Just last month the Israel Electric Corporation imposed a number of blackouts when a combination of high summer temperatures and several brief power plant snafus brought the utility close to its maximum generating capacity. The company recently reported that usage this summer was 9% more than last summer, mainly due to our love of air conditioning. During peak times 42% of electricity demand was for cooling.
There's a reason for the IEC ad campaign urging us to keep our home and office thermostats at 25 degrees Celsius in the summer. For each degree below that level, energy consumption increases by 5%. But there is another option, one that is relatively cheap, more effective than persuading consumers to turn up the thermostat and could make conventional air conditioners ancient history.
We are talking not about a new technology, but rather a relatively old one that is gaining new interest with the surge in energy costs and pollution concerns. You won't find it at the nearest home appliance store, but rather 120 meters underground.
Geothermal heat pumps uses the earth as a heat sink (in the summer) and a heat source (in the winter) to cool and heat buildings. Water or other liquids are circulated through pipes buried in the earth, where the temperatures remain relatively stable. The cooled or heated liquid is then used to cool the building in summer and warm it in winter.
"Conventional air conditioners pull the heat out of the room," explains architect David Knafo. "The problem is that the heat ultimately reaches the air conditioning unit" on the roof or the exterior of the building, "at which point it is introduced into the atmosphere. When it's 35 degrees Celsius, in the middle of summer, you're pushing this heat into air that's already very hot," Knafo says, adding that this uses a tremendous amount of energy, which he likens to "pushing a pile of clothes into an already stuffed closet."
Maintaining the analogy, the "closet" in a geothermal heat pump, the ground, is relatively empty, and can more easily absorb the summer heat or winter cold.
The heat pump has three components: pipes in the building, pipes buried underground near the building and a pump that transfers heat efficiently between the building and the ground. The pipes inside the building are located under the floors and within the walls. In the summer the water circulating in the pipes pulls the heat out of the air in the building. The pump pulls this warmed water out of the building and into the ground, which cools it down before it flows back into the building.
Since the ground temperature is relatively stable year-round, at around 20 degrees Celsius, in the winter the system can be used to heat the building.
"Instead of spitting the heat pulled out of the building into the atmosphere, we send it into the earth," Knafo says, adding that a depth of 20 meters to 30 meters is deep enough for the ground to be 20 degrees. "The system draws away heat without needing additional energy, reducing the building's energy consumption by 50%," he said.
Sheetrock was innovative 20 years ago
Knafo's firm, Knafo Klimor Architects, designed the "green" elementary school in Kfar Sava, the first in Israel to meet Leadership in Energy and Environmental Design (LEED) Gold standards for construction and for energy savings. The building was built partially from recycled material and was designed to collect rainwater for irrigation as well as to recycle "gray" water, in addition to the geothermal heat pump for heating and cooling.
The heat pump system cools the entire building and includes 20 absorption holes, 120 meters deep and 20 centimeters in diameter, that were drilled near the building. "They are completely covered, you could build a playground, parking lot or garden on top of them without having any concerns," says Knafo. "This system is very efficient for buildings with large open spaces such as classrooms, libraries or museums. Within five years such systems will be common. Today you wouldn't come to me to talk about this innovation known as sheetrock, but in Israel they were considered innovative 20 years ago," Knafo says.
Israelis are familiar with geothermal energy mainly due to Ormat Technologies, which uses heat expelled from within the earth to create steam that powers a generator to create electricity.
Geothermal heat pumps were introduced in the United States in the 1940s and in Europe in the '60s. Around 2 million such systems are in operation worldwide.
"Geothermal heating and cooling has been in use for 70 years," says Nimrod Basri, CEO of Geo Energy, which has been in the field for three years. "In China this technology is mandated for some buildings. It is used in 70% of new buildings in Sweden, and you can also find it in the Zurich airport and Berlin's Reichstag. We're not inventing anything new," Basri says.
"As opposed to traditional air conditioning, when I express heat into the earth I need to calculate exactly how much heat and warmth are needed when," Basri says. "When planning a project, we analyze everything to the smallest details: windows, openings, the number of people using the space, the type of lighting, the ground and even whether there are trees shading the building ... and then an engineer calculates the optimal number of holes to drill."
Geothermal systems offer benefits in the winter, too, as Basri explains: "Regular air conditioning systems suck up heat and spit it outside. But when you spit that heat into the earth, some of it stays there as a kind of reserve. In the winter I can use this to heat a pool, or water for my shower. Now you see hospital roofs with air-conditioning units next to oil-powered water heaters. Why?"
Basri's company, Geo Energy, built the heat pump for the Kfar Sava school. The company's first projects in Israel were smaller ones, for private homes, as proof of concept. "This field involves a lot of engineering in both the design and execution stages, so you need to start modestly," says Basri. "We began taking on larger projects only in the past year, among others for the Nir Etzion Hotel and the new Van Leer Institute building in Jerusalem."
A geothermal heat pump can be installed in any building as long as there is sufficient space around it to drill the bore holes.
"I'm not sure you could install it in Tel Aviv's Azrieli Center mall, but next to the Ayalon Mall in Ramat Gan is a big parking lot and you could drill below it," Basri says. "You install underground pipes that meet German standards, and they could last for 70 years without maintenance."
The start-up costs for a heat pump are relatively high, but Basri says the savings in electricity costs are 40% to 75%. "Each building is different, and the prices vary accordingly. For a single-family home the cost is between NIS 60,000 to NIS 200,000. Uninsulated buildings take more energy to heat and cool. For a large building it takes three to seven years to recoup the investment," Basri says.
The Kfar Sava school, for instance, is well insulated. "Ninety percent of the work is good insulation. It may be boring, but it's effective," Knafo says. The school also has an air purification system that circulates air through the classrooms. "The standard is to have an air conditioning unit in every classroom and the students sit there for an hour, breathing the same air," says Knafo. "Studies have shown this decreases concentration levels by 25% and hurts grades. Israeli students aren't stupid, they're just being suffocated. So we added a ventilation system that replaces 6 cubic meters of air per student per hour."
Here comes the sun
Geothermal heat pumps aren't the only alternative to traditional air conditioning. The new building of Tel Aviv University's Porter School for Environmental Studies, which is being built to LEED Platinum standards, will have solar-powered air-conditioning, for instance.
"That's the next advance in air conditioning," says engineer Yehoshafat Aharoni, who planned the Kfar Sava school's air-conditioning. "Using solar collectors we heat water much like a home solar water heater does. We'll use the hot water much like old-fashioned absorption refrigerators did, so when the water heats up it will suck heat out of water flowing into the building. In the winter we'll send the hot water straight into the building in order to heat it. This saves 70% of the energy that would be used by electric air conditioners, Aharoni says.
"In China and India, in areas that lack electricity infrastructure, absorption refrigerators were very popular in the past few decades, and these are now the countries leading the field," Aharoni says, adding, "We purchased the Porter School's refrigerator in China, even though Israel had a flourishing absorption refrigerator industry in the 1960s."
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