Page 50 - Zero Net Energy Case Study Buildings-Volume 2

CASE STUDY NO. 8
IBEW-NECA JATC TRAINING FACILITY
tor remains as originally planned, providing some pleasant direct sunlight to the central common space, where diffuse controlled daylight is not really required.
The daylighting is coordinated with the operation of electric lighting, which consists of simple T8 fluorescent lamps in linear pendant light fixtures. The electric lights are dimmed in response to daylight sensor readings and programmed light levels as appropriate for each space. Generally, light levels are set at 50-75 footcandles in workshop spaces and 20 footcandles in computer classrooms. LED light sources are used only in high spaces with industrial area fixtures.
Natural Ventilation
The local marine climate provides for the opportunity for “free cooling” for much of the year, which aligns with the predominant demand for cooling of the many internal spaces. During normal op- erating hours, sufficient natural ventilation for free cooling is achieved by using the retrofitted openable windows in the clerestory bands at the exterior walls as the air inlets and the operable vents in the sides of the new roof monitors as the air outlets. Air transfer openings are used in in- ternal walls to provide the cooling air to the other interior building spaces using the high operable vents in the roof monitors above those rooms. The height of the roof monitors creates a certain amount of air buoyancy and also a natural drafting effect as exterior breezes pass over the roof.
To make sure that this method of creating airflows through the building is reliable and would work at the level of a room occupant, the design team carried out a CFD analysis (“computational fluid dynamics”) for typical spaces. This analysis showed that the desired quantity and path of airflow could be achieved under typical outdoor air conditions at the site.
This natural ventilation approach is designed only for “free cooling” purposes; it is not intended to satisfy minimum fresh air requirements for the building occupants under full heating or cool- ing operation, so there are no CO2 sensors in the spaces. When the windows and roof monitor vents are open, the HVAC system is not permitted to operate in heating or cooling mode. The HVAC system fans, however, can move additional untreated cool outside air in specific spaces as needed to augment the naturally drafting ventilation airflow there.
Heating, Ventilating and Cooling Systems
As in Case Study No. 7, the DPR Construction Office Building, the design engineers recognized the importance of avoiding the use of a central HVAC system with large fans and ductwork ex- tending through the building. A distributed approach with smaller fans and smaller local ductwork, the more energy-efficient approach, was adopted. With the JATC Training Facility, however, the nature of the program spaces and the large floor plate of the building can often require heating of one space at the exterior while cooling another space at the interior. This can occur when outdoor air temperatures are moderately low, requiring heat at perimeter spaces, while there are high populations in the interior classrooms that therefore require cooling at the same time. This relative prevalence of simultaneous heating and cooling suggests a split system design for the HVAC system.
An energy-efficient design of a split system, given the preferred distributed approach with local fresh air supply, is to use fluid rather than air to add and remove heat from spaces in the building. This is accomplished using a VRF (variable refrigerant flow) HVAC system, which utilizes a cen- tral condensing unit and a smart manifold combined with local fan coil units distributed around the building and serving the different thermal zones. With this system, heat can be removed from zones requiring some cooling and distributed to other zones calling for heating; this can be done with a simple transfer of fluid at low overall use of energy.
The distributed fan coil units have individual outside air inlets to provide fresh air locally, without the need for large and lengthy duct runs. As noted in the discussion of Natural Ventilation, the HVAC system uses a mixed mode operation to make maximum use of free cooling using outside air. When a building zone is in natural ventilation mode, the heating and cooling mode cannot operate. Similarly, when a zone is in heating mode or cooling mode, the minimum required fresh air is introduced at the individual fan coil unit serving that zone. In addition, there is a Night Flush mode of operation, which uses all fan coil units to run at 100% outside air to precool the building at night when outdoor air temperatures are low enough and predicted daytime temperatures will require cooling operation during the following day.
A stand-alone solar thermal system supplies domestic hot water (DHW) for the building.
Zero Net Energy Case Study Buildings: Volume 2
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