Webinar: Route map to Net Zero Construction

Emissions Analytics is pleased to welcome Daniel Marsh and Carl Desouza from Imperial College London as our guests to discuss the “Route map to Net Zero Construction.”

Construction machines are typically diesel powered and, depending upon their age and application, can produce relatively high levels of NOx and particulates in urban environments. The construction industry is determined to reduce its environmental impact and meet NetZero targets, but choosing the right path can be daunting when numerous alternatives exist. There is no one size fits all solution.

Our webinar will discuss results from various projects that were led by Imperial College London, alongside Emissions Analytics’ real-world emissions testing services.

This is not intended to be a definitive guide or to provide prescriptive answers, simply to share independent test results and support sharper industry discussion.

Construction: the neglected source of urban emissions?

Real-world emissions test results from building sites

Emissions data on construction equipment is scarce, often out-of-date and gathered in unrealistic conditions.  These machines fall within the generic category of non-road mobile machinery (NRMM), or ‘off-road’.

This segment of machinery is often overlooked in preference for passenger cars or heavy goods vehicles, but, like non-exhaust emissions, it is a source of growing importance to urban emissions.  As wider exhaust emissions are brought down, so the share from construction sites may well rise as a proportion of the whole.  Regulations in this area have lagged behind heavy-duty goods vehicles, while there remain many older engines in service – 25% of the registered London fleet in 2019.

To understand the situation better, Emissions Analytics, together with Kings College London, conducted an extensive real-world field test on 30 different construction machines, including nine different types ranging from static generators to telehandlers and excavators.

The 2016 London atmospheric emissions inventory estimates that the construction sector contributes 34% of the total PM10 (including fugitive dust), 15% of PM2.5 and 7% of the total nitrogen oxides (NO_x) – the largest, third largest and fifth largest sources, respectively.

It can be seen immediately that construction sites are an important part of any regulatory effort to improve urban air quality.

The purpose of our field test mirrored the approach we have taken with other classes of vehicle, namely to compare regulatory standards with real-world emissions, premised on the possibility that real-world emissions are typically higher than their laboratory counterparts.

The results of our extensive field test can be summarised as follows:

• Absolute improvements are clear from construction equipment certified to the latest regulatory stage, resulting mostly from deployment of better engine management and after-treatment technology.

• Exceedances of certification values were observed, although were not as widespread as with light-duty vehicles before the introduction of Real Driving Emissions testing.

• Significant variability exists between machines.

• Emissions are sensitive to engine load.

Across the board we found that the highest NO_x emissions were from older construction machines, typically Stage III-A and III-B, but which reduced in the newer Stage IV engines owing to more advanced engine management systems and exhaust after-treatment, as shown in the left-hand chart below. Average Stage VI emissions are down 78% on the prior stage.

However, we also found that Selective Catalytic Reduction (SCR) systems could be better. They perform poorly when an engine is left to idle for longer than ten minutes, whereupon the exhaust temperature falls below 200 degrees Celsius, which explains many of the high conformity factors among Stage IV machines shown in the right-hand chart above.  However, it should be emphasised that a conformity factor above 1.0 does not necessarily entail any non-compliance as these tests were undertaken on machines performing routine work rather than according to the mandated test cycle for certification.

The issue of falling exhaust temperature can be seen in this example of a 129kW excavator operating with regular 15-minute idling periods. The instantaneous NO_x emissions and exhaust temperature are shown in the graph below. During idling, the exhaust temperature falls and then on resumption of work there is a large spike in NOx emissions. Overall, the exhaust temperature is below 200 degrees Celsius for 42% of the time. This demonstrates the importance of careful thermal management of after-treatment systems to ensure low real-world emissions.

Another aspect concerns generators, which typically being ‘static’ are overlooked as NRMM. In fact they comprise 5% of the London fleet of NRMM and have a fundamental role to play on almost every construction site. While in London they only needed to be type-approved to Euro Stage III-A historically, with no exhaust after-treatment to control for NO_x or particle emissions, approval to the new Stage V is required from 2020.

We also found that numerous generators exceeded their regulated limits for NO_x emissions. The 80, 200, 320 and 500 kVA generators were 1.25, 1.08, 1.58 and 1.46 times their respective EU Stage III-A NOx emission standards. The 320 and 500 kVA generators emitted above their standards at all loads, while the others showed the worst performance at low and high loads.

On a positive note, the generator we tested that had been retrofitted with SCR yielded an 85% reduction in NO_x emissions. While this wasn’t good enough to comply with Stage V emissions, it represented a strong reduction in emissions at all engine loads: on the ISO 8178 test cycle they fell from 6.03 g/kWh to 0.95 g/kWh. We found that the introduction of an exhaust filter reduced particle number by two orders of magnitude and to within the future Stage V particle number limit of 1 x 1012 # per kWh.

By the nature of the ISO 8178 test, it is possible to plot the NO_x emissions against the load demand on the generator, as shown in the chart below.

In all cases, there is a characteristic U-shaped relationship, with the lowest emissions per unit of work done occurring between 25% and 50% of maximum load.  The lowest emissions on average were seen on the mid-size, 200kVA, generator, although it obviously had power limits at the top end.  These results illustrate the benefit in choosing the best sized generator for a given task: too small and the emissions are higher as well as the lack of top-end power; too large are the emissions are also higher.

In summary, there are some echoes, but less extreme, of the issues of NOx exceedances for passenger cars in this test work on construction equipment and generators. Overly-downsized engines and poor after-treatment calibration in both cases can lead to elevated emissions. However, these results show significant progress in NO_x reduction at Stage IV, and early evidence is showing further improvements at Stage V. The focus here has been on NO_x as our results show few exceedances on particle emissions – again similar to passenger cars since the Euro 5 regulatory stage.

Putting this in the wider context of greenhouse gas emissions, although there are no CO₂ standards for non-road machinery, cities are likely to be conscious of any trade-offs between better air quality and climate change effects. Indeed, our tests show a 9% increase in CO₂ emissions from Stage III-B to Stage IV, although that comes after a 40% reduction from Stage III-A to III-B. This shows that the perennial tension and trade-offs in controlling different pollutants, and will continue to provide policy dilemmas that can only be resolved by use of real-world testing.

Do a PhD with King’s College London and Emissions Analytics

Characterising non-road mobile machinery emissions through portable emissions testing and emissions inventory development

An exciting opportunity exists to investigate the emissions from vehicles and generators on construction sites working with academic, industry and government partners to deliver a scientifically ground breaking and policy relevant PhD. Current emissions inventories estimate that Non-Road Mobile Machinery (NRMM) contributes approximately 10% of the NOX and PM10 emissions within London. However, there is a large uncertainty in this estimate as very few real-world emission measurements have been made of these sources, instead relying on engine test beds and activity estimates have been based on simplified assessments of construction activity. This project aims to address both of these aspects by undertaking state-of-the-art Portable Emissions Measurement System (PEMS) tests on NRMM machinery and utilising the latest information available through London’s NRMM register to assess the fleet activity. An opportunity also exists to test innovative emissions abatement solutions to provide policy-relevant scenario testing for emissions abatement.

For full details about the project, please visit http://www.kcl.ac.uk/health/study/studentships/div-studentships/aes/green.aspx