Image: Helsinki Energy

Why Helsinki Feels Like Heaven

How Finland’s capital uses an underground lake for air conditioning.

May 18 2015, 9:00am

Image: Helsinki Energy

"Is it hot in here, or is it just me?" you ask as you crank down the air conditioner, thankful for its cooling effect but dreading next month's energy bills. Summer has come to visit the northern hemisphere once again, and soon many will be seeking relief from the heat—and that usually means turning up the AC.

The air conditioner, once considered a luxury, is now entirely banal: it is in our cars, our offices, our homes, our malls, our theatres, our planes—many of us cycle through short transitions from one climate controlled environment to the next. In fact, the proliferation of air conditioners has increased to such a degree that it has slowly begun to modify humans, lowering our species' threshold for heat.

According to a study published by Proceedings of the National Academy of Sciences last month, researchers found that increased use of air conditioning is likely to drive domestic energy usage up by 83 percent over the next century. Given that last summer was the hottest on record, an unfortunate milestone that looks as though it might be surpassed this year, this probably doesn't seem all that surprising. These rising temperatures, coupled with rising standards of living around the world, means that more people are looking for ways to beat the heat, something which really doesn't bode well for the environment.

In a study published in 2009 in the journal Energy Policy, the authors predicted a 72 percent increase in air conditioning energy demand by next century, a product of both climate change and income growth in developing nations. In the more immediate future, America will have been surpassed by China as the world's foremost consumer of electricity for AC by the end of this decade, a grim prediction considering the US already consumes more electricity for air conditioning than the sum total electricity consumption of the African continent, which is home to over one billion people.

Already predicting our contemporary crisis back in 2002, Singapore's environmental minister Lim Swee Say reminded a bunch of business leaders that "air-conditioning plays a crucial role in our economy. Without it, many of our rank-and-file workers would probably be sitting under coconut trees to escape from the heat and humidity, instead of working in high-tech factories."

Willis Carrier came up with the idea for the modern air conditioner while loitering around a Pittsburgh train station on a foggy night in 1902. Staring through the mist made Carrier realize that he could dry air by first passing it through water to create fog, an epiphany which resulted in Carrier's 1906 patent for an "Apparatus for treating air," which is generally recognized as the first modern air conditioner.

Despite the genius of Carrier's invention, air conditioning is nonetheless incredibly environmentally destructive because it relies on hydrofluorocarbons, otherwise known as "super greenhouse gasses," to function. In a city like Singapore, such ecologically callous survival tools can simply not be sustained.

Luckily for Singaporeans and residents of other cities with warm climates, scientists may have found an environmentally responsible solution to this crisis in the most unlikely of places—300 feet under the Finnish capital of Helsinki.


Running through the center of Helsinki is Esplanadi Park, a popular attraction for both tourists and the city's nearly 600,000 residents. Yet it is what lies below this park that is of special interest: a massive cavern that is used to supply the residents of Helsinki with cheaper, greener, and more efficient air conditioning.

The idea behind Helsinki's facility beneath Esplanadi Park is relatively simple: each night, nearly seven million gallons of water from the Baltic Sea is pumped into the underground reservoir to cool for the evening, and during the day this water returns to the surface and is distributed throughout the inner city to help cool buildings. The water flows to the subterranean cavern at night to cool again, and the cycle resumes again the following day, part of a process known as district cooling.

The science behind district cooling has been around for centuries, finding its roots in the 14th century in a French village

District cooling is a centralized method of production and distribution of "cooling energy," in which pipelines deliver chilled water to industrial and residential buildings in a particular district. These buildings are equipped with special units which allow them to make use of this water to cool the air used in their air conditioning system. Given that air conditioning consumes an estimated 5 percent of global electricity supply, district cooling's ability to circumvent this prodigal use of a precious resource marks a crucial step in our journey to sustainable existence.

