What type of cooling tower is better – FRP or concrete towers? Aslan Barazi weighs their comparative merits to facilitate an informed choice.

Since the beginning of the district cooling era in the Gulf region, which began in the UAE over a decade ago, FRP (Fibre Reinforced Polyester) cooling towers have taken the lead. This is because of the material’s ability to withstand harsh climatic conditions of the region, which include factors, such as high ambient temperature, high humidity and high sea air salinity in this area. However, concrete cooling towers are a tried and tested option. There are many concrete cooling towers still in operation in the region that are more than 35 years old, thanks to their inherent efficiency and longevity. This article addresses some of the key features and differences between the two types of cooling towers – concrete and FRP towers.

It is worth mentioning here that each country seems to have its own preference in cooling towers. For example, the UAE appears to be partial to FRP cooling towers, while Kuwait seems to prefer concrete cooling towers. It is interesting to note that there are many examples of old and new towers that use ceramic tile file with a 25 year standard warranty on the fill, for both plant room size projects and small scale projects.

Both concrete and FRP towers have their advantages. An FRP cooling tower comes with a single FRP body, with either a stainless steel construction or an FRP pultruded structure.

On the other hand, a concrete cooling tower is made of 100% corrosion free material. This is because manufacturers take into account the fact that even SS316 in the cooling towers has been shown to oxidise and turn brown, requiring regular cleaning.

An FRP tower is lighter in weight and has a higher stress/strain ratio, especially when made by reputable cooling tower manufacturers, who use an FRP pultruded structure.

Some cooling tower manufacturers offer the option of a double FRP wall, which gives it a life span comparable to a concrete cooling tower, provided it is correctly specified at the time of listing quality specifications. With minimal alterations, it also becomes an FM approved fire rated cooling tower. This is an important factor from a safety point of view. In case of a fire, the fire can be safely contained within the cooling tower cell, without the possibility of it spreading to the neighbouring cell.

Another advantage in the case of the double FRP wall is that it substantially reduces noise levels, since the air medium between the two FRP walls acts as a sound insulator. In addition, a double wall FRP cooling tower looks better.

The point to be noted here is that there is an additional cost for a double FRP cooling tower compared to the single wall corrugated FRP structure – normally in the range of a 1.15 multiplier. It can be argued that the additional cost is justifiable, if we factor in the fire safety aspect, lower noise level, longer life and higher tower stability, compared to a single wall FRP tower. Its visual appeal, of course, is an added advantage.

At this juncture, it is also important to remember that a material density of FRP/glass composite of no less than 12 oz to 16 oz per square foot FRP ingredient is required for the long life and structural integrity of a cooling tower. There are numerous instances of cooling towers either failing or, worse, collapsing, when cooling tower manufacturers have compromised on the quality of material and have supplied cooling towers using material with thickness of lesser density, for example six oz per square foot or eight oz per square foot thickness.

Concrete cooling towers, on the other hand, have a long history, globally, and in the region, thanks to their longevity, compared to FRP cooling towers. Interestingly, what makes them a more economical option in the region is the lower cost of pouring concrete, when compared to Europe or the United States. Having said that, it can be argued that the concrete needs to be competitively priced, when taking into account the overall pricing of the tower. Which means, the total concrete scope of the cooling towers should be part of the civil contractor’s total scope, including procurement and labour cost, for better economies of scale.

When we compare the life cycle cost (LCC) between a concrete and an FRP cooling tower, a concrete cooling tower seems to emerge as the clear winner in the long run, particularly in the region. If they are manufactured by a reputable company, and are properly maintained, concrete cooling towers can be expected to last for about 50 years – the same longevity as that of a building. This criterion could also be applied, in all probability, to the ceramic tile fill (25 years warranty) that comes along with the tower. Comparatively speaking, a standard quality FRP tower has an average life span of about 20 to 25 years by industry standards, and therefore, needs to be replaced twice during the life of a building. Lower in the rung is the tower with a PVC fill, with an average life of seven to nine years, and would, therefore, need to be replaced five to six times over the average life of a project.

It needs to be noted that a PVC fill is more efficient and occupies less space than the tile-fill variety. Normally, a tile-fill tower may take15% to 25% more space than an FRP or a PVC-fill tower. A tile-fill tower, however, has the advantage of longer life, and is clog free and maintenance-free, allowing practically any kind of water quality to pass through it, without any worry about the effect of heat transfer on the fill medium, as it happens in the case of the more sensitive PVC-fill tower.

In the case of a PVC-fill tower, a slight nudge or tilt may alter the effect of water trickling over the fill, making the water take the path of least resistance. This would, in turn, reduce the overall cooling tower’s heat transfer performance. Additionally, concrete cooling towers have lower noise levels than conventional FRP (single wall) cooling towers, due to the inherent properties of concrete.

