The Interview
Q&A with María Moya
1. Can you explain how the study was conducted and why it was important to assess different parts of Spain, building types (existing and new-build schools) and orientations (south and east facing)?
Overheating in schools is becoming an increasingly important issue across Europe as climate change leads to more frequent, longer and more intense heatwaves. Classrooms that were designed for historical climate conditions are now experiencing indoor temperatures that can negatively affect comfort, health and learning performance. We wanted to better understand how much dynamic solar shading can contribute to addressing this challenge.
Spain provides an excellent case study because it encompasses a wide variety of climate zones, from the mild oceanic climate of the north to continental and hot Mediterranean climates in the centre and south. This diversity allowed us to evaluate the effectiveness of dynamic solar shading under very different environmental conditions.
In this first phase, the research was based on dynamic thermal simulations using DesignBuilder with the EnergyPlus calculation engine. A second phase is planned to validate these findings through measurements in real occupied school buildings, allowing us to compare the simulated results with actual building performance.
We also wanted the study to reflect the diversity of the existing school stock. For that reason, we analysed both existing and newly designed school buildings. Since schools are mainly occupied during the morning and early afternoon, we focused on south- and east-facing classrooms, where solar gains have the greatest impact during teaching hours. This allowed us to evaluate realistic operating conditions and obtain conclusions that are directly applicable to school design and refurbishment.
Ultimately, the study offers designers, school managers and policymakers practical evidence that passive solar control should be considered a fundamental component of school design and refurbishment strategies, regardless of the specific climate.
2. The study found that dynamic solar shading reduced overheating by an average of 73%. From a building performance perspective, how significant is that result?
Before discussing the results, it is important to understand how overheating was assessed. In this study, we used Cooling Degree Hours (CDH), a widely recognised indicator that measures not only how often indoor temperatures exceed a comfort threshold, but also by how much. In other words, it combines both the duration and the intensity of overheating into a single metric. This provides a much more meaningful assessment of occupants' thermal exposure than simply counting the number of hours above a given temperature.
The simulations evaluated overheating using two reference thresholds, 26°C and 28°C, which represent different levels of thermal discomfort. Looking at degree-hours above these temperatures allows us to compare how effectively different solar shading solutions improve indoor comfort.
The average reduction in overheating across all the scenarios analysed was 73%, which is a very significant improvement in building performance. However, this average also reflects the diversity of climates included in the study. The percentage reduction naturally varies depending on local climatic conditions.
For example, in the Atlantic climate of Bilbao, the most effective external shading system completely eliminated overheating above 28°C, achieving a 100% reduction in cooling degree-hours. In the much hotter southern climate, represented by Almería, the same solution still reduced overheating above 28°C by 79%. Similar trends were found for the 26°C threshold, with reductions of 82% in Bilbao and 61% in Almería.
These results highlight an important point. In the warmest climates, mechanical cooling will still be necessary during the hottest periods. However, dynamic solar shading can dramatically reduce both the frequency and severity of overheating, as well as the energy required for cooling. In milder climates, the combination of high-performance automated external solar shading, designed to achieve low total solar energy transmittance (gtot), together with appropriate natural ventilation - as modelled in this study - may even avoid the need for air conditioning altogether under many summer conditions.
3. What do the findings tell us about the causes of overheating in schools? Does this suggest solar gains through glazing are a primary driver?
The study confirms that overheating in schools cannot be attributed to a single factor. It results from the interaction between outdoor climate, solar gains, internal heat gains, the thermal characteristics of the building and the way it is ventilated and operated.
Schools are actually a particularly interesting building type because classrooms have a very high level of internal gains caused by occupants. A relatively large number of pupils and teachers occupy a comparatively small space for several hours, generating a significant amount of heat. In many cases, these internal gains are of the same order of magnitude as the solar gains entering through the glazing.
One of the most interesting findings of the study is that, by introducing effective dynamic solar shading, solar gains can be reduced to the point where internal gains become the dominant source of heat in the classroom. This demonstrates how much unwanted solar radiation can be prevented from entering the building and highlights the effectiveness of external solar shading as a passive cooling strategy.
The research also underlines the importance of natural ventilation. In our simulations, automated solar shading was always combined with an appropriate ventilation strategy. These two passive measures work together: solar shading limits heat gains during the day, while ventilation helps remove accumulated heat whenever outdoor conditions allow it.
4. Many people immediately think of air conditioning when discussing overheating. Does this research suggest schools should focus first on preventing heat from entering buildings?
Absolutely. One of the clearest messages emerging from this research is that preventing heat from entering the building should always be the first step in any overheating strategy.
This aligns closely with the Ladder of Cooling, a framework recently promoted by European Solar Shading Association (ES-SO) to illustrate the hierarchy of measures that should be considered before relying on mechanical cooling. The concept is simple: the most sustainable cooling energy is the energy that never needs to be produced.
