Energy conservation in buildings: design and monitoring of an office building with a GSHP and a phase - change thermal storage system

The paper describes a recently completed office building, located in the industrial area of Chieri (25 km SE of Turin), which incorporates several energy saving features: high energy performance envelope, reversible GSHP for year-round HVAC, hot and cold phasechange storage, variable-flow water pumps, low temperature heating / high temperature cooling terminals (chilled beams), green roof. The HVAC system uses different solutions according to the destination of each area: primary air and ceiling-mounted fan coils in the ground floor, and active chilled beams in the offices and meeting rooms. The AHU allows sensible heat recovery with an air-to-air cross-flow heat exchanger, and heat recovery from the heat pump condenser for summer humidity control. Two water-to-water reversible ground-source heat pumps (GSHPs) provide hot water in winter, and chilled water coupled with recovered hot water in summer operation. The winter heat source / summer heat sink is a geothermal field consisting of 31 borehole (vertical) single pipe heat exchangers, 100 m deep. Both the hot and cold hydronic circuits include a phase-change storage tank using eutectic salts. The storage tanks are connected in parallel to the GSHPs allowing a significant reduction of installed HP capacity. Variable flow rate pumps with inverter control are used for hot and cold water circulation. A yearly energy analysis was developed, in which the proposed system performance was compared with a conventional alternative, consisting of a gas-fired boiler and an electrically-driven air cooled water chiller. The energy analysis indicated a 46% reduction in primary energy consumption. The estimated system payback time is 8.6 years.