Variable speed everything

Reaching a goal of doubling U.S. energy productivity by 2030 will require strong focus on improving energy efficiency in commercial buildings, which is attainable through the many proven technologies available today.

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Over the past few years, it seems I’ve been able to increasingly recite what has become one of my favorite mantras: “variable speed everything.”

This is in part because, on a national level, there has been a growing conversation around doubling U.S. energy productivity by 2030. Reaching that goal will undoubtedly require a strong focus on improving energy efficiency in commercial buildings. Today, existing buildings comprise 99% of the total building stock — using almost 36% of U.S. electricity and 21% of primary energy, making them an ideal target in the pursuit of greater energy productivity.

Fortunately, the energy performance of buildings is predicted to improve significantly in the decades ahead. From 1980 to 2009, for every percent of growth in U.S. commercial building space, primary energy consumption grew by 1.19%; however, the U.S. Energy Information Administration estimates that, from 2009 to 2035, every percent of growth in space will increase energy consumption by only 0.79%.

How will those predicted energy savings be obtained? Through the many proven technologies available today — such as variable speed… everything.

Today, 40% of the energy in commercial buildings is consumed by HVAC equipment, meaning mechanical system efficiency will have to improve substantially. Reducing energy consumption can be achieved through mechanical equipment with the flexibility to modulate capacity and lower speeds — such as variable speed compressors, fans, and pumps. Variable speed equipment also enables systems to better match capacity with demand to operate efficiently at part-load conditions.

For example, a retrofit where two 150-ton chillers were replaced by one 150-ton variable speed chiller resulted in an efficiency improvement of 42% — nearly double the energy productivity of the original chillers.

But variable speed equipment will need to be taken as part of a holistic approach that includes a focus on renewables, demand response, and energy storage. Advanced load control and demand response capabilities can help to relieve the grid during peak periods — and variable speed equipment not only improves efficiency, performance, and comfort, but also has the capability to help utilities address peak demand concerns through new demand response initiatives that allow them to intelligently control the speed of the unit during a peak event, while minimizing the impact on occupants.

In Pittsburgh, Pennsylvania, an installation of more than 150 variable speed drives onto various processes such as domestic water supply and fan at pump motors at the U.S. Steel Tower — the city’s tallest building, providing more than 2.3 million square feet of commercial space — produced annual energy savings exceeding $1.1 million. The reduction in energy consumption of 34% also enabled the property management

company to obtain rebates from the local utility, and the variable speed technology aided participation in its demand response programs.

Imagine the possibilities when deployed on a greater scale.

Moving to “variable speed everything” is a step in the path to doubling our energy productivity and making our buildings more sustainable. But we also need supportive regulations and standards and the right package of incentives to encourage the broader deployment of these technologies.

We’re on our way, but the journey is far from over.

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