Document YrQadew1511RpdYKnZz7QKRZy

170 CHAPTER 12 Hcnner Bird: Air recovery for economical air enwrfiiWitn* (Industrial Refrigeration, September 1954, p.'20). Homer Bird: Air recovery-for:churches-and fbnr.1^ (Church Property Administration, May-June, 1955). G. H. Hein:; Odor control by catalytic -n<4 higb-teperature oxidation- (Conference on Recent Advances in "Odor: Theory, Measurement andControl, New York Academy of Sciences, November 1963). - ..- ' JapOtBe: Threshold approach to estimating adsorber per formance (Conference oh Recent Advances in Odor: Theory Measurement' and Control, New York Academy of Sciences, November 1963). .. / R-:Ij. Kuehner: The validity of practical odor measurement methorte (Amuds;Neu> York Academy of Sciences, VoL 58, Art 2, March 24,1964, p. 175). '% . . > ' K. M. Michels et al; Odor and Olfaction--A Bibliography, 1918- 60 (Perceptual and Motor Skills, Monograph Supplement 6-v15 Purdue University, 1962). Odor Measurement arid Contrd: Proceedings, Third Annual Symposium- on Problems of Air'PoOidion (Franklin Institute Latnrawnes for Research and Development, Philadelphia. 1958). N^York?N*Y *W52)^ SibUogmphy (Airkem Inc., 1965 Guide And Data Book S**or Abstracts: A quarterly (ASHRAB, New York, 1964) N. A. Richardson and W. C. Middleton: Evaluation of Filt*+* fa. Rerntmng Irritants from the Air (University of California 57-48, Lba Angeles, June 1957). '. N. R. Rowe: Odor control with activated charcoal (Atr Pollu, Association Journal, Vol. 13, No. 4, April 1963). A?'_ R-. nowe:. Removal, of Contaminant Gases and Vapors by Mal963) *A2nencaa Association for Contamination Control, J&nnan Sharpe: Air Purification as a Means of Reducing Air Conditioning .Equipment and Duct Sizes (Air Conditioning and RefrigerationCalifornia State Polytechnic College, San TIenry^Sle& and'Amos Turk: Air Conservation Engineering (Connor Engineering Corp.`, Danbury, Conn., 1953): . .Amos Turk: Odor Measurement and Control (Air Pollution Abatement Manual, Chapter 13, Manufacturing Chemists Away^. action, 1960). , Vwssmao: Odor control in air-conditioned spaces (In dustrial Refrigeration, August I960; p. 16). - Wairen Viesaman: Ventilation control of odor (Conference on Recent Advances in Odor: Theory, Measurement and Control New York Academy gf Sciences, November 1963). - - CHAPTER 13 AUTOMATIC CONTROL FUNDAMENTALS: Types of Control Systems and Action/ System Components; Controls for Hoofing, Ventilating, andAir-Condition. 5ysfems; Controllers and Controlled Devices, Auxiliary Control Equipment; Controls for Refrigerof/on Equipment; DESIGN COORDINATION: Eqv/pmerrf Selection and layout; location of Controllers; Control of Steam, .Wafer or Air Flow; Zone Control- Control Application Limitations; Precautions; CONTROL APPLICATIONS: Centra/ Fan Systems; Temperature ' Control in Hot Water Systems; Zoned Steam and Water Systems; Terminal Equipment PRESENT-DAY standards of comfort, combined with back. It depends for its operation on a prearranged relation capacity and rapid response of -modern heating and ship between' outdoor temperature and heat input to the piling equipment, make automatic controls an essential part building, and room temperature has no effect on the con of heating, ventilating, refrigerating, and air-conditioning sys troller. tems. These automatic controls respond to variables such as temperature, relative humidity, and pressure. They operate TYPES OF CONTROL SYSTEMS individually or in sequence to maintain the desired conditions Control systems are divided into five main groups accord throughout the system and in the occupied space. A factor' ing to the primary source of energy:. that has the subject of automatic control somewhat rcpfiiamg has been the matter of terminology. Many different expressions have sometimes been used to convey a single idea or concept. This chapter, therefore, will attempt to use and ripfinn the terms that are most common and suitable, so that they will be readily understood. The terms'and definitions uyH are also selected to conform, as nearly as possible, to automatic control terminology used by engineers in other fields of controL PART I: FUNDAMENTALS OF AUTOMATIC CONTROL A control system, Fig. 1, consists essentially of (1) a' con troller, (2) a controlled device, and (3) a source of energy. A controller is a device which measures a variable condition such as temperature, humidity, pressure, and liquid level and produces a suitable action or impulse for transmission to the controlled devices. Thermostats, bumidistats, and pressure con trollers are examples. . A controlled device reacts to the impulse received from a controller and varies the flow of the control agent. It may be a valve, damper, electric relay, or a motor driving a pump, fan, etc. The control agent is the medium manipulated by the con trolled device. It may be air or gas Sowing through a damper; gas, steam, water, .etc., flowing through a valve; or an electric current. The controlled variable ia the condition, such as temperature, humidity, or pressure, being controlled. = /. Most control systems, of which Fig. 1 is typical, form a closed loop. That is, the controller measures and responds to 1. A self-contained system combines the controller and con trolled device in one unit and employs the power of the meas uring system to effect the necessary corrective action. The meas uring system derives its energy from the process under control, without amplification by any auxiliary source of energy, and may be of the sealed-bellows or remote-bulb type, as described under Types of Sensing Elements. Temperature changes at the bellows or the remote bulb result in pressure or volume changes of the enclosed media, which are transmitted directly to the operating device of the valve or damper. ' 2. A pneumatic system utilizes compressed air, usually..at a pressure of 15 to 25 paig, as a source of energy. This is supplied to the controller, which in turn regulates the pressure supplied to the controlled device. 3. A hydraulic system utilizes a suitable liquid under pressure as the source of energy. The pressure often is considerably higher than in a pneumatic system,- but in other respects the systems are similar. Hydraulic systems are mainly used in applications where large forces are required for operation of the controlled devices. 4. An electric system utilizes electric energy, other low or line voltage, as the energy source. The electric energy, supplied to' the controlled device is regulated by the controller, either directly or through relays. 5. An electronic system also utilizes electric energy,,but em ploys an electronic amplifier to increase the minute. voltage valuations of the measuring element to values required for operation of standard electrically controlled devices. There are three types of "mtang elements now being used: resistance elements, thermocouples, thermistors. Combination elec tronic-pneumatic systems utilize oompressed air for operation of the controlled device by converting the output of the electronic amplifier into suitable air-pressure changes, by means of an eleo* tronic-pneum&tic transducer. changes in the controlled variable and actuates the controlled device to bring about an opposite change which is again measured by the controller? This system of transmitting information about the results of an action or operation tack to its origin is known as feedback, and makes true automatic control possible. An open-loop system is sometimes employed in control circuits, but it does not provide complete control. An out SOURCE OF. OENERGY vUIRCVTOEANMRTRPIAOEBRLLLAEETDU.RE)(*/(R-E-SE-M-E-L-ONE--TMS--EI-EN' NGB6TtULB) , I CONTROLLED .DEVICE (VALVE) .CONTROL AGENT-, (STEAM)T door thermostat arranged to control the. flow of heat to a building in proportion to the load caused by changes in [U_f.ED_BAC AIR FLOW ` outdoor temperature is an example. This system has no feed- Th* CaacraJ responsibility for this chapter is to TC 10.1,' Control. Fig. 1 .... Essentials of a Control System. 171