Ahhh....the comforts of home. If a home is “efficient,” surely it’s “comfortable,” right? Not necessarily.
While “energy efficiency” has commonly been quantified by calculated measures in the home building business, discussions of “thermal comfort” traditionally involve more subjective evaluations. Human comfort depends on an occupant’s metabolism and the clothing being worn. It can be influenced by sunlight coming through windows on a hot day, the size of the heating and cooling system, the level of insulation in walls, and other architectural and design factors. Occupants perceive it from the air temperature surrounding them, the air circulation that prevents a room from feeling “stuffy,” humidity levels, and several other factors.
The home building industry is committed to delivering high-performance homes. To that end and with an eye on innovation, IBACOS believes the industry needs a way to objectively measure, predict, and compare a home’s overall ability to deliver comfort to its occupants. We call it a Thermal Comfort Rating Metric, or a TCRM, to help builders deliver on their commitment.
Because thermal comfort and energy efficiency are not the same, we can’t accurately predict a home’s thermal comfort using only energy-efficiency metrics. We also don’t think that the complex ways comfort is measured by building scientists translate well for builders and home buyers. The TCRM could be a single number, a score, or an index—much like RESNET’s Home Energy Rating System—from, say, 0 to 100. While the HERS Index represents the ability of the home to save energy, a simple TCRM would gauge the ability of the home to maintain comfortable conditions—two very different and possibly competing concepts.
Who would benefit from a TCRM? Everyone. Let’s consider today’s buyers, who have greater awareness of energy efficiency, sustainability, and conservation. They appreciate quality, value, and simplicity. A TCRM would enable them to gauge how well a home—a combination of systems, materials, and assemblies—would provide thermal comfort. It would give them a way to consider how much they weight comfort in the context of energy efficiency and home cost.
For builders and trades, the comfort callbacks that traditionally have been an industry issue are not disappearing in today’s low-load homes. Many builders reserve a substantial amount of money per house to cover insurance and warranty callbacks. Likewise, a warranty callback costs an HVAC contractor $250 to $400 per instance. A thermal comfort rating system could better tune buyers’ expectations to the homes they are buying and would help develop a commissioning list that would allow better comfort performance to be built into homes, thereby reducing the number of callbacks. Builders would also gain better insight into the values of their customers and be able to focus energy savings strategies in areas that also provide the most comfort, for example, if that’s what buyers in their market demand.
Likewise, a TCRM could be used to improve individual systems of a home. For example, there is a need for heating and cooling equipment to be "right-sized” now more than ever. A TCRM can help guide HVAC system selection by bringing specific performance attributes to the forefront as part of a value discussion that includes comfort.
Finally, a TCRM also could help builders differentiate themselves, allowing comparison of their homes’ performance and comfort against those of their competitors. Ultimately, a TCRM would be a means to quantify comfort before the sale and during the build process, as well as a tool to help manage buyers’ expectations and risks associated with comfort to show that the comfort performance delivered is as promised.
What IBACOS is seeing in our research data and hearing from builders and buyers is that some comfort problems are not being solved by low-load homes. In fact, the evolution toward low-load homes seems to create new opportunities for comfort to be an issue. Simple things such as balancing airflow from ducts have become more challenging and more important than ever. Also, the orientation of the home now plays a greater role. For example, a concentrated area of windows can allow localized solar gain, but the thermostat doesn’t respond because the areas of the home close to the thermostat are meeting the thermostat temperature setting. Likewise, today’s codes and building standards are not able to define a home’s ability to provide thermal comfort in a language that the home building industry can use. But these codes and standards, and the science behind them, can certainly be used to help develop components of a TCRM.
During the next few years, IBACOS plans to work with the industry to conduct research to weigh the many aspects of comfort delivery, compare differences by climate zone and house size, and give consideration to factors such as architecture, enclosure type, heating and cooling systems, and occupant preferences. Yes, it’s a huge undertaking that must incorporate complex sciences ranging from physics to psychology. By working with key industry leaders, builders, manufacturers, and codes and standards organizations, IBACOS seeks to validate the approach and ultimately bring a Thermal Comfort Rating Metric to the residential marketplace.
