My house has a Rheem RCQD6024aAS air conditioner. They typically keep the set-po

Question

My house has a Rheem RCQD6024aAS air conditioner. They typically keep the set-point of their thermostat in their house to 83 oF because the unit tends to ice over if they try to run a higher flowrate of air. The system just cannot handle the high flows and then ice forms on the coils of the heat exchanger and then they stop working. If the were running this system on July 20 of this year, and the unit was cooling the air to 50 oF and was running the tons of capacity for the unit, what would be the rate of condensation of the water and the volume of humid air in m3/min that could be sent through the unit, using Raoult's law to solve this problem . State all assumptions made.

Explanation / Answer

When homeowners leave the home for more than three to four hours at a time during peak heat periods, they oftentimes close their windows and doors which will result in no home ventilation. While they’re out, the indoor home temperature rises considerably. For example, it can be 95 degrees outside and by the time you arrive home the indoor temperature has risen to 88 degrees.

This is an uncomfortable temperature for most families so turning on the air conditioner is the logical solution, usually set in between 73 to 75 degrees. Unfortunately, even if the air conditioning never turns off, it may take hours to lower indoor room temperature (as a whole) from 88 degrees to 75 degrees.

When you know you’ll be out of the house during peak heat hours, leave the air conditioner on to a reasonable temperature (78 to 80 degrees). That way, when you return home you can adjust the thermostat to a comfortable 75 without stressing out your air conditioner

Each central air system works to cool air by 15 to 20 degrees at a time. As an example, if the indoor air temperature is at 80 degrees, the AC system takes that supply of air and subtracts 15 to 20 degrees of heat before releasing it back into the home air supply. Because it mixes with the other 80 degree air that has not been conditioned yet, the air you feel will be cooler but not necessarily the temperature that you set on your thermostat. It takes time for the indoor air to reach temperature equilibrium.

However, if you detect the mixing of conditioned air and the indoor air supply is not the reason for poorly conditioned air there may be a greater issue. Though air is still conditioned, it is less efficient, working twice as hard to cool the same amount of air.

One of the biggest misconception homeowners have about their central air system is that a lower number on the thermostat indicates colder air. This is technically untrue.

When the air conditioning turns on, it does not matter to what temperature the thermostat is set; heat is removed from the indoor air supply in constant increments of 15 to 20 degrees, depending on the humidity level and outdoor temperature.

A good maintenance call scheduled regularly eliminates issues with poor or dirty filtration. From stuffed filters to build-up over the evaporator coils, keeping your central air system clean not only benefits the system itself but the sanitation of the air you breathe inside of your home.

When air filters are not replaced or cleaned out it adds strain upon the AC because it is now more restrictive than before. This means less air gets through the filter and less air is conditioned. If this happens, it also causes the evaporator coils to ice up while the system overheats.

The evaporator coils are hollow tubes through which refrigerant flows. Once the refrigerant reaches the evaporator coils, the coils grow cold so that the indoor air supply that passes over them are cooled before returning into your home. Something as simple as a dirty filter can stop this process because less room temperature air passes over the coils which in turn ice up.

Likewise, poor air flow due to dirty filters encourages the system to overheat and shut down. This is because a central air system needs a heat source to function and restricted air flow means the same amount of energy is used for less and less air.

Filters that are not serviced are the number one reason to system shut-downs

Have your preferred HVAC technician visit to service your AC system. Be sure to replace filters and have the evaporator coils and drip pans cleaned. These areas collect water and are prone to microbiological growth

Homeowners, new and old, have a tendency to think that their air conditioning system is an open system. This is not the case. Contrary to popular belief, there is no need to refill your refrigerant supply.

Given that your AC system was installed properly and there are no leaks that have accumulated during its lifespan, the same supply of refrigerant is recycled each and every single day.

However, if your refrigerant supply does experience a leak, it requires the attention of a HVAC technician as soon as possible. Refrigerant is a gas that damages the ozone layer if released into the atmosphere. Your technician can repair the leak and restore its proper supply.

When your refrigerant supply does drop due to a leak, the system is less efficient because it has less cooling power to work with. If your AC system previously cooled indoor air in 20 degree increments, it now may be cooling in 10 degree increments; the air conditioner works harder to condition the same amount of air.

HVAC technician repair the leak, refill refrigerant and recalibrate.

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