Michael Bruvel had recently built an above-ground pool in his backyard when he suffered an experience familiar to many pool owners in the warmer months.

The Darwin local would jump in after going for a run or spending time outdoors in the humid build-up, only to find it was like getting into a warm bath.

"That was really the catalyst for me starting to work on a low-cost way to work it out," Mr Bruvel said.

"Of course there are refrigeration systems and air conditioner-style processors to cool your water, but they're very expensive and very energy intensive."

For most people, a better option might seem obvious: erect a shade sail to block out the sun.

But Mr Bruvel didn't want a shade sail; he enjoyed swimming beneath the stars at night without having to remove a heavy sail each time.

Instead, over two arduous years he devised an elaborate cooling system using the fundamentals of heat transfer to slash his pool's temperature.

"It's basically a low-energy system for cooling medium to large bodies of water like swimming pools and aquaculture facilities," he said.

"It's suitable for use in the tropics and any other areas that get really hot."

Remarkably, the device doesn't rely on anything other than the water already in the pool.

The web-enabled system pumps water droplets at a precise size and angle. ( ABC Radio Darwin: Jesse Thompson )

What makes a pool warm?

To devise the technology, Mr Bruvel drew upon what he knew about the factors that make a pool warmer than desirable.

By far the main culprit, he said, was heat from the sun and an environment's ambient temperature, which will continue to heat a body of water until it and the ambient temperature match.

"If you're getting day after day where the temperature isn't getting below 28 degrees, eventually your pool will get to 28C or whatever the long-term average is for that ambient temperature."

The size and shape of your pool is another factor.

Because the water's surface is where most of the sun's heat transfers, and smaller bodies of water heat up quicker than large ones, a shallow pool with a large surface will heat up quickest.

"It's sort of that surface area that's exposed either to the sun or the atmosphere that's a determining factor," Mr Bruvel said.

"A big, deep pool will stay quite cool as well."

How do you cool it?

Between 2:30am and 5:00am each day, panels of jets attached to the side of Mr Bruvel's pool have been pumping water back over the pool's surface.

The size of the droplets the jets spray are like a Goldilocks formula; too small and they risk being carried away by wind, too large and the relationship between volume and surface area becomes skewed so heat transfer is less effective.

"Basically they're coming out of the jet at the temperature of the pool, and then as they pass through the air they take on the temperature of the surrounding air," Mr Bruvel said.

By turning the system on early in the morning when the ambient temperature is coolest, Mr Bruvel has reduced his pool temperature by as many as five or six degrees.

"This pool used to be stuck out in the blaring sun and it used to get 32 degrees plus, and even with my early prototypes I was getting it down to 28."

Mr Bruvel's pool communicates with a web-based computer system. ( ABC Radio Darwin: Jesse Thompson )

The inventor is fine tuning technology that will allow web-enabled algorithms to make decisions about when to activate the jets based on weather forecasts.

The jets will switch on automatically when they have the greatest capacity to reduce the pool's temperature to the desired range.

"I've also developed a cost-calculation algorithm that can look at what the temperature target is and what the existing climatic conditions are," Mr Bruvel, who works in air quality analysis, said.

"Then you can input the price of water and the price of power, and it can develop a cost estimate for you to reach a given temperature target.

"That's just a little quirky thing I'm working on on the side."

Eventually, he said, this would allow users to learn whether it was cheaper to cool off by lowering their pool's temperature, turning on their air conditioner, or even opening a can of beer.

Mr Bruvel has a provisional patent for the product and is seeking feedback from the market.

Prototypes he has lent to other people's pools are showing signs of success.