Many businesses and organisations need a secure, constant supply of hot water and space heating. To cope reliably with this need and to meet fluctuations in demand, many establishments build in boiler over-capacity at their premises.
Managers often keep boilers running on stand-by, ready to boost heating or hot water supplies as soon as required. However, this is both economically and environmentally costly. Industrial and business sites throughout the UK could make significant savings on stand-by boiler operations by installing a simple device known as a Flue Isolation Damper (FID).
The Bloxwich Hospital, in Walsall, installed FIDs on each of its boilers, improving both energy efficiency and environmental performance. The hospital’s experiences are documented in the Energy Efficiency Best Practice Programme (EEBPP) Good Practice Case Study 382, entitled Energy And Cost Saving In Hot Water Boilers Through The Use Of Isolation Dampers, which is available free from the EEBPP.
Although peak winter demand for heating and hot water never exceeds 400kW, Bloxwich hospital operates three 300kW low pressure hot water (LPHW) natural draughting boilers to meet its fluctuating demand. These boilers spend up to 80% of the time on stand-by, ready for immediate operation.
However, in addition to the energy consumed keeping the boilers in stand-by mode, energy is lost via the natural air flow through the boilers to the flue. The air flow carries any boiler heat given up through convection outside via the flue. This represents a significant loss in terms of overall operating costs. The Walsall Community Health Trust, prompted by studies indicating that a 10% energy saving could be achieved by installing FIDs on the hospital’s boilers, decided to install an automatic flue damper system.
FIDs close off the flue from the boilers, preventing heat loss by natural air flow. When the gas burner switches off a close signal automatically shuts the damper in about eight seconds. A torsion spring re-opens the damper, in about three seconds, once the temperature falls. A dual interlock prevents the burner firing unless the damper is fully open. For safety, in the event of a power loss, the damper will always fall to the open position.
Fuel consumption figures before and after FID installation show that gas consumption fell from 1200MWh to 800MWh between 1992-1998. Power required for the FIDs is only 6 watts. Operating without FIDs each boiler had suffered mean stand-by heat losses of 5.2kW; these losses were completely eliminated by installing FIDsDuring the first four years of operation there were no major problems and only two minor repairs were required.
Installing FIDs saved the hospital approximately 12.1% in annual fuel charges for the three boilers, which translates into annual cost savings of £1,073. The total installed cost of the FIDs was £1,950, and the minor repairs which were required cost £200, giving a payback period on investment of 1.9 years.
Reducing fuel use has also cut atmospheric emissions of carbon dioxide and nitrogen oxides from the hospital’s boilers by 12.1%. These benefits will grow the more the boilers are used. Boiler usage at Bloxwich hospital is 18.5%, but if it increases the payback period will reduce.
The savings realised at the Bloxwich hospital could be repeated at many industrial and business sites across the UK. In addition to economic benefits, the significant energy savings accruing from the installation of FIDs could be valuable to firms facing the constraints of Integrated Pollution Prevention and Control (IPPC) regulations.
The Environment and Energy Helpline is a free service provided by the Government’s Environmental Technology and Energy Efficiency Best Practice Programmes.For further information and copies of GPCS 382, Energy And Cost Saving In Hot Water Boilers Through The Use Of Isolation Dampers, contact the helpline.
Tel: 0800 585794