The performance of these systems is totally dependant on the accuracy of remote input data and its programming to satisfy the promises of efficiency and energy savings. This is especially true if it is to be accomplished without negatively impacting mandated ventilation rates. To ignore minimum ventilation rate requirements is to magnify the already burdensome financial risk and direct health costs due to IAQ-related injuries and illness. Highly accurate and economical measurement products are now available to provide the electronic data input for unit ventilator or ERV intake control. Minnesota statutes now require schools to monitor both outside airflow rates and total supply flow rates to each classroom going into service or renovated after July 1, 2002.
Airflow control is much more stable and reliable than differential pressure control.
In Mr. Williams' example, the exhaust fan speed can be much more easily controlled at a constant volumetric differential, between measured intake flow rates and the ducted exhaust rates. It would provide the greater precision and a more energy efficient means to achieve positive building pressurization. Direct measurement is the only way minimum outside air could be efficiently and reliably controlled at a continuous rate.