Reducing the carbon footprint of heating and cooling is a key mitigation measure in cities. This means phasing out fossil fuels, electrifying heating, and scaling energy-efficient heating and cooling technologies. By harnessing the power of good design and nature-based solutions, we can limit demand for heating and air conditioners (ACs).

Proven technologies  

  • Solar heater collector and boiler isolated on white Solar heater collector and boiler isolated on white

    Plug-and-play solar water heaters

    Nexol’s photovoltaic (PV) water heaters are a plug-and-play solution that can operate using either heating rods or a heat pump. They can…
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    Plug-and-play solar water heaters

    Nexol Photovolthermic AG
    Solar heater collector and boiler isolated on white
    Getty Images /© KangeStudio

    Nexol’s photovoltaic (PV) water heaters are a plug-and-play solution that can operate using either heating rods or a heat pump. They can also be fitted with a smart controller powered by either alternating or direct current (AC or DC) that autonomously determines whether grid electricity or PV energy should be used – with a preference for the latter. At the technology’s core is a semiconductor element, which absorbs thermal energy from the ambient air and feeds it into a water tank. The company supplies various products. The NEX P40, for example, is a PV water heater that could reduce the electricity needed to heat water by half.

    • Contracting type: For sale
    • Technology level: High
    • Country of origin: Germany
    • Availability: Worldwide
  • Waste heat recovery from buildings Waste heat recovery from buildings

    Waste heat recovery for cooling and heating in buildings

    Recovered waste heat from buildings’ gas boilers is compressed using iHandal’s Heatfuse™ technology. The energy is then channeled into reheating…
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    Waste heat recovery for cooling and heating in buildings

    iHandal Energy Solutions
    Waste heat recovery from buildings
    © iHandal

    Recovered waste heat from buildings’ gas boilers is compressed using iHandal’s Heatfuse™ technology. The energy is then channeled into reheating and/or cooling the building through an energy-efficient heat pump. The Heatfuse™ technology aims to replace inefficient boilers and chillers and use recovered waste heat from AC condenser units or other equipment. As the technology can operate at very high temperatures and deliver water up to 140°C, their biggest market growth is currently in industrial sectors such as food and beverage, health care and pharmaceuticals.

    • Contracting type: For sale
    • Technology level: High
    • Country of origin: Malaysia
    • Availability: Asia
  • EnerTwin: your own home power plant EnerTwin: your own home power plant

    Micro combined heat and power (CHP) technology

    The EnerTwin is a small-sized power cogeneration system that uses a boiler and micro turbine to generate electricity for domestic use. While the…
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    Micro combined heat and power (CHP) technology

    Micro Turbine Technology BV
    EnerTwin: your own home power plant
    © Micro Turbine Solutions

    The EnerTwin is a small-sized power cogeneration system that uses a boiler and micro turbine to generate electricity for domestic use. While the EnerTwin needs energy from a grid to start up, it can operate on fuels such as liquefied petroleum gas (LPG), biogas or biomethane provided decent quality fuels are fed into the system. It is also certified for 23 percent hydrogen mix and models suitable for higher proportions of hydrogen will be released in the future. The EnerTwin currently works with the standard European grid system but a version is planned for the North American market. For cooling needs rather than heating, the EnerTwin would need to be combined with a cooling device such as an absorption chiller to convert the heat output into cooling output. For both power and heating needs, the EnerTwin’s microturbine solution uses off-the-shelf components combined with in-house fuel-saving components.

    • Contracting type: For sale
    • Technology level: High
    • Country of origin: Netherlands (Kingdom of the)
    • Availability: Europe
  • The water chiller in the mechanical room of a large building The water chiller in the mechanical room of a large building

    Absorptive cooling from industrial waste heat

    AGO GmbH provides absorption chillers for industrial use that reuse industry process heat waste for cooling purposes. Using natural refrigerants…
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    Absorptive cooling from industrial waste heat

    AGO GmbH
    The water chiller in the mechanical room of a large building
    Getty Images /© BrianBrownImages

    AGO GmbH provides absorption chillers for industrial use that reuse industry process heat waste for cooling purposes. Using natural refrigerants such as ammonia and water, the absorption chillers can meet the cooling needs of food, beverage, chemical, pharmaceutical and other industries (between +5°C and –40°C). The basic technology behind absorption chillers was patented in 1859. The heat source, such as hot water or steam, causes the absorbent to release the refrigerant gas, which then goes through a condensing process to convert it into a liquid. The liquid refrigerant absorbs heat from the surrounding areas, creating a cooling effect, and then returns to the absorbent to restart the cycle.

    • Contracting type: For sale
    • Technology level: High
    • Country of origin: Germany
    • Availability: Worldwide
  • Intelligent whole house ventilation, heating, cooling and hot water for domestic homes. Intelligent whole house ventilation, heating, cooling and hot water for domestic homes.