The underground lake under Esplanadi Park is the second such district cooling facility in Helsinki and only became operational last month. The first underground lake in Helsinki's Pasila district came online in 2012, but the Esplanadi Park cavern has managed to dwarf its predecessor; its volume is roughly three times that of the Pasila facility.

The science behind district cooling has been around for centuries, finding its roots in the 14th century in a French village called Chaudes-Aigues Cantal, which used wooden pipes to distribute warm water to the villagers. The use of cold water in this process however, was not seen until 1889, when the Automatic Refrigerator Company in Denver, Colorado began operating the world's first district cooling system.

Despite the manifold benefits of using district cooling as opposed to installing individual electricity driven air conditioning units in buildings, the technology was slow to catch on. As with many good things, the main obstruction to its implementation has been money.

District cooling implies a massive infrastructural commitment, whether it is laying pipe, blasting out subterranean caverns, or simply building the actual power plants. Given the uncertain future of the energy market, it is often difficult for local governments to make a case for such enormous development projects in the absence of any certainty regarding its profitability.

"In Helsinki, cooling and heating networks are market based systems," said Helsinki Energy district cooling manager Koski Kosti. "So the question should not be 'Is Finland going to implement this system on a wider scale?' but rather 'Are there other companies building these networks in Finland?' The answer is yes."

Those at Helsinki Energy see the city going completely carbon neutral by 2050

As Kosti noted, despite the reluctance of many municipalities to implement district cooling infrastructure, numerous smaller institutions have committed to the system with astounding results. A case in point is Cornell University, which revitalized its pre-existing cooling system so that it could pump frigid water from nearly 300 feet below Cayuga Lake's surface through the university's pipe system, tapping into an essentially endless supply of eco-friendly air conditioning. The university had previously used heat pumps to cool the water in its district cooling system, but by implementing lake-source cooling, the campus was able to declare an 86 percent reduction in energy use from this previous system.

Like Cornell, the Helsinki city government also sees the incredible benefits of making use of district cooling to help combat energy costs and pollution, while simultaneously meeting the rising demands for air conditioning. According to those at Helsinki Energy, businesses that adopt this method of cooling are estimated by Helsinki energy to cut their carbon dioxide emissions by 80 percent, eliminating over 220,000 pounds of emissions each year per business.

What is more, over 80 percent of district cooling production is based on energy that would have otherwise been wasted, a remarkably efficient feat.

"We aren't generating energy—we are actually recycling it," Kosti said.


It is an ambitious project, but those at Helsinki Energy see the city going completely carbon neutral by 2050 through the use of clean thermal energy processes such as district cooling. Although it is easy to dismiss this grandiose goal out of hand by arguing that a place where temperatures hover well under 60 degrees Fahrenheit for the majority of the year probably doesn't require that much air conditioning, city officials say the demand for AC is quickly rising due to repeat record breaking temperatures in the capital.

It is unlikely these rising temperatures will hamper the district cooling systems, which have already been successfully deployed in much hotter, arid climates such as Qatar, where it is not uncommon for temperatures to approach 120 F in the summer.

In order to meet this rising AC demand while still aiming for carbon neutrality, officials will have to increasingly rely on district cooling and other methods of energy production. The recent completion of the Esplanadi Park facility is evidence of their commitment to this goal.

Helsinki's district cooling system is neither the first nor largest in the world: several other cities have adopted or plan to adopt its methodology, including Toronto, Amsterdam, Sydney and Paris. What makes Helsinki's system unique is its integration of district cooling, district heating, and the production of energy into one system, in a process called trigeneration.

Like its counterpart in cooling, district heating is a remarkably efficient and clean source of thermal energy. The principles behind district heating are very much the same as district cooling, insofar as the centralized distribution of energy goes. The primary difference is that district cooling works by using chilled water rather than electricity to cool buildings, whereas Helsinki's district heating primarily harnesses the waste heat generated in electricity production to heat the buildings. When district heating is combined with the production of electricity (Combined Heat and Power production, or CHP) in a process known as cogeneration, the energy which would normally be lost in production of electricity as waste heat is harnessed and utilized in the process of district heating.

