Research on Thermal Conditions in Ventilated Large Space Building

K e y w o r d s : CFD; Large space building; Thermal conditions; Thermovision; Ventilation. 4/2018 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 169 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T The Si les ian Univers i ty of Technology No. 4/2018 d o i : 1 0 . 2 1 3 0 7 / A C E E 2 0 1 8 0 6 3 A . P a l m o w s k a , G . M i c z k a 170 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 4/2018 movements. The difficulties in design of a ventilation system include: heat gains that accumulate upwards (at the ceiling level) of the hall, causing so-called air (heat) cushion, supply and deposition of cold air layers in the lower part of the hall and the amount, type and location of so-called point heat sources [6]. Moreover, usually only a small portion of the entire volume is occupied, therefore energy efficiency may be achieved by special strategies aimed at directing ventilation air and thermal conditioning to the occupied zone. Vertical air streams driven by temperature differences gather large momentum in tall buildings. Resultant cold down-drafts from vertical surfaces may have severe comfort implications. Large enclosures are often found in unique buildings where no previous experience exists. Therefore careful analysis of the ventilation design is advisable [3]. Large space building is characterized by complex geometry and complex phenomena of air, heat and moisture flow. Nowadays conducting research for such a facility is possible by the CFD technique, which is particularly applicable where measurements in the facility are difficult or impossible, and where traditional engineering methods do not work [7]. Annex 26 in the IEA project recommends CFD when studying large complex facilities [3]. However, the CFD technique has its limitations. Numerical simulation of the flow field in large enclosures presents many difficulties due to the large size of the enclosure and the complicated flow field. Furthermore, a high number of control volumes or flow cells is needed to represent the flow. This adds to the complexity of simulating phenomena such as turbulence and increases the risk of numerical errors [3]. In the case of large-scale objects, a compromise between the real size of the model in relation to the available computing capabilities of the servers and for the possibility of obtaining reliable results plays on important role. Thus, the geometry of the tested object has to be simplified. Moreover, the CFD technique requires a good definition of the tested object and therefore acquiring boundary conditions, most often through measurement or calculation. In practice, it can be difficult to obtain such data, in particular in the case of industrial buildings where there are various types of technical equipment or complex technologies and the measurements cannot interfere with the manufacturing process. In this case, the use of thermovision is worth of attention. Thermographic measurements are an effective and non-destructive diagnostic method. The main advantage of this technique is the fact that measurements are made during normal operation of devices, without the need to disturb the technological process. Using a thermovision camera, an image of the temperature field of the tested object is obtained, with a resolution of up to 0.1°C. Thermographic diagnosis is widely used in facilities where the source of the problem manifests itself with the change of the temperature distribution on its surface, and therefore also in industrial or production plants [8]. So far, including thermovision in CFD research has been done for a large scale sports facility and it was shown in [9], while examples of general studies of large objects, experimental or numerical, in [4, 5, 10]. Finally, the use of CFD to study complex physical processes in the built environment requires model validation. Typical methods for validating CFD results are the following: – the comparison of simulation results with reducedscale or full-scale experimental data: the most popular method, which generally involves graphical comparison of computational results and experimental data. If the CFD results mostly agree with the experimental data, the computational results are declared validate; – benchmark solutions; – analytical solutions. In a given application, the results of computer calculations do not have to be verified by methods used in scientific works, because the purpose of calculations is not to achieve precise numerical results, but only to check whether the results indicate incorrect thermal conditions of ventilation systems operation and, consequently, reduce the likelihood of such conditions occurring in fact. Verification of the results can take place each time in the real object. The presented analysis is a great importance for the current state of knowledge and can be also widely used in practice, for example, to reduce energy consumption