I live in Minnesota, and this time of year is bone-chillingly cold, dark more than 15 hours a day, and a potential nightmare for new HVAC system operators. With the onset of winter, I frequently hear stories of frozen pipes/components in new HVAC systems or in HVAC systems with new operations personnel. Sometimes these events are the result of failed hardware or controls; however, sometimes the freeze-ups are the result of insufficient training and/or documentation of how a system needs to be winterized.

The industry standard commissioning process includes development of a systems manual to supplement the equipment O&M manuals provided by equipment manufacturers. The systems manual is intended to document at least the following information about each commissioned system:

  • Design and operational intent;
  • Configuration of individual components within each system;
  • Control sequences of operation;
  • Control device calibration schedule;
  • Preventive maintenance plan;
  • Recommissioning plan; and
  • Non-automated operational instructions.

It is the non-automated operational instructions section in which winterization plans and processes should be defined. Winterization of a system (if needed) is almost never fully accomplished with the central BAS. There are usually a number of manual actions required, such as opening valves and draining water piping and other components potentially exposed to freezing temperatures. It may also be necessary to manually close building openings used for warm weather ventilation/cooling when sub-freezing outdoor air could be detrimental to the contents of a mechanical or electrical equipment space. The type, number, and timing of winterization activities is always unique to each building and HVAC system.

If winterization requirements are not thought through by the design and construction team, clearly documented in the systems manual, and communicated during operator training, the building operators will end up figuring it out the hard way. That is not good for the new equipment and components, the designers and contractors who will be called back to help when something freezes, or the building occupants whose HVAC system performance could be compromised under some of the most severe weather conditions.

The following are a few examples of winterization processes which, if intended by the design and construction team, should be documented for operator reference:

  • Draining cooling towers and related exterior piping.

- Are there enough drain valves? Where are they located?

- Is all of the piping pitched to a drain valve with no trapped low spots?

- Is there a floor drain or utility sink capable of receiving the drained water?

- Does any ancillary equipment need to be drained (solid separators, pumps, etc.)?

  • Draining outdoor air-cooled chillers and related exterior piping.

- Same questions as for cooling towers.

  • If there is a glycol solution in an outdoor air-cooled chiller:

- Presumably the glycol stays in the chiller and exterior piping year-round.

- Is it required to keep the chiller powered in order for internal heaters to activate during cold weather?

- Are there any circumstances under which the chilled water pumps should energize during cold weather?

  • Draining an air-handling unit’s chilled water coils.

-  How to ensure no water remains in or accumulates in the drained coils.

-  Is there a “Canadian vent” configuration that requires manual positioning of valves to allow warm AHU supply air to pass continuously through the coil?

Winterization directions may also benefit from some “do not” directions as well. For example, it is a risky proposition to fill or flush chillers or coils with a glycol solution during the winter when they are normally connected to pure water systems in the summer. This can be detrimental to the water systems if the coils and chillers cannot be thoroughly flushed to remove all traces of glycol before opening the equipment to their water systems in the spring. The resultant low glycol concentrations have proven to be breeding grounds for undesirable microbes, resulting in fouling of piping and coils.

Winterization is just one example of non-automated operational instructions that should be included in a systems manual. Every building and system will have unique manual intervention requirements, and the commissioning professional is in a good position to ask questions during design, construction, and start-up that will tease out exactly what those are for each project.