Urban water bodies like ponds or canals are commonly assumed to provide effective cooling in hot periods. Some of the evidence that feeds this assertion is based on remote sensing observations at relatively large scales. Such observations generally reveal reduced surface temperatures of water bodies during daytime, relative to their urbanized environment. This is to be expected because of the extremely large heat capacity of water in combination with its ability to transport heat away from the water surface by turbulent mixing. However, this also implies that the cooling of a water body may proceed only slowly, which may result in higher night-time surface temperatures. This can lead to water bodies contributing to night-time urban heat islands. The existence of a surface-air temperature gradient is a necessary, but insufficient condition for water bodies to influence their environment. In order to noticeably affect the atmospheric temperature, the cooler or warmer air near the water surface needs to be transported to the urban surroundings. Furthermore, for humans such effects are generally only relevant if they are present at a height of 1-2 m. This requires the fetch over the water to be sufficiently large, so that the internal boundary layer can grow to these atmospheric levels. Furthermore, since not only temperature but also wind (ventilation), humidity and radiation contribute to the heat load of humans, possible cooling or heating effects need to be considered in terms of physiologically meaningful quantities, such as the Physiological Equivalent Temperature (PET). Taking such considerations into account, it is no surprise that the effect of water bodies on their atmospheric surroundings are generally found to be small or even nearly absent when considering evidence from atmospheric measurements.Although there are indications that proper combinations of shading, evaporation and ventilation interventions around water bodies can help to keep their surroundings cooler during summer, it is virtually unknown how these strategies can be optimally combined in designs to counter urban heat effectively. The ‘Really cooling water bodies in cities’ (REALCOOL) project explores possible cooling effects of such combinations for relatively small urban water bodies (characteristic horizontal dimension up to a few tens of meters, maximum depth 3m). The goal is to create evidence-based design guidelines of cooling urban water environments — design prototypes — meant for application in urban and landscape design practice.This presentation will address the cooling effects of the design prototypes evaluated with micrometeorological simulations. Special attention will be paid to the cooling effects of the water bodies in the designs. These were assessed using ENVI_MET version 4.1.3., which allows the user to choose the intensity of turbulent mixing of the water. Comparisons with observations and results from water temperature simulations with a model that assumes perfectly mixed water (the “Cool Water Tool”, CWT) showed that enhancing the turbulent mixing in ENVI_MET strongly improves water temperature simulations. Three design experiments were implemented in ENVI_MET: Exp1) testbeds, which are spatial reference situations derived from an inventory of common urban water bodies in The Netherlands, characterized by the shape and dimensions of the water body and the type of urban environment; Exp2) testbeds in which the area occupied by the water was replaced with the paving materials or vegetation flanking the water body in the original testbed; Exp3) design options with optimal combinations of shading, evaporation and ventilation. All simulations were performed for the same set of meteorological conditions, representing a typical heatwave day in The Netherlands. The initial water temperature depends on the water depth and was determined from simulations with the CWT, run for the same heatwave day repetitively until a quasi-equilibrium state was reached.Model outcomes from ENVI_MET were evaluated for the normally warmest period during daytime (around 15:00 CET) and the coolest period during night-time (around 5:00 CET) in the summer, using water temperature just below the water surface and using air temperature and PET at a height of 1.5m. The cooling effect is defined as the difference in air temperature and PET, respectively, between the different design experiments. The differences were computed from the spatial averages over two areas: the area directly above the water surface (Exp1, Exp3) or its replacement (Exp2) and the area directly bordering the water (like quays and sidewalks, called “pedestrian area” hereafter).The simulations with ENVI_MET suggest that the cooling effect of small water bodies on the air temperature is quite small and often negligible (Exp1-Exp2). This is also true for the optimized designs (Exp3-Exp2). The presence of the water body in the testbeds reduced the daytime air temperature in the afternoon by at most 0.8°C directly over the water body and 0.6°C in the pedestrian area (Exp1-Exp2). PET was reduced by at most 1.8°C and 1.9°C, respectively. During night-time, there was a very slight warming effect in a majority of cases, of at most 0.3°C in air temperature. Warming effects in terms of PET were even smaller. The optimized designs led to a reduction of water temperature of at best 0.5°C, relative to the reference situations (Exp1-Exp3). Air temperature was reduced by at most 0.8°C, relative to the temperature in original testbeds. The Physiological Equivalent Temperature (PET) could be reduced by as much as 7°C at 15:00 CET, but this difference was mainly due to shading effects of trees, not to the presence of water.We conclude that small urban water bodies like the ones tested here may not be the most relevant adaptation measure to create cooler urban environments. Their size may simply be too small to have meaningful thermal effects in their surroundings, in accordance with micrometeorological theory on the development of internal boundary layers. Only for water bodies that are sufficiently large cooling effects may become noticeable. This is then also true for possible warming effects. However, the openness of urban water bodies and their surroundings allows ventilation and provides room for trees that provide shade. The combination of these aspects which both lead to cooling effects was found to dominate favourable changes in daytime PET in particular.
