Islands of Fun
The Islands of Adventure theme park is just one part of a large complex in Orlando called “Universal Studios Escape.” Dennis Rosolowski, director of maintenance, Universal Studios Escape (Orlando, Fl) directed the design and installation of the chilled water system and brought the system online. “We basically had to bring the system online in stages. The first stage consisted of the start-up phase, which was initiated in April of 1998. In December of 1998 and January of 1999, a preopening was conducted. In February of 1999, the theme park had its ‘soft’ opening. Finally, the Grand Opening was conducted in May 1999. Naturally, we found some installation problems, but nothing major. We now look forward to our first winter, which I am sure will cause us to make new adjustments due to seasonal changes,” he said.New Chiller System
The design of the central chiller plant for the theme park is an undertaking of colossal proportion. The 60 facilities served are varied in nature: shows, rides, offices, restaurants, merchandise stores, etc. The design conditions for the chiller system are assumed to be at 4,800 tons. The chiller can supply 5,300 tons of maximum cooling.Balancing the Islands of Adventure theme park chilled water distribution system was a major concern for Universal Studios. One concern was that the first facility is only 200 ft from the chiller plant discharge, while the last facility is 1,500 ft from the plant discharge. This means that the first facilities off of the distribution system could receive a water differential pressure of a little over 100 psi. Ordinary two-way control valves cannot operate properly with differential pressures that high. Valves at the end of the distribution loop do not see pressure differentials this high.
The next concern involved the wide fluctuation in pressure throughout the entire distribution system. The pressure differential between the first and last facility in the distribution system can range as high as 80 psi. Wide fluctuations in system pressure due to demand surges, seasonal changes, setpoint changes, and piping hydraulics can cause control valves to “hunt” excessively for the proper valve stem position that will meet the load requirements.
Bahram Hooriani, Holmes & Narver (Orange, CA) (formerly principal mechanical engineer, Universal Studios Escape, Orlando, FL), handled the engineering design for the project. Bahram states, “There were basically two problems here: one is the dramatic pressure drops throughout the system due to its enormity and another is the wide range of flows experienced by the system as a whole. Both must be considered in the overall design.”
Design Options
Due to the vast size of the Islands of Adventure chilled water distribution system, system balancing and diversity are critical issues. Universal Studios decided to utilize a pressure-independent control valve, the Delta P valve by Flow Control Industries (Woodinville, WA, www.flowcontrol.com). The Delta P valve does not need a pressure-reducing valve, balancing valve, or tertiary pumps.The Delta P valve internally maintains a constant differential pressure across the valve stem. Despite the fluctuations in the upstream and downstream pressures across the valves in the distribution system, the differential pressure across the control portion of the valve (the stem) never varies. Thus, so long as the differential pressure across the valve stem remains constant, the flow remains constant through the valve. A change in the rotation of the valve stem is required to change the flow. This is accomplished by placing a spring-actuated plug at the valve body discharge. The plug and the valve stem are both contained within the valve body. However, the valve is designed so that the spring maintains a constant differential across the valve stem as the inlet and outlet pressures across the valve body change.
The spring is calibrated and adjusts the plug position at the valve discharge. This alters the internal valve discharge pressure to keep a constant differential pressure across the valve stem, usually 5 psi.
Since the differential pressure across the valve stem is constant, the flow is constant. The Delta P valve is thus independent of system pressure. The flow will not change unless the setpoint is changed. When the setpoint is changed, only then will the valve stem position change, and only then will flow change.
“By utilizing the pressure-independent valve, we eliminated the use of both the pressure regulating valve and the balancing valve. Thus, we could commission the park’s entire hydronic system in one shot. There was no need to perform a system balance because by using the Delta P valve, the system is automatically and dynamically balanced at all load conditions,” said Hooriani.
Smooth Sailing
Using the Delta P valve solved the two main problems for the Universal Studios Islands of Adventure chiller project: high system pressure differentials for valves nearest to the chiller plant and wide pressure fluctuations throughout the entire distribution system.Rosolowski states, “Our start-up problems have been fairly routine, for instance, reprogramming a control loop; or something like that. All considered, the Delta P valve has meet all of our demands and requirements. The only problem we have experienced with the valve is cleaning off the sand that blows through our theme park.”