Another feature of concrete cooling towers is that they can be constructed as part of the architectural design and, therefore, have aesthetic appeal. This also makes the cooling towers more flexible, as far as space is concerned. The client or consultant, therefore, can allocate a separate space for the towers, instead of installing them in the plant room. This is an added advantage, especially if space in the plant room is a constraint.

A caveat: though concrete cooling towers offer a wide range of innovative possibilities, clients who want to opt for them need to factor them in at the project’s design stage itself and work in tandem with the architect and the mechanical engineer.

In conclusion, it can be said that both FRP and concrete cooling towers are feasible options for a client to consider. The choice depends upon design factors, LCC cost analysis, available project time scales, space considerations, noise levels, safety, tower fire rating and issues of operation and maintenance.

The writer is the Executive Director of IMEC Electro Mechanical Engineering. IMEC are the Exclusive Representatives of CCS Cooling Towers, USA. He can be contacted at imec@emirates.net.ae

Though VRF systems often prove to be better than air-cooled chillers and traditional ducted splits, they have certain inherent limitations. Dharmesh Sawant demonstrates that connecting fresh air systems and VRF systems will yield greater benefits.

With the recent EHS and ESTIDAMA regulations, stakeholders of most projects are racing against time to earn maximum credits to get the approval from the authorities. This trend has encouraged the real estate and construction sectors to adopt green building practices that are ultimately beneficial to the end-users, who had earlier been sidelined and left out of the value chain.

Given the scenario, quite often, the Variable Refrigerant Flow (VRF) system has been found to be useful, thanks to the high EER (above 12, as per ASHRAE 90.1) and the use of R-410A, which is an eco-friendly refrigerant with zero ODP. Apart from that, the part-load efficiency of VRF systems is also better than that of air-cooled chillers and traditional ducted splits, due to their innovative DC inverter compressor technology and precise control of refrigerant flow to the evaporator coil, with the help of multiple sensors in the refrigerant line.

Earlier, however good the VRF system was, it had an inherent limitation when it had to be used for fresh air systems. Since the VRF system works on the control logic integrated with the evaporator coil, which controls the frequency of the DC inverter compressor, it was, therefore, used only with the factory-tested and designed indoor units.

These indoor units have inbuilt electronic expansion valves, which throttle as per the cooling demand. Also, it has its PCB in the indoor unit, which communicates constantly with the outdoor units at an interval of two seconds. Owing to this limitation of the VRF system in the fresh air system, it is either connected to chilled water, making it difficult to maintain two different systems – VRF for the re-circulating FCU and chilled water for the fresh air system. Or else, the entire system is connected to the chilled water system, increasing capital as well as operating costs.

Looking at the positive side, if it is possible to connect the fresh air system to the VRF system, the benefits compared to chilled water system are as follows:

Reduced capital cost up to 25%

A VRF system needs fewer components – VRF condensing unit, indoor units and connecting copper pipes. The valve packages are all in-built, unlike chillers, which need pumps, chemical dosing plants, valve packages, three-way valves, chillers, chiller manager, makeup water arrangements, etc. This increases the cost of the chiller system. Owing to this characteristic, a VRF system proves less cumbersome for contractors, as they only have to coordinate with fewer vendors.

Chillers are normally kept in remote chiller yards to keep the noise levels away from the main building. This increases the pipe network cost. In the VRF system, however, the condensing units are kepts close to the AHU, thus reducing the pipe cost.

Reduced operating cost by up to 30%

The daily range of temperature in the Middle East is quite high. This translates into a highly variable fresh air load. The DC inverter varies its frequency as per the ambient temperature (fresh air load), thus optimising power consumption. The NPLV figures of the VRF system go as low as 0.58 KW/TR for the horizontal development, with reduced separation between indoor and outdoor units.

Reduced connected electrical load

The VRF system has lower connected electrical load of 1.2 KW/TR, compared to 1.7KW/TR, including pumps at 460C for horizontal development with minimal separation between the indoor and outdoor units. This reduces the size of the transformer, lowering the infrastructure cost.

Ease in commissioning

One of the nightmares of commissioning agents in the chiller system is its hydronic balancing. In the case of the AHU connected to the VRF system, it can be commissioned with the help of a software. As a result, all the important parameters can be viewed on the laptop.

Better control of finances in a phased development

In the case of a VRF system connected to the AHU, the project finance is directly proportional to the development phase. But in case of a chiller system, you need to pay a higher cost than the development phase. For example, in the final stages, if a 50 classroom school is made in two phases of 35 and 15 respectively, within a year’s gap, the capital cost in the case of the VRF will be 70%. But in a chiller system, you need to lay the pipe an install the chiller for the total capacity of 50 classrooms.

