basics:internal_heat_capacity
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basics:internal_heat_capacity [2010/07/28 16:10] – edit | basics:internal_heat_capacity [2022/01/18 15:34] (current) – [Literature] yaling.hsiao@passiv.de | ||
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+ | ====== Internal heat capacity ====== | ||
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+ | The article on [[planning: | ||
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+ | The influences of parameters which have a dynamic effect, like the heat capacity, can only be observed with non-stationary processes and only using procedures which accurately calculate instationary processes based on the laws of physics. The DYNBIL simulation software is a validated program for dealing with thermally instationary processes in buildings. A comparison of measured results from buildings and the calculations carried out using DYNBIL has been published in [[Basics: | ||
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+ | The so-called operative temperature, | ||
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+ | In the case represented here, the temperature increase between the smallest and highest daily value is not more than 4 °C. It is evident that during the hot spell it is significantly cooler in the house than the peak value of the temperature outside. | ||
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+ | In order to obtain the results given below, many simulations based on the entire year were carried out for various residential buildings with respectively controlled varying characteristics. | ||
+ | * In the first part, the internal heat capacity was varied, | ||
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+ | * in the second part, the externally applied thermal protection was varied. | ||
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+ | Each " | ||
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+ | ===== The internal heat capacity ===== | ||
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+ | ==== The influence of the internal heat capacity on the annual heating demand ==== | ||
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+ | This diagram shows that in a Passive House, energy savings definitely result if an additional effective internal storage mass is added. | ||
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+ | * **Why is the influence so small? | ||
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+ | * **Why is the influence so high all the same?** In fact, for this building there is a certain seasonal storage effect. | ||
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+ | An increase in the storage capacity is often associated with changes in the materials used. Then a higher storage capacity even results in an increase in the heating demand. | ||
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+ | ==== The influence of the internal heat capacity on the summer comfort ==== | ||
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+ | An important boundary condition for a realistic simulation result is that the windows in this building can be tilted open in the summer whenever required. The influence of window opening is much greater than the influence of the internal heat capacity. This is why the PHI always recommends openable windows in each room of a Passive House (see [[Operation: | ||
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+ | The illustration below shows the following: | ||
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+ | * The frequency of overheating events (left axis, red curve) as a percentage of the hours in a year in which the operative temperature exceeds 25 °C. This is a measure of the “discomfort” or more correctly, the length of the periods in which comfort does not prevail. | ||
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+ | * The annual heating demand (right axis, green curve). This hardly varies and is nothing new; it confirms the result already obtained above.\\ | ||
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+ | in\\ the summer (from [[basics: | ||
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+ | The illustration indicates that the frequency of overheating events decreases significantly as the storage mass accessible from the room is increased, assuming a small internal heat capacity to begin with. The simulation gave the same result for passive cooling in other European climates too. Apart from that, the summer case study mentioned here also revealed improved levels of comfort, irrespective of the ventilation strategy used. Of course, in summer the indoor climate in a well-ventilated room is better than that in a room with a lower air exchange. Although the internal heat capacity plays a less significant role than the air exchange, it does make a difference after all. | ||
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+ | __Note:__ in the Summer Sheet of the Passive House Planning Package ([[Planning: | ||
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+ | ===== Thermal insulation ===== | ||
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+ | ==== The influence of thermal insulation of the building envelope on the annual heat demand ==== | ||
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+ | The diagram shows that better insulation has a great influence in the Passive House too. Due to the increase in insulation thickness as indicated, energy savings of around 60 % can be achieved (from about 13 kWh/m²a down to only 5 kWh/ | ||
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+ | * **Why is the influence still so great?** It is a widely held view that insulation that is “even thicker” than the good insulation already present initially serves no purpose, (because the insulation does not have any effect on other heat losses which predominate). This view is incorrect, as proven by the analysis shown. The reason for this is that in the energy balance of a Passive House, it is actually the transmission heat losses that are still dominant or recurrently predominant – ventilation heat losses are very small due to the heat recovery; and the losses through windows are over compensated by their solar gains. | ||
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+ | * **Why don’t we recommend even better insulation in spite of this?** It is not worthwhile to increase the level of insulation above that which is necessary for achieving the Passive House Standard. Although thicker insulation continues to save additional heating energy (even down to zero, if insulated thickly enough), saving from 2007 kWh/a to 791 kWh/a only " | ||
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+ | ==== The influence of the thermal insulation on summer comfort ==== | ||
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+ | In the illustration below, the following is presented: | ||
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+ | * The frequency of overheating events (left axis, red curve) as a percentage of the hours in a year on which the operative temperature exceeds 25 °C. This is a measure of the “discomfort” or more correctly, the length of the periods in which comfort does not prevail. | ||
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+ | * The annual heating demand (right axis, green curve). | ||
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+ | The illustration shows that based on the given boundary conditions(residential use, windows tilted open as needed, solid construction), | ||
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+ | ===== Conclusion ===== | ||
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+ | The internal storage capacity of a residential building in the Central European climate only has a small influence on the annual heating demand. | ||
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+ | However, the internal heat capacity is not the most important influencing parameter for summer comfort. | ||
+ | * Possibilities for increased ventilation, | ||
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+ | * shading from high solar gains | ||
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+ | * and restriction of internal heat loads | ||
+ | are the more important parameters. | ||
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+ | ===== Literature ===== | ||
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+ | **[AkkP-05]** Energiebilanz und Temperaturverhalten; | ||
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+ | **[AkkP-33]** Passivhaus-Schulen; | ||
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+ | **[Feist 1993]** Feist, Wolfgang: Passivhäuser in Mitteleuropa; | ||
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+ | **[Feist 1998a]** Feist, Wolfgang: Passivhaus Sommerklima-Studie; | ||
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+ | **[Schnieders 2009]** Schnieders, Jürgen: **Passive Houses in South West Europe** — A quantitative investigation of some passive and active space conditioning techniques for highly energy efficient dwellings in the South West European region. 2< | ||