Trane SYS-APM001-EN manual Plant Expansion, Alternative fuel, Thermal storage

System Issues and Challenges

situation. Electrical generation can be outsourced to avoid internal capitalization.

A variation of electrical generation uses an engine indirectly- or directly- coupled to a chiller. Either variation produces chilled water using an alternative fuel such as natural gas or fuel oil. The indirect-coupling method allows the chiller to operate using an alternative fuel or electricity from the grid. An engine directly-coupled to a chiller can only run using the alternative fuel.

Alternative fuel

Some designers prefer to employ chillers that use fossil fuels or perhaps renewable fuels. Examples are absorption chillers using natural gas, steam, hot water, landfill gas, biodiesel, or waste-to-energy boilers. Plants with these chillers, discussed in detail elsewhere30, allow the owner to take advantage of expected fuel rate separations.

Thermal storage

Another successfully applied alternative-energy source is thermal storage. Chillers make either ice or chilled water during times of lower electricity costs. The energy is stored in tanks and then discharged to satisfy cooling loads during times of high electrical costs. Other manuals and an Engineers Newsletter describe the use of thermal storage in detail. 31, 32, 33, 34, 35

Use any of these technologies to provide value to the building owner through judicious use of alternative fuels.

Plant Expansion

Plant expansion can be performed easily in either a primary–secondary or variable-primary-flow system by adding another chiller and pump to the system. The two major considerations will be whether the chilled-water distribution pipes will be able to handle the flow and how to install the new chiller while other chillers are still providing cooling. When the new system flow rate complies with good piping practice and the pumps can deliver the water, the process works well.

To maintain chilled-water flow during installation of a new chiller, some plants are constructed with piping stubs in place for the new chiller. In this way, the new chiller can be installed while the system is still operating, then the valves in the stubs can be opened.

When decoupled systems are used on large campus-type systems, added loads are often located some distance away from the original loads. Yet, planners like the idea of somehow hooking the new loads to the existing system. The “double-ended” system discussed in “Chiller sequencing in a double-ended decoupled system” on page 54 is one way of handling this requirement.

SYS-APM001-EN Chiller System Design and Control 83