All the above benefits are made possible by integrating the AHU and the VRF condensing units with the help of a control kit and an expansion kit. The architecture of the system is as follows below.

A total of eight outdoor units amounting to 700 KW can be connected to a single AHU, giving more flexibility to contractors/consultants. The following options are available with the AHU:

• a) Heat recovery wheel or heat pipe
• b) Temperature/humidity sensors in return and supply air
• c) Damper actuator for fresh air and return air

A total of eight outdoor units amounting to 700 KW can be connected to one AHU, giving more flexibility to the contractors/consultants. The following options are available with the AHU:

• a) Heat recovery wheel or heat pipe
• b) Temperature /humidity sensors in return and supply air
• c) Damper actuator for fresh air and return air
• d) Differential pressure switches across the filters
• e) Valves for the humidifiers
• f) Operation of the motorised damper, as per the CO2 sensors
• g) Operation of the motorised damper, as per the smoke detector

The entire system is BMS-compatible through LONWORK or BACNET gateway. Thus, it offers the benefit of high EER of up to 12~12.5 due to DC inverter scroll compressor, high efficiency DC inverter condenser fan motor, high efficiency sub-cooling heat exchanger and wide louvre condenser fins. Above all, it offers reversible heating cycle.

The condensing unit comes in modular design, with each module having two compressors – one inverter and the other, constant-speed scroll. Therefore, even if one compressor fails, the other compressor comes on automatically, with auto back-up function.

The condensing system is easy to commission with the help of a Monitoring Viewer by hooking the system to the laptop. This provides a real-time view of various important parameters of the air conditioning system, like suction, discharge pressure, sub-cooling temperature, superheat temperature, ambient temperature, and refrigerant inlet and outlet temperature (see Figure1 and Figure2 below).

In addition to this, with the help of the control kit that integrates AHU and VRF system, it is possible to control as well as monitor the AHU parameters using an AHU Viewer.

As shown in the screen shot (Figure 3 below), we can easily check the following:

• Fan and damper condition
  • — Fan ON/OFF, damper opening angle
• AHU condition by sensor installed in each part
  • — Mandatory sensor (RA/SA temperature)
  • — Other sensors (SA/RA humidity/OA/Mixing air, CO2, etc.)
• Control condition
  • — Operation mode (cooling, heating, fan, power saving)
  • — Setting temperature/humidity
  • — Supply and return fan operation

Green fresh air solution with VRF technology has found increasing acceptability in the region, thanks to the enforcement of green building practices by ESTIDAMA, as many stakeholders look for a solution in the design stage to achieve the required credits.

A few of the applications where fresh air units are feasible are schools, mosques, villas, horizontal office buildings (up to 10 storeys), cultural centres and museums.

The writer is Senior Manager, LG Commercial AC. He can be contacted at: dharmesh.sawant@lge.com.

Lack of adequate and efficient ventilation systems with the right airflow rate is a health hazard. Good IAQ is an essential requirement of modern living, says Gaetan Pierrefeu.

Ventilation is a basic need. It is required to ensure proper Indoor Air Quality (IAQ) and level of comfort, and improve the quality of life for people. A system of continuous air renewal is necessary for health, by the process of elimination of pollutants – CO2, Volatile Organic Components or VOCs – as well as odours, spores or germs. It also reduces the humidity rate, and by extension, the development of moulds and acaroids.

A few of the traditional ventilation solutions, such as wind towers or the barajeel system used earlier in the region, ensured basic comfort for residents through a natural system of cool air renewal inside local dwellings, until the 19th century, as can be exemplified by the Bastakya district in Dubai. The need for ventilation is, therefore, old, basic and vital.

Air conditioning and split-unit technologies came into the region later to cope with high temperatures. But the noise they generate and low thermal comfort they provide are the two main reasons why central AHUs and FCUs have gained popularity in recent times. These systems generally ensure a greater level of cooling due to high cooling loads and lack of proper insulation. This has obviously led to high energy consumption.

The first step in the evolution towards sustainability is, therefore, to work on the envelope of the building to ensure an efficient system of building insulation, air tightness and shade. On the flip side, though these will lead to better energy savings by reducing the cooling load (low heat transfer and low air leakage), they will also increase the need for an efficient ventilation system, bringing outdoor air to cure and improve the IAQ. Indeed, all pollutants and VOCs trapped inside buildings will have to be removed effectively through a continuous ventilation system.

Absence of such an adequate ventilation system with the right airflow rates will increasingly give rise to health issues, especially for the most fragile – children and seniors. In fact, some of the prevailing health disorders can be traced to building-related illnesses.

