The Earth, Wind & Fire research
Hypothesis
The point of departure for the research Earth, Wind & Fire with the sub concepts of the Ventec Roof, Climate Cascade, and Solar Chimney being an integral part of the (architectural) building design culminates into the following hypothesis:
- An integrated approach between Architecture/Construction and Climate Design is able to exploit available environmental energy in the form of earth mass, wind, and sun for a mainly energy neutral air conditioning of a building.
- The sub concepts can be modelled and validated, providing them with reliable support in practical design processes.
- The sub concepts may be used alone or in combination to contribute to the energy neutrality of buildings.
Research Questions
From the hypothesis, the following research questions can be derived:
- What are the potential opportunities of the sub concepts of the Ventec Roof, Climate Cascade, and Solar Chimney for achieving natural air conditioning in buildings?
- What are the design criteria for the Ventec Roof, the Climate Cascade, and the Solar Chimney for achieving:
- The desired volume flow for favorable indoor air quality?
- Thermal comfort in the indoor environment?
3. What are the potential opportunities of the three subconcepts for active energy generation with wind and the sun?
4. To what extent can the Earth, Wind & Fire concept contribute to zero energy buildings?
5. Which reliable design tools and/or mathematical models can be developed for use in practice?
6. What are the preconditions for the implementation of this strategy in existing buildings?
The Research
The study Earth, Wind & Fire was conducted to theoretically and empirically validate the aforementioned hypothesis on the basis of the research questions ad section 1.6.
For this cause, the research team Earth, Wind & Fire was formed as a joint project between the TU Delft, TU Eindhoven, and VVKH Architects. Principal investigator of the project was Ben Bronsema, BEng, REHVA Fellow, assisted by academic staff of the Faculties of Architecture of Delft and Eindhoven Universities of Technology. Several specialized activities are outsourced-see the figure below.
The research was guided by an advisory board composed of prominent representatives of Dutch architecture (BNA), the building industry (SBR), and the installation sector (TVVL/VNI).
For a detailed description of the research project, see “Project Earth, Wind & Fire – Towards new concepts for air conditioning of buildings” (Bronsema, B. 2007).
The research was conducted with funding from the Ministry of Economic Affairs, Agriculture, and Innovation, Energy Research Subsidy scheme: long term (Article 18b).
The results of the research are reported in compact form in the present thesis.
A detailed reporting is made in the following final reports dated March 2012 (in Dutch – available online):
(I) Earth, Wind & Fire – Research Solar Chimney and Solar Façade.
(II) Earth, Wind & Fire – Research Natural Ventilation, Wind and the Ventec Roof.
(III) Earth, Wind & Fire – Research Climate Cascade and Climate Geo-Concept.
(IV) Earth, Wind & Fire – Indoor environment: Symbiosis of Architecture and Climate Technology
The partial reports (I) through (III) provide a detailed report of the three studies and guidelines for the design of the responsive components including (I) Solar Chimney or Solar Façade, (II) the Ventec Roof and (III) the Climate Cascade.
Part (IV) discusses the necessary interaction between architecture and climate technology and presents the main points of sections (I) through (III). In this section, a case study is also presented. The four sections are independent units and individual reading.
Organizational structure research project Earth, Wind & Fire
Modeling, Simulation and Validation
The research and development of the Ventec Roof, the Climate Cascade, and the Solar Chimney or Solar Façade are developed according to the method of modelling, simulation, and validation as illustrated in the figure below.
Modelling and Simulating
One of the objectives of the research “Earth, Wind & Fire” is providing climate engineers and architects with reliable data for designing this innovative concept of air conditioning. Only when these are available will clients and designers be ready to put the concept into practice in actual projects. This objective can be achieved with the help of validated simulations.
“Simulation is the process of creating a simplified model of a complex system and the use of this model to predict and analyse the behaviour of the actual system” (Hensen, J. 2003).
Several studies have demonstrated that building simulation is more than just software (e.g. Hensen, J.L.M. 2003). It must be considered as a “science” for which two essential skills are required:
(1) The knowledge and expertise to understand the complex system including the associated relationships that is sufficient domain knowledge;
(2) The ability to translate this understanding into a logical representation with suitable simulation software. (Hensen, J. 2004):
Domain Knowledge (1) was extensive in the principal investigator. Computer simulations (2) have been accomplished by experts who possess the above necessary skills.
