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Typical manufacturers of residential condensing boilers:
Typical manufacturers of residential condensing boilers:


* [http://www.baxi.co.uk/ Baxi]
* [http://www.potterton.co.uk/ Potterton]
* [http://www.mainheating.co.uk/ Main]
* [http://www.weil-mclain.com/ Weil-McLain]
* [http://www.weil-mclain.com/ Weil-McLain]
* [http://www.burnham.com/ Burnham]
* [http://www.burnham.com/ Burnham]

Revision as of 13:38, 22 May 2008

A condensing boiler is a hot water heating device designed to recover energy normally discharged to the atmosphere through the flue. When a condensing boiler is working at peak efficiency the water vapour produced by the burning of gas or oil in the boiler condenses back into liquid water - hence the name "condensing boiler". The boiler uses a heat exchanger so that incoming air or water cools the exhaust, forcing the condensation of the water vapour it contains; this heats the incoming air (if an air-to-air heat exchanger is used) or pre-heats the water (if an air-to-water heat exchanger is used). A small proportion of the extra efficiency of the condensing boiler is due to the cooling of the exhaust gases, but the majority of the energy recovered is from the condensation of the water vapor in the exhaust gases. This releases the latent heat of vaporization of the water - 2260kJ/kg (970btuh/pound) of condensate (the water vapour released whenever one burns fuels containing hydrogen).

The actual operating efficiency of a condensing boiler depends on the ambient air temperature and the relative humidity. If the incoming air is at 100% relative humidity, the condensing boiler will operate at its maximum efficiency (since it can - in theory - condense all the extra water vapor introduced by combustion). As the relative humidity falls, so will the actual efficiency of the condensing boiler (because less of the water vapor produced can be recovered from the exhaust).

Usage

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 1st April 2007 (warm air central heating systems are exempt from these regulations). In the United States the there is a tax rebate for the installation of condensing boilers. In Western Canada energy suppliers now offer energy rebates when these systems are installed in multi-unit dwellings. The increase in natural gas prices in North America has encouraged the retrofit of existing boiler installations with condensing equipment.

Efficiency

Condensing boiler manufacturers claim that up to 98% thermal efficiency of fuel conversion can be achieved in normal domestic use, compared to 70%-80% with a conventional design. Typical condensing boiler efficiencies are around 90%, which brings most brands of condensing gas boiler in to the highest categories for energy efficiency; in the UK they receive a "SEDBUK" (Seasonal Efficiency of Domestic Boilers in the UK [1]) Band A or B energy efficiency rating, while in North America they typically receive an Eco Logo and/or Energy Star Certification.

Reliability

They have a reputation for being less reliable and require professional installational and regular service and may suffer for the lack of familiarity with them among installers and plumbers. In reality, gas condensing boilers have only one extra element to be installed - the drain pipe for the condensate collected during operation. This comprises a short length of inexpensive plastic waste pipe.

Exhaust

The water that condenses out tends to be mildly acidic (pH between 3 and 4) because of the impurities in the fuel, chiefly sulfur and nitrogen, but no special treatment is necessary in most applications. The relevant parts of the boiler have to be constructed of materials that will withstand this acidity, typically aluminum. Since the final exhaust from a condensing boiler has a lower temperature than the exhaust from a conventional boiler a fan is always required to expel it, with the additional benefit of allowing the use of low-temperature exhaust piping (typically PVC in domestic applications) without insulation or chimney requirements. This allows for the added benefit of flexibility of installation location. One UK company, Atmos Heating Systems [2], have patented a drain free system which negates the need for a drain pipe.

Cost

Condensing boilers are up to 50% more expensive to buy and install than conventional types in the UK and the US. However, as of 2006, at UK prices the extra cost of installing a condensing boiler should be recovered in around 2-3 years[citation needed] through lower fuel use, and 2-5 years[citation needed] at US prices. Obviously the exact figure will depend on the efficiency of the original boiler installation, boiler utilisation patterns, and costs associated with the new boiler installation.

Images

See also

References

  1. ^ http://www.sedbuk.com/
  2. ^ http://www.atmos.uk.com/

Typical manufacturers of residential condensing boilers:

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