A Solution in Abeyance!
Heat pumps offer a highly efficient, eco-friendly alternative to traditional air conditioners and furnaces, consuming less energy and emitting minimal greenhouse gases, but their adoption must accelerate to significantly curb urban emissions
With the increasing number of hot days in the year across the world, as well as greater occurrences of extreme weather events, the demand for air conditioning is only going to increase in the coming years. This is going to be particularly high in the hot tropical countries in Africa and Asia, where air conditioning remains limited by the cost. However, as incomes rise and extreme heat conditions increase, there will be a massive jump in air conditioners sold. If we continue down the path shown by the rich countries of Europe and the USA, greenhouse gas emissions on account of heating and cooling are going to explode. The least we can do is to make heating and cooling more efficient.
Improving Efficiency: The Promise of Heat Pumps
One of the ways to improve efficiency in heating and cooling is the increased use of Heat Pumps. A Heat Pump is more efficient because it does not generate heat but transfers heat from a hot source to a cold space and vice versa. Heat Pumps work on the same principle as a refrigerator: a compressor moves a refrigerant through its refrigeration cycle (this cycle includes a) compression of the refrigerant, which raises its pressure and temperature, followed by b) condensation whereby the heat is released, followed by c) expansion whereby the refrigerant passes through a valve reducing heat and temperature, and partially vaporizing the refrigerant and d) evaporation, whereby the low pressure refrigerant absorbs heat from the surrounding area and cools it, and vaporizes. This vaporized refrigerant is again drawn into the compressor, repeating the cycle). A Heat Pump also consists of a Heat Exchanger which extracts heat from the source and passes it on to a heat sink through another heat exchanger. In addition to heating air, Heat Pumps can also be connected to water tanks to provide hot water. Large scale industrial size Heat Pumps are commonly used in heating large industrial applications. There are various types of Heat Pumps: Air to Air, which basically transfer hot air from one place to another, Ground or Geothermal, which collect heat from the ground and pump it into homes and Absorption or Gas Fired Pumps, which use thermal energy.
Heat Pumps can also be used for cooling using the same principle in reverse. The compressor now collects heat from inside the home and pushes it outside. A Heat Pump which cools typically has a heat exchanger (which is a coil) with a fan. To cool the air, chilled water is pumped through the fan coil, which draws warm air from the room and cools it before pushing it back into the room. Since Heat Pumps only transfer heat from one place to another, they are far more efficient as compared to Air Conditioners. With an Air-to-Water Heat Pump, most of the energy needed to run it comes from renewable energy and only 25% of the energy needed to operate it comes from the grid. If Ground-to-Air Heat Pumps are used, even more heat energy is used from the ground, with only 20 per cent of the energy coming from the grid. While Heat Pumps offer an attractive alternative to Air Conditioners and Furnaces, they have to be handled carefully. The installation has to be proper to ensure proper ducting and no leakages. The refrigerant/coolant and the wiring of electric resistance auxiliary heat strips have to be correctly installed. Since the transfer of hot air is the most fundamental operation, it has to be ensured that the air flow is sufficient (typically, 400 cubic feet per minute of airflow is ideal for one tonne of air conditioning capacity).
Conclusion
Heat Pumps are a great alternative to conventional air conditioning and furnaces since they can run on lesser energy and emit a fraction of greenhouse gases. While the initial cost of Heat Pumps is high, their running cost is much lower and the lifetime costs works out in their favour as compared to Air Conditioners and Furnaces. Moreover, they are far more efficient as compared to conventional tools. The use of Heat Pumps is growing but needs to become more widespread to reduce greenhouse gas emissions from the heating and cooling of residences and offices in urban areas around the world.
The writer is Additional Chief Secretary, Department of Mass Education Extension and Library Services and Department of Cooperation, Government of West Bengal