Basic modeling [1]
In the development of the various concepts, simple calculation models were being formed which provided a first impression of the feasibility and potential of the corresponding draft. Such models are close to the engineering practice and enable a swift evaluation of alternatives that is partly based on experience and intuition. Employing scientific and technical information from the repertoire of the HVAC engineer, mathematical descriptions of the heat transfer and flow at the macro level were drawn up. Use was made of the Handboek Installatietechniek[1] (ISSO 2002), the Taschenbuch für Heizung + Klimatechnik (Recknagel et al. 2010), the ASHRAE Handbooks Fundamentals (ASHRAE 2001), and HVAC Systems and Equipment (ASHRAE 2000). For certain subjects, scientific publications were consulted.
The formulas employed are related to stationary conditions, of course, however, by discretization, the processes could be quasi dynamically simulated employing MS Excel. This method yielded not only valuable insight into the underlying phenomena of heat transfer and flow but also the coupling of both. Many uncertainties became evident which revealed the requirement for further simulations at a higher resolution level.
Numerical flow modeling with CFD [2]
The basic analyzed concepts with the Excel calculation models have been developed into virtual prototypes utilizing CFD numerical flow models which provided insight into the heat transfer and flow patterns at the micro level. This allowed the physical effects to be further analyzed and, using simulation techniques, determine whether and to what extent models could be scaled up to full size components.
CFD analysis provides a prompt insight into the processes of new concepts which are difficult to obtain in any other manner. This is a significant advantage in the development of responsive elements as making physical prototypes is very expensive.
Using CFD analysis, performance of different concepts could quickly be calculated and optimized. Based on optimized virtual physical prototypes, physical prototypes were created, saving time and money.
“The main disadvantages are the complexity of CFD and the sensitivity of the results to be chosen for the model parameters. The user must make many decisions in the execution of a simulation, and these can greatly affect the accuracy of the results. As a safe starting point, we would argue that, for CFD, results are not applied on the presumption of innocence. On the contrary: “CFD results are wrong, until the contrary is proved”. Verification and validation of CFD simulations are essential. Following the validation, then accurate measurements are required.” (Blocking, B. 2010)
The study Earth, Wind & Fire utilizes CFD virtual prototypes of the Cascade Climate, the Ventec Roof, and the Solar Chimney, and the performance, thereof, is analyzed and optimized. Based on the virtual prototypes of these responsive elements, physical scale models are constructed for experimental research -see section 1.8.5.- which were subsequently employed to validate the CFD simulations. The physical models are, in turn, also prototypes for the corresponding elements in the actual building practice. Using CFD, it can be examined whether the tested scale models are representative of the full-sized models.
Due to limitations in computer capacity, CFD has (not) yet achieved the level required for coupled dynamic yearly calculations. For this purpose, the dynamic Building Simulation Model ESP-r has been applied which is calibrated and validated based on the data obtained from the measurements in the physical research models.
The execution of CFD simulations, preparation of the analytical model, determination of the grid, discretization of the flow field, and the simulation process including visualization and analysis of the data is a complicated process. Knowledge of the relevant professional field is essential as is the knowledge of numerical calculation techniques. CFD simulations for the research Earth, Wind & Fire are also under the auspices of the research conducted by recognized external experts.
Dynamic simulation with ESP-r [3]
The Excel calculation model and the CFD simulation model are employed as tools for the calculation and design of the Climate Cascade and the Solar Chimney under stationary conditions. For the study of the dynamic behavior and estimates of the annual energy performance of these responsive elements, the dynamic simulation model ESP-r is employed. This model offers designers the ability to study the complex relationships between the exterior and interior of a building based on architecture, building mass, air flows, and climate control facilities. It is flexible and powerful and, therefore, very suitable for the simulation of innovative techniques.
