Iron – major component of steel but susceptible to corrosion
Thursday, 17 May 2012 12:58
glyniss
Iron is possibly the most used and most important metal today. Ancient Egyptians learned how to use iron before the First Dynasty, which started pre 3000 BC. The probability is that the Egyptians found iron in meteorites, some of which are very rich in iron.
As they fashioned meteoric iron into small tools and ornaments they had no inkling iron would turn out to be the fourth most abundant element in the earth on which they stood.
From around 1200 BC, people learned how to smelt iron metal from earth ores and use it for making many diverse products. It is still and probably always will be called the Iron Age. Iron was common to early Asian civilisations. In Delhi, India, a pillar made out of iron built in 415 AD still stands. It weighs 6 500 kg and remains in remarkably good condition after nearly 1 600 years. Early Chinese civilisations also knew about iron. Workers there learned to work with iron as early as 200 BC. A number of iron objects, including cannons, remain from the Han period, from 202 BC to 221 AD. It was not until 1786, however, that scientists determined quantitatively what it was in steel that made it a more useful metal than iron. Three researchers, Gaspard Monge (1746-1818), C A Vandermonde, and Claude Louis Berthollet (1748-1822), found that small amounts of carbon mixed with iron, produced alloys which we know as steel.
The term ‘steel’ actually refers to a wide variety of products. Various forms of steel all contain iron and carbon. They also contain one or more other elements, such as silicon, titanium, vanadium, chromium, manganese, cobalt, nickel, zirconium, molybdenum, and tungsten. Two other steel-like products are cast iron and wrought iron. Cast iron is an alloy of iron, carbon, and silicon. Wrought iron contains iron and one or many other elements. In general, wrought iron contains very little carbon.
Corrosion of iron
Huge amounts of money are lost every year because of corrosion. Much of this loss is due to the corrosion of the iron content of steel, although many other metals may corrode as well. The problem with iron and other metals is that the iron oxides formed by oxidation do not firmly adhere to the surface of the metal. They flake off easily leaving behind ‘pitted’ surfaces. Extensive pitting eventually causes structural weakness and disintegration of the metal. Other metals such as aluminium and copper form very tough oxide coatings which bond strongly to their surfaces preventing them from further exposure to oxygen and corrosion. Elements such as silicon, chromium and nickel used in steel alloys provide varying degrees of resistance to corrosion by forming protective layers on iron surfaces. Other types of surface coatings include galvanising, provide long term protection against corrosion on steel surfaces because oxidised exterior layers of these materials [the zinc in galvanising] do not flake off but continue to form an integral part of the protective coating.
The word ‘corrosion’ is often wrongly used to describe the reactions of many chemicals, particularly acidic chemicals, on iron and other metal surfaces. This incorrect usage is also associated with degradation of metal surfaces by micro-organisms, particularly the well-known anaerobic Sulphate Reducing Bacteria (SRB) which does not attack metals directly but produces hydrogen sulphide which hydrolyses with any water present forming sulphurous and sulphuric acids. Corrosion as such, occurs in the presence of moisture. For example when iron is exposed to moist air, it reacts with oxygen to form rust.
 The amount of water [X H2O] in the iron oxide (ferric oxide) varies as indicated by the letter ‘X’. The amount of water present also determines the colour of rust, which may vary from black to yellow to orange brown. The formation of rust is a very complex process which is thought to begin with the oxidation of iron to ferrous (iron ‘+2’) ions.
Both water and oxygen are required for the next sequence of reactions. The iron (+2) ions are further oxidised to form ferric ions (iron ‘+3’) ions.
The electrons provided from both oxidation steps are used to reduce oxygen.
The ferric ions then combine with oxygen to form ferric oxide [iron (III) oxide] which is then hydrated with varying amounts of water. The overall equation for rust formation may be written as:
The formation of rust can occur at some distance away from the actual pitting or erosion of iron as illustrated in figure 1. This is possible because the electrons produced via the initial oxidation of iron can be conducted through the metal and the iron ions can diffuse through the water layer to another point on the metal surface where oxygen is available. This process results in an electrochemical cell in which iron serves as the anode, oxygen gas as the cathode, and the aqueous solution of ions serve as a ‘dissolved - salts bridge’.
The involvement of water accounts for the fact that rusting takes place more rapidly in moist conditions as compared to a dry environment such as a desert. Many other factors affect the rate of corrosion. For example, the presence of dissolved salts in the water greatly accelerates the rusting of metals. This is due to the fact that the dissolved salts increase the conductivity of the aqueous solution formed at the surface of the metal which enhances the rate of electrochemical corrosion.
Protecting normal non-stainless carbon steel surfaces against exterior corrosion from ordinary rainwater and atmospheric oxygen has long been done with paints. Extra protection for more aggressive environments is provided by tougher coatings such as epoxies. Internal wetted areas of steel machinery and pipes are another matter entirely, as although some machines, such as galvanised cooling towers and evaporative condensers, have internal water passage anti-corrosion protection. Most steel water pipes do not. Therefore, whenever non-stainless steel pipes are installed for open evaporative cooling water circuits, closed cooling water circuits, and hot water circuits, the potential for iron corroding wetted surfaces must be addressed.
