Page 101 - Zero Net Energy Case Study Buildings-Volume 2

Proof of concept was provided by computer modeling of air flow through a three-dimensional model of the main space, using computational fluid dynamics (CFD) software8 for different wind and temperature conditions. The computer modeling verified that even from high windows on the north side of the building, air would effectively and reliably move at the required volume flow rates through the space at the level of the occupants.
Heating, Ventilating and Cooling Systems
The basic mechanical heating and cooling system is a hydronic radiant system embedded in the concrete slab. The heating hot water is created by an array of solar thermal panels, with an auxiliary thermal storage tank. Three residential-size electric heat pumps provide backup to the solar thermal component so that sufficiently hot water is always available for the heating system. Currently, the solar thermal panels are providing about 50% of the total amount of energy for the hot water being used for radiant space heating. The air source heat pumps provide the balance.
The chilled water for cooling via the radiant slab is provided by the heat pump system. Because of the mild climate and small building size, the HVAC design is not a split-system where simulta- neous mechanical heating and cooling in different zones may be required (as with Case Study No. 8, the IBEW-NECA Training Facility).
The building’s total HVAC system is a combination of the radiant slab system and the passive ventilation system, controlled by the building management system (BMS) to function in a Mixed Mode of Operation so that energy use is minimized. The sequence of operations is programmed into the BMS so that all equipment and components function appropriately for each different mode of operation.
Mode 1. Heating Season Operation. In this mode, the radiant heating system is on and the passive ventilation system admits the minimum amount of outdoor air as required by code.
Mode 2. Swing Season Operation. No heating required and the amount of outdoor air re- quired for fresh air and (at times) cooling varies. The wind chimney drives the air flow through the building spaces.
Mode 3. Cooling Season Operation—Good Wind Conditions. Increased amounts of outside air are required for cooling purposes. Designated skylights open to allow movement of larger volumes of outdoor air.
Mode 4. Cooling Season Operation—Poor Wind Conditions. System design includes back- up fans at skylight shafts to engage and ensure air flow under poor wind conditions and for night purging9 using cool night air. (Skylights are closed.)
Mode 5. Operation in Peak Cooling Events. Outdoor air is too warm for cooling, so full cool- ing mode with radiant slab cooling via heat pumps engages. The passive ventilation system admits the minimum amount of outdoor air as required by code.
The range of temperatures at which occupants are comfortable is increased by the use of large room fans in all but the large public space, where such fans would be impractical. These room fans are placed on manual control only, so occupants are required to understand their function and their availability. This was actually a problem for the general public in terms of best operation of these room fans—see the comments in Post-Occupancy: HVAC, p. 28.
8 Airpak by Fluent Inc.
9 Night purging involves flushing the building with cool night air in order to use the thermal mass of the building and its contents to pre-cool the building and absorb heat on the following day.
Zero Net Energy Case Study Buildings, Volume 2
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WEST BERKELEY BRANCH LIBRARY
CASE STUDY NO. 10