When addressing urban heat problems, climate- conscious urban design has been assuming that urban water bodies such as canals, ditches or ponds cool down their surroundings. Recent research shows that this is not necessarily the case and that urban water bodies may actually have a warming e ect, particularly during late summer season nights. There are however indications that water can have a cooling potential if brought together with the right shading, evaporation and ventilation strategies. Yet, it is not clear how this should be achieved. Knowledge on such spatial configurations should thus be developed and made available to design practice. This challenge is directly addressed by the “REALCOOL” project, a research aiming to define design prototypes showing the physical processes behind the e ective cooling potential of urban water bodies, that design professionals can take as conceptual design frameworks.
Small urban water bodies, such as ponds or canals, are commonly believed to solve urban heat problems but recent research shows that the cooling effect of large urban water bodies on hot summer days is quite limited and can actually induce a night-time warming effect. However, shading, vaporising water and proper natural ventilation might help to keep urban water bodies and their surroundings cooler. But how to combine these strategies in urban design?The ‘Really cooling water bodies in cities’ (REALCOOL) research project explored the most effective combinations of shading, water vaporisation and natural ventilation around small urban water bodies. Optimal cooling strategies were developed for common urban water bodies in temperate climate zones. They are now made available to designers as virtual design prototypes
Op dit moment wordt elektronica veelal actief gekoeld door middel van een geconditioneerde luchtstroom die geforceerd langs een heat sink wordt gevoerd. Het conditioneren van deze luchtstroom kost veel energie en de benodigde luchtbehandelingsapparatuur vergt grondstoffen. Als voorbeeld kan een datacenter dienen waarbij tot wel 30 % van de benodigde energie wordt gebruikt voor het koelen van de elektronica. Dit projectvoorstel richt zich op onderzoek naar een alternatieve methode voor het koelen van elektronica. Het gaat daarbij om het passief koelen van elektronica d.m.v. een gesloten vloeistofcircuit op basis van natuurlijke convectie. Een 3D geprinte heat sink geeft de warmte af aan een circulerende vloeistof. Via een hoger gelegen warmtewisselaar geeft deze vloeistof de warmte aan de buitenlucht af. Deze passieve manier van koelen bespaart energie en grondstoffen en kent andere voordelen die in de inleiding worden genoemd. Fontys heeft een experimentele opstelling gebouwd waarmee testen zijn gedaan. De heat sinks worden voor het experiment 3D geprint in metaal. Het printen biedt de vormvrijheid die vaak nodig is voor een efficiënt ontwerp dat in staat is het vermogen af te voeren. Het onderzoek bij Fontys is uitgevoerd op door het bedrijfsleven aangeleverde cases. De resultaten wijzen uit dat deze passieve manier van koelen in de aangereikte gevallen werkt. Het betreft echter een experimentele opstelling, met maximaal 3 warmtebronnen en beperkte vermogens. Middels dit project Cooling of Electronics by Natural Convection (CENACO) wil Fontys samen met de consortiumpartners onderzoeken of de methode ook op industriële schaal toepasbaar is. Er moeten reële specificaties worden gedefinieerd. De opstelling moet worden opgeschaald. Voor een juist ontwerp zijn thermal-flow simulaties en onderzoek naar de mogelijkheden om heat sinks te printen nodig.
Zuyd University and partners will develop novel coatings that contribute to a reduction in energy consumption of houses and buildings. The built environment currently consumes 46% of all energy, mainly for heating and cooling. A strong reduction is required as part of the transition towards sustainable energy. This is expressed by ambitious targets set by the Parkstad region, which has set itself the target to be energy neutral in 2040. For the Window of the Future Zuyd University (lectoraat Nanostructured Materials) and DWI (post-doc) aims to develop infrared regulating coatings that keep the heat inside in winter and outside in summer. These coatings are expected to strongly contribute to reduction of energy consumption. We will develop coating materials for application on glass windows, which are transparent for visible light to allow maximal daylight entering the building, and simultaneously regulate the transmission and reflection of IR heat. Kriya and Physee (SMEs) will advise Zuyd on technical and economic challenges related to the development of IR regulating glass windows. OMT Solutions (SME) and SGS Intron will advise on characterization and the performance validation. The need for such windows is confirmed by TNO/The Brightlands Materials Center as central challenge in their Optoelectronics program. They contribute largely to this project. Large demonstrator windows will be coated, and installed in test houses for real-life testing and quantification of the energy reduction. Zuyd (lectoraat Solar Energy in the Built Environment) will quantify the impact of smart IR regulating windows on the energy transition by comparing their impact to other available technologies, e.g. solar cells. In this quantification, Zuyd will focus on the Parkstad region. Together with Parkstad and Maastricht University (Ph.D. student), Zuyd will also quantify the socio-economic impact, and promote the societal acceptance of smart IR regulating windows.
