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Instantaneous hot water systems have become commonplace within the process industry, forming the basis of design over the traditional storage calorifier.  With plenty of aspects to consider to ensure the maximum effectiveness and reliability of these systems, Angelo Giambrone, Healthcare business development manager at Spirax Sarco UK explains why looking at the bigger picture can help.

How can hot water be generated on-demand, without the need for stored volumes?  Over the last 20 years or so, we have seen a shift in the way hot water for both process use and hand washing is produced. Traditionally, storage calorifiers were used, consisting of a large tank capable of generating heat within a mass of water using a heat transfer coil heated by steam.  While this approach is familiar to many, the problem is that the stored water volume continually radiates heat, which therefore limits efficiency levels, plus it can introduce a point of risk for legionella. 

The modern solution?  Plate heat exchange technology.  Plates can deliver high levels of heat transfer within a very compact housing – generally around a third of the size of an equivalent calorifier.  Its rapid heat transfer results in the ability to produce hot water instantaneously, eliminating the need for large hot water storage tanks, removing the inherent standing losses and reducing the legionella risk.

With an understanding that hot water can be produced at a rate to suit the demand, how are large quantities of thermal energy distributed around site to heat this water? Well, steam is the ideal medium. Steam contains large amounts of energy in every kg, typically 23 times more energy per kg than a water system!  The result?  Smaller pipes, lighter pipes and less space needed in the plantrooms and ducts – a compact, pump-free way of distributing large amounts of energy across site.

The importance of achieving dry steam must be considered when designing a new installation or managing an existing system.  Distributing the steam at high pressure keeps pipe sizes small, resulting in a low pipe surface area and minimising radiation losses.

We want good quality, dry steam arriving at the heat exchanger in order to maximise efficiency and minimise steam consumption.  Wet steam contains a proportion of water and hence effective steam trapping of the mains is important in achieving good quality steam.

Non-condensable gases should be removed from the distribution system, as they create a barrier to heat transfer.  This is achieved with the use of air vents fitted at strategic points in the pipe system.  Gases can also be minimised with good practice in the boilerhouse.  This can be done though correct water treatment and by keeping the boiler feedwater temperature high to allow dissolved oxygen to be driven out of solution, before it reaches the boiler - typically at least 85^oC in an atmospheric hotwell.  Pressurised deaeration is the best way to de-oxygenate the feedwater, as it allows the water to reach temperatures above 100^oC, driving non-condensable gases out of solution. 

This is why the bigger picture is so important.  Taking action in the boilerhouse and in the distribution system directly influences the quality of the steam and hence the effectiveness of the heat exchangers in the plant rooms which are being used to generate hot water. 

By avoiding reliance on storing hot water and by employing best practice across the site, users such as manufacturing plants and the healthcare industry are able to improve energy efficiency, reduce the risk of legionella and deliver reliable, consistent hot water to processes and people alike.

Find out more about Spirax Sarco’s packaged plate heat exchangers today.