The Solar Chimney and the Climate Cascade are modelled in ESP-r using a thermal and flow network comprised of nodes whereby the interconnected heat and mass flows can be simulated. The thermal and the flow network are interrelated: In the Solar Chimney, the temperature increase of the air induces an upward thermal draft which creates a flow. In the Climate Cascade, the temperature drop of the air induces a downward thermal draft that, together with the aerodynamic and hydraulic draft, causes a flow. The magnitude of the flow determines, in turn, the temperature of the air.
The thermal network and the flow network can, in principle, be integrated in the ESP-r model building. On the one hand, this enables flexible use of the building model but, on the other hand, it is a difficult and cumbersome application. In the research, the ESP-r model, therefore, is used to simulate the performance of the Solar Chimney and Climate Cascade as stand-alone elements.
For the calculation of the annual energy performance, the reference year NEN 5060:2008 is used in the research.
In order to work with ESP-r, experienced users are required who possess a thorough knowledge of the physical processes to be simulated. The ESP-r models and simulations are designed and created by specialists of the unit Building Physics and Systems at TU Eindhoven. The simulations are calibrated and validated based on measurements in the physical models and can be considered sufficiently reliable.
Validation by measurements in a physical model [4]
Based on the basic modelling in Excel and the examination, verification, and detailing of them employing CFD simulations, physical models are constructed of the Solar Chimney, the Climate Cascade, and the Ventec Roof. Using these under various conditions and in real time, the actually occurring phenomena of heat transfer and flows are measured. Obviously, these are scale models but with such dimensions that the processes could be reliably monitored and recorded.
On the basis of the measurement data from the physical models, the Excel calculation model and the CFD and ESP-r simulation models have been calibrated and validated in a feedback loop.
The functional design and main dimensions of the physical models are determined by the principal investigator. Design, engineering, and implementation are realized by Peutz. In order to calibrate and validate the ESP-r simulation, the instrumentation in the Solar Chimney is under the auspices of the research team, designed by the TU Eindhoven, and materialized and installed by Peutz.
Computational model for practice [5]
A calculation model for practice based on the results of the research allows architects and engineers the ability to somewhat elaborate and dimension the concepts for actual building designs. For the Solar Chimney, a dominant architectural building element, a user-friendly calculation model has been developed. In the conceptual phase of the building design, the architect can use this model to vary the dimensions of a Solar Chimney and directly read the associated performance.
For the conceptual design of a Ventec Roof and a Climate Cascade, overall design data is recorded. The HVAC engineer always bears the final responsibility for the sizing of these elements in the final design.
Relationship between the models
The relationship between the various models is illustrated in the figure above. Each model has its own scope, and exchange of information between the models and verification with the physical model measurements can, in principle, be achieved with a high degree of reliability.
For the Earth, Wind & Fire concept, it would be ideal to model and simultaneously simulate the processes of heat transfer and flow in the Climate Cascade and Solar Chimney within the same computer domain. Due to limitations in computer capacity, CFD has not yet achieved the level required for the desired dynamic real-time calculations. Therefore, the building simulation model ESP-r is utilized for this purpose.
For the Ventec Roof, coupling of the air flows outside and inside the building is not a realistic option due to the significant differences in the geometrical scale of the urban environment (1-5 km) and the ventilation openings in the building (0.01 to 1 m). This would require a very extensive grid with high resolution and prohibitively high computing costs.
The Research Process
The basic procedure of basic modelling → detailed modelling → simulation → validation has worked well and also provided a fruitful cooperation between the engineering practice and the scientific approach.
The basic analytical modelling based on the repertoire of the HVAC engineer provides insight into the thermodynamic processes by which the intuitive “approximately science“[2] (Verheijen, A.P.J.M. 2002) is trained. Herewith, direction may be provided and counterweight offered to the detailed but, for the HVAC engineer, less accessible scientific approach. In some cases, the results of simulations were falsified by intuitive common sense. On the other hand, intuitive and seemingly logical assumptions were sometimes surprisingly falsified by the results of the scientific simulations.
