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D.7.1 High Performance Engineering Design
By now, the building envelope serves multiple roles. It protects the occupants from changing weather conditions and it plays a key part in meeting the occupants’ comfort needs. The heating, ventilating, air-conditioning, and lighting (HVAC&L) systems complement the architectural design, govern the building’s operation and maintenance costs, and shape the building’s long-term environmental impact. The architectural design maximizes the potential for a high-performance building, but it is the engineering design that actually makes the building a high-performance building.
Designers of high-performance buildings depend on building energy simulation tools to understand the complicated interactions between the HVAC&L systems and the building envelope. These tools also prove invaluable to the designer when comparing HVAC&L strategies and selecting the best systems to meet the building’s lighting and space conditioning requirements. High-performance buildings cannot be designed using only rules of thumb or conventional wisdom.
D.7.1.1 Lighting System Design
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Building Heat Gains |
The single largest operating cost of commercial buildings in the U.S. is lighting. Lighting systems represent one-third or more of the total electrical energy costs of a commercial building. They also introduce heat into the space and increase building cooling loads. Because lighting systems significantly impact a building’s operating cost and energy performance, evaluate options for the lighting systems before considering strategies for a low-energy HVAC system. Also, take advantage of day-lighting opportunities whenever possible.
A building designed to take advantage of daylighting will have electric lighting system controls that turn the electric lights off or dim them when sufficient daylighting is available. The electric lights operate only to maintain set lighting conditions that the daylighting cannot meet. Less waste heat from the electric lighting system is then introduced to the space, which in turn reduces the building’s cooling loads. The following are characteristics of a well-engineered lighting design:
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Saves energy costs and decreases polluting power plant effluents
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Responds to the varying daylight levels throughout the day
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Improves indoor environmental quality making occupants more comfortable and productive
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Tailors to individual’s lighting needs through the building
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Decreases building cooling loads resulting in smaller, less expensive space cooling equipment
D.7.1.2 HVAC System Design
Space conditioning loads are a close second to lighting systems in terms of the most costly components to operate in commercial buildings in the U.S. Through good architectural design resulting from the engineer participating in the architectural design process, the building will have daylighting, solar gain avoidance, and other energy-efficient architectural strategies. In other words, the envelope will minimize heating, cooling, and lighting energy loads. It is the engineer’s responsibility to design the HVAC systems to complement the architectural design. Remember to account for the benefits of good lighting design - primarily reduced cooling loads - when sizing the HVAC system.
Consider advanced engineering design strategies early in the design process to allow time for making modifications to the architectural design to accommodate these strategies. Use computer simulation tools to evaluate the effect of the advanced architectural strategies when calculating HVAC system loads. Also, be familiar with the intended building activities and the resulting impact on internal loads.
Plug and process loads impact the HVAC system design, especially in buildings housing energy-intensive laboratory and research activities. Recommend energy-saving equipment options for minimizing these loads. Reducing plug and process loads will decrease internal heat gains from this equipment, reduce building cooling loads, and decrease production of effluents from burning fossil fuels to produce electricity to operate this equipment.
Finally, develop a controls strategy that will operate the HVAC&L systems with the maximum comfort to the occupants at the minimum cost. Metering and evaluation is also important for providing continuous feed-back for improvement.
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