Friday, 25 November 2016

Something in the air

One of the main topics at last week's CIBSE Building Performance Conference and Exhibition, indoor air quality is fast being recognised as a priority concern in the world of wellbeing. But in a field where marginal gains are everything, being on top of your data is very important Arie Taal from the Department of Mechanical Engineering at The Hague University has produced research into eliminating faults in HVAC using a BMS

Carbon Dioxide based demand control ventilation (DCV) can reduce heating/cooling loads by up to 30% and fan power consumption by up to 35%.  DCV maintains the CO2 concentration in a room within an appropriate range by adjusting the supply air flowrate.  CO2-based DCV is the most commonly used control method with CO2 sensors installed in the main return air duct.  Nowadays, the increased requirement for smart buildings, combined with a decrease of CO2 sensor prices, has resulted in buildings being equipped with more sensors.

A common issue occurs when one of the CO2 sensors encounters a fault.  This can be down to a lack of maintenance or incorrect sensor placements in rooms.  In a DCV system, a fault can mean that the estimated energy savings and air quality is not guaranteed.  In 1993 the Automatic Background Calibration (ABC) method was developed to calibrate CO2 sensors with the idea that CO2 levels would drop outside normal levels in buildings that are not occupied on weekends or weekday evenings. However, placement of sensors can become a problem as rooms on the inner side of a building or rooms with well-sealed windows may never drop outside of these baseline levels.
Properly controlled ventilation can have a big impact
 on a buidling's energy consumption
Alongside Dr Yang Zhao and Prof Wim Zeiler at the Department of the Built Environment, Eindhoven University in the Netherlands, Mr Taal has been working toward a systematic method of diagnosing faults in CO2 sensors.  Using automatic fault detection, diagnosis and self-correction in CO2 sensors would be a proactive method in air conditioning systems to solve this problem.  The premise of Mr Taal’s study has been to show how the automatic commissioning of CO2 sensors in air conditioning systems is achievable using benchmark values obtained in one of two methods.

In conventional methods, sensor faults are detected by comparing their measurements with benchmark values.  These values can be obtained manually, measured by technicians, or calculated automatically using other available measurements.  The latter is more common because it can be done automatically in the building management system (BMS).  Practical issues arise in air conditioning systems because there are no sensors equipped to measure the CO2 generation rate, CO2 concentration in the supply air and the flow rate of the supply air in m3/s.  In the development of models for CO2 sensor fault detection, the lack of information poses a real challenge.

It is important to test the sensors without
outdoor air, and with solely outdoor air
In an effort to eliminate the threat posed by this lack of information the idea is to perform one of two test methods under specific operating conditions to ascertain the required benchmark levels.

The first is to recycle air without adding any outdoor air for between one and two hours to create 100% return air ventilation.  By closing all windows, doors and fresh air dampers in air handling units the measurements of all CO2 sensors should theoretically be the same.  The second test is full outdoor ventilation, to supply fresh air into the building without any recycling for between one and two hours.  Again, at the end of the time period all of the CO2 sensors should be the same and equal the CO2 concentration of the ambient air.

Faulty sensors will be detected if their readings are different from the assessed benchmark values.  A faulty sensor can be detected if its measurements are obviously higher or lower than other sensors.

In the first method, the degree of fault is then measured from the difference between the defective sensor and the average measurement of the other faultless CO2 sensors. The second compares the faulty sensor reading to the ambient CO2 concentration both looking for a negative or positive bias in CO2 levels when measured against the benchmark.

Self-correction is the final step in the process where all of the information is taken from the faulty sensor for adjustment.  Using the assessment results from the fault diagnosis the CO2 bias can be corrected.  The results of the detection, diagnosis and self-correction will then be reported to technicians for reference.

Together with his team, Mr Taal produced a simulation of their works on the first floor of a school building at The Hague University in Delft.  In their experiment, nine rooms were used with a CO2-based DCV applied to control the amount of supply air to each room in order to keep the CO2 measurements within the benchmark.  Separate experiments were conducted to simulate different conditions. The first simulates a fault free operation and a second introduces faulty sensors to show the impacts of automatic fault detection system.

