WHAT CAN BE DONEThe ideal, energy efficient building would have compensating air equal to actual exhaust air requirements - no more, no less. A positive pressure can result in excessive energy operating costs, particularly if overhead doors are opened frequently or for long periods. A positive pressure can also drive fumes into office areas and other spaces. If a building has a negative pressure condition, several things can be done to improve the efficiency and comfort of the facility including:A) Evaluate the existing exhaust systems1) Consider how much exhaust is actually required to accomplish the ventilation goal. Excessive exhaust is extremely expensive to operate. For example, if natural gas costs $9.00 per Mcf, in Northern Indiana a single 48" ( 20,000 CFM) exhaust fan, could cost as much as $37,200 each year. Do the math - over a fifteen year period, that single exhaust fan could waste over $550,000.2) Operate exhaust fans and makeup air heating systems only when necessary for proces or safety requirements. The savings to operate makeup air heating equipment for only one shift, five days per week can be significant. For example, operating makeup air heating equipment for only one shift can save approximately $1360 per 1,000 CFM each year in Madison, WI.3) Investigate local ventilation instead of general ventilation. Localized capture of heat or contaminants is usually much more effective and energy efficient than general ventilationB) Install automatic controls1) Install temperature control or a timing device for automatic control of exhaust systems. In many cases, the addition of a simple thermostat or time clock can significantly reduce operating costs. If the building doesn’t need the exhaust, it doesn’t need the makeup air.C) Install air cleaning or heat reclaiming equipment1) In many cases, a combination of general air cleaning and localized exhaust can provide a very effective and efficient means of improving indoor air quality while reducing exhaust requirements D) Install additional makeup air equipment1) Proper makeup air equipment may be as simple and inexpensive as an outside air intake louver or it could require separate makeup heating equipment to bring in and condition outside air. The best, energy efficient approach for a particular building can only be determined after careful evaluation of all building characteristics, process requirements, and employee considerations.