in standards and point out their flaws, but the intent here is to realize that Energuide 80 is by no means the pinnacle of performance, but rather the minimum requirement moving forward. There are houses being constructed to other standards that demand much greater overall energy efficiency. We will look at these other standards moving forward…