Where do Flue Gas Analysers Fit into the UK Government’s Decarbonisation Plans?

When the UK government announced, in March 2021, that £1 billion of already-allocated funds would be redirected to projects designed to reduce greenhouse gases, the energy sector sat up and listened. And with good reason – as it turned out, £171 million will be allocated to an industrial decarbonisation plan that focuses on hydrogen gas generation and carbon capture and storage technologies.  

However, the news extended beyond green energy production and is relevant to domestic and industrial HVAC applications. In a gesture that reflects the role HVAC engineers and manufacturers can play in sustainability, more than £900 million will be spent upgrading public buildings, like schools and hospitals, with greener fittings such as heat pumps, solar panels and insulation, which will reduce carbon dioxide (CO2) emissions.

But where does this leave the individual households and business units that many HVAC staff visit daily? That is a question that several commentators have asked, and it seems that – for now at least – the main drive to reduce the environmental impact of privately-owned heating and plumbing systems will continue to come from the manufacturers, engineers and installers working in the HVAC sector. 

And that’s quite a responsibility. According to the Office for National Statistics, in 2020, there were approximately 27.8 million households in the UK; government statistics from 2019 indicate that around 15% of greenhouse gas emissions in the UK (specifically of carbon dioxide, along with methane, F gases and nitrous oxide) came from those residential settings. That’s a lot of excess CO2 to clean up. 

So, what can HVAC people do to help decarbonisation? 

If they have decent equipment, heating engineers and plumbers can help to reduce that figure by 15%. For example, they are well placed to measure CO2 and other greenhouse gases: while most flue gas analysers will measure CO2, some can also measure NO/NOx (for example, the Sprint Pro 5 and Sprint Pro 6) well.  

A flue gas analyser that gives a wide range of easy-to-read and interprets measurements allows engineers to see when appliances are not working correctly and whether an upgrade (for example, to a government-subsidised heat pump) might be in order. 

This is a pressing need: many households hang onto appliances for as long as possible, even though older appliances tend to be much less environmentally friendly than their modern counterparts. This is bad enough for the environment, but using a malfunctioning older appliance is the worst of all possible outcomes. 

A good flue gas analyser will provide the readings required to convince many customers to decarbonise their homes or businesses more effectively. It will also allow the engineer to fix many problems in more modern and efficient appliances, bringing them back to their original operating standards and protecting the planet once more. 

Helping to reach net zero 

In late 2021, the UK government set out its plan to reach net-zero emissions by 2050 and every heating engineer in the country has a part to play in that project. While checking flue gases may be an everyday event for many HVAC engineers, the fact remains that household and business emissions account for a substantial proportion of CO2 output and emissions of other dangerous gases. While persuading a single household to operate with lower carbon emissions may not seem like a big deal, the impact can be very substantial when this is scaled up across the country. 

How Long will my Gas Sensor Last?

Gas detectors are used extensively within many industries (such as water treatment, refinery, petrochemical, steel and construction to name a few) to protect personnel and equipment from dangerous gases and their effects. Users of portable and fixed devices will be familiar with the potentially significant costs of keeping their instruments operating safely over their operational life. Gas sensors are understood to provide a measurement of the concentration of some analyte of interest, such as CO (carbon monoxide), CO2 (carbon dioxide), or NOx (nitrogen oxide). There are two most used gas sensors within industrial applications: electrochemical for toxic gases and oxygen measurement, and pellistors (or catalytic beads) for flammable gases. In recent years, the introduction of both Oxygen and MPS (Molecular Property Spectrometer) sensors have allowed for improved safety.  

How do I know when my sensor has failed? 

There have been several patents and techniques applied to gas detectors over the past few decades which claim to be able to determine when an electrochemical sensor has failed. Most of these however, only infer that the sensor is operating through some form of electrode stimulation and might provide a false sense of security. The only sure method of demonstrating that a sensor is working is to apply test gas and measure the response: a bump test or full calibration. 

