Although HVAC typically represents 40 percent of a commercial building's total energy use, energy efficiency historically has taken a back seat to occupant comfort in commercial-building HVAC design. With energy prices on the rise and commercial-building owners searching for ways to be more competitive, satisfy corporate social-responsibility objectives, and meet new government mandates, however, energy efficiency is becoming a greater and greater priority.

Today, HVAC systems must do more than provide a comfortable environment. They also must:

• Achieve the highest levels of energy efficiency to minimize operating expenses.
• Sustain reduced energy levels to ensure savings over time.

As difficult as energy-efficient HVAC can be to achieve, it can be even harder to sustain. Even the newest state-of-the-art HVAC systems can experience "drift," or degradation in performance resulting from malfunctioning mechanical and control equipment.

This article will discuss methods of mitigating performance drift to increase energy efficiency and sustain operating-cost reductions.

Conventional Solutions
The HVAC industry has developed a variety of approaches to optimizing HVAC-system performance. The most widely recognized is recommissioning, a process that includes an assessment of a system, identification and correction of mechanical and control issues, development of new operating procedures, and, often, implementation of new energy-efficiency strategies.

One such energy-efficiency strategy is the use of variable-speed equipment and custom-developed control methodologies. While some level of savings usually is achieved with this approach, it is not without risk. Custom solutions are unproven, can take weeks or months to program, and require hands-on functional testing to verify a system is working as designed. Additionally, without real-time measurement and verification, determining whether predicted energy savings have been realized and/or are being sustained is difficult.

With recommissioning, building operating-efficiency improvements typically range from 5 to 20 percent. Because recommissioning is focused on improving efficiency at a single point in time, however, recommissioned plants—even ones maintained to the highest standards—are subject to drift until they are recommissioned again.

Savings Opportunity
Building operators able to maintain HVAC systems consistently and mitigate performance drift have the opportunity to reduce operating costs reliably over the long term. This is vitally important to ensuring investments in energy reduction achieve expected returns.

A new means of ensuring optimized plant operation is the use of enterprise applications with integrated software solutions. Today, integrated software solutions capable of networking all of the equipment in an HVAC system and optimizing energy-system operation for maximum energy efficiency are available (Figure 1).

HVAC systems capable of providing occupant comfort, as well as annual wire-to-water energy efficiency of 0.4 to 0.6 kw per ton, achieve a new standard of HVAC-system performance: ultrahigh.

Integrated Software Solutions
Today, commercial-building owners and operators are reducing HVAC energy consumption by 30 to 60 percent with networked applications combining advanced relational-control methodologies and Web-based measurement, verification, and management services. Mineta San Jose International Airport in San Jose, Calif., for example, reduced HVAC energy use by more than 1.25 million kwh, or 50 percent, in 12 months by implementing an integrated software solution that includes control-software components that automatically and continuously optimize the operating efficiency of the entire HVAC system based on real-time building loads.

Since implementing the integrated software solution, Mineta San Jose International Airport has maintained a monthly wire-to-water energy efficiency of 0.61 to 0.65 kw per ton.