Asean energy award: Gas-fired air conditioning system

Bonifacio Gas Corporation in Manila, Philipines, was the recipient of an Association of South-east Asian Nations (ASEAN) Energy Award in July 2001 for a liquefied petroleum gas-fired (LPG) absorption system for the air conditioning requirements of the Fort Bonifacio Development Corporation’s (FBDC) Building E.

The building, which serves as offices for the FBDC, forms part of the Fort Bonifacio Global City, the newest business district in the heart of Metro Manila.

The objectives of the project were:

  • to promote absorption technology as an alternative and energy efficient solution for the air conditioning requirements of existing and future buildings within the country;
  • to support the vision of developing an environment-friendly global city;
  • to have in place an operating system which can serve as a showcase for the technology; and
  • to share the technology with other operating companies in the region.

The increasing interest in absorption technology is based on the need to use energy safely and reliably while protecting the natural environment through the prevention of the further depletion of the ozone layer by chlorofluorocarbons (CFCs), particularly in countries where there is a big disparity between electricity rates and those of alternative energy sources, such as LPG and natural gas (the Philippines is second only to Japan in terms of this disparity between electricity and gas).

The basic principle of an air conditioning unit is that cooling is achieved utilising the latent heat released by a refrigerant as it evaporates. However, whereas a compressor-driven system uses a compressor to pressurise the vaporised refrigerant and water cooling to condense it, the absorption system uses an absorbent to absorb the vaporised refrigerant and a heat source to release it. In this case water is the refrigerant and a solution of lithium-bromide (LiBr) is the absorbent.

The basic operating cycle of the single effect absorption system involves only four stages – evaporation, absorption, generation and condensation. Cooling water flows through absorber and condenser chillers. The cooling water in the condenser cools the refrigerant vapour from the generator. The cooling water in the absorber absorbs heat released by the vaporised refrigerant as it is absorbed by the LiBr.

In the case of the BGC system, it has been further improved so that it is capable of double effect, utilising the vapourised refrigerant as an extra heat source.

The benefits of the project are as follows:

  • It is environment friendly, as it does not contain CFCs, and the two key components – water and LiBr – are safe and non-polluting.
  • Energy savings are made, as the system uses LPG, which is cheaper than electricity;
  • Electric power peak shaving is possible as the absorption chillers are used to reduce electricity base rates during high demand periods, enabling the electric power plant to be downsized by about 70%.
  • Continuous operation during power outages can be maintained, as the absorption chillers need up to only 75 kVA for their largest units (the unreliable power supply in the Philippines being one of the main drivers behind the project).
  • The double effect absorption cycle results in a high coefficient of performance of 1.2.
  • Maintenance costs are low as there are few mechanical components.
  • The system can be converted to natural gas, when this becomes commercially available, with only minor revision of the burner.
  • The absorption chillers provide simultaneous cooling and heating, operating efficiently at various cooling, heating ratios.

The project has also helped develop interfaces with companies working or based in other ASEAN countries, resulting in technology transfer and exchange of information on best practices. BGC is currently working also on a bigger project using the same technology for another building within the IT Zone of the Bonifacio Global City.