High performance passive buildings are comfortable by design: quiet, draft free, and evenly warm.
Unlike conventional buildings that rely on energy-intensive mechanical equipment to blast hot or cold air to compensate for uncomfortable design flaws – design flaws that we have all taken for granted as “normal” – high performance buildings deliver comfort through their very construction.
As the image above shows, an assessment by the US Department of Energy’s finds that the comfort delivered by Passive House buildings is dramatically superior to both ENERGY STAR and conventional buildings.
Why? First, high performance passive buildings are comfortable because they are built airtight. (Worried about indoor air quality? Read here about the fresh air ventilation strategies that provide superior air quality to high performance buildings.) By controlling the movement of air, we are also controlling the movement of heat and moisture, two fundamental determinants of human comfort. Nobody enjoys a damp, cold draft on a blustery winter day. Airtight construction eliminates the air leaks that rob structures of comfort. Second, passive buildings are comfortable because they are thermal bridge-free. A thermal bridge is any building element that cuts across a building’s insulation, or “thermal envelope,” and facilitates the transfer of heat between inside and outside. Thermal energy is so good at finding the path of least resistance that thermal bridges can become superhighways of thermal loss from a building and make interior surfaces cold and uncomfortable. By carefully detailing building assemblies and wrapping the exterior of buildings with continuous, monolithic insulation, high performance building designs can eliminate these energy-sapping thermal bridges.
Our goal is to isolate, or “thermally break,” the building’s interior from the outside environment. A uniform thermal break with superinsulation creates even interior surfaces temperatures in a building, a key component to occupant comfort. Because the human body is such a sensitive sensor of hot and cold surfaces nearby (radiant temperature), a cold wall will make you feel chilly, even if the air temperature is a warm 72 degrees. The natural occupant response is to crank up the thermostat and burn energy blasting warm air into the building. But that mechanical response doesn’t address the actual cause of the discomfort. By providing even, warm surface temperatures, high performance envelopes address the problem at its root through passive means.
These even conditions also help establish even ambient air temperatures in a building. Because warm air rises and cold air falls, the uneven surface temperatures and leaky envelopes of conventional buildings means that air at head level can be too warm while air at your feet is too cold. Or the air on the second floor is unbearably warm while the ground floor is chilly. The natural occupant response? Crank up that thermostat, maybe open a second story window. Again, this not only wastes energy, it doesn’t address the root cause of the problem. High performance buildings and their even surface temperatures provide constant, comfortable air temperatures throughout the building.
High performance buildings are also draft-free. This is partly thanks to the airtight construction that eliminates air leaks through the building envelope. But even an airtight building can be drafty if full of cold interior surfaces. These cold interior surfaces cause convection currents. Take the inside face of a typical mediocre window, for example. Warm interior air will hit that cold surface, cool, drop, skid out along the floor, warm back up, rise, hit the windowpane again, and repeat the cycle. Behind every poor window you’ll have a nice draft established by this loop. Even if interior air temperatures are 72 degrees, if you’re sitting next to a window you’ll be uncomfortable with that draft on the back of your neck. High performance buildings with good windows and thermal bridge-free construction solve this problem.
Comfort has a powerful visual component, as well. Occupant happiness depends on access to views outside and natural daylight, especially in the Pacific NW. Contrary to the myth of the Passive House as a windowless “thermos,” high performance buildings and generous glazing are naturally complementary. In fact, when deployed well, high quality windows are often “energy positive,” meaning the daylighting benefits and passive solar gains captured by the windows more than offset any thermal loss through them.
These energy positive windows do raise the potential for overheating during certain hours of the day, in non-winter months. That’s why solar management systems (eg. operable exterior shades) should be part of most high performance building projects. That way the building can capture passive solar energy when it’s needed and shield it when it’s not.
All these strategies come together to elevate occupant comfort to levels that are simply in a different league than those we experience in “normal” buildings. Here’s what the owner of Pumpkin Ridge Passive House has to say about his experience:
“When you put a little more thought and a little more attention into the engineering of the house, you have a house that’s really comfortable, that you really enjoy, that you can stay in for the rest of your life and that you don’t want to leave. I don’t know that I can say that for any other houses that I’ve lived in.”