Charlie Mowbray, Senior Product Manager, Ideal Heating – Commercial
Regulatory changes have removed the majority of domestic and commercial non-condensing pressure jet boilers from the market. However, those that remain, that can operate in condensing mode, can represent a good option for users with large heating loads – including heat networks – or where large capacity backup is required to support primary low/zero carbon heat sources.
Boilers that operate with a pressure jet burner are common in industrial applications but have been largely removed from the domestic and commercial heating spheres. Several regulatory changes have been responsible for this, including the Energy related Product (ErP) Directive, the Medium Combustion Plant Directive (MCPD) and the uplift to Building Regulations Part L.
These changes are necessary to reduce emissions and improve overall energy efficiency of the buildings and the systems within. Many pressure jet boilers designed to work in commercial applications have been unable to comply and have been withdrawn from the market. But not all. Those that can be operated in condensing mode are able to achieve the new, more demanding efficiencies and emission limits when matched to a suitable burner.
What is a condensing pressure jet boiler?
The term “pressure jet” has become synonymous with large shell & tube boilers where a fanned burner with associated fuel controls is mounted to the combustion chamber. For a pressure jet boiler fuelled with gas this fuel is mixed with air that is blown through the burner by a fan, and ignited at the combustion head of the burner.
Burner controls ensure proper fuel / air ratio and mixing across the range of operation, for efficient and complete combustion. It also determines the shape and direction of the flame.
All commercial pressure jet burners used on gas or oil boilers work in this way, but only those that are fully able to operate in condensing mode are compliant.
Condensing pressure jet boilers, such as our Evojet range, feature a double return condensing system (connections for high or low temperature return water) which enables them to keep the temperature difference between the heat exchanger wall and the return water high, thus maximising the formation of condensation.
Not all pressure jet boilers can be operated in condensing mode. Those that are constructed from standard steel or iron, as opposed to high grade stainless steel, will, in time, corrode from the condensate which can be mildly acidic. Condensate from oil fired operation can be extremely corrosive. So even with boilers constructed from high quality materials, condensing oil fired operation is only permitted on ultra-low sulphur fuel types. Given the variability of fuel oils, in this respect condensing operation is largely limited to gas fired installations.
Why opt for a condensing pressure jet boiler
In domestic and commercial settings, pressure jet boilers are rarely the first option to turn to as high-efficiency condensing boilers can achieve several megawatts. Our Imax Xtra EL condensing boiler is available in 1240kW outputs as a dual unit, for example, and our Evomod will achieve an output up to 1MW from a single unit solution. Plus, you have the option to cascade boilers.
The problem with this approach comes when plant room space is limited as cascades can, in some instances, take up quite a large floor area and present challenges installing all the flues and pipework to each boiler. This is where it is worth considering a condensing pressure jet boiler, which can deliver several megawatts from a single unit. Our latest Evojet models have outputs up to 3000kW
With a reduced number of pressure jet boilers overall, due to the high capacity of each individual boiler the system design and installation work for a pressure jet boiler can be considerably less complex in terms of the number of connections and the pipeline you have to put in, and the number of pieces of equipment you’ve got to deal with.
In the domestic sector, condensing pressure jet boilers are therefore mostly suited to heat networks.
Important considerations
Condensing pressure jet boilers may be able to deliver high outputs from a comparatively small footprint, but they need to be considered carefully as they are not the ‘easy’ option when it comes to heating.
Firstly, specialist installers and commissioning engineers are required who have the appropriate training for this type of equipment. The people who operate and maintain them also need suitable training, especially on the health and safety aspects such as Pressure Systems Safety Regulations; these are far more complex than your typical commercial boiler.
A robust water treatment and ongoing maintenance regime is essential to ensure safe and reliable operation. Inadequate water treatment will result in scale and corrosion, reducing the efficiency of the installation and potentially reducing the working life. Furthermore, the condition of the water supply used to initially fill the system can directly impact the quality of the overall heating system, if the water treatment is not correct.
Revaluate your options
Where there is high demand for heating and hot water, as to be found in heat networks in housing developments, delivered efficiently with minimum emissions, don’t exclude pressure jet boilers from your considerations when weighing up the best option for your application. Pressure jet boilers may have been around for some time, but modern commercial condensing pressure jet boilers and burners might well surprise you yet!