The hidden menace of corrosion in heating and cooling systems

Written by Reginald Brown, Senior Consultant at BSRIA

Written by Reginald Brown, Senior Consultant at BSRIA

Most buildings services engineers will have come across a heating or cooling system that has not received water treatment and still appears to function perfectly and another that has apparently been treated but experienced serious corrosion related failures. Why should one be vulnerable and the other not? The answer is that most common metals are subject to corrosion but the rate of corrosion and risk of failure depends on a variety of factors including the chemical and microbiological environment, temperature, flow rate and not least the thickness of the metal.

In many respects water is the ideal heat transfer medium for building services. It has a reasonably high specific heat, is liquid over a convenient temperature range and is non-flammable, non-toxic and freely available. The downside is that water is an electrolyte that facilitates corrosion in metallic pipework and components. One might think that the obvious solution is to use plastic pipework but this can actually increase the risk of corrosion of the corrodible components that remain.In a steel pipework system, the dissolved oxygen in the system water will rapidly be used up as it reacts with the large area of corrodible surface but the loss of metal thickness should be insignificant. In a plastic pipework system there are few corrodible components so oxygen concentration will remain higher for longer and the corrodible materials will continue to corrode at a high rate. This means that almost all water based heating and cooling systems should have some form of water treatment to control corrosion, and it may be even more important in plastic pipework systems.

The usual construction programme for large building projects involves installation and pressure testing of pipework followed by pre-commission cleaning and commissioning several months later. During the gap between pressure testing and pre-commission cleaning the system may be both stagnant and still contaminated with manufacturing and construction residues. This is an ideal environment for the development of biofilm and corrosion.

In traditional steel pipe systems (using BS 1387:1985 or BS EN 10255:2004 medium or heavy grade pipe) this is not too much of a problem. The relatively thick pipe (at least 3.2 mm for 1 inch nominal bore and larger) can tolerate the initial corrosion due to the oxygen in the fill water and biofilm development during subsequent stagnation conditions. Provided the pre-commissioning cleaning is carried out effectively, ideally with a biocide wash prior to chemical cleaning, there should be minimal impact on the lifetime of the system.

Thin wall steel pipes and steel panel radiators may not be so fortunate. The thickness of 25 mm nominal bore thin wall carbon steel pipe is only 1.5 mm while a typical steel panel radiator is only 1.3 mm thick. If the initial corrosion was spread uniformly across the metal surface it would not be problem but what tends to happen is that small patches of the surface become anodic relative to their surroundings and are preferentially corroded leading to rapid localised pitting. If dissolved oxygen levels persist or are replenished due air ingress, continuing additions of fresh water or permeation through non-metallic materials then the pitting can progress to perforation. Components that should last 25 years can be perforated in a few months. This is one of the most frequent types of corrosion failure reported to BSRIA and can result in expensive remedial works even before the building is occupied.

Water treatment chemicals work by inhibiting the corrosion process, either by coating the surface of the metal (anodic inhibitors) or otherwise blocking the corrosion reactions (cathodic inhibitors). However, inhibitors are not the solution to poor closed system design or operational deficiencies and certainly won’t work to best effect in a dirty system i.e. one with a high level of suspended solids and/or biological contamination. Also, the system operation must allow the inhibitors and other water treatment chemical to be maintained at an effective concentration and circulated throughout the year.

In summary, the factors necessary to avoid pitting corrosion of steel components in closed systems are:

  1. Minimise the delay between first fill and pre-commission cleaning.
  2. Carry out effective pre-commission cleaning of the pipework system.
  3. Establish, monitor and maintain effective water treatment and water quality as soon as possible in the life of the system.
  4. Circulate water throughout the system on a daily basis to avoid stagnation.
  5. Avoid ingress of oxygen from inadequate pressurisation or excessive fresh water additions.
What happens in the first few weeks of the system can prevent pipe corrosion like this over the next 25 years

What happens in the first few weeks of the system can prevent pipe corrosion like this over the next 25 years

What happens in the first few weeks of the life of the system will influence its fate over the next 25 years. You can’t easily see what is going on inside a pipe but get it wrong and you could be looking at major remedial works in a tenth of that time.

A detailed discussion of corrosion and the use of inhibitors and other chemicals is contained in BSRIA BG50 Water Treatment for Closed Heating and Cooling Systems. Pre-commissioning cleaning is described in BSRIA BG29 Pre-commission cleaning of pipework systems. Guidance on the monitoring of water quality in closed systems is contained in these documents and BS 8552 Sampling and monitoring of water from building services closed systems – Code of practice.