    Intelligent whole-house HVAC system with heat recovery

    This product is a fully integrated household solution combining exhaust-air and air-sourced heat pump technologies for ventilation, heating and…
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    Intelligent whole-house HVAC system with heat recovery

    Ventive
    Intelligent whole house ventilation, heating, cooling and hot water for domestic homes.
    © Ventive

    This product is a fully integrated household solution combining exhaust-air and air-sourced heat pump technologies for ventilation, heating and hot water systems. It replaces traditional boilers, hot water cylinders and ventilation units and is suitable for energy retrofits. An internal heat recovery system enables further efficiencies and real-time performance monitoring helps optimize its energy use and performance. A 10 kWh thermal store enables the heat pump to generate heat at night using off-peak electricity and in the summer the heat pump tempers the incoming air to cool down the house without using extra electricity.

    • Contracting type: For sale
    • Technology level: High
    • Country of origin: United Kingdom
    • Availability: United Kingdom
  • This is a factory barrels in industrial areas with aluminum as outer cladding photographed in summer This is a factory barrels in industrial areas with aluminum as outer cladding photographed in summer

    Transpired solar air collector

    Transpired solar air collectors are a type of solar heating technology of relatively simple design using dark-colored perforated metal cladding…
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    Transpired solar air collector

    Conserval Systems Inc.
    This is a factory barrels in industrial areas with aluminum as outer cladding photographed in summer
    Getty Images /© Helmut Feil

    Transpired solar air collectors are a type of solar heating technology of relatively simple design using dark-colored perforated metal cladding mounted on a south-facing wall of a building. The cladding is mounted with a gap between it and the building’s structural wall. As sunlight heats up the metal, a fan pulls outside air through the perforations and into the space behind the cladding. The air that passes through – which can be heated up to 22°C above the ambient air temperature – is drawn into the building and distributed through the ventilation system. Researchers at the National Renewable Energy Laboratory (NREL) and engineers at Conserval Systems Inc. have developed the technology, currently marketed as the SolarWall system. The system has a short payback period and can convert up to 80 percent of the solar energy into usable heat.

    • Contracting type: For sale
    • Technology level: Low
    • Country of origin: United States
    • Availability: Worldwide
  • Nubian life Nubian life

    Nubian vaults

    The association La Voûte Nubienne is addressing the issue of affordable housing in sub-Saharan Africa with a traditional, low-carbon building…
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    Nubian vaults

    La Voûte Nubienne
    Nubian life
    Getty Images /© Dina Moanes

    The association La Voûte Nubienne is addressing the issue of affordable housing in sub-Saharan Africa with a traditional, low-carbon building technique that uses only earth bricks and earth mortar, thereby reducing deforestation pressures. The Nubian Vault structure has thick raw earth walls, which significantly alleviate high temperatures inside the building. Studies on Nubian Vault design in Burkina Faso and Senegal have validated the significant thermal comfort increase compared to houses with corrugated metal roofs. The association trains local builders to create a market for the building technique while adapting it to the climatic conditions and traditional know-how of the Sahel region. Properly maintained, the homes can last for 50 years or more.

    • Contracting type: Service
    • Technology level: Low
    • Country of origin: Egypt
    • Availability: Sahel region
  • Energy efficiency and energy saving concept. Closeup of vacuum solar water heating system on the house metal roof. Energy efficiency and energy saving concept. Closeup of vacuum solar water heating system on the house metal roof.

    Evacuated tube solar collectors

    The product is a solar collector for space and domestic hot water heating using evacuated tubes filled with fluid. Evacuated tube collectors can…
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    Evacuated tube solar collectors

    Hydro Solar Innovative Energy
    Energy efficiency and energy saving concept. Closeup of vacuum solar water heating system on the house metal roof.
    Getty Images /© Lex20

    The product is a solar collector for space and domestic hot water heating using evacuated tubes filled with fluid. Evacuated tube collectors can produce higher temperatures than flat-plate solar collectors as they increase the surface area available to the sun and absorb heat from different angles. They are thin tubes, often made of copper, filled with a fluid such as water. The tubes are situated inside a larger sheet of glass or in plastic tubes. As the system is partially in a vacuum, heat loss to the outside environment is reduced. Hydro Solar’s evacuated tube collectors are particularly suitable for cold Northern climates.

    • Contracting type: For sale
    • Technology level: Medium
    • Country of origin: Canada
    • Availability: Worldwide
  • Modular ICE storage cell for storing cold energy in Commercial building Modular ICE storage cell for storing cold energy in Commercial building

    Modular ice storage cell for cold energy storage in commercial buildings

    this technology offers a modular energy storage solution for HVAC systems. It involves transforming commercial building cooling systems into…
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    Modular ice storage cell for cold energy storage in commercial buildings

    Nostromo
    Modular ICE storage cell for storing cold energy in Commercial building
    © Nostromo

    this technology offers a modular energy storage solution for HVAC systems. It involves transforming commercial building cooling systems into efficient energy storage assets. Using water as the primary medium for energy storage, Nostromo’s IceBrick system consists of a modular unit that integrates with commercial building cooling systems. During periods of low electricity demand, excess energy is used to freeze water within the IceBrick, creating ice as a form of energy storage. When energy demand is high, the IceBrick utilizes the stored ice to provide cooling without the need for additional energy consumption.

