Advantages of double-wall brazed plate heat exchangers in potable water applications

By: SWEP North America

Brazed plate heat exchangers (BPHEs) are one of the most efficient ways to transfer heat.  They are designed to provide unparalleled performance with the lowest life-cycle cost. Choosing brazed technology for your next heating or cooling project will bring many benefits, including savings in space, energy, and maintenance across HVACR and industrial applications.  BPHEs are quickly winning ground, thanks to their many advantages over older technologies (i.e. plate & frame, shell & tube), and consistently deliver successful results in many types of applications and projects.

BPHE technology embraces double-wall models suitable for a wide range of applications such as hydronic heating, district heating, radiant floor heating, gas boilers, solar domestic hot water systems, snow melting, heat pumps, and domestic and potable water heating systems.  They are suitable for many industrial applications too, including food, pharmaceuticals, chillers, transformer oil cooling, and lubricating oil cooling. Double-wall, high-quality BPHEs combine the high efficiency and compactness of the BPHE with the advantages of double-wall technology.  Double-wall BPHE technology ensures that liquids do not mix and makes any internal leaks visible – important factors in applications where safety is a priority.

While double-wall BPHEs are well established in European installations, they have also already been proven in applications in North America.  One example is a biomass application for a large pellet manufacturer in the US, where a solution for cooling gearbox oil was being sought. Traditionally, the oil was cooled with a fan coil that lost energy to the atmosphere.  Installing a double-wall BPHE instead enabled the energy to be captured from the hot oil and used to heat domestic hot water. The energy saved with this BPHE solution was around 27,000 kW per year (92127834 Btu/hr.), giving the end user payback in 20 months.  In another North American case, double-wall BPHEs provided an optimized solution for a leading water heater manufacturer. Here, they were used in instant water heating applications and domestic hot water for tank heating. When combined with a BPHE, the boiler need not heat the water to such a high temperature to achieve a suitable temperature for the end users.  BPHEs have therefore been able to displace older shell & tube technologies in these types of applications. The double-wall BPHE can heat water to the desired temperature so rapidly and effectively that it is not only more energy efficient, but also imposes a smaller load on the boiler.

Above all, however, is the huge benefit of double-wall BPHEs in preventing water contamination in potable water applications.  In the Netherlands, for example, the government requires double-wall technology in district heating networks. On safety grounds, this technology has been used in a large majority of tap water heater installations over recent decades.  At first glance, the heat transfer task in this case does not appear particularly complicated. However, there are two challenges. First, Dutch law prohibits single-wall heat exchangers in tap water applications with heat loads over 45 kW (153546.39 Btu/hr.).  Second, the maximum pressure drop on the hot water side must not exceed 15 kPa. The double-wall BPHE has been proven to solve this problem in the most efficient and reliable way possible. Should a leakage occur, for example due to corrosion, water will seep out between the vented double walls to the atmosphere.  The water seeping out from the BPHE gives a visual alarm that something is wrong. Contamination of the tap water by the heating water delivered by the energy company can therefore be prevented. The double-wall philosophy could assure the quality of the tap water for all European citizens, but the Netherlands is still the only market to have adopted this very useful technology to a significant extent.  However, awareness of the technology is increasing in other countries. The German government, for example, recommends double-wall technology in tap water applications without making it a legal requirement.

When considering double-wall BPHE suppliers, look for those combining extensive expertise with a wide product range.  If you are also seeking the additional security of third-party verified performance, check that your BPHE supplier can offer AHRI-certified double-wall products.  AHRI’s certification programs are well-recognized performance verifiers for heating, air conditioning, and commercial refrigeration equipment. Products connected to a program are tested annually by independent third-party laboratories, contracted by AHRI, to verify that they conform to performance ratings specified in data sheets and selection software.  This enables buyers to evaluate and make a fair comparison when selecting products for their HVAC installations.

 

Conclusion

Double-wall BPHEs are designed to deliver high thermal efficiency while at the same time providing a leak detection feature – this proves to be an excellent solution for potable water applications.  Contact SWEP today to find out more about our range of double-wall BPHEs and how they can provide optimized solutions for your applications!

 

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