In evaporative water circuits, potential corrosion is normally much lower than in closed circuits due to higher pH levels resulting from increased dissolved calcium and magnesium carbonate salts due to these circuits running at cycles of concentration of six or higher. Regular bleed-off of circulating water also prevents build up of contamination by small amounts of iron corrosion products flaking off from steel surfaces from time to time. Chemical treatment of open water circuits is normally done by automatic dosing into supply make-up water so it is easy to maintain minimum levels of anti-corrosion chemicals.
Closed water circuits are seldom equipped with automatic chemical dosing systems and because, theoretically, there are no circulating water losses, an initial one-off dosage of chemicals is expected to prevent, or at least reduce to an extremely low level, the formation and progress of electrochemical corrosion cells as shown in figure 1 for periods ranging from 90 days to a year. From a chemical point of view, this is possible provided there are no water leaks, sufficient chemicals are dosed which do not react with the water, the internal wetted steel surfaces are genuinely clean to start off with, and there is a way of getting the required chemicals into the circulating water without any delay.
Current practice in South Africa for monitoring closed water circuits which, in HVAC installations are either hot or cold circuits, is to take samples of circulating water and test them at regular intervals which is normally every 90 days. Since the water circuits are closed, any water contamination showing up in the tests must be internally generated, coming from the wetted steel surfaces. Undissolved or suspended particles are virtually always iron corrosion products – the iron oxides and hydroxides referred to earlier. Low levels of iron found are assumed to indicate correspondingly low rates of iron corrosion. If corrosion coupons were originally installed they can be cleaned and weighed making calculations of amounts of steel lost per year possible. A further indication of corrosion is a significant decrease in the pH of the circulating water which is explained by the end of the previously detailed overall equation for rust formation [- - - - -+ 8H+[aq]] adding hydrogen ions to the water. Lower pH water holds more iron in solution which further complicates linking test results for iron in water with actual corrosion rates of steel. On a practical level therefore, when iron test results show high iron concentrations – upwards from about five milligrams per litre – calculations of the rate of metal loss from weight loss data of corrosion coupons determines what corrective actions are needed. The generally accepted maximum reduction in the thickness of a representative steel coupon is 0,02 mm per year.
Iron corrosion in steel is irreversible so it is imperative to reduce it as much as is practically possible in the continuously increasing number of cooling and heating water circuits in which ordinary non-stainless steels are used. Fifty years ago, when low dosages of chromate anti-corrosion chemicals were permitted, corrosion rates of below 0,01 mm per year were the norm. The next best anti-corrosion agent, zinc, joined chromium on the banned list in 1980. Today, the two most widely used anti-corrosion treatment systems are based on two other metals, molybdenum and boron, both of which are under scrutiny for any evidence of accumulative toxicity. Of the two, boron is the more popular in the well known ‘boron nitrite’ form which does reduce corrosion rates to below 0,02 mm per year when properly applied and maintained. However, boron nitrite has become a relatively high cost item in maintenance budgets for HVAC installations which feels out of place by both users and suppliers for a straightforward chemical treatment system which has been unaltered for over 60 years. It seems, in fact, puzzling that at present there is no indication whatsoever of any potential for improved replacements for the molybdate/boron products for such a large and growing market compared to, for example, what has been done with refrigerants in this era of continuously developing technology.
World class cooling for a world class theatre
Thursday, 17 May 2012 11:12
glyniss
 Virtually invisible and almost inaudible, the HVAC system brief for the new theatre in Soweto had the word ’challenge’ written all over it.
By: Ilana Koegelenberg in association with Lindsay Lund and Pedro Gans from Ubunye Engineering Services
(Photo credit: courtesy T de Oliviera, Chibwe Afritects SA)
The Soweto Theatre is one of the seven legacy projects of the 2010 FIFA World Cup, designed to ensure Johannesburg and its residents continue to benefit from the football tournament long after it finished. City of Joburg Property Company developed the theatre, which is a first of its kind for Soweto, and Promusica Theatre has been commissioned to operate it once it opens.
The theatre is situated on Bolani Road in Jabulani, Soweto, and consists mainly of three venues: a 420-seater auditorium with an end stage and fly-tower, as well as two smaller theatres with capacities of 180 and 90 respectively. In addition, the building complex hosts two wing buildings; an orchestra pit, a multi-level back stage area with a double volume green garden atrium sheltered by top mounted sky lights, as well as surrounding dressing rooms, laundry, stores and ablutions for the actors.
For each area the HVAC systems were specially customised according to expected capacity, emphasising the interaction between audiences and sound attenuators, to comply with the theatre’s design noise criterion (NC) of NC-25, as demanded by the acoustic consultant.
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Fresh air ducting leads into the dressing rooms |
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HVAC Engineer Pedro Gans, explains the roof mounted cooling system |
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Supply air diffuser configuration in the main auditorium |
Design specifications:
The most essential specification Lindsay Lund, Managing Director of Ubunye Engineering Services, received when coming on board for the Soweto Theatre project, was the sound aspect, which had to be given special consideration. This is a specification unique to theatres and the brief required noise levels, particularly from equipment, not to exceed NC-25 at any given time. This meant the break-in noise from outside the theatre had to be taken into account, ensuring it did not influence the integrity of the theatres. With this in mind, a unique specification was established for HVAC equipment and sound attenuators to be selected for this project.
