BSEE


and nitrogen dioxide (NO2). It can cause lung irritation and respiratory infections as well as being linked to cancer, asthma, strokes, and heart disease. Typically, a by-product of


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Bill Sinclair, technical director, Adveco, outlines the balancing act UK cies face as they aempt to decentralise power whilst addressing rising concerns over the cost of NOx on the health of the populaon


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 NO2 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. 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.


Decentralised energy


Traditional energy generation by coal, gas and oil-fired power stations comes with several issues, it is NOX heavy, it is extremely expensive, and we are in short supply at peak times. It therefore became popular to look at the alternatives: renewables which help with both carbon and NOX emissions but not the cost; and decentralised energy in the form of microgeneration (photovoltaics) and cogeneration (combined heat and power, or ‘CHP’) which not address emissions and cost, but also supply issues by generating at peak times. As such, low carbon electricity’s share of generation has currently risen to a record 50.1 per cent across the UK with 33.4 per cent generated by renewables, delivering a major shift away from generation in large power stations and making cities more self-sufficient and resilient in terms of meeting energy needs.


uAdveco TOTEM mCHP installaon


But, as old, primarily coal-fired power plants go offline and are replaced by unpredictable supplies like solar and wind, 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 would be more expensive. This


includes high temperature flow rates for domestic hot water heating and when it is very cold outside. Both are situations where heat pump coefficients of performance fall and the energy cost increases beyond that of gas.


The decentralised approach to energy generation, has within London, for example, been justified as a means of reducing carbon emissions to meet targets set for 2025 and making the city more self-sufficient and resilient in terms of meeting its energy needs. Most of the city’s current air pollution and NOX arises from road traffic and buildings rather than from power generation, however this


decentralised energy approach has made emissions from energy production an additional factor since large scale power plant was located on the outskirts for the exact reason of reducing air pollution. With many of London’s existing heat networks developed around CHP systems, the GLA has now begun to voice concerns over adverse air quality impacts. Although all CHP with a catalytic converter is cleaner than the grid because of the advantage of heat recovery, and the NOX emissions from the production of electricity can be reduced on a national scale, at the local scale 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. It is therefore of great importance that the NOX emissions from new CHP units within built-up areas are lower than condensing boilers to have a positive effect on levels of NOX.


The 2018 EcoDesign directive, which came into force last September, sets a NOX emission limit for CHP units at 240mg/kWh. Despite the level of emission being approximately equal to those that would result from producing heat from a boiler and electricity from conventional power plants, the response of the London Plan to the technology is less enthusiastic. Accepting that there remains a strategic case for CHP systems to support area-wide heat networks,


24 BUILDING SERVICES & ENVIRONMENTAL ENGINEER OCTOBER 2019


these installations will now be considered on a case by case basis to ensure they are ultra-low emission, since, by adopting a decentralised energy approach these emissions would be within city boundaries. For those who see the advantage of decentralised production of energy and heat at point of consumption from CHP but recognise the potential NOX emission issues at 240mg/kWh, Adveco provides an alternative with TOTEM, a gas-fired micro-CHP unit that exceeds expectations of ‘very low levels’ of NOX, meeting Euro 6 standards for emissions.


NOx emissions 95 per cent lower than EcoDesign demands


The extent of possible emissions reductions can be estimated by comparing two m-CHP units, using one that meets the 2018 EcoDesign limit of 240mg/kWh versus an ultra-low emission unit such as the TOTEM, which is independently certified at 10mg/kWh. Using a unit of 20kW electrical output, a gas input of 70kW, in 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 the first unit will be 109.2kg/year, compared to


4.55kg/year for Adveco’s ultra-low NOX alternative unit. Local air quality will also be improved because the m-CHP offsets the run hours of a dirtier condensing boiler.


Despite the advantages of decentralisation of energy production through use of CHP, the risk of increasing air pollution in the local area must be acknowledged. Whilst almost 50 per cent of NO¬X pollution in London, for example, is currently attributed to automobiles, the impact of ‘dirty’ CHP systems should not be ignored. It is therefore vital to choose the lowest NOX emitting equipment available when designing a CHP based-system.


www.adveco.co Read the latest at: www.bsee.co.uk ‘ The


decentralised approach to energy generaon, has within London, for example, been jusfied as a means of reducing carbon emissions


’ uAdveco CHP servicing


major contributing factor to poor air quality are Nitrogen Oxides (NOX), the most toxicologically significant being a


combination of nitric oxide (NO)


COMBINED HEAT & POWER


Targeting urban air quality when cogenerating heat and power


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