MECHANICAL VENTILATION AND EQUIPMENT
Mechanical ventilation systems for controlling conditions in individual zones can move a constant or variable supply of conditioned air to handle all or some of the heating and cooling loads. They are classified as all-air, air-water, and all-water systems. All-air systems include single-duct, dual-duct and multizone. The systems can be designed to operate at Constant Air Volume (CAV) or Variable Air Volume (VAV). Air-water and all-water systems are categorized as two-, threeand four-pipe. The Air Handling Unit (AHU) is the main air conditioning and treatment equipment. A typical AHU consists of a single volume unit with a supply fan, heating coil, cooling coil, humidifier where necessary, filters, mixed air economizer dampers, and sound attenuator. The air distribution is a key element for the successful operation of central systems to deliver the air to the conditioned spaces in an efficient way, satisfying the indoor environmental conditions as economically as possible. The air is then distributed by the ductwork and is delivered by the air-diffusion outlets. Proper circulation and exhaust must satisfy the indoor environmental quality. Mechanical ventilation systems provide great flexibility for controlling the indoor conditions, if properly designed, installed, commissioned, operated, and maintained. Proper controls can optimize their use, enhance flexibility, and improve energy efficiency. On the other hand, poor design, installation, and performance can lead to serious Indoor Air Quality (IAQ) problems, and cause thermal and acoustical discomfort, with a high energy cost.
Diagnostics for Outdoor Air Ventilation and Economizers
Today, most problems with building systems are detected as a result of occupant complaints or alarms provided by building automation systems. Building operators often respond by checking space temperatures or adjusting setpoints (or thermostat settings). The root causes of operation problems not diagnosed, so problems reoccur and the operator responds by making another adjustment. The BACnet TM standard will contribute to easier implementation by providing a standard mechanism for communication between diagnostic software and devices.
Hapten inhibition of passive antidextran dextran anaphylaxis in guinea pigs. Role of molecular size in anaphylactogenicity and precipitability of dextran fractions.
High titred antidextran antisera have been raised in rabbits by prolonged immunization with soluble conjugates between isomaltose oligosaccharides or dextran mw 4,400 and bovine serum albumin in complete Freund’s adjuvant. Guinea pigs sensitized with such antisera exhibited anaphylactic shock on i.v. challenge with fractions of hydrolyzed B512 dextran. The severity of anaphylaxis depended on the amount of sensitizing antibody and the dose and molecular size of the challenging dextran fraction. In maximally sensitized animals, fractions of mw 3,600 or larger were anaphylactogenic and smaller molecular size fractions were nonanaphylactogenic. In submaximally sensitized animals, dextran fractions of mw 10,500 or less were foundnonanaphylactogenic. In addition, nonanaphylactogenic dextran fractions produced desensitization, i.e. protection from anaphylaxis due to subsequent or simultaneous injection of more high molecular and anaphylactogenic dextran fractions. When the molar ratio in a mixture of nonanaphylactogenic/anaphylactogenic fractions was about 7.6, protection was complete with reduction of mortality from 100 to 0%. A molar ratio of 1.9, corresponding to a 13-percent by weight admixture of nonanaphylactogenic dextran, still significantly reduced mortality from 100 to 50%. From the ability to form precipitates with antidextrans and to elicit anaphylaxis in sensitized guinea pigs, and from the absence of these properties, the approximate molecular size range of bivalent and monovalent dextran B512 fractions was found to correspond to mw 3,600 and mw 1,430, respectively. The practical applicability of hapten inhibition is discussed.