How FSL solved the wax moulding air temperature issues

Always difficult joining a discussion about someone’s issue with cooling and heating.

There will be some history, an injured party perhaps, maybe involving a product and a temperature specification and perhaps a victim. In this case workforce (40 persons) requiring a comfortable working environment and also a raw material with an inability to co-operate when overheated beyond a specified temperature control limit.

The process in this case was the manufacture of wax compressor blades for jet engine investment casting requiring the tightest of manufacturing tolerances. During the summer both the workforce and the wax product overheated; creating problems for staff and management.

We received a call from the air conditioning equipment manufacturer via the contractor involved with the project. The air-handling unit had been upgraded to correct the problem; two more cooling coils with accompanying condensing units were added to the ductwork but still the air was too warm for both people and wax moulding engine blades alike.

On visiting site all seemed in place, air-handling unit, ductwork, air distribution system. The building was tall, ten meters, with some solar heat gain from the structure, heat from a number of sources. A number of points came to our attention, we noticed the air returning from the factory was collected at low level, practically at floor level and the duct was not insulated and thus deceived the air handling unit of the true return air temperature. In fact, the air in the eight-meter vertical duct was heated by two degrees. We measured the heat generated in the factory; the figure was 65kW.

We obtained the air-conditioning unit rating from our colleague, it was 80kW. Neither of the additional coils were included in our sum. (Both were out of action)

So why was the system unable to deal with the heat in summer when during colder months it performed so well and easily managed the cold? In this case we looked no further than the ductwork itself. The ductwork was fitted with nozzles at intervals along the length, they pointed downwards, perhaps at eight or nine metres from floor level. The nozzles merely collected the heat stuck at the roof, (remember no extraction here – it’s down at the floor!) and drove it back down to low level over the workforce – the result, despite mixing with the air from the A/C unit outside was the overheating, the complaints and a sticky wax.

The simple remedy was to replace the high-level nozzles with an arrangement of fabric ductwork about half a meter in diameter to gently diffuse the air, draft-free above the workforce and production. We fitted the socks about five meters above the floor to allow the cooler air to mix with the room air; our friendly contractor completed this and in one stroke restored the equilibrium; work force happy as well as the wax – although noncommittal on this point.

The inductive effect of the nozzles in the factory was obvious. A nozzle designed to drive air downwards will transfer a greater or lesser proportion of that air with the main jet; the two airstreams will inevitably mix together. This is the process of air ‘induction,’ the mixing of nozzle air with the local surrounding air. The reservoir of hot air at roof level may not have been foreseen, but the effect on the room temperature was certainly significant.