MechChem Africa talks to Booyco Engineering’s MD Brenton Spies, along with Grant Miller, executive director, about purpose-engineered HVAC systems that are designed to best suit the harsh operating conditions experienced in the military, rail and mining sectors, where extreme temperatures, vibration and dust make commonly used units functionally inadequate, unreliable and prone to very early failures.
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“There is a misconception that our mobile HVAC solutions are over-engineered, making them more expensive than they need to be, particularly in comparison to the mass-produced systems designed for use in typical heavy goods vehicles (HGVs). But these vehicles seldom run off motorways and they are typically designed for cooler climates,” begins Grant Miller, executive director of Booyco Engineering.
“Our systems are not designed or manufactured for road transport vehicles,” adds Booyco Engineering’s MD, Brenton Spies. “Those systems can be rapidly assembled in high volumes in factories anywhere in the world, for use by any vehicle OEM looking to minimise the selling cost of their HGVs,” he says.
“At Booyco, we have developed a range of purpose-designed HVAC units for the harsher conditions typically found in African mining markets. The first and most important differentiator is that our systems are rated for use at ambient temperatures of 45 °C to 50 °C, while the road transport units tend to be designed for cooler climates, where 35 °C is seen as the accepted maximum operating temperature.
“This makes a huge different to the cooling performance required from the HVAC system. Our systems are designed to cool the cabin down to 25 °C in a 45° to 50°C ambient. To do this in an ambient temperature that is 10 to 15 °C higher, means that the cabin temperature change required from our systems can be as high as 25°C, while the mass-produced units are generally only designed to reduce the temperature by 10°C. In terms of the heat that needs to be rejected, this difference is huge,” explains Miller.
In order to eject this additional heat, larger components are needed, such as larger condenser coils and more powerful fans. “While our systems may seem oversized, they will work in the hot ambient temperatures and off-road environments they are designed for, while cheaper road-based systems will struggle,” he adds.
Cooling capacity is specified in terms of kilowatts (kW) of cooling, which often leads to confusion when people compare our systems to conventional HVAC units. If we specify 3.5 kW of cooling capacity for a unit cooling a cabin in a 45 °C ambient down to a 25 °C internal temperature, it is significantly different from a unit delivering 3,5 kW of cooling in a 35 °C ambient to the same 25 °C internal temperature.
Getting a little more technical, systems are generally designed for condensing temperatures of 60 °C. Therefore a system that is designed for a 35 °C ambient, has a 25 °C temperature difference to enable heat to be rejected from the cabin and into the surrounding environment. This means a much smaller condenser or outside coil can be used.
But if operating in a 50 °C ambient temperature with the same condensing temperature of 60 °C, the temperature difference is only 10 °C, hence a much smaller available temperature difference and therefore a much larger condenser coil is required to reject the heat into the hotter surroundings,” he explains, adding that, when it comes to rejecting heat using HVAC systems, it is the differential that matters most: the smaller that differential, the larger the coils, fans and compressors needed to achieve the cooling capacity required. “If you use a system designed for a
35 °C ambient in 45 to 50 °C ambient temperatures, one of two things can happen. Either the whole system will trip because the temperatures are outside the system’s operating envelope, or the unit will find a balance point at a much lower net cooling capacity. To put this into numbers and compare apples with apples, if we take a system rated to provide 3.5 kW of cooling in a 35 °C ambient with a cabin temperature of 25 °C, and operate it in the design conditions we use, the system will only provide 2.8 kW of cooling, which will result in a cabin temperature of
30 to 32 °C,” notes Miller. “The converse is also true of our system, if our Booyco system is used at
35 °C ambient, it will provide 4.3 kW of cooling and be able to cool the cabin down to around 18°C”
“In principle, our systems include larger and more expensive HVAC sub-systems because these are necessary to do the job. They are not over-engineered, they are purpose engineered,” continues Spies.
“In addition, our systems are more robustly built to cater for the off-road nature of the equipment we are cooling: dump trucks, drill rigs, dozers and excavators, for example. All these machines often have to cope with excessive vibration levels. From experience, we know that only welded structures can cope with these harsh conditions, and we use thicker gauge
(2.0 mm) steel plate. Tar road-systems rely on a less-expensive pop-rivetted structure and much thinner sheet sections, which, under vibration, get destroyed in very little time,” he adds.
Dust is another issue. It is everywhere and, for health and safety reasons, Booyco often includes scavenger fans and HEPA filters to maintain the air quality inside the cabins. The scavenger fan creates cyclonic air flow that allows the coarse dust to be gathered from the outer area of the fan, while the cleaner air flows though the centre. The remaining fine dust is then collected in a HEPA cartridge filter capable of removing over 99.95% of sub-micrometre particles. “These are add-ons however, so when there is no need to include them, we don’t. We design into the application and we only size and include components based on what is needed,” says Spies.
In addition, the cooling fin spacing needs to be larger to limit dust build up, which will quickly impair the cooling capacity of inadequately designed systems, again causing less heat to be rejected, lowering the effective cooling capacity.
“Another issue is that the draw down time is exponentially longer for systems designed for 35 °C. Even with our systems, it might take 10 to 20 minutes to reduce the inside temperature of a closed cabin, which can be 20° above ambient, to a comfortable level for the operator. With smaller systems, getting down to comfortable temperatures will take much longer, and the engine must be on for that period, so the operating costs are higher.
“Anyone who has to report on HSE standards needs to take particular note of this. Having a comfortable cabin temperature is a legal requirement, not just a nice thing to do for employees,” says Spies.
“Simply put, it is not sensible to pay money for a lower cost system that will not work in the conditions. And if someone claims that a lower cost system is the same as ours, be cautious! If it costs much less it is not likely to work – and it certainly won’t work for long.” warns Miller.
“There is a difference. Beware of being duped,” he concludes.