When specifying a hot water storage system, sizing will be key to ensuring a building’s demand for hot water is met. George Linder, Product Manager of Cylinders at Heatrae Sadia, explains how to size unvented hot water storage systems according to the application and usage of commercial buildings.
Generally, an unvented hot water heating system is fed directly from the cold water mains, delivering pressurised hot water to all outlets. Where there is continuous or substantial demand for instant hot water without loss in performance, unvented hot water heating systems can provide large scale, commercial capacity and fast flow rates to satisfy even the highest demands with fast heat recovery times.
Striking a balance
In a commercial building, the calculation becomes less about the size of the property and more about peak demand and hot water usage patterns, as understanding hot water usage on an individual-by-individual basis can be a near-on impossible task.
There is a careful balancing act to consider - under-sizing the hot water storage system will mean there is not enough hot water for the building’s occupants while oversizing it will mean a vast amount of energy is wasted. If sized correctly, the system should meet the needs of the building without its occupants ever having to wait for it to become operational.
Predicting peak demand
With all schemes, it is important to be able deliver sufficient hot water during a building’s busiest period. Different sectors have different demand patterns. For example, domestic homes will have a completely different usage pattern to the likes of schools, offices and hotels.
A school, for example, has set opening and closing hours and its pattern of hot water usage is likely to be fairly regular and continuous without noticeable peaks in demand. Other commercial use buildings have a very high hot water usage, particularly at certain parts of the day. For example, a hotel will often experience extremely high hot water usage over a period of around two hours in the morning and in the evening when guests are using showering facilities and on-site kitchen facilities are in use.
Sizing and recovery
There are some key factors that help with the sizing of hot water generators effectively in commercial buildings. These include: the number of sanitary outlets and items such as kitchen appliances; their respective flow rates or cyclic consumption; how many busy peak periods are likely; the duration of each peak period and the time in between each spike; the number of occupants.
Sizing and recovery go hand-in-hand. Only once you have assessed the maximum demand, frequency of delivery and the recovery time necessary, can you determine the size of the vessel required to meet the end-user’s hot water needs.
While it can be easy to oversize hot water storage systems, for commercial buildings which are already faced with large running costs for the building’s services, making savings on hot water usage can go a long way. Heatrae Sadia has dedicated personnel to help and support in any calculations, and can be contacted through specifier@heatraesadia.com.
To register for Heatrae Sadia’s CPD course on unvented hot water systems, please visit www.heatraesadia.com/specification/cpd
