Tag Archive for: emissions

NOx On Effect

A major contributing factor to poor air quality, nitrogen oxides are a group of gases that are mainly formed during the combustion of fossil fuels. The dominant portion of these gases is nitric oxide (NO) which in turn can react with other gases in the atmosphere to form nitrogen dioxide (NO) the most toxicologically significant of the nitrogen oxides.  These reactions take place very quickly and are reversible, so the two gases are referred to together as NOx. Short-term exposure to concentrations of NO can cause lung irritation and respiratory infections, but medical studies have also linked the gas to cancer, asthma, strokes, and heart disease. In addition, NOx can cause changes to the environment, so consideration should be given to its control as part of your organisation’s sustainability activities.

Typically, a by-product of the combustion of hydrocarbon fuels, it is especially problematic in city centres due to idling traffic. In large parts of the UK, the atmospheric levels of NO are considerably higher than European legal limits and the Royal College of Physicians believe it directly leads to as many as 40,000 deaths each year with an estimated cost to the country of £20 billion in healthcare and lost working days.

Critically as greater political and legal weight is brought to bear on addressing climate change it is worth remembering that nitrogen oxides also act as precursors for the formation of ozone, which is not only damaging to health but has adverse effects on the environment through oxidative damage to vegetation. Introduction of N to the environment both directly as a gas and in precipitation can also change soil chemistry and affect biodiversity.

This has led to widespread recognition that more needs to be done to address the issue of NOx, from transport to energy production, distribution, and consumption in buildings.

Traditional energy generation by coal, gas and oil-fired power stations comes with several issues, including being NOx heavy. It, therefore, became popular to look at the alternatives: renewables which help with both carbon and NOx emissions. As such, low carbon electricity’s share of generation has risen delivering a major shift away from generation in large power stations. Since 1990, wider industrial emissions of nitrogen oxides to air have reduced by 74%, although estimates of projected emissions to 2030 suggest further action is required if we are to meet government emission reduction targets. These industrial reductions mean that most of a city’s current air pollution and NOₓ now arise from road traffic and buildings.

The most recent published annual air quality assessment providing data from 2010 until 2019, shows the UK was in compliance with commitments to current emission ceilings for nitrogen oxides. However, the UK continues to be non-compliant with the limit value placed on the annual mean NO concentration at several locations in urban areas. At these locations, it has been estimated that up to 80% of the NO concentration originates as NOx emissions from road transport. But buildings still stand as a key potential contributor to the other 20%.

Managing NOx Emissions From Commercial Properties

In 2018, the European Union’s Energy-related Products Directive (ErP) was used to begin phasing out the installation of less efficient equipment across Europe, including the UK. This would be achieved by establishing minimum performance standards for new equipment, with greater focus placed on heating and water heating performance in buildings. The new ErP directive enforcing maximum NOx emissions from boilers and water heaters which were set at 56mg/kWh for gas/liquefied petroleum gas (LPG) and 120mg/kWh for oil-fired products. At the time the EU predicted the new directive would produce a 20% reduction in energy consumption and emissions when replacing older equipment with ErP-compliant products

The drive towards net zero and the reduction of carbon in buildings is helping to further drive down NOx and where new builds are opting for heat pump and direct electric hot water and heating applications gas to the premises is excised. So no gas, no flues, no NOx. Refurbishing existing properties is more complicated, with low-temperature Air Source Heat Pump (ASHP) based systems typically unable to efficiently address demands. Under these scenarios, a combination of solar thermal and gas top-up for water heating is preferable and leaves sites futureproofed for next-generation green gas technologies. Realistically hydrogen grid connectivity is unlikely for the majority of the UK until the mid-2030s at the earliest, so attention needs to be applied to how gas-based systems can be optimised now to reduce emissions to levels even lower than those established under the ErP directive.

