The energy price cap increased by 54% in April, affecting approximately 22 million customers. The increase is driven by a record rise in global gas prices over the last six months, with wholesale prices quadrupling in the last year.
Although Ofgem set the price cap twice a year, increases in household energy bills in the months ahead are inevitable. Ofgem’s Chief Executive recently told the Business, Energy and Industrial Strategy Committee that, in October 2022, the price cap is expected to rise to “the region of £2,800”, an additional 42% on April’s increase.
With the current situation in mind, the need to use renewable energy wherever possible has only been strengthened. The push for ‘greener’ heating technology will see heat pumps become one of the preferred methods which, in turn, will require hot water storage, to maximise their potential benefit.
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.
A standard indirect cylinder will not work as efficiently with the heat pump input because the heat exchanger is simply not large enough, or designed correctly, to extract sufficient heat from the lower temperatures supplied. This was highlighted during recent Hot Water Association (HWA) tests, where it was shown that a cylinder with the specially designed heat pump coil reduced the heat up time by more than 30% compared to a standard indirect coil.
Many consulting engineers and even heat pump manufacturers recommend 3m2 surface area of 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 a heat pump cylinder differs from an indirect or solar cylinder, with most 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 let the heat pump perform most efficiently. This multiple pass coil design has been shown in recent HWA tests to provide 75% extra reheat performance compared to a standard indirect coil.
The cylinder is fitted with an integral immersion heater and thermostat, which raises the stored water temperature to 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 pumps.
During our own testing to establish the performance of varying metals, it was noted that copper had over nine times better thermal conductivity (233, compared to stainless, which was only 26). This would ultimately mean that the heat pump does not need to work as long to reheat the cylinder compared to the stainless steel alternative, further reducing the energy consumption and running costs.
Newbuild properties generally provide 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, such as ECOflow, to fit the available space is crucial to many projects. While there are many heat pump cylinders manufactured to standard configurations, there are a huge number of installations that require slimline or horizontal cylinders.
Having the flexibility to produce cylinders in a variety of diameters, heights, or even with tailor-made tapping positions, makes the installer’s job easier and allows the installation to go ahead. In addition, it is important to remember that rectangular tanks, although not unvented, can still provide mains pressure hot water. With the major benefit of a tank design requiring circa 27% less space than the equivalent cylinder, they can provide the perfect solution for space restricted installations.
The HWA has introduced a technical standard, Hot water storage vessels for Domestic Purposes for use with Heat Pumps, to sit alongside EN 12897 (for boiler heated indirect cylinders) to ensure that the UK carbon footprint reduction transition to heat pump use is maximised.
The technical standard includes guidance on test criteria, so that installers are 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.
Heating Ventilating & Plumbing (HVP) magazine is the leading plumbing and heating magazine for installers, getting the news to you first and crafting unbeatable journalism to give you the professional edge over your competitors.
If you'd like to keep up-to-date with the latest developments in the heating and plumbing industry, why not subscribe to our weekly newsletters? Just click the button below and you can ensure all the latest industry news and new product information lands in your inbox every week.
Subscribe to receive your free copy of HVP every month.