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Mind the NOx - at what cost

30th April 2018
Mike Hefford Remeha CHPs General Manager

Achieving high performance heating can require a fine balancing act to ensure that maximum energy efficiency matches minimum environmental impact, says Mike Hefford, Remeha CHP’s General Manager. Beware giving with one hand only to take away with another.

As heating manufacturers, our goal is to help building services professionals achieve the most energy efficient delivery of comfort in a building with minimum impact on the environment. And as heating regulations grow ever tighter, so technology must become increasingly sophisticated to meet the changing requirements. This can require a fine balancing act to ensure that product compliance does not come at a cost to energy performance.

Take the move to reduce NOx emissions from heating. Almost all buildings emit air pollution due to combustion in their heating, cooling or electricity generation systems. Poor air quality has been linked to asthma, lung and heart-related conditions. So encouraging a maximum level of NOx emissions from heating is a welcome move.

The danger arises if positioning a product to achieve ultra-low emission levels comes at a cost to its performance. Take the BREEAM 2018 New Construction manual, which encourages new NOx emission targets for combustion plant for heating and hot water.

The Building Research Establishment (BRE) has broadened the newly named Pol 02-Air Quality credit to include benchmarks for particulate matter and VOC emissions that could have a negative impact on health and wellbeing, as well as NOx. BREEAM 2018 also takes into consideration the sensitivity of the location of the development, for example if it is in an Air Quality Management Area (AQMA).

The move coincides with the impending EU Ecodesign Directive that will enforce mandatory NOx emissions levels for space heating up to and including 400kW from 26 September 2018 under the Energy-related Products Directive (ErP).

For some technologies the proposed BREEAM 2018 benchmarks, specifically for NOx emissions, are far more challenging than those set out within the current Pol 02-Pollution credit, especially for new developments located in AQMAs.

A case in point is the gas boiler that under ErP 2018 must comply with maximum NOx emissions of 56 mg/kWh. When installed on a site in an AQMA to provide both heating and hot water, it would need to achieve a NOx level of less than or equal to 24 mg/kWh to gain the maximum number of credits (down to two from the previous three). If outside of an AQMA, a NOx level of less than or equal to 27 mg/kwh would need to be achieved. This is in comparison to the current BREEAM 2014 criteria where a value of less than or equal to 40 mg/kWh is required to gain the maximum credits.

While some Class 6 NOx condensing boilers as they currently stand might struggle to meet the new NOx thresholds, modifications are readily available to enable them to do so. The problem is that applying them could adversely affect boiler performance. It’s the classic scenario of giving with one hand and taking away with the other.

Hence the balancing act. Applying fan dilution to the flue system (see IGEM/UP 10 Edition 4), for example, would help a condensing boiler achieve the proposed NOx benchmark as well as reducing carbon monoxide and carbon dioxide emissions. But it would also increase pluming at lower, street levels, bringing new nuisance issues surrounding air quality. Additionally there would be financial and energy repercussions due to the need for modification.

In other words, striving for lower NOx emission levels beyond where the technology currently stands could have a detrimental effect on the ability of the product to deliver high performance heating and lifetime efficiency.

Combined Heat and Power (CHP) is another example. The UK has a binding commitment to reduce greenhouse gas emissions by 80% by 2050 when compared to 1990 levels, with carbon budgets set in place to achieve this. The government has clearly identified heat networks in its Clean Growth Strategy as a central part of its emissions reduction plans to provide low carbon heating in dense urban areas.

CHP is acknowledged as one of the most effective means of reducing emissions and generating high grade heat for use in heat networks. However schemes using CHP as it currently stands as part of an energy-efficient services strategy may not achieve full credits under the proposed Pol 02-Air Quality credit. Again, applying modifications such as a Selective Catalytic Reduction (SCR) system will enable CHP to achieve the new thresholds – but at significant capital and running costs for the end user.

While BREEAM is a voluntary scheme, it is increasingly influential in driving environmental performance practice. For this reason, some of the proposed new NOx thresholds could have far-reaching, albeit unintended, repercussions. Reducing the role of CHP in these situations to achieve the full credit, for example, would be directly counter to one of government’s key aims to reduce regulated carbon emissions from heating.

In summary, as an industry, our focus must remain on achieving well-controlled, high performance heating systems and optimising lifetime efficiency from our equipment. Yes, we need to mind the NOx, but we must ensure that it’s not at the expense of high efficiency heating or affordable energy costs. Let’s just hope that we are successful in maintaining the fine balance.

This article originally appeared in the March issue of CIBSE Journal.