We engineers sometimes get so caught up in HOW to do something we lose sight of WHY we’re trying to do it in the first place. So it was refreshing to listen to the recent episode of the 99% Invisible podcast, Thermal Delight, for some new perspectives on comfort in buildings; ideas primarily gleaned from leaders in the fields of architecture and design. I’d encourage everyone to listen to it for themselves as it raises some thought-provoking ideas around comfort in buildings. If you’re pressed for time, skip ahead to about 18:00.

When HVAC and building controls engineers talk about comfort, the discussion primarily revolves around setpoints. The default response to any issue or complaint regarding comfort is “Are we meeting setpoint?”, followed closely by “Do we need to change the setpoint?”. Research would suggest that this approach reveals a poor grasp of the factors that actually go into determining whether or not someone is comfortable in a space. It assumes a very static view of comfort when, in reality, comfort is relative and impacted by a number of factors that are continuously varying. Knowing that it is very easy to see why HVAC systems that depend on static setpoints with limited input from occupants have an extremely low rate of satisfaction. We like different things at different times, and our preferences are shaped by our mood, age, cultural norms, clothing choices, outside conditions, to name a but few of the variables. There are no handy calculations that tell you how to factor these things in, so it’s no wonder that the engineers who design HVAC systems have long focused almost exclusively on variables they can reliably control.

Worse yet, the principals upon which most HVAC systems have been designed and are controlled are simply out of step with the science of comfort. How we achieve comfort is also not only about space temperature, but also includes things like radiative factors, air movement, and even which specific body parts are being heated or cooled. Dumping hot or cold air into a space, as most HVAC systems do, is actually not the best way to make people comfortable. Human beings are much more complicated in this regard than thermistors, yet these devices mounted on the wall around offices everywhere remain the principal means of providing feedback on conditions to the HVAC control system.

Fortunately, solutions are starting to emerge from industry and academia to address these shortcomings. Individual comfort controls, for example like the system offered by Comfy and a growing number of control system vendors, allow occupants the ability to provide direct feedback into the building automation system. This essentially turns the occupants into the sensors and provides the ability to directly measure and respond to the main thing we really care about, whether or not the people in the space are comfortable. This is certainly a significant step forward from relying solely on space temperature thermostats for feedback.  Many in the industry worry that turning over control to occupants will mean chaos and endless thermostat wars but, if implemented correctly, personalized HVAC controls have been shown to greatly improve occupant satisfaction as well as productivity. Work is being done currently to take this concept even further by using AI trained on large datasets of occupant experiences to predict in advance occupant comfort preferences.  The machines will know what we want before we do.

While there is no doubt that we can make the comfort experience “less bad” by making HVAC systems more responsive to occupants, rethinking the fundamentals of how we deliver thermal comfort has the potential to allow us to achieve true Thermal Delight in our buildings. We have all experienced this at one time or another; think about the sensations associated with experiences a cool summer breeze or sitting in front of a fire. There can be a tremendous pleasure associated with thermal comfort. Most HVAC systems, designed first and foremost to provide stable indoor air temperature, are simply incapable of delivering this kind of experience. Research in this area is focusing on so-called personal comfort devices. These include the humble operable window, but also ultra-quiet desk fans, heated foot pads, and advanced office chairs with heating and cooling built in. The office of the future will start to look more and more like our cars in terms of their comfort systems.  These personal comfort devices can be IOT enabled so that they integrate and work with the base building HVAC systems. Traditional HVAC probably isn’t going away any time soon, the necessity of maintaining good air quality and reasonable ambient conditions remains, so these systems will have to work together.

[an error occurred while processing this directive]Perhaps most surprisingly, there is an abundance of data to show that this greatly improved comfort can be achieved while using significantly less energy in our buildings. These energy savings arise from the ability to have much wider deadbands on space temperature setpoints. Space temperatures can be allowed to drift to a much greater degree knowing that occupants have the ability to adjust their own comfort. Modelling suggests that these widened deadbands can save between 15%-30% of the HVAC energy in a building, depending on climate. In addition to energy savings, there is also the very real operating savings associated with reduced hot/cold calls, not to mention the tremendous impact of improved occupant productivity.

For too long our industry has focused on the physics of comfort, largely ignoring the psychological and physiological aspects. We have once again played right into the stereotype of our profession by designing systems that work reasonably well for the engineer but have poorly served the needs of the people in the buildings. It’s time we focused on better understanding how people actually experience thermal comfort and design systems that can truly deliver thermal satisfaction and even, dare I say it, enjoyment.