Pipes background - illustration

+ Good quality data is required to ensure that a building’s hot and cold water system is the right size.

Design engineers often get very excited about systems that reduce the environmental impact of our buildings, like solar hot water systems and rainwater harvesting. Our designs are (rightly) influenced by regulations, codes and standards. But regulations, codes and standards do not always keep pace with how buildings, systems and people interact. We need up-to-date data.

For example, engineers estimate the maximum demands placed on hot and cold water systems so that the systems will provide water at the required temperature and flow rate. The designer needs to consider the likely maximum demand at any one time, which in turn determines the size of the water system. This is fairly easy for a home but more complex for a hospital or a student accommodation block, where demand is harder to predict. This estimation has a knock-on effect on associated equipment such as the size of the central hot and cold water plant – including pumps and pipe sizes. 

The design data underpinning these codes was mostly collated in the 1970s, based on the ‘loading units’ methodology. But water appliances and patterns of use have changed dramatically since then. New water appliances have appeared and others have become more efficient. If the codes are followed, it is likely that hot and cold water systems will be oversized (and therefore not as economical) which can also lead to other costs such as increased space take, increased energy and water use as well as lower throughput of water and the water quality issues that brings.

Across the world, there are many methodologies to tackle this simple design issue and they all aim to provide the designer with a way of estimating the peak (simultaneous) hot and cold water loads. They either build up the loading using a factor for each group of water using appliances or they use diversity factors to estimate the peaks.

Working internationally, the UK industry has recognised that fundamental design data used for sizing hot and cold water systems is out of date. So a team has begun to collect new data that will inform a new methodology. Arup has helped pull together support from across the industry working with Heriot Watt University to develop proposals that will ‘right-size’ hot and cold water supply systems. If we get this right, then it will reduce their environmental impact, as well as lower capital and operating costs.

So while renewable technology and water-saving innovations can make a big contribution to environmental problems, we need to bear in mind that they’re only one part of the system. To maximise energy and water savings, we need to make sure that all our estimates are based on up-to-date, accurate data.