Ching Dictionary of Architecture: Heat - Thermal Comfort

Ching Dictionary of Architecture: Heat - Thermal Comfort

Thermal Comfort = Human comfort as determined by the ability of the body to dissipate the heat and moisture it produces by metabolic action.

Psychrometric chart = A chart relating the wet-bulb and dry-bulb readings from a psychrometer to relative humidity, absolute humidity, and dew point.

dry-bulb temperature = the temp. recorded by the dry-bulb thermometer in a psychrometer. Indicated as vertical lines on the psychrometric chart

psychrometer = an instrument for measuring atmospheric humidity, consisting of two thermometers, the bulb of one being dry and the bulb of the other being kept moist and ventilated so that the cooling that results from evaporation makes it register a lower temp. than the dry one, with the difference between the readings being a measure of atmospheric humidity.

wet-bulb temperature = The temp recorded by the wet-bulb thermometer in a psychrometer. Indicated as diagonal lines on the psychrometric chart

Comfort zone = Range of dry-bulb temperature, relative humidity, mean radiant temp, and air movement judged to be comfortable by a majority of Americans and Canadians tested. This comfort zone varies with climate, the season of the year, type of clothing worn and the activity level of the individual. Also called Comfort envelope. Plotted location on the psychrometric chart.

dew point = the temp. at which air becomes saturated with water vapor. Also called dew-point temp.

Effective temp. = A temp. representing the combined effect of ambient temp, relative humidity and air movement on the sensation of warmth or cold felt by the human body, equivalent to the dry-bulb temp. of still air at 50% relative humidity which induces an identical sensation.

Humidity ratio = the ratio of the mass of water vapor to the mass of dry air in a mixture of air and water vapor. Also called "mixing ratio".

Relative humidity (rh) = The ratio of the amount of water vapor actually present in the air to the max. amount that the air could hold at the same temp., expressed as a percentage.

Absolute humidity = The mass of water vapor present in a unit volume of air.

Specific humidity = The ratio of the mass of water vapor in air to the total mass of the mixture of air and water vapor.

Hygrometer = Any of various instruments for measuring the humidity of the atmosphere

Enthalpy = A measure of the total heat contained in a substance, equal to the internal energy of the substance plus the product of its volume and pressure. The enthalpy of air is equal to the sensible heat of the air and the water vapor present in the air plus the latent heat of the water vapor, expressed in Btu per pound (kilojoules per kilogram) of dry air. Also called heat content.

Adiabatic heating = A rise in temp. occurring without the addition or removal of heat, as when excess water vapor in the air condenses and the latent heat of vaporization of the water vapor is converted to sensible heat in the air.

Mean Radiant Temperature (MRT) = The sum of the temperatures of the surrounding walls, floor and ceiling of a room, weighted according to the solid angle subtended by each at the4 point of measurement. Mean radiant temp. is important to thermal comfort since the human body receives radiant heat from or loses heat by radiation to the surrounding surfaces if their mean radiant temp. is significantly higher or lower than the air temp.

Radian heat = Heat energy transmitted by the radiation of electromagnetic waves in contrast to heat transmitted by conduction or convection.

Evaporative cooling = A drop in temp. occurring without the addition or removal of heat, as when water evaporates and the sensible heat of the liquid is converted to latent heat in the vapor. also called adiabatic cooling.