Paul Sands of Stokvis Energy Systems offers an insight into how plate heat exchangers (PHEs) can help bring the best from renewable energy sources and solve other issues for building services professions.
With oil as well as wholesale energy prices on an upward trajectory again, and new nuclear seemingly no nearer to coming on line, renewable heat sources are increasingly seen as both sustainable and economically attractive by policy makers.
In fact, the planet’s gradually diminishing fossil fuel reserves and environmental pressures are making technologies, such as solar thermal, ground or water source heat pumps and harvesting waste heat, worthy of consideration for many new residential and mixed-use developments. High performance plate heat exchangers are ideally suited for different applications within such schemes.
One of the most stable sources of renewable energy is open water, including rivers, estuaries and lakes, though harvesting it is complicated both practically and from the aspect of protecting aquatic life.
For a recent project drawing water from the Thames near Waterloo, however, a Stokvis bare plate heat exchanger was installed to transfer heat from the river water to water source heat pumps. The unit operates at 99% efficiency while protecting the WSHP’s components contamination and corrosion. Where salt water is involved, stainless steel plates can be swapped for titanium.
Plate heat exchangers can similarly operate on the input/primary side for projects drawing waste heat from power plants and industry, or as an interface where individual buildings connect into the heat mains of a district heating scheme; also referred to as heat networks. Then at the consumer end of the distribution mains, specifiers can make use of standard or custom built heat interface units (HIUs) to deliver space heating and domestic hot water for occupants.
Another application for plate heat exchangers is growing in popularity due to the number of ‘tall buildings’ being constructed; while hundreds more are planned around our major cities. In these instances, PHEs are used as a pressure break, where heating, water service or chilled water is being pumped up multiple storey heights.
Typically, where boilers are located in a basement plant room and the maximum working pressure is say 6.0 Bar, a pressure break can be created at the appropriate point on the riser with a plate heat exchanger to ensure the maximum pressure on the boiler does not exceed 6.0 bar, this pressure break could be created again if necessary, as the risers continue up the building, though sensibly there would be a couple of degree drop in temperature which must be taken into account at the starting point.
In other applications, bare plate heat exchangers can be utilised to convert from a medium temperature hot water system, to a low temperature one for the delivery of services; or simply specified to protect boilers against contamination from old pipework in retrofit situations.
Such is their versatility that bare plate PHEs are also widely used in industry: interfacing with steam circuits, or being used to heat chemicals in process engineering.
With pressure to continue building upwards in our congested urban areas, and a growing reliance on renewable or sustainable heat sources in place of fossil fuels, it seems the specification of high efficiency plate heat exchangers can only grow.