AIR MOVEMENT
Technological leaps of AHUs
The next generation of air handling units is pushing the boundaries in terms of low leakage and thermal transmission which is, in turn, having a positive impact on energy consumption and ultimately whole-life cost- savings, says Andrew Latus, regional sales manager at Klima-Therm.
O
n the face of it, there is not much room for improvement in air handling units (AHUs). An AHU is, after all, essentially just a fan in a box – what more can be done to improve this simple technology? In fact, the answer is quite a lot – AHU construction has evolved to a whole new level with the latest robotic manufacturing techniques helping to produce an innovative new product that can be constructed from a single piece 50mm thick insulated sandwich panel. ■ Both inner and outer surfaces are constructed from galvanised sheet steel and coated with polyurethane, but other materials, such as stainless steel, are available.
■ The insulation is made from self- extinguishing, injected polyurethane insulation of minimum 47 kg/m3
■ A male to female coupling system between sections, along the entire perimeter, ensures an airtight seal between sections.
Furthermore, fan technology is evolving to the installation of electronically commutated motor (ECM) variable speed fans, incorporating a motor with built-in inverter and rectifier to DC voltage. Built-in controls also enhance energy performance and improve site leakage levels.
Since the latest construction removes a significant opportunity for air leakage, it is possible to achieve an exceptionally low air leakage level on site, with a leakage level of 0.15 l/sec/m2 of surface area for 400 Pa negative pressure test, and 0.22 l/sec/ m2
density.
■ Grooves are cut into the 50mm thick sandwich panel at the appropriate distance and the plate folded over to form a ‘C’ shape. Small corner brackets are added to improve stability during the manufacturing process, and to provide a fixing to bolt the AHU sections together.
■ The ‘C’ shaped profile is finished with a frame of the latest generation PVC-RAU plastic material, specifically designed for external use with excellent UV and atmospheric pollutant resistance.
■ Inspection doors and closing panels are fixed to complete the enclosure. They consist of the same sandwich panel material with step profile to incorporate a double insulating gasket with high compression resistance, and locked tight with the latest high-quality GRP rotary clasps to ensure air tightness.
24 July 2019
the need for a belt drive and the energy losses from this type of drive. The space taken up by the ECM fan is also less than a centrifugal fan, particularly with larger air volumes, ensuring AHU lengths are kept to a minimum when multiple fans are employed.
Built-in controls allow for optimisation in the operation of the components in the AHU and, since all penetrations into the AHU are made in the factory and sealed, the exceptionally low air leakage levels are maintained, whereas controls system installed on site are not necessarily optimised for the components installed, with cable and monitoring component penetrations installed in a less controlled manor, leading to increased leakage rates.
for 700 Pa positive pressure test – the requirements for L1 air leakage test to BS EN 1886 – achieved in a site test.
For thermal properties, the polyurethane insulation significantly enhances the thermal transmittance properties, achieving a T2 classification to BS EN 1886 using the 50mm panel thickness, and T1 with greater panel thickness.
The thermal bridging factor is also radically reduced due to the innovative construction and materials used, improving the thermal bridging factor to TB1 to BS EN 1886.
The use of ECM fans leads to reduced energy consumption since the inverter is built into the motor – leading to reduced line losses – and the motor technology uses a rectifier to provide DC voltage to the windings, providing more fine control of the performance and energy savings.
Like a conventional plug fan, the ECM fan is directly coupled to the motor and this removes
The enhanced thermal bridging and thermal transmittance factors reduce the condensation levels and energy consumption at medium to peak operating ambient conditions as, for example, a warm sunny day will have less effect on the internal environment of the AHU than a conventional AHU construction where the heat gain will affect the cooling load required from the internal components due to heat gain through the AHU skin.
The dramatically reduced air leakage ensures the fans and coils are not having to process a significantly greater quantity of air, reducing fan, boiler and chiller energy consumption by more than 10%.
Typical standard construction has leakage levels in excess of 1.32 l/sec/m2 negative pressure and 1.9 l/sec/m2 positive pressure.
at 400 Pa at 700 Pa
Maintenance is an important consideration when it comes to AHUs. It tends to be out of sight and out of mind.
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