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Help, mould attack!

Not to worry – decidedly, dual rotary inverter compressors can help eliminate moisture, mould and other fungi

| | Jul 19, 2017 | 11:06 am
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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!



Dharmesh Sawant is Sr Sales Manager – AC B2B at LG Electronics. He can be contacted at dharmesh.sawant@lge.com


CPI Industry accepts no liability for the views or opinions expressed in this column, or for the consequences of any actions taken on the basis of the information provided here.

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One comment on “Help, mould attack!”

  1. Hello Dharmesh,
    Thanks for the summary on inverter compressors. I would also like to add to your succinct comments. More than keeping the evaporator coil loaded with cold refrigerant to wring out the incoming moisture laden outside air, inverter driven systems also maintain indoor thermostat temperatures much closer to their occupant settings thus avoiding the repetitive equipment on / off cycle with its parallel indoor temperature overshoot / undershoot of the thermostat temperature.
    Inverter systems run longer and slower providing more consistent indoor temperatures as well as lower indoor humidity levels to help mitigate mold growth.
    Additionally as an extra bonus they are much less expensive to operate if they are correctly installed and charged with refrigerant.

    Finally, if you combine an inverter system with a humidistat, building owners can actually maintain a higher indoor air temperature because by lowering the indoor humidity level it feels much cooler than it actually is. However, the system must also have a variable speed indoor fan motor to fully take advantage of using a humidistat.

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