Is your building future weatherproof?
Future weather will bring increasingly higher temperatures and humidity. This poses a challenge for the indoor climate in our buildings, as cooling and ventilation system design is based on historical weather data that is more than 10 years old.
If we don’t change our design practices, our buildings will overheat.
In this article, Frederik Winther – Senior Specialist Manager in Ramboll Denmark – along with his colleague Dragos Bogatu, explore the challenges that the future climate poses to our buildings’ ventilation and air conditioning systems and outline the change in approach to design and solutions needed to mitigate them.
Frederik works for almost 12 years at Rambøll Danmark’s main office in Copenhagen. Started as a consulting engineer in the Department of Indoor Climate and HVAC. After 3 years at Rambøll he started his PhD project on Intelligent Glazed Facades. Did research on the potential of facades in future low energy buildings as well as experimental investigations on the performance of advanced facades. He has developed numerical calculation methodologies for advanced facade technologies such as PCM in glazing, dynamic g-/U-value technologies.
Having been awarded his PhD degree he was employed at Rambøll working in greater depth with facade design and numerical analysis of thermal building simulations and CFD calculations. His work consists of consultancy work for many projects.
We talk with Frederik about Ventilation and Air Condition System Design Adaptation to Climate Change and the subsequent challenges, approach and solutions.
Original article was posted by Frederik in LinkedIn https://www.linkedin.com/feed/update/urn:li:activity:7208776945730265089/
Ventilation and air conditioning system design adaptation to climate change: Challenges, approach, and solutions
Future weather will bring increasingly higher temperatures and humidity. This poses a challenge for the indoor climate in our homes, but especially in large buildings, as cooling and ventilation system design is based on historical weather data that is more than 10 years old. If we don’t change our design practices, our buildings will overheat. A change in mindset but also policy recommendations are required.
Expected changes in the Danish climate.
Denmark’s future climate won’t only include more frequent storms, heatwaves, and heavy rainfall. It will also become warmer, with increased humidity. This is evident from DMI’s new Climate Atlas for Denmark’s weather [1] based on projections from the UN’s climate panel and Aalborg University, Department of the Built Environment, covering the period from 2030 to 2100.
Annual temperatures are expected to rise by over 3°C. Looking at the number of heating degree days (HDD) – a measure of coldness – they will decrease by almost 30%, from 3319 HDD in the period 2001-2010 to 2271 HDD in 2090. Humidity will also increase significantly, as shown in Figure 1, based on data projections from IPCC [2], [3]. The number of hours per year with water content higher than the current 12.5 g/kg (which we currently design our ventilation systems for) will rise from 67 hours (~9 workdays) to up to ~250 hours (~34 workdays) by 2040.
Figure 1. Humidity levels as a function of projected weather data in Copenhagen,
Denmark compared to the Danish design reference year [2], [3], [4].
At the same time, rising temperatures and humidity will impact our perception of heat. Higher humidity makes it harder for the skin to dissipate heat. When combined with high temperatures, heat transfers from the air to the skin, making us feel significantly warmer.
Both existing and future buildings must adapt to significantly different conditions than what we are used to. Failing to account for the warmer and more humid weather, will have detrimental consequences for the indoor climate and the cooling and ventilation systems we rely on.
Homeowners are already grappling with warmer and more humid weather.
If anyone doubts that these changes affect the indoor climate of our buildings, they need only ask homeowners. In the survey ‘Danskerne i det byggede miljø’ [5], conducted by Realdania and Videnscentret Bolius, over 12% of residents in homes built after 2000 report that their homes are too hot. Especially during the summer, overheating is a real issue. The challenge lies in larger window areas present in new buildings and changes in architectural preferences, which do not provide the same opportunities for natural ventilation and solar shading as older homes do.
Mechanical ventilation and cooling are not common practice in Danish homes.
Therefore, the indoor climate challenges, in newer residential construction, cannot be directly compared to large-scale buildings. However, it does emphasize the consequences of a changing climate on our indoor environment and the need for change in design approaches.
Historical weather data does not consider climate change.
Despite projections showing our climatic future, we still use 10-year-old historical weather data when designing cooling and ventilation systems. While we gradually adjust the standards we design for, the changes are insufficient given the climate shifts we anticipate. We risk having buildings where cooling and ventilation systems cannot maintain satisfactory air quality and humidity levels for their intended use. The consequence is overheating.
