Exergy Management between a Building and Its Environment for Residential HVAC

Efficient use of a large quantity of low-grade energy that is available in the earth surrounding a typical residential structure can be realized by designing a HVAC system directly integrating the ground source with a dynamic building envelope. A continuous air duct constructed within the dynamic envelope is configured such that preconditioned air in the basement can be circulated between the shells of the wall. The result is that a large portion of the heat loss through the wall is the geosolar heat extracted from the ground, reducing the load of the home heating system. Air in the ventilation system may also be passed through the heat reservoir such that make-up air is prewarmed and cleaned before entering the interior. This geothermal component of the heating system is further enhanced by increasing the ambient temperature of the earth with unwanted heat absorbed by the roof of the structure during the summer months. The roof of the structure is fitted with narrowly spaced runs of cross-linked polyethylene (PEX) pipe just below the roof surface. Water circulating between these coils and the ground serve to transfer summer heat into the ground while cooling the building. A horizontal blanket of insulation around the perimeter of the building allows heat removed from the roof to be retained for winter use. In addition, cool air from the ground can also be circulated through the dynamic walls during the summer to keep the structure cool. An extensive study involving this integrated building system has been carried out for the last 3 years, and observations of system performance are reported in this paper.