ASHRAE Terminology

water from on-site sources (i.e., air-conditioning condensate, stormwater, etc.) that is collected and treated to acceptable levels for nonpotable uses.

liquid formed by condensation of a vapor. In steam heating, water condensed from steam, in air conditioning, water extracted from air, as by condensation on the cooling coil.

pump used to transfer condensate from one point in a system to another receiver, usually installed with a receiver tank and a float valve, the pump being controlled by tank level.

a variation of solution heat exchangers, used on steam-fired, double-effect machines and on some single-effect, steam-fired machines. Uses the condensed steam to add heat to the solution entering the generator.

removable plug or key-operated draw-off valve intended to permit the removal of fluids or condensates.

phenomenon encountered when the condensate does not wet the cold surface but settles in the form of separate droplets.

steam heating in which a return pipe carries both condensate and air. The return pipe is always above the waterline in the boiler in a gravity system.

(1) general: piping arrangement to maintain a common liquid level or pressure between two or more chambers. (2) refrigeration: piping arrangement on an enclosed compressor to equalize refrigerant gas pressures in crankcase and suction, also a device for dividing the liquid refrigerant between parallel low side coils, also a piping arrangement to divide the lubricating oil between the crankcases of compressor operating in parallel or in tandem. (3) steam: piping arrangement to equalize steam header pressure and condensate return pressure in a steam boiler.

phenomenon encountered when the condensate wets a cold surface to form a continuous film that separates this surface from the vapor.

(also known as steam systems), a steel tank that allows any superheated condensate to be vaporized into saturated steam. The tank is usually vented to atmosphere.

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.

condensate return arrangement for low-pressure steam heating systems, featuring a constant waterline in the boiler.

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.

(1) device that is capable of discerning the loss of refrigerant charge in a refrigerating machine and of reacting to protect the apparatus from motor burnout. (2) splitting of a condensate line to permit vapors to pass above and condensate to pass below an obstruction.

piping system in which the condensable vapor withdrawn from the supply main passes into a heating unit and returns as condensate to the same supply main.

plate, wall, or partition that is designed to perform one or more of the following functions: (1) prevent contact of food with refrigerated surfaces, (2) prevent dripping of condensate on food, (3) regulate and/or direct circulation of refrigerated air.

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.

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.

(1) in a refrigeration system, where the connections between the evaporator outlets and the low pressure receiver through which the mixture of vapor and overfeed liquid is drawn. (2) in a steam system, where a return pipe carries condensate, the pipe is usually located below the level of the waterline in the boiler.