Growing your own: home made CHP

Alternative energy company Energetix, with commercial back-up from E.ON, is set to launch its Genlec micro combined heat & power unit this autumn. PEi takes a sneak peak at this potentially revolutionary distributed generation device.

Adrian Hutchings & Geoff Barker, Energetix Group plc, UK

Micro combined heat and power (CHP) appliances are expected to represent the next generation in domestic heating products with a mass-market appeal. Energetix Genlec has developed a domestic micro CHP product that generates electricity whilst heating the home, saving energy costs and allowing individual home-owners to contribute to combating climate change. The market potential for micro CHP is significant with over seven million domestic boilers sold in Europe each year.

Energetix Genlec, based at Capenhurst Technology Park, Capenhurst, near Chester, in the UK has developed an Organic Rankine Cycle (ORC) based micro CHP system. A Genlec enabled appliance consists of a Genlec ORC module that includes a scroll expander, a heating circuit including a primary heat exchanger and a conversion and control interface.

Choosing the right technology

Prior to Energetix embarking on the development of its ORC technology it evaluated various alternative approaches. The initial issues were the selection of the core technology after fuel cells and Stirling engine technologies were reviewed and rejected because of their complexity and cost.

The selection of the Battelle technology was based on its potential to use mass produced components, and the first main challenge was confirming this potential and the selection of these components.

The design was undertaken by Energetix’s new products design team and tested in its facilities and a dedicated test house based at the Capenhurst site. Recently Genlec units were shipped to Energetix boiler manufacturing partners in continental Europe.

Energetix expertise in taking complex technology and creating low complexity, low cost products has ensured that no specialist software is required beyond CAD, data collection and analysis software. The Genlec system is based on the well-understood Rankine cycle, which in reverse operation is the thermodynamic cycle used in fridges and the main development programme has been refining this thermodynamic processes.

The Genlec module

The Genlec module comprises of a scroll expander, condenser heat exchanger, organic fluid pump and evaporator heat exchanger configured in a closed circuit. The pump pressurizes the fluid, circulating it around the closed circuit. The pressurized liquid enters the evaporator and is vaporized by the indirect heat from the boiler.

Internals of the Genlec ORC unit
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This high pressure vapour then goes through the scroll expander which is coupled to an electrical generator that produces the electricity. The reduced pressure organic vapour then passes through a condenser that transfers the heat to the central heating circuit of the house providing both space heating and hot water.

The organic working fluid having been condensed returns to the start of the cycle and circulating pump, continuously being pumped around the circuit whilst demand for heating is called for by the appliance controller. The ORC module delivers 1 kW of electrical output in ratio to the input power to the Genlec module. A schematic of the process is shown below in Figure 1.

Figure 1: Schematic illustrating how the Genlec module produces both power and heat
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Core Technology

Scroll compressors are mass produced for the refrigeration and air conditioning markets. Energetix takes these scroll compressors and with minor modifications run them in reverse to operate as a scroll expander. When in normal operation they are driven by a motor to compress a gas, however, once modified to operate in reverse compressed gas is injected into the scroll which then expands, rotating the scroll expander which in turn drives a generator to produce electricity.

Despite the simple nature of this core component, Energetix has international patent protection on the Genlec technology utilizing this type of device, which incorporates a static scroll element and a moving scroll element. Pressurized gas enters the centre of the scroll and causes the movable scroll to rotate creating a progressively expanding pocket of gas until it is ejected out of the device into the circuit.

The Genlec technology is positioned to be integrated into any boiler company micro CHP appliance design and is flexible in configuration enabling boiler companies to tailor product to their own style.

Control and mains

The conversion and control module of a Genlec appliance performs the appliance control and mains interface, comprising a standard gas controller and an ORC module control and electrical mains interface. The gas controller performs the conventional functions of fan speed/ gas control, ignition and flame monitoring standard in conventional gas appliances.

The ORC control and mains interface provides control for the ORC matching its operation to that of the primary heat exchanger and the electrical interface to the mains. This device has been developed to comply with the new standard, EN50438, Requirements for the Connection of Microgenerators in Parallel with Public Low Voltage Distribution Networks.