in industrial facilities and other large buildings by the use of the CFD method. Only a few examples of similar research can be indicated in the literature as e.g. [11, 12]. In this paper, the basic numerical simulations of air and heat flow in a ventilated industrial large-scale facility were undertaken. Thermal imaging measurements were made to identify heat sources. Calculations were carried out for two cases. The possibility of reducing the supply airflow rate without affecting either technology safety or thermal comfort was examined. R E S E A R C H O N T H E R M A L C O N D I T I O N S I N V E N T I L A T E D L A R G E S P A C E B U I L D I N G E N V I R O N M E N T e 4/2018 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 171 2. OVERVIEW OF THE TESTED FACILITY AND ITS NUMERICAL MODEL The test object, located in the Mazowieckie Voivodeship in Poland, was a processing hall (with a non-rectangular shape) with a floor area about 1550 m2 and a maximum dimensions 74 × 25 m (length × width). The average and maximum hall height are 6.5 m and 9 m, respectively. Its total volume is over 10000 m3. This hall is located inside the facility of the entire production plant, therefore part of the partitions are internal partitions. The sources of heat are various types of machines, devices, and technologies for food production. The ventilation system consists of displacement diffusers placed under the ceiling at the height of about 4 m. It consists of 2 supply and exhaust systems (SYS1 and SYS2), each with a capacity of 30000 m3/h, equipped with water heaters, and coolers, heat recovery, dampers, filters, fans. It is a continuous air ventilation system i.e. system without the possibility of reducing the flow (no regulation of the fan rotation speed). The performance regulation is done through the use of regulating dampers. Air handling units are located on the roof of the building. The object’s geometry was prepared on the basis of as-built drawings and inspection of the object. The geometric model was prepared in the SpaceClaim software. It includes real dimensions of the facility and technical equipment such as machines, devices, technologies. It also contains a lighting system, people, walls, gates, and a supply and exhaust ventilation systems. Fig. 1 shows the numerical model of the tested facility with significant equipment elements, whose parts were enlarged in Fig. 2, detail C. Due to the complicated geometry, diffusers were simplified to solids consisting of rectangular flat surfaces (Fig. 2, detail A), whose active field was equal to the maximum effective area of supply openings, in fact round, in order to maintain the air flow velocity of 1.5 m/s, recommended in this type of diffusers. Exhausts were modeled as flat, round surfaces with real dimensions along with a drip tray underneath (Fig. 2, detail B). All technical equipment was simplified to rectangular blocks divided into smaller areas (Fig. 2, detail C), in order to be able to separate areas with different temperatures in boundary conditions. Lighting and people were modeled in a simplified manner as rectangular heat sources. 3. CALCULATION CASES AND THEIR BOUNDARY CONDITIONS In this study, it was examined how the ventilation system works in design conditions and in conditions where amount of supply air was reduced. Therefore numerical simulations were carried out for two basic cases: a) case 1 – variant with the design amount of supply air; b) case 2 – variant with amount of supply air reduced by 40%. For each case, the ventilation air mass flow rate and its temperature were taken into account in boundary conditions in air supply openings, and static pressure in exhaust openings. Temperature and emissivity were set on the surfaces of the technical devices. Heat gains from lighting and 4 people were related to the surface of their model. The surface temperature was set for the walls and gates, only for the roof, the heat transfer coefficient and the temperature of the outdoor air were included. Information on the temperature distribution on the surfaces of devices and walls surrounding the hall was taken from thermovision measurements with the use of FLIR E50 camera (Fig. 3). Outdoor, indoor and supply air temperature was measured. The emissivity of surfaces and heat Figure 1. The numerical model of the tested facility (isometric view) Figure 2. The numerical model of the tested facility with marked details: detail A – diffusers; detail B – exhaust; detail C – technical equipment A . P a l m o w s k a , G . M i c z k a 172 A R C H I T E C T U R E C I V I L E N G I N E E R I N G E N V I R O N M E N T 4/2018 transfer coefficient of the roof were determined. Surfaces of technical equipment or technological elements for which the temperature was set at boundary conditions were shown in the Fig. 4. The boundary conditions were summarized in Table 1, 2. 4. NUMERICAL PROCEDURE The numerical calculations were carried out using ANSYS CFX