Unique Integration of Hot Water Heat Recovery into Low Exergy Heating

There are many technologies aimed at reducing energy demand of ventilation systems, but thefocus in these designs has remained on the airheating system and exhaust losses. In fact, atypical daily exhaust air requirement for oneperson has the same quantity of exergy as thewater fi-om a typical shower, and thus heatingsystems must also consider hot water.This project presents the exergy analysis ofintegrating wastewater heat recovery into abuilding heating system. A heat pump providesroom conditioning and hot water heating. The"low exergy" heating minimizes the temperaturelift required by the heat pump as well as thetemperature differences at heat transfer surfacesin the heating system. This maximizes theperformance of the heat pump and minimizesthe exergy destroyed in the system. An exergyanalysis provides a detailed loolz at the energydemand and the appropriateness of the qualityof the energy utilization. The exergy analysis ofthe system is part of the research in the Swissparticipation in the IEA ECBCS Annex 49: LowExergy Systems for High PerformanceBuildings and Communities.The analysis shows that the exergy availablein warm wastewater can be used to augment theevaporator temperature of the heat pump. Theroom heating system functions with large heattransfer surface areas (i.e. TABS) at 30 C, andwhen hot water needs to be produced at highertemperatures, the temperature lift of the heatpump reniains low by augmentation from hotwastewater. The optimization and performancecharacteristics of this high performance systemare presented.