Elvendon Country Estate Chooses 'Green Heat' from Talbotts.

Elvendon, a residential, farming and sporting estate in rural Oxfordshire has recently undertaken a major building refurbishment programme, centred on Elvendon Priory.
This has included a completely new environmentally-friendly distributed heating system designed, supplied and installed by Talbott's Ltd, the leading UK bio-fuel and waste-to-energy specialists. The groundbreaking new system incorporates some of the
most advanced control technologies ever used for this type of heating installation.

Elvendon Country House - 12k Background
Located in the Chiltern Hills near the Oxfordshire village of Goring-on-Thames, Elvendon is a privately-owned commercial estate, comprising 304 hectares of managed woodland, farming and residential property. The estate is centred on Elvendon Priory, an historic listed building originally established during the 11th Century by a local religious order. Extensively re-built in the 1920s, for most of its history the Priory has remained a private residential and farming property, eventually being acquired by the present owners in 1997 as a family home.

Under its new ownership, the estate has implemented a major programme of modernisation and refurbishment for all the principal buildings and infrastructure. The multi-million pound, 2-year investment programme has included extensive structural alterations, building extensions and renovation of the Priory as a modern domestic residence. The programme has also included replacement of the existing expensive and inefficient combination of gas and oil-fired boilers with a state-of-the-art, biomass-fuelled, ultra-high efficiency distributed heating system designed to serve the entire Priory complex. Designed, engineered and installed by Stafford-based Talbott's Ltd, the leading UK specialist in advanced waste-to-energy thermal recycling systems, the groundbreaking new heating plant incorporates some of the most advanced computer-based control technologies of their kind in the world. These enable a standard high efficiency combustion unit from the Talbott's range to be tailored to meet the specific requirements of this unusual and highly specialised installation.

Computer Control - 10kTalbott's Control Panel integrating sophisitcated Programmable Computer Controller (PCC) which allows complete control of fuel handling and the combustion system.

Completed during 1999, Elvendon Priory has been totally modernised as a family home while retaining many of its original historic design features and interior fixtures, including period stained-glass and extensive traditional timber flooring, panelling, staircases and structural fitments.

Outdoor swimming pool - 15k A large outdoor heated swimming-pool has been constructed and an adjoining stable-block completely renovated. This self-contained complex now includes a modern suite of offices, board room and conference room facilities, a squash court with spectator gallery, garaging and a variety of additional plant and utility rooms. All facilities, together with the estate manager's cottage are connected to the distributed heating and potable hot water network, fed from the Talbott's centralised, biomass-fired combustion unit and heat exchanger system.

The Technology Underneath
Based on a standard C4 unit with a rated output of 300kw/hour using advanced waste-to-energy combustion technology pioneered by Talbott's, the Elvendon Priory distributed heating system is fuelled entirely by renewable biomass in the form of woodchips, a CO2-neutral fuel. These are supplied principally from chipped and screened brash, forestry woodwaste and farm maintenance residue from the estate's own sustainable resources.

Woodchip Silo - 13kFuel is stored in a top-fed silo [pictured right] with a diameter of two metres and a capacity of seven cubic metres, which provides a continuous supply for between three and five days depending on heat demand.

Woodchips from the storage silo are fed to the combustion module by a screw auger via an agitator and air-locked rotary valve. The raw fuel is passed slowly beneath a ceramic extension to the combustion zone, ensuring that even the wettest fuel is transferred to the grate area pre-dried and pre-heated. Motor-driven fan blowers supply pre-heated primary and secondary air to the combustion zone, while an induced draught fan with integral grit arrestor is mounted downstream between the exhaust port of the combustion unit and the stack. Combustion air is also circulated outside the ceramic firewalls, lowering the temperature differential across the outer casing of the combustion module, minimising thermal losses.

