Introduction

Cooling in Southern Europe has never been a luxury. With hot summers part of the climate and the impact on human productivity well known, building tradition and societal customs solved the challenge: thick walls, shutters, deep shade, narrow alleys, and siesta. It is the north that still needs to adapt. Towns, buildings, and habits developed and were designed to keep humans warm. Hot days were rare and tropical nights the exception; despite extremely hot summers occurring more often, [1] cooling did not make it into standard design. This needs to change to accommodate the new reality of each summer being the coldest ever experienced — in hindsight [2].

The past weeks' headlines support the point. France recorded its hottest May Day on record, a national average of 24.4°C [3]; the same week, the United Kingdom logged 34.8°C, beating its all-time May record by a full two degrees [4]. And the summer is yet to come.

This trend comes at a cost for humans. The 2026 Lancet Countdown estimates roughly 62,000 heat-attributable deaths in Europe in 2024, with heat-related mortality rising in 99.6% of monitored regions [5]. And the burden falls unequally, as the poorest are least able to keep their homes cool in summer or warm in winter [6]. This makes it a topic for the policy agenda: indoor environmental quality becomes a matter of public-health responsibility. Without policymakers picking it up, individuals will act by adding individual air-conditioning to attics and facades — and this creates an additional problem, as the individual solution is often the least efficient, least equitable, and least attractive available. An increase in household air-conditioning, if left uncoordinated, will add gigawatts of electricity to peak summer demand [7]. The International Energy Agency (IEA) has long warned that cheap and inefficient cooling equipment will be one of the largest drivers of global demand for electricity to 2050 [8].

It does not have to be the case. Architects and engineers know it to be unnecessary if old building traditions are used and passive measures are exhausted first [9][10], followed by the most efficient active cooling solutions, with individual cooling units treated only as a last resort. A new thought is emerging that contributes to the cause: active cooling, done well, wastes nothing. The waste heat it rejects from one person's building becomes the energy source for another's heating and hot water [10][11].

This article will show that efficient cooling technology is available and argue the main challenge to be one of societal and policy innovation [12].

Cooling is not the problem; cooling done badly is

Cooling done right can be achieved without a huge increase in energy demand [13]. The common fear that an ever-warmer Europe results in walls of humming air-conditioners and a summer electricity crisis is real. It will only turn into reality if the need for cooling remains uncoordinated, left to the individual decision-maker. 

Cooling done badly is a problem. Cooling done right is achieved by a mix of available solutions and technologies combined most efficiently. It’s the coordinated approach to build a system that makes all the difference. And such an integrated heating and cooling system effectively increases comfort, costs little to run, and can even give energy back. 

The challenge remains undisputed. The IEA projects that, without efficiency action, energy demand for space cooling will more than triple by 2050, the global stock of air conditioners rising from 1.6 to 5.6 billion. And it’s not the sheer number that makes the problem; it is the fact that most often cheap and inefficient units are purchased. The same IEA report finds that today's average unit runs at less than half the efficiency of the best available technology [8]. Across Europe, cooling degree-days were already almost four times higher in 2022 than in 1979; the totals remain largest in the Mediterranean (Greece rose from 169 to 421, Italy from 76 to 289), but the steepest relative increases fall where the stock is least adapted [14]. A University of Oxford study names Switzerland, the United Kingdom and Norway as the countries facing the world's most dramatic relative rise in cooling days. And they are ‘dangerously unprepared’ as their buildings were designed to hold heat in, not to get it out [15].

What is an air conditioner other than a heat pump in reverse mode? Where the heat pump moves energy available outside the house to the inside to heat, a cooling machine takes the energy from the inside of the house and moves it to the outside. A refrigeration cycle, the basis of both machines, can heat and cool, and depending on which side you use, the very same device is a fridge, an air-conditioner, or a heat pump. Cooling and heating are two sides of the same coin. This very fact is the key to everything that follows: a machine that makes cold necessarily makes heat at the same time, and the question is only whether we waste that heat or use it.

‘Renovation first’ was never quite right — and now it is wrong

A recent survey documents the problem worsening with every heatwave: a deeply retrofitted, airtight, heavily glazed building with no ventilation or cooling concept can overheat dangerously [16]. The north-south gap makes the exposure plain: only 5–10% of German homes have any active cooling, against 50–70% in Spain and Italy. It will be the northern, heating-optimised, insulated stock that is most likely to become a summer trap.

The conclusion is not ‘don't insulate’; the conclusion is that the envelope and the technology must be optimised together to provide indoor environmental quality in summer and in winter. Shading, glazing ratio, thermal mass and night ventilation belong in the same design conversation as the heat pump, the storage and the controls. ‘Renovation first’ should give way to ‘optimise the system for thermal comfort’.

