Background
CBS Television City was built in a series of phases. The initial phase included two adjacent buildings, the studio complex (containing four state-of-the-art studios, three sizeable rehearsal halls, dressing rooms, an office and administration area) and much more. Spanning 8.5 acres at an estimated cost of $12 million to CBS, the complex demands 1,100 tons of air conditioning capacity. Because of the need to keep performers and audiences comfortable inside heavily lighted, heat-intensive studios, the cooling requirements - and the demand for HVAC system flexibility - have always been higher than average.
CBS executives and engineers knew they needed to find a way to combat excessive electrical bills, while developing a system with the ability to generate extremely low water temperatures.
What they found was thermal energy storage (TES). A method of deriving energy from melting ice, TES systems allow the transfer of stored cooling energy from melting ice to the building load. The process can literally save thousands of dollars in energy costs each year because ice is produced at night, during off-peak, less-expensive hours (depending on the utility's rate structure).
At CBS, the stored energy is then discharged for cooling during on-peak hours (from noon to 6 p.m.), the time of day when electrical costs are at their highest.
Because CBS engineers had been pleased with their decision to install TES tanks during the complex's initial expansion in 1992, they knew TES was the answer to lowering their electricity bills. The question, however, was what role TES should play in the sequel to the expansion that had already proven successful.
Planning the Second Installation
Despite the known ability of TES to lower energy costs by managing time-of-use rates proactively, most engineers want to know the answer to at least one question before including TES in their specific projects: "How long is the payback period?"
Facilities manager Gary Gillet, controls technician Tom Amato, and other members of the CBS engineering team were no different. The mammoth studio contracted with Energy & Mechanical Systems Consultants, Inc. (EMSC), Santa Monica, CA, to conduct a feasibility study on the benefits - and potential payback - of thermal energy storage before proceeding. EMSC developed a study designed to resolve three major challenges:
In addition, the study addressed whether CBS would benefit from expanding its existing TES capacity. EMSC found that TES would, in fact, not only be feasible, but would also greatly increase system flexibility and maximize the use of high-efficiency chillers.
Although flexibility, efficiency, and energy-saving benefits were major reasons for installing TES a second time, they certainly were not the only ones. In particular, CBS needed to adjust the chilled-water supply to lower-than-normal temperatures, a feat that could not be achieved by a traditional system alone.
According to the feasibility study, TES would allow CBS to lower the chilled-water supply to the central system from between 44o and 45oF, to around 40o to 42oF - a major benefit to facility engineers charged with keeping superstars and audiences comfortable in densely packed TV studios.
To achieve CBS' goals, the EMSC engineering package recommended four key components:
The ice storage tanks from FAFCO (Chico, CA) were static glycol models. According to the manufacturer of TES equipment, these tanks use a cold glycol-water solution that circulates from the chiller into a storage tank with heat exchangers submerged in water. During the charge cycle, columns of ice form around the heat exchangers. During the discharge cycle the ice melts, transferring the cold energy to the building load.
A rectangular, rather than circular, tank design is a major reason why CBS selected the FAFCO models. Engineers realized the rectangular-shaped tanks of different sizes could more easily fit into a fairly tight opening in the wall of the chiller plant, and the existing storage space included both sloped and horizontal floors. The manufacturer's modular, multi-size approach also made installation easier by allowing for on-site assembly, if necessary. According to the feasibility study:
Overall Payback
From the perspective of the new design as a whole, the system met all expectations. The chiller plant performed according to the design intent, and the chiller, pump, heat exchanger, and controls all met their performance specifications.
As for the cost-saving impact of TES, results exceeded initial expectations significantly.
A post-installation study commissioned by the City of Los Angeles Department of Water and Power, and conducted by Ayres & Ezer Associates, Los Angeles, showed that projected annual savings in electric bills were $228,473, nearly $53,000 more than the $175,734 projected in the original feasibility study.
Payback on the system was also shorter than anticipated. Payback on the TES component itself was achieved in 18 months, helped by a rebate of $269,000 from the Department of Water and Power. Without the rebate, payback still would have been less than 30 months, a shorter period than originally anticipated.
CBS executives and engineers involved believe TES has proven to be an excellent performer. And, even in the wake of utility deregulation and a diminishing number of utility rebates, they still believe TES offers an attractive means of lowering energy costs.
