planning:calculating_energy_efficiency:dynamic_simulation
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planning:calculating_energy_efficiency:dynamic_simulation [2020/08/05 11:57] – [Special features of the computer-aided simulation] wfeist | planning:calculating_energy_efficiency:dynamic_simulation [2020/08/07 23:16] – [Dynamic Simulation using DYNBIL] wfeist | ||
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====== Dynamic simulation of a building' | ====== Dynamic simulation of a building' | ||
- | \\ | + | ==== Dynamic Simulation using DYNBIL ==== |
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|Fig. 1 A typical room model used in instationary simulation of a buildings \\ thermal performance; | |Fig. 1 A typical room model used in instationary simulation of a buildings \\ thermal performance; | ||
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- | ==== Models used for Simulation ==== | + | Dynbil is a multizone dynamic thermal building simulation program developed at the Passive House Institute. Dynbil also takes into account moisture storage and moisture transport processes. The room model works with one air node and one radiation node, which are clearly separated from each other. Heat transmitted to interior surfaces is calculated depending on the location in the room and the actual temperature difference; for exterior surfaces, the complete solar and infrared radiation balance and the influence of wind speed are taken into account. Heat transfer (radiative and convective/ |
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+ | A single room (" | ||
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+ | In the meantime, additional features have been added such as simulations of moisture transport and ventilation models. | ||
+ | Although DYNBIL models the building components very accurately (see e.g. comparison of simulated and measured temperatures within the wall), the focus is the whole building perspective (fig. 2). The entire building | ||
+ | Another aspect of the whole building approach is the integration of all system components including the consideration of thermal comfort, ventilation, | ||
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+ | |Fig. 2 Several zones will be connected to a building model with air flows between the zones as well as components connecting the different zones.| | ||
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+ | Dynbil has been validated with the detailed measurements in the first Passive House (located in Darmstadt Kranichstein; | ||
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+ | ==== General Considerations on Models used for Simulation ==== | ||
The actual task in dealing with the questions of indoor climate and energy balance results from the high level of complexity which the "house and heating" | The actual task in dealing with the questions of indoor climate and energy balance results from the high level of complexity which the "house and heating" | ||
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Quite often, therefore, even with computer supported simulation models, the " | Quite often, therefore, even with computer supported simulation models, the " | ||
- | * Unordered List ItemAs | + | * As a rule, the digital algorithm itself lacks direct clarity (it is mastered by discretion). Therefore, even experienced users often find it difficult to read simple facts that can be generalized from EDP models. |
Example: | Example: | ||
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According to the explanations in the last sections, such a question does not arise: simulation and measurement have different functions in the cognitive process and complement each other. The simulation can neither make measurements completely superfluous (validation of models is only possible via measurements) - nor is it practical and sensible to want to answer all questions by measurements (statements that can be generalized can never be obtained by at most a finite number of measurements). | According to the explanations in the last sections, such a question does not arise: simulation and measurement have different functions in the cognitive process and complement each other. The simulation can neither make measurements completely superfluous (validation of models is only possible via measurements) - nor is it practical and sensible to want to answer all questions by measurements (statements that can be generalized can never be obtained by at most a finite number of measurements). | ||
- | Especially in the field of research into the thermal behavior of buildings, there is a widespread basic skepticism about simulation: Many practitioners only trust statements about the annual heating requirements of houses if they are important | + | Especially in the field of research into the thermal behavior of buildings, there is a widespread basic skepticism about simulation: Many practitioners only trust statements about the annual heating requirements of houses if they are validated by " |
+ | * According to the results already available today, the heating requirement is extremely sensitive to a number of parameters that can be changed by the user (eg the internal temperature and the air exchange). Measurements are therefore only to be regarded as usful data source if these parameters are also recorded in a suitable manner (e.g. internal temperature profile, tracer gas measurement of the air exchange) or checked in some other way (e.g. by permanently setting them with control organs) or by measurements within very large samples. (All these paths have been used in the development of passive houses.) | ||
+ | * The dependency on the external climate is also very high: In different years at the same Central European location (e.g. in Frankfurt am Main) the annual consumption of the same building can deviate by more than 50% with the same user behavior. Measured values can therefore only be compared if they relate to the same climate. Realizing this is quite difficult: without resorting to arithmetic corrections (the theoretical models need a basis: the usually used heating degree day correction is a very primitive and a quite questionable model), this can only be done by simultaneous measurements at the same place. | ||
