Examination of Domestic Cold Water Systems

The design of domestic cold water systems is inherently based upon the fixture unit or demand unit method. Therefore, it is fundamentally necessary to understand these water demand units and how to interpret them in order to design efficient water systems that enable a balance between capital cost (where oversizing leads to elevated capital cost) and engineering good practice. Recent sustainability initiatives aimed at reducing water usage encourage the uptake of devices such as flow limiters, spray and percussion taps and low flow appliances and have driven peak water demands down in buildings. Maintaining water movement within the cold water system prevents overheating and helps to maintain a healthy hygienic system. Stagnation exacerbates overheating and may contribute to contamination by micro-organisms. To promote movement of cold water within pipework systems there has been a recent move towards adopting strategies that were not traditionally incorporated into cold water pipework design such as, a secondary cold water return circuit and end of line solenoid flush (dump) valves. These are an added expense, contribute to wasted water or energy and should therefore be carefully considered when incorporating into domestic cold water systems taking cognisance of the other contributory factors such as the building water usage and turnover, building air tightness standards and sanitary ware specification. Also water conservation in buildings is another reason to have an appropriately sized system for the potential water consumption as older appliances had larger flow rates than present; this subsequently has a knock-on-effect on the buildings drainage pipework, system selections and sizing, for example WCs.

This paper presents an examination into the importance of sizing a cold water distribution system appropriately and the effect of modern building design standards on operational performance. Finally, through the experience of multiple engineers from many consultancies over several years, a summary of cold water services issues caused in modern buildings is presented and potential strategies to mitigate against excessive temperatures and promote water movement and turnover is given.