The introduction to the advanced CFD models for the Ventec Roof and the Climate Cascade yielded excellent simulation results and was an instructive experience for the investigator. This also applies to the dynamic simulations with the ESP-r model where the basic stationary approach would have been impossible. It was particularly pleasing that the basic analytical and the detailed models of the Cascade Climate and Solar Chimney yielded similar results. It can be a lesson for climate engineers to not be overly eager to intervene with sophisticated computer models too early but, instead, first utilize the “approximately science” on the basis of his/her familiar knowledge of thermodynamics and hydrodynamics.
Summary
Building blocks of the concept are fundamental physics, technological expertise, design creativity, and an understanding of practical applicability. The Earth, Wind & Fire concept is construed as scientifically relevant by the methods of modelling, simulation, and validation.
The Earth, Wind & Fire concept is also socially relevant as the validated models and formulas are available for practical application and thus can contribute to the goals of zero energy buildings and independence from fossil energy sources.
Application of the earth, wind & fire concept
The developed Earth, Wind & Fire concept must be regarded as a central air conditioning system for buildings that can replace the building’s central mechanical system. Decentralized systems for heating and cooling at the workplace level such as climate ceilings, fan coil units, radiators, etc. can be perfectly combined with this concept.
The Earth, Wind & Fire concept is an overall concept. This does not imply, however, that the responsive building elements which are developed in this research can only be applied together. A stand- alone application of a Solar Chimney or a Solar Façade, a Ventec roof or Climate Cascade in office buildings is perfectly feasible.
The Earth, Wind & Fire concept can be applied to any architectural style, classic, modern, international, postmodern, bioclimatic, etc. It is the architect who shapes the design of the building as a “climate machine “.
Newly built construction projects can obviously be entirely designed according to the Earth, Wind & Fire concept. Additionally, in the event of extensive renovations of existing buildings, the concept can also be applied either in part or in its entirety. A Ventec roof and a Solar Chimney are possible additions to a building as well. Existing façades can be converted to Solar façades, and existing installation shafts can be converted to a Climate Cascade.
The urban context
The precondition for optimal operation of Natural Air Conditioning according to the Earth, Wind & Fire concept is that the influence of wind and the sun on a building is not substantially impeded by the surrounding buildings. Ideally, the wind should have free access to the Ventec Roof, and the Solar Chimney should not be constructed in the shade of other buildings.
For the operation of the Ventec Roof, the difference in height between buildings has the most significant influence. For the solar chimney, lateral spacing in the urban environment is more influential. Due to the great potential contribution of a Solar Chimney to the heating demand of a building, the urban boundary conditions for the Solar Chimney prevail; however, optimal solar access has been demonstrated as possible at generally accepted urban boundary conditions.
This section of the research, of course, could not be validated and has a global and general character. For specific situations, it is recommended to employ wind tunnel research and/or solar software, if necessary, combined with research in a solar simulator.
Case study
The annual construction of office buildings in the Netherlands comprises only a small percentage of the existing building stock. Application of the Earth, Wind & Fire concept is, therefore, especially important for major renovations of existing buildings. In order to investigate this feasibility, a case study is performed using an existing office building which is virtually equipped with Natural Air Conditioning according to the Earth, Wind & Fire concept. The case study served both as a design exercise and to evaluate the energy performance of the concept in an actual building. The beginning point was that the design should be viable architecturally, structurally, and climatologically not only virtually but also in practice. The design is, therefore, constructed at the Preliminary Design level. The design exercise demonstrates that applying the Earth, Wind & Fire concept to this case-study office is very well feasible.
An analysis of the energy performance indicates that the total building-related annual primary energy consumption in the reference situation of app. 110 kWh.m-2 is, through this virtual intervention, reduced to approximately 1/3 of its original value. With the energy yield from the Ventec Roof, the building produces a surplus of energy of approximately 20%.
Conclusions
Ventec Roof
The Ventec Roof is a dominant architectural element and a typical expression of Climate Responsive Architecture. As an integrated approach of Architecture/Construction and Climate Design, it can make an important contribution to Natural Air Conditioning of zero energy buildings. For the design, validated design tools and computational models are available. The Ventec Roof is also intrinsically safe by preventing short-circuiting fresh air and second hand ventilation air.