    • Contracting type: For sale
    • Technology level: Medium
    • Country of origin: Israel
    • Availability: Israel, United States
  • Ventilated facadefacade Ventilated facadefacade

    Ventilated facade

    Eliane TEC provides ventilated facades that regulate temperature, air and light. The ventilated facades are integrated into a building’s envelope…
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    Ventilated facade

    Eliane TEC
    Ventilated facadefacade
    Getty Images /© Lari Bat

    Eliane TEC provides ventilated facades that regulate temperature, air and light. The ventilated facades are integrated into a building’s envelope to create a gap between the exterior and inner walls. As air circulates between the walls during warm weather, it is heated through a “chimney effect,” whereby air is pushed upward and building temperature reduced. Conversely, during cold weather, the air gap balances the temperature of the building and reduces moisture risk.

    • Contracting type: For sale
    • Technology level: Medium
    • Country of origin: Brazil
    • Availability: Worldwide
  • hvac engineer install heat recovery ventilation system for new house. copy space hvac engineer install heat recovery ventilation system for new house. copy space

    Cooling system heat recovery units

    Boostherm’s heat recovery technology enables waste heat from cooling operations to be recycled for hot water use in residential and commercial…
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    Cooling system heat recovery units

    Ecolactis Boostherm
    hvac engineer install heat recovery ventilation system for new house. copy space
    Getty Images /© Ronstik

    Boostherm’s heat recovery technology enables waste heat from cooling operations to be recycled for hot water use in residential and commercial buildings, or for low temperature space heating. The company claims that 100 percent of the heat normally rejected by cooling system condensers can be recovered to preheat sanitary hot water at 55°C and above. This reduces both energy usage and costs associated with heating and cooling needs. Advanced simulation tools assess total energy needs before installation.

    • Contracting type: For sale/service
    • Technology level: High
    • Country of origin: France
    • Availability: Worldwide

Frontier technologies  

  • Low-tech passive cooling: Modular passive cooling for outdoor use Low-tech passive cooling: Modular passive cooling for outdoor use

    Natural passive cooling for outdoor use and building facades

    This modular passive cooling system harnesses natural elements to create thermal comfort without relying on electricity. Combining evaporative…
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    Natural passive cooling for outdoor use and building facades

    Ant Studio Pvt. Ltd
    Low-tech passive cooling: Modular passive cooling for outdoor use
    © CoolAnt

    This modular passive cooling system harnesses natural elements to create thermal comfort without relying on electricity. Combining evaporative cooling and natural ventilation, the modular design allows for easy installation. The design resembles a beehive structure with cylindrical pots. Water runs over the surface of the cylinders in a circulating system to cool the hot air passing through the terracotta cones. The studio offers customized building facades as well as passive cooling structures for outdoor use, including as art installations in public spaces. To enhance the cooling effect, the outdoor systems incorporate water features such as misters, fountains or water walls, which utilize the evaporative cooling process to lower temperatures further.

    • Contracting type: For sale/service
    • Technology level: Low
    • Country of origin: India
    • Availability: India
  • Vacuum solar water heating system Vacuum solar water heating system

    Low-cost solar heating and cooling

    Solar Polar is a startup that designs and makes low-cost, modular solar thermal technologies for heating and cooling. As an off-grid system,…
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    Low-cost solar heating and cooling

    Solar Polar Ltd
    Vacuum solar water heating system
    Getty Images /© Dovapi

    Solar Polar is a startup that designs and makes low-cost, modular solar thermal technologies for heating and cooling. As an off-grid system, their technology can replace gas and electrical heating and cooling and is specifically adapted to rural areas. Their cooling technology uses an absorption refrigeration system that operates with lower-GWP refrigerants. The company is currently developing a solar heater which stores energy in thermal slats that sit under a concentrator lens on a double-glazed glass panel. When needed, the slats are turned over, and the stored energy is projected downward onto the heater which gives off heat at very long-wave infrared radiation.

    • Contracting type: For sale/service
    • Technology level: High
    • Country of origin: United Kingdom
    • Availability: United Kingdom
  • 3d rendering of photovoltaic cell on solar panel, condenser unit or compressor on rooftop. Eco building with system technology for future. To generate electrical power or direct current electricity. 3d rendering of photovoltaic cell on solar panel, condenser unit or compressor on rooftop. Eco building with system technology for future. To generate electrical power or direct current electricity.