Combustion zone - 10kThe complete combustion unit with overall dimensions of just 2 metres in length, 1.5 metres wide and 2.53 metres high, together with the fuel storage and handling systems are housed in an existing small outbuilding in the grounds of the Priory. As all parts of the Priory including the outbuildings have listed building status, no external alterations were permitted. To avoid the use of a conventional exhaust stack, the floor-level was lowered to accommodate the entire installation within the existing building, using a single external red clay chimney 'pot'. The design also enables woodchip fuel to be easily fed by a wheeled mechanical loader through a roof-mounted access hatch to the silo, without any alteration to the original building outline.
Biomass-fuelled waste-to-energy combustion units from the Talbott's standard range for conventional industrial or commercial applications are primarily designed to operate continuously at optimum peak output, often as part of an integrated waste management system. As fuel efficiency is not a primary concern, surplus heat from this type of system is dumped. In contrast, the new biofuelled C4 unit now operating at Elvendon Priory has been custom designed as an ultra-high efficiency energy-saving system to provide maximum fuel economy and minimum operating costs. Representing a major technological advance, the complete fuel handling and combustion system is controlled through a Programmable Computer Controller (PCC). This allows a continuous low pressure flow of hot water at between 80C and 85C at 1.5 bar to be supplied by the combustion unit under all conditions, irrespective of ambient temperatures, operating regimes and demand levels. At the same time, the system ensures efficient total combustion, generating lower emissions levels than an equivalent domestic gas-fired boiler.

Hot Water unit - 14kOutputs from temperature sensors in the combustion zone, heat exchanger and flue gas exhaust train are fed to the pre-programmed PCC which is in turn linked to solid-state, Omron inverter- controlled, variable speed ac drives. These are used to power the induced draught fan, combustion air blowers and fuel handling motors which have a combined output loading of some 6.25 kW. The drive speeds are continuously monitored and accurately controlled to maintain the hot water output temperature set-point, whilst ensuring that complete combustion takes place at the optimum temperature using the minimum volume of fuel. Producing less than 2 per cent ash by volume, the unit is routinely de-ashed on a two-week cycle using a manually controlled vacuum extraction system.

The pre-programmed PCC incorporates a simple panel mounted push-button control unit and visual display as the man-machine interface. This has been specially designed to enable the entire system to be easily operated and controlled by non-specialist, untrained estate staff. However, the groundbreaking computer-based monitoring and control equipment also includes data acquisition and storage, together with an on-line remote communications facility. This advanced system not only enables up to 300 hours of continuous operating data to be monitored, either on-site or remotely from Talbott's headquarters in Stafford, but also enables engineers to re-set, adjust or re-programme the complete heating system on-line from virtually any remote terminal or lap-top, without the need to visit the installation.

An Easy-to-Use Solution
Elvendon Priory's Estate Manager Mr Sean Absolom has found the new heating system remarkably easy to operate. "It was rather daunting at first to have to use such a high-tech system" he commented, "but I soon found that the controls were simplicity itself to use and the visual display provided an instant readout of all the main functions. The system has been running now for some 3,000 hours since it was installed and has operated perfectly." he added.

Constant-temperature, low-pressure hot water is circulated in a semi-sealed system through a total of three remotely-located plate-type heat exchangers from AEL Ltd, each incorporating three-way automatic temperature control valves. The heat exchangers are coupled to an independent secondary system using the potable water supply, to provide domestic heating and hot water, with priority to the main house. During the summer months and at times of low demand, the outdoor swimming-pool, with a normal operating demand of 80 kW, can operate as an excess-capacity heat-dump, providing an efficient, balanced and optimised system.

All services, including the piped heating system, are housed in a large, specially constructed access duct running the entire length of the Priory, ensuring that the original fabric of the listed building has remained virtually unaltered. All other parts of the heating distribution network are laid direct-in-ground to each location, using special ultra low-loss insulated piping to give negligible temperature-drop across the entire network.

The Bottom Line
The specially-designed state-of-the-art heating control system now in operation at Elvendon Priory represents a world-first by Talbott's for this type of application. It not only provides major fuel savings for an already very low-cost, renewable-energy biofuel, but also slashes the total operating costs of the system, reducing the electrical power requirement by no less than 50 per cent, compared with an equivalent standard combustion unit. Although the existing mains-gas supply is just sufficient to provide basic emergency back-up heating, a full gas-fired equivalent of the new distributed system would require a new, high-capacity gas pipeline. In addition to the very high costs and major disruption of such an installation, the annual projected cost of fuel alone for a gas-fired heating system amounts to a staggering figure. The new, clean, green, high-technology system from Talbott's runs continuously with negligible fuel and operating costs, giving the lowest possible cost of ownership over its projected lifetime, with a realistic capital outlay.

Talbotts Ltd. can be contacted by telephone at +44 (0)1785 213366. Alternatively they can be e-mailed at sales@talbotts.co.uk or you can visit their website www.talbotts.co.uk for more information.

Text and Pictures Copyright © 2000, Talbott's Ltd.