The first priority is therefore to minimise heat gains through passive measures, such as well-designed building envelopes, effective dynamic solar shading and appropriate glazing. The next step is to make use of natural cooling opportunities, particularly night-time and cross ventilation whenever climatic conditions allow. Only once these passive strategies have been optimised should mechanical cooling be considered to deal with the remaining loads.
5. External shading systems delivered the strongest results. Why were these more effective than internal blinds and screens?
The difference lies in where the solar energy is stopped.
External shading systems intercept solar radiation before it reaches the glazing. Part of the solar energy is reflected back to the outside, while the energy absorbed by the shading device is largely dissipated to the outdoor environment through convection and long-wave radiation which is stopped by the glass. As a result, much less heat enters the building.
Internal blinds and screens work differently. By the time sunlight reaches an internal shading device, it has already passed through the glazing and entered the building. Although the blind or screen reflects part of the radiation back towards the window, it also absorbs a significant amount of solar energy. Because the shading device is located indoors, most of this absorbed heat is re-emitted into the room as long-wave thermal radiation and transferred to the indoor air by convection, increasing the cooling load.
The glazing itself also plays an important role. While it is relatively transparent to incoming solar short-wave solar radiation, it is much less transparent to the long-wave heat radiation emitted by the warmed blind or screen. As a result, a large proportion of this heat is trapped inside the room rather than escaping back outdoors.
That does not mean internal blinds and screens are ineffective. They still improve thermal comfort and can make an important contribution, particularly in existing buildings where external shading cannot easily be installed. However, when the objective is to minimise overheating and cooling demand, preventing solar energy from entering the building is always more effective than trying to manage it once it is already indoors.
6. Is overheating fundamentally a solar gain problem, a ventilation problem, or a combination of both?
It is undoubtedly a combination of factors. Overheating results from the interaction between solar gains, internal heat gains, ventilation, the thermal performance of the building envelope, occupancy patterns and the local climate. There is no single solution capable of addressing all these aspects on its own.
The results of our study reinforce the importance of adopting an integrated design approach. Dynamic solar shading, natural ventilation, insulation, glazing and the overall building envelope should not be considered as independent elements, but as components of a single strategy designed to work together.
Overheating requires a holistic approach in which passive strategies are designed to co-operate, creating comfortable, resilient and energy-efficient learning environments with the lowest possible energy demand.
7. The study found an average 43% reduction in cooling demand. What are the implications for school energy consumption, operating costs and sustainability objectives?
Reducing cooling demand by 43% means more than lower energy consumption. It also reduces peak cooling loads, allowing smaller HVAC systems to be installed. This lowers not only operational energy use and associated carbon emissions, but also the embodied carbon associated with manufacturing, transporting and installing mechanical cooling equipment.
Although the recent Guidehouse study focused on the residential sector, it reached a similar conclusion: reducing cooling demand through passive measures has benefits throughout the whole life cycle of the building. Our research shows that the same principle also applies to school buildings, where effective dynamic solar shading can substantially reduce both the cooling load and the environmental impact of mechanical cooling systems.
8. Many European countries, including the UK, are experiencing increasingly frequent heatwaves. What lessons from this Spanish study should school leaders, architects and policymakers take away?
Southern European countries have lived with hot summers for generations, so solar shading has long been part of climate-responsive architecture. As heatwaves become more frequent across Europe, this experience offers valuable lessons. However, these solutions are still far from being used to their full potential. In many buildings, shading devices are operated manually, and once air conditioning is available, occupants often feel less need to adjust them. As a result, solar shading is frequently underused, even though it could significantly reduce cooling loads before mechanical systems are needed.
9. Are school design standards evolving quickly enough in Spain to address rising temperatures and future climate conditions?
They are certainly evolving, but probably not quickly enough. There is growing recognition of the need to update climatic data, give greater priority to passive design strategies and explicitly address summer comfort and overheating in building regulations. This is a very positive direction.
However, there are still mixed signals. Some recent renovation programmes for schools and healthcare buildings have placed a strong emphasis on installing air conditioning, while giving much less attention to passive measures that reduce cooling demand in the first place. We believe these approaches should be complementary, with passive solutions such as dynamic solar shading considered as the first line of defence and mechanical cooling used only for the remaining demand.
10. If there is one message you would like school leaders, architects and policymakers to take from this research, what would it be?
The main message is that we should reduce the need for cooling before increasing the cooling capacity. Our study shows that dynamic solar shading is one of the most effective passive strategies for reducing overheating and cooling demand. In milder climates, it may even avoid the need for mechanical cooling under many conditions. In warmer climates, it can substantially reduce the size and operating time of HVAC systems.
