Is your HVAC system running efficiently? It might sound like the beginning to the oldest prank call in the book, but its a serious question worth asking of your facilities.
If you and your customers are comfortable in the space, the answer is probably “yes”. But the cost of comfort is high with HVAC systems accounting for nearly 30% of total energy consumption for a commercial building in the U.S. While room temperature and humidity may be within standard comfort ranges, HVAC systems are often consuming far more energy than necessary.
Here, our experts review some common opportunities for energy savings to ensure your HVAC system is truly working for you – and your bottom line.
Three Opportunities to Improve HVAC Systems
- Converting rooftop units to variable air flow operation
Most single-zone rooftop units are set to operate on a constant volume, delivering the same volume of air into the building regardless of the actual cooling load. Fan motors are working at full power, even during part-load.
Pro Tip: When a fan speed control is added to the supply fan with a variable-speed drive and associated controls, the fan motor will provide a variable air flow system. This allows the rooftop unit to reduce energy consumption in response to reduction in cooling load, converting energy cost into savings.
- Coordinating controls
This past summer, an investigation at a large restaurant uncovered three rooftop units operating in cooling mode – and a fourth stuck in heating mode. While the dining area was comfortably cool, three rooftop units had to overcome the excess heat being added by the fourth. Simultaneous heating and cooling inflates operating costs, and this intensifies as temperatures reach greater extremes.
Pro Tip: Energy studies on commercial building reveal that common HVAC control issues can lead to simultaneous heating and cooling among other operational inefficiencies. To avoid these common pitfalls:
- Identify and correct misaligned internal Air Handling Unit (AHU) setpoints, allowing the economizer to eliminate mechanical cooling during specific outdoor air temperature ranges.
- Assure the warm-up and setback modes of the AHU include no outside air intake.
- Conduct a full Supply Air Temperature (SAT) setpoint reset for constant volume systems, and assure proper adjustment for humidity levels; conduct a more limited SAT reset on variable air systems to minimize reheat.
- Managing ventilation based on building use
Every person exhales 100x the amount of carbon dioxide compared to outside air. To maintain air quality, proper ventilation is needed to bring fresh air into occupied space. However, most HVAC systems are set to operate under the assumption of maximum occupancy at all hours of every day. This brings in more outside air than necessary which can increase operational costs during both heating and cooling periods.
Pro Tip: Address this by reprogramming the current ventilation settings based on occupant load, or implement active controls that continuously optimize ventilation to minimize energy waste.
- Re-evaluate the ventilation rates for each area according to the latest building and energy codes, as well as changes in occupancy patterns.
- Implement a Demand Control Ventilation (DCV) system to constantly monitor indoor air quality and automatically eliminate excess ventilation.
Sustaining HVAC efficiency
Among our own clients, we often find that up to 30% of annual energy savings can be captured through low to no cost operational measures. However, as creatures of habit, it’s not uncommon for individuals to fall back to their old ways – unless they are reminded and motivated to do otherwise.
Monitor performance. Track the energy consumption of your HVAC system using properly located energy meters. Normalize this energy usage data to account for current weather conditions using Heating Degree Days (HDD) and Cooling Degree Days (CDD). This information will help you focus on the systems and equipment responsible for increased energy use and assure sustained performance. Many of the opportunities described above can be detected using this method.
Establish accountability. Assign someone to be accountable for HVAC system performance. This individual should be responsible for knowing the systems present and expected performance, investigating variances when detected and leading corrective actions.
Strive for continual improvement. Set a goal using HVAC performance indicators such as HVAC-energy-per HDD or CDD to challenge your teams on continuous improvements and drive greater efficiencies and energy savings in commercial buildings.
To learn more about efficiency programs, download our free eBook.
Contributed by: Joseph Dorey, Paul Stiller and Jacob Freeman, of Schneider Electric Energy & Sustainability Services.