Condensing boiler
4277518
224193031
2008-07-07T19:13:45Z
ABShippee
5217999
/* Efficiency */ The just-previous edit's reflecting a misunderstanding, this note a) adds another web resource and b) adds the importance of combining heating tasks.
A '''condensing boiler''' is a 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]] 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]] can be achieved,<ref>http://www.viessmann.co.uk/downloads/CondensingBoilers.pdf Viessmann High Efficiency Boilers</ref> compared to 70%-80% with conventional designs (based on the [[higher heating value]] of fuels). Typical models offer efficiencies around 90%, which brings most brands of condensing gas boiler in to the highest available categories for energy efficiency. In the UK, this is a "SEDBUK" (Seasonal Efficiency of Domestic Boilers in the UK <ref>[http://www.sedbuk.com/ Sedbuk<!-- Bot generated title -->]</ref>) Band A efficiency rating, while in North America they typically receive an Eco Logo and/or [[Energy Star]] Certification.
When installed in real houses, the performance of condensing boilers is typically 4-5% lower than in laboratory tests by groups such as SEDBUK.<ref>http://www.carbontrust.co.uk/publications/publicationdetail.htm?productid=CTC726 Carbon Trust Micro-CHP Accelerator</ref> This gives typical seasonal efficiencies of 82-89% in the UK ([[higher heating value|HHV]]). Part of the efficiency drop is because boilers are often oversized for the thermal demand of the property, giving return temperatures over 50°C from the heating system, which prevents significant condensation in the heat exchangers.<ref>http://www.carbontrust.co.uk/publications/publicationdetail.htm?productid=CTC726 Carbon Trust Micro-CHP Accelerator</ref> Better education of both installers and owners could be expected to raise efficiency up towards the reported laboratory values. Natural Resources Canada <ref>http://oee.nrcan.gc.ca/publications/infosource/pub/home/Heating_With_Gas_Chapter3.cfm?attr=4 Office of Energy Efficiency, Natural Resources Canada</ref> also suggests ways to make better use of these boilers, e.g. combining the space and water heating systems.
==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 [[plumber]]s. 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 (mechanical)|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 <ref>[http://www.atmos.uk.com/ Heating Systems - domestic gas combi boilers and solar thermal hot water<!-- Bot generated title -->]</ref>, 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{{Fact|date=November 2007}} through lower fuel use, and 2-5 years{{Fact|date=November 2007}} 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==
<gallery>
Image:DSCN5370.JPG|Viessmann Vertomat Condensing Boiler
Image:condensevapor.JPG|Condensing Boiler Exhaust Vapour
Image:DSCN4452.JPG|Viessmann Vitodens Condensing Boiler
Image:DSCN4767.JPG|Stainless Steel Exaust w/ Condensate
</gallery>
==See also==
*[[Energy efficiency in British housing]]
==References==
{{Reflist}}
==External links==
{{external links}}
*[http://www.nef.org.uk/energysaving/boilers.htm Condensing boilers page] on the website of the UK National Energy Foundation
*[http://www.cnv.org//server.aspx?c=2&i=98 Centralized Plant] on the website of [[Lonsdale Energy Corp]]. of North Vancouver, BC, Canada
*[http://www.city.vancouver.bc.ca/Greaterdot_wa/index.cfm?fuseaction=GVTV.storyDet&Storyid=411 North Vancouver's Heating Plant Video] on the website of GVTV, A public Affairs Website/Show in Vacouver, BC, Canada
*[http://oee.nrcan.gc.ca/publications/infosource/pub/home/Heating_With_Gas_Chapter3.cfm?attr=4 Comparisons of different boiler systems available in North America] on the Natural Resources Canada website
*[http://www.chapmanburner.com Condensing Boiler Installer in Vancouver BC, Canada] Condensing Boiler Installer with Pictures of Condensing Boiler Installations
*[http://www.environmentalchoice.com/ Eco Logo Program, Canada] Information on the Eco Logo Program in Canada
*[http://www.weil-mclain.com/downloads/literature/ultragas/ultratechlit.pdf Technical summary of Weil-Mclain Ultra condensing boilers]
*[http://www.viessmann.de/web/germany/com_publish.nsf/AttachmentsByTitle/ts-condensing-technology.pdf/$FILE/ts-condensing-technology.pdf#search=%22%22condensing%20boiler%22%20heat%20exchanger%20diagram%22 Condensing Boiler Technology (Viessmann)] Technical document (pdf file - 900KB)
*[http://www.malvernboilers.co.uk/pdfs/malvern%20_30%20_major_spares.pdf Exploded diagram of condensing boiler (Malvern Boilers 30)] (pdf file - 71KB)
*[http://www.wholesaleheating.co.uk/CONDENSING-COMBI-BOILERS.html Condensing Boilers] Useful information on condensing boilers and a comparison of UK domestic condensing combi boilers
*[http://www.atmos.uk.com/product_group.asp?section=000200130005 Atmos Drain Free] Information concerning the Atmos Drain Free boiler
*[http://www.gasmaster-ind.com Gasmaster Industries] Stainless Steel Condensing Boilers
*[http://www.homeheatingguide.co.uk/condensing-boilers.html Condensing Boiler] Information at Home Heating Guide
Typical manufacturers of residential condensing boilers:
* [http://www.weil-mclain.com/ Weil-McLain]
* [http://www.burnham.com/ Burnham]
* [http://www.viessmann.ca/ Viessmann]
* [http://www.htproducts.com/products/munchkin Munchkin]
* [http://www.atmos.uk.com Atmos Heating Systems]
* http://www.hydrothermkn.com/
* http://www.knowsomethingmore.com/
[[Category:boilers]]
[[Category:Residential heating]]
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