This poses problems for building occupants, affecting well-being, health, and cognition. It’s also a challenge for building operators, as operating undersized systems becomes more expensive. Lastly, it’s an environmental concern because energy-intensive systems consume more than they should.
Consider an average office building as an example. Calculations suggest that without other adjustments, we should increase the size of cooling surfaces in ventilation systems by up to 25% and enhance cooling system efficiency by up to 50% by 2040 compared to current Danish standards. Even by 2030, within the lifespan of new installations, the increase is significant.
In some cases, simply increasing performance won’t suffice. In extreme cases, existing systems may need improvement or complete replacement with more powerful ones to handle future weather conditions. On the other hand, undersized cooling and ventilation systems are costly to operate due to high energy expenses and maintenance costs.
The solution is a climate resilient design.
Climate resilience refers to the ability of the designed systems and assets to withstand shocks and stresses as well as the ability to bounce back following future climate predictions related to climate change. A resilient building, Figure 2, is able to withstand and recover from disruptions generated by climate change, globalization, and urbanization [6], [7], [8]. It can shelter its occupants and ensure comfort and productivity even during periods of high temperature and humidity, increased pollution, and pandemics. The design and plan for maintenance and refurbishment need to accommodate the influence of current and future weather data, which need to cover the expected lifespan of the building, typically minimum 50 years. However, a resilient design also requires data collection and analysis to ensure that the building performance is not compromised.
Figure 2. Climate sensitive (A) versus climate proof (B) design.
A climate resilient design can thus be fostered by:
- Planning and designing buildings, systems and assets that are flexible/adaptable to respond to future climate conditions such as extreme climate events i.e., heat waves, extreme rainfall, outdoor pollution, and which have spare capacity.
- Defining indoor thermal requirements such as dress code tolerances, comfort criteria, and energy use based on an open dialogue with the asset-owner allows for designing a building that is both flexible and energy efficient.
- Capturing data for building performance and user experience to better understand the potential performance gap in relation to indoor climate and energy use, especially during extreme weather events.
Resilient design framework.
- Case-by-case optimization is required to find the technology that is suitable for both climate and regulations. The framework encompasses an optimization design process in response to contemporary, medium, and long-term future changes in climate. Building resilience is then assessed for each architectural design and system combination as a function of climate following the latest scientific findings, as shown in Figure 3. The analysis and hence the building resistivity to climate change and associated risks, is based on the severity of outdoor thermal conditions, security of energy supply and variability in zonal indoor temperature, humidity and pollution [9].
Figure 3. Resilient building design (adapted from IEA EBC Annex 80 [8]; icons from icons8 [9]).
The design process of efficient heating, ventilation, and air conditioning starts from the expected climate conditions, e.g. hot and humid or cold and dry, and the frequency, intensity, and duration of extreme events, e.g. heatwaves and/or outdoor pollution. This leverages the knowledge of specialized engineers and architects to select adequate passive and active technologies for the climate at hand and hence saves time and resources on iterative quantitative assessments.
The qualitative thought process behind the selection of the appropriate technologies depending on their expected performance is shown in Figure 4. The goal is to select technologies that mitigate the impact of the outdoor environment, adapt to a changing climate, and even restore the building to equilibrium after a potential extreme event [10]. For example, thermal mass can absorb heat gains and delay an increase in air temperature. Dynamic solar shading can reduce the impact of solar heat gains, while an effective heat sink such as the ground or night sky can provide sustainable heat dissipation. Still, thermal mass and sky radiative cooling may not be effective in locations with insignificant diurnal temperature swings such as extremely hot and humid climates.
However, a low operational carbon assumes the proper operation of combined passive solutions, active systems, and renewable energy sources. Once an appropriate combination is selected, the power of simulation tools and analyses is leveraged, ensuring an optimized system.
