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A strong heat load in buildings and cities during the summer is not a new phenomenon. However, prolonged heat waves and increasing urbanization are intensifying the heat island effect in our cities; hence, the heat exposure in residential buildings. The thermophysiological load in the interior and exterior environments can be reduced in the medium and long term, through urban planning and building physics measures. In the short term, an increasingly vulnerable population must be effectively informed of an impending heat wave. Building simulation models can be favorably used to evaluate indoor heat stress. This study presents a generic simulation model, developed from monitoring data in urban multi-unit residential buildings during a summer period and using statistical methods. The model determines both the average room temperature and its deviations and, thus, consists of three sub-models: cool, average, and warm building types. The simulation model is based on the same mathematical algorithm, whereas each building type is described by a specific data set, concerning its building physical parameters and user behavior, respectively. The generic building model may be used in urban climate analyses with many individual buildings distributed across the city or in heat–health warning systems, with different building and user types distributed across a region. An urban climate analysis (with weather data from a database) may evaluate local differences in urban and indoor climate, whereas heat–health warning systems (driven by a weather forecast) obtain additional information on indoor heat stress and its expected deviations.
Techno-economic comparison of membrane distillation and MVC in a zero liquid discharge application
(2018)
Membrane distillation (MD) is a thermally driven membrane process for the separation of vapour from a liquid stream through a hydrophobic, microporous membrane. However, a commercial breakthrough on a large scale has not been achieved so far. Specific developments on MD technology are required to adapt the technology for applications in which its properties can potentially outshine state of the art technologies such as standard evaporation. In order to drive these developments in a focused manner, firstly it must be shown that MD can be economically attractive in comparison to state of the art systems. Thus, this work presents a technological design and economic analysis for AGMD and v-AGMD for application in a zero liquid discharge (ZLD) process chain and compares it to the costs of mechanical vapour compression (MVC) for the same application. The results show that MD can potentially be ~40% more cost effective than MVC for a system capacity of 100 m3/day feed water, and up to ~75% more cost effective if the MD is driven with free waste heat.
In this paper, we describe the PALM model system 6.0. PALM (formerly an abbreviation for Parallelized Large-eddy Simulation Model and now an independent name) is a Fortran-based code and has been applied for studying a variety of atmospheric and oceanic boundary layers for about 20 years. The model is optimized for use on massively parallel computer architectures. This is a follow-up paper to the PALM 4.0 model description in Maronga et al. (2015). During the last years, PALM has been significantly improved and now offers a variety of new components. In particular, much effort was made to enhance the model with components needed for applications in urban environments, like fully interactive land surface and radiation schemes, chemistry, and an indoor model. This paper serves as an overview paper of the PALM 6.0 model system and we describe its current model core. The individual components for urban applications, case studies, validation runs, and issues with suitable input data are presented and discussed in a series of companion papers in this special issue.
Mit längerfristigen Nutzerbefragungen in zwei unmittelbar benachbarten Bürogebäuden in Freiburg wurden das Temperaturempfinden der Nutzer und deren Zufriedenheit mit dem thermischen Raumkomfort zweimal täglich erfasst. Ein Bürogebäude wird im Sommer mit einem maschinellen Nachtlüftungskonzept konditioniert und das zweite verfügt über eine Betonkerntemperierung und eine Zu‐ und Abluftanlage. Auf Basis der vorhandenen Daten aus der Erhebung wurde mit Hilfe von Regressionsanalysen ein Modell zur Vorhersage der Komforttemperatur berechnet und mit den Modellen in DIN EN 15251 verglichen.
The energy system of the future will transform from the current centralised fossil based to a decentralised, clean, highly efficient, and intelligent network. This transformation will require innovative technologies and ideas like trigeneration and the crowd energy concept to pave the way ahead. Even though trigeneration systems are extremely energy efficient and can play a vital role in the energy system, turning around their deployment is hindered by various barriers. These barriers are theoretically analysed in a multiperspective approach and the role decentralised trigeneration systems can play in the crowd energy concept is highlighted. It is derived from an initial literature research that a multiperspective (technological, energy-economic, and user) analysis is necessary for realising the potential of trigeneration systems in a decentralised grid. And to experimentally quantify these issues we are setting up a microscale trigeneration lab at our institute and the motivation for this lab is also briefly introduced.
