People often want to know whether they can change their existing ducted evaporative system over to a new ducted reverse cycle (HVAC) air conditioning system by using all the same ductwork and outlets. The simple answer is no. Below is a list of reasons as to why you cannot simply change the system over to become a reverse cycle (HVAC) system.
Firstly, reverse cycle grilles (or outlets) are usually placed near windows and away from the doors. This allows the air to condition the heat/cold that comes in directly through the windows. The airflow for a reverse cycle system should also take the longest route back from the outlet to the return air grille. If an outlet was placed next to a door, the air would simply be sucked back underneath the door towards the return air grille and the room would have hot spots near the window.
The problem with evaporative grilles is that they are usually located by the doorways. The evaporative units airflow should take the longest possible path through a room and out of the window. If they were located right next to a window, the air would simply flow out the window and hot spots would be caused near the doorways and in the far side of rooms.
Due to these reasons it is not advised to place reverse cycle grilles in a same spot where a ducted evaporative grille was previously located. Although it is possible to do it will severely lessen the effectiveness and capacity of the system. The best option is to start fresh and put the new reverse cycle grilles in the correct desired location as required. However, this would mean you would need to patch and paint the holes in the ceiling left by the removal of the old evaporative grilles and this can be a costly job.
Another option would be to add extra grilles as needed. You can consider leaving grilles near the doorways from the evaporative system and add extra grilles by the windows if needed.
Another problem encountered when swapping the systems over is that the old ducting cannot be used. The ducting used for evaporative units is far larger than that required for reverse cycle ducted air conditioners. Evaporative units use ducting around the 16-20 inch mark. This large size duct is used by evaporative air conditioners as the air is extremely fast blowing and it aims to draw in air to the amount of 40 times the cubic area of your house per hour. Reverse cycle ducting is mostly only around the 12 inch mark in diameter. This is because reverse cycle air conditioning is far slower moving than it’s evaporative counterpart.
Evaporative ducting is also usually only slightly if at all insulated. Reverse cycle ducting should always be insulated by a minimum of 2 inches to preserve the cooling/heating and to prevent condensation from occurring.
So if you want to swap your current evaporative system over to a new reverse cycle ducted system, you are best to start from scratch. Be sure to get quite a few quotes for the cost to patch and paint the ceiling before starting any work. And if air conditioning contractors tell you they can simply swap a system over using the existing duct and outlets, ask lots of questions and be wary as they may not be around to help you out once you have paid good money and your system is not working effectively.
In some cases using the existing grilles can be an option, but it would make the system less effective.