ABSTRACT

Solving Equation involves tedious computation and the Chartered Institution of Building Services Engineers guide publishes tables for the flow of low temperature hot water at 75°C in clean, medium grade, black steel pipes to B81387: 1967. However, chilled water flowing in pipelines is likely to be at about 7.5°C and cooling water at about 30°C. The minimum working pressure of the water in the system must always exceed the saturation vapour pressure corresponding to its temperature; otherwise water will flash to steam. A safety margin of 12 K, beneath the boiling point related to the pressure of the water, is necessary. The full chilled-water flow rate passes through each chiller and this gives a high pump head with potentially high energy consumption for the primary pump. The chilled water flow temperature might be 5°C, on the right-hand end of the diagram next to a cooling water flow temperature of 26°C, to give a difference of 21 K.