    Compact solar desiccant cooling air conditioner

    Freescoo is a compact plug-and-play solar air conditioning system for ventilation, heating and cooling of buildings. Its key feature is its…
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    Compact solar desiccant cooling air conditioner

    Solarinvent
    3d rendering of photovoltaic cell on solar panel, condenser unit or compressor on rooftop. Eco building with system technology for future. To generate electrical power or direct current electricity.
    Getty Images /©RonFullHD

    Freescoo is a compact plug-and-play solar air conditioning system for ventilation, heating and cooling of buildings. Its key feature is its compactness, with every component available in a single casing. The sun’s heat is used to drive the cooling process based on the phenomenon of adsorption, which enables the extraction of moisture from the air through microporous materials. Water is used as a refrigerant and heat is stored in the form of dry silica gel (a desiccant material). The device can be integrated with a solar PV panel for off-grid applications.

    • Contracting type: For sale/collaboration
    • Technology level: Medium
    • Country of origin: Italy
    • Availability: Italy
  • Linear electric motor for energy-efficient heating and cooling Linear electric motor for energy-efficient heating and cooling

    Linear electric motor for energy-efficient heating and cooling

    Cooling and heating devices are often limited in their efficiency. Traditional rotary motor technology, which is central to compression…
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    Linear electric motor for energy-efficient heating and cooling

    Magtor Compressor Limited
    Linear electric motor for energy-efficient heating and cooling
    © Magtor

    Cooling and heating devices are often limited in their efficiency. Traditional rotary motor technology, which is central to compression requirements in many cooling and heating devices, has been around for many years and achieved few efficiency improvements in the past decade. Magtor aims to replace the traditional rotary-based electric motors that currently dominate the market with their direct linear electric motor that can achieve higher levels of energy efficiency. The technology uses long-distance magnetic attraction and repulsion to deliver linear power on both the outstroke and the backstroke of the motor. Magnetic plates on both sides of a fixed electromagnet are connected via a shaft and move from side to side based on single-phase voltage. As this proprietary technology removes the need for a crankshaft, the company claims that energy efficiency can be improved by more than 30 percent. The technology is currently in the deployment phase.

    • Contracting type: For sale/licensing
    • Technology level: High
    • Country of origin: Monaco
    • Availability: Austria

Horizon technologies  

  • Two air source heat pumps installed outside of new and modern city house, green renewable energy concept of heat pump Two air source heat pumps installed outside of new and modern city house, green renewable energy concept of heat pump

    Cooling device combining vapor compression, evaporative cooling and renewable energy

    Gree, the world’s largest manufacturer of residential ACs, and Tsinghua University have developed a cooling technology with a climate impact five…
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    Cooling device combining vapor compression, evaporative cooling and renewable energy

    Gree + Tsinghua University
    Two air source heat pumps installed outside of new and modern city house, green renewable energy concept of heat pump
    Getty Images /© brebca

    Gree, the world’s largest manufacturer of residential ACs, and Tsinghua University have developed a cooling technology with a climate impact five times lower than currently available ACs. The technology combines vapor compression refrigeration, evaporative cooling and ventilation with renewable energy sources and free cooling whenever possible. The technology’s various cooling and ventilation modes operate automatically, either individually or in parallel, depending on external weather conditions. Key elements that enable a lower carbon footprint are the integration of photovoltaics that reduce dependency on the grid, as well as an efficient compressor and low-GWP refrigerant.

    • Contracting type: For collaboration
    • Technology level: High
    • Country of origin: China
    • Availability: N/A
  • Cooling surface coating harnessing the power of the sun Cooling surface coating harnessing the power of the sun

    Cooling surface coating harnessing the power of the sun

    SolCold’s cooling coating film uses sunlight radiation to cool down objects. The stronger the sun, the stronger the cooling effect. This active…
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    Cooling surface coating harnessing the power of the sun

    SolCold
    Cooling surface coating harnessing the power of the sun
    © SolCold

    SolCold’s cooling coating film uses sunlight radiation to cool down objects. The stronger the sun, the stronger the cooling effect. This active cooling coating can be applied to any surface exposed to sunlight, such as cars, reducing the need for air conditioning. This technology can save over 50 percent in cooling consumption and costs while reducing carbon emissions. During tests, the air inside a car whose rooftop and dashboard were coated with the film was found to be 13°C cooler than in one without. The patented technology is based on “anti-stokes fluorescence” technology that combines nanotechnology, physics and chemistry. Four main layers of films and filters are applied to the targeted surface: (i) a smart filter layer that blocks sunlight’s heating wavelengths and amplifies “useful” wavelengths; (ii) an active cooling layer that uses solar radiation; (iii) a cooling matrix layer; and (iv) a reflective and radiative cooling layer. The technology is currently in the development stage.