BSRIA also runs a Pre-commission cleaning of pipework systems training course and provides independent failure investigations for all types of building plant and systems including pipweork corrosion.

This article was first published in Modern Building Services.

Indoor Air Quality a health and wealth issue for us all

Peter Dyment, Camfil

Peter Dyment, Air Quality and Energy Consultant – Camfil Ltd.

Indoor Air Quality is a slightly vague concept to most people. When asked they tend to adopt the Goldilocks principle. Not too hot, not too cold, not too damp, not too dry. This reflects the fact that for many generations now we have had the means to control our home and work environment with comparatively little discomfort and little attention being required.

However the golden age of low cost energy and apparently limitless resources seems to be coming to an end. Sustainability is the order of the day. We are all waking up to the real value of energy and the environmental cost involved when linked to our population growth. One cost is the realisation that in cities and near busy roads in the UK there is no longer such a thing as clean fresh air.

We all breathe air to live and if it is polluted or carries airborne diseases we can fall ill as a result. Airborne hazards such as Carbon monoxide or longer term indoor threats like Radon release are sometimes a problem but the toxic fine combustion particles mainly from traffic emissions and some power stations are the major health risk to the public at large.

Technology to the rescue, if we can’t control the weather and have trouble on a national level controlling air pollution then the solution is we can at least try is to control Indoor Air Quality. Ventilation is needed into buildings to replenish used Oxygen from the air and displace the Carbon Dioxide we all exhale.

The British and European standard that gives us the Indoor Air design parameters is the rather long titled BS EN 15251:2007 Indoor environmental input parameters for design and assessment of energy performance of buildings addressing indoor air quality, thermal environment, lighting and acoustics’. This also adds the parameters of light and sound levels which can enhance or blight an inside environment.

There has been concern expressed that in the urgent quest for energy savings in large building HVAC systems engineers have been turning off or turning down plant to save energy at the expense of poor building Indoor Air Quality.

A useful European study called Healthvent has recently produced a report that attributes the levels of Burden of Disease for Indoor Air on indoor sourced pollutants and outdoor sourced pollutants respectively. The ratio shows that approximately twice as much BOD can be shown to come from outdoor sourced pollution.

To save building energy losses it has been usual practice to make building envelopes as well sealed as possible as shown by BSRIA testing. This also has the added benefit of helping stop ingress of outside sourced air pollution into the building. Healthvent identified three strategies to reduce outdoor sourced air pollution coming into the building.
1. Optimal dilution using ventilation
2. Effective Air Filtration to reduce PM2.5 by 50%
3. Source control of pollution

Effective Air Filtration was shown to be the easiest measure to implement and give the best reduction of incoming pollution with minimum effort.

Anybody can now access through the internet information on air pollution levels in their locality. There is a national monitoring network run by DEFRA and the local authorities. The Kings College website even allows Londoners to enter their post code and directly get a map of historic readings on their doorstep(example below)

pm2 5 map bsria

The recent study by Rob Beelen and his team on PM2.5, published in The Lancet, estimates that for every increase of 5 microgrammes per cubic metre (5 µg/m3) in annual exposure to fine-particle air pollution (PM2·5), the risk of dying from natural causes rises by 7%. A simple calculation indicates a routine increase in the mortality rate in central London of over 20% as a result of high levels of PM2.5 mainly from traffic emissions.

Natural causes of death in this instance can be respiratory and cardio vascular disease and recent analysis of data by the Campaign for clean air in London has highlighted that air pollution is one of the exposure categories causing all the top four male death categories and four of the top five female death categories in London i.e. Ischaemic heart diseases; Malignant neoplasm of trachea, bronchus and lung; Chronic lower respiratory diseases; and Cerebrovascular diseases.

It can be seen that the evidence is now compelling and action is now required both at a national level and on a personal level to ensure the air we all breathe is clean and healthy.  Some measures such as effective air filtration and air sealed buildings can mitigate exposure to this air pollution in the short term.

Peter Dyment is Air Quality and Energy Consultant at Camfil Ltd (BSRIA Member). Camfil Ltd also has two other excellent sites for readers: 

BSRIA is running an event looking at living with the problems of Indoor Air Quality.  To find out more and to book onto the event got the BSRIA website.

Making buildings better – measuring for improved building performance

Andrew Eastwell, BSRIA CEO

Andrew Eastwell, BSRIA CEO

BSRIA has always been in the business of measuring, whether it is a physical quantity such as temperature or pressure, a market assessment such as volume of product imported to a given country or a softer, more management-orientated value such as a benchmark or satisfaction score. Measuring is a fundamental characteristic of our industry’s operations and it is in BSRIA’s DNA.