Nevertheless, another critical factor is the optimization criteria, i.e. the limits imposed on the indoor environment. In a changing climate, it is not only our systems and design but also our mindsets that require adaptation. A mixed-mode based control [11] can be used which combines tight temperature limits generated by the expectation of a mechanically cooled building with relaxed temperature limits created by the human body adaptation and control over the environment (e.g. clothing and window opening). Relaxed temperature limits may be the solution during shoulder and summer seasons, but especially during heatwaves when building systems are not capable of removing the entire cooling load. The relaxed temperature limits can then be offset by elevated air movement produced by fans [12] even in hot and humid climates in combination with air conditioning systems [13]. Granted that feasibility studies of environmental and productivity impacts are conducted; the remaining question is still the time lag required between operation transitions to avoid diminishing occupant expectations with the indoor environment.
Figure 4. Performance of resilient technologies against heatwaves, power outages, and air pollution [10], [14], [15].
Missing link: incorporating a risk factor for future weather into our standards.
Currently, voluntary sustainability certifications like DGNB [16] already value the ability to ‘provide information about the building’s thermal robustness’ by conducting indoor climate simulations based on future weather data. Unfortunately, this isn’t yet a requirement in our building regulations, even though we already have the necessary future weather data projections.
The industry and our policymakers should implement changes to ensure the building sector is resilient. The solution is straightforward: our technical standards should adapt to work with both historical weather data and a risk factor for future weather, considering years like 2050 and 2100.
Moreover, a change in expectation and indoor environment recommendations is required, with design criteria for mixed-mode approaches, especially with respect to future climates. By doing so, we can design both our existing and new buildings to handle climate change. This way, we can adhere to the Paris Agreement [17] and reduce the building sector’s impact on climate change and curtail greenhouse gas emission and hence global warming.
We owe it to ourselves, our children, and the environment.
References
[1] Dansk Meteorologisk Institut, “Klimaatlas.” Accessed: Jun. 15, 2024. [Online]. Available: https://www.dmi.dk/klima-atlas/om-klimaatlas
[2] K. Calvin et al., “IPCC, 2023: Climate Change 2023: Synthesis Report. Contribution of Working Groups I, II and III to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change [Core Writing Team, H. Lee and J. Romero (eds.)]. IPCC, Geneva, Switzerland.,” Intergovernmental Panel on Climate Change (IPCC), Jul. 2023. doi: 10.59327/IPCC/AR6-9789291691647.
[3] Meteotest AG, “Meteonorm.” 2024.
[4] Danish Meteorological Institute, “Danish reference year.” 2019. [Online]. Available: https://www.dmi.dk/publikationer/
[5] Videncentret Bolius and Realdania, “Danskerne i det byggede miljø 2023,” 2023.
[6] S. Attia, P. Holzer, S. Homaei, O. B. Kazanci, C. Zhang, and P. Heiselberg, “Resilient Cooling in Buildings – A Review of definitions and evaluation methodologies”.
[7] Y. Alfraidi and A. H. Boussabaine, “Design Resilient Building Strategies in Face of Climate Change,” vol. 9, no. 1, 2015.
[8] C. B. Field, V. Barros, T. F. Stocker, and Q. Dahe, Eds., Managing the Risks of Extreme Events and Disasters to Advance Climate Change Adaptation: Special Report of the Intergovernmental Panel on Climate Change, 1st ed. Cambridge University Press, 2012. doi: 10.1017/CBO9781139177245.
[9] C. Zhang et al., “IEA EBC Annex 80 – Dynamic simulation guideline for the performance testing of resilient cooling strategies – Version 2”.
[10] C. Zhang et al., “Resilient cooling strategies – A critical review and qualitative assessment,” Energy and Buildings, vol. 251, p. 111312, Nov. 2021, doi: 10.1016/j.enbuild.2021.111312.
[11] J. J. Aguilera, D.-I. Bogatu, O. B. Kazanci, C. Angelopoulos, D. Coakley, and B. W. Olesen, “Comfort-based control for mixed-mode buildings,” Energy and Buildings, vol. 252, p. 111465, Dec. 2021, doi: 10.1016/j.enbuild.2021.111465.
[12] European Committee for Standardization, “EN 16798-1:2019, Energy perfromance of buildings – Ventilation for buildings – Part 1: Indoor environmental input parameters for design and assessment of energy performance of buildings addressing indoor air quality, thermal environment, lighting and acoustics.” 2019.
[13] M. G. Kent et al., “Energy savings and thermal comfort in a zero energy office building with fans in Singapore,” Building and Environment, vol. 243, p. 110674, Sep. 2023, doi: 10.1016/j.buildenv.2023.110674.