A SCHEME AND METHOD OF CALCULATION FOR VENTILATION AND AIR CONDITIONING SYSTEMS OF ICE ARENAS

Journal of Technology, Vol. 32, No. 2, pp. 139-146 (2017) 139 A SCHEME AND METHOD OF CALCULATION FOR VENTILATION AND AIR CONDITIONING SYSTEMS OF ICE ARENAS Melkumov Viktor Narbenovich Chuykin Sergey Vladimirovich* Department of Heat and Gas Supply and Oil and Gas Business Voronezh State Technical University Voronezh, Russia 394006, R.U. Key Words: ice arena, ventilation, air conditioning, air distribution, mathematical modeling. ABSTRACT This article presents a new scheme of air distribution for air conditioning systems of indoor ice arenas and proposesa method of calculating parameters of the microclimate zone of the ice field in this scheme. The developed mixed scheme differs from existing ones by adoption of multi-stage mixing of outdoor and recirculated air, removed from the upper and lower parts of the maintained area of the premises. To calculate the parameters of the microclimate zone of the ice field a graphic-analytical method using IDdiagrams was adopted. The results of numerical calculations show that the implementation of air distribution in the cold season according to the proposed scheme reduces energy costs for heating of supplied air bypossibly 15%, compared to the most economical of existing schemes. I. INTRODUCTION One of the key factors in the formation of air flows in artificial indoor ice arenas is the cooling surfaces in the lower part of the maintained area which may cause air flows of different temperatures to disintegrate. Thus, due to differences in density, both cold and hot air accumulates in the lower and upper part of an ice rink respectively hindering air circulation and reducing the efficiency of microclimate systems. As a result, for ventilation and air conditioning systems to operate optimally, extra calculation of the development of ventilation flows considering gravitational forces must be performed [1, 2]. In addition, due to the fact that there will be areas with different microclimate parameters within a single premise (ice arena area and spectator seats), differences between temperatures of these areas must be considered. Failure to comply with parameter guidelines of the indoor air of an ice skating arena may reduce ice quality and cause fog over the ice field. In addition it should be remembered that the condition of the ice field will depend on how evenly temperatures are distributed over the ice surface. Temperature increase in either area will result in the ice becoming soft, posing a threat to the health and safety of athletes and referees. Ice of a thickness of 25 to 50 mm is deemed as suitable to skate on. Thicker ice may cause higher costs in maintaining temperature of the ice surface as each extra 10 mm of ice needs a reduction in temperature by a cooling device by 1 [2]. This type of ice surface consists of a lot of layers with relatively small individual crystals that do not enter the upper layers of the ice. At the same time condensation, evaporation and interaction of skates with the ice at an optimal temperature are within the crystals [2]. This can be accounted for due to the lower thermodynamic stability of the ice boundaries when compared to the major crystal mass. Therefore monolith ice with a large crystal structure should be poured with lower ice growth intensity. Formation of a high-quality ice surface and temperature distribution on an ice surface is detailed in [3]. Apart from maintaining ice quality and preventing fog over its surface, ventilation and air conditioning systems should take into account health and safety of ice users. This is achieved by controlling the * Corresponding author: Chuykin Sergey Vladimirovich, e-mail: ser.chu88@yandex.ru

140 Journal of Technology, Vol. 32, No. 2 key microclimate parameters of temperature, moisture content, relative humidity and enthalpy of the interior air. The above parameters mainly depend on the thermal and air modes of the maintained area of the ice arena. Therefore when considering design of microclimate systems it is important that a suitable air distribution scheme and accurate calculation of the air flows primarily caused by reduced temperature of the ice arena surface is achieved. It is also to be noted that in the immediate vicinity of the ice surface, through the entire operating temperature range, air reaches a dew point [1] causing condensation of residual moisture. The choice of a more viable and energy-efficient scheme of air distribution depends on architectural and planