UTHealth East Texas – Operating Suite Comfort
The facility faced significant difficulty maintaining the proper temperature and humidity in the operating suites while simultaneously maintaining the proper amount of outside ventilation air. In addition, the facility had some very challenging space constraints for any additional equipment.
The operating suites require very specific temperature and humidity for better patient outcomes as well as staff comfort while performing medical procedures. In addition, there are very specific requirements for addition of outside ventilation air. One can imagine that the summer conditions of East Texas pose a significant challenge, from both a temperature and humidity perspective. These requirements are mandated by state and federal governments.
The space constraints for equipment were considerable, as the existing equipment rooms were full of equipment. In addition, the air handling equipment for the operating suites were located below grade on the front side of the hospital.
The first order of business was to determine what the requirements for temperature, humidity and quantity of outside ventilation air for the operating suites being served needed to be. The challenge for summer dehumidification was to remove as much moisture from the outside air as possible, plus any moisture that would be generated in the operating suite from people, etc. After considerable discussion between Mr. Robert Layton, Director of Engineering at UTHealth East Texas, the engineers at Hammel, Green and Abrahamson and others, the leaving-air temperature and airflow requirements were set at 45°F leaving-air tempeature and 13,000 cfm of ventilation air.
Given the above requirements, with very little room for additional equipment, the UTHealth East Texas engineering staff, the mechanical contractor, Wellborn Mechanical Services and Mechanical Concepts, LLC began investigating alternatives to get the conditioned air required.
For perspective, the ventilation air is drawn through a ground level grate that covers a concrete outside air intake that is approximately eight (8) feet wide and fifteen feet deep. All the outside air for the building enters through this concrete vault.
Following were some of the alternatives:
- Add direct expansion cooling coils to the entering side of the air handling units a put the air cooled condensing units on a low roof or the ground in front of the hospital.
- Add glycol cooling coils to the same air handling units and put the glycol chilled and associated pumps and tanks on the roof.
- Add a separate air handling unit to subcool the air and then provide cool dry air to the air handling units serving the operating suites. This system would require the addition of a glycol chiller to be able to provide 45°F ventilation air.
Through considerable discussion and many iterations of design, the hospital decided to utilize an air handling unit that would fit in the outside air vault and still allow for adequate space for access, as well as outside air for the balance of the facility. The unit configured was approximately 48” wide x 144” tall x 330” long. The air handling unit components included MERV 8 and MERV 11 filters, preheat coil, series glycol coils, Ultra Violet coil protection and multiple fan array. The air handling unit was provided by ClimateCraft™ and consisted of true thermal breaks, stainless steel coil casings and drain pans, access sections between all components, direct drive plenum fan array with auxiliary motor removal system, Danfoss™ variable frequency drives, UVResources® ultraviolet coil protection, MERV 8 and 11 filtration, as well as high efficiency moisture eliminators on the inlet with damper. Additionally, full size access doors with windows and lights for inspection were provided.
The cooling side of the process was a little more problematic. Mentioned previously, the mechanical room is below grade and full of equipment. In addition, the owner was reluctant to put a chiller on the exterior in front of the facility. Again, after weighing all the various alternatives, the owner decided to utilize a water cooled Multistack™ Modular chiller in conjunction with Armstrong DualArm® pumps for redundancy.
The modular glycol chiller system was configured with multiple, dual compressor modules that could easily be loaded on the elevator and fits through a 36” door. The chiller utilized a glycol storage tank to accommodate adequate system volume, which was located in the vault outside the mechanical room. Additionally, since the central plant was located nearly 1000 ft. from the mechanical room, getting central plant condenser water to equipment room was not feasible. In lieu of running condenser water from the central plant, the facility opted to utilize return chilled water for condenser water with the various head pressure control options included on the chiller for proper operation. This proved to be highly successful. In addition, the preheat coil was configured to utilize return chilled water as preheat in the winter when temperature can dip to around 20°F. The side benefit of doing this was that the return water is lower slightly, thus reducing the central plant chiller load in the winter months.
The benefits of the revision to the operating suite ventilation system was felt immediately, as the calls from the nursing staff with temperature and humidity issues was reduced from multiple daily occurrences to zero. The moisture remove rate from the system is approximately 325,000 gallons per year, which is nearly the amount of water in an Olympic size pool.
This project could not have been accomplished without a very close working relationship between the UTHealth East Texas engineering team, the Wellborn Mechanical Services team, the Hammel, Green and Abrahamson engineer and Mechanical Concepts, LLC. The various suppliers: ClimateCraft, Multistack, Armstrong Pumps, and Danfoss all optimized their equipment to work cohesively with each other to give UTHealth East Texas a highly efficient solution to a considerable problem.