Mechanical Technology February 2015

⎪ Heating, cooling, ventilation and air conditioning ⎪

have also been installed to minimise the energy consumption associated with drawing in fresh outside air while exhausting stale air. “We look at using energy wheels on all of the projects we do,” De Bod reveals. “We have now installed 55 heat re- covery wheels and we have developed considerable experience in their advantages and cost effectiveness,” he says. These wheels, also known as rotary heat exchangers or rotary air-to-air enthalpy wheels, are slowly rotating heat exchangers that transfer heat from the exhaust air to the cool incoming air during cold days and transfer cooling from the exhaust air to the warm incoming air during hot days. The cool exhaust air is channelled through an aluminium honeycomb structure, chilling that half of the wheel. As the wheel rotates, the chilled half of the wheel enters the air stream of the warmer incoming air, which is chilled by the wheel before passing into the air conditioning system. “Typical savings of 5.0 W e /m 2 or more of air conditioned space can be achieved during very warm or cold days,” says De Bod − substantial when conditioning 22 000 m 2 of space. Why are these wheels not more widely used? “Engineers tend to be conservative and new technology such as this requires a relatively complex pay-back calculation. The savings analysis depends on temperature variations for every hour of every day in a year, so some work is required to do a proper cost analysis,” he suggests, adding that the payback period for their use is generally not more than three or four years. “We have also pioneered the use of the more advanced Kyoto energy recovery wheels in data centres in South Africa and have completed the first phase of a special data centre project that is entirely cooled through two Kyoto wheels. A key issue with data centres is keeping dust out. A closed environment has to be created. Energy wheels enable the cooling and the air to be transferred back into the data centre without allowing dust to penetrate through the wheel. The end result is a very high efficiency system with a COP-equivalent approximately 30% higher than standard raised floor data centre cooling system designs,” he says. The facility was rated and certified as a Tier 3 building by the US-based Uptime Institute and “could set the trend for data centres of the future,” De Bod believes. Citing another interesting project, he describes a laboratory system developed for Kansai Plascon to ventilate 18 chemical benches. “This is one of the very few displacement-ventilated laboratories in the country. Instead of blowing air into the space or sucking it out, we introduce very low velocity air into the space from the bottom of each bench. This air then gently rises and fills the space, displacing hot, stale and contaminated air at the top. The system works exceptionally well, at high ef- ficiency and, because the fresh cool or warm air is introduced at the feet of the laboratory workers, the system maximises comfort levels,” he says. “As a result of its experience with displacement cooling systems, WSP has won contracts for more similar laboratories. We have also successfully pioneered the displacement ventilation system for almost all of the smoking casinos in South Africa.” “We offer a highly professional service specifying premium HVAC products, because we believe that only premium products offer the required energy efficiency, reliability and service sup- port should things go wrong. Since such a high percentage of the total ownership costs are made up of electricity and other operating costs, the pay back periods on premium equipment is usually very short,” he advises.

“Developers are understanding these principles more and more, as are tenants. Developers can now charge higher rent for an energy efficient building and many international organisations, which are under pressure from interna- tional parent companies to comply with ‘green’ principles, are willing to pay these higher rents if the building matches their environmental expectations. “We try to practice what we preach as a core business philosophy,” De Bod assures. “We offer a practical approach, reliability and professionalism and are innovative and energy conscious about every decision we take,” he concludes. q The laboratory HVAC system developed for Kansai Plascon is one of the very few displacement-ventilated laboratories in the country. Instead of blowing air into the space or sucking it out, very low velocity air is introduced into the space from the bottom of each bench.

Mechanical Technology — February 2015

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