Improving Long-Term HVAC Performance

Cumulative impact of three operational strategies helped a multi-tenant office building recertify LEED and boost its ENERGY STAR score.

Facility executives seeking to demonstrate leadership in energy efficiency are grappling with the ENERGY STAR updates that rolled out last August, which raised the bar for certification. This update revised the baseline for calculating the rating from 2003 consumption data to 2012 consumption data. As a result, facility engineers using the system for energy benchmarking saw their score drop an average of 12 points with the new energy baselines from U.S. EPA. While this might be discouraging for some, it shows the system is working; over time, we’ve improved the energy efficiency of our buildings. And the message is clear: to retain a leadership position in energy efficiency, facility teams need to continue to invest in that efficiency.

Over the last nine years I’ve worked with facility managers at a 1.4 million square foot multi-tenant office building to achieve three LEED certifications. Work began in 2009 when the LEED-EB: O&M rating system was released, and the first certification was earned in 2010. The building was recertified in 2014 and again in 2019. The building had a good ENERGY STAR rating when the initial work began, but to maintain that same good rating requires a vigilant engineering team that is always seeking out opportunities for improvement.

Looking back, the team implemented dozens of relatively small, but cumulatively impactful projects that have:

  • Reduced annual energy consumption by 11.3 billion BTUs, avoiding $700,000 in additional costs annually.
  • Reduced annual greenhouse gas emissions by 42%, or the equivalent annual electric consumption from 1,400 homes.

A large part of that success involved making improvements to the facility’s HVAC system.

Below are three strategies for improving HVAC performance over the long-term that should be considered when retro-commissioning spaces or building new structures.

1. Adjustments to operating schedules and night setback temperatures

This is an easy, no-cost strategy to implement, and yet we still see this issue at buildings with on-site engineering teams. Maintaining occupied conditions 24/7 for a space that is used 60 hours per week means the space is only seeing beneficial use for 35% of the time.

2. Program duct static pressure reset

We find AHU supply fans are often set to maintain a constant static pressure regardless of load conditions. This consumes excessive energy when the building is experiencing partial load conditions (which is most of the time). Implementing a static pressure reset schedule slows down the supply air fan and avoids energy use. We use similar strategies with the AHU discharge air temperature and chilled water supply temperature, adjusting setpoints dynamically to respond to the current building conditions.

3. Optimum start for chiller and air-side systems

Once a night setback schedule is implemented, the engineering team should determine when to start the HVAC system each morning. Time required for the building to warm up (or cool off) depends on weather, and often on the day of the week (Mondays take longer due to the system being off over the weekend). By learning the building’s patterns and performance, an optimum start program leverages the power of data from your building automation system (BAS) to automate and “optimize” the “start” time.

Read the full article in Facility Executive.