What is Dew Point and how does it affect my Home Air Conditioner?

Simply, it is a measurement of the amount of water in the air. What it’s actually telling us, though, is at what temperature the moisture will begin to fall out of the air in the form of condensation.

Think of air as a sponge, which can hold a maximum amount of an exact amount of water. If you squeeze the sponge, it cannot hold as much, and the excess water will fall out. At a given temperature, air can hold an exact amount of water before it is completely saturated.

If we begin to cool the air, it is like squeezing the sponge. If we squeeze it hard enough, we make the sponge smaller and eventually, water falls out.

So, on post tropical storms and high dew point / humid days we find ourselves with issues on where to set the AC Cooling point to.

Dew Point and setting my AC

Let’s first understand what outdoor dew point tells us. The higher this number is, the more moisture is in the air. Humid climates like the Southern Queensland. have extended periods of high dew point over 20.°C and It’s not uncommon for coastal regions to experience periods of extremely high dew points of 24°C!

Knowing what your outdoor dew point is can help you understand why condensation forms inside a duct, a wall, or another place where moisture droplets shouldn’t form.  In fact, the ONLY place we want to see condensation form is on an evaporator coil. Anywhere else is undesirable.

Let’s say that you notice Mould in your home.  Biological growth forms as a result of condensation. You know that the outdoor dew point sometimes gets above 23°C, and humid air travels right through porous materials like wood and insulation you have the AC set to 20-22 degrees – you will have issues! When the humid air hits a wall surface below its dew point temperature, condensation will form, leading to this growth. This can happen inside a wall where it can go unnoticed for a long time. Is the answer a dehumidifier?

A dehumidifier will help but only treats the symptoms, not the cause, by drying the inside of the building. The problem is high dew point air from outside is getting inside. The house needs to be air sealed. If it never had an effective water vapor barrier, such as house wrap, installed, this could be a major project.

What can I do to fix the issues:

If the filter is clogged or dirty, the airflow to the evaporator coil will be blocked or restricted causing the temperature to drop. If the evaporator coil gets too cold it freezes over and ices up. When the AC is off, the indoor unit will stop trying to draw air causing the unit to warm up and therefore melting the ice. This drips an excess amount of water into the drip tray. This is why it is essential that your filters are cleaned every month and the whole system serviced annually.

• Are all of the windows and doors shut properly (including the rooms you are not using)
• Insulation / ventilation If there is no insulation on the ceiling (in the roof cavity) than the watermarks will affect the ceiling. This is one of the most common causes for water leaks. Have you looked at solar whirly birds to ventilate the roof cavity https://acstore.com.au/blog/2020/06/12/more-efficient-air-conditioning/
• Is the unit set to a reasonable and achievable desired temperature for the day, if temperature is lower than the dew point, air conditioner sweating may occur once the metal/plastic grille drops below this temperature.

Can an Air Conditioner reduce humidity

There are many air conditioning systems that are able of regulating humidity. It has an evaporator coil that condenses water vapour from the air. This occurs when the hot and humid air in your home comes in contact with the cold evaporator coil.

The liquid then condenses in the air, making your home less humid. The moisture collected by the evaporator coil goes to a drain to be sent outside, away from your home. But keep in mind that it also depends a lot on the type of air conditioner system that you have and the years it has. Modern air conditioners are more efficient in regulating humidity at home than older ones. Panasonic and LG are great air conditioner brands with Dry function or air purification features.

Contact us for servicing and installation of a new Air Conditioner with Dry function. Remember when your evaporator coil is covered in dust and dirt, it cannot remove all the heat and moisture that should be removed at home. Even if the coil is not dirty enough to prevent the air conditioner from cooling your home, it may still be dirty enough to perform the correct removal of moisture.