On a tropical island where air conditioning provides a measure of comfort from the heat, cooling costs account for a significant portion of a residential, commercial, industrial and government utility bill.

For an institution such as the Guam Department of Education, operating and maintaining nearly 3,000 air-conditioning units across schools and offices puts a dent into the department’s monthly energy bill.

GDOE spends about $12.3 million on power, according to the Bringing Energy Savings To Schools study, which was funded by the Guam Power Authority.

The study provided several recommendations to reduce GDOE’s power consumption. GPA General Manager John Benavente recommended tapping into solar-assisted thermal air-conditioning units, which he said would use a block of about five or 10 units to cool the school, “almost like central air.”

Lynn Scott, chief operations officer at Green Energy Solutions Inc., broke down the basic elements behind solar-assisted thermal air conditioning. GESI is the solar thermal dealer for the patent holder on Guam and the Commonwealth of the Northern Marianas Islands.

Solar Thermal technology

Scott showed a prototype of a solar thermal collector – a proprietary system consisting of 20 glass cylinder tubes each lined with thin solar heat-conducting film. Inside the cylinders are high-pressure copper coils that serve as a heat exchanger. The tubes are in a rack made from corrosion-resistant aluminum.

“Solx Energy out of Great Britain owns the patent for solar thermal technology for refrigeration and air conditioning. One of their products under that patent is called Thermx, a solar thermal collector. What it does is it helps the AC’s compressor run less,” he said.

While the setup resembles a solar water heater system, the solar thermal system is designed for refrigerants, according to Scott.

“You don’t see a lot of electrical wires, not a lot of moving parts. It is a very simple setup,” he said.

The anticipated life span of a solar thermal collector system is at least 25 years, according to Scott. “You will end up replacing your aircon three or four times long before you lose the use of your solar thermal.”

Practical application for solar thermal.

According to Scott, the compressor is basically the major energy consumer in an air-conditioning unit. He said a typical compressor has two primary functions — to heat the refrigerant freon gas and to push the gas through the system.

While a typical compressor uses electricity to perform these functions, the solar thermal collector uses the sun to heat the refrigerant gas and kinetic energy to push the gas around the coils.

According to Solx Energy, the collector can be integrated with cooling and heating systems to reduce energy consumption by an average of 30 to upwards of 50 percent with minimal space requirements. Scott said the technology can be used for schools, government buildings, and commercial and industrial facilities.

The solar-assisted thermal technology also can be combined with other systems to optimize its benefits.

To illustrate the potential energy savings, Scott provided an example of a GESI project that combines solar-assisted thermal technology for a warehouse facility on island. For the project, GESI is installing a 60-ton VRF (variable refrigerant flow) air-conditioning unit attached to the solar thermal collector, LED lighting and photovoltaics.

“With everything combined for that project – lights, changing to VRF, adding the solar thermal and adding solar PV – they should be able to reduce their energy consumption by around $9,000 a month,” Scott said, adding, “Their power bill is usually $13,500 a month. When we are done, we should see around 80 percent reduction in their power bill.”

The technology also could work for the GDOE school system, according to Scott.

“The schools are great. The reason for that is, with a VRF multisystem, the classrooms are just right in a row, so the installation is quite simple,” Scott said. “The majority of the schools on Guam also have nice flat roofs that are single story, so the collector can be tucked up in a roof and you won’t even see it.”

A VRF multisystem consists of a single outdoor condensing unit, which is connected to several indoor cooling units. “Solar thermal works with all brands of VRF because it is a modulated compression system,” according to Scott. A modulated compression system is a component in an air-conditioning unit that regulates capacity based on the cooling demands of the space.

The cost of installing a solar thermal collector depends on several factors, including the location of the setup and the type of air-conditioning units, among others.

For more on Solar Thermal Air Conditioning systems in South Africa – click here.