ASHRAE Terminology

apparatus in which the walls are cooled in order to condense and trap vapors, can be used to reduce pressure.

product of minimum height (h) and minimum width (b) of the front opening of a sand trap louver assembly with the louver blades removed. Also see core area of an air terminal device.

surface cooled below –244°F (–153°C, 120 K) in order to condense vapors. Can be used to reduce pressure.

piping arrangement for collecting oil or liquid refrigerant from suction gas prior to entry to a compressor.

(1) leak in a liquid system. (2) liquid which appears on thawing frozen food, water melting from evaporator, or water droppings from a cooling surface. (3) pipe or a steam trap and a pipe considered as a unit that conducts condensation from the steam side of a piping system to the water or return side of the system.

method of separation and automatic return of liquid refrigerant from an accumulator in the low side to the high side of the plant.

(1) capability of a building, assembly, component, product, or construction to maintain serviceability for which it was designed over at least a specified time, based on assumed levels of use and maintenance. Compare to serviceability. (2) the average expected service life of a system or facility. Individual manufacturers quantify durability as design life, which is the average number of hours of operation before failure, extrapolated from accelerated life tests and from stressing critical components to economic destruction.

device, usually applied at a dust-generating source, that traps dust particles suspended in the air or gases passing through it. Compare to filter.

system that traps dust particles in the gas or airstream passing through it.

see steam trap.

steam trap that relies on the density of water to raise a float-and-lever mechanism to operate a valve head. It discharges condensate as it forms and enters the trap body. It includes a thermostatic balance pressure or bimetallic air vent to allow free passage of air on start up and discharges incondensable gases reaching the trap during operation.

a device or arrangement of the piping entering and leaving a water heater constructed to counteract the convective forces of the heated water (thermosiphoning) during standby periods.

see steam trap.

steam trap in which the inlet is channeled to the bottom of the trap body so that the condensate enters underneath the inverted bucket. A small hole in the top of the bucket helps discharge incondensable gases and entrapped air. The outlet from the trap is at the top and, as long as the trap is filled with steam, it floats in the condensate and keeps the outlet closed. The valve opens when the trap fills with condensate, sinks, and discharges the condensate into the return line.

(also known as liquid slug), accidental trapping of liquid refrigerant at any point in the system.

device for collecting liquid refrigerant at a given point in a refrigerating circuit.

trap with an adjustable bellows and steel valve head located downstream of the steam system. It operates on temperature rise, with the setpoint adjustable from the outside. It discharges at a fixed temperature for protection from freezing and for high-capacity venting requirements.

device for separating and collecting oil at a given point in a refrigerating circuit.

represents the net amount of infrared radiation absorbed by gases in the atmosphere. The radiative forcing of a gas depends on the efficiency with which it traps infrared radiation and its concentration in the atmosphere. Atmospheric concentration depends on emission rates and the atmospheric lifetime of the gas.

in freeze drying, the pressure of the gas (usually air) at the trap.

device intended to allow the passage of outdoor air or exhaust air while minimizing the ingress of airborne sand. Also see louver.

in a refrigeration system, an arrangement for gravitational separation of the larger impurities from a refrigerant.

device for allowing the passage of condensate and preventing the passage of steam, or for allowing the passage of air as well as condensate. Common steam trap types include float and thermostatic (F&T) traps, inverted-bucket traps, and thermodynamic traps.

accumulator installed in the suction line between evaporator and compressor to trap liquid carryover from the evaporator and to prevent it from reaching the compressor.

steam (disk) trap constructed with a cap containing a steel disc, which fits against a flat seat. Condensate, discharging at close to saturation temperature, increases in velocity and draws the disc down toward the seat, due to the lower pressure caused by the increased velocity (Bernoulli effect). Condensate discharging from high to low pressure flashes off and creates the closing pressure above the disc within the cap. As this flash steam condenses, pressure is dissipated, and the cycle repeats. The trap has limited air venting capabilities.

trap installed on the discharge side of a heating unit and designed to pass air freely on start-up and condensate at a subcooled temperature, but to prevent steam vapor passing into the return. It can have a bellows or encapsulated metallic diaphragm containing a small quantity of volatile liquid. At the bottom of the diaphragm or bellows is attached a hardened, self centering valve head operating on the pressure side of the valve seat. At ordinary temperatures and atmospheric pressure, the valve is fully open to permit free passage of air and cold condensate. The trap discharges at a fixed temperature below that of steam saturation temperature and closely follows the steam pressure/temperature curve.

trap installed where low-temperature discharge is required. It incorporates a bimetallic element that, when heated, deflects and causes a downstream valve head to be drawn up, closing the orifice. It discharges air and cold condensate freely on start-up.

device for preventing passage of one type of fluid, often while allowing other fluids to proceed. Compare to steam trap.

(1) opaque ice in which air or salts present in the raw water are trapped. (2) saturated vapor containing liquid droplets in suspension.