FMs can take the pressure off costs, energy expenditure and safety when delivering hot water to a commercial building, says Stephen Lynch.
1. Size any storage hot water capacity correctly
It can be tempting to opt for the most powerful system possible to avoid under-performance. But over-specification can cause its own problems, so it is vital that a comprehensive assessment of demand is carried out. This involves looking at what the hot water is needed for, as well as any use patterns that a building may display. This will help to establish what size storage water heater is required and indicate other aspects such as recovery time.
Physical space can often be a key factor in sizing the system, as finding a location for a large storage water heater can sometimes be problematic. In these cases, it is possible to reduce size by increasing the electrical rating of a water heater. An increased kW rating can help to deliver additional hot water over the same period of time, however, the electrical supply may be limited – and this needs to be taken into account.
2. Use mains or boosted pressure where possible
An unvented water cylinder is able to draw water directly from the mains supply, which helps to guarantee maximum flow-rate performance. It also negates the need for a cold-water tank, helping to save space on the premises.
In some circumstances it may not be possible to connect directly to the cold-water mains, such as in large commercial projects or high-rise buildings. In these cases, the water pressure can be boosted using a pump and a suitably sized break tank.
3. Make sure hot and cold water are at a balanced pressure
Hot and cold water should both be delivered at the same pressure to delivery outlets, to make sure the system is operating correctly. This is achieved by using pressure-regulating devices on the hot and cold-water feeds.
An unbalanced pressure can prevent mixing valves from working correctly, which can ultimately lead to water being delivered at incorrect temperatures – increasing the threat of scalding. It can also cause a backflow of water in one direction, which increases the risk of contamination and may contravene local water regulations.
To stop this happening a double-check valve on the cold-water feed is required to protect the cold water main from backflow contamination.
4. Keep water heaters as close to the final outlet as possible
Not only will keeping water heaters close to the final outlet reduce the risk of legionella, but this will also guarantee that hot water is delivered to outlets in a timely manner (within 60 seconds), compliant with current CIBSE guidelines.
For larger systems, where outlets may be a significant distance away from the hot water store, secondary returns should be specified to ensure that there is adequate hot water supply at every point of use.
When designing systems that incorporate a return, it is important to keep the stored temperature above 60°C, circulation temperature above 55°C, and the delivery from the hot tap – or the hot port of a thermostatic mixing valve (TMV) – above 50°C.
5. Quality of delivered hot water should be paramount
For certain applications, such as healthcare, the quality of the water is absolutely critical. With water systems that use sacrificial anodes there may be may a risk of magnesium particles being delivered to the outlets.
In these instances, high-grade copper or stainless steel tanks should be specified to optimise the water quality and reduce continuing maintenance costs. Some systems have the added advantage of a built-in legionella protection cycle and integral smart thermostatic controls. Ultimately, this will help to increase the lifespan of a product, and to improve the performance and safety of a hot water system.
Stephen Lynch is business development manager - commercial and corporate specification at Heatra Sadia
