By MICHAEL DERU, PhD, Engineering Manager, Commercial Buildings Research Group, National Renewable Energy Laboratory

According to the U.S. Energy Information Administration, HVAC accounts for approximately 38 percent of U.S. commercial buildings’ primary energy consumption and a slightly higher percentage of their greenhouse-gas emissions. We have seen incredible gains in efficiency made with lighting, going from incandescent and T12 fluorescent bulbs to high-efficiency LEDs, but there are even greater advances to be made with HVAC. Gains of 20 percent to 30 percent easily can be made by replacing older degraded equipment with new high-efficiency equipment. Even more savings are possible with an integrated engineering approach yielding optimized system designs combined with highly efficient controls.

This all means there is tremendous opportunity for HVAC engineers to apply intelligent design and operation to achieve cost savings and improved thermal performance. Luckily, there have been great improvements in the performance of HVAC systems and in sensors and controls in recent years, providing a solid starting point. However, the biggest savings are in proper design and operation of HVAC systems.

In a one-for-one replacement, a new high-efficiency rooftop air-conditioning unit (RTU) can use less than half of the energy of an old degraded RTU. However, it may be difficult to make an economic case for the highest-efficiency units. One retailer developed an “optimized re-engineered” approach taking advantage of reduced lighting loads, a redesigned ventilation system, improved controls, and tighter design criteria to reduce installed cooling tons (and costs) by an average of 30 percent and achieve a 40-percent reduction in HVAC energy and operation costs over an already efficient system. Thirty-percent energy savings have been seen in chilled-water-system replacement scenarios, according to the U.S. Department of Energy’s Better Buildings Solution Center.

You don’t have to replace HVAC systems to see significant savings. Most HVAC systems do not operate anywhere close to their optimal efficiency. Retrocommissioning or retrofitting existing systems can provide significant savings. Many building owners have achieved significant savings with existing RTUs by installing advanced RTU control retrofit packages that can provide 20-percent to 50-percent savings with one- to four-year payback periods.

If you are an engineer or energy manager looking for significant energy savings, take an integrated, holistic approach to your building and building systems. First, reduce loads. Then, take a close look at the HVAC-system requirements to optimize the design and controls. Properly size HVAC systems, turn things off when they don’t need to run, and use variable-speed fan and pump drives for improved part-load performance. Unfortunately, there is not a one-size-fits-all solution for buildings. The challenge with HVAC systems is that they are more complicated than other building systems, and more time and energy has to be put into a solution; however, incredible performance gains can be achieved with proper application of an intelligent approach to design and operation.

The fun part about being a HVAC engineer is that there always is something new to learn about. Future HVAC systems will be even more efficient, with very low greenhouse-gas contribution, as we shift to new refrigerants and non-vapor-compression cooling and heating. Always keep learning and applying sound engineering practices to get the best results.