Condensing boilers are gas or oil-fired water heaters. They achieve high efficiency (usually greater than 90% at higher heat value) by condensing moisture in the exhaust gases and restoring latent heat from vaporisation, which otherwise would be wasted. This solid vapor leaves the system in liquid form, through the sewer. In many countries, the use of condensing boilers is mandatory or encouraged with financial incentives.
Video Condensing boiler
Working principle
In a conventional boiler, the fuel is burned and the hot gas generated passes through the heat exchanger where much heat is transferred to the water, thus raising the water temperature.
One of the hot gases produced in the combustion process is water vapor (steam), which arises from burning the hydrogen content of the fuel. The condensing boiler extracts additional heat from the waste gas by condensing this vapor into liquid water, thus recovering the latent heat of evaporation. Typical efficiency improvements can reach 10-12%. While the effectiveness of the condensation process varies depending on the temperature of the water that goes back to the boiler, it is always at least as efficient as a non-condensing boiler.
The resulting condensate is slightly acidic (3-5 pH), so a suitable material should be used in the area where the liquid is present. Aluminum and stainless steel alloys are most commonly used at high temperatures. In low temperature regions, plastics are most cost-effective (eg, UPVC and polypropylene). Condensate production also requires the installation of condensate condensate drainage systems. In ordinary installations, this is the only difference between condensing and non-condensing boilers.
To economically produce a condenser boiler heat exchanger (and for equipment to be adjusted during installation), the smallest practical size for its output is preferred. This approach has resulted in heat exchangers with high combustion side resistance, often requiring the use of a combustion fan to move the product through a narrow passage. It also has the advantage of providing energy for the exhaust system because the incinerated gases are typically below 100 ° C (212 ° F) and thus, have a density close to the air, with less buoyancy. The combustion fan helps pump out the exhaust gases.
Maps Condensing boiler
Usage
Condensing boilers now largely replace the earlier, conventional designs in powering domestic central heating systems in Europe and, to a lesser extent, in North America. The Netherlands was the first country to adopt them widely. In Europe, their installations are strongly encouraged by pressure groups and government agencies concerned with reducing energy use. In the United Kingdom, for example, all new gas-heating center boilers installed in England and Wales since 2005 should be high efficiency condensing boilers unless there are exceptional circumstances; the same regulation applies to oil-fired boilers from April 2007 (warm central heating system is exempt from this rule). In the United States, there is a Federal tax credit for the installation of condensing boilers and additional rebates from power companies in several states. In Western Canada, energy suppliers now offer energy rebates when the system is installed in multi-unit homes. The decline in natural gas prices in North America has resulted in increased retrofitting of existing boiler installations with condensing equipment.
Efficiency
Manufacturers of condensing boilers claim that up to 98% thermal efficiency can be achieved, compared to 70% -80% with conventional design (based on higher calorific value of fuel). Typical models offer approximately 90% efficiency, which brings most of the gas condensing boiler brands into the highest category available for energy efficiency. In the UK, this is a SWED (Seasonal Efficiency Domestic Boiler in the UK) Band A efficiency rating, while in North America they usually receive Eco Logo and/or Energy Star Certification.
Boiler performance is based on heat transfer efficiency and is highly dependent on the size/output of the boiler and the size/output of the emitter. System design and installation is very important. The radiation matching to the Btu/Hr output of the boiler and the emitter/radiator design temperature considerations determines the overall efficiency of the space and the domestic water heating system.
One of the reasons for the decrease in efficiency is that the design and/or application of heating systems provides heat boiler temperature at more than 55 ° C (131 ° F), which prevents significant condensation in heat exchangers. Better education from both installers and owners can be expected to improve the efficiency of laboratory values ​​reported. Natural Resources Canada also suggests ways to use this boiler better, such as incorporating space and water heating systems. Some boilers (eg Potterton) can be diverted between two flow temperatures such as 63 ° C (145 ° F) and 84 ° C (183 ° F), only the first being 'full condensation'. However, boilers are usually installed with higher flow temperatures by default because domestic hot water cylinders are generally heated to 60 ° C (140 ° F), and this takes too long to achieve with a flow temperature of only three degrees higher. Nevertheless, even partial condensation is more efficient than traditional boilers.
Most non-condensing boilers can be forced to condense through simple control changes. Doing so will greatly reduce fuel consumption, but will quickly destroy lightweight steel components or cast iron from conventional high temperature boilers due to the corrosive nature of the condensate. For this reason, most of the boiler heat exchanger condensers are made of stainless steel or aluminum/silicon alloys. External stainless steel economizers can be fitted to non-condensing boilers to enable them to achieve condensing efficiency. Temperature control valves are used to integrate hot-water supply into the back to avoid thermal shock or condensation inside the boiler.
The lower the temperature back to the boiler is more likely in condensation mode. If the back temperature is kept below about 55 ° C (131 ° F), the boiler must remain in condensation mode making low temperature applications such as radiant flooring and even an old cast iron radiator suitable for technology.
Most of the new domestic condensing boiler manufacturers produce a basic "fit all" control system that produces the boiler running in condensation mode only at the beginning of heating, after which the efficiency decreases. This approach should remain beyond the old model (see the following three documents published by Building Research Establishment: Information Papers 10-88 and 19-94; General Information Leaflet 74; Digest 339. See also AM3 Manual Application 1989: Condensing Boiler by Chartered Institute of Building Services Engineers).
Control
The domestic condensation boiler control is essential to ensure that it operates in the most economical and fuel-efficient way.
Almost everything has a modulator burner. Burners are usually controlled by embedded systems with built-in logic to control the output of the burner to fit the load and provide the best performance.
