Mechanical Technology February 2015

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Heating, cooling, ventilation and air conditioning

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Mechanical Technology — February 2015

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

or more

of air conditioned space can be achieved during very warm

or cold days,” says De Bod − substantial when conditioning

22 000 m

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.

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.