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One method developed was to reduce the amount of outside air introduced in a building to a minimum. This saved energy, since there was less outside air to heat and cool; and also saved operating dollars as energy cost skyrocketed.

Reducing outside air became the law. The federal government issued "energy guidelines" which were adopted by some states. Other states developed their own guidelines. Unfortunately, there was no time to exhaustively study the impact on the building occupants due to this reduction of outside air. As we discovered later many buildings reduced the outside air to a level that caused discomfort and, in some cases, sickness. The phenomenon became known as "Sick Building Syndrome".

Guideline requirements included a standard for outside air based on occupancy. The figure most often given was five-CFM per person maximum or 0.033 CFM per square foot based on one person per 150 gross square feet.

In practice these figures are so small that outside air needs for general exhaust, toilet exhaust and to pressurize the building often exceeded the code. The new ASHRAE standard 62-1989 provides a table based on type of occupancy specifying outside air requirements. For normal office occupancy this is 20 CFM per person minimum.

This standard was developed to ensure that adequate oxygen is delivered to the occupied space and the change rate is sufficient to reduce toxic gases, particulates and other pollutants to safe levels.

Existing buildings designed to operate using "energy crisis" outside air quantities can present a problem under the new standard.

For example an increase in the cooling load for an office building ranging between 20 to 25% is possible when changing from 5 CFM to 20 CFM per person. It is unlikely that sufficient spare capacity is available in the cooling plant.

Heating plants often have spare capacity but have a problem with distribution and coil sizes. Further, mixed air temperature was sufficiently high to avoid preheat coils. By quadrupling the amount of outside air many systems will need a preheat coil added to the system.

One possible solution is the heat exchanger. This device which is available in many configurations has been used in Europe for many years on all types of facilities including private homes and in the United States in R&D facilities.

It is worth noting that some state codes have always required greater amounts of outside air based on occupancy. New York is one of these. The intent of the new guidelines however require that the absolute quantity of outside air delivered to a space remains the same under all operating conditions. This means that for variable air volume (VAV) systems the outside air must remain the same even though the total supply air is reduced. Many present day systems are not designed this way and outside air is proportional to the supply air delivered to the space.