Thermisch angetriebene (Adsorptions-)Kältemaschinen können mit einem verhältnismäßig geringen elektrischen Energieaufwand bzw. mit einer hohen elektrischen Leistungszahl Kälte bereitstel-len. Wird die zum Antrieb erforderliche Wärme aus industrieller Abwärme bereitgestellt, ist diese Kältebereitstellung energetisch effizienter als die Kältebereitstellung über eine Kompressionskäl-temaschine. Wird die Wärme jedoch in Kraft-Wärme-Kopplung bereitgestellt, ist die primärenergetische Bewertung sowohl von mehreren Teilwirkungsgraden als auch den Primärenergiefaktoren für den eingesetzten Brennstoff und die erzeugte bzw. bezogene elektrische Energie abhängig. Eine umfangreiche Messkampagne im Sommer 2018 liefert unter realitätsnahen Randbedingungen in einer Labor umgebung detaillierte Energiekennzahlen für einen typischen Tagesgang des Kältebedarfs. Damit gelingt es, Teilenergiekennwerte für die Planungspraxis abzuleiten und das Gesamtsystem energetisch mit einer konventionellen Kompressionskältemaschine zu vergleichen.
Mit der Messung des Wärme- und Kälteverbrauchs im Labor gelingt es, sowohl thermisch träge als auch agile Flächentemperiersysteme unter praxisnahen, dynamischen Bedingungen messtechnisch zu bewerten. Werden Nutzwärme- und Nutzkältebedarf berechnet und ins Verhältnis zu den gemessenen Verbräuchen gesetzt, können die Aufwandzahlen für die Nutzenübergabe ece für verschiedene Flächentemperiersysteme und in Kombinationen mit anderen Übergabesystemen unter verschiedenen Nutzungsbedingungen und für unterschiedliche Betriebsführungsstrategien bestimmt werden. Damit stehen Aufwandszahlen auf Basis kalorischer Messungen zur Verfügung, die je nach Aufgabenstellung entweder produkt- oder objektbezogen in der Planung komplexer Energiekonzepte verwendet werden können und die tatsächlichen Aufwandszahlen eh, ce für den Heizfall bzw. ec, ce für den Kühlfall genauer als Literaturwerte bzw. projektbezogen beschreiben
Experimental Investigation of the Air Exchange Effectiveness of Push-Pull Ventilation Devices
(2020)
The increasing installation numbers of ventilation units in residential buildings are driven by legal objectives to improve their energy efficiency. The dimensioning of a ventilation system for nearly zero energy buildings is usually based on the air flow rate desired by the clients or requested by technical regulations. However, this does not necessarily lead to a system actually able to renew the air volume of the living space effectively. In recent years decentralised systems with an alternating operation mode and fairly good energy efficiencies entered the market and following question was raised: “Does this operation mode allow an efficient air renewal?” This question can be answered experimentally by performing a tracer gas analysis. In the presented study, a total of 15 preliminary tests are carried out in a climatic chamber representing a single room equipped with two push-pull devices. The tests include summer, winter and isothermal supply air conditions since this parameter variation is missing till now for push-pull devices. Further investigations are dedicated to the effect of thermal convection due to human heat dissipation on the room air flow. In dependence on these boundary conditions, the determined air exchange efficiency varies, lagging behind the expected range 0.5 < εa < 1 in almost all cases, indicating insufficient air exchange including short-circuiting. Local air exchange values suggest inhomogeneous air renewal depending on the distance to the indoor apertures as well as the temperature gradients between in- and outdoor. The tested measurement set-up is applicable for field measurements.
Drawing off the technical flexibility of building polygeneration systems to support a rapidly expanding renewable electricity grid requires the application of advanced controllers like model predictive control (MPC) that can handle multiple inputs and outputs, uncertainties in forecast data, and plant constraints amongst other features. In this original work, an economic-MPC-based optimal scheduling of a real-world building energy system is demonstrated and its performance is evaluated against a conventional controller. The demonstration includes the steps to integrate an optimisation-based supervisory controller into a standard building automation and control system with off-the-shelf HVAC components and usage of state-of-art algorithms for solving complex nonlinear mixed integer optimal control problems. With the MPC, quantitative benefits in terms of 6–12% demand-cost savings and qualitative benefits in terms of better controller adaptability and hardware-friendly operation are identified. Further research potential for improving the MPC framework in terms of field-level stability, minimising constraint violations, and inter-system communication for its deployment in a prosumer-network is also identified.
This paper presents a framework for numerical building validation enhancement based on detailed building specifications from in-situ measurements and evidence-based validation assessment undertaken on a detached sustainable lightweight building in a semi-arid climate. The validation process has been undergone in a set of controlled experiments – a free-float period, and steady-state internal temperatures. The validation was conducted for a complete year with a 1-min time step for the hourly indoor temperature and the variable refrigerant flow (VRF) energy consumption. The initial baseline model was improved by three series of validation steps per three different field measurements including thermal transmittance, glazing thermal and optical properties, and airtightness. Then, the accurate and validated model was used for building energy efficiency assessment in 12 regions of Morocco. This study aims to assess the effect of accurate building characteristics values on the numerical model enhancement. The initial CV(RMSE) and NMBE have improved respectively from 14.58 % and −11.23 %–7.85 % and 1.86 % for the indoor temperature. Besides, from 31.17 % to 14.37 %–20.57 % and 9.77 % for energy consumption. The findings demonstrate that the lightweight construction with the use of a variable refrigerant flow system could be energy efficient in the southern regions of Morocco.
Passive solar elements for both direct and indirect gains, are systems used to maintain a comfortable living environment while saving energy, especially in the building energy retrofit and adaptation process. Sunspaces, thermal mass and glazing area and orientation have been often used in the past to guarantee adequate indoor conditions when mechanical devices were not available. After a period of neglect, nowadays they are again considered as appropriate systems to help face environmental issues in the building sector, and both international and national legislation takes into consideration the possibility of including them in the building planning tools, also providing economic incentives. Their proper design needs dynamic simulation, often difficult to perform and time consuming. Moreover, results generally suffer from several uncertainties, so quasi steady-state procedures are often used in everyday practice with good results, but some corrections are still needed. In this paper, a comparative analysis of different solutions for the construction of verandas in an existing building is presented, following the procedure provided by the slightly modified and improved Standard EN ISO 13790:2008. Advantages and disadvantages of different configurations considering thermal insulation, windows typology and mechanical ventilation systems are discussed and a general intervention strategy is proposed. The aim is to highlight the possibility of using sunspaces in order to increase the efficiency of the existing building stock, considering ease of construction and economic viability.
Energy Performance of Verandas in the Building Retrofit Process (PDF Download Available). Available from: https://www.researchgate.net/publication/303093420_Energy_Performance_of_Verandas_in_the_Building_Retrofit_Process [accessed Jul 5, 2017].
The current methods used to assess the energy performance of ventilation devices do not consider all the aspects necessary for a comprehensive evaluation of decentralised ventilation concepts and can only be partially adapted to their needs. In order to improve the energy evaluation and to ensure the comparability of different systems, a calorimetric method was developed and implemented in test facilities for the evaluation of two decentralised devices: one equipped with a recuperative counter flow heat exchanger and one with a regenerative heat exchanger. This method, based on direct measurements of the heating load in an insulated test room, includes the effect of the electrical consumption of the fans on the energy performance of the ventilation devices. The calorimetric evaluation method was extended to a seasonal evaluation on the basis of a heating-degree-day method implemented for a warm, a cool and a moderate location in Europe: Athens, Strasbourg and Copenhagen. All the results are above 50% efficiency for both devices, even in Athens where the use of heat recovery ventilation is not usual.
Energy efficiency and hygrothermal performance of hemp clay walls for Moroccan residential buildings
(2023)
Hemp-based building envelopes have gained significant popularity in developed countries, and now the trend of constructing houses with hemp-clay blocks is spreading to developing countries like Morocco. Investigating the hygrothermal behavior of such structures under actual climate conditions is essential for advancing and promoting this sustainable practice. This paper presents an in-depth experimental characterization of a commercial hemp-clay brick that has been exposed to the outdoor environment for four years, in addition to field measurements on a building scale demonstration prototype. Additionally, the study simulates 17 representative cities to assess the hygrothermal performance and energy-saving potential in each of Morocco's six existing climate zones, using the EnergyPlus engine. The experimental campaign's findings demonstrate excellent indoor air temperature and relative humidity regulation within the hemp-clay wall building, leading to satisfactory levels of thermal comfort within hemp-clay wall buildings. This is attributed to the material's good thermal conductivity and excellent moisture buffering capacity (found to be 0.31 W/mK and 2.25 g/m2%RH), respectively). The energy simulation findings also point to significant energy savings, with cooling and heating energy reductions ranging from 27.7% to 47.5% and 33.7% to 79.8%, respectively, as compared to traditional Moroccan buildings.
Unter dem europäischen Programm Intelligent Energy for Europe (IEE) fanden sich acht europäische Partner zusammen, um im Rahmen des Projektes ThermCo Lüftungs‐ und Kühlenergiekonzepte für Nichtwohngebäude mit niedrigem Energieeinsatz im Hinblick auf die Energieeffizienz und den thermischen Raumkomfort zu bewerten (siehe Teil 1 dieser Veröffentlichung in Bauphysik 34 (2012), Heft 6. Mit Hilfe einer Simulationsstudie für ein typisches Bürogebäude wird das Potenzial unterschiedlicher Lüftungs‐ und Kühlstrategien unter Berücksichtigung von Energieeffizienz und Raumkomfort für verschiedene europäische Klimazonen bewertet. Die Ergebnisse weisen eine hohe Wirksamkeit von Nachtlüftungskonzepten im nord‐europäischen Sommerklima mit verhältnismäßig niedrigen Außentemperaturen nach. Im mitteleuropäischen Sommerklima bietet das Erdreich ein ausreichend niedriges Temperaturniveau für den effizienten Einsatz von wassergeführten Flächentemperiersystemen. Im südeuropäischen Sommerklima kann eine aktive Kühlung über Luft die hohen und schnell fluktuierenden Kühllasten effizient abführen.
In 35 deutschen und 7 europäischen Büro- und Verwaltungsgebäuden wurden auf Basis von Monitoringkampagnen über mehrere Betriebsjahre Raum- und Außentemperaturwerte in zeitlich hoher Auflösung erfasst und der thermische Raumkomfort im Sommer standardisiert nach der Komfortnorm DIN EN 15251:2007-08 detailliert ausgewertet. Ergänzt wird die Auswertung um Kurzzeitmesskampagnen über zwei sehr warme Wochen im Sommer in unsanierten bzw. teilsanierten Bürogebäuden, errichtet im Zeitraum von 1960 bis 1975. Die untersuchten Gebäude mit ihrem jeweiligen Kühlkonzept lassen sich in sechs Kategorien einteilen: ohne Kühlung, passive, luftgeführte und wassergeführte Kühlung sowie Mixed-mode-Kühlung und Vollklimatisierung. Im Quervergleich aller Gebäude werden die Kühlkonzepte gleichermaßen nach dem thermischen Raumkomfort und thermischen Kühlenergiebezug bewertet. Detaillierte Komfortuntersuchungen nach der Europäischen Komfortnorm DIN EN 15251:2007-08 geben Hinweise auf die Wirksamkeit der eingesetzten Kühltechnologien in den jeweiligen Klimazonen. Daraus lassen sich Handlungsempfehlungen für die Planungspraxis und den Gebäudebetrieb ableiten.
Since 2003, most European countries established heat health warning systems to alert the population to heat load. Heat health warning systems are based on predicted meteorological conditions outdoors. But the majority of the European population spends a substantial amount of time indoors, and indoor thermal conditions can differ substantially from outdoor conditions. The German Meteorological Service (Deutscher Wetterdienst, DWD) extended the existing heat health warning system (HHWS) with a thermal building simulation model to consider heat load indoors. In this study, the thermal building simulation model is used to simulate a standardized building representing a modern nursing home, because elderly and sick people are most sensitive to heat stress. Different types of natural ventilation were simulated. Based on current and future test reference years, changes in the future heat load indoors were analyzed. Results show differences between the various ventilation options and the possibility to minimize the thermal heat stress during summer by using an appropriate ventilation method. Nighttime ventilation for indoor thermal comfort is most important. A fully opened window at nighttime and the 2-h ventilation in the morning and evening are more sufficient to avoid heat stress than a tilted window at nighttime and the 1-h ventilation in the morning and the evening. Especially the ventilation in the morning seems to be effective to keep the heat load indoors low. Comparing the results for the current and the future test reference years, an increase of heat stress on all ventilation types can be recognized.
In this article we outline the model development planned within the joint projectModel-based city planningand application in climate change (MOSAIK). The MOSAIK project is funded by the German FederalMinistry of Education and Research (BMBF) within the frameworkUrban Climate Under Change ([UC]2)since 2016. The aim of MOSAIK is to develop a highly-efficient, modern, and high-resolution urban climatemodel that allows to be applied for building-resolving simulations of large cities such as Berlin (Germany).The new urban climate model will be based on the well-established large-eddy simulation code PALM, whichalready has numerous features related to this goal, such as an option for prescribing Cartesian obstacles. Inthis article we will outline those components that will be added or modified in the framework of MOSAIK.Moreover, we will discuss the everlasting issue of acquisition of suitable geographical information as inputdata and the underlying requirements from the model's perspective.