When you think of comfort,
perhaps the first thing you think of is a plush leather couch, or maybe it is a sunny beach, it could even be a crackling fire. Whatever comes to your mind, it probably doesn’t include shivering or sweating. Safe to say, then, that perhaps the first principle of comfort is the right temperature. While those of us who are married certainly know that our spouse’s ideal temperature can be different from our own; science has taught us a lot about thermal comfort in the home. Some of the basics are:
- Understanding heat transfer
- Mean Radiant Temperature
- Hot and cold surface temperatures
- Air movement
While these are only the basics of thermal comfort, most builders and even HVAC contractors do not understand them; yet the many assumptions and decisions they make when building a home can have an adverse effect on your personal comfort. The American Society of Heating, Refrigerating, and Air conditioning Engineers (ASHRAE) has an entire publication devoted to this. Has your HVAC contractor even heard of it?
Click the expandable sections below to learn more about the consistency of ICF homes.
Understanding Heat Transfer
Have you ever been outside in 50 degree air, yet comfortably warm when the sun is shining brightly on you? Or have you ever felt chilly, even when the air temperature was 70 degrees? If so, you have experienced heat transfer through radiation, and it is not related to air temperature. Radiation is the primary way our bodies experience temperature in our homes.
“Heat rises”. We’ve all been told that for years, and most of us have probably repeated it at one point or the other. But did you know that it is wrong? The second law of thermodynamics states that heat moves from hot to less hot. True enough, warmer air that rises, while cooler air sinks. We will take this up a little later. For now, consider what the second law means for our comfort in our homes.
In winter, the coldest thing in the house is typically the windows, with the walls being a close second. Even if you have an Energy Star rated window, it can perform as low as R-3.1! That is hardly impressive. That feeling of being cold is heat moving OUT of our bodies, and being radiated to a colder surface.
Ideally then, we want the surface temperatures in our home to all be very similar to each other, and the MRT to be very close to the HVAC setpoint—the temperature at which we set our thermostats. If our homes are built in such a way that allows the windows, walls, and basement floor to have surface temperatures significantly cooler than the ideal air temperature, we will be uncomfortable next to them. We will want to sit in front of the fireplace, or move away from the windows toward the inner part of the room.
Even Temperature and Humidity
What we experience as discomfort is in principle uneven temperatures. Room to room or even within a room. Particular rooms in the home may be warmer or cooler than other rooms for many reasons, such as poor HVAC design, greater heat loss, or more air leaks.
At R-Value Homes we relieve the frustration of moving to the inner part of a room, or wearing layers in the home; or the annoyance of overcooling to try to remove the humidity, or running a humidifier to keep from getting a shock every time you hug your kids. We do this by carefully selecting our materials and components to maintain highly consistent surface temperatures and MRT throughout the home, to reduce air leakage so much the HERS rater thinks his blower door is broken, and incorporating HVAC systems designed for comfort, not low price.
Mean Radiant Temperature (MRT)
The temperature that we actually feel in the home is the mean (average) radiant temperature—the average of all the surface temperatures our body “sees” at any given moment. This is why a room with many large windows can feel cooler than one without windows, when the air temperature is the same. While the air temperature can affect and be affected by the MRT, we don’t feel the air temperature in our home, we feel the MRT.
As we intuitively know, moving air impacts our comfort; and inside a conditioned home, it is always an aggravating feeling. Air movement can come from many sources, including:
- HVAC system moving intermittent high volumes of air (link to HVAC page)
- Leaking walls, windows, floors allow airflow when the wind kicks up (Link to Airtight page)
- Convective loops
- Convection causes drafts, even when the HVAC system is not running, and even if the house were perfectly airtight (its not). Here’s how it works: Warm air next to a cool surface, such as a window or wall, cools off and sinks, causing warm air from the interior of the home to move in and take its place. This air then cools off and sinks, and the process repeats. The greater the temperature difference between the interior and exterior of the home, the greater the convection, the more uncomfortable the occupants.