To improve combustion efficiency, condensing gas water heaters and boilers operate so that the water vapor in the exhaust – which contains about 464 kJ/kg of latent energy – condenses on the heat exchanger and not in the flue or outside the building. Designed so that the highest efficiency is at the low end of the firing range, condensing boilers typically operate at 94-95% combustion efficiency. Correctly sized and professionally commissioned, a cascade system for larger demands with high-efficiency pre-mix burners provides a high 1:20 modulation ratio. This large modulation range, along with built-in cascade control ensures that efficiencies are maximised no matter the heating load of the building. With the input of the appliance easily altered to closely match the load, the system is better able to derive as much heat out of the exhaust gases as possible.

With a high-efficiency pre-mix Fecralloy burner, such as employed in the Adveco MD & AD product ranges, ideal combustion efficiency can now be achieved of up to 107% (net)/98% (gross) reducing energy costs and producing ultra-low emissions. The low CO (19ppm) and NOx (27mg/kWh) emissions, from a hot water system built around a high efficiency condensing water heater or boiler (Class 6 appliance) easily satisfy the requirements of the current Energy-related Products (ErP) directive.

In the drive to achieve net zero, and control dangerous emissions, there remains a clear need to address legacy ‘dirty’ buildings. Currently ignored in terms of mandated policy or government support, commercial building refurbishment represents a core challenge for the UK’s climate future. Organisations looking to make steps towards a more environmentally friendly built environment may initially reject any fossil fuel-based option, but the reality is modern systems are advantageous both economically and environmentally and they bridge towards more enveloping carbon neutral and renewable options. If your building’s hot water or heating system predates 2018 then there are advantages to be gained from switching to the latest generation of gas-fired water heaters and boilers, if your system is closer to 15 or 20 years old then you really should be giving serious thought to upgrading appliances. The addition of solar thermal preheat is then going to take your system to the next level in terms of cost and carbon reduction into the 2030s and beyond.

Micro-CHP and The Urban Balancing Act.

Micro-CHP and The Urban Balancing Act

Adveco expert Bill Sinclair, Technical Director.Adveco’s Technical Director, Bill Sinclair, discusses balancing concerns over the cost to health from NOx emissions with the advantages of using micro-CHP in urban commercial building projects.

A by-product of the combustion of hydrocarbon fuels, Nitrogen Oxides (NOx) are a major contributing factor to poor air quality, the most toxicologically significant being a combination of nitric oxide (NO) and nitrogen dioxide (NO₂). It can cause lung irritation and respiratory infections as well as being linked to cancer, asthma, strokes, and heart disease. The Royal College of Physicians believes it directly leads to as many as 40,000 deaths each year with an estimated cost of £20 billion to the country in healthcare and lost working days. This has led to widespread recognition that more needs to be done to address NOx emissions with attention more than ever-shifting to encompass the production of emissions from the built environment.

With a greater emphasis on renewables to make our cities more self-sufficient and resilient in terms of meeting energy needs, low carbon electricity’s share of generation has currently risen to a record 50.1% across the UK with (33.4% of which is generated by renewables). But, as old power plants go offline and are replaced by unpredictable supplies like solar and wind, combined heat and power (CHP) becomes increasingly advantageous. Able to reduce a building’s reliance on the grid, yet when demand is high such as when it is cold and dark, provide a more reliable power source, CHP also has the added benefit of providing high-grade heat at lower cost in conditions where a heat pump coefficient of performance falls and the energy cost increases beyond that of gas.

Although all CHP with a catalytic converter is cleaner than the grid, localised NOx emissions from ‘dirty’ cogeneration should be a concern. Where CHP is used to offset condensing boiler run hours, if the CHP is dirtier than the condensing boiler then the local emissions are worsened. Despite air pollution and NOx mainly arising from road traffic – half of the current NO­x pollution in London is attributed to vehicles – emissions from decentralised energy production are now being seen as a contributing factor. It is therefore of great importance that the NOx emissions from new CHP units within built-up areas are lower than condensing boilers if they are to have a positive effect.

Setting a new threshold for emissions

Micro-CHP (Combined Heat and Power) in urban commercial building projects.The 2018 EcoDesign directive sets a NOx emission limit for CHP units at 240mg/kWh. This threshold, despite being approximately equal to emissions that would result from producing heat from a boiler and consuming electricity from conventional power plants, is too lenient. Air quality has been a critical driver in the revisions within the London Plan which now treats CHP with a lot less enthusiasm – although still accepting that there remains a strategic case for CHP systems as long as the NOx emissions are equivalent or lower than those of ultra-low NOx gas boilers.