A potentially serious problem with an HVAC system can be detected
simply using a BMS

Using two operating methods to obtain CO2 benchmarks, 100% return air ventilation and full outdoor air ventilation; faulty sensors can be detected, diagnosed and self-corrected using a BMS.  From the simulations, results show that after 45 minutes there are obvious differences between functional sensors and those that are faulty.  After an hour and a half the positive or negative bias can be accurately measured.

Theoretically, the proposed methods are effective ways to detect faulty CO2 sensors, effectively diagnoses the state of failure and to automatically remove the fault.  The ability to automatically detect, diagnose and repair faults is vital to the effective running of DCV systems.

Friday, 11 November 2016

Bridging the gap

The performance gap is the big problem of our times in the building services industry, and hundreds of column inches are devoted to products created to fix it each year. Ahead of his presentation at the CIBSE Conference Casey Cole, Managing Director of Guru Systems, presents an alternative view: That process, not technology, is the answer  

New buildings in the UK consume far more energy than predicted by their designers - up to 10 times more according to an Innovate UK study. This performance gap doesn't arise because we lack technology. Studies by the UKGBC and others conclude that it's the result of failings throughout the project life-cycle, from concept to handover.

Performance gaps may arise because clients are unclear about what they want; project teams don't understand the impact of their design choices; contractors substitute products and materials on the fly and then install them poorly; or quality assurance is lax, with employers' agents either blind to the problems or willing to let shoddy work escape their net.

What goes doen on paper often doesn't make
it to bricks-and-mortar
There's no doubt about it - we've got trouble right here in the UK building industry. But innovation on its own won't solve the problem. The Internet of Things isn't coming to the rescue. Because the performance gap isn't a technology problem - it's a problem of people, information and accountability.

That's a sobering realisation, because we've all drunk the same Silicon-Valley-brand of neoliberal Kool-Aid. We know that given the right market signals, some whizzy new technology that no one has yet thought of will appear and address any problem you can name: from climate change to… well, to the performance gap.

But not this time. Any purely technological solution would simply be papering over the cracks in our poorly functioning buildings, cracks that were put there by project teams.

There's a positive side to our realisation: if we don't need new technologies to close the performance gap, then we already have the tech we need. Indeed, I think we do. But, that technology must be used to empower clients, engineers and all of us on the project team to do our jobs better. Here's how:

The first step is to collect data from existing buildings. Organisations like CBx, Digital Catapult and Guru Systems, the company where I work, are already doing this. This data is being collected from utility meters (e.g. smart meters and heat meters), building energy management systems and other monitoring systems. By analysing this data, we can understand which factors have the biggest influence on performance.

We can then set clear performance requirements and explicit means of measuring them. These must be measurable before the building reaches practical completion, while the people who can put it right are still on site. It's no use specifying kWh/m2/annum or any other target that can only be calculated once the building is occupied. By the time they can be measured, the project team will have long since moved on. So, we must define requirements for the characteristics that are measurable before occupation and that lead to good performance in operation.

Collecting in-use data from buildings rather than relying on projections is key
Most importantly, clients must make performance requirements contractual. Those clear, measurable objectives must be written into the invitation to tender and then into contract. The lead contractor and the rest of the delivery team must know from the outset what's expected of them (and that they'll be held accountable for achieving it). We have a number of clients that have now adopted this approach for heat networks and they've shown that, once it's contractual, everyone's incentives align and the gap between expectation and outcome closes.

Casey Cole is speaking on ‘Are you ready for a digital future?’ at the CIBSE Building Performance Conference on Thursday, November 17 from 10:25am to 11:20am.

Friday, 4 November 2016

The great phase-out

We wrote about the end of HFCs earlier in the year, but after an amendment to the 1989 Montreal Protocol on Substances that Deplete the Ozone Layer made in October 2016, their days are well and truly numbered. Brought in as a refrigerant gas to replace ozone-depleting CFCs, HFC use will be reduced by 85% across the world by 2045 to cut greenhouse gas emissions. Now the race begins to replace them. With many contenders in the running Simon Lamberton-Pine, Managing Director of DPAC UK, makes the case for the natural alternative 

It all came out of the blue – mainly because we had all forgotten that this was going to happen – hadn’t we? However, what this worldwide news has done has been to heighten the awareness of the fact that air conditioning and refrigeration equipment does indeed contain harmful gases that are damaging our environment.