Electrochemical Sensor  

Electrochemical sensors are the most used in diffusion mode in which gas in the ambient environment enters through a hole in the face of the cell. Some instruments use a pump to supply air or gas samples to the sensor. A PTFE membrane is fitted over the hole to prevent water or oils from entering the cell. Sensor ranges and sensitivities can be varied in design by using different size holes. Larger holes provide higher sensitivity and resolution, whereas smaller holes reduce sensitivity and resolution but increase the range. 

Factors affecting Electrochemical Sensor Life 

There are three main factors that affect the sensor life including temperature, exposure to extremely high gas concentrations and humidity. Other factors include sensor electrodes and extreme vibration and mechanical shocks.  

Temperature extremes can affect sensor life. The manufacturer will state an operating temperature range for the instrument: typically -30˚C to +50˚C. High quality sensors will, however, be able to withstand temporary excursions beyond these limits. Short (1-2 hours) exposure to 60-65˚C for H2S or CO sensors (for example) is acceptable, but repeated incidents will result in evaporation of the electrolyte and shifts in the baseline (zero) reading and slower response. 

Exposure to extremely high gas concentrations can also compromise sensor performance. Electrochemical sensors are typically tested by exposure to as much as ten-times their design limit. Sensors constructed using high quality catalyst material should be able to withstand such exposures without changes to chemistry or long-term performance loss. Sensors with lower catalyst loading may suffer damage.  

The most considerable influence on sensor life is humidity. The ideal environmental condition for electrochemical sensors is 20˚Celsius and 60% RH (relative humidity). When the ambient humidity increases beyond 60%RH water will be absorbed into the electrolyte causing dilution. In extreme cases the liquid content can increase by 2-3 times, potentially resulting in leakage from the sensor body, and then through the pins. Below 60%RH water in the electrolyte will begin to de-hydrate. The response time may be significantly extended as the electrolyte or dehydrated. Sensor electrodes can in unusual conditions be poisoned by interfering gases that adsorb onto the catalyst or react with it creating by-products which inhibit the catalyst.  

Extreme vibration and mechanical shocks can also harm sensors by fracturing the welds that bond the platinum electrodes, connecting strips (or wires in some sensors) and pins together.  

‘Normal’ Life Expectancy of Electrochemical Sensor 

Electrochemical sensors for common gases such as carbon monoxide or hydrogen sulphide have an operational life typically stated at 2-3 years. More exotic gas sensor such as hydrogen fluoride may have a life of only 12-18 months. In ideal conditions (stable temperature and humidity in the region of 20˚C and 60%RH) with no incidence of contaminants, electrochemical sensors have been known to operate more than 4000 days (11 years). Periodic exposure to the target gas does not limit the life of these tiny fuel cells: high quality sensors have a large amount of catalyst material and robust conductors which do not become depleted by the reaction. 

Pellistor Sensor 

Pellistor sensors consist of two matched wire coils, each embedded in a ceramic bead. Current is passed through the coils, heating the beads to approximately 500˚C. Flammable gas burns on the bead and the additional heat generated produces an increase in coil resistance which is measured by the instrument to indicate gas concentration. 

Factors affecting Pellistor Sensor Life 

The two main factors that affect the sensor life include exposure to high gas concentration and poising or inhibition of the sensor. Extreme mechanical shock or vibration can also affect the sensor life. The capacity of the catalyst surface to oxidise the gas reduces when it has been poisoned or inhibited. Sensor life more than ten years is common in applications where inhibiting or poisoning compounds are not present. Higher power pellistors have greater catalytic activity and are less vulnerable to poisoning. More porous beads also have greater catalytic activity as their surface volume in increased. Skilled initial design and sophisticated manufacturing processes ensure maximum bead porosity. Exposure to high gas concentrations (>100%LEL) may also compromise sensor performance and create an offset in the zero/base-line signal. Incomplete combustion results in carbon deposits on the bead: the carbon ‘grows’ in the pores and creates mechanical damage. The carbon may however be burned off over time to re-reveal catalytic sites. Extreme mechanical shock or vibration can in rare cases also cause a break in the pellistor coils. This issue is more prevalent on portable rather than fixed-point gas detectors as they are more likely to be dropped, and the pellistors used are lower power (to maximise battery life) and thus use more delicate thinner wire coils. 