Based on the amount of people per theatre, the National Building Regulations (NBR) required a particular amount of fresh air to be supplied to the building. Normally the ratio of fresh air to total air supplied varies between 15 percent and 20 percent, with the return air comprising 80 to 85 percent of the total air. For the main auditorium however, the fresh air supply is 47 percent of the total air supplied, using a design criterion of 7,5 l/s/person. “The fresh air ratio is quite substantial, leading to over-pressurising of the treated space and a need for a special exhaust system design to ventilate the fly-tower over the stage. We had to take into account the given rate of air changes per hour in the fly-tower’s volume and take care not to create any air draughts or affect the stability of the hanging sceneries in any way,” Lund explaines. “Besides being an unacceptable nuisance during a stage performance, moving sceneries could pose a serious threat to the actors on stage.”
Another important instruction was to not affect or compromise the architectural aesthetic design of the hyperbolic and parabolic curved surfaces of the buildings. This meant HVAC equipment and ducting was not allowed to be visible in the theatre’s treated spaces. However, in other areas such as the two double-volume foyers of the auditorium, exposed ducting was allowed, and in fact used as a feature by the architect.
The HVAC design
Theatres
Air-conditioning systems were installed throughout the three theatres to ensure comfort of patrons and actors. This meant taking into consideration various factors, such as:
Solar heat gains,
Lighting loads, especially those from working bridges used during shows,
The latent and sensible heat released by a high-density population in a treated space, and
The heat losses of the treated spaces during the winter season.
Bearing in mind the structural restrictions as well as the noise limit, the above was achieved with specialised equipment, ducting silencers, insulation and adequate sizes of air terminals.
No chillers, chilled water circuits, circulating pumps or cooling towers were used in this project because, as Lund says, “There was simply nowhere to put them without destroying the aesthetics of the building”.
Ideally the relative humidity (RH) should have been 50 percent, but this was uncontrolled in this project. “We designed with a RH of 58 percent for the auditorium and 54/55 per cent for the smaller theatres to achieve an adequate feeling of comfort for the occupants,” Pedro Gans, HVAC Design Engineer Ubunye, explaines.
| Conditions |
Temperature |
| Summer inside |
22°C dry bulb |
| Winter inside |
21°C dry bulb |
| Summer outside |
31°C dry bulb |
|
20,6°C wet bulb |
| Winter outside |
2,2°C dry bulb |
The main factors influencing the heat load’s design were:
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The latitude of the treated space,
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The altitude above sea level,
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The geographical orientation of the building,
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The amount, size and type of windows to be used,
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Structural overhangs/external louvers, to reduce the inherent shade factor of the window panels selected,
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The size, amount and type of glass used for the roof mounted sky lights, and
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The type of insulation used on, or under roofs and walls (which needs adequate acoustic and adequate thermal properties).
After comparing several systems from various suppliers, air-cooled Dunham-Bush heat pump units were selected for the theatres’ cooling and heating requirements. All three theatres are served by a self-contained, reverse cycle, roof-top mounted air cooled package.
The standard unit design includes an air-conditioning supply fan (blower section) with a double-width double inlet centrifugal fan and forward curved blades. “These fans are quieter but their performance curve was not to our satisfaction,” Gans says. “Therefore, we requested the fans with backward curved blades. These performed better, consuming less electricity while also providing lower running costs. They were unfortunately noisier. But thanks to the adequate internal lining of the supply and return ducts, and correctly sized sound attenuators, this was not an issue.”
The roof units were mounted on three-inch static deflection steel springs to absorb noise created by low frequency vibrations. Originally the unit and corresponding springs were intended to rest on reinforced concrete plinths which were rather wide. However, the technical architect on the project, Tony de Oliveira, Chibwe Afritects SA, was concerned that the relatively long plinths could interrupt the free flow of rain water to the storm water pluvial design inlets. De Oliveira proposed using concrete stubs instead to support the air handling units.
“The architect’s proposal was feasible, but required the base of the roof-mounted air-conditioning units to be reinforced with special steel frames so springs could be installed in the corners of the units’ footprints,” Gans says. “The beauty of the Dunham-Bush air cooled package units is the manufacturer’s flexibility to provide tailor made changes to accommodate architectural designs and structural restrictions. Other factors which helped us favour these units were the quality and reliability of the equipment, the reasonable market related price and Dunham-Bush’s good service centre.” The air handling units use heat pumps when in heating mode. This means there is no need for using electrical heating elements in winter, reducing electrical power usage.
Correct ventilation in the fly-tower is achieved by using a combination of air-conditioned air to relieve over-pressurisation of the auditorium and an adequate supply of fresh air, 7,5m above the stage floor. This mixture is then extracted near the top of the fly-tower, about 18m above the stage floor.
Sound attenuators were selected to ensure maximum velocity does not exceed the 8m/s in the silencer’s airways, as well as not exceeding a total static pressure drop of 40Pa. To manage the airflow, bulkier silencers, which had to be hidden away, were installed. Where possible, the core velocity of the air through the air terminals is between 1,7m/s and 2,2m/s (never above 3m/s).