The aerodynamic performance of the Ventec Roof depends on the wind speed at roof height which is primarily determined by the height of the building and its surrounding buildings. Employing wind tunnel research, boundary conditions have been formulated for optimizing the Ventec Roof in an urban context. The case study illustrates that the application of a Ventec Roof to an existing building is a realistic option.
Climate Cascade
The Climate Cascade is an inconspicuous architectural element unless it is utilized for cooling atria. For indoor climate conditions, however, the Climate Cascade is an essential building element not only for conditioning ventilation air but also for generation of necessary positive pressures for air distribution in a building.
Research was initially only focused on the use of the Climate Cascade for cooling ventilation air during summer. Throughout the course of the research, the other seasons were included in this study so that its aerodynamic performance could also be utilized throughout the year. Essential for the study was the experimental mock-up in which the psychrometric performance could be measured even under extreme summer and winter conditions. The experimental set-up demonstrated that a Climate Cascade is a robust and universal building component which can be employed for cooling/drying and heating/humidification of ventilation air in all seasons.
The basic computational model and numerical simulation model are both validated by the experimental mock-up. Both models can predict the psychrometric and aerodynamic performance of a Climate Cascade with a high degree of accuracy.
The Coefficient of Performance (COP) of a Climate Cascade depends on the water/air ratio and the height of the building and may vary from 50 to 15 in buildings of 4 to 20 stories. An obvious variant of the concept which, incidentally, has not been worked out, makes a COP of 100 feasible at 20 floors, which emphasizes the energy efficiency of the concept.
Some possible risks of using a Climate Cascade have also been investigated. Because of low water temperatures, the Climate Cascade is intrinsically safe against the growth of legionella bacteria and other pathogens. A correct execution of thermal bridges excludes the condensation risk at outer partition walls.
Summarizing, it can be concluded that the Climate Cascade is an important contribution to Natural Air Conditioning and zero energy buildings. Validated design tools and computational models are now available. A case study has shown that the application of a Climate Cascade in an existing building is a realistic option.
Solar Chimney
Like the Ventec Roof, the Solar Chimney is a typical expression of Climate Responsive Architecture. Exploiting the sun as a driving force for extraction of ventilation air, an essential contribution to Natural Air Conditioning of buildings is attained. Even more significant is the importance of the Solar Chimney as an absorber of solar energy which can be employed for heating buildings, thus contributing significantly to the energy neutrality of buildings.
An experimental mock-up is used during the four seasons for measurements of temperatures and air velocities as a function of the incidental solar radiation and the outside temperature.
The measurements provided a valuable overview of the complex thermodynamic processes in a solar chimney. The basic thermal and flow models are validated by implementation of measurements in the experimental mock-up and proved accurate enough to provide a base for a computational model for practical use. A dynamic simulation in ESP-r was calibrated and validated based on the measurements in the experimental mock-up.
It is the architect who, in the conceptual design phase, lays the foundation of a successful architectural integration of a solar chimney in a building. For this intuitive and interactive design phase, a user-friendly computational model has been developed to be utilized by architects. With one mouse click, architectural variants and the inherent energy consequences can be illustrated.
The thermal efficiency of a Solar Chimney, defined as the ratio of the heat absorbed by the airflow and the incidental solar radiation is mainly determined by the properties of the glass wall. A good choice can yield an average annual efficiency of approximately 60%.
The highest energy performance is delivered by a Solar Façade, a facade covering a Solar Chimney. This Solar Facade is applied in the case study to demonstrate if the application of the concept in existing buildings is a realistic option.
In spring and autumn, solar heat can be exploited directly or through short-term storage for heating the building. During summer months, long term storage is required in order to use the solar heat during the heating season. Several systems for heat storage are briefly and conceptually explained.
It has been demonstrated that a Solar Chimney is able to satisfy a substantial portion of the annual heating demand of a building and that, with a Solar Façade, in principle, the entire heating demand can be met. This applies to energy-efficient buildings with an annual heating demand of 50 kWh.m-2.
Summarizing, it can be concluded that the Solar Chimney is an important contribution to Natural Air Conditioning and zero energy buildings. Validated design tools and computational models are now available.