Johannesburg-based renewable energy company Voltas Technologies has installed, and is monitoring, a solar-thermal driven air-conditioning system at the Netcare Moot hospital, in Pretoria.

"It is an important time for us in South Africa - we are starting to see some movement in solar technologies as people become more open to the idea," explains Voltas Technologies director Cristian Cernat.

He adds that the government stance on renewable energy is encouraging, particularly with the regulator's recent release of the renewable energy feed-in-tariff, and consumers have more confidence in the technologies and the benefits.

The solar plant is situated on the roof of the Moot hospital, and the air-conditioning absorption chiller unit is powered by hot water, which is heated through 50 collectors. These solar collectors operate at 91% efficiency, and the water can reach temperatures of up to 120 ºC.

Voltas explains that the absorption chiller is powered by solar energy collected in the evacuated tube solar thermal panels. The thermal energy is delivered to the absorption chiller using a Glycol (antifreeze) solution and a simple, but carefully designed, system of pipes, pumps and controllers.

Air conditioning is an imperative function for the hospital, not only in wards to keep patients comfortable, but in operating theatres, where air-conditioning is vital for successful surgeries.

Netcare national technical manager Peter Schilder explains that the system is being very carefully monitored, and, while the technology is proven to work, the financial success of the installation will dictate whether or not the healthcare company will roll out solar plants at its hospitals nationwide.

Netcare wished to test the benefits of solar technology to the company, in terms of energy security and independence, cost savings, as well as environmental benefits.

The return on investment is expected to be achieved in about six years, although if the electricity price continues to increase, it could be sooner, explains Cernat.

The plant at the Moot hospital was installed on September 18, and monitoring and research on the system continues, as Voltas Technologies aims at identifying exactly how many square metres of solar absorption is required to power the unit. In Europe, an average 3 m2 of solar absorption area is required for 1 kW of cooling, but South Africa has more powerful irradiation for a longer duration, and indications are that a substantially smaller area is required.

The project also seeks to demonstrate the relationship between the storage and the optimal operation of the absorption chiller. The storage material used is also an aspect that will be tested.

Power conservation from conventional electricity supply is constantly monitored, and Voltas will present the data to Eskom, so that a baseline of potential savings can be established. Cernat says that initial data shows that between 60% and 70% electricity savings are expected.

"The solar industry will thrive if we pass on the knowledge - once we have achieved results, it is important to share them," says Cernat.

He tells Engineering News Online that the company is interested in collaborating with universities in South Africa, and is inviting students interested in writing theses on solar technology or solar plants, to conduct their research at the Voltas installation.

The power produced by the solar plant is between 35 kW and 48 kW, and the ambition is to scale up the project to reach about 170 kW to 200 kW, and this would also manage the hospital's water heating needs, as well as daily air conditioning requirements.

The solar installation is turned on at 08:00 and turned off at about 18:00, and is used in combination with the standard compression chiller, which powers the air-conditioning needs at night. Currently, it is estimated that there is a 50:50 split in power provided from solar, and power from conventional sources for the air-conditioning needs.

The collectors are connected to two large 6 000-l storage tanks, and a number of three-in-line pumps are used for fluids circulation which, together with the 100-W pump internal to the chiller, brings the electrical power required by the installation to about 5 kW. In electrical coefficient of performance (CoP) terms, the system has a CoP of ten.

Cernat adds that the agreement between Voltas Technologies and the Japanese multinational absorption appliances manufacturer Yazaki makes this kind of installation possible in our country.

The installation is controlled, and remotely monitored through the Internet and parameters are logged, through a Carel BMS system called PlantVisorPro.

"The installation is the first of its kind in South Africa, and is being developed concurrently with other solar water projects for the Netcare Group," concludes Cernat.