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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Energy ef ciency is a pressing area of concern in the modern healthcare industry. On one hand, unlike many other industries, hospitals have stringent health and safety requirements that make energy reduction dif cult. In addition, certain portions of hospital buildings may be required to maintain cooler temperatures and higher air-change rates just to meet minimum code requirements. Given specifi c state or federal guidelines outlining the protocols for hospital mechanical designs, it becomes challenging to fi nd areas where potential energy savings are possible. However, these savings are possible and the return on investment is high for those hospitals willing to investigate the opportunities. One of the most common areas that facility managers will investigate for energy inef ciency measures is the hospital central plant. After all, the plant is working overtime to support the constant cooling, heating and emergency power needs for spaces typically spanning hundreds or thousands of square feet. Still, while the plant itself is a large source of energy use, it's not the only one to be considered. Some of the highest savings can be found simply in analyzing systems controls and airfl ow management. Whole-system approach P2S recently completed a study of a San Diego, California area hospital's central plant. Through testing, it was de- termined that simultaneous heating and cooling was occur- ring during ambient conditions above indoor temperature setpoints. This equated to 10 percent of the chilled water plant's tonnage output at any given moment. This hospital, like many others, have constant volume air handling systems with hot water reheat for tem- perature control at the zone level. The facilities management team decided to look at its entire system to determine how much reheating was happening throughout the hospital. What they found is that the supply air temperature control of air handling units was generally set to a constant temperature in the low 50s, with a reset func- tion based on zone demands. This resulted in the maximum reheating of all airfl ow in the hospital at all times. This "setting it and forgetting it" method was forcing constant cooling and reheating of air, which in turn caused energy costs to remain unnecessarily high. Selecting critical zones and using them to reset air handler supply air setpoints reduces chilled water demands. This does mean that a program of getting critical zones tied into the building control system is necessary if they are not already. It is also essential that these critical zones have adequate airfl ows for the room loads that they serve so the zone is not indicating a 100 percent cooling demand at all times. At one of the hospital's other facilities, several other energy-conservation measures have been implemented with great success. One of these involves the chilled water system supply water tempera- ture. Much like the supply air temperature for air handlers, the chilled water temperature for a hospital is often set for the low 40s temperature to satisfy the worst-case cooling requirement without resetting throughout the day. In a hospi- tal, operating rooms often gov- ern the temperature of chilled water plants. Because ORs are maintained at temperatures of ANALYZING SYSTEMS CONTROLS, TEMPERATURE, AIRFLOW AND PRESSURES TO DETERMINE LONG-TERM ENERGY EFFICIENCY BY MICHAEL GILMORE & PAUL LUSTER BEYOND THE CENTRAL PLANT BUILDING CARE & OPERATIONS ISSUE FOCUS Heating hot water (Btu/hour x 104) and coincident OSA temperature for Scripps Memorial Hospital, Encinitas, California . SAN DIEGO AREA HOSPITAL: SAMPLE ENERGY COSTS (PER YEAR) Before Controls Analysis After Controls Analysis Total: $563,057 Total: $480,707 Per SF: $3.21 Per SF: $2.74 Total savings: $82,350/year 36 Medical Construction & Design | J U LY/AUGUST 2015 | MCDM AG.COM

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