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Thermal Comfort

Short term thermal comfort evaluations are sometimes conducted in Building America field test houses to evaluate the thermal comfort effect on different types of windows, sliding glass doors, window shades and radiant heating and cooling systems. For windows, the measurement set is normally located 4 feet away from windows. For radiant heating and cooling systems, it is usually located at the center of the room. Long term evaluation of thermal comfort is generally not recommended, because thermal comfort is generally not an issue in mild seasons, and is likely to be a concern only under extreme weather conditions. It is also recommended to avoid placing the measurement set in direct sun light, which causes local discomfort that does not truly reflect the building components and systems performance and cannot be evaluated effectively by the radiant asymmetry sensor.

The thermal comfort parameters are mean radiant temperature (MRT), air temperature, air velocity, relative humidity, clothing level, and metabolic rate. The thermal comfort instrument set that is usually deployed in the field includes: a MRT sensor, a radiant shielded dry bulb temperature sensor, a temperature and relative humidity (T&RH) sensor, a hot wire anemometer, a radiant asymmetry sensor, and a data logger with software calculating thermal comfort with user input clothing level and metabolic rate. The sensors are located in series on a rack, as shown in the figure below. The short term measurement will generate predicted mean vote (PMV) and percent of people dissatisfied (PPD), as the most comprehensive index of human object thermal comfort [1].

Alternately, in the retrofit context, operative temperature measurement using MRT and air temperature may be used to as a metric for partial thermal comfort prediction. In high performance homes, operative temperature measurement does not have much value, as its operative temperature readings always normally come close to air temperature readings.

Photos shows a thermal comfort instrument set up during a field test. It consists of one metal bar resting atop a tripod with several sensors emanating upward from the bar including: an MRT sensor, a radiant shielded dry bulb temperature sensor, a temperature and relative humidity sensor, a hot wire anemometer, and radiant asymmetry sensor.

Thermal comfort instrument set during a field test.
Ed Hancock

 

References:

1. ASHRAE. 2004b. ANSI/ASHRAE Standard 55-2004, Thermal Environmental Conditions for Human Occupancy. Atlanta: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.