Types of Hot Water Systems
A hot water system recirculates heated water through a series of pipes to radiators or air handler units, which then release the heat to the surrounding air. The system is normally powered by a boiler, which burns a fuel such as natural gas or oil to generate heat that’s then circulated through the building. The system can also be boosted by solar or hydronic (heat pump) heating, and may use a storage tank, a continuous flow or an instantaneous system.
The most common domestic hot water (DHW) systems are the cylindrical floor standing electric or gas storage tanks found in homes and apartments, which typically have a capacity that’s sized to meet the average household’s DHW needs. These systems are simple and work well for most households, with the main advantage being their relatively low running costs.
However, the efficiency of these types of systems is significantly improved when alternative energy sources are used. Using a heat pump to provide DHW is an option that provides energy savings of up to 60% when compared with a gas or electricity system, and can be the best choice in hotter climates.
Hot water systems can be classified as one-pipe or two-pipe, with a two-pipe system having an expansion tank to compensate for variations in volume of the stored water. The expansion tank is usually a closed system that compresses and expands to compensate for changes in water volume. The expansion tank also acts as a buffer, providing the optimum temperature to ensure that the temperature of the water delivered to the outlet is consistent with the demand.
One-pipe systems, which are more commonly seen in older properties, don’t have an expansion tank. This means that the water pressure fluctuates with use and can lead to the emergence of ‘cold spots’, where the hot water supply stops working. This type of system is also less efficient, and uses more energy to operate.
Electric instantaneous hot water systems are the most popular system type in Australia, with gas storage systems following closely behind. These systems heat the water on demand and only run when a tap is turned on, which minimises standby energy consumption. Gas instantaneous hot water systems also have the added benefit of being able to take advantage of cheaper ‘off peak’ electricity rates during the night.
Some DHW systems can be configured to use the same boiler system that’s used for hydronic heating. This allows a single investment to be used for both DHW and comfort heating, increasing energy efficiency. However, it’s important to ensure the hot water system is designed for these dual purposes and that adequate logic is in place to make this work effectively.