Over the course of email exchanges with Kosti spanning several months, it became increasingly clear that he sees district heating and cooling as the future of energy production, and not without reason.

"DHC [district heating and cooling] is about optimizing energy flows across the city and minimizing total emissions and primary energy in an economically sustainable way," said Kosti. "[Are] there some other demands for future energy systems?"

Salmisaari power plant. Image: KFP/Wikimedia Commons

In 1953, the Helsinki city council voted in favor of creating CHP and DH facilities for the city's use, and the first plant at Salmisaari opened its doors the same year, producing 180 megawatts (MW) of heat with 92 percent efficiency when using coal as fuel. In the last six decades, a number of other CHP plants have opened their doors in Finland, slowly transitioning from the use of coal as fuel to relatively cleaner alternatives such as natural gas. This has not resulted in any loss of efficiency, however, and the newer plants such as Vuosaari B, now generate up to 470 MW of electricity (and nearly the same amount of heat) with over 90 percent efficiency. The choice, it seems, was well worth it: Helsinki energy boasts that the amount of energy annually saved by the use of CHP is enough to heat 500,000 detached homes, a significant reduction considering that Helsinki has roughly 600,000 residents.

As though harnessing the heat wasted in electricity production wasn't efficient enough, the Finnish energy giant ramped up their efficiency even more, turning the process of cogeneration into trigeneration through the use of absorption refrigerators. The point of absorption refrigerators is to produce chilled water with heat, which is accomplished by removing the heat from the refrigerant (water vapor) at a low pressure and then ejecting this heat via the condensation of the refrigerant at high pressure. The result is that hot water vapor is turned into chilled liquid water which is then circulated through Helsinki for use in cooling local businesses and residencies.

There are forecasts that the implementation of district cooling will skyrocket in the near future

The primary impediment to this trigeneration system becoming completely clean is that the source energy used in CHP is still based in fossil fuels such as coal and natural gas. Yet how long this will stay the case remains to be seen. As mentioned earlier, Helsinki has come a long way from its first coal burning CHP plant in 1953. Over the years, Helsinki's new facilities have begun to implement steadily cleaner fuel to produce energy—coal gave way to natural gas and recently natural gas began to give way to recycled solar energy and "pellet fuel."

The technical name for this pellet fueled energy is "biomass co-combustion," which is essentially a fancy way of saying that a shitty old coal plant has been converted to burn biomass instead. This is the case with Helsinki's Salmisaari plant, which began experimenting with burning wood pellets for fuel this year. Biomass co-combustion has been shown to be an ecologically friendly source of fuel insofar as it reduces environmental impacts and fails to deteriorate air quality in cities. If this source of fuel proves to be efficient and is implemented on a city-wide scale, Helsinki may very well reach their goal of carbon neutrality, having created an entirely carbon neutral source of electricity and thermal energy production.

Heating and cooling pump under Katri Vala park in Finland. Image via Helen

The trigeneration process currently being utilized in Helsinki is a localized version of a global future. Despite the forecast for a rapidly rising demand for air conditioning, there are also forecasts that the implementation of district cooling will skyrocket in the near future, especially in and around the Middle East which is expected to represent 40 percent of the district cooling market by 2019. Signs of this shift are already apparent in Qatar and the United Arab Emirates, although whether this trend will continue remains to be seen.

Kosti remains hopeful that the trend will continue to grow, largely due to the innumerable untapped possibilities latent in trigeneration processes. "One must also remember that DHC is not a static system," he told me. "It is developing constantly and in the future the networks will be even more efficient."

The recent explosion of interest in this industry seems to buoy Kosti's observations and given that the world is only getting warmer, we can only hope cities like Helsinki can keep discovering ways to keep us cool.