Efficient Air Conditioning

Efficient air conditioning & building design that maximises natural cooling helps improve energy efficiency

Efficiency measures can reduce the electricity used for air conditioning by 60-75%. Photo by on1stsite licensed under creative commons.

Good building design can reduce cooling demand and increase the thermal comfort of occupants. The size and running costs of air-conditioning can be significantly reduced by:

  • Minimising solar gain (by proper orientation & shading)
  • Improving thermal inertia (by minimising the building’s thermal sensitivity)
  • Utilising natural ventilation
  • Efficient design and rational operation of the air-conditioning system [1].

In commercial buildings in Brazil almost half of the electrical demand is due to air conditioning [2]. It has been suggested that energy efficient design measures in commercial buildings in Brazil could reduce the electricity used for air conditioning by 60-75% [3].

Operation of Air Conditioning

In commercial and public buildings, air-conditioning systems should be zoned where possible so that air conditioning is used only when and where necessary. This can improve energy efficiency and the thermal comfort of building users. Where active cooling is necessary, mechanised cooling systems (fans) are more energy efficient than air conditioning and generate less carbon emissions. These should be used where practical. Air conditioning should be installed with efficiency in mind – ducting and refrigerant lines should be carefully planned and well-insulated to maximise cooling potential and energy efficiency [4].

Simply having a rational temperature control strategy can result in savings of up to 50 % cooling energy and 60 % fan energy without compromising thermal comfort. Maintaining temperature control during working hours and allowing temperature to float at other times can result in significant savings [5]. A full analysis of building use should be carried out, and a rational air-conditioning strategy should be developed.

Solar Thermal Air Conditioning

This harnesses thermal energy from the sun to drive chillers. These systems are becoming more common, but they are not widely available in Brazil. Given the renewable nature of the Brazilian grid, their potential to reduce greenhouse gas emissions in the context of Rio de Janeiro is limited. In addition, the potential cost implications of such systems is unclear – they add significant up-front cost and complexity to projects. See the article on Solar Thermal Cooling in this toolkit.

Split System Air-Conditioning

When smaller split system air-conditioning units are used, high energy efficiency units should be sourced – ideally with an energy efficiency rating of at least five stars.

Heat Recovery

Heat is an inevitable by-product of air conditioning that is usually wasted – often contributing to unwanted urban heat build-up. This waste heat can be harnessed and used to heat water. This would be particularly useful in the Rio de Janeiro residential sector, where air conditioning and electric showers account for a large proportion of the overall electricity usage. See the article on air conditioning and water heating in this toolkit.

References

  1. O. D. Corbella, “Learning from Built Examples in Rio de Janeiro: 18th Int. Conference on Passive & Low Energy Architecture,” 2001. [Online]. Available: http://www.usp.br/fau/cursos/graduacao/arq_urbanismo/disciplinas/aut0264/Material_de_Apoio/Corbella_Yannas_2001_Rio.pdf
  2. T. R. M. T. Konigami, “EFICIÊNCIA ENERGÉTICA EM EDIFICAÇÕES COMERCIAIS, DE SERVIÇOS E PÚBLICAS,” Master’s Thesis, UFBA, 2011. [Online]. Available: http://www.ppgee.eng.ufba.br/teses/99424061e9e771b735f8e7056f6ba3d8.pdf
  3. H. Geller, de M. J. Gilberto, R. Schaeffer, and M. T. Tolmasquim, “The Efficient Use of Electricity in Brazil: Progress and Opportunities,” Report, American Council for an Energy-Efficient Economy. Washington DC, 1997.
  4. Cairns Regional Council, “Sustainable Tropical Building Design: Guidelines for Commercial Buildings,” 2011. [Online]. Available: http://www.cairns.qld.gov.au/__data/assets/pdf_file/0003/45642/BuildingDesign.pdf
  5. I. M. Budaiwi, “Air Conditioning System Operation Strategies for Intermittent Occupancy Buildings in a Hot-Humid Environment,” Eighth International IBPSA Conference, 2003. [Online]. Available: http://www.ibpsa.org/proceedings/BS2003/BS03_0115_122.pdf