The second-generation, wall-mounted Genlec unit installed at Energetix’s test house
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The heating circuit for a Genlec appliance has many similarities to a conventional gas appliance, comprising of a heating circuit that transfers the heat from the combustion of the natural gas to the evaporator of the ORC module, and a gas train comprising of a gas valve, fan, burner and flue. The main element of this heating circuit is a single primary heat exchanger within which the conventional gas burner is located. This primary heat exchanger provides the total heat output required by the appliance, which is typical of primary heat exchangers in conventional gas heating appliances such as condensing boilers.

A Genlec enabled appliance has been demonstrated to perform at least as well as a Band A condensing boiler, with efficiency figures greater than 90 per cent. The primary heat exchanger element of the heating circuit ensures condensing performance and thus high efficiency.

Unique selling points

The specific unique selling points of the Genlec system over competitive technology such as Stirling engines and fuel cells include: low weight; wall mountable; ease of assembly and appliance integration, straight forward installation process; low manufacturing cost; rapid start/stop characteristics with no loss of performance with multiple start/stop cycles; and consistently high level of efficiency while modulating the heat power of the boiler.

These selling points together with the use of readily available mass manufactured components will translate into benefits that include energy efficiency, low installation price, faster payback and reduction in carbon emissions.

The main advantage of a Genlec system compared to a conventional boiler is that it also produces electricity as it produces the heating and hot water for the home. The advantage of this is that gas is normally about three times lower in cost than electricity, and thus mean energy savings for the home-owner.

This cost ratio is driven by the fact that generating power in a central power station and sending it to a home only delivers about a third of the energy to the home. With micro CHP over 90 per cent of the energy can be delivered to the home.

The benefits are therefore greater than just saving the home owner money, it could lead to a reduction in gas used by the country, and therefore reducing the dependence on gas imports and the need for emergency gas storage. Micro CHP also reduces carbon emissions. It is estimated that Genlec could save between 1-1.5 tonnes of carbon dioxide per home per year compared with existing domestic boilers.

Entering the marketplace

Energetix Genlec has had a Genlec micro CHP demonstrator in a test house for over a year to evaluate operational performance and a Genlec enabled Daalderop boiler was exhibited at the VSK Expo in February this year. The company is also working with European heating manufacturers and energy utilities in taking the Genlec micro CHP appliances successfully into the market. The Genlec micro CHP appliances is particularly attractive to the existing routes to market for high efficiency boilers as it has a good fit with the existing supply chain i.e. the manufacturer to the wholesaler and installer through to the consumer.

In addition, energy utilities are developing their own routes to the market for micro CHP by establishing, Energy Service Companies (ESCos), with the intention of providing an integrated solution to their customers in the form of equipment supply, installation, after care and financial services. For example E.ON recently acquired UK-based heating services company, CHN Group.

Recently Energetix Genlec signed an agreement with E.ON UK, the UK’s leading power and gas company à‚— generating and distributing electricity, and retailing power and gas à‚— and is part of the E.ON Group, the world’s largest investor-owned power and gas company.

Under the agreement, E.ON, through its Sustainable Energy Solutions team will fund the testing and evaluation of Genlec micro CHP systems at the Energetix Genlec facility at Capenhurst Technology Park. The testing will be conducted in accordance with the British Standards Institute’s Publicly Available Specification 67 à‚— the UK’s draft performance specification document for micro CHP test methodology à‚— and will be verified by independent experts EA Technology.

The evaluation, which is scheduled for completion in the first half of 2008, will verify with third party accreditation the energy savings and operational performance achieved during testing of the Genlec micro CHP system, assess its commercial value and appraise its economic potential.

After the evaluation, a number of Genlec enabled micro CHP boilers will undergo initial field trials with E.ON before a large deployment of Genlec enabled micro CHP units in a market seeding programme, with Genlec based appliances planned to become part of the highly respected E.ON micro generation portfolio.

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