Care for Building Systems During Low or No Occupancy

Buildings with low or no occupancy need special care and maintenance to keep the building systems in sound working order. Experts from District Energy and NALCO Water have some suggested measures to help keep your building safe and help you save energy.

Save Energy

Building systems have design specifications, and it is best to consult with your system design engineer and controls contractor before making significant changes to the way that you are are operating your building systems to confirm that your plans align with the building system design.

• Verify your building is operating with outdoor temperature reset function. As the outside air temperature increases the building loop temperature should automatically adjust down to as low as 120 °F. Reducing the building loop temperature will reduce thermal losses and the constant cycling of control valves.

• You may be able to lower zone temperature setpoints in heating mode or raise temperature set points in cooling mode. Regardless of the setpoint adjustment, HVAC systems should be kept operational to avoid freezing issues from cool overnight temperatures and to avoid excess humidity and potential mold growth during warmer rainy or humid days.

• Please note that the lower the interior temperature of a building, the more condensation that will form on the inside pane of exterior windows. Take care to protect moldings, woodwork, and other materials that could become water damaged from drips and pooling.

If you are planning to make changes in your cooling system programming and would like to better understand the impact to your system efficiencies and your District Energy budget, please contact our team.

Prevent Legionella

The bacteria Legionella can develop in stagnant (unmoving), unheated water in a building’s plumbing, including domestic hot water and potable water systems. The lack of chlorinated water flowing through pipes, combined with irregular temperature changes, can create conditions ripe for the bacteria that causes Legionnaires’ disease. Legionella can be transmitted through water or mist and cause Legionnaires’ disease in people which can lead to a severe type of pneumonia. Historically people have contracted Legionnaires’ disease from showers, sinks, pools, hot tubs, cooling towers, fountains, and ice machines.

If you or your building team are not experienced in Legionella prevention, please contact a water treatment professional for help in preparing your building for occupancy. Your domestic water connects to sinks, showers, laundry, dish washers, coffee makers, and more.

• The domestic hot water should remain operational and circulating to prevent Legionella. If you have a recirculating pump it will be important to leave it running. The energy use is minimal and the benefit of avoiding Legionella colony formation is excellent.

• Before your building returns to full occupancy cleaning, disinfecting, and replacement of filters may be recommended for a range of equipment and systems.

• To better understand the precautions that you can take for the safety of your building occupants and systems refer to the ANSI/ASHRAE Standard 188-2018 Legionellosis and other resources that the ASHRAE website provides.

• When the time comes that you are re-occupying the space, it is recommended to perform a thermal flush of the system to get the piping hot enough to stress and kill any potential colonies that may have formed when the water was stagnant (unmoving). This can be done by temporarily adjusting the hot water to achieve a temperature above 125 °F (e.g. 140 °F), and maintaining it for at least 2 hours (the longer the better). After the hold time, flush all of the outlets especially the ones at the end of lines and those furthest from the heat source(s). If you cannot adjust setpoints to 140 °F on your system, contact a water treatment professional.

• ASHRAE offers many resources on building and operations guidance including “Guidance for Building Operations During the COVID-19 Pandemic.”

• Reuters News published a story recently on carefully re-opening buildings to prevent Legionnaires’ outbreaks.

Building systems need some care when building programming shifts due to low or no occupancy. A few precautions to keep your systems in working order and reduce the risk of the bacteria Legionella in your potable water or HVAC systems can help prepare your building plumbing to return to partial or full occupancy.

This article was written in collaboration with water treatment experts from NALCO Water an Ecolab Company. If you are looking for water treatment support, you can contact Chad Ahlers for guidance at NALCO Water an Ecolab Company by phone at 763-614-9651 or email

If you have questions about your District Energy connection, please contact our team at 651.297.8955, email, or support request form.

Additional resources:
Ecolab offers several free webinars focused on water safety in COVID-19 response.