|
A condensing boiler utilizes the latent heat of water produced from the burning of fuel, in addition to the standard sensible heat, to increase its efficiency. In a conventional boiler, fuel is burned and the hot gases produced are passed through a heat exchanger where much of their heat is transferred to water, thus raising the water’s temperature. One of the hot gases produced in the combustion process is water vapour (steam), which arises from burning the hydrogen content of the fuel. A condensing boiler extracts additional heat from the waste gases by condensing this water vapour to liquid water, thus recovering its latent heat. A typical increase of efficiency can be as much as 10-12%. The effectiveness of this condensing process varies, it depends upon the temperature of the water returning to the boiler, but for the same conditions, it is always at least as efficient as a non-condensing boiler. The condensate produced is slightly acidic, 3-5 pH, so the choice of materials used in the wetted areas have to be suitable. At high temperature most commonly used are aluminium alloys and stainless steel, in the low temperature areas plastics are most cost effective, for example uPVC and polypropylene. The production of condensate also requires the installation of a heat exchanger condensate drainage system. For a basic installation this is the only difference required compared to a non-condensing boiler. For the heat exchanger within a condensing boiler to be economic to manufacture, and for the appliance to be manageable at installation, the smallest practical size for its output is preferred. This has produced heat exchangers with very high combustion side resistance and so the use of a combustion fan to move the products through narrow passageways has been adopted. This also has had the benefit of providing the energy for the flue system as the expelled combustion gases are usually below 100C and no longer have much natural buoyancy. Condensing boilers are now largely replacing earlier, conventional designs in powering domestic central heating systems in Europe and, to a lesser degree, in North America. The Netherlands was probably the first country to take them up in a large way. In Europe, their installation is strongly advocated by pressure groups and government bodies concerned with reducing energy use. In the United Kingdom, for example, since 2005 all new gas central-heating boilers fitted in England and Wales must be high-efficiency condensing boilers unless there are exceptional circumstances, and the same applies to oil-fired boilers from 1 April 2007 (warm air central heating systems are exempt from these regulations). In the United States, there is a Federal tax credit for the installation of condensing boilers and additional rebates from power companies in some states. In Western Canada, energy suppliers now offer energy rebates when these systems are installed in multi-unit dwellings. The decrease in natural gas prices in North America has not hindered the retrofit of existing boiler installations with condensing equipment From Wikipedia, the free encyclopedia : Manufacture of boilers and radiators for central heating |