The need for accurate and more comprehensive measurement has been increasing in response to the revolution that is the low carbon agenda. Revolution is no idle description either. In just over a decade, carbon signatures of new buildings have been required to fall to “nearly zero” – yet few owners were even aware of their building’s operational carbon use at the start. In looking backwards over the past few years, I think BSRIA can be proud of its role in promoting the increased use of through-life measurement embedded in processes such as Soft Landings and the associated building performance evaluations.

There is another BSRIA process that is associated with the collection of measurements. This is the process that turns detailed, often randomly accumulated and frequently disconnected data and information into documents that can be used by our members to guide them in their work. A couple of decades ago this process was greatly enhanced by the availability of a managed construction research programme that not only contributed funds from central government but much more importantly brought focus and long term stability to the accumulation of knowledge. This stability was crucial since it enabled individuals to establish research skills and careers with enduring value to the sector they served. Loss of this programme has also resulted in a loss of cohesion between frontline companies willing to collaborate within the longer term research process.

There is a however a new kid on the block that may be about to revolutionise the traditional measure/analyse/publish process that has dominated research and guidance in our sector.

As disruptive technologies go, Big Data has managed to remain under the public radar quite well until the recent disclosures of the USA “Prism” project. Under Prism, colossal quantities of data harvested from both open and private sources are analysed to identify supposed threats to homeland security. It is the use of automatic analytics software combined with large arrays of sophisticated new sensing technologies that makes Big Data techniques so intriguing for the built environment sector.

By way of example, consider the problem of maintaining comfortable temperatures in a space. Traditionally we have used lab research on volunteers to establish what “comfort” requires. Ole Fanger took years to generate his widely used algorithms but they still do not cover all the possible variables that affect perceived comfort. We now use a thermostat, with a setpoint guided by Fanger, and assume that all is well with our occupants. In the new paradigm, cameras utilising facial recognition software will be capable of spotting yawning (too hot, too much CO?) or sluggish activity (too cold). This data is available for every worker in a given space and a “voting” system used to optimise comfort over the group.

But of course there is more. This data could be available from many sources in a Prism type environment. There would now be the potential to mine the data to establish new benchmarks feeding back to the design process that can be tailored to the particular activity type. Schools, offices, homes and shops each can be analysed not just to establish a single setpoint value but to understand in great detail the envelope or distribution of responses. At last, proper large scale data sets can aid our work – and most of what we need to do this is already available through installed BEMS.

There is one further gain possible from this approach. Traditional academic research leading to refereed papers and thence to institutional guidance can take half a working lifetime to complete. Big Data results can be achieved in hugely reduced timespans. Take the case of adverts you see on Google – these are tailored specifically to you based on purchase decisions you may have only made via unconnected sites a few hours earlier. Scary but true.

Big Data is where BIM, Smart Cities, performance contracting and responsive design meet. It challenges all the preconceptions of professional codes, cuts swathes through the notion of privacy and opens up “our” market for knowledge to an entirely new set of competitive players. The next decade is going to be seriously exciting and I am sure BSRIA will remain strong to its ethos of Measuring and Managing in this startling new environment.

BSRIA provides a range of services to conduct and support BPE, from the complete evaluation to providing energy monitoring instruments and benchmarking building performance.

Proving the future – how to keep up with Building Regulations

"From a standing start in 2006 to today, the builders have grasped the importance of air tightness testing as a proxy for quality of construction and the contribution good airtightness makes to energy efficiency" Mike Smith, Engineering Director

“From a standing start in 2006 to today, the builders have grasped the importance of air tightness testing as a proxy for quality of construction and the contribution good airtightness makes to energy efficiency” Mike Smith, Engineering Director

The rapid adoption of airtightness testing and the ability of the industry to achieve the right result first time in 89% of tests is one of the success stories of the UK construction industry over the past decade. The BSRIA Compliance team tested over 10,000 dwellings and 720 non-dwellings in 2012 and found the average dwelling airtightness value was 4.89 m3/(hr.m2) envelope area at 50 Pa (against a maximum regulatory value of 10 m3/(hr.m2)).

From a standing start in 2006 to today, the builders have grasped the importance of airtightness testing as a proxy for quality of construction and the contribution good airtightness makes to energy efficiency. The testing itself is rigorous, robust and, arguably, now at a very low economic price. It has respectability provided by UKAS accreditation for non-dwellings testing, the training of testers and, in the case of dwelling testing, registered testers through the Airtightness Testing and Measurement Association (part of the British Institute for Non-Destructive Testing).