    • Contracting type: For collaboration
    • Technology level: Medium
    • Country of origin: Israel
    • Availability: Israel, Singapore
  • No-refrigerant heat pump component No-refrigerant heat pump component

    No-refrigerant heat pump component

    Blue Heart has developed an engine for use in heat pumps that replaces the cold circuit part that otherwise contains refrigerants. Blue Heart’s…
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    No-refrigerant heat pump component

    Blue Heart Energy
    No-refrigerant heat pump component
    © Blue Heart Energy

    Blue Heart has developed an engine for use in heat pumps that replaces the cold circuit part that otherwise contains refrigerants. Blue Heart’s solution consists of a sealed tubular circuit filled with helium, which has zero GWP. Using thermoacoustics, the technique creates sound waves in a closed circuit to generate heat and cold. The compact size of the product compared to the conventional cold circuits in heat pumps means that the final devices are smaller and more affordable. The technology works with various heat sources, including ground, brine, water, air, photovoltaics and district heating.

    • Contracting type: For collaboration
    • Technology level: High
    • Country of origin: Netherlands (Kingdom of the)
    • Availability: N/A
  • Close-up of black full inverter heat pump outside in the garden, near wooden pool house on a sunny day. Lens flare on the image. Close-up of black full inverter heat pump outside in the garden, near wooden pool house on a sunny day. Lens flare on the image.

    Electrocaloric heat pump

    Heat pumps often use compressor technology that relies on refrigerants which contribute to global warming. Solid-state heat pumps, by contrast,…
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    Electrocaloric heat pump

    Fraunhofer IPM
    Close-up of black full inverter heat pump outside in the garden, near wooden pool house on a sunny day. Lens flare on the image.
    Getty Images /© NAPA74

    Heat pumps often use compressor technology that relies on refrigerants which contribute to global warming. Solid-state heat pumps, by contrast, include electrocaloric systems that can operate using fluids such as water instead of refrigerants and which are significantly more energy efficient. When an electric field is applied to electrocaloric materials, the material heats up and the heat is dissipated via a heat sink, cooling the material down again. When the electric field is removed, the material instead cools down and can absorb thermal energy from a heat source. The effect is reversible, so that the heat pump can be used for both heating and cooling. Researchers at the Fraunhofer Institute for Physical Measurement Techniques (IPM) are working on the development of electrocaloric heat pumps, which they believe to be a disruptive technology for the industry that will completely replace compressor-based heat pumps and mitigate global warming impact from heating and cooling.

    • Contracting type: For collaboration
    • Technology level: High
    • Country of origin: Germany
    • Availability: N/A

Innovation examples

  • Panorama of desert town Naein in Iran Panorama of desert town Naein in Iran

    Shavadoon natural ventilation systems in Iran

    Shavadoon is an Iranian indigenous technique for natural ventilation developed in the city of Dezful. It consists of an underground cavity that…
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    Shavadoon natural ventilation systems in Iran

    Panorama of desert town Naein in Iran
    Getty Images /© mathess

    Shavadoon is an Iranian indigenous technique for natural ventilation developed in the city of Dezful. It consists of an underground cavity that utilizes the Earth’s average temperature to provide thermal comfort in the hot and semi-humid climate. Shavadoons have traditionally been used as resting places, or for storing and refrigerating food. They are constructed between 5 and 12 meters underground where temperatures are around 20°C cooler than the outside temperature during the hottest days of summer. They consist of various components, including a wide entrance located in the courtyard and a stairway leading to the main hall, which serves as the central activity area. Shavadoons also feature small rooms separated from the main hall by a maximum one-level difference. Some Shavadoons have interconnected rooms with vertical canals for light and ventilation purposes. Integrating this traditional technique into modern apartments can help reduce energy consumption and modern studies have investigated the optimal Shavadoon shapes to offer maximum ventilation rates.[67,68]

  • City road, Casa de Campo. Madrid Spain City road, Casa de Campo. Madrid Spain

    Giant “wind garden” to cool Madrid

    A giant “wind garden” inspired by ancient Middle Eastern wind towers is being built in a park in Madrid, Spain. The architectural structure…
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    Giant “wind garden” to cool Madrid

    City road, Casa de Campo. Madrid Spain
    Getty Images /© apomares

    A giant “wind garden” inspired by ancient Middle Eastern wind towers is being built in a park in Madrid, Spain. The architectural structure applies nature-based solutions and has a spiral form made of mosses and ferns. This draws down cool breezes from above the treetops into the garden and nearby streets, acting as a giant air conditioner. The park structure is designed to lower local temperatures by 4°C and reduce cooling needs in nearby buildings. The 14.5 hectare park, to be developed by landscape architecture firms West 8 and Porras Guadiana, will open in 2025.

  • Beautiful high angle panoramic view from Copenhagen city to Sweden on a sunny October day 18th, 2020. Beautiful high angle panoramic view from Copenhagen city to Sweden on a sunny October day 18th, 2020.