 Backstage
In the general backstage area, where the external peripheral dressing rooms, laundry, stores and ablutions are located, the architect provided natural ventilation. For the rest of the internal areas, mechanical ventilation was installed to supply the required fresh air (7,5 l/s/ person in air-conditioned spaces) to the dressing rooms. Mechanical extraction fans were installed in internal ablutions to provide a negative atmospheric ambient.
For the internal dressing rooms on the ground and first floors, the DAIKIN VRV III compact air-conditioning system (heat recovery type) was selected by Lund. This three-pipe system has branch controllers installed throughout to ensure the individual temperature control is available to individual occupants of the dressing rooms.
The main air-conditioning system is a Variable Refrigerant Flow (VRF) system with evaporators installed in dressing rooms and condensers located on Level three, at the plant rooms and roof levels of Theatres A and B. In principle, between 8 and 12 evaporators, depending on capacity, were connected to one large condensing unit. The condenser regulates itself to suit the air-conditioning demand from the occupants and controls the refrigerant levels and usage.
The VRV condenser has one inverter and two compressors, with the inverter dealing with the initial demand load. When the inverter capacity reaches a maximum level, it ‘dumps’ the load onto the first compressor, and is then ready to take on more loads.
Toilets
For the toilets, a mechanical extract ventilation system with LUFT fans and AMS sound attenuators were installed. It operates 24/7 to eliminate the possibility of bad odours permeating through the building. The air is extracted through wall-mounted extract grilles, which have volume control dampers of the opposed blade type working at a rate of 60 l/s for toilets and urinals, and 80 l/s for showers. Air is exhausted to the atmosphere through galvanised sheet metal ducts complete with mechanical fans and silencers.
The make-up air is drawn into toilet spaces through undercut doors from the surrounding spaces.
Meeting the sound criteria
To make sure the sound criteria was not exceeded, Gans had to calculate the sound along the airflows in the ducting, silencers and air terminals. He used the method of NC-# (where # represents a given decibel (DB) pressure spectrum for the frequencies from 63Hz to 4000Hz) to achieve this.
The main principle used was to subtract DB energy from the noise source to the air terminal. Once this was achieved, the DB power spectrum had to be converted to a DB pressure spectrum by taking into account factors such as:
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The distance between the air terminal and the listener,
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The number of air terminals treating the space,
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The position of the air terminals. For example, if the terminals have flush mounted on walls/bulkheads, or are they positioned inside the treated space as ceiling mounted air terminals, and
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The space volume and the sound characteristics of the treated space, be it soft, medium or hard room, which relates to the speed in a certain time frame with which the room can absorb the reverberations.
The type of ducted fan, whether it’s in-line centrifugal or axial, will be the noise source. In case of supply fans, the level of energy emitted at the discharge end of the fan, measured in DB power and servicing a spectrum of frequencies depends on:
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The total air flow handled,
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The total pressure that the fan has to overcome, (total static pressure plus dynamic pressure),
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The type of fan used, and
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The power of the electric fan motor selected.
The initial parameters are measurements made in laboratories and specified by the manufacturer of the relevant fan used.
Using conceptual calculation methods given by ASHRAE, the airflow travels along the duct run and the DB power spectrum reduces in function if it is a straight duct section or a duct fitting such as bends, distribution chambers, branched off sections or special selected silencers with adequate sound insertion where the silencer absorbs the spectrum of DB power. It is important to consider that each type of duct fitting used has a noise spectrum regeneration, measured in DB power. This will depend on the type of fitting used and the air flow velocity in the duct run.
Ducting
All air-conditioning ducts were internally insulated with 50mm sonic liners to maintain a reasonable temperature differential between incoming fresh air at ambient temperatures, and the air-conditioned space it was treating.
For external ventilation ducting, which is exposed to prevailing weather conditions, 50mm high-density fibre glass mats and a final layer of 50mm gypsum plaster was used. “We chose to insulate the externally exposed ducting, both fresh air and extract air systems, to reduce the potential of generating unacceptable noise levels in the ducting during a stage performance,” Gans says. Then external insulation also prevents heat gains.
To achieve NC-25 in the treated space, it was necessary to use low duct velocities of five to six metres per second.
Challenges
The ventilation of the fly-tower was a particularly challenging task as it needed a substantial amount of air to achieve the changes per hour as required by the National Building Regulations, SANS 10400. The slow ascending mass of air has to extract the heat created in the tower’s stratification zone and at the same time avoid causing any drafts that could destabilise the hanging sceneries and jeopardise the safety of the actors on stage. The heat being extracted is normally between 30kW and 70kW or even more, due to the incandescent lights irradiating an incandescent load of thermal energy.
Another challenge was customising the equipment to keep the noise levels at an adequate and comfortable level. “The last thing anyone wants when enjoying a performance is to have the noise from the air-conditioning interfering, especially during recordings, or to feel uncomfortable drafts in the theatre space during the performance,” Gans explaines. This meant he had to review the HVAC design to ensure these systems worked as desired, right from inception.
The constant interaction between the fans and the sound attenuators, together with proper internally lined supply and return ducting, and the low velocity air movement through ducts and air terminals, were very important to maintain the requested noise criteria level.
