While condensing technology in commercial gas-fired boilers has probably been developed as far as the laws of physics allow in terms of increased combustion efficiency, oil fired technology in the commercial sector has lagged behind – until now. This is due to the practical difficulties arising from the process of condensing flue gases from burning oil, which is highly corrosive to metal. As most traditional non-condensing oil-fired boilers have heat exchangers constructed from a metal material, guaranteed for life by some leading manufacturers, the application of conventional condensing technology would very quickly adversely affect the operating performance and life of such an appliance.
But with established manufacturers offering commercial oil-fired boilers providing high seasonal boiler efficiencies in line with Part L2 of the Building Regulations, why does the industry need to perfect oil-fired condensing technology for larger commercial applications?
Energy using Products Directive
ICOM Energy Association is involved in negotiations with the UK’s Department for Communities and Local Government (DCLG) and the European Commission’s (EC) chosen consultants, regarding the formulation of the Energy Using Products (EuP) Directive.
In August 2008 ICOM reported that the requirements being set out by the EC: “On heating equipment for both efficiency and emissions are very stringent”. It stated that a 20% increase in energy efficiency in each new commercial building was being sought by the DCLG. Placing ever more stringent restrictions on the plant was not considered viable– with commercial boilers currently working at around 95% efficiency, any further gains were thought likely to be minimal.
The building design and plant selection was considered vital plus a responsibility to maintain the plant’s initial efficiency for the life of the building. The need was acknowledged for further integration of the current high efficiency boilers with solar panels and alternative low carbon energy sources including bio-fuels.
The EuP regulations being introduced in 2010 set the goal for all plant available in the UK to be as efficient as the current best 10% by 2016, with clear targets for 2010, 2013 and 2016. It was thought particularly difficult to meet the new NOx limits of 20ppm – with a 40ppm allowance if renewables are used to satisfy at least 30% of the load.
ICOM expressed the belief that this figure was unachievable with oil heating in the UK, and only just reachable with gas heated commercial boilers. With the risk that equipment not reaching the new EuP figure may not receive a CE marque, and therefore not be saleable in Europe, the industry could be facing considerable concerns here.
High efficiency innovation
An innovation that takes us a step closer to meeting the requirements of the EuP Directive and other carbon reduction legislation is, therefore, an exciting development in the oil heating sector. A recent UK trade exhibition saw the launch of a high efficiency, high output steel pressure jet boiler with a patented carbon heat exchanger that can safely and efficiently condense and even clean the flue gases. There is currently no other oil-fired boiler on the market with the carbon heat exchanger vital for these boilers to operate in condensing mode.
With carbon making up part of the heat exchanger, the acid does not react with it or cause heat exchanger corrosion. The heating gas passes through the carbon block and the water is heated through the pipes (see Figure 1). This allows heat to be recovered from the boiler flue gases to achieve higher efficiencies without degradation of the heat exchanger by acidic by-products of oil.
This range of one-piece steel shell forced draught high efficiency boilers achieve outstanding performance using advanced three pass combustion chamber technology, coupled with a state of the art flue gas heat recovery heat exchanger. The appliance is a combination of low temperature boiler and an external condensing heat exchanger which can be used with both gaseous and liquid fuel burners.
The external carbon style heat exchanger incorporates a series of carbon blocks, a feeding pump, safety devices and flue connection. It can increase the efficiency significantly, compared to this type of low temperature boiler without the carbon heat exchanger, typically by as much as 8.55% with oil (*10% increased efficiency with gas firing), resulting in a net efficiency of 102.5%, at 30-40°C.
Flue gases leaving the low temperature boiler are guided through the vertical channels of the condensing heat exchanger. Water channels inside the carbon block transfer heat by the cross flow principle. The end caps on the carbon block divert the water flow in either direction. (see Figure 2) A series of single carbon
blocks are hydraulically interconnected. (see Figure 3) The integral feeding pump feeds a proportion of the heating return circuit through the heat exchanger. The pump is selected on the basis of the flow rate required through the heat exchanger to optimise heat recovery from the flue gases.
The compact dimensions of both the 98kW and 131kW models means that these boilers can be quickly and easily installed and are, therefore, the perfect solution not only for new build but, most importantly as part of a low carbon replacement heating system that could be integrated with other LZC technologies in an existing building which is being upgraded, especially where there is no mains gas.
Carbon reduction opportunities
However, there are very many sites in non gas regions where cast iron sectional boilers have for many years been the heating equipment of choice for many types of commercial buildings and public facilities including, for instance, schools. Their extremely long service life made them an attractive investment but so durable are they that though they still have plenty of service life ahead of them there may be a need for the heating equipment to achieve greater energy efficiency in order for the building to comply with new energy performance regulations.
This could be achieved, at least in part, by the introduction of condensing boilers and possibly further enhanced by integration with other LZC solutions, such as ground or air source heat pumps or solar thermal water heating equipment. However a cast iron sectional boiler is likely to be physically challenging to remove and replace, but much of the carbon reduction benefit is lost if these new technologies are coupled to a standard efficiency boiler. So what can be done in such cases to improve energy efficiency and lessen carbon emissions?
Until now the only solution has been to fit, where compatible, oil and dual fuel burners that are suitable for use with Liquid Bio Fuels, in addition to the conventional Gas Oil Kerosene and Ultra Low Sulphur Diesel. These easily retrofitted burners are generally 100% suitable for existing applications with slight modifications required, regardless of the fuel type selected.
Bio fuel applications can provide a very cost effective alternative renewable energy solution with considerable CO2 savings, particularly in areas where condensing technology is not a viable option. But the sustainable argument for the use of bio fuels is by no means conclusive and neither is the development of this valuable energy source.
Now this dilemma can be overcome for a large proportion of these installations, as the new carbon condensing oil-fired technology can be retrofitted to compatible cast iron sectional boilers!