Sustainable Technology: HVAC

Sept. 1, 2007

Energy Efficiency: the Elegant Alternative

By Kent W. Peterson, PE

Everybody is affected in one way or another by buildings - we are born in them, we live in them, we work in them, and in many cases we are healed in them. Collectively, buildings professionals provide comfortable, healthy, safe buildings that improve the quality of life. On the flip side, the energy consumed by these buildings is helping fuel a new crisis - a crisis of global energy availability and increasing greenhouse gas emissions.

The U.S. Energy Information Agency recently reported that world energy consumption is projected to grow by 71 percent from 2003 to 2030. Residential and commercial buildings already account for roughly 40 percent of total primary energy use in the United States and the European Union. With HVAC&R and water heating responsible for a significant percentage (75 percent of residential and 64 percent of commercial building site energy use), design teams must think of the mechanical systems as not only comfort and health solutions but also as potential solutions for the world's energy problem.

It is time for the building industry to move beyond simply selecting right-sized HVAC systems. Today, design engineers must improve their knowledge in building envelope performance, thermal mass effects in buildings, passive solar, daylighting, and human comfort and must become experts in delivering high-performance buildings.

The knowledge, materials, and processes exist today to make substantial improvements in both the energy and environmental impacts from buildings. Integrated building design (IBD) is a collaborative process that can help 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 on its site and in its community and at how materials, systems, and products of a building connect, interact, and affect one another.

IBD recognizes that interaction among all building disciplines is required to achieve overarching building design goals such as sustainable buildings, superior IEQ, building security, and critical operations. Commitment and participation of these parties, starting as early as possible and at all stages of the design process, is necessary to optimize the building as a whole.

Employing high-performance HVAC equipment in conjunction with IBD can result in significant energy savings. Typically, a 30-percent reduction in annual energy costs can be achieved with a simple payback period of about 3 to 5 years. These figures apply to buildings that offer conventional comfort (e.g. 70 degrees Fahrenheit in winter, 76 degrees Fahrenheit in summer).

If the thermal comfort zone is extended through natural ventilation and air movement in summer and lower air temperatures in winter (made possible by highly insulated and, therefore, warmer wall and window surfaces), even higher savings can be achieved. It is important to note that highly energy-efficient design using high-performance HVAC equipment typically requires more effort and more collaboration from the design team than a conventional, sequential approach.

Passive solar heating makes use of building components to collect, store, and distribute solar heat gains to reduce the demand for space heating. It does not require the use of mechanical equipment because the heat flow is by natural means (radiation, convection, and conductance) and the thermal storage is in the structure itself.

When selecting HVAC systems, designers can reduce annual energy consumption by considering part-load performance, a critical consideration for HVAC sizing. Most heating and cooling equipment only operate at their rated, peak efficiency when fully loaded (that is, working near their maximum output). HVAC systems, however, are typically only required to meet peak design heating and cooling conditions about 1 to 2.5 percent of the time. HVAC systems must be selected to minimize annual energy consumption and not just peak energy demand.

Through a systematic analysis of these interdependencies and leveraging integrated building design strategies to achieve multiple benefits, a much more efficient and cost-effective building will result.

Kent W. Peterson ([email protected]), fellow ASHRAE, is vice president and chief engineer of P2S Engineering Inc., Long Beach, CA. As 2007-08 president of ASHRAE, Peterson emphasizes innovation in the quest for sustainability in the built environment. He encourages ASHRAE members and the industry to be more innovative in their thinking, more daring in their creativity, and more dedicated to their pursuit of best practices that will dramatically improve building energy performance.

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