Whether or not to turn on the air conditioner has been a common dilemma for most households during the hot summer days. Although air conditioners bring immense relief from the heat and humidity, some people avoid using them because they want to keep their electric bills down and protect the environment. Indeed, conventional air conditioners are a major contributor to the global warming as they consume a lot of energy and release hydrofluorocarbon (HFC) that is also a greenhouse gas.
In the search to find alternative methods of improving thermal comfort in buildings, a team of scientists from Turkey and Italy have developed an air cooling system that uses geothermal energy to meet the cooling demand of an indoor area sized up to 140 square meters (or 42 tsubos).
Geothermal energy, which mainly comes from the molten rock within the Earth’s interior, is one of the few renewable energies that provide continuous power generation for the base-load demand. The most common way to exploit geothermal energy is to harvest the steam that is created when the underground water is boiled by the heat that is constantly emanating from the planet’s interior. This steam, which erupts out of the ground in the form of geysers, is converted into electricity via generator turbines and then used for various purposes, such as powering air conditioning equipment in homes.
Another way to use geothermal energy is to draw the hot underground water into homes and feed it into a heat-driven absorption cooling/heating system. This method, which is more “natural” and direct, can lower the indoor temperature in the scorching summer months or raise it in the freezing winter months without using much electricity.
The new air cooling system designed by the team of Turkish and Italian scientists directly uses the hot geothermal liquid. It consists of a pump for drawing the heated groundwater and a vapor absorption chiller (VAC) that is primarily responsible for cooling the ambient air. To test the system, the team has placed it below the ground floor of a single-family house in Turkey. The house is about 140 square meters and has access to heated groundwater. According to the team’s study, this geothermal-assisted solution is able to maintain the indoor temperature of the house within a comfortable range during all seasons.
Absorption refrigerators, which include VAC, use heat to generate the absorption cooling cycle that in turn lowers the environmental temperature. The heat can come from various sources, including the waste heat from industrial equipment. The air cooling system devised by the Turkish-Italian team has two major advantages over the conventional air conditioners. First, it operates under minimal power requirements due to having no moving parts. Second, its VAC unit uses ammonia as the refrigerant instead of HFC. On the whole, the Turkish-Italian project shows that absorption cooling/heating systems based on geothermal energy or other heat sources have the potential to sharply reduce power consumption and greenhouse gas emissions for buildings.
The Turkish-Italian team has conducted several energy and exergy analyses to assess the performance of its air cooling system. Based on the findings of these analyses, the team has made additional improvements to the operational properties of the VAC unit (e.g. pressure, temperature, ammonia concentration, and flow rate) in order to raise the energy conversion efficiency.
The data from the team’s study indicate that the VAC unit reaches its optimal operational state when the temperatures of its condenser, evaporator, and boiler are at 30, 2, and 90 degrees Celsius respectively. When the VAC unit is at that state, its coefficient of performance (i.e. the ratio of useful cooling provided to the work required) hits 0.3. The higher the coefficient value, the lower the power consumption.
So far, the solution from the Turkish-Italian team has demonstrated that it is able to meet the cooling demand of a residential home that has around 140 square meters of floor space. The up-front cost for setting up the entire system is quite high, coming to around US$3,500 (or NT$100,000). However, the savings on the electric bills are immediate and huge. With the example in Turkey, the team estimates that the payback period is just 6.4 years. At the same time, there are other benefits such as the reduction of carbon footprints.
In the recent years, government and private agencies have become more interested in trying out geothermal-based air conditioning systems in their renovation projects for old buildings on account of the advances in related technologies. Take New York for example. The city’s well-known St. Patrick’s Cathedral has replaced its conventional air conditioning units with a geothermal solution for both sustainability and aesthetic reasons. Likewise, several facilities managed by the city have adopted the technology, including the Queens Botanical Garden, the Brooklyn Children’s Museum, and the lion house at the Bronx Zoo. Cornell University’s Technology Campus on Roosevelt Island also has 80 geothermal wells for providing cooling, heating, and hot water to the main campus buildings.
Using heat radiating from the Earth’s interior to help survive the increasingly hot summers is somewhat of a paradox. Nevertheless, the demand for air conditioning worldwide is expected to surge as the ongoing climate change brings forth more extreme heat waves. Through the adoption of the geothermal-assisted air cooling technology, people may become less dependent on electric air conditioners and reap substantial economic benefits for being energy efficient in the future.
(This article is an English translation of news content provided by EnergyTrend’s media partner TechNews. The photo at the top of the article shows a geothermal power plant and its credit goes to Pixabay.)