    District cooling lowers Copenhagen’s cooling emissions by 70 percent

    In Copenhagen, Denmark, district cooling has proven to be a highly effective solution for reducing CO2 emissions and cutting costs in comparison…
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    District cooling lowers Copenhagen’s cooling emissions by 70 percent

    Beautiful high angle panoramic view from Copenhagen city to Sweden on a sunny October day 18th, 2020.
    Getty Images /© Scharvik

    In Copenhagen, Denmark, district cooling has proven to be a highly effective solution for reducing CO2 emissions and cutting costs in comparison to conventional cooling methods. The city has experienced increasing demand for cooling due to rising temperatures, leading the Greater Copenhagen Utility Company (HOFOR) to implement the district cooling system. This comprises an underground network of pipes and multiple cooling plants that primarily use seawater to chill the water supplied to customers. During the winter months, the system utilizes seawater pumped to the cooling plant to produce chilled water for customers, which is considered zero-carbon cooling. Seawater with a temperature of 6°C or lower is directly used to cool the water. However, in the summer months when seawater is not sufficiently cold, energy is required to cool the water. The system serves commercial buildings, such as banks, hotels, department stores and offices, as well as providing year-round cooling for servers and other processes. The district cooling system is continually expanding to accommodate future customers and meet growing demand. HOFOR opened the first cooling plant in 2010 and a second in 2013. In 2019, a new cooling plant was built in the Ørestad area to provide climate-friendly cooling to numerous office buildings.

Good design can go a long way

In ancient Persia, windcatchers – or bâdgirs – were a common architectural element. These towers would catch the breeze and channel it down through the house to cool the interior. Vernacular architecture around the world has provided…
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Good design can go a long way

In ancient Persia, windcatchers – or bâdgirs – were a common architectural element. These towers would catch the breeze and channel it down through the house to cool the interior. Vernacular architecture around the world has provided thermal comfort through natural heating, cooling and ventilation solutions for centuries.

In many places, we are now constructing buildings in ways that make mechanical devices indispensable, adding to the growing climate impact of heating and cooling (see box 2.1).[27] Mechanical heat recovery systems have replaced natural ventilation in larger buildings and ACs have largely enabled us to disregard local climatic factors during building design. Meanwhile, the growing size of buildings has led to the replacement of local building materials in favor of concrete. Concrete can give rise to overheated indoor spaces in tropical regions during hot seasons, necessitating further use of ACs.[28]

Vernacular architecture elements can still play a major role in heating and cooling decarbonization today. This approach involves reestablishing a balance with the natural elements and reintroducing tried and tested techniques in modern ways, through passive design. To encourage this process, an increasing number of countries are now establishing mandatory or voluntary building energy codes and energy efficiency standards. Active and passive strategies, particularly for reducing heating demand, are popular in North America and Europe.
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Passive heating and cooling

In cold or moderate climates, optimizing solar energy absorption through building and window orientation, insulation and improvements to the building shell are common strategies for reducing heating demand. Heat from the sun can also be absorbed…
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Passive heating and cooling

In cold or moderate climates, optimizing solar energy absorption through building and window orientation, insulation and improvements to the building shell are common strategies for reducing heating demand. Heat from the sun can also be absorbed by and transferred to building elements.[29] To stay cool in summer, the simple use of shades, window screens and appropriately sized openings can often be sufficient.

In hot climates, insulation and the careful selection of sustainable construction materials with the right thermal properties could reduce the energy required for cooling by 10 to 40 percent.[30] Depending on the region, passive cooling can also involve ventilation shafts, green roofs or reflective roof coatings and double-glazed windows as well as careful consideration of building layout.[31,32]

Energy demand for heating and cooling can also be managed at consumer level. Technology can influence behavior and nudge us toward better use of heating and cooling devices. Examples include metering systems that increase awareness and offer financial incentives for reduced energy usage.


Box 2.1 GHG emissions from heating and cooling

Heating is the largest end-user of energy, accounting for 40 percent of energy-related CO2 emissions. In buildings, heating accounts for 80 percent of the direct CO2 emissions. Fossil fuels still dominate, with renewables making up just 11 percent in 2022.[33] Meanwhile, global heat consumption is expected to increase by 6 percent between 2022 and 2027.[34] While cooling is largely electrified, the heating sector is lagging behind in electrification.

Whether for the homes, transport or industry, demand for cooling is also growing. Devices such as ACs are deeply embedded in society. In many countries, they are a symbol of rising income levels and comfort, with global warming contributing to their demand. By 2050, around two-thirds of households worldwide could have an AC (figure 2.2).[35] In 2020, GHG emissions associated with space cooling and refrigeration represented over 10 percent of global emissions.[36]

Energy usage accounts for 70 percent of AC emissions. The rest is due to refrigerant leakage.[37] While refrigerants such as hydrofluorocarbons (HFCs) are not major greenhouse gases, they are the fastest growing globally.[38] Refrigerants with low GWP are available on the market. However, this is a sector where policy intervention is crucial. Without policy intervention, emissions from AC and refrigeration are projected to rise 90 percent above 2017 levels by 2050.[39]


 
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Heating and cooling retrofits

Natural heating, cooling and ventilation is particularly important in emerging economies with rapidly growing cities as new construction offers opportunities to consider energy efficiency from the outset. Well-designed cities could save…
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Heating and cooling retrofits