Indeed, high level of CO2 concentration in a building can often be traced to an occupant’s poor health, a feeling of discomfort and performance degradation. For example, sick-building syndrome reportedly affects the health of employees and reduces work hours. This obviously has a direct bearing on efficiency and productivity. Apart from poor IAQ, the development of new construction and furnishing materials has generated diverse VOCs, which are health hazards.

It is only logical, then, that we direct our collective effort to improving the quality of air inside buildings in which we spend 90% of our time, and where the indoor air is usually two to five times more polluted with formaldehyde, benzene and toluene, than the outdoor air. Here, it must be mentioned that a lot of people are still unaware of the health risks posed by bad indoor air quality.

Many countries in the world have chosen carbon dioxide as an IAQ indicator that reveals the pollution level in the atmosphere, mainly caused due to human activities and materials.

The CO2 threshold value from European standard EN 13779 for non-residential premises is fixed at 800ppm (parts per million) above the outdoor level, which is between 350 and 400 ppm, depending upon the building’s location and the prevailing season. Therefore, in order to ensure the correct level of IAQ, concerned authorities and designers should enforce the common threshold. A daily average air change rate of 0.5-0.6 ach (air change per hour: Vol/hour) for housing is considered sufficient to achieve the CO2 concentration limit of 800ppm above the outdoor level, and a relative humidity of 60% at 18° to 20°C during occupancy.

In the light of this, many types of demand-control ventilation systems have been developed to modulate airflow rates, taking into account the real occupancy inside a building and the working hours. These systems can be timer-controlled. They generally modulate airflow according to optical detection, CO2 or humidity levels, preferably with a minimum airflow for dwellings. Indeed, humidity is also a tracer for a ventilation system, as in every breath cycle, people consume some amount of oxygen and exhale CO2 and H2O in identical quantities.

Other efficient ventilation systems combine the approach of IAQ and demand-control ventilation, with energy-recovery ventilation for further energy consumption control. These systems transfer heat directly to the outdoor air for free pre-cooling, in order to limit cooling from the central AHU or decentralised HRV units, which are used more and more in new designs, especially in schools.

A secondary benefit of good ventilation is that the air can act as an efficient carrier of calories or frigories, naturally present in the outdoor air, which may be warmed by the sun (recovery in the back of a solar cell), or cooled down in the ground (through geothermal ducts), or both, through a heat pump.

As far as countries in the Middle East without any specific ventilation regulations are concerned, in the public interest, it is vital to consider the requirements that define and specify the need for ventilation.

For a healthy IAQ and from the hygiene point of view, dwellings have to benefit from an air renewal and pollutant extraction system, especially from certain areas like the bathroom and kitchen, to avoid health hazards due to high indoor air pollution rates and condensation. As the first step in this direction, CO2 concentrations calculated over one year should not exceed 1,200 ppm for more than two per cent of the year for conventional dwelling occupancy.

It must be remembered that breathing clean air is an inalienable right, as much as the right to drinking water. But, apart from a hygienic environment with high IAQ and low pollutant concentrations, thermal comfort during winter and summer is also a human need.

The writer is Managing Director of Aldes Middle East. He can be contacted at pierrefeu-gaetan@aldes.com

While Qatar 2022 spells good news for the HVACR and related sectors and professionals, it comes with a number of challenges. Pratibha Umashankar highlights them.

Qatar, geographically a mere speck on the world map, successfully marketed itself as a viable venue for the 2022 football World Cup. The event is as much an image-building exercise, as an economic strategy. The authorities believe that their sight is set beyond the World Cup, in terms of financial dividends.

The country is reportedly investing over $30 billion into its infrastructure out of a $40 billion earmarked for the event. The new international airport is slated to be ready by 2013, and reportedly comes with a price tag of $13billion. According to a statement issued by Moody’s Investor Service, on December 5, as reported by Global Arab Network (Banking goals – Qatar gears up to host World Cup), it pegs the government spending to $57 billion over the next decade, for infrastructure development projects and upgrading of existing transportation systems.

With world-class air conditioned stadiums; accommodation and other facilities for visiting teams, officials and spectators, on the cards, Qatar will witness tremendous spurt in all-round growth, which will certainly impact the HVACR sector. Ramiz Gabrial, a consulting engineer, who was ASHRAE Oryx Chapter’s President till January 2011, affirms that the HVACR sector, as a whole, will be positively impacted by the event. “I believe that the positive impact will extend beyond Qatar, as there will be many major projects that will require dedicated research and development programmes to ensure that they meet or exceed expectations of Qatar Football association, FIFA and the world,” he says.