The biggest challenge however, was fulfilling the prerequisite of adequately hiding all HVAC equipment. For Lund and his team, achieving the interaction of the mechanical, structural and architectural design, without compromising the aesthetic criteria of the architect, was especially challenging, he admitted. “They wanted the air-conditioning ducting to be as invisible as possible,” Lund says.
The architectural design of the theatre made fulfilling this request even harder, because it was unlike any normal building with straight walls and service shafts which allow access to all sections of the building). “The unusual hyperbolic and parabolic shape of the exterior walls, whilst enhancing the unusual shape and unique appearance of the building, also made installing ducting and HVAC units quite a challenge, and almost impossible, at times,” Lund explained.
After lengthy discussions with the project’s technical architect, De Oliveira, , suitable design solutions were found and implemented. The equipment and bulky ducts were to be located on the roof. This meant the roof had to be altered to incorporate a curved precast concrete shell dome along the periphery of the outside walls of the three theatres. The ventilation fans, ducting, domestic and fire fighting water tanks, complete with pumps with supply reticulation piping, as well as the three big roof-top mounted self-contained air cooled DX units were fitted here.
Budget and schedule
The HVAC budget allocated for this project was originally R6,2 million, and although final numbers are still being counted, Lund can confirm their side of the project was completed comfortably within the budget.
The HVAC installation was done by the successful tenderer, Total Air Control, with the project director, Jamie Wearne and his site agent, Wikus De Jager. “They are to be commended for their dedication to the success of this project, and their flexibility to adapt readily to several design changes introduced throughout the project,” Lund says.
Despite the Soweto Theatre not meeting the original project schedule, Lund explained it was not due to any technical delays on the HVAC side at all. The HVAC component of the project was completed on schedule. Originally 10-12 months were allocated for the project but it was later extended to 14 months.
Lund is happy with the project’s development, “So far, all the HVAC systems Ubunye have installed in the Soweto Theatre are working well and the client seems satisfied with the work.”
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Frans never settles for second best
Thursday, 17 May 2012 10:38
glyniss
 For Frans van Aardt there is more to buildings than just bricks and cement
By: Ilana Koegelenberg - senior staff writer
From the motoring industry to managing consulting engineers, Van Aardt’s journey to the top has taken him around the world. Currently the director for the Pretoria branch of Charles Pein and Partners. (CP&P), there is still a lot to do, he says.
Career path
After school, Van Aardt studied mechanical engineering at Technikon Pretoria, completing his final year as an exchange student in Germany where he focussed on research and development particularly.
The 32-year-old started his career in the Netherlands, working for Tank Systems and mostly servicing Shell’s facilities and commissioning the design and implementation of emission control of bulk fuel storage around the world. In 2005 he returned to South Africa, where he continued to work for the company, establishing relationships with local petrochemical companies alike.
In 2006 Van Aardt swopped industries and took up a position at CP&P as a design engineer. He continued to grow and in 2010 acquired a third of the shareholding in CP&P as director of the Pretoria branch from the late Trevor Larkin, upholding the full range of services offered by the company.
Job satisfaction is very important to him: “I love my job. If you do what you enjoy, then you do it well.”
On the job
Van Aardt enjoys the design aspect of his job as well as the onsite visits. “I love seeing a concept evolve from being on paper to an actual building.” He sees buildings as living organisms, not just structures. “You have to read your building to see what the best options are.”
When it comes to work ethics, Van Aardt aims to deliver the best quality within his abilities. “I try to be ethical and honest in everything I do.”
He is motivated by his religion: “I have a responsibility to wake up in the morning and try and make a difference in the lives of everyone who crosses my path.”
Recent projects Van Aardt was involved with include the Clearwater Mall Phase II development and the Royal Bafokeng Sport Palace for the Soccer World Cup, to name a few.
Future plans
“I’ve come to a point where I want to be career wise and now it’s important to grow the business and build on our current achievements. There is great potential in the HVAC&R industry, especially with energy-efficient systems. I think efficiency in design will be emphasised in the future.”
Wise words
Van Aardt’s advice to young people entering the industry is simple: “Don’t settle for second best and don’t stagnate in your career. Set goals for yourself and once you’ve achieved them, set new ones. It takes commitment to get where you want to be.”
VRFs: Exploring your options
Thursday, 17 May 2012 09:11
glyniss
 Are VRF systems here to stay or is the technology being oversold?
By: Ilana Koegelenberg - senior staff writer
Some call it VRV (Variable Refrigerant Volume), others VRF (Variable Refrigerant Flow), but the issue isn’t what to call this air conditioning system, but rather whether it is as ideal as manufacturers claim it to be.
What is VRF?
VRF allows multiple air handling units (possibly up to 48) to be connected to a modular external condensing unit. The refrigerant flow to each air handling unit can be varied using either an inverter controlled variable speed compressor, or multiple compressors of varying capacity in response to changes in the cooling or heating requirements within the air conditioned spaces.
VRF systems using external compressor/condenser units require no internal plant room space and offer great flexibility through the many types of air handling units available. It is available in heat pump and in heat recovery mode.
Heat recovery
According to Shaun Scannell, Branch Manager of DAIKIN, heat recovery offers the perfect solution for stabilising the air temperature by providing all the features of a heat pump system – and the added flexibility of simultaneous cooling and heating from one refrigerant pipe network.