The staircase: passive, efficient, individual

If cooling is a public responsibility, the order in which we reach for solutions matters as much as the solutions themselves. The cheapest, cleanest and most durable cooling is the cooling you never have to generate. Hence, we should start with passive measures first. Before relying on active cooling, the planner, the architect, and cities must do the work. Buildings need to be designed for low heating and low cooling demand. Start from the outside: orientation to the south reduces heating demand; external shading (shutters, blinds, overhangs) stops solar gain before it enters. Trees next to buildings can block the sun; street trees and green space lower local air temperature and break the urban heat island. Then continue on the inside: thermal mass, light surfaces, cross-ventilation and night cooling were simple passive cooling measures, and they still work. The southern European city has known this for centuries.

The potential is large and measured: a Swiss study found that window shading and night ventilation together could cut cooling demand by 84% under a mid-century climate [17]. These measures cost the least over a building's life; they serve everyone inside rather than only those who can run a unit, and they carry no operating emissions. They belong in every new build as standard and must be considered in every renovation. And even this is not a new idea; if anything, it’s not known well enough: the United Kingdom's ‘cooling hierarchy’, embedded in the London Plan, already requires designers to exhaust passive measures before resorting to active cooling [18].

Efficient active cooling second. Passive measures shrink the cooling load but are not enough during multi-day heat waves and the increasing number of tropical nights. The second stage is active cooling done properly: efficient, low-emission, and planned at the scale of the building or the block rather than the window. A heat pump in cooling mode typically delivers three to four units of cooling for one unit of electricity. But it also generates four to five units of waste heat. If this heat can be recovered in a hot water tank, an individual ground source or a shared ambient temperature thermal network, it contributes to a low-energy demand, renewable and circular energy system. In combination with local photovoltaics (PV), the electricity to cool the building is generated when the sun makes cooling most necessary. 

This coordinated approach is superior to individual cooling solutions bought and installed in panic mode for three reasons: 

• efficiency (design cooling into the building, fed by a low-temperature thermal network, rather than bolting on a box);
• noise (centralised or well-sited plant instead of a facade of rattling condensers); and
• appearance (integrated cooling is often invisible, freeing roof and facade for photovoltaics or greenery).

And yet, the better solution requires more coordination, making it less attractive when a fast solution is perceived as necessary. 

While they should be considered last, individual units serve a purpose. If fast solutions are needed, especially when it comes to protecting vulnerable groups (elderly, chronically ill) in existing buildings, individual air conditioning will remain a genuine, sometimes life-saving necessity. The same applies if changes to the building envelope are not feasible for time or cost reasons. 

The problem is not this solution per se; the problem is making the individual unit the default. When cooling is left entirely to individuals, the least efficient machines, with various designs, clutter our facades, often resulting in high running costs and high sound emissions. As cooling needs continue throughout the day, uncoordinated, inefficient operation puts load on grids at the very moment they are most stressed. This challenge is real: the UK's Climate Change Committee warns that up to 92% of existing homes could overheat under 2°C of warming by 2050, and of course the householders will respond by adding cooling equipment [18]. If policy accepts the obligation to protect citizens against overheating, it has to create a legal framework that sets a preference for passive and collective solutions and avoids incentivising individuals to make a short-term, immediate choice. 

_{Figure 1.  Visual clutter as a result of individual air-conditioning choices. Source: Yonhap / EHP, taken from The Guardian for illustrative purposes.}

Cooling innovation, part one: waste no heat

Cooling deserves to be designed rather than improvised. To provide cooling, a refrigerant cycle must move the heat from the inside of the building, lift it to a higher temperature level and discharge it outside. If this is done via air, that heat is lost and even contributes to urban heat islands. If the heat is discharged through liquid and fed into the ground or a thermal network, either the ground serves as a seasonal heat battery, or the network transports the energy to another user for which it becomes the energy source for heating/hot water. If you need cooling, you always have heat for free [10].

And this is the case more often than not. See Figure 2 for a conceptual illustration: hotels, hospitals, spas, and many other buildings need cooling and heating at the same time in the same building. They can cool their rooms while heating hot water; offices can shift heat from a north-facing part (that needs cooling) to the southern part of the building (that needs heating). Waste heat from cooling for some becomes the energy source for space heating and domestic hot water for others. With gas still responsible for a large share of hot-water production, supplying that hot water from otherwise-wasted heat is a low-hanging fruit of decarbonisation. It applies to those areas of Europe with little heating but tremendous cooling and hot water demand. The principle scales beyond a single building: link buildings with opposite load profiles through a low-temperature, or ‘cold’, network, and one building's rejected heat becomes its neighbour's heat source, making separate cooling and heating plant redundant. The city becomes a thermal balancing system [12]. The European Environment Agency points to exactly this: ambient-temperature thermal networks (also called fifth-generation district heating and cooling, 5GDHC), and reversible heat pumps paired with on-site PV are a route to cutting a district's total energy demand [19].