+ | * In addition, inaccuracies in the measurement itself must be expected: "If you measure, you measure manure" | ||
- | ===== References ===== | + | Typical examples of questions that arise in energy related building planning are the following: |
+ | - Is it worthwhile to increase the proportion of south windows in a building from 50 to 60% in order to save heating energy? | ||
+ | - How is the indoor climate influenced in summer by changing the color of the outer facade? | ||
+ | Questions of these types can also be asked regarding the window structure, the floor covering, the roof construction and the like. From the parameter studies documented in [Feist 1994], it follows that the influence of each of these individual parameters on the annual heating consumption is not very high (e.g. we expect (1) to relate to a building with Swedish building standard 1980 result in a saving of 5.6% with triple glazing). The change in consumption, | ||
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+ | The situation is also comparable with (2): the differences that occur due to different window positions, especially at night in the summer indoor climate, are many times greater than the influence that is actually to be examined. | ||
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+ | The examples dealt with show that questions such as (1) or (2) that are decisive for building planning can only be answered by direct field measurements in question with unacceptable effort or with the usual measurement accuracy. The situation becomes completely absurd when not only the influence of one parameter, but - as usual - a whole range is required (window size, type of window, proportion of frame, shading, curtains, wall color, wall insulation, wall storage capacity, roof insulation, Roof ventilation, | ||
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+ | The questions mentioned are thus typical examples of tasks that can be solved with the help of thermal building models (usually EDP-supported) | ||
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+ | * considerably faster (an annual simulation run per building variant costs a few secaonds computing time (in 2020; in 1994 it was approx. 1 h)) | ||
+ | * in greater variety and | ||
+ | * with better accuracy and reliability | ||
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+ | as with direct field measurements. The last point may be surprising, so here is a brief explanation: | ||
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+ | Of course, simulations are only more accurate and reliable if the underlying model has been sufficiently validated. How this can be done will be explained later. | ||
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+ | With a validated model, the unchanged parameters and boundary conditions in the treatment of every question can be kept exactly the same (" | ||
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+ | Now there may be an objection that there is no interest in the effects of "such small" influences if they are lost in the noise of the main parameters. This objection is not valid for two reasons: | ||
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+ | - The accumulation of some of the individually small influences results in noteworthy changes in building behavior (e.g. the "low energy house" type has approx. 70% less heating heat consumption compared to the type " | ||
+ | - In a large group (e.g. of some hundreds of buildings) the small savings of perhaps 5%, which are hidden in individual cases by other parameter influences, emerge significantly from the noise. | ||
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+ | The first reason shows a way for the metrological validation of the models: large differences in cumulative changes can be reliably monitored. However, this does not relieve the need to determine the individual changes, otherwise it could be that a particularly expensive " | ||
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+ | The second reason also shows a basic way for a validation: the measurement in very large samples, in which accidental influences such as different indoor climates average out. To do this, however, the buildings must be sufficiently identical in their entirety - which also means high expenditure. In Sweden (Täby [Blomsterberg 1990], Valdemarsrö [Lange 1990], Taberg [Fredlund 1989]) such measurements were actually carried out in settlements with more than 18 similar residential units. - It is clear that this method is also hardly suitable for answering the multitude of questions - after all, some of the model validations carried out stem from this work. | ||
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+ | From the considerations so far it follows quite clearly: | ||
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+ | |**The method of choice for answering typical questions of structural influences on the indoor climate and heating energy consumption is the use of thermal computer aided building models. - On the other hand, validation of such models thus becomes one of the most urgent tasks of research.**| | ||
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+ | In practice, this finding has long since become established: | ||
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+ | ==== References ==== | ||
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+ | **[Blomsterberg 1990]** Blomsterberg, | ||
**[Feist 1994]** Thermische Gebäudesimulation; | **[Feist 1994]** Thermische Gebäudesimulation; | ||
- | Thermal building simulation, first edition, | + | Thermal building simulation, first edition, |
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+ | **[Fredlund 1989]** Fredlund, B.: Blocks of flats with glazed verandas, Taberg; Swedish Coun¬cil for Building Research, Stockholm D3:1989 \\ | ||
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+ | **[Johnston 2020]** Johnston, D. et al: Are the energy savings of the passive house standard reliable? A review of the as-built thermal and space heating performance of passive house dwellings from 1990 to 2018. March 2020, Energy Efficiency, DOI: 10.1007/ | ||
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+ | **[Lange 1990]** Lange, E.: Radhus i Valdemarsro, | ||
planning/calculating_energy_efficiency/dynamic_simulation.txt · Last modified: 2020/08/07 23:26 by wfeist