At first glance, district heating and cooling (DHC) sounds like the most modern of technologies. However, these networks of pipes that convey heated or cooled water into and between buildings have been around as far back as ancient Rome[i], where they were used to heat thermal baths, temples, even greenhouses.
DHC has come a long way since then, especially when used in tandem with combined heat and power (CHP) plants that produce heat and electricity simultaneously[ii]. Two factors in particular make these interrelated processes so successful and sustainable: (1) their greater energy efficiency compared to conventional fossil fuel plants and (2) their adaptability to a variety of fuel sources.
While the Drawdown Organization[iii] focuses only on district heating (not cooling), we’ll examine both technologies in this post. If district heating supplies only 10% of global heating demand by 2050, it can save an estimated 9.5 gigatons[iv] of CO2 emissions. Even with an estimated implementation cost[v] of $460 billion USD, the $3.5 trillion saved in energy costs makes the effort worthwhile in both economic as well as environmental terms. When we add cooling into the mix, the possibilities become even more exciting.
How It Works
In simplest terms[vi], district heating and cooling (DHC) connects buildings that use thermal heating and cooling through networks of pipes leading to and from a central plant (or plants). Localized heat exchangers and refrigeration units replace separate boilers and air conditioning units[vii], ensuring that individual buildings can regulate their own thermostats even though they are supplied collectively. Ideally, the energy generated comes from renewable, low- or zero-carbon sources like biomass or geothermal; currently, however, most of the energy comes from fossil fuels[viii].
Why It’s So Environmentally (and Economically!) Effective
Most modern DHC infrastructure, particularly in the Americas[ix] and Europe[x], emerged during the oil crises of the 1970s, when embargoes caused petroleum prices to skyrocket. Thus, one of the most compelling arguments in favor of DHC for people and organizations who are less invested in sustainability is its potential to increase a nation’s energy independence and thus its energy security. (In fact, the IEA’s 2002 policy paper on DHC[xi] lists sustainability and security as its top two benefits: “District heating and cooling (DHC) is an integrative technology that can make significant contributions to reducing emissions of carbon dioxide and air pollution and to increasing energy security.”)
Even when oil prices stabilized, DHC remained popular because of its vastly increased efficiency compared to conventional fossil fuel plants and individualized energy systems. At best, fossil fuel plants operate at an efficiency somewhere around 35-40%[xii]. Most of the energy lost is “waste” heat, with the rest lost during transmission and distribution from plants to buildings.
In comparison, DHC and the CHP (Combined Heat and Power) plants have an average efficiency around 65-75%[xiii]. This increased efficiency lowers both CO2 emissions and energy costs throughout the supply chain. When individual households and businesses pay less for energy, those savings not only result in a better standard of living but also enable consumers to spend more on other goods, thereby driving up national GDP[xiv].
Yet, economics also offers the most common resistance to DHC, since it requires significant up-front infrastructure investments[xv] if no system is already in place. As the IEA notes, focusing solely on short-term profits[xvi] make DHC seem like a difficult ask; however, return on investment can occur as quickly as 6 years[xvii], as observed in the Danish capital of Copenhagen.
Examples of District Heating
Copenhagen in particular (and Denmark more broadly) is the standout example when it comes to DHC. In 2016[xviii], 98% of the capital’s buildings were connected through DHC, with 63% of the country’s total population getting their heat from it. Having committed to ending fossil fuel consumption by 2050, the Danes recognize that DHC is the way forward; even their vaunted wind power comprises only 8%[xix] of their entire energy production (45% of yearly electricity). Ultimately, the nation looks to replace all non-renewable energy sources with heat pumps[xx] powered by wind, solar, and other means.
A lesser-known DHC system[xxi] currently provides cooling to some of the most famous buildings in the world: Paris’s Musées du Louvre and d’Orsay (as well as the famous department store Galaries Lafayette, the Paris Opéra, the National Assembly, and the Ministry of Defense). Over 52km of pipes connect over 500 buildings in the French capital, drawing water from six cooling plants located underground. Compared to buildings using conventional air conditioning, these buildings emit 20% fewer CO2 emissions and have 30% less refrigerant leakage. Equally important, DHC works particularly well with historic buildings whose preservation guidelines prevent the installation of traditional A/C units.
In the U.S., DHC/CHP systems predominantly serve industrial functions[xxii], providing power and heat to factories. Increasingly, however, hospitals and universities are taking advantage of their existing building networks to switch to DHC/CHP. In 2008, DHC powered 72 downtown districts and 330 university campuses. Presumably, that number has only grown higher in the last decade.
District heating may only rank 27th[xxiii] on Drawdown’s top 100 solutions to reverse climate change, but that ranking is mainly predicated on its extremely small share (0.01%) of current global heating demand. As more and more cities recognize the potential of this highly efficient and adaptable technology, however, its importance is likely to grow.
[i] Drawdown, 99.
[iv] Drawdown, 99.
[vii] Drawdown, 99.
[xv] Drawdown, 99.