Chapter 8 - All-Water Systems

Abstract

In an all-water system, space cooling and/or heating is provided by chilled and/or hot water circulated from a central refrigeration/boiler plant to terminal units located in, or immediately adjacent to, the various conditioned spaces. Heat transfer to/from the room air occurs via forced or natural convection. Except for radiant systems, radiant heat transfer is usually nominal due to the size and arrangement of the heat transfer surfaces. All-water systems can be employed for both heating and cooling. Heating water is supplied either through the same piping network used for chilled water in summer or through an independent piping system. The study explains system concept and shows that all-water systems, typically installed, can be classified into three basic types: two-pipe systems, in which the terminal units are served by two water pipes—a supply and a return. Chilled or hot water is circulated alternately through the single closed loop to the terminals; three-pipe systems, in which each terminal has a separate chilled- and hot-water supply but only a single, common return; four-pipe systems, in which two separate piping systems supply and return either hot water or chilled water to separate coils (or a single dual-use coil) within the terminal units. In addition, the chapter discusses two-pipe systems, two-pipe system plus supplemental heating, two-pipe systems with total electric heat, and four-pipe systems.