Reliability
Condensed boilers are claimed to have a reputation for being less reliable and may also suffer if done by installers and plumbers who may not understand their operations. Unreliable claims have been contrary to research conducted by UK-based Building Research Establishment (see Establish Research Establishment).
In particular, the 'picking' problem arises with the initial installation of the condensing boiler, where a plume of condensed white vapor (as small droplets) becomes visible at the outlet. Although not essential for boiler operations, pluming is an aesthetic problem that causes much resistance to the condensing boiler.
A more significant problem is the acidity (pH 3-4) of condensate. Where this is directly related to boiler heat exchangers, especially for thin aluminum sheets, can lead to faster corrosion than traditional non-condensing boilers. Older boilers may also have used thick casting heaters instead of sheets, which have slower time constants for their responses but are also resistant, with their mere mass, to corrosion. Acidity of condensate means only a few materials that can be used: stainless steel and aluminum fitting, mild steel, copper or cast iron is not. Poor design or construction standards may have made a heat exchanger from some of the longer-lasting condenser boilers.
Initial testing and annual monitoring of heat transfer fluids in condensing boilers with aluminum or stainless steel heat exchangers is highly recommended. Maintenance of slightly alkaline fluids (pH 8 to 9) with anti-corrosion agents and buffers reduces corrosion of aluminum heat exchangers. Some professionals believe that the condensate generated on the burning side of the heat exchanger can pose a danger to the aluminum heat exchanger and shorten the life of the boiler. Statistical evidence is not yet available because condensation of boilers with aluminum heat exchangers has not been used long enough.
Establishing Research Establishment
The Building Research Establishment, which is the UK's premier research body for the building industry, produces leaflets on domestic condensing boilers. According to the Building Research Establishment:
- a reliable modern condensing boiler like a standard boiler
- condensing boilers is no more difficult to repair, nor does it require more frequent servicing
- service is not expensive; the only additional (small) task is to check the correct function of the condensate channel
- condensing boilers is not difficult to install
- In all operating conditions, condensing boilers are always more efficient than standard boilers
Exhaust
Condensate discharged from the condensing boiler is acidic, with a pH between 3 and 4. Condensing boilers require exhaust pipes for condensate generated during operation. It consists of a short length of polymer pipe with a steam trap to prevent exhaust gas being ejected into the building. Condensate acid properties can be corrosive to iron pipes, waste pipes and concrete floors but do not pose a health risk to residents. Neutralizing, usually composed of plastic containers filled with limestone or limestone aggregates or "chips" (basa) can be installed to raise the pH to an acceptable level. If a gravitational channel is not available, a small condensate pump must also be installed to lift it into the proper drain.
Primary and secondary heat exchangers are made of a material that will withstand this acidity, usually aluminum or stainless steel. Since the final disposal of the condensing boiler has a lower temperature than the exhaust from the atmospheric boiler 38 Â ° C (100 Â ° F) vs. 204 Â ° C (400 Â ° F), mechanical fans are always required to remove it, with the added benefit of allowing the use of low-temperature drain pipe (usually PVC in domestic applications) without insulation or conventional chimney requirements. Indeed, the use of conventional brick pyre, or metal funnel is specifically prohibited due to the corrosive nature of the exhaust products, with the special exception of steel and aluminum specially valued in certain models. The preferred ventilation material for most condenser boilers available in North America is PVC, followed by ABS and CPVC. Polymer ventilation allows for additional benefits of mounting location flexibility including blockage of side walls that saves unnecessary penetration from the roof.
Cost
Condensing boilers are up to 50% more expensive to buy and install than conventional types in the UK and US. However, in 2006, in the UK the price of additional charges for installing condensation instead of conventional boilers should be restored for about 2-5 years through lower fuel usage (for verification, see the following three documents published by Building Research Formation: Information Paper 10-88 and 19-94 General Information Leaflet 74 Digest 339 See also Case Study in AM3 Application Manual 1989: Condensing Boilers by Chartered Institute of Building Services Engineers), and 2-5 years at US prices. The exact numbers will depend on the efficiency of the original boiler installation, the boiler utilization pattern, the costs associated with the installation of the new boiler, and how often the system is used. The cost of this boiler is decreasing because the government's enforced bulk taking effect and the manufacturers are pulling out the less efficient old model, but the production cost is higher than the longer type because the condensing boiler is more complex.
Increased condensation boiler complexity is as follows:
- increase the size of the heat exchanger, or the addition of a second heat exchanger (it is important that the heat exchanger is designed to withstand the acid attack from the "wet" exhaust gas)
- The need for a fan-assisted flue (because the cooler flue gas has less buoyancy). Many non-condensing boilers also have this feature, but
- because the cooler exhaust gas produces condensate, it needs to be drained, so the boiler is thrown into sewage or sewer
With respect to modern boilers, there is no other difference between condensing and non-condensing boilers.
Reliability, as well as initial cost and efficiency, affect total cost of ownership. One of Britain's most prominent administrative companies claimed in 2005 that it had made thousands of calls to improve the boiler, and that its greenhouse gas emissions from its vans may be greater than the savings made by switching to environmentally conscious boilers. However, the same article shows that the Heating and Hotwater Information Council, along with several installers, have found that modern condensing boilers are as reliable as standard boilers.
Gallery
See also
- Energy efficiency in UK housing
- OpenTherm
References
External links
- European Patent Patent for removal of condensate-free elimination.
- Condensed boiler page on the UK National Energy Foundation website
- A comparison of the various boiler systems available in North America on the Natural Resources Canada website
- Exploded diagram of condensing boiler (Malvern Boilers 30) (pdf file - 71KB)
- In residential gas condensation boiler design (pdf file - 1.28MB)
Source of the article : Wikipedia
0 Comments