By Kent W. Peterson
Innovation through energy efficiency and reduced resources is not typically incentivized by the typical project-delivery methods used today; building decisions are often made without recognizing the life-cycle benefits that improved efficiency creates.
System performance needs to be better benchmarked by our industry. Buildings rated on their actual peak and annual energy performance would trigger better design, construction, and operation. Building owners can benefit from increased energy performance and reduced costs by setting clear energy-performance goals for all projects; the industry should then measure and report the energy use of all buildings.
To ensure energy efficiency, the building industry would benefit from going beyond simply selecting the right-sized HVAC systems. Design engineers play an important role in building energy use and must improve their knowledge about building-envelope performance, thermal-mass effects, passive solar, daylighting, and human comfort, and must become experts in delivering high-performance buildings. HVAC systems play a substantial role in creating sustainable buildings, but those systems alone cannot achieve optimal sustainability. By bringing design teams together through integrated building design, the team's collective knowledge and processes can create a truly high-performing building.
Integrated building design (IBD) is a collaborative process that can achieve high-performance, low-energy, sustainable buildings by considering all design variables together. IBD looks beyond the immediate building to how the building and its systems can be integrated with supporting systems, and at how materials, systems, and products connect, interact, and affect one another.
Interaction among all building disciplines is required to achieve overarching building design goals. Early commitment and participation of these parties that extends throughout all stages of the design process is necessary to optimize overall performance.
Historically, buildings have been designed using a linear design process where elements are defined and developed in a sequential, isolated process. Architects, contractors, mechanical engineers, and consultants work separately on each element of the building, making design goals difficult to achieve.
As an example, reducing envelope loads has a substantial impact on energy use. A design element such as reducing solar loads is a key aspect in this, but entails multiple issues (and the other team members):
- Building orientation (architects, owners, energy consultants).
- Shading (architects).
- Glass selection and glass area/location (architects, owners, mechanical designers, modelers/energy consultants).
- Passive solar gains via increasing building mass (architects, owners, mechanical designers, modelers/energy consultants).
These teams may not interact in a traditionally linear design process. The IBD process also helps to assure an optimized design through the collaborative generation of multiple design options and to evaluate using an iterative design process. Using analysis tools such as building information modeling (BIM), energy modeling, and life-cycle analysis is crucial in IBD to support design decisions.
Understanding IBD concepts enables thinking and practicing in an integrated fashion to meet the demands of high-performance building projects. Building performance goals must be set early in the concept phase. It is important to establish quantitative goals for annual energy consumption and annual energy costs.
HVAC systems should be a major consideration when setting energy goals. High-performance HVAC equipment, in conjunction with integrated building design, can result in significant savings. The initial costs of a building and HVAC system that achieve a 30-percent reduction in annual energy costs can usually be recouped within 3 to 5 years when the building achieves conventional comfort levels of 70 degrees F. in winter and 76 degrees F. in summer. Additional savings can be achieved by extending the thermal comfort zone through natural ventilation and air movement in summer, and through lower air temperatures in winter (via highly insulated, warmer wall and window surfaces). While it may require more effort and collaboration among the design team, highly energy-efficient design utilizing high-performance HVAC equipment can result in significant energy savings.
HVAC systems should be selected to minimize annual energy consumption and not just peak energy demand. Most heating and cooling equipment only operates at its rated peak efficiency when fully loaded (working near its maximum output), which is typically required only about 1 to 2.5 percent of the time. Designers can reduce total energy consumption by considering part-load performance of equipment, which is a critical consideration for HVAC sizing.
Through integrated building design, HVAC systems can operate more efficiently. This effort in the beginning of a building's life is small compared to the lessened impact on our environment that sustainable buildings can provide.
Kent W. Peterson, Fellow ASHRAE, is the 2007-2008 president of ASHRAE and is vice president and chief engineer at P2S Engineering Inc. (www.p2seng.com), Long Beach, CA.