Introduction
Central plants, for this course, include boilers, producing steam or hot water, and chillers, producing chilled water. These pieces of equipment can satisfy the heating and cooling requirements for a complete building. In a central plant, the boilers and chillers are located in a single space in the building, and their output is piped to all the various air-conditioning units and systems in the building. They are used in all types of larger buildings. Their initial cost is often higher than packaged units and they require installation floor area as well as space through the buildings for distribution pipes. Central plants generally require less maintenance than numerous smaller package systems and the equipment usually has a longer life.
This central plant concept can be extended to provide heating and cooling to many buildings on a campus or part of a town. The equipment for these larger systems is often housed in a separate building which reduces, or avoids, noise and safety issues.
We will be discussing some of the advantages and disadvantages of central plants and then we will go on to consider the main items of equipment found in central plants: boilers, chillers and cooling towers.
Boilers are pressure vessels and their installation and operation are strictly prescribed by codes. Their general construction, operation, and main safety features will be discussed.
Chillers come in a huge range of sizes and types and we will briefly introduce them. We will discuss their particular requirements for chilled water piping and specialized control.
The job of the chiller is to remove heat from the chilled water and reject it to the condenser. The condensers are often water-cooled. The cooling water is called “condenser water.” The condenser water flows to a cooling tower, where it is cooled before it returns to the chiller to be heated once again. This will be discussed in detail in 10.4.
Cooling towers are devices used to cool water by evaporation. Water is sprayed or dripped over material with a large surface area, while outdoor air is drawn through. Some water evaporates, cooling the bulk of the water before it returns to the chiller.