Natural heating, cooling and ventilation is particularly important in emerging economies with rapidly growing cities as new construction offers opportunities to consider energy efficiency from the outset. Well-designed cities could save 25 percent of heating and cooling energy usage.[40] Meanwhile, cooling and heating retrofits are an important option in industrialized countries and cities with aging building stock. However, the rate of green retrofitting of existing buildings is low. For instance, although 75 percent of European buildings are energy inefficient, only between 0.4 and 1.2 percent of the whole stock is renovated annually.[41]

In addition to retrofitting and enhancing energy efficiency of buildings, heating and cooling systems themselves can benefit from retrofits. Replacing conventional heating systems with heat pumps can be challenging, generally necessitating renovation for their installation. Often, significant infrastructure is already in place – central heating, piped gas networks and boilers for apartment and office buildings. Combining hybrid heat pumps with existing gas-fired boilers can minimize efficiency drops. Another transitional alternative includes retrofitting existing heating systems by replacing fossil fuel boilers with natural gas or biomass boilers fueled by agricultural and forestry residues.

However, depending on the feedstock source, biomass boilers could exacerbate competition for agricultural land needed for food production. Electrification of heating, such as through heat pumps, is a far better option from a climate perspective. Furthermore, electrification allows for integration with renewable energy sources.
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Inefficient technologies are still dominant

Scaling the use of efficient heating and cooling technologies is a key measure for reducing the climate impact of these functions. While passive design and retrofits may be more sustainable ways of managing demand, progress in these…
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Inefficient technologies are still dominant

Scaling the use of efficient heating and cooling technologies is a key measure for reducing the climate impact of these functions. While passive design and retrofits may be more sustainable ways of managing demand, progress in these directions is not fast enough in some of the world’s most rapidly expanding cities.[42,43,44]

Minimum energy performance standards, energy efficiency labelling and incentive programs are important measures for stimulating uptake of energy-efficient technologies.[45] But generally, top-down regulation is sparse and, despite better alternatives being available on the market, the most commonly sold units are often several times less efficient.[46]

While passive design and retrofits may be more sustainable ways of managing demand, progress in these directions is not fast enough in some of the world’s most rapidly expanding cities.

It is difficult to estimate the GHG mitigation potential of more energy-efficient technologies. But studies have shown that the world can avoid up to eight years of global emissions (at 2018 levels) over the next four decades through efficiency improvements and transitioning to refrigerants with a low GWP.[47] For instance, more efficient ACs could reduce cooling energy demand by 45 percent.[48]
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The growing impact of heat pumps

Over the past five years, global sales of heat pumps have grown at an average rate of 10 percent per year. [49] Europe is seeing the fastest growth (figure 2.3) and nearly half of the…
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The growing impact of heat pumps

Over the past five years, global sales of heat pumps have grown at an average rate of 10 percent per year. [49] Europe is seeing the fastest growth (figure 2.3) and nearly half of the installed capacity today is in North America with the other half in China. In colder regions, like Scandinavia, heat pumps already meet between 40 and 60 percent of heating needs.[50]

ACs and heat pumps are technically similar. However, heat pumps can offer both heating and cooling. They can therefore replace both fossil fuel boilers and inefficient ACs. The climate mitigation potential of heat pumps relies largely on the technology that it is replacing, the share of renewable energy in the electricity grid and the type of refrigerant used. However, the International Energy Agency (IEA) estimates that replacing fossil fuel boilers with heat pumps could reduce GHG emissions by 500 million metric tonnes by 2030.[51]

Heat pumps and ACs transfer heat from one location to another through compression and decompression of a heat-absorbing refrigerant. Such systems can require ductwork, with pipes and tunnels running through the building. They can also be ductless, in which case they are suited for retrofitting buildings or adding heating, ventilation and air conditioning (HVAC) such as geothermal HVAC to specific rooms. Heat pumps draw heat from air, water or geothermal sources, often via separate indoor and outdoor components.[52] While they are more efficient than ACs, they do have drawbacks such as noise, outdoor space use and exhaust heat emission which exacerbates the urban heat island effect.[53]

The need to reduce heating and cooling energy consumption has fostered innovative new technologies. Electrocaloric heat pumps could offer refrigerant-free cooling in the future, but are still at R&D level. Other solutions, such as solar-driven heating and cooling units, could become a more common alternative sooner, especially considering that cooling units are needed most in solar-intense regions and seasons. Examples include solar concentrator collectors that are integrated with absorption chillers to provide the chilled water used in ACs, or ACs that are sold packaged with accompanying solar panels and converters. However, solar-driven systems are space consuming and typically not the most efficient or cost-effective solutions. Scaling renewable energy grid integration should be a priority.
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Alternative refrigerants

A major problem of ACs and heat pumps is the negative climate impact from refrigerants. Although regular maintenance can prevent many leaks, gases may escape when the units are repaired or decommissioned. Naturally, leakage is less of a problem…
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Alternative refrigerants

A major problem of ACs and heat pumps is the negative climate impact from refrigerants. Although regular maintenance can prevent many leaks, gases may escape when the units are repaired or decommissioned. Naturally, leakage is less of a problem when using refrigerants with a lower GWP.

