Page 75 - Zero Net Energy Case Study Buildings-Volume 2

Natural Ventilation
Windows are openable at the perimeter of the building, including all glazing using the electro- chromic glass. The skylights are automatically opened by actuators as part of the “night flush- ing” of the building for pre-cooling during the warm months. The ground level windows are also opened at night automatically during the night flushing operation, but the amount of opening is limited to maintain security; the security alarm system is designed to further protect against unauthorized entry.
As part of the passive systems design for the building, larger spaces requiring fresh air, such as large conference rooms, are prescribed to be located at the perimeter of the space so that they can be passively ventilated and cooled. This information is provided to tenants as part of the “driver’s manual” for the building and an explanation of the passive systems used in the building to achieve ZNE performance.
Heating, Ventilating and Cooling Systems
The HVAC system consists of distributed air-source heat pump units (two units at 11 tons each). These units are basically back-up heating and cooling for the passive systems of the building. They are sized for large group events; as a result, they operate at partial loads under normal conditions, an efficient mode of operation.
If private offices are built as part of the tenant improvements, individual comfort control is achieved by using Therma-fusersTM 4 at each of the private offices. This device eliminates the need for a separate system for these office spaces.
Like most ZNE buildings, the design also includes large ceiling-mounted room fans to create air movement for comfort, thereby allowing a higher cooling temperature setpoint for the HVAC sys- tem. The high ceilings in buildings of this type lend themselves to this particular energy-saving strategy.
The basic sequence of operations is the mixed-mode type. When outdoor temperatures are moderate and can be used for cooling, windows and skylights open for natural ventilation. If the outdoor temperature rises, the large ceiling fans are engaged. For higher outdoor temperatures still, the windows and skylights close automatically and the air-conditioning units operate to cool the spaces.
Domestic Hot Water
The building utilizes a standard solar thermal hot water system with storage and electric resis- tance backup for domestic hot water (DHW).
Plug Loads
The information given to tenants at the time of leasing includes recommendations for energy- efficient (Energy Star®) equipment. Installed circuit metering on tenant space provides feedback and information to tenants about their plug load use.
4 Therma-FusersTM are ceiling air diffusers operating as an integrated Variable Air Volume (VAV) zone of temperature control. These diffusers include a thermostat, modulating damper and diffuser in a single package.
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SPECULATIVE OFFICE BUILDING AT 435 INDIO WAY
CASE STUDY NO. 9