Patent of the Month: Heat Pumps U-bend U-turn

Currently, around 14%¹ of the UK’s greenhouse gas emissions can be attributed to heating or cooling buildings, with around 90% of the country’s homes still being heated by traditional oil or gas boilers². Earlier this year, the International Energy Agency (IEA) warned that gas boilers must be banned by 2025 if the UK is to meet its net zero targets.

Electric heat pumps are seen as among the most viable low-carbon alternatives to gas boilers, however, their installation is currently estimated to cost the average household around £10,000³. Improvements in this technology are therefore needed to enhance efficiency and reduce cost.

Mitsubishi Electric Corporation is one of the companies at the forefront of this technology and has recently been granted a UK patent (GB2561098) for an improvement in the heat exchangers used in heat pumps.

Typically, these heat exchangers include a serpentine path of heat transfer tubes (see figure below) that pass through a series of radiator plates to enhance heat transfer to the environment. In a heat pump or air conditioning apparatus, refrigerant flows through these tubes and transfers heat to, or from, the surrounding air.

However, problems can arise with current methods of connecting the U-bend portions (3) to the flat elongated tubes.

There are a number of existing techniques that aim to solve this, but each comes with its own issues. The first option involves introducing an extra joint between the flat tube and the U-bend, with a flat cross section at one end and a circular cross section at the other. However, this technique involves more junction points between the flat tubes and the joints, increasing the chance of defects. As well as this, the extra material adds to the overall cost of the end product.

Another technique involves the end portions of the U-bends being formed into a flat shape to match the flat tubes. However, the changes in flow path shape cause pressure losses, resulting in performance degradation. A third option involves U-bends with a uniformly flat cross section being made by bending a flat tube into a U-shape. However, this process causes a decrease in the wall thickness of the outer portion of the U-bend leading to a reduction in pressure capacity.

Mitsubishi Electric Corporation’s invention provides a new way of manufacturing the U-bend portion that addresses some of the above problems.

First, a U-bend (30A) is created by bending a circular tube into a U-shape. Next, the U-bend (3) is flattened before being twisted so that the cross section of each of the end portions (5) align and register with the cross sections of the staggered flat tubes (1). Finally, both end portions (5) are expanded, to give a flat U-bend, which is ready to be joined directly to the flat tubes by brazing.

Mitsubishi’s method enables the entire U-bend to be flattened in one step, meaning the flow paths are uniformly flat in cross section, eliminating the need for joint parts used to convert the cross-sectional shape. Additionally, the smooth change in the orientation of the end portions helps to reduce pressure losses in the flow paths. This invention represents an important development in heat pump technology, helping to improve overall operation and reduce costs.

Mitsubishi Electric Corporation’s UK patent means it is able to prevent competitors from manufacturing, importing and even marketing heat exchangers that include the new design. Given the recent push for the development of low carbon solutions for heating, Mitsubishi’s patent could prove to be a highly valuable asset, providing the business with up to 20 years’ exclusivity in the UK. It may also help it to gain market share for the supply of clean heat to sectors including residential, agriculture and industry.

Mark Sugden is a UK and European patent attorney leading the Housing & Construction group at European intellectual property firm, Withers & Rogers.

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