Evaporative versus refrigerated cooling systems

Mark Bryson - Sunday, February 05, 2017

You’re building a new house. You’ve chosen a land and home package through Berstan Homes. Or you are contemplating a knock down rebuild of your house and you know Berstan Homes are the experts in this field.

Now you need to decide which cooling system to install. There are three main choices on the market – ducted evaporative cooling, ducted refrigerated cooling and single room refrigerated cooling.

How they work

An evaporated cooling system draws warm air from outside through wet filter pads. Water from the pads evaporate as the warm air moves through them, cooling and humidifying the air. The cool air then circulates through the house. The unit is installed on the roof, and ducting delivers the air to each room. The same ducting cannot be used for ducted central heating.

Refrigerated, or split, air conditioning, use indoor and outdoor units to cool the existing air in the house. Warm room air is drawn over the indoor unit’s coil, which extracts the heat by refrigeration within the coil, which is then moved outside and expelled. While this process occurs, any water in the air condenses on the cold indoor unit and drains away. The air that is blown back into the room is cooler, drier and usually filtered. It is also called a reverse cycle as it reverses the process for heating in winter.

Split air conditioners are installed on the walls in separate rooms. Ducted systems have the unit in the ceiling cavity with ducting delivering cool air to each room. The same ducting system can be used for heating.

Cost comparison

Evaporative cooling systems cost far less to run than refrigerated systems, but they rely solely on electricity. Operating costs are between 11-16c per hour. However, the unit needs to stay on for much longer than a refrigerated system and temperatures will never get as low. Generally, they cool to 10 degrees below the outside temperature. Doors and windows must be left open while it is operating so it works efficiently.

Operating costs for refrigerated systems vary depending on the size of the house. A single room unit ranges from 27-38c per hour. Ducted systems cost between 36-54c per hour. A zoned unit is more efficient as it restricts cooling to infrequently used rooms, resulting in energy savings.

Cost efficiencies depend on how and when the systems are used. Both systems benefit from being put on early on a hot day, keeping the inside temperature constant, rather than trying to cool a very hot house rapidly in the late afternoon.

Pros and cons

If you live in a high humidity area, evaporative air conditioning isn’t an option. While Melbourne is generally a dry climate, there are some hot, humid days when you need an efficient air conditioner. If you have limited water, evaporative systems can use around 25-40 litres of water an hour. Water costs should be added to the running costs when making price comparisons.

Evaporative systems can raise humidity in the house, affecting those with respiratory problems. Leaving doors and windows open can increase the security risk.

However, if you crave fresh air, these systems will change the entire volume of air in the room every two minutes, eliminating staleness and smells.

In contrast, refrigerated cooling systems work best when all doors and windows are closed as it recycles the air. This can make it difficult with children and animals constantly going in and out.

The ceiling outlets for an evaporative system can be a significant source of air leakage in winter, allowing warm air to escape and increasing power bills. Covers are available to fit over the outlets, reducing leakage.

Single split air conditioners have been criticised for making one room too cold while not reaching all areas of the house. A ducted refrigerated cooling system eliminates this problem and, while the initial cost is higher, it is more cost effective than progressively adding more single units around the house. The ducted system can run on both gas or electricity.

Expert opinion

Berstan Homes director, Mark Bryson, has a clear favourite.

“Ducted refrigerated cooling is the only way to go when doing a new home build. It can run on gas or electricity and is far superior to an evaporative system,” he says.

“The big advantage is that the same system can be used for heating in the winter.”

Costs range from $10,000 for a small, basic system in an apartment to around $14,000 in an average, single story home. Expect to pay $16,000 or more for a ducted system in a large two-storey home.

Mark says a ducted refrigerated system in a 30Sq Berstan home would cost $16,000. “However, when spending an average of $400,000 on a new home build, the cost is relatively minor.”

It is crucial to get expert advice on the right system for the size of the house. A 4.2kW system would only cool a small area effectively. While the initial cost is low, it would have to run continuously to cool the room, which would make energy costs rocket and significantly reduce the life of the system.