Variable-volume ventilation systems

In thermal models, the ventilation airflow rates normally arc input parameters, to be defined by the user or to be calculated by the program on the basis of a nominal air exchange or flow rate) and some control parameters (demand-controlled ventilation, variable air volume flow ventilation systems), in airflow models, on the other hand, room air temperatures must be defined in the input (see Fig. 11.49). 

Forced convective Far convectors These units give a high heat output for volume of space occupied by the unit, together with the ability to distribute the heat over a considerable area using directional grilles. May be used to bring in heated fresh air for room ventilation. Rapid response to conhol by individual thermostat. By use of variable speed motors rapid warm-up available in intermittent systems Altered fresh air inlet facility. Electric supply required to each individual unit. 2 to 25 kW. 

Variable air volume (VAV) laboratories are rapidly replacing traditional CAV laboratories as the design standard. These systems are based on fume hoods with face velocity controls. As the users operate the fume hoods, the exhaust volume from the laboratory changes and the supply air volume must adapt to maintain a volume balance and room pressure control. An experienced laboratory ventilation engineer must be consulted to design these systems, because the systems and controls are complex and must be designed, sized, and matched so they operate effectively together. 

Conceptually, the most straightforward way to demonstrate the ventilatory effects of brain hypoxia is to expose peripherally chemodenervated animals to a hypoxic environment. The results of sueh studies, however, are not uniform with the major eonfounding variable being arousal state. In awake, unanaesthetized, chemodenervated animals both exeitation and depression have been reported (as reviewed in Ref 2). The response most often observed consists of tachypnea with variable effects on tidal volume and httle or no ehange in alveolar ventilation. In one study, the tachypnea was related to an inerease in systemic metabolic rate and reversed by adrenergic blockade (3). 

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