A Thermal store is one of the most popular types of hot water cylinders, especially in rural locations where multiple fuel sources are being used and high rise developments where mains pressure is required without the discharge complications that an Unvented cylinder can bring.
There are generally two approaches to the design and manufacture of a thermal store. Firstly the coil based thermal store and secondly, thermal stores featuring an external plate heat exchanger (PHE).
With the coil type thermal store, the domestic water passes through an extra-long high efficiency copper coil, drawing heat from the surrounding thermal store of water, to deliver mains pressure hot water at the required temperature.
The thermal store with external Plate Heat Exchanger, on the other hand, uses a far more complex way of delivering hot water and features more components - pump, PHE, flow switch and wiring centre, while they work extremely well, there are obviously more components to potentially go wrong.
The external Plate Heat Exchanger approach was originally developed to overcome the inferior thermal transfer properties of stainless steel. The method directs the cold mains through the flow switch and one side of the PHE, which then activates a primary pump to circulate the thermal store water round the other side of the PHE.
The coil type thermal store offers many benefits over the plate heat exchange model, mainly due to the simplicity of the system. The use of the coil means that there are less moving parts and therefore is less likely to go wrong. This makes them particularly attractive in rural locations, where power cuts are more likely and in social housing developments where access for repairs can be difficult.
The very nature of the thermal store means that both options may be susceptible to the build-up of lime scale in areas where there is hard water, however this is easily addressed by ensuring that the correct amount of inhibitor is added to the system.
At McDonald Engineers, all of our thermal stores are manufactured using copper and the vast majority feature the coil system. We believe simplicity is most effective and this system does not have the potential issues which can be associated with the plate heat exchanger set up.
In fact the only time we would recommend using an external plate heat exchanger is where the thermal store is going to be installed in an area which are especially susceptible to hard water or when an extremely high flow rate is required.
But as with all projects, we would always recommend discussing all of your options with our technical sales team who can advise on the best possible solution.