“The heat recovery function is achieved by diverting exhaust heat from indoor units in cooling mode to areas requiring heating, and uses a branch selector unit to switch the indoor units from cooling to heating mode,” Scannell says. The VRF system keeps running costs at an absolute minimum by controlling each zone individually and being able to shut down completely in unoccupied areas.
 Piping
Joseph Kaseke, After Sales Technical Manager Digital Air Solutions Samsung, explains that VRF is made from copper piping and uses R-410A refrigerant, making it more environmentally friendly. “The piping is generally smaller than that of water piping, but you need more pipes. The system is very flexible and so are the piping options. It can be customised to suit your needs.” This could make it a good option when taking on refurbishment projects.
Many manufacturers have even developed computer programs to help make the piping design easier and more efficient. These programs tell you exactly how much piping is needed as well as the amount of refrigerant required.
Digital scroll versus inverter technology
VRF systems can be divided into two categories: those working with digital scroll compressors and those using inverter technology. Manufacturers such as Samsung use digital scroll compressors in their VRFs, while Mitsubishi and DAIKIN use inverter technology.
Digital scroll compressor
The compressor capacity is changed by varying the relative amount of time in loaded and unloaded states, which are changed by opening or closing the pulse width modulating (PWM) valve. Capacity is determined by the sum of the time averaged in loaded and unloaded states, and its range is continuous from 10 percent to 100 percent. Regardless of capacity, the compressor always rotates at constant speed.
Inverter technology
Inverter technology controls compressor and fan motors to adjust in speed according to demands put on the system during differing loads. Once the desired temperature is reached, loading falls to zero and the system switches off. As the temperature increases the system will need to re-start at which time it will draw a large amount of current. Each time it starts, it draws amperages of around six to eight times higher than normal running current, forcing the electrical demand curve to move sharply up and down during varying levels of operation.
Owner and managing director of AConsult, Trevor Johnstone stresses the importance of taking application into consideration when choosing between technologies: “Despite inverter technology technically being more efficient, I find the digital scroll systems simpler and more robust. They work better, for example, when installing in a remote building in Angola, where you don’t want complicated maintenance.”
A history in brief
VRFs were first introduced in Japan during the mid-1970s oil crisis. Being a country without a surplus of oil to begin with, they needed a more energy efficient air conditioning option. They also required a more compact system, as space was becoming a big issue. The rest really is history:
1987: The original VRF air conditioning system was introduced into Europe by DAIKIN in a standard-format single outdoor unit which could operate up to six indoor units connected to it.
1991: The heat recovery system was introduced, offering simultaneous cooling and heating from different indoor units on the same refrigeration circuit.
1994: The leap to inverter technology was made, enabling the operation of up to 16 indoor units from just one outdoor unit.
2003: The world’s first R-410A operated VRF system was introduced and up to 40 indoor units in heat recovery, as well as heat pump format, could be connected to a single refrigerant circuit.
2005: Water cooled VRFs hit the market, and were available in both heat pump and heat recovery versions.
2009: A geothermal version became available, using geothermal heat as a renewable energy source.
Advantages
The advantages of a VRF system are numerous and impressive, from the engineer through to the end user – manufacturers are quick to point out how there is something to appeal to everyone.
Engineer and architect: Freedom of design and technological flexibility are every architect’s dream and every engineer’s goal. VRF systems give you the opportunity to make the most of any space or structure as well as innovative solutions to address any design challenge. Advantages include the software-based design tools which make designing easy; innovative piping networks provide more flexibility for more customisable design options; the system is easily integrated into Building Management Systems (BMS); and floor-by-floor installation is possible.
Contractor: From studying the blueprints to when installation is complete, the process is generally quick, smooth and efficient. Compact and lightweight units, along with flexible piping and wiring design, simplify the entire process so faster turnaround time per project is achieved. With improved time and labour efficiency comes increased productivity and greater profitability.
Building owner: Superior zoning and spacing capabilities, energy efficiency, unmatched reliability and fast installation are just some of the advantages. With advanced zoning technology there is complete control over the entire building – floor by floor, zone by zone – providing you with two more highly important benefits: enhanced energy efficiency and lower operating costs.
End user: Imagine a system that allows you to create the perfect environment with the ideal temperature while quietly using responsive and intelligent technology. VRF provides a controlled, personalised comfort zone.
 Possible challenges
There are however, some disadvantages to the VRF system which manufacturers might not make known. Mechanical Engineer at MADD Consulting Engineers CC, Mervyn Aereboe, who has been in the industry for over 40 years and has worked with VRFs for 15 of them explained: “The system is unforgiving and if you get it wrong, there is no way you can fix it completely.”
Refrigerant leaks: The biggest concern when installing a VRF system is the possibility of refrigerant leaks. Long refrigerant runs and large numbers of connections could result in significant refrigerant leakage which could cause safety issues and repair difficulties. Though the refrigerant used by this system is safe, if it leaks and the limit density is exceeded, there is a risk of injury due to a lack of oxygen. National Sales Manager of Airco, Andrew Ross, explains that in situations where there is anything more than a 10 percent refrigerant leak, all the gas has to be dumped and recharged completely; it’s an expensive exercise. “You can’t just indefinitely keep topping up R410-A because the concentrated blend of gas alters as it leaks.”