_{Figure 2: Ambient loop network collecting the waste heat from cooling, serving it as a heat source for all. Source: Qvantum Industries AB.}

Cooling innovation, part two: rely on sun and wind

If we use more cooling, the load on the grid increases, and our grids are not made for that [20]. To avoid cooling overloading the grid, we have to adapt, and with a modern approach we can. Cooling demand peaks when the sun is highest, and so does PV generation. Cooling and solar power are, almost literally, made for each other: the load rises with solar irradiation that produces the electricity to meet it [21]. Adding wind, which often fills the evening and the shoulder seasons, and the match improves further.

_{Figure 3: Illustration of the coincidence between cooling demand and PV generation. Source: own, based on claude.ai modelling [21].}

Two things turn that coincidence into a system. The first is thermal and electrical storage. A well-insulated building, a chilled-water or ice tank, or simply the structure's thermal mass lets a cooling system run hard when solar power is abundant and coast through the evening peak without drawing from the grid: the heat pump system becomes a thermal battery. The second is controls that read weather forecasts, prices, and occupancy to shift cooling into the solar hours and pre-cool before the peak, flattening the very demand curve the uncoordinated approach would spike. There is a small caveat: either the building is solid enough to also store the cold or has enough space to store the cold in a water tank and distribute it later through fan coils. If these conditions are met, a fleet of cooling systems is not a burden on a renewable grid but a source of the flexibility it needs.

Put the two pillars together, and the arithmetic changes completely. In the individual solution case, two machines are installed to do two jobs, wasting half the energy. The integrated approach does both jobs with one system, recovers the heat, and runs the whole thing on sun and wind (see table 1 for a comparison).

_{Table 1: Comparison of uncoordinated and coordinated approaches to cooling (Illustration, no real project). Source: own.}

The solutions exist but lack policy guidance

Efficient heat pumps that cool, heat and recover waste heat are commercially available today; low-temperature networks run in more villages and cities, photovoltaics, storage and smart controls are mature, and costs are falling fast. ‘Cooling done right’ can be bought off the shelf. The challenge is on policymakers and society: how can we make the good outcome the default rather than the lucky exception?

There is a concrete and unflattering example of the gap. Europe has known since 2013 how to count the renewable energy a heat pump delivers in heating mode. For cooling, no equivalent definition or accounting method was put in place, even though the Renewable Energy Directive referred to cooling dozens of times [13]. Efficient, renewable-powered cooling that recovers its own waste heat is among the most useful things a building can do. But for years it has been close to invisible in the statistics that steer policy and funding. What is not measured is not rewarded, and what is not rewarded is not built at scale.

The moment to fix this is now. And it is not an easy task. The first EU strategy on heating and cooling did put the topic on the agenda [22] but did not lead to decisive action. The system integration strategy touched on the need to take an integrated approach, but was left without a trace shortly after publication [23]. The heating and cooling plans, mandatory from the Energy Efficiency Directive, remain insufficiently transposed and implemented [24]. In 2026, a third attempt can be observed: the European Commission is preparing a dedicated EU Heating and Cooling Strategy, with publication planned for the second half of 2026, explicitly intended to address integrated infrastructure planning, district heating and cooling, and waste-heat recovery [25].

It is the first chance in a decade to give cooling the standing heating already has. But policy must go beyond adding another chapter on accounting for renewable cooling. The strategy must recognise that renewables-based, integrated heating and cooling is the holy grail of an efficient energy system catering to the comfort needs of its users. It requires a definition, an accounting method for statistics (accounting for the parallel provision of heating and cooling), and business models that reward waste-heat recovery and ambient-temperature networks. Building codes and renovation rules should set a preferred order: passive, then efficient active, then individual rather than leaving it to a homeowner in a heatwave. Such a preference gains in importance when it comes to poorer households. Access to cooling should not depend on income [26], and a preference order that needs to be adhered to by all especially protects the poor and vulnerable.

Conclusions

Cooling is no longer optional in the part of Europe built to stay warm, and rising heat has turned it from a question of comfort into one of survival and of fairness. But cooling is not a problem if it is done right. Exhaust passive measures first, efficient active cooling next, individual solutions as the last resort. Drive the whole system with sun and wind and always recover the heat that cooling rejects. The technologies to do all of this exist today. The challenge is the process of deployment by humans: the societal habits, the difficulty of finding agreement, the distribution of expertise across industries. Underlying this is the challenge of a decisive policy framing to make the efficient, equitable path the obvious and economically viable one. ‘Optimise for comfort’ must be the new norm, addressing the new normal of a warming world through architectural design principles, an optimised envelope and machines efficiently providing heating, cooling and hot water at the same time.

