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Kensa / Design and manufacture of heat pumps for easy installation

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Away from the gas grid, oil and electricity are often used to supply heat to buildings and both contribute significantly to carbon emissions in the UK.

Yet alternatives are not so hard to source. Take Kensa’s heat pumps. What they do is simple, namely taking low-grade heat from outside a  building and pumping it inside.

Over 3,000 tonnes/year of CO2 saved.

Over 1,000 heat pumps sold by 2008.

Installations deliver about 26 GWh of heat.


Over a third of UK energy consumption is for space heating, and there is room for significant growth in sustainable energy sources. Direct electrical heating is a common choice in areas that do not have mains gas available, but it is expensive and results in high carbon emissions. Heat pumps provide a more efficient way of using electricity for heating, with every unit of electricity delivering three to four units of heat. In terms of carbon emissions they are much better than oil or coal, and can even be better than natural gas, the lowest-carbon fossil fuel. Heat pumps extract heat from air, earth or water, so there is an effectively limitless heat supply.

Staff of Kensa heat pumps coiling up the piping that is made into a slinky before being placed underground.

The organisation

Kensa Engineering was founded in 1999 by Richard Freeborn (now Chairman) and Guy Cashmore (now Technical Director). Richard had spent two years previously developing a heat pump for heating and cooling yachts, while Guy had prior experience in heating and ventilation. Kensa’s Managing Director, Simon Lomax, joined the company in May 2007 and brought with him experience in running businesses of various sizes, including one specialising in underfloor heating. In 2008, Kensa employed 25 people and had sold over 1,000 heat pumps.

Technology and use

Heat pump background

A heat pump extracts low grade energy from a source outside the building in which it is installed, and concentrates this to provide heat to the inside of the building. A refrigerant is used within the heat pump to transfer and concentrate the energy, and for systems that take the heat from the  ground or water, a mixture of water and antifreeze is used in the energy absorbing external loop. The heat pump itself has three main components, as shown in the diagram below:

Ground source heat pump (courtesey of Kensa Ltd).
  • Evaporator, where the refrigerant absorbs heat from the liquid
    that has passed through the external source and evaporates into a gas.
  • Compressor, which compresses the refrigerant, concentrating the
    energy, so that it reaches a sufficiently high temperature for the
    required heating demand.
  • Condenser, where the refrigerant gives up its heat to the liquid
    going out to the building heating system and condenses back into a

The diagram above shows a ground loop being used to extract heat, but water (ie. a lake or stream) can also be used as the heat source. Air can also be used as the heat source, through using a heat exchanger similar to that in an air conditioning unit. When the ground is the source of heat, the loop can be installed in a trench, usually in the form of a coiled pipe known as a ‘slinky’. If space is limited a vertical borehole can be used.

Kensa takes low-grade heat from outside a building and pumps it inside.

Heat pump efficiency is expressed as the Coefficient Of Performance (COP), which indicates how much heat is supplied per unit of electricity used. Ground and water source heat pumps used for heating buildings in the UK typically have COP values between three and four (i.e. three to four units of heat are delivered for each unit of electricity used to run the system), although this will vary according to the climate and required building temperature.

The Kensa kit

Kensa is unique in selling a kit that makes the installation of a heat pump simple for a plumber or DIY enthusiast to accomplish, and reduces installation costs. The key elements of the kit are:

  • Integration of components. The main unit contains the heat pump, the water pumps for the ground loop, the heating distribution systems, the electrical switchgear and electronic controller. By integrating all these components into a single unit, Kensa is able to ensure more reliable operation and is able to provide detailed advice to installers and owners.
  • Pre-coiled slinky. Because Kensa orders large quantities of pipe for making slinkies they are able to buy it in the exact lengths required. They are able to make ten pre-coiled slinkies at their factory in the time it would take an installer to make just one, and all the installer needs to do is lay the slinky in the trench they have dug and separate the coils along the bottom of the trench.
  • Manifold board. Kensa supplies a ‘manifold board’, which includes all the parts required to connect the indoor and outdoor sections of the system, making installation quick and simple. The board also provides the necessary connections to fill the ground loops and purge the system of air during commissioning.

How users pay

Kensa has four main groups of customers: housing associations, commercial property developers, installers and self-builders. 55% of kits sold so far have gone direct to clients and about half of these are doing their own installation, while the rest are using an installer. Kensa is approved under the Low Carbon Buildings Programme (LCBP), which means that its direct customers are eligible for LCBP grants. In addition, Kensa takes responsibility for quality control of the installers it has mentored, this means that the customers of these installers can also qualify for LCBP grants. In 2008, the typical cost of a Kensa heat pump ranged between £450 and £1,200 per kW installed, including all plumbing and civil works required.

The workshop manager putting the finishing touches to a Kensa heat pump.

Kensa is also partnering with leading energy suppliers to provide CERT funded grants for social housing providers and commercial developers, with the amount of the grant based on the size and type of the property, the fuel it is displacing and whether the occupants are a priority group. These grants can be considerable and are designed to benefit technologies which reduce CO2 emissions into the environment.

Training, support and quality control

Kensa takes a rigorous approach to quality control; the design of its heat pump minimises the chance of faults, and makes them simple to diagnose. Kensa is ISO9001 approved for the design and manufacture of heat pumps, and is the only business in the UK approved by BERR for both the manufacture and installation of ground source heat pumps. Kensa has also worked with its suppliers, helping them to improve the quality and reliability of their products. Every heat pump is sold with a 24 month return-to-base warranty, and any problems can be diagnosed remotely or Kensa can send an engineer to site if required.

Kensa has mentored over 50 installers through the Building Research Establishment under the (now lapsed) Clear Skies scheme, and continues to train more every year. This training includes specific training days, demonstrations and individual support. Kensa helps installers commission the heat pumps by talking them through the steps over the phone, ensuring that everything is operating correctly.

Digging a trench.


Each heat pump typically produces 1.55 MWh/year per kW installed, and the total generation for all Kensa heat pumps sold so far is about 26 GWh/year. This results in an annual reduction in CO2 emissions of about 3,600 tonnes.

The key benefit for most heat pump users is reduced energy bills compared to alternative heat sources, but the increased comfort of having a continuous background level of heat is also important. For people living in fuel poverty the reduced bills can make a significant difference to their finances

Although Kensa supplies heat pumps throughout the UK, many customers are in Cornwall and the South West. This is a region in which many properties are off the mains gas grid, and therefore rely on more costly heating. Kensa’s customers include housing associations that are improving the standard of their properties.

Potential for growth and replication

Combined with Kensa’s marketing plans, the kit opens up the possibility of building a large network of small businesses capable of installing heat pumps throughout the UK.

There is huge potential for the use of heat pumps in the UK, not just in new build, but also in the refurbishment of existing housing stock, especially in millions of houses that are off the gas grid. Some older buildings are less suitable for the use of heat pumps, because of small radiators, micro-bore central heating or lack of land space for a borehole.

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