Luckily this can be avoided with proper installation. According to Robert Larkan, Senior Sales Engineer of Samsung’s Digital Air Solutions, “refrigerant leaks usually occur due to bad installation, not because of faulty products”. Fortunately, most systems have leak detection built into the equipment to help manage this risk.
Extra equipment: The need for a separate ventilation system to satisfy code requirements for delivery of outside air, which offsets some of the retrofit advantages of the VRF system, could be a disadvantage. Each indoor VRF unit should also be supplied with a condensate drain with access to a water collection system.
Cost: President of SAIRAC and principal mechanical associate for WSP, Mike Veldon, explains that cost is one of the reasons VRFs took so long to become popular locally. “They’re usually about R400/m2 more expensive than your average split unit system.” Installation costs are highly dependent on the application, construction and layout of the building, and also on whether the installation is new or retrofit. Lack of familiarity with the technology adds to VRF costs.
According to André Burger, Engineering Manager at Climatron Projects, one must consider the following criteria to determine the ideal HVAC system for a building: temperature, humidity, and space pressure requirements; capacity requirements; redundancy; spatial requirements; first cost; operating cost; maintenance cost; reliability; flexibility and life cycle analysis. “In close collaboration with the client and engineer, a suitable system must be selected to fulfil the requirements of both the technical and owner’s needs,” he explained. “Because these factors are interrelated, the owner and design engineer must consider how these criteria affect each other. The relative importance of factors, such as these, differs with different owners and often changes from one project to another for the same owner.”
Flexibility: Another big disadvantage is the lack of flexibility once the system is installed. Once in, it becomes problematic to alter a VRF. Burger: “If the layout configuration changes in a building fitted with VRF systems, it is difficult and sometimes expensive to change or adapt the VRF system to suit a new layout.”
Malfunctioning: Another possible setback may arise due to South Africa’s many power outages. This can cause the CPU to lose memory which means it has to be reprogrammed. Also, VRF is a central system and if the central condenser fails, the entire system connected to it is affected.
Rated capacity: As with all air conditioning equipment, there is a basis for the equipment rating and the unit capacity to be rerated for the site conditions. When this is done, the unit’s performance may be less than the standard rating. “If anyone wonders why 200W/m2 works for split and VRF systems – as a rule of thumb – look at the de-rating on the equipment when selected properly and this will explain why you need to double what you get in your heat load calculation for the nominal unit capacity,” Aereboe said.
Delivery time: Delivery time may be a problem. Supplies can take up to 12 weeks with no stock kept locally. Aereboe stresses that “you could be forced to compromise the system because the client wants to occupy the building before you can acquire units. This is a problem I find repeating itself on a lot of the projects I am involved with.”
Life expectancy: Generally VRFs’ life expectancy is lower than that of chilled water systems. Burger explained that the life expectancy of VRFs is usually about 15-20 years, while chillers can survive 20-25 years.
Multi-Zone Hybrid hits the market
After noticing the interest being shown in VRFs, Viking Air Conditioning (a local manufacturer of packaged air conditioning equipment) decided to get involved. They considered the combination of an imported VRF condensing unit with a Viking air-handling unit and found it practically and commercially viable and so Viking proceeded to manufacture their first units.
“There are great opportunities in this hybrid concept and in future Viking is planning to integrate the air-handling and condensing unit components on one common base, so that the new Viking Hybrid Packaged Unit can be offered as a pre-piped, pre-wired and pre-commissioned package, ready for installation,” John Bennett of Viking Air- Conditioning explains.
As a refinement for the above ‘hybrid’ concept, it is possible to add individual room indoor units to the common system, to cater for smaller individual areas that may be differently zoned or require separate temperature control. The condensing units used on these hybrid systems would typically contain variable capacity scroll/rotary compressors, eco-friendly refrigerant and reverse-cycle heating.
Hitting the SA market
The first VRF system installed locally was in the The Star building, around 20 years ago, by DAIKIN. But since then, the product has been slow to take off, with other manufacturers only getting on board in the last five to ten years.
Traditional barriers to new technology have hampered market acceptance of VRF systems. These barriers include natural resistance to change and unwillingness of users to be subjected to the uncertainty of using a new, unproven technology. “South Africa is a very traditional country. The new technology went through an initial negative, apprehensive stage,” Marco Ferdinandi, Marketing Director of Mitsubishi Electric Air Conditioning SA, says. “It was a confidence issue really.”
Other barriers common to this and most new technologies include performance uncertainties, lack of knowledge of design, operation, servicing and maintenance, and ownership costs. Ross believes cost has had a big impact on VRF’s popularity in the past. “Split units were cheap and they got the job done. South Africa has always been slow to shift onto new technology and the tremendous skills gap in the industry made people hesitant to consider something unfamiliar.”
Kaseke considers the lack of energy consciousness in the past as another reason for the technology’s slow entrance into the local market. “Now that green star ratings are becoming more sought after, VRFs are becoming huge.” Veldon shares this belief: “Eskom only recently, in the past five years, started fining excessive electricity use, making everyone more energy conscious; never mind the cost of electricity sky-rocketing. Before this, VRFs were simply too expensive to even consider.”
