A traditional gas boiler operates at 70-80°C, therefore providing a higher kW output through a standard indirect coil than a heat pump, which generally operates at 55°C. As the heat pump is a lower temperature heat source, it is essential to maximise the heat transfer to the water held within the cylinder.

Many consulting engineers and even heat pump manufacturers recommend 3m² surface area of the heating coil. Measuring a heat exchanger performance purely by its surface area is inaccurate, especially when comparing coil types such as a plain, copper integron (finned) or stainless steel corrugated heat exchanger.

The internal coil design in an ECOflow heat pump cylinder differs from a POWERflow indirect or solar cylinder, with the heat pump cylinders incorporating either a double or triple pass coil. What is critical is that the purpose designed heat exchanger provides optimised heat exchange, low pressure drop and allows higher flow rates to allow to heat pump to perform to its most efficient.

The ECOflow heat pump cylinder is fitted with an integral immersion heater and thermostat, which raises the stored water temperature to the 60°C during its pasteurisation cycle, in line with guidance from the Hot Water Association (HWA), avoiding the risk of Legionella. The thermostat brings the immersion heater on at a temperature just below the heat pump maximum and switches it off at between 60-65°C, maximising the direct energy extracted by the heat pump and ensuring it is safe to use at the tap.

The Benefits Of Using Copper

Copper and stainless steel are the two most common materials used in hot water cylinder manufacturing and their associated heat exchangers today. This is primarily due to their high levels of resistance to corrosion.

It is a well-known fact, that between the two materials, copper provides a superior heat transfer. Due to its high thermal conductivity, it becomes more beneficial to use, where maximising lower grade heat supplied from most heat pump manufacturers.

During recent testing conducted to establish the performance of varying metals, it was noted that Copper had over 9 times better Thermal conductivity at 233, compared to stainless which was only 26, showing why copper is the perfect choice for transferring heat.

Bespoke Manufacture Requirement

When designing new build properties, the house layout provides sufficient space for the heat pump and cylinder installation. Unfortunately, this is not necessarily the case when it comes to retrofit applications.

Being able to manufacture a bespoke cylinder to fit the available space is crucial to the project proceeding. Whilst there are many heat pump cylinders manufactured to standard configurations, there are a huge number of installations which require slimline or horizontal cylinders and having the flexibility to produce cylinders in a variety of diameters, heights or even with tailor made tapping positions, all of which are offered by the ECOflow range. All this makes the installers job easier and allows the installation to go ahead.

Setting the Standard

The HWA recently introduced a specific heat pump standard to sit alongside EN 12897 (for boiler heated indirect cylinders) and to ensure that the UK carbon footprint reduction achievable by a transition to heat pump use will be maximised by the matching with correctly designed hot water cylinders.

Within the standard, there is guidance to the test criteria so that installers will be able to compare the wide array of available cylinders on a like for like basis. With heat pumps varying in the way they operate; it will ultimately allow installers to match the correct cylinder to the chosen heat pump.

Click here for more information and more tips on our heat pump cylinder solutions, both standard and bespoke designed options.