How do I know when my sensor has failed? 

A pellistor that has been poisoned remains electrically operational but may fail to respond to gas. Hence the gas detector and control system may appear to be in a healthy state, but a flammable gas leak may not be detected. 

Oxygen Sensor 

Long Life 02 Icon

Our new lead-free, long-lasting oxygen sensor does not have compressed strands of lead the electrolyte has to penetrate, allowing a thick electrolyte to be used which means no leaks, no leak induced corrosion, and improved safety. The additional robustness of this sensor allows us to confidently offer a 5-year warranty for added piece of mind. 

Long life-oxygen sensors have an extensive lifespan of 5-years, with less downtime, lower cost of ownership, and reduced environmental impact. They accurately measure oxygen over a broad range of concentrations from 0 to 30% volume and are the next generation of O2 gas detection. 

MPS Sensor  

MPS sensor provides advanced technology that removes the need to calibrate and provides a ‘True LEL (lower explosive limit)’ for reading for fifteen flammable gases but can detect all flammable gases in a multi-species environment, resulting in lower ongoing maintenance costs and reduced interaction with the unit. This reduces risk to personnel and avoids costly downtime. The MPS sensor is also immune to sensor poisoning.  

Sensor failure due to poisoning can be a frustrating and costly experience. The technology in the MPS™ sensor is not affected by contaminates in the environment. Processes that have contaminates now have access to a solution that operates reliably with fail safe design to alert operator to offer a peace of mind for personnel and assets located in hazardous environment. It is now possible to detect multiple flammable gases, even in harsh environments, using just one sensor that does not require calibration and has an expected lifespan of at least 5 years. 

Why it’s Important to Measure Nitrogen Oxide (NOx)?

In the EU and UK it is now obligatory for all new domestic heating and plumbing products (rated up to 400 kw) to comply with maximum nitrogen oxide (NOx) emission levels. This is line with a great deal of international regulation: NOx emissions are controlled by law or regulation in many countries (including the US, Canada, Australia and Singapore) and these may vary further by sector (maritime and automotive may have their own specific codes and limits, for example). 

The regulation of NOx required because this gas is a major pollutant, associated with thousands of deaths worldwide through its effects – both direct and indirect – on human health. It has been associated with asthma in children, lung inflammation and a host of other respiratory disorders, as well as cardiovascular damage. NOx is dangerous to animals, plants and ecosystems and is a major constituent of acid rain and smog. 

Despite its singular name, NOx is actually a collective term for nitrogen oxides – a family of highly reactive and poisonous gases – which are produced when fossil fuels are burned. Although NOx pollution is a global problem, large cities are particularly badly affected through vehicle exhaust fumes and heating system emissions; around a third of any large city’s NOx pollution comes from heating. In addition, nitrogen dioxide reacts in sunlight with other gases (such as volatile organic compounds) to generate ozone, which is a greenhouse gas.  

Why measure NOx?

Since NOx emissions are increasingly regulated, they must be measured to ensure compliance with relevant directives. The measurement of NOx from boilers and other domestic appliances is also carried out to check that these are running safely, and to ensure the owner/operator and those around them are not being exposed to excessive NOx. 

Measuring NOx with a flue gas analyser/combustion analyzer

As well as having to meet the demands of regulation, the HVAC sector recognises the growing importance of NOx measurement due to the worldwide focus on sustainability and green issues, and awareness of its harmful effects on health. This is reflected in a growing market for combustion analyzers that calculate NOx (e.g. the Sprint Pro 5 and the Sprint Pro 6).  

In the short to medium term, demand for NOx measurement seems likely to increase; the reduction of NOx emissions is a key component of sustainability policies worldwide and HVAC engineers and designers are prioritising the design of better, cleaner forms of heating (which will have to be benchmarked, verified and maintained).  

Over time, highly efficient, ultra-low-NOx systems are likely to dominate, and the measurement of NOx will therefore become an increasingly important parameter and a more prominent part of day-to-day work in the HVAC sector. 

Our Sprint Pro 5 and 6 models come complete with dedicated NO sensors allowing for a range of NO and NOx measurement options