©2013 This excerpt taken from the article of the same name which appeared in ASHRAE Journal, vol. 55, no. 7, July 2013.
By Michael Fullerton, P.E., Member ASHRAE
About the Author
Michael Fullerton, P.E., is a principal at TME, Inc., Little Rock, Ark. He is a certified ASHRAE Healthcare Facility Design Professional and a member of the Arkansas ASHRAE chapter. This project also won ASHRAE's Refrigeration Comfort Cooling Award for Project Excellence.
How do you keep a hospital running while replacing all of the infrastructure components? You need an exceptionally solid plan. The Medical Center, a 700,000 ft2 (65 030 m2) hospital located in Columbus, Ga., developed an 18-phase strategic master plan enacted over a seven-year period. The target ENERGY STAR rating after all of the infrastructure projects are completed is 75 (up from 24). The scope of Phase 2 included converting the existing chilled water plant from a constant volume primary secondary system to a variable primary system. Chillers 1 and 2, the plate and frame heat exchanger and associated pumps were replaced while Chiller 3 remains in the facility.
The project also included a renovation of the existing heating water system. The existing heating water pumps were equipped with variable frequency drives. The existing steam-fired heating water converters were also replaced. All of these central plant modifications had to be performed without shutting the hospital down. A new heat pump chiller (Chiller 1), which produces 42°F (6°C) chilled water and 15°F (66°C) heating water simultaneously, was installed in the hospital. The use of this technology raised the ENERGY STAR rating from 24 to 58. The project also reduced the total amount of CO2 produced by 3,388 tons per year.
The existing chilled water system consisted of three chillers. Chiller 1 was a 650 ton (2286 kW) centrifugal water-cooled chiller installed in 1980. Chiller 2 was a 750 ton (8040 kW) centrifugal water-cooled chiller installed in 1980. Chiller 3 is a 1,280 ton (4502 kW) centrifugal water-cooled chiller installed in 1993. Chiller 1 and Chiller 2 used R-12 refrigerant. Chiller 3 uses R-123 refrigerant. Each chiller was designed with a dedicated chilled water pump. The piping system was designed with circuit setters for constant volume pumping. Chiller 1 and Chiller 2 were piped in series while Chiller 3 was piped in parallel with the series chillers. There was also a plate and frame heat exchanger for free cooling installed in parallel to the chillers. The chiller plant did not have a refrigerant monitoring system.
The hospital had two independent heating water systems. The first heating water system had two steam heating water converters with three constant volume pumps installed in 1980. The second heating water system had one steam heating water converter with two constant volume pumps installed in 1993.
The existing steam system has two 400 hp (3924 kW) fire tube boilers that were installed in 1981. The boilers produced 150 lb steam at 15,000 lb/h for the humidifiers, sterilizers, and heating water.
The existing chilled water, heating water, and steam piping were insulated with fiberglass. Most of the existing piping labels were missing from the piping. The outer layer of the insulation was torn from years of maintenance.
The new chilled water system replaced Chillers 1 and 2. Chiller 1 is a 600 ton (2110 kW) water-cooled heat pump chiller that produces both heating water and chilled water. Chiller 2 is a 1,200 ton (4220 kW) centrifugal water-cooled chiller with an adaptive frequency drive. The existing Chiller 3 is reused as a backup chiller.
Chiller 1 uses R-134a refrigerant, and Chiller 2 uses R-123 refrigerant. The piping system was converted to a variable primary pumping system. New chilled water pumps with variable frequency drives were installed. All of the existing circuit setters have been removed. The heat pump chiller is piped in series and parallel, depending on the mode of operation. During the heat pump mode, the chiller will be in series. When the chiller is changed to chiller mode, the chiller will be in parallel. A new refrigerant monitoring system is installed between the new chillers.
The hospital’s two independent heating water systems were combined into one system. Two of the steam heating water converters were replaced with new converters. The three existing constant volume pumps were equipped with variable frequency drives, and the triple-duty valves were removed. The second heating water system converter and pumps were removed. The heating water produced from the heat pump chiller was piped in parallel to the new heating water converters. The existing steam fire-tube boilers have been reduced to low fire, and now are only required to produce 75 lb steam.
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