As sensitive topics go, this perhaps is one of the most prominent, and represents a nightmare scenario for consultants, contractors, suppliers and tenants. Indeed, the issue of tackling mould, owing to moisture build-up in villas, has the potential to bring the very best of professionals to their knees.

In my 15 years of experience living in Dubai, I have come across several complaints, especially from occupants of villas. I have seen the crease-lines forming on their forehead over moisture on walls, causing gradual degradation of paint and clear signs of colour change owing to mould.

One of the reasons for moisture build-up is air conditioning equipment, specifically ducted-split units with constant speed compressors. Generally, villas don’t use 100% treated FAHU, as it is not economically feasible, owing to the low quantity of fresh air – in the range of 300-400 CFM for a typical four-bedroom villa. The untreated fresh air is directly connected to the mixing box, and the mixture of return and fresh air is passed over the evaporator coil.

Once the set temperature is achieved, the compressor trips, stopping the flow of refrigerant in the evaporator coil. But the indoor fan is still running, drawing the untreated hot and moist air. The compressor doesn’t come back again, till a gradient of one degree C is achieved or till the time-delay relay is triggered, whichever is longer (usually 10-15 minutes). It is during this time that moisture enters the occupied zone.

The problem is more prominent during some months of the year, when the ambient temperature is 34 degrees C Dry Bulb Temperature/32O degrees C Wet Bulb Temperature.

Vexed professionals tried to work out a makeshift solution – that of switching the indoor fan off during the compressor trip cycle, but tenants started complaining, as there was no air flow draught. An additional disadvantage of the makeshift approach is that the frequent start/stop of the compressor consumes more energy and puts an extra burden on the compressor.

The problem is greatly reduced nowadays in ducted splits through deploying an inverter compressor. Once the set temperature is achieved, the inverter compressor modulates its frequency (speed) to lower levels and stabilises, unlike the tripping-off that happens in constant speed compressors. This means a constant flow of the refrigerant is maintained in the evaporator coil, allowing the mixture of return air and hot, moist fresh air to dehumidify completely. Additionally, the soft-start feature of the inverter compressor and the reduced frequency of the start/stop of the compressor ensure that the running current is maintained at a low level.

It is heartening to note that more and more manufacturers are coming forward with inverter compressor technology in conventional ducted-splits, something that was only available in VRF systems, earlier. I hope consultants make a note of this point and look at the inverter-based system for the benefit of their clients. One of the common questions I get in relation to inverter-based systems is, “Are they expensive?” And I counter that with, “But, compared to what?” If more consultants start specifying inverter-based systems, it would lead to healthy competition, which will drive the prices lower – simple market dynamics at work, folks! There is a precedent to this, in the form of VRF systems, where the price per tonne of refrigeration has come down from AED 4,500 to AED 3,200, and even lower. Touché!