Sindoni Consulting & Management Services Inc.: Kaiser Permanente San Diego Central Medical Center

Commissioning, retro-commissioning; HVAC; health care facility; and new construction

08/09/2018


Engineering firm: Sindoni Consulting & Management Services Inc.

2018 Commissioning Giants rank: 16

Project: Kaiser Permanente San Diego Central Medical Center

Location: San Diego, CA, United States

Building type: Hospital/health care facility; parking garage/service station

Project type: New construction

Engineering services: Commissioning, retro-commissioning

Project timeline: May 2012 to March 2017Commissioning budget: $855,470

 

Challenges

Active chilled beams (ACBs) in patient rooms

Maintaining the patient room temperature within defined heating and cooling set points while staying above the building management system (BMS)-calculated dew point temperature.

Background

Supply air is provided at a constant volume and a constant temperature (55°F). Air is exhausted via a hard-balance (e.g. not regulated). The T-24 mandated temperature dead-band of 5°F is maintained with a heating set point of 70°F and a cooling set point of 75°F. A 6-way control valve throttles "non-condensing" chilled water (NCCHW) at a constant temperature of 57°F, or "low-temperature" heating hot water (LTHHW) at a constant temperature of 120°F to the ACB. Upon a loss of control power, the 6-way control valve actuator (0 to 90 deg) spring-returns to 0 deg. The 6-way control valve and actuator provides 100% to 0% LTHHW as it modulates from 0 to 33 deg, no flow as it modulates from 34 to 66 deg, and 0% to 100% NCCHW as it modulates from 67 to 90 def. The BMS monitors the patient room temperature and humidity to calculate the ambient dew point temperature.

The sequence of operations mandates that if the BMS-calculated dew point temperature is less than 4°F below the NCCHW supply temperature (e.g. > 53.01°F), then the 6-way control valve actuator is commanded to a 45-deg position (e.g. no flow). Separately, a moisture switch is installed on the ACB supply header. If the moisture switch trips, then control power to the spring-return-to-0-deg actuator is interrupted and the ACB reverts to a full heating mode of operation (100% LTHHW). The status of the moisture switch is not monitored by the BMS and, when this occurs, the space temperature increases in an uncontrolled fashion. When facilities personnel view the BMS operator work station graphics, they see a BMS command of 100% to the 6-way control valve actuator (90 deg corresponding to 100% cooling), yet an increasing patient room temperature. Without the capability of knowing the moisture switch status, facilities personnel are required to perform a physical, above-ceiling inspection in the corridor adjacent to the patient room.

Solutions

ACB condensation prevention measuresWithout adding cost to the project, the sequence of operations has been revised to allow the BMS-calculated dew point temperature to drift up to 2°F below the NCCHW supply temperature (e.g. > 55.01°F) before the 6-way control valve actuator is commanded to a 45-deg position (e.g. no flow). When this occurs, the 6-way control valve actuator remains in a no-flow position until the BMS-calculated dew point temperature falls below 55°F (which corresponds to 2°F or more below the NCCHWS temperature of 57°F) for 15 minutes-at which time modulation of the 6-way control valve actuator resumes. While the status of the moisture switch is still not monitored by the BMS, a pro-active (anticipatory) BMS alarm condition has been defined and programmed to annunciate an increasing, BMS-calculated dew point temperature prior to activation of the moisture switch-and associated interruption of control power to the spring-return-to-0-deg actuator, precipitating a full heating mode of operation (100% LTHHW) and uncontrolled patient room temperature.

Recommendation

While not implemented on this project, monitoring of the moisture switch status by the BMS and providing the facilities staff with the capability of monitoring the moisture switch status from the BMS operator work station graphics would allow for initial response remotely-either by increasing the NCCHW supply temperature set point or by manually commanding the BMS output for the 6-way control valve actuator to 45 deg (no flow).

It is acknowledged that more frequent monitoring of the BMS-calculated dew point temperature would be required to determine when the NCCHW supply temperature can be decreased, or the manual override of the BMS output command for the 6-way control valve actuator can be released. However, BMS monitoring of the moisture switch status would provide some means of pre-action where none currently exists.



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