In 2017 IMEG was commissioned to review, provide solutions, and implement solutions to optimize the chilled water plant operation during low load periods at the U.S. District Courthouse for the Northern District of Iowa in Cedar Rapids. The building was completed in 2012 and was designed with, and continues to operate using, metric units.

The facility operators were struggling with system transitions to and from the building’s winter waterside economizer, chiller short cycling, and loss of chilled water temperature control. Without reliable chilled water temperature control, damage to agency-owned computer equipment could result. IMEG led the retro-commissioning team comprised of the chiller manufacturer, original controls contractor, and facility operations team.

The cooling plant consists of two 1230Kw (350-ton) magnetic bearing chillers, one 492Kw (140-ton) magnetic bearing chiller, and one plate and frame heat exchanger. Three cooling towers mounted on the roof coupled with remote interior condenser water basins are responsible for plant heat rejection. A primary secondary pumping design is used by three constant volume primary and three variable secondary pumps for chilled water distribution.

Through meetings and observations, the following issues were identified:

Short cycling was occurring on the larger 1230Kw chillers that should not have been operating during low load times. The smaller chiller should have been operating at low load times.

The larger chillers’ condenser water 3-way valve control, which is responsible for chiller head pressure (low load) control, is a butterfly