Energy Efficiency

District Energy’s customer service engineers visit customer buildings and with property managers to evaluate opportunities for improved energy efficiency of equipment associated with the distribution of hot and chilled water throughout a building. The engineers also depend on the distribution system’s performance tracking to identify building connections that may be in need of repair or replacement. These efforts not only enhance and maintain the distribution system’s efficiency but they help the building manager maintain a high performing building.

Our team partners with many organizations that provide customer support, engineering services, and rebate opportunities. For more information on improving your building’s efficiency, contact us by email.

Ask the Engineer
Summer Transitions | Hot Water Return Temperatures

Summer Transitions
After an extended Minnesota winter, the warmer weather has arrived and with it comes the annual transitioning of your building’s systems from winter to summer. Below are suggestions to help you maximize the efficiency and operation of your building’s system.

• Blow down your main service strainers and your air handler strainers. Blow down should be done annually.
• Refill your cooling coils and check for leaks.
• Make sure your control valves are responding and maintaining a proper return temperature of 56°F or higher. (Reminder: District Energy requires a 14°F Delta T for the months of June –September. The system sends 42°F supply water and requires at least 56°F return water.)
• Check to ensure the control valve has the full range of motion. Confirm that the valve can positively shut off when not in use.
• Exercise your cooling pumps and check for leaks and bad bearings.
• Inspect insulation on cooling equipment and piping. If the insulation is in poor condition or there is no insulation, repair or install immediately or in the fall after cooling season ends.
• For two-pipe systems that require a seasonal changeover, verify that the valves are properly configured and secured from heating mode to cooling mode.

Why does District Energy require a return temperature of 160°F or lower?
District Energy delivers hot water to its customers for a variety of uses from heating buildings to melting snow on sidewalks and driveways. In order to keep rates down, District Energy requires its customers to maintain a return temperature that is 160°F or lower. The district system is designed for a 90°F temperature difference between the supply and return temperatures. This allowed District Energy to reduce the size of the piping network and to limit the pumping requirement for the central plant.

On the building side, typically buildings that operate air handlers, fan coils, and finned tube radiation maintain a maximum 180° F supply water temperature and a return water temperature of 150° F to the hot water heat exchanger. A proper return water temperature back to the exchanger ensures that the district’s return water temperature will be 160°F or lower. The goal is to keep the district system’s return water temperature at or below 160 °F to lower the flow velocity in the distribution pipes.

When return temperatures are high, distribution losses increase and efficiencies decrease. Capacity diminishes because more gallons of hot water are required to provide the same amount of heating to a customer. More gallons delivered to customer buildings requires more pumping, resulting in higher electricity costs. Higher return temperatures and elevated flows cause more wear and tear on the metering and mechanical equipment. All of this effort to reduce return water temperatures is producing results that benefit all customers. In 2012 we saw our return water temperature average 157.1°F for the year, 2.9°F lower than system design!

Maintaining low return temperatures is a great way customers can reduce maintenance headaches and save money, too. We recommend you review your hot water meter in your building near the service entry point of the hot water lines. The supply and return water temperatures are available for inspection to see how your system is performing. The customer service team reaches out to customers we have identified as having high return water temperatures, but always feel free to contact us if you have any questions about your system

 “My team’s goal is to help customers gain the highest value from our system by reviewing onsite equipment and providing maintenance recommendations to ensure a building’s energy efficiency.   We take great pride in the one-on-one relationships we develop with our building engineers, managers and owners that allow us to understand the exact challenge they face – whether it’s solving a heating or cooling problem or helping lowering energy usage.”  —Jeff Volovsek, Manager, Energy Delivery Services

District Energy St. Paul is operated and managed by Ever-Green Energy.