References

[1] Gerstengarbe, F.-W.; Werner, P. C. (1992): The time structure of extreme summers in Central Europe between 1901 and 1980, Meteorologische Zeitschrift No. 6, 1992, p. 285 - 289.

[2] We experience the “coolest summer of the rest of our lives” is a framing widely attributed to the expectations, that all future summers will be warmer than the current on. 

[3] Kothari, R. (2026): Seven deaths linked to record-breaking May heat in France. In: The Watchers. 26.5.2026. Download on 18.6.2026

[4] Paddison, R. (2026): ‘Mind-bogglingly crazy’: Europe’s deadly, early heatwave is smashing records. In CNN, 26.5.2026, Download on 18.6.2026

[5] Kriit H, Chen-Xu J, Semenza J et al. (2026): The 2026 Europe report of the Lancet Countdown on health and climate change: narrowing window for decisive health action. The Lancet Public Health, 2026; 11, e386-e407. Download on 16.6.2026

[6] Paniello-Castillo, B., Chen, ZY., Shartova, N. et al. Socio-economic factors impact vulnerability to and burden of heat- and cold-related mortality in Europe. Nat. Health 1, 647–656 (2026). Download on 16.6.2026

[7] Wanjiku, R. (2026): Heatwaves: Will air conditioning save Germany? Heinrich Böll Stiftung EU, 10.2.206. Download on 17.6.2026

[8] IEA (2018): The future of cooling. Download on 17.6.2026

[9] On vernacular building traditions for passive cooling see https://en.wikipedia.org/wiki/Vernacular_architecture

[10] Nowak, T. (2026): If you need cooling, you get the heat for free! Article posted on LinkedIn. 19.1.2019

[11] Roaf, S. (2001): Eco House: A Design Guide.

[12] IDM Energiesysteme (no year): Waste heat as a heat-pump source and Qvantum Industries (2026): Thermal energy networks. Downloaded on 16.6.2026

[13] Nowak, T. (2018), What is renewable cooling? Article on LinkedIn, 25 August 2018. Downloaded on 16.6.2026

[14] Eurostat (2024): Statistics explained: heating and cooling degree days. Download on 16.6.2026

[15] Miranda, N.D., Lizana, J., Sparrow, S.N. et al.(2023): Change in cooling degree days with global mean temperature rise increasing from 1.5 °C to 2.0 °C. Nat Sustain 6, 1326–1330 (2023). Download on 16.6.2026

[16] Cantz, B. (2026): Hitze-Falle Altbau: Warum Dämmen ohne Lüftungskonzept im Sommer versagt, Telepolis 18.6.2026, Download on 18.6.2026

[17] Silva, S.; Eggiman, S.; Fiertz, L. et al. (2022): Opportunities for passive cooling to mitigate the impact of climate change in Switzerland. In: Building and environment. Vol. 208 Download on 16.6.2026

[18] Climate Change Committee 2026): A Well-Adapted UK - The Fourth Independent Assessment of UK Climate Risk (CCRA4-IA). Download on 16.6.2026

[19] European Environment Agency (2022): Cooling buildings sustainably in Europe: exploring the links between climate change mitigation and adaptation, and their social impacts. 10.11.2022. Download on 15.6.2026

[20] Pandiani, L. (2021): Rising energy demand for cooling. Download on 16.6.2026

[21] Coincidence of solar irradiation and cooling demand illustrated using claude.ai and material compiled in Mert Erbey, M; Filiz Tumen Ozdil, N. (2026): Forecasting the European Union's space cooling potential using the cooling degree-day factor (1970–2024) Accessed on 16.6.2026

[22] European Commission (2016): An EU Strategy on Heating and Cooling. COM/2016/051 final. 16.2.2016 Download on 16.6.2026

[23] European Commission (2020): Powering a climate-neutral economy: An EU Strategy for Energy System Integration. 8.7.2020 Download on 16.6.2026

[24] Energy cities (2025): EU tracker – local heating and cooling plans. The state of play in member states Online ressource

[25] European Commission (2025): EU Heating and Cooling Strategy — call for evidence. 28.5.2025. Download on 15.6.2026 Final strategy to be published in Q2 2026.

[26] Cornelis, M. (2026): Too hot to cope: why cooling must become Europe’s next social right. In: EUSEW Newsblog, 27.4.2026. Download on 18.6.2026