North Dorchester High School – New Construction

The installed HVAC system for the North Dorchester High School is a combination Geothermal system / Variable Refrigerant Flow (VRF) system as follows:

The School utilizes Ground coupled heat pumps which are water source heat pumps that operate at extended water temperature ranges. Ground coupled heat pumps do not require heat rejection and generation equipment, such as cooling towers and supplemental boilers associated with standard water source heat pumps.

Variable speed distribution pumps are being used for circulation of the heat transfer fluid.  The heat transfer fluid is water.

The terminal heating/cooling equipment system consists of several indoor terminal fan coil units connected via refrigerant piping to multiple interior compressorized units.  The system is provided with specialized “branch selector” boxes provided by the manufacturer that are able to redirect refrigerant flow to all units in each zone served by a “branch selector” box.  This arrangement allows simultaneous heating in one zone and cooling in another zone.  This arrangement also permits the refrigerant system to act as a heat recovery system.  Heat removed from a zone operating in cooling is transferred to a zone requiring heat.  All indoor units are provided with variable speed fans, allowing the fan to operate with the minimum required fan power to heat and cool the space.  Each indoor unit is also  provided with a dedicated thermostat to permit individual space temperature control. 

The compressorized sections consist of one or more variable speed compressors.  The variable speed compressors allow the compressorized section to speed up and slow down as required to provide only the amount of heating and cooling as required by the system.  The result is a significant reduction in the power consumed by the compressor(s) for heating and cooling the building.  The compressors used in this system are connected to a geothermal ground loop system.  For this system, the Earth is used as the heat sink for both heat rejection and heat absorption accomplished by circulating fluid through piping loops installed in vertical wells. 

The water source heat pump units are primarily constructed to be the re-circulating air type do not have sufficient capabilities to condition the ventilation requirements associated with the spaces.  Therefore, separate Energy Recovery Ventilators with heat wheels designed specifically for the conditioning of outside air were provided.  These units, operating at 100% outside air, are ducted directly to each space to comply with current ventilation requirements.   The Energy Recovery Ventilators are provided with chilled and heating water from a dual temperature system.  In addition, each ERV has been provided with an enthalpy wheel, heat pipe, variable speed fans, and air flow monitoring stations.  The dual temperature system will consist of water to water geothermal heat pumps creating chilled and heating water. 

The energy recovery ventilators are provided with variable frequency drives and demand controlled ventilation.  The ventilation system monitors the carbon dioxide levels and allows the ventilation system to reduce airflow rates when the occupancy and carbon dioxide levels allow.

Project Type: K-12,