When it comes to heating and hot water provision in the light commercial sector, no two buildings are identical. Roy Marsden, Product Manager at Heatrae Sadia, explains the considerations that need to be made when it comes to specifying the best unvented water heater for the building in question.
Every building is different with any number of combinations possible when it comes to water composition, fuel and water supply, and that’s before you consider the usage and demand for hot water from end-users. As such, a one-size-fits-all approach cannot be taken, and specifiers must consider several factors before committing to a particular hot water solution. It’s also crucial to not overlook the legal requirements which need to be met in the manufacture, installation and operation of unvented systems.
Considering Fuel
We often discover that specifiers have preconceptions around fuel types. However, all fuel types can be utilised when specifying or installing an unvented storage system, whether it is oil or LPG; gas; electric or a renewable source of energy.
Water Supply
Specifiers must ensure it is of adequate pressure and provides a suitable flow rate to meet any periods of peak demand. With an unvented system, the supply should be adequate to meet both the hot and cold peak demand simultaneously.
Peak Demand
It’s important to consider the application and how this impacts usage and demand. For example, while hotels may have extremely high hot water usage over a period of a few hours during the morning and evening, a school has set opening and closing hours so its pattern of hot water usage is likely to be fairly regular and continuous without noticeable peaks in demand.
Sizing and Recovery
In order to assess the size of the vessel required to meet the end user’s hot water needs, you must assess the maximum demand, the frequency of delivery, and the recovery time required. While recovery requirements will usually dictate the heating power required, this can also be dependent on the fuel type used and the output available, especially where electricity is the primary heat source, and the maximum power available can be limited.
Water Treatment and Water Composition
Key things to look out for in terms of water composition include the chloride level, the water hardness, and the level of suspended particles. Most pressure reducing valves will include a strainer mesh to prevent particles impairing the operation of the valve.
Control of Bacteria Growth
While a tank may be well-designed and compliant, if it’s installed in a poorly designed system, bacterial growth can become an issue. However, control of the conditions for bacteriological growth is achievable, whether it’s through changing thermal conditions or via chemical methods of disinfection, or UV treatment in large commercial installations.
Secondary Returns or Maintenance Trace Heating
Secondary returns or maintenance trace heating is often specified alongside larger systems, where outlets are potentially a significant distance away from the hot water store. For systems incorporating a return, it’s important to keep the circulation temperature above 55°C and to ensure temperature at the hot port of a thermostatic mixing valve (TMV) is above 50°C after one minute of delivery.
Longevity of Components
When it comes to choosing components, material can play a significant role in their longevity. For example, higher-grade stainless steels, dezinc resistant brasses and alloy sheathed elements cope well under high pressures and temperatures and should be considered depending on the application.
Discharge
According to Building Regulation ADG3, any discharge from an unvented system should be visible at some point and safely conveyed to an appropriate place open to the atmosphere where it will cause no danger to people in or about the building.
For more information on Heatrae Sadia’s latest Multipoint Eco range of unvented water heaters, please visit: https://www.heatraesadia.com/products/cylinders-and-hot-water/electric-unvented-storage/multipoint/multipoint-eco