The mantra should be “Build tight, ventilate right”. As fabric standards improve, driven on further by the 2013 Building Regulations, the role of passive and mechanical ventilation systems increases in importance. Unfortunately in the world of unintended consequences, we are seeing dwellings achieving better airtightness values than the designer intended which of course means less air leakage (and associated energy waste), but this is only useful if the designed-in ventilation systems can cope with these outcomes. In a nutshell the infrastructure supporting domestic ventilation engineering has not developed at the same pace as the improvement in building airtightness.

There is of course significant current activity to help remedy this problem but, as is so often the case, we are now on the back foot with increasing numbers of examples of poor installations and the inevitable questioning of the value of mechanical ventilation solutions.

The systems we are talking about are not complex but they are sensitive to errors. What is missing is not so much the technology or science but the widespread creation and adoption of proper codes of practice. Mechanical ventilation (MV) systems and the more complex MV heat recovery (MVHR) systems have to be site tested to ensure they are extracting and supplying appropriate amounts of ventilation. In the course of its compliance testing BSRIA is seeing two main kinds of problems.

The first is the performance of the specified equipment in a given situation, i.e. that the fan is correctly selected to match both the actual application and the inherent system losses that the system components will introduce. In simple terms this comes down to understanding the resistance characteristics of ductwork and its routing and the resistance of terminal units both inside and out. There is a widespread misunderstanding that ventilation fan outputs are usually quoted with outputs measured in “free air”. In reality they have to overcome backpressures from fittings. Even where kits are bought we see alternative terminal units used, usually to meet architects demands for aesthetics.

The second is the actual installation of the associated ductwork where there is a very poor understanding of the dramatic effect on performance that can arise from bad workmanship.

In a recent case BSRIA found approximately one metre of flexible ductwork that had been stuffed into the cavity wall for a straight through the wall installation that is approximately 300 mm thick. An additional 100 mm dogleg had been introduced on site to match the actual positioning of a porch structure. The result was a lot of fan noise with almost zero movement. The fan, when bench tested with zero back pressure, had a performance of 22 l/s, the designed performance including the ducting was 20 l/s however the actual performance was 5 l/s.

As part of the “catch up” in dealing with the rapid rise in the use of domestic ventilation we have identified that the act of measuring MVHR performance using published guidelines will give false results if the correct equipment or correction factors are not used. There is an easy remedy but not widely used at present. The automatic volume flow meter with pressure compensation – more commonly known as a “powered diff” will provide an instantaneous and accurate value. A more common hooded anemometer will impose a back pressure on the terminal, ducting and fan under test and the readings must be corrected (post use) specifically for both the anemometer model and the actual fan under test. More detail on this can be found in BSRIA’s “Domestic Ventilation Systems – a guide to measuring airflow rates – BG46/2013”.

And all of this is compounded by a lack of thinking regarding operational needs, limited controls, and poor instructions to the user, especially on what maintenance is required to keep performance at its peak.

So, airtightness demands have led to unforeseen consequences and something of a reaction against the use of mechanical ventilation. What then can be done to avoid making the same mistakes on other systems and concepts?

With fabric issues now largely dealt with in the Building Regulations it is likely that new focus will fall on the efficiency and operation of the MEP services in dwellings. If modelling and measuring the thermodynamics of a brick wall is difficult imagine how complex a multivalent heating system is going to be! And before being put into use, these complex integrated systems will need commissioning and possibly proving as well.

The Zero Carbon Hub has recognised that we will need to devise new test methods and regimes that, for example, will evaluate how the solar thermal collector performance meets expectations when linked with the ground source heat pump system that serves hot water generation, underfloor heating and thermal storage, in concert with a biomass boiler or room heater. Before regulation stimulates the market we need to have good practice guidance and proven on-site commissioning and test processes in place. This work is urgent and needs significant central support. With the next revision of Part L expected for 2016 – this time aimed at achieving zero (or nearly) carbon homes, time is not available to embark on a protracted negotiation with innumerable and varied industrial interests. Certainly industry’s support will be available but only for a properly directed and centrally funded programme.

If we fail to put into place a mechanism to improve the on-site verification of performance of new systems we will only have ourselves to blame for the next set of well publicised “failures to launch” and the consequent set back of achieving national aims.

BSRIA provides a range of Compliance Testing services for stress-free compliance to Building Regulations including airtightness (Part L), sound insulation (Part E) and ventilation testing (Part F).

Follow

Get every new post delivered to your Inbox.

Join 55 other followers

%d bloggers like this: