Mind the NOx – at what cost?

High-performance heating requires a fine balance between energy efficiency and environmental impact, says Remeha’s Mike Hefford

As heating manufacturers, our goal is to help engineers achieve the most energy efficient delivery of comfort in a building, with the minimum impact on the environment.

As heating regulations grow tighter, technology must become more sophisticated to meet the changing requirements. This can require a fine balancing act to ensure product compliance does not come at a cost to energy performance.

Take the move to reduce NOx emissions from heating, for example. Almost all buildings emit pollution caused by combustion in their heating, cooling or electricity generation systems. Poor air quality has been linked to asthma, and lung and heart 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 proposed Breeam 2018 New Construction manual, which will encourage new NOx emission targets for combustion plant for heating and hot water. The BRE has broadened the newly named Pol 02-Air Quality credit to include benchmarks for particulate matter and volatile organic compounds (VOC) emissions that could have a negative impact on health and wellbeing, as well as for NOx. In its Breeam 2018 draft, it 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, which will enforce mandatory NOx emissions levels for space heating up to, and including, 400kW from 26 September, 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.

Applying modifications could adversely affect boiler performance

A case in point is a 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 supply 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 an AQMA, a NOx level of less than, or equal to, 27 mg/kwh would be needed. This compares to the current Breeam 2014 criteria, for which 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 might struggle to meet the new thresholds, modifications are readily available to enable them to do so – but applying them could adversely affect boiler performance. Hence the balancing act.

For example, applying fan dilution to the flue system (see IGEM/UP 10 Edition 4) would help a condensing boiler achieve the proposed NOx benchmark, and reduce carbon monoxide and carbon dioxide emissions. But it would also increase pluming at lower, street levels, bringing new nuisance issues around air quality. Additionally, there would be financial and energy repercussions caused by 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 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, compared with 1990 levels, with carbon budgets to achieve this. In its Clean Growth Strategy, the government has clearly identified heat networks as a central part of its emissions-reduction plans to offer 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, as it currently stands, schemes using CHP 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 system, will enable CHP to achieve the new thresholds, but at significant capital and running costs for the end user.

While Breeam is voluntary, it is increasingly influential in driving environmental performance practice, so some of the proposed NOx thresholds could have far-reaching repercussions. Reducing the role of CHP to achieve the full credit, for example, would be counter to one of government’s key aims to reduce regulated carbon emissions from heating.

As an industry, our focus must remain on achieving well-controlled, high-performance heating systems and optimising lifetime efficiency from our equipment. We need to mind the NOx, but not at the expense of high-efficiency heating or affordable energy costs.

  • Breeam 2018 is due for publication on 7 March.
  • Mike Hefford is general manager at Remeha CHP