The spill-over effect is likely to be two-fold: benefit for other related sectors and to countries in the region. “The computer and energy simulation fields will get more focused on, as these unique projects will benefit from the available technologies,” says Gabrial. “In return, the same projects will benefit the HVAC profession, as it will create feasible business opportunities for many local, regional and global consulting firms to invest in further developing the technology.”

The volume of work will also give a positive nudge to two other important areas: Project design and construction management. Gabrial believes that the time frames that will be set for various projects and associated challenges will lead to major development in these fields.

“Facility management is another field that will have to get higher focus and get upgraded to required standards,” Gabrial adds. He elaborates: “The volume of work will require large number of HVAC professionals at all levels – senior and junior designers and managers, CAD professionals, energy and other computer simulation professionals and construction managers at all levels. This large and concentrated need will sharpen and shape many professionals who will work from inside or outside Qatar. Accordingly, the whole profession will benefit from the experience.”

Despite rich predicted pickings for the HVACR sector, especially of the low-hanging fruits from mega projects, the situation comes with its attendant challenges. Gabrial lists some of them:

• Procurement of equipment and materials from reputable manufacturers: Due to the volume of work, the industry needs to be careful about the source of equipment and materials they will bring in. Globally, all manufacturers would want to take a share in this market; some may not have the acceptable standards and/or certifications.
• Lack of sufficient design detailing: As the volume of work intensifies, consulting engineers may tend to leave some of the important design detailing for the contractors to take care of and, hence, leave a gap that could create future contract- or facility-management issues.
• Water consumption: Water-cooled systems will be used to serve large projects. This will create an increased water demand to cover the required cooling water volumes.
• Shortages and rising costs of building materials and equipment could be another challenge. This could lead to projects being delayed or, worse still, shoddy workmanship, with mounting deadline pressures. Also, depending heavily on outside skilled workforce, equipment, material and outsourced jobs might prove to be detrimental to the sector, if there are weak links in the other end of the supply chain.

With Qatar, in particular, and the HVACR sector, in general, pushing for green technology, whether the growth is at the cost the environment is another issue that needs to be addressed. “One specific area that will definitely receive major attention is sustainability and green building design,” agrees Gabrial. “Qatar has taken big steps in supporting and implementing sustainable building designs and solutions. Energy and water conservation, reducing carbon footprint of buildings and the use of regional materials, are among the issues that will get major attention as part of the sustainable design effort.” He cites the example of Qatar Foundation as an important player in the effort in the sustainability and sustainable building design movement in Qatar, which is a major element of the design, procurement and construction phases of each coming project.

In this context, the role of the local ASHRAE Chapter gains significance. “ASHRAE Oryx is already focusing on issues that are of interest to the HVAC profession on energy, water and major equipment selection,” Gabrial says.

The January issue of the ASHRAE Oryx Chapter’s journal, in an article titled, FIFA 2022 – The engineering challenges, succinctly sums up both the onus and the rewards: “The amount and type of construction projects that will take place during the coming 12 years will be the dream of any construction professional. However, this excitement and thrill impose added responsibility on us. We are morally responsible to make sure that the hard work that was put to win the FIFA 2022 Bid is translated to bigger success in building world-class facilities that tells the world another great story about what dedication and determination can achieve.

“The mechanical engineers will have their share of the challenge, as these facilities will have to be designed to satisfy specific environmental conditions. Sustainable and Green building designs will be another mission to show our commitment to the environment.”

Calling it an “intense engineering experience that is going to be built in Qatar”, the journal says that the lessons learnt can serve the profession in the long run. The sector, therefore, will certainly be a beneficiary of the World Cup, probably financially, but certainly professionally.

Climate Control Middle East analyses cooling optimisation through combined VSP and PICV installations

As topics go in a region that captures just one percent of the world’s available fresh water, yet hosts 5% of the world’s population, the issue of energy consumption doesn’t get much hotter.

Add international climatic pressure, existing and incoming regional strategic targets and a shiny new end-user driven business model to the mix, and in-depth evaluation of energy efficiencies becomes compelling.

The design, construction, operation and maintenance of cities and communities has a huge impact on natural resources and the environment. The challenge is to build smart throughout the supply chain.

With this in mind, Climate Control Middle East paid a visit to Technoflow at its testing and development laboratory, headquartered in Dubai. Below we bring you straight forward information on how HVAC energy savings can be achieved through a combination of variable speed pumps, PICVs, pressure sensors and control valves.

Fig 1. Varying conditions in a system with pump pressure controlled to maintain constant pressure at system extremities (Source: CIBSE KS 7)

Until recently the majority of large chilled or heated water based air conditioning systems were designed for constant flow and utilised three or four port temperature valves to divert the required amount of water flow through in room heat exchangers, such as fan coils. The local heating or cooling load is influenced by a number of factors including the outside air temperature which will vary over the year and therefore, cooling or heating degree days vary over the year as outside air temperature changes.

