Teaching an old school new tricks

The El Paso Independent School District, El Paso, TX, commissioned Alegro Engineering, L.P., to implement IAQ improvements to two elementary schools and one middle school, to provide individual classroom control during heating and cooling seasons and maintain humidity at 60%. Alergo Engineering designed a system with central AHUs and variable flow terminal units with hot water reheat coils to each space and classroom. The hydronic portion of the systems included air cooled chillers and constant flow primary pumping systems, while all secondary pumping systems were provided with two-way valves. The AHU preheat coils were selected to increase the temperature from the local winter drybulb to 90F. All reheat coils were selected to increase the temperature from 53, while the AHU supply air temperature, wither by pre-heating the air or by bringing enough outside air (OA) to maintain temperature during the winter months, is at 90 to maintain space temperature.