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Heating and Cooling Costs in Commercial Buildings

Jul 12, 2017 9:31:44 AM

Energy costs meter commercial building

The U.S. Department of Energy (DOE) has found that about 40% of energy costs for the average commercial building are spent on heating, cooling and ventilation. This equates to about 7.5% of total costs for the average office building, since 19% of total costs are energy costs.

In 2012, a DOE study found that U.S. commercial building owners could save an average of 38% on heating and cooling costs if they install an energy efficient HVAC control system. The range of cost savings (22% to 56%) determined by the study depends on building size, building use, regional climate and local utility costs.

Imagine if you were the building owner or operator who helped your tenants save between 30% and 50% on their energy bills each month by making an energy efficiency HVAC investment, which typically earns a three-year back or less.

Time-of-use utility rate structures, which also are dependent on local utility costs, may be costing you and building tenants a lot of avoidable expense each month. How can you fix this?

  1. Shifting some energy use or business operations from peak demand to partial- or off-peak hours can provide substantial cost savings.
  2. Energy efficient HVAC and lighting controls should be at the top of the list along with energy efficient lighting and minimizing heating and cooling leaks.
  3. Utilities also offer demand-response programs, which can help your building and its tenants take advantage of discounts offered by the utility company when you reduce your energy load during peak-demand hours.

Energy efficiency in your HVAC system could involve using latent cooling toward the end of the workday, retrofitting your HVAC system for Outside Air Optimization (OAO), demand control ventilation or a system that provides Dynamic Airflow Balancing (DAB) to better balance building zones and conserve energy.

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The Path to Greater Heating and Cooling Efficiency

According to DOE, over 60% of commercial building floor space is served by packaged HVAC units, including outdoor rooftop units (RTUs) and indoor air handling units (AHUs). It is common for RTU and AHU supply fans to run continuously regardless of heating and cooling needs, just to maintain ventilation airflow. This is a significant energy drain, and it is inefficient.

The energy necessary to keep up this constant speed of the supply fan moving air in the ventilation system rises exponentially with the airflow rate (energy = fan speed3). Thus, optimizing your HVAC system and reducing the necessary airflow rate can significantly reduce energy use.

HVAC Fan Speed to Energy Use

In addition to the energy demand from constant speed supply fans, the majority of RTUs currently operational on U.S. buildings have economizers (outdoor dampers) stuck in one position, which is often fully open, because the enthalpy sensor on the unit has failed. This means outside air is constantly being drawn into buildings regardless of its quality and the outside temperature. Such outside air intake can have serious cooling and heating cost impacts.

Optimizing outside air intake can provide free cooling when the air outside is a lower temperature than indoor air while also balancing the indoor humidity level. The image below depicts an optimized RTU with functioning economizer (actuator), mixed-air temperature (MAT) sensor and CO2 sensor, which can measure outdoor and indoor air enthalpy when combined with pressure sensors and a local weather data feed.

Rooftop unit heating and cooling with sensors, economizer and airflow

The packaged RTUs and AHUs use compressor coils to chill air and heating coils to heat air. Chilling and heating these coils consumes a lot of energy. If an RTU economizer is stuck in the open position, the entire unit must consume more energy to maintain the desired air temperature in the building during all seasons.

This translates into extremely inefficient energy use in the cold winter environment of Minnesota or the hot summer environments of Texas or Minnesota. Outside air must be cooled or heated, down or up 50 to 100 degrees to make indoor spaces comfortable in such extreme environments.

RTU efficiency inspections with a licensed technician should be your first step. An HVAC system optimization retrofit should be under consideration when you are looking to reduce heating and cooling costs for your building in any climate.



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