part or assembly that aids the effec­tiveness of equip­ment without changing its function.

1. vessel for storing low-pressure-side liquid refriger­ant; also known as a low-pressure receiver, surge drum, surge header, or surge tank.

2. pressure vessel whose volume is used in a refriger­ant circuit to reduce pulsation.

3. pressure vessel connected to more than one circuit of a pneumatic system to obtain the average pressure of the connected circuits.

4. apparatus to store cold by accumula­tion of ice on a coil.

1. conformity of an indicated value to an accepted standard value, or true value. Quan­titatively, it should be expressed as an error or an uncertainty. The property is the joint effect of method, observer, apparatus, and environ­ment. Accuracy is impaired by mistakes, by systematic bias such as abnormal ambient temperature, or by random errors (impreci­sion).

2. degree of freedom from error, that is, the degree of confor­mity to truth or to a rule. Accuracy is contrasted with precision, e.g., four‑place numbers are less precise than six‑­place num­bers; nevertheless a properly computed four‑place number might be more accurate than an improperly computed six‑place number. 3. ability of an instrument to indicate the true value of a measured physical quantity. Compare precision, reliability, repeatability.

ACH (ACPH)

air changes per hour.

1. science of the production, transmission, and effects of sound.

2. characteristics of a room that deter­mine the qualities of sound therein, relative to hearing.

word formed from the initial letter, or groups of letters or words, in a set phrase.

form of carbon made porous by special treatment by which it is capable of adsorb­ing various odors, gases, and vapors.

device, either electrically, pneumati­cally, or hydrauli­cally operated, that acts as a motor to change the position of movable devices such as valves or damp­ers.