AWG Performance Starts with the Weather

AWG Performance Starts with the Weather

Dew point, RH, and temperature are the three environmental factors that determine how well an AWG performs.

Three environmental factors determine how well an atmospheric water generator (AWG) performs: dew point, relative humidity (RH), and temperature.

Scott Sloan, senior engineer for Therma-Stor and Origen, monitors all three to understand how the machine operates under real-world conditions.

1. Dew point: The measure of how much water is in the air—the more water you have, the easier it is to remove. “Dew point is the overriding factor for capacity,” he says.
2. RH: While it can be measured in different ways, Sloan views RH as a measure of how easy it is to remove water from the air. “The closer you get to 100% RH, the easier it is to pull that water out of the system,” he says. “The farther you get, the more energy you have to spend pulling that water out.”
3. Temperature: Temperature affects both performance and machine reliability. High temperatures can pose safety concerns for the machine, while below-freezing temperatures create defrosting problems. “When the system goes in and out of defrost, it has to remove ice from the coils and does not remove any water during defrost periods,” he explains.

Of the three, the cold is the one that fights back the hardest.

Overcoming the Cold

The efficiency of an atmospheric water generator drops significantly in cold temperatures.

“Water freezes at 32 degrees, and once you get closer to that temperature, it gets harder and harder to pull that water out,” Sloan says. “Operators have to jump through more hoops and try different defrost systems.”

At the 32-degree mark, operators no longer condense water on the coil—they start condensing ice, which eventually turns into an ice block. Then, they have to send airflow through the coil without the compressor running in an attempt to melt the ice.

“Now you’re making water by building ice and melting ice,” Sloan explains. “That’s hard on the compressor, and it’s not very efficient. We want to keep liquid water on that coil for as long as humanly possible.”

Controlling defrost is especially difficult for operators, as the coil freezes up and mitigation programs must be run to keep the machine up and running. “We try to keep the system running above freezing, so it gives us a bit more low-temperature capacity.”

Operating in High Heat

While defrost is the biggest challenge AWG operators face, operating the machine in high heat is also difficult. Prolonged operation in extremely high temperatures stresses machine components, making mechanical failures, warranty claims, and damage to the equipment more likely.

“High temperatures are our biggest vulnerability for equipment failure,” Sloan says.

The same stress applies in any area where peak temperatures are expected for long periods of time. Geography compounds the problem. Machines deployed in extreme climates face heat stress that few operators anticipate.

August in Aruba, for instance, when it’s 110 degrees consistently, Sloan recommends halting production during the mid hours of the day.

“Let the machine run when it cools down a little bit,” he says. “You’re still going to produce a lot of water outside of the peak temperature times of day. Suspending operation between noon and three p.m. still lets you hit your daily production rates during off hours.”

In Aruba, shutting the system down at noon is an easy fix. But some climates don’t offer that predictability.

Managing Temperature Changes

Seasons change, and the temperature changes along with it.

“You’ve got global change you’re contending with and the unpredictability of nature,” Sloan explains. “Even in optimal climates like the Pacific Islands, Caribbean, and Central America, you’re going to have days where you don’t reach full production because of weather volatility.”

He specifically mentioned Savannah, Georgia. While the city is extremely hot and humid in the summer, it experiences harsh winters as well. December, January, and February, Sloan says, would be extremely difficult for an operator there. Even on its best days, the system would only produce 25 to 30% of its total capacity.

In the summer months, however, an operator in Savannah would get more predictable production. But there is a chance that May will be cooler than expected—fall and spring are never a sure bet.

“Operators need to have a stronger mitigation strategy for seasonality,” he says. “That could mean employing a water tank or supplementing your water production and collection through rainwater or traditional means.”

Common Misconceptions About Environmental Conditions

Operators often assume that AWGs can operate anywhere in the continental U.S. year round, but they can’t.

There are established climate zones around the world, and North America has zones one through eight. The higher the zone number, Sloan says, the colder the temperature and the lower the dew point. For that reason, refrigerant-based atmospheric water generators best serve zones one, two, and three.

Zone 1: Central America, Hawaii, and South Florida.
Zone 2: North Florida, Mexico, and South Texas.
Zone 3: South California, the middle band of Texas, South Mississippi, Louisiana, and Georgia.

AWGs perform best in Zone 1 and Zone 2. When the machine runs in Zone 3, it starts to run into seasonality challenges.

In a location like Georgia, the system can operate at peak production for up to nine months out of the year but there will be periods in the fall and winter when production rates will be reduced.

Dew point, RH, and temperature determine whether an AWG thrives or struggles. Know your climate, and the machine works. Ignore it, and the machine will remind you.