We’re so used to overhead forced-air ventilation, heating and cooling systems that we neglect to design buildings with other technologies for comfort. The figure below shows the four key variables for human comfort: air temperature, relative humidity, air movement and radiative temperature (the temperature of surfaces). Think of your own experience standing next to a cool brick or concrete wall on a warm day but not feeling uncomfortable because of the radiant-cooling effect of the wall. Or, consider a masonry or brick stove (the old “Russian” stove) radiating heat for hours even after a fire is out.

In commercial buildings, radiant cooling strategies are getting a new look, through the introduction of “chilled beams” (fins with water tubing that can circulate cool water, providing a surface that appears cool to our bodies even with warmer-than-normal air temperatures). Radiant floors can also be used for heating in cooler climates or for cooling in buildings that require year-round air conditioning. They can also be used in assembly spaces (such as an atrium of a larger building) when exact temperature controls are not required. One LEED Gold-certified renovation project even poured a thin concrete slab on top of an old wooden floor to install radiant heating tubing.

The benefit: often the size of other building HVAC systems can be reduced, saving money on initial costs, since less air movement is required for comfort (and since most fan systems are sized for cooling, not just for ventilation). In addition, air temperatures can vary by 3ºF to 4ºF in either direction outside of a normal range, without occupants feeling uncomfortable. With higher air temperatures, less energy is required for cooling and less fan power is used for air movement. Elementary physics tells us that hot or cold water contains a lot more heat (heat capacity) than the same volume of air, and that far less energy is required to pump water than to blow air to get the same comfort effect. Why fight nature?