However, the future of VRF seems bright. “There is definitely great potential with this product on the South African market,” said Scannell.
Training matters
When it comes to installation, Burger emphasises that VRF systems are not suited to be installed by standard refrigeration technicians without training. “Consideration to correct welding techniques, pipe routes and lengths must all be kept in mind when installing these systems.” To address the problem of technicians not having the right qualifications for installation, many manufacturers have opened training centres specifically dedicated to VRF training. Most manufacturers refuse to let anyone install their equipment until they’ve undergone training. This is mainly because VRF systems are a bit more complicated to install and if not done correctly, numerous problems could surface. Luckily in South Africa, manufacturers are giving their full support with training.
“Training plays an integral role for the future of VRF. If we want the product to be user-friendly, we need to give training. At Samsung, we are very strict with who gets to install our products and we’d like to keep error to a minimum,” Kaseke explained.
DAIKIN also offers a full set of training courses, all the way from basic installation to maintenance, to ensure the product is installed correctly. They also do site inspections and commissioning. Mitsubishi’s training centre trains between 200 and 300 people a year. “The VRF systems offered by different suppliers differ in complexity and installation procedures required,” says Burger. “It is therefore necessary and important that technicians be well versed in each specific system’s installation requirements. If these requirements are not met, warranties and performance will be affected.”
Maintenance
Without regular maintenance an air conditioning system will not function effectively; its efficiency will be significantly reduced, and this in turn could lead to the need for costly repairs. Maintenance of a VRF system is pretty basic provided you don’t have any refrigerant leaks. Routine maintenance would consist of cleaning the outdoor coils and replacing the indoor filters and requires skilled maintenance technicians.
Successful projects
When it comes to installing VRF systems, one must keep in mind the first priority should always be to meet the client’s needs and therefore it’s important to understand the brief. “VRF is a very good system, but each application has its solution and you have to decide what your needs are,” Paul Dergeloo, deputy managing director/sales and service director of DAIKIN, says.
Examples of successful VRF projects include: the Formula 1 hotel in Pretoria (installed system: Samsung); the Soweto Theatre (DAIKIN); and the 27-storey high Green Park Building in Sandton (Nashua/Reutech). A Mitsubishi VRF system has been installed in the Central Government offices, a 25 000m2 project.
Oversold or undersold?
When it comes to VRF, opinions vary. From contractors, to consulting engineers and manufacturers, everyone has their own idea of how competitive this system is. Most manufacturers are completely in favour of the system, but not everyone is convinced.
Ross believes VRF technology is being exaggerated. “VRF has a place if it’s installed correctly and no renovations are planned, then it’s a good idea. But I think it’s being oversold. VRF is a niche market and it shouldn’t be used for everything.”
Ian Pretorius, Technical Manager of Solar Services, agreed: “These systems only really save energy when in heat recovery mode and when using inverter technology. But now certain chillers have these features too.”
Botha is convinced chillers will be making a comeback soon. “The industry went through a phase where everyone installed VRFs almost by default when designing a new building, but that should change again soon,” he says.
Johnstone: “Yes, I think the system is oversold, but so are all air conditioning systems. Sales people get paid to only tell you the positive aspects. It is important to know the technology and to apply the right solution for the project, and not just rely on the supplier. Engineers must take the responsibility to know their design and what they’re doing. Don’t rely only on the manufacturer’s software to tell you what to do.”
“I have no strong feelings for, or against the system, and when I do use it, it’s because I see it as the best compromise for the particular building, weighing up all the various systems’ advantages and disadvantages,” says Aereboe. “There is always development in our industry. VRV/VRF is only one development.”
“VRF systems offer substantial benefits in particular developments over some of the more traditional systems. It would however be wrong to make a statement that a VRF system is always the answer,” says Burger. “We always explain to our clients that we try to offer the best solution for the application.”
“VRFs are definitely not the one and only – it all depends on your project,” consulting engineer, Tom Esterhuizen of Tom Esterhuizen and Associates, emphasises.
VRF versus Inverter DX
In September 2011, C3 Climate Control Consulting Engineers (Pty) Ltd (C3CCCE) did an independent report, comparing the costs of different HVAC systems for its Reunert Offices project. The report details the life cycle costing of Inverter DX air conditioning units compared to VRF air conditioning units. The total area to be served was 1489m2 over two floors.
The report found the following:
The cost for an inverter DX split system was R895 781,92 which equates to around R602/m2*.
The cost for the VRF system was R1 174 399, which equates to around R789/m2*.
The overall energy efficiency of the VRF system was 13 percent better than the efficiency of the inverter split units and will result in a payback period of approximately 4½ years.
The life cycle analysis costing of the air conditioning system includes the electrical consumption cost, as well as escalation of the electrical tariff and the maintenance cost of the system.
The initial capital input for the VRF system is the most expensive, however it presents a good payback period in terms of the operating costs of the VRF system compared to the operating costs of the Inverter DX split system.
C3CCCE’s conclusion: “We would recommend the VRF system be installed as the system is not only the most energy efficient but also the most cost economical over a period of five years.”
*This excludes 14% VAT; escalation; associated builder’s work and mark-up; associated electrical costs and any additional ventilation not specified above.
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