Preston Commons
The Preston Commons facility comprises two buildings located at 8115 – 8117 Preston Road in Dallas, Texas. Both the East and West buildings at this facility are eight story buildings on a braced steel structure with a curtain wall of stone tiles and insulated glass providing the decorative exterior finish. The buildings were built in 1990 and have not undergone any significant modifications since the original construction aside from a few mechanical upgrades.
Target energy use for this type of building taken from the US DOE’s Energy Information Administration CBECS energy use Table for office buildings located in the West South Central United States. Their number is 92.3 kBtu/ft2/year. These buildings are at 67.34 kBtu/sf/year, indicating that the buildings have an EUI below the average (more energy efficient), indicative of the energy conscious practices and upgrades in the buildings.
EE&D engineers identified 4 Low Cost / No Cost Measures and 3 Capital Improvement Measures. Added together the overall annual kWh reduction is estimated at 1,210,374 saving $85,482 per year. The total estimated cost of the identified measures is $99,980 with a simple payback of 1.2 years. This combined savings is 18% of the existing energy use and 13% of the existing energy cost.
Cooling for each floor of both buildings is provided by a central air handling unit (AHU) on each floor. Each AHU is fed chilled water from the central chiller plant which is shared between the two buildings. Air is supplied to the building at approximately 55° F and 1.5” static pressure, both of which are variable and can be adjusted by the Building Automation System (BAS).
The central chiller plant consists of two chillers, both of which are original to the building. Both the 650 ton and the 350 ton are York centrifugal chillers, providing chilled water to a common supply loop which is then pumped to each building with separate chilled water pumps. Condenser water is supplied from two induced draft cooling towers, both of which have fan VFDs.
Cooling for each floor of both buildings is provided by a central air handling unit (AHU) on each floor. Each AHU is fed chilled water from the central chiller plant which is shared between the two buildings
The heating and ventilation for each floor is provided through a variable air volume air distribution system served by the eight air handlers in each of the two buildings. Air is distributed through a ducted supply air system to terminal boxes located within the occupied spaces. Pneumatically controlled terminal boxes are control space heating and cooling, with each box having a dedicated temperature sensor/controller that acts as the control point. All heating for the facility is provided through the electric reheats installed within the fan powered perimeter terminal boxes.
The Building is equipped with a Building Automation System (BAS) with custom built graphics. All major equipment in the building is controlled with start/stop/status and temperature set points, including AHUs, chillers, pumps, cooling towers, and exhaust fans. The BAS does not extend to the terminal VAV boxes serving the spaces. These are controlled with individual pneumatic thermostats.