Isaac Occhipinti, Head of External Affairs at the Hot Water Association (HWA), runs through a new design guide which sets out how stored hot water solutions can be incorporated into heat networks.

The industry develops at a challenging pace and it can be hard to keep up while still maintaining knowledge across the board. To assist engineers, the HWA has produced a design guide for an area of the industry which is still something of an unknown quantity in the UK – heat networks.

Hot water storage based solutions in heat networks have been used for decades and have many benefits over systems utilising instantaneous hot water technologies. The HWA Design Guide for Stored Hot Water Solutions in Heat Networks 2018 provides design guidance, and advice for engineers who are looking to specify stored hot water solutions working within a heat network.

Design challenge

As heat networks can range from a couple of dwellings running off a central heat source to larger district heating systems that feed thousands of consumers, it is important to note that there is no ‘one fits all’ design solution.

In recent times, there has been a drive in the heat network industry to promote the benefits of generating hot water instantaneously, while underestimating the benefits of the stored hot water solution. The design guide aims to offer an alternative for designers of heat networks by explaining a design methodology that allows stored domestic hot water solutions due consideration within the design and planning processes.

Although not exhaustive, the guide looks at the different stored hot water solutions that are available. It lists the merits of heat networks with stored hot water solutions, and sets out design guidelines for systems that incorporates stored hot water within each home. Designers should be aware that there are a number of other ways of storing energy within heat networks, such as the use of integrated thermal stores within dwellings. However, this particular guide solely concentrates on storing domestic hot water within each dwelling.

The design guide does not aim to provide a specification for manufacturers to design and produce to, but does set out applications advice to system designers which will enable them to incorporate stored hot water solutions within their heat network design, and sets out a procedure which takes the designer through the process of sizing the fundamental parts of a heat network that incorporates stored hot water in each home. It is acknowledged at this stage that this may not be appropriate for all systems and dwellings, and the designer may have to deviate from the prescribed process.

It is also worth mentioning that the increased flexibility that stored hot water solutions offer the designer will undoubtedly mean that no one system will fit all, and as such this design guide doesn’t aim to stifle that creativity.

Taking advantage

Hot water storage solutions have a range of benefits, especially when compared with their counterparts. Systems incorporating a hot water store within each dwelling work on the Flywheel Principle, requiring relatively little energy to keep the whole system topped up. The key to this is storing the hot water required for certain peak periods of the day, allowing the demand for hot water to be separated from the supply. This means that the hot water can be generated at times outside the peak demand periods of the day and at rates that level the load on the system. If we consider a typical demand profile of daily hot water usage, we see that typically most of the water is consumed over two three-hour periods, one in the morning and one in the evening.

We believe that this guide will become a useful tool for heat network designers and engineers. It is available for download from