اثرات جریانات هوایی، انتشارحرارت داخلی و رطوبت در دقت و صحت مدلسازی مصرف انرژی و پارامترهای داخلی در ساختمان غیرفعال

Passive buildings compared to the standard ones require significantly less energy for heating, so the correct models of every “energy using” building's components are very important. This paper analyzes how various models of the internal heat and moisture gains, as well as natural air flows between building zones, influence the accuracy of the calculation of the energy performance, indoor temperatures and absolute humidity in a single-family passive building. A simulation environment used a detailed twelve-zone TRNSYS model of a house with HVAC system. The model included natural air flows between zones, and internal heat and moisture gains, defined as precisely as possible. The gains were allocated on the basis of special protocols of use filled by the occupants during the two-week measurement. The measurement data was also used for validation of the model. The verified model constituted a basis for calculation of energy performance and simulation of air temperature and absolute humidity change in a building with significantly limited air flow between zones, and heat and moisture gains defined according to standards. The standardized values of heat and moisture gains were defined on the basis of the standard ISO 13790 and national regulations in Poland. The simulations have shown that precise methodology of calculation of heat gains and air flows between building zones is very important for proper computation of energy performance and simulation of indoor temperatures and absolute humidity in passive buildings. Results of carried out analysis have shown e.g. that the difference in energy need for heating calculated using precise and simplified methods of internal heat gains determination was 30,1%.

Passive buildings compared to the standard ones require significantly less energy for heating and ventilation, while internal heat gains are almost the same. The energy demand for heating in passive buildings is less than 15 kWh/m2, while for example in new residential in Poland – 60–120 kWh/m2[1]. Heat gains cover about 20% of whole energy loss in the case of a standard building and up to 65% in a passive house [2]. This fact leads to two important conclusions. Firstly, increasing the heat gains, e.g. by appropriate orientation of windows, may contribute to a significant reduction of energy need for heating. Maximization of gains can at the same time cause increase of energy need for cooling, which was confirmed in the article of Enshen [3]. Secondly, a fluctuation of internal heat gains can cause significant change of the internal air temperature and requires specific control strategies. Appropriate control is necessary to obtain good thermal comfort as well as high energy efficiency. That is why, if we want to predict correctly the internal environment conditions in a very low-energy buildings (like passive buildings – nearly zero-energy buildings) and calculate correctly their energy needs, we have to use precise building and system models. What is even more important, much attention should be paid to the appropriate determination of internal heat and moisture gains as well as airflows between building zones, all of which factors are often determined in a simplified way. For example, simplified methodology defined in standard ISO 13790 [4] can be suitable for buildings with standard energy need, but for very low-energy buildings the methodology has to be more precise. Otherwise real energy performance of buildings can be higher than calculated and energy savings lower than predicted. This aspect is particularly important due to the recast of the Energy Performance of Buildings Directive and implementation of ‘nearly zero’ energy buildings [5].

The simulation results confirmed the significant impact of internal heat and moisture gains as well as airflows between the building zones on indoor temperatures, absolute humidity and energy performance of passive houses. The most influences were noticed in values of the relative air humidity and energy need for heating. In the analyzed house the difference in absolute humidity of the exhausted air was 35.7% (for the models with and without moisture gains). The difference in energy need for heating calculated using precise and simplified methods of internal heat gains determination was 30.1%. Decrease of energy need was caused by oversizing of heat gains in simplified method. Oversizing of gains probably increased energy need for cooling. The difference between calculated and measured mean values of indoor air temperature in individual zones did not exceed 0.6 K, except WC and technical room, where they were twice higher (for the simplified method of internal heat gains determination). Proper modeling of air exchange in the building proves very important. Omission of the natural airflows between rooms can lead to significant errors in calculation of energy need, indoor temperatures and absolute humidity, which corresponds especially to complex, interconnected models of buildings with heating system. If the temperature sensor of controller is located in closed room, the heating capacity of system and energy need of the whole building will significantly depend on indoor air temperature in this room. Where there is neither air, nor heat or moisture exchange between room with controller's sensor and other rooms, the values of temperature in this room strongly depend on heat gains and do not represent average air temperature in the whole building. As a result, the heating system may deliver significantly more (or less) energy to the building than needed. In the analyzed passive house, energy need for heating in the case of simulation with closed doors between rooms was 25.5% lower than in the case of open doors (with natural airflows). At the same time, average air temperature in house was 0.27 K lower and the average standard deviation was 0.14 K higher.