Cooling or heating water, whilst providing an effective method of indoor climate control by pumping it around a building, if the heat exchanger is bypassed at the last moment without extracting the absorbed heat, this is extremely wasteful in energy. As the full heating or cooling load on a building occurs for 5% or less of the year, it is extremely important to match the power absorbed into a heating or cooling system to the actual load placed upon it.

Manufacturers of pumps, fans and other equipment have successfully utilised variable speed drives that can slow motors to reduce power consumption at periods of low demand.

By combining variable speed pumps and two port temperature control valves (that throttle closed rather than divert through a bypass port) together with pressure sensors and pump controllers, a water based air conditioning system can operate under variable flow conditions in response to the varying heating and cooling loads on the building.

Due to the pump affinity laws, if pump speed is reduced to 25% of its maximum then the flow is also reduced to 25%, the pump head is reduced to 6.25% and the pump power output is reduced to only 1.6% (i.e. 0.25% of 6.25%) of its maximum. Actual pump power consumption (electrical energy) is likely to be a little higher than 1.6% due to a reduction in pump efficiency, as shown in Fig 1., but this will be marginal.

Unfortunately there are unwanted pressure fluctuations in the pipework as pumps change speed and two port valves open and close in a variable flow system. These result in underflows and overflows and corresponding undercooling and heating or overcooling and heating at the part load condition. However, this unwanted side effect can be managed by careful use of differential pressure control valves or the installation of pressure independent balancing & control valves at each of the in room heat exchangers.

A recent study conducted by Frese and Grundfos in Denmark demonstrated that when a variable speed pump, end point pump sensor and pressure independent balancing & control valves (see Fig. 4) were installed on a typical variable flow system then 76% of electrical pump energy consumption could be saved relative to the same system fitted with a constant speed pump and manual balancing valves.

Furthermore overflows and underflows were eradicated and supply and return water temperatures were guaranteed as the system remained dynamically balanced at all load conditions.

Despite the dramatic savings in pump electrical energy consumption, this is only half of the story, due to beneficial effect of maximising ΔT (the difference between system supply and return temperature). The energy consumption of a chilled water cooling system is comprised of three main parts, i) the energy cost to chill the water, ii) the energy cost to pump the water around the system and iii) the energy loss from the return pipework.

It is also very important to maintain a high ΔT in efficient heating systems in order for condensing boilers to work in condensing mode at all load conditions.

Fig 4. Variable speed pump with end point control and pressure independent balancing & control valves

The cost to operate the chiller can typically account for as much 40% of the energy use in cooling systems but their efficient operation is often impaired due to elevated return temperatures caused by overflows in variable systems or blending of supply and return water in primary headers or through chillers that have been staged off.

Furthermore, on large distribution systems, the heat losses from lengthy return pipework can be minimised if the return temperature is maintained as close to atmospheric temperature as possible.

Pressure independent balancing & control valves maintain system design ΔT at all load conditions and eradicate losses through inefficient chillers working when they are not required and by minimising the temperature gradient to atmosphere in the return pipework to the plantroom.

Air filtration, as we all know, is the process of separating dispersed particles from a dispersing fluid by means of porous media. To complete such a process, it is evident that filter fibres are expected to separate and retain particles on or within the filtration medium. Filters are either used to purify air or collect airborne particles for sampling and research purposes.

Evidently, air filtration is a preventive measure to protect the respiratory systems of human occupants indoors, and also the HVAC equipment. This can be done through mechanical filtration to reduce contaminant concentrations, which vary, depending upon the nature of the application.

The success of any filtration system depends upon its ability to capture the right contaminants in the right quantity with least resistance to air flow.

HISTORY OF DUST AND AIR FILTERS

Figure 1: Different particles arrested around the fibre of a filtration medium

Air filters can be traced back two thousand years. It started during the Roman times, with the recognition and awareness of dust as a harmful agent causing problems. The famous artist, Leonardo da Vinci, had long ago stated that a wet cloth could be used as protection from fumes in warfare. In 1556, Georg Bauer, the German chemist and metallurgist, recommended ventilation to lower the concentration of dust in mines, in his posthumously published work, De Re Metallica.

The early developments in the field of air filters were made without a real understanding of the basic principles of filtration. The inability to comprehend different parameters of the filtration process forced researchers to rely on empirical results for the development of the filter performance.

Even though the filtration theory of large particles was introduced when Stokes Law was first derived in 1850, the mechanics of aerosol filtration were developed in Germany only during the 1920s, by Freundlich and Engelhard.