The cogeneration industry has not been sitting on its laurels, and a new generation of ‘clean’ CHP brings all the advantages of onsite, on-demand cogeneration, and exceeds the London Plan’s expectations of ‘very low levels’ of NOx, meeting Euro 6 standards for emissions. More compact and much cleaner, micro-CHP units (in accordance with EU standards at 50kW or less rated electrical power) are available with far lower emission rates. This is the case for the TOTEM m-CHP, for example, which is independently certified at just 10mg/kWh.

If we compare a CHP meeting the 2018 EcoDesign limit of 240mg/kWh to that of a TOTEM m-CHP, we can demonstrate the real difference in the latest generation of CHP. Using a unit of 20kW electrical output, a gas input of 70kW, in a situation with an average annual run time of 6,500 hours for a standard application such as a hotel or apartment block, the yearly NOX emission from a ’dirty’ CHP will be 109.2kg/year, compared to 4.55kg/year for Adveco’s TOTEM. And remember, this option is also improving local air quality because the m-CHP is used to offset the run hours of a condensing boiler which at emissions over 30 mg/kWh is dirty compared to the CHP.

Hybrid futures

There will always be projects where in certain circumstances m-CHP will have a place and other renewables are closed out due to limitations of either the site or the technology. By the same token, we would never advocate m-CHP for every building. As is so often the case in the commercial world, each project will have its specific requirements, requiring a more bespoke approach to the provision of hot water, heating and power generation.

Increasingly we hear from consultants who are struggling to pass any kind of gas or gas CHP based heating system because of the issues around NOx emissions, despite the advantage of the high-grade heat necessary to meet the needs of commercial projects. Simply opting for heat pumps, providing a lower grade of heat, isn’t a practical alternative. One answer then is to use a combination of two or three technologies to provide a high heat, low cost, low NOx system.

This is particularly relevant to large buildings where a heat pump alone is simply not suitable. These projects need an additional, high-grade source of heat. Now, that essentially takes you to gas, but if the building is big enough, after the heat pump, but before the gas, can sit m-CHP to provide low NOx and very low running costs.

We can also make a case for using Combined Heat and Power in existing buildings which already have gas boilers and do not have the electrical supply needed to utilise a heat pump. Again, it does not make sense to fit just a heat pump. But we do not want to use CHP to offset low-temperature heat pumps, it has to sit after a heat pump, offsetting the gas heater. Such an approach will still offer some carbon savings, definitely cost savings and, if that CHP is a low NOx appliance when compared to the boiler, then we also have NOx saving. At worst such a system is going to be carbon neutral, but cost and NOx effective.

The move towards all-electric in smaller buildings also reopens the door for solar thermal with better payback case and better carbon savings. Used in conjunction with low-temperature commercial Air Source Heat Pumps (ASHPs) in an arrangement to ensure that it offsets the high-grade source, it offers an alternate hybrid approach that does not require CHP. But we believe gas-fired m-CHP will continue to play a necessary role as part of many hybrid systems, achieving effective water temperatures for commercial applications whilst balancing running costs and savings.

As with any project, design what is best for the building. We would never advocate ignoring the risk of increasing air pollution locally with “dirty” CHP systems, so if Combined Heat and Power is the best fit for your project’s needs then it is vital to choose the lowest NOx emitting equipment available. Right now, the Mayor of London is supporting the city’s Cleaner Heat Cashback scheme for SMEs, proposing scrapping of old gas boilers and replacing them with a variety of options including new efficient gas boilers. If we can demonstrate that m-CHP, either standalone or in a hybrid system, can offset condensing boiler run hours and make emissions cleaner then there is surely a place for the technology, even in the centre of our busiest cities.


Adveco. Commercial Air Source Heat Pumps (ASHP).Discuss your next project with Adveco whether it’s a hydrogen-ready CHP or commercial Air Source Heat Pumps (ASHP).

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