Case study: Theater renovation includes VRF
When renovating the Columbia College Chicago Getz Theater Center, a six-story downtown Chicago building, McGuire Engineers presented a number of mechanical, electrical and plumbing design options. The college ultimately chose a solution involving heat recovery variable refrigerant flow systems with a water-cooled dedicated outside air system unit to provide heating and cooling. The steam radiators for the top three floors were to remain, so the steam boiler plant was redesigned and the DOAS unit was provided with a steam heating coil.
Two outdoor VRF systems were implemented to limit the total amount of refrigerant in the system as required by the strict Chicago code, and outdoor units were zoned with a mix of multiple interior and exterior zones. This allowed the building to use the more energy-efficient method of transferring waste heat to other locations on the same system. Grouping the east-facing units on one VRF zone and west-facing units on another allows heat to transfer from the latter zone to heat air in the former simultaneously, therefore reducing compressor energy.
The Getz Theater Center will produce higher latent loads during a performance when the audience is at full capacity. To properly condition the space with a VRF system, McGuire Engineers used a psychrometric chart to calculate the various temperature and humidity processes in the system. The team found that providing drier air to the space initially — by overcooling at the DOAS unit — and then reheating it, would help combat the latent load introduced by theatre occupants. Providing air at a dew point of 50 F allowed the system to stay within ASHRAE’s recommended range. The mixed air in the space was calculated to be 75 F at a relative humidity of 60 percent on a design day, when the theater was at maximum capacity.
In coordination with the sound consultant and the architect, the VRF units were located on the opposite side of an acoustically separated wall, above toilet rooms allowing the condensate pumps to operate without any fear of noise complaints.
Exhaust air was not able to be routed back to the DOAS unit due to space constraints and geometry of the existing building, so the engineering team considered morning warm-up. It was decided that the VRF units would operate to maintain a constant temperature through the coldest days of the year. Operating engineers were given the option to reset the temperature of the VRF system when the school would be closed for an extended period of time. Steam coils on the DOAS can operate to supply a higher output temperature to more quickly heat the building.