In the early 1930s, the first efforts to study air filtration scientifically were made – once again in Germany – by Albrecht and Kaufmann. They made their original approaches to a theory of the mechanisms of aerosol filtration by fibrous material. In 1930, the Danish Scientist, Nicolaij Louis Hansen discovered the resin filter.

In this method, resin particles were added on the surface of the filter material. The electric field arising from the use of resin was found to enhance the efficiency of the filter exceptionally, with an appreciable impact on the filter’s resistance. The technique was employed by the Danes, Dutch, French and Italians by 1933.

THE IMPORTANCE OF CLEAN AIR

Air filters play an important role in our daily activities, whether it is domestic, commercial or in industrial applications. Air filters constitute an integral part of providing clean air to buildings and maintaining the rated energy efficiencies of HVAC equipment.

In applications such as hospitals, air conditioning systems are run throughout the year, and involve extensive use of pleated High Efficiency Particulate Arrestance (HEPA) filters with 100% fresh air. Aerodynamic and efficient HEPA filters are in great demand due to escalating energy costs worldwide.

Figure 2: Types of air filters used in air conditioning and gas turbines (EMW Filtertechnik)

As far as enhancing power generation and reducing fuel consumption is concerned, filters are also used to provide clean air to the gas turbine air intake.

When we think of conditioning the atmospheric air, intuitively, the first thing that comes to our mind is controlling its temperature and humidity. However, conditioning the air also involves treating it to provide the required cleanliness level by removing the existing contaminants. This can be achieved by using air filters as the first stage in the HVAC system. If we take a look at any HVAC system, it becomes evident that the air filtration section is at its forefront.

In any given environment, both the outside and inside air may contain contaminants with concentration levels beyond the accepted limits, and thus, warranting air treatment. Therefore, air filters are required to treat the outside air to introduce it indoors, and / or re-circulate the indoor air through filters to attain the desired air quality.

While air re-circulation seems to be a quick over-the-counter solution to reduce cost, this option needs to be exercised with caution, as it could cause further contamination. In fact, making the HVAC system the source of air contamination, rather than the line of defence. In applications such as clean rooms, and specifically operating theatres, 100% fresh air is an absolute must. Further, hospital indoor air must be treated prior to exhausting it into the environment.

Obviously, this may be a difficult fact to accept for some designers, end-users or even owners, as they will then be required to install air filters on the exhaust. But the question that poses itself is, why should residents in the area breath hospital air? In other words, why in our neighbourhood?!

UNDERRATING THE ROLE AIR FILTERS

Whenever the subject of air filtration is addressed, its role and importance is usually underestimated.

However, during the first trip to the moon in 1969, massive clean rooms were required, where computers which managed the highly sophisticated flight planning could be housed. Such an enhanced level of clean room standards were facilitated by the use of high-efficiency air filters, which have now become an integral part of the electronic industry and deemed the standard for fabrication for delicate electronic chips, such as microprocessors.

Dust fouls the heat sinks found in personal computer power supplies, causing over-heating and leading to failure. Submicron dust particles pose a major challenge to the micromachining industry, since they block the narrow area in their system, causing malfunctions. Air filters are also used in operating theatres, to prevent post-operative infection and to provide sterile air for preparation of pharmaceutical products.

INDOOR AIR QUALITY – WHAT WE DESIRE AND DESERVE

Recently, the emphasis has shifted to indoor air quality, and consequently, the role of air filters has been highlighted. As we spend most of our time indoors, whether living at home, driving to work, working in the office or spending time at the mall or restaurants, in one way of another, we constantly subject our respiratory system to indoor air. This predominance of an indoor lifestyle brings several important questions to the fore: What kind of air are we breathing? Who controls its quality? Who monitors the performance of air filters to ensure that they do what the catalogues claim they do? And, finally, what international standards govern such performance to ensure that end-users get the air quality they desire and deserve?

The writer is Iyad Al-Attar, Regional Director, EMW. He can be contacted at iyadalattar@yahoo. com.

WEG Electric Motors

Saying that thanks to its robustness and reliability, the standard 3-phase squirrel cage design of electric motor has been around for over a century, despite probably achieving its optimum levels of performance, WEG Electric Motors has introduced Wmagnet series of permanent magnet (PM) motors, as a viable alternative. WEG, supplier of electric motors and related control equipment, said that the new motors have been designed for applications where constant torque, Iow vibration and low noise levels are required.

The manufacturer claims that the Wmagnet series can be used in elevators, compressors and conveyors. Because they can operate self-ventilated over a wide speed range, the motors are also ideal for use in applications where gearboxes need to be eliminated to save space, it adds.

