Medical Construction & Design

JUL-AUG 2015

Medical Construction & Design (MCD) is the industry's leading source for news and information and reaches all disciplines involved in the healthcare construction and design process.

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65-68 F and relative humidi- ties no greater than 60 percent during procedures, chilled wa- ter temperatures typically are kept at 42 F in order to meet these requirements. Even with this requirement for the ORs, there are many hours in the year, throughout the early morning, late evening and non-peak cooling months that the low 40s chilled water temperature is not required to meet all the hospital's cooling needs. By utilizing air side economizers on air handlers controlled to be the fi rst level of cooling and integrated with the chilled water system, reset of the chilled water plant's supply water temperatures can be achieved for up to 30-40 percent of the plant's operating hours throughout the year. The facility looked at a few critical air handling units throughout the chilled water system and monitored their chilled water valve positions. By doing this they could make sure that no air handler was out of control (100 percent open) and reset the chilled water temperature down to maintain all valves in control. It also provided input to the reset control sequence to reduce the chilled water supply air temperature when all valve positions were satis- fi ed. The primary goal of the strategy was to have at least one valve at a 95 percent open position at all times and all others at something less. Examining additional measures Additional measures were implemented to control overall chilled water system pressure setpoints in order to main- tain adequate control valve operation. By monitoring the ambient dry bulb and dew point temperatures, the chilled water plant pressure control setpoint could be adjusted up and down throughout the day based on the change in these ambient conditions. The range of pressure for this facility at a remote location from the plant was as low as 4 PSI dur- ing nighttime winter months and as high as 18 PSI during the daytime in the summer months. The control strategy has two rates of change, which reset the system pressure setpoint. The fi rst is based upon the change in dry bulb, which is at a slower rate of change; the second is based on the change in dew point, which is at a higher rate of change. This control sequence took time along with trending data to refi ne the rates of change for the system. Over time, increased reductions in pumping brake horsepower resulted for many hours of the year with no loss in chilled water system performance. The fi nal area being considered to reduce energy consumption is directed at the airfl ows for unoccupied spac- es. The number of required air changes varies depending on whether the room is occupied or unoccupied, and the dif- ference can be signifi cant. In California, the requirement for an operating room with re-circulated air varies from a maximum of 20 air changes to a minimum of just six. This means if the building controls or sensors are not set to limit air changes when the room is unoccupied, the system will continue to change air at the maximum levels, thereby costing the hospital money in excessive airfl ow and added brake horsepower at the fan. The hospital learned all these energy-conservation measures require the zone level controls and airfl ows be functioning correctly to imple- ment. So when most facilities are looking to add more central plant equipment to solve capacity problems, this facility looked at controlling airfl ow, temperature and system pres- sure to limit capacity require- ments and improve overall system ef ciency. Although the 24/7 nature of the hospital presents dif cul- ties when it comes to energy savings, there are still many savings to be realized, even beyond ef cient central plant design. By analyzing connect- ed loads and the fl ow of energy throughout a building, as well as the system controls in place to guide these fl ows, hospitals can fi nd extraordinary savings. Even more, because hospitals are designed to last decades, such studies present a solid return on investment — ensur- ing savings now and long into the future. Michael Gilmore is healthcare market leader, and Paul Luster, P.E., is senior mechanical engineer, for P2S Engineering. BUILDING CARE & OPERATIONS ISSUE FOCUS MCDM AG.COM | J U LY/AUGUST 2015 | Medical Construction & Design 37

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