Evaporative Cooling: Does It Work in Newcastle?

Short answer: evaporative cooling is cheap to run and works well in dry heat, but it adds moisture to the air to cool it. On the coast, where summer afternoons are already humid, it does the least on the days you need it most. For a home in Newcastle or Lake Macquarie we recommend reverse cycle, which cools a closed house on a muggy day and heats it in winter. Evaporative makes much more sense in the drier upper Hunter, around Singleton and Scone.

That's our position. Here's the reasoning, and the numbers behind it.

How evaporative cooling works

An evaporative cooler is a fan, a water pump and a set of wet pads, usually in a box on the roof with ducts into the ceiling. It pulls hot outside air through the pads. As the water evaporates it takes heat out of the air, and the cooler, damper air is blown through the house.

Two things follow from that. It needs a steady supply of fresh outside air, so some windows or doors have to stay open. And it only works as well as the outside air lets it. Dry air soaks up water fast and cools a lot. Air that's already humid takes up much less, and cools much less.

A reverse cycle (refrigerated) system works differently. It moves heat out of the house through a refrigerant circuit, the same way a fridge does, and it pulls moisture out of the room while it cools instead of adding it. The house stays closed, and the same unit runs backwards in winter to heat.

What the humidity numbers say

The Bureau of Meteorology publishes long-term averages for weather stations across the Hunter. The figure that matters for evaporative cooling is afternoon humidity in summer, because that's when you're running it. These are the January averages for mean 3pm relative humidity:

Station	January mean 3pm humidity
Newcastle (Nobbys Signal Station)	72%
Williamtown RAAF	59%
Cessnock Airport	46%
Jerrys Plains Post Office	47%
Scone Airport	41%

They're long-term averages from the Bureau's climate statistics, and February is similar or a touch more humid at every one of them. The pattern is the point: humidity falls the further you go from the sea. A hot afternoon in Mayfield or Hamilton is a damp one. A hot afternoon in Scone is a dry one.

Government energy advice puts it plainly. The ACT's guide says evaporative coolers are reasonably effective in hot, dry climates and less effective when it's humid, and the federal YourHome guide says they work best where humidity is low. Newcastle's coast is the second case.

Where evaporative cooling does suit

Out west, the numbers turn in its favour. Around Singleton and Scone, summer heat is drier, and an evaporative system can bring a hot house down comfortably for a fraction of the power. If you live there, have a large house, like plenty of fresh air through it and don't mind the windows open, it's a fair choice. Jerrys Plains, between Singleton and Muswellbrook, averages 47 per cent on a January afternoon. Our air conditioning in Singleton page covers the town and the bigger blocks out past it.

Cessnock and the vineyards are drier than the coast too, and on the humidity numbers alone evaporative cooling is a fair option there. It still can't heat, and Cessnock winters are colder than Newcastle's, so most of the homes we see there choose reverse cycle anyway.

What it costs to run

The federal government's YourHome guide says an evaporative system's running costs can be low, because only the fan and a small water pump use power. It also notes that many units have large, inefficient fan motors, so the saving varies by model. Then there's water, which reverse cycle doesn't use at all. YourHome puts a central evaporative system at 25 litres or more an hour on hot, dry days.

We'd add one coastal caveat to the running-cost case. A cheap system that can't get the house cool on a 72 per cent humidity afternoon hasn't saved you anything. A reverse cycle system also cools a closed house, so the insulation and draught sealing you paid for keep working while it runs. Running costs depend on the house and the model, so we won't put dollar figures on it here.

The heating question

This is where reverse cycle pulls well ahead for most families. An evaporative cooler only cools. A reverse cycle system also heats, and government energy advice describes it as the most efficient form of space heating, three to six times cheaper than other heating types. Newcastle winters aren't harsh, but most homes still want heat from May to August. With evaporative cooling, that means a second system.

Humid nights on the coast

There's one more coastal problem, and it's the one people notice in bed. On a sticky January night in Newcastle the air outside is warm and damp, and an evaporative cooler can only push more of that air through the house with extra moisture added. A reverse cycle system draws water out of the room as it cools, which is why the drain outside drips all evening. Drier air feels more comfortable at the same temperature. If a reverse cycle unit ever starts dripping inside instead, our guide to an air conditioner leaking water explains why.

What we recommend

• A Newcastle, Lake Macquarie or Port Stephens home: reverse cycle. A split system for one or two rooms, or ducted air conditioning with zones for the whole house.
• A large, open home in the upper Hunter: evaporative is worth a look, especially if winter heating is already covered.
• Somewhere in between, like Cessnock or Maitland: lean reverse cycle unless you're set on open windows and the low running cost.

If you're torn between a split and ducted, our guide to split system vs ducted goes through it house by house.