The production of harmful chlorofluorocarbons (CFCs) as refrigerants in ACs and heat pumps has been phased out under the globally agreed Montreal Protocol on Substances that Deplete the Ozone Layer. While their most common replacement – HFCs – have no impact on the ozone layer, they are still potent greenhouse gases. Therefore, the Kigali Amendment to the Montreal Protocol aims to also phase out HFCs.[54]

Replacing refrigerants with a high GWP with better alternatives could avoid 0.1 degrees Celsius of global warming by 2050.[55] Several promising alternatives have emerged, including natural refrigerants such as ammonia, propane (R290) and CO2. However, some refrigerants face challenges related to flammability and cost, and require technological improvements. 

Refrigerant leakage represents less than a third of the GHG emissions from cooling technologies. The rest is due to energy usage. Therefore, the use of low-GWP refrigerants alone will not be sufficient to tackle the overall climate impact from the sector.[56] However, switching to better alternatives is a no-regret solution with low marginal abatement costs, and alternatives are available.
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From individual to district heating and cooling

As cities grow large and dense, centralized energy distribution systems such as district heating and cooling supply becomes an increasingly relevant alternative. Compared to individually installed heat pumps, boilers and ACs, district systems…
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From individual to district heating and cooling

As cities grow large and dense, centralized energy distribution systems such as district heating and cooling supply becomes an increasingly relevant alternative. Compared to individually installed heat pumps, boilers and ACs, district systems can reduce energy usage and costs while enabling renewable energy integration.[57] Cities like Copenhagen, Denmark and Geneva, Switzerland have combined their district systems with heating from external heat pumps and natural cooling from surrounding seawater and lakes. Next-generation district heating and cooling systems can provide both heating and cooling simultaneously by recycling waste heat from chillers.

As cities grow large and dense, centralized energy distribution systems such as district heating and cooling supply becomes an increasingly relevant alternative

District cooling consumes between 20 and 30 percent less power than conventional alternatives. Efficiency is, however, highly dependent on the availability of natural heat sinks and vapor absorption systems as well as larger chiller systems.[58, 59] District heating systems are more common than district cooling. In 2021, more than 10 percent of buildings’ heat demand was met by district heating networks globally.[60] However the implementation of both district heating and cooling is still relatively limited and installation is uneven across the world.[61]
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Equal access to cooling is a growing concern

Between 1.8 and 4.1 billion people in the Global South are believed to lack access to residential cooling.[62] In addition to structural measures to reduce people’s vulnerability to extreme…
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Equal access to cooling is a growing concern

Between 1.8 and 4.1 billion people in the Global South are believed to lack access to residential cooling.[62] In addition to structural measures to reduce people’s vulnerability to extreme heat, achieving equity in terms of cooling necessitates the provision of public spaces to cool down. Air-conditioned cooling centers, such as libraries and malls, or even dedicated chilled facilities during extreme heatwaves, are becoming important means for adapting to climate change in cities.

But local and public cooling can also be provided through urban greening.[63] Trees and water bodies that offer temperature relief and shade are great nature-based alternatives with a multitude of co-benefits. As the urban heat island effect takes its toll on increasingly warmer cities, equal access opportunities to cool down are imperative for maintaining decent living standards and saving lives.
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Leapfrogging done right

Emerging technologies present an opportunity for countries to make significant progress toward low-carbon heating and cooling. Countries experiencing a surge in sales of ACs can benefit greatly from adopting low-GWP refrigerants and…
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Leapfrogging done right

Emerging technologies present an opportunity for countries to make significant progress toward low-carbon heating and cooling. Countries experiencing a surge in sales of ACs can benefit greatly from adopting low-GWP refrigerants and high-efficiency heaters and coolers. However, the technology choices are numerous and require ambitious investment. The right solutions must urgently be made affordable and accessible to avoid a wrong leapfrog approach and cause a lock-in effect for suboptimal refrigerants and technologies.[64]

Similarly, the energy to fuel these solutions must be carefully chosen. For instance, many residential and district heating systems are increasing the share of biomass, often using wood pellets and wood chips. The risk of exacerbating competition for land needed to produce biomass feedstock must be considered. As appliances and systems for heating and cooling last longer than a decade, converting fossil fuel boilers to systems that burn biomass could result in a potentially damaging fuel lock-in for European countries.[65]

Wood is still the largest biomass energy source today. However, some scientists and environmental groups have raised concerns that simply cutting down trees and burning them can release more CO2 emissions and be even more harmful than burning fossil fuels.[66] Growing biomass on already cleared land with measures in place to restore soil carbon can mitigate this challenge to some extent.
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