It lists the following product features and advantages:

The WMagnet motors reduce size by up to 50%, weight by up to 36%, and deliver higher efficiencies (up to 97.5%) compared to equivalent size induction motors.

They are, generally, at least one frame size or core length smaller than the equivalent induction motor, and in some cases, can be two frame sizes smaller. Therefore, the cooling system is reduced for the same torque/power ratio, and consequently, there is a reduction in the levels of noise from the fan coupled to the motor shaft.

They are manufactured with high energy magnets (NdFeB) in their rotors. These deliver a significant reduction in energy losses compared to an induction motor, resulting in a lower temperature rise of the motor and increased operating life.

As these energy (Joule) losses (RI2) account for a significant portion of total losses in induction motors, the PM motor delivers much higher efficiencies (up to 97.5%), exceeding the new harmonised IE (International Efficiency) standards: IE2, which comes into force in July 2011, IE3, and also, attains IE4.

It can operate on a wide speed range (up to 7,300 rpm in special cases) with constant torque. This is controlled by a version of WEG’s CFWO9 VFD, which has been specially developed for the Wmagnet range. The CFW09 employs its vector control technology to effectively drive the WMagnet from zero speed up to the field weakening region.

According to WEG, in one of the first field applications for the WMagnet motors, Buettner, a Brazil-based textile manufacturer, purchased three WMagnet motors from WEG, and has been able to reduce its annual power consumption by 33% and increase its machine utilisation by 80%. These twin gains have delivered substantial savings in production costs and have also improved the company’s profitability in a highly competitive global market, WEG claims.

It quoted Aires Fantoni, Electrical Maintenance Supervisor at Buettner: “Our goal is to replace all of our standard induction machines with WEG WMagnet motors within three years.”

Marek Lukaszczyk, European Marketing Manager for WEG added, “As demonstrated by the Buettner application, the WMagnet motors are ideal for applications where eliminating a gearbox is essential; the motors can do this because they can operated self-ventilated over a wide speed range.”

Carlisle HVAC

Claiming that it has come up with the answer to HVAC’s cleaning and sealing inaccessible ductwork problem, Carlisle HVAC has announced the introduction of its Inspection, Sealing and Advanced Cleaning Robotic System, or ISAAC for short. ISAAC HVAC Robotic System can help improve indoor air quality and decrease heating and cooling costs without significant interruption to building occupants, says Carlisle. It further claims that the robotic solution enables efficient sustainable retrofit of existing HVAC systems.

“We’re proud to have added ISAAC to the arsenal of powerful HVAC repair and remediation solutions at Carlisle HVAC,” said Billy Prewitt, Manager of Marketing, Carlisle HVAC. “ISAAC, in conjunction with our new Hardcast RE-500 Robotic Delivered Insulation Encapsulant and RS-100 Interior Water- Based Duct Sealant, offers three major benefits in one package: duct system inspection, air quality improvement, and greater energy efficiency,” he added.

Carlisle HVAC lists the following product features and advantages:

• The ISAAC HVAC Robotic System is capable of hard-to-reach remediation that would otherwise result in much more costly renovations.
• It is no longer necessary for employees to crawl around ductwork and cut access holes every eight feet – tasks that often lead to injuries and worker compensation claims.
• It is equipped with an integrated digital video recorder, which, combined with the included personal computer software, creates a powerful inspection and documentation tool.
• It helps to mitigate energy loss by properly sealing ductwork, resulting in increased airflow and reduced operational costs.
• It can improve a building’s indoor air quality, purging the system of long-unnoticed particulate.
• The sealants and encapsulants products are anti-microbial, meaning they do not provide a food source for bacteria.

Method used to produce ultra-pure water at reduced capital costs and energy use

A heat and power plant in Northeast China has announced that it has recently adopted the integrated membrane system to replace a conventional water treatment process. It has adopted Liqui-Cel Membrane Contactors to reduce operating costs and energy use, while providing superior outlet water quality, the announcement said. The Liqui-Cel Membrane Contactors supply a 1-2 ppm level of CO2 to the EDI, which improves silica removal, it claimed.

An integrated membrane system is an industrial water treatment system that combines multiple membrane-based water treatment processes into a single system.

According to the announcement, the system consists of four major membrane-based water treatment components: Ultrafiltration (UF), Single Pass Reverse Osmosis (RO), Liqui-Cel Membrane Contactors (LMC) and Electrodeionisation (EDI).

Though for many years, double-pass RO+EDI systems have been a widely used water treatment combination to produce ultra-pure water, as pressure has increased for engineers to reduce maintenance and operating costs, alternative system designs are being considered, that utilise Liqui-Cel Membrane Contactors for deaeration with RO and EDI, the announcement added.