SPONSOR CPD PROGRAMME Continuing professional development (CPD) is the regular maintenance, improvement and broadening of your knowledge and skills, to maintain professional competence. It is a requirement of CIBSE and other professional bodies. This Journal CPD programme can be used to meet your CPD requirements. Study the module and answer the questions on Predicting domestic hotwater use in commercial, institutional and multiresidence buildings completed module is equivalent to 1.5 hours of CPD. Modules are also available at www.cibsejournal.com/cpd This module explores the issues around assessing domestic hot-water demand in order to optimise plant and distribution network sizes and capabilities The estimation of demand for domestic hot water (DHW) in buildings continues to provide an area of uncertainty in building services design. The primary objective is that the hot-water service should be capable of meeting peak demands while attempting to maintain optimum plant and distribution network sizes and capabilities. A contemporary and future-looking DHW system design may vary significantly from historic norms, and so deserves careful assessment to maintain appropriate hot-water supplies while minimising environmental and financial impact. Hot water systems, which are employed in practically every occupied building in the UK, are increasingly important elements in the design of sustainable and resilient built environments. As the standard of thermal performance in the building envelope improves, the heat required for the DHW becomes a more significant proportion of a buildings heat demand. In smaller low-rise buildings, systems supplying hot-water outlets are increasingly being directly fed without interim cold-water storage so directly impacting the predicted demand on wholesome cold-water supply. Also, in larger buildings, advances in pumped, pressure controlled water systems are delivering increased precision in design flowrates. Alongside this, the increasingly urgent need to reduce the lifecycle carbon impact of engineered systems means that designers must account for both the embodied, as well as the operational, carbon impact. Optimisation is therefore the key, but without appropriate data on hot-water consumption to inform that system design, it is very unlikely that systems will be installed and operate economically in water usage, cost, and carbon terms while also being able to meet the primary need of delivering hot water to building users. In Mohammeds recent paper1 it is noted that water use in buildings has reduced significantly in recent years, owing to increased user awareness of environmental impacts and the adoption of water efficiency measures. However, the paper reports, despite considerable changes in water end use and users behaviour, there have been no corresponding changes in sizing methodology and no significant update to the design equations. Therefore, as reported by Tindall,2 it would appear this leads to oversizing of water systems in buildings. The method adopted for estimating the demand on the hot-water system will depend on the type and application of the system that is being designed, and will also be subject to the building layout, distribution and type of water outlets, and the pattern of hot-water usage across the day. CIBSE Guide G3 relates that the size of plant required is determined by the draw-off rate and pattern of consumption in each day, and that the hot-water storage capacity should be related to both the design consumption and recovery rate. In the UK, hot-water production and storage temperatures must www.cibsejournal.com May 2021 75 CIBSE May 21 pp75-78 CPD 179.indd 75 23/04/2021 16:17