Creativity in HVAC design. Part 2

Second article in this series. Describes a second type of system that supplies 100% outdoor air, and is projected to save significant energy over standard HVAC. Notes that nearly all schools and large buildings in the US and many other nations operate on the principle that, to control energy costs, building ventilation systems must recycle a majority of indoor air that is already heated or cooled. In the name of energy conservation, many building owners and managers set their ventilation systems to bring in too little outdoor air. This frequently allows carbon dioxide and other indoor air pollutants from increasing to undesirable concentrations. The system in question is a geothermal HVAC system which is competitive in cost and is expected to avoid 20% to 40% of annual energy costs. Energy is derived from a closed-loop pond system. Claims that the 100% outdoor air system with heat recovery consumes 38% less energy than the conventional recirculation system at design conditions. In essence, the system, with a 70% effective wheel, is equivalent in operating cost to a conventional system that brings in only 30% outdoor air. The total cost avoidance includes reduced labour costs. The hybrid system pumps the relatively warm pond water through coils of tubing to 179 water to air heat pumps inside plenum closets in classrooms and other spaces inside the school. An added advantage of the system is that each classroom has its own heat pump and thermostat.