As consumers (who own refrigerators and air conditioners) we take the equipment for granted. For those of us who have grown up with refrigeration as part of our daily lives, do we give a second thought to the refrigerants being used and the potential impact on the environment? Of course we don’t! As a result, do we even know about the alternative refrigerants available and the resulting changes to the equipment we will need? For those of us involved in Commercial HVAC equipment supply, then we of course are all too aware, and there are plenty of manufacturers now offering alternatives to the conventional HFCs, ourselves included!

HFCs can take a hidden toll on a building's carbon footprint
However, the current main (non HFC) alternatives for the larger buildings/applications are using either Ammonia, CO2 or Propane and they all have different considerations when it comes to selecting these as suitable alternatives to a building's commercial cooling system: Ammonia is highly toxic; it is well suited to large industrial systems, but less cost effective at small and medium sizes. HCs are highly flammable; they are excellent refrigerants for very small hermetically sealed systems but safety used to be an issue for medium and large sizes – although that has now changed somewhat.

For the purpose of this article we are considering the use of R290 (Propane) and its suitability, as well as ensuring safety considerations and precautions are taken into account, as after all this is an inflammable gas! Propane has been used and selected in hundreds of projects for many years, its global warming potential (GWP) vs HFCs is well documented and it is currently the preferred alternative for large and small A/C replacement projects.

Safety is a primary concern where highly inflammable
gases are used
For larger commercial and industrial buildings, equipment is available with duties up to 1,000Kw in single packaged Air Cooled units, which can be mounted externally However, when considering replacing water cooled chillers that are installed inside a building then adequate safety systems have to be considered, (just like commercial gas boilers)

However, getting and transporting Propane for servicing is not that easy and fully licensed suppliers are the best alternative, rather than trying to get a service engineer to transport it! The applications for equipment using R290 (propane) as a natural refrigerant are widespread, covering comfort cooling, process cooling, close control (Data Centre) and general refrigeration (food storage). For example, natural refrigerants are helping the Colruyt Group to save money and deliver its environmental targets, with this leading Belgian retailer moving to hydrocarbons for 100% of its in-store cooling needs

Natural refrigerants avoid the issues concerned with the use of the fluorinated gases. Additionally, these refrigerants offer greater energy efficiency than their fluorinated counterparts – resulting in further reductions in greenhouse gas (GHG) emissions. The most suitable natural alternative in the air-conditioning sector is R290 (propane), which has a low GWP and has high energy efficiency. The large-scale use of R290, however, has been curtailed due to outdated and restrictive safety standards. These were designed decades ago (not taking into account advances in safety features) and over exaggerated concerns related to the inflammable nature of R290 and other hydrocarbon-based refrigerants.

There are some efforts to update international safety standards and make them more accommodating for the use of R290 in all types of air-conditioning systems. However, because of the large commercial interests of the fluorinated gas industry, these efforts are not likely to reach fruition in the near future! Customers who are interested in switching their rooftop-condensing unit from R22 to R290 (propane) sometimes find their efforts get stuck because of a lack of technical knowledge among local installers or technicians, or the absence of standards allowing hydrocarbons in these type of applications.

170 countries agreed to phase-out HFCs at the United Nations in October 2016
Many compressor manufacturers are well advanced into the production of various types using Propane and these should translate into more new equipment as time progresses. One of the biggest challenges is changing the vast quantity of domestic refrigerators, (that is for another article). Additionally, the refrigerants being used in Commercial Refrigeration equipment is now also being considered seriously for replacement with natural refrigeration alternatives. Plenty has been written already about developing nations and their extended phase out schedule and that is a whole other discussion.

UK based M&E Consultants, Contractors and FM Businesses should now be considering Natural Refrigerants as an alternative (particularly if they are involved with replacing older large packaged air cooled units) and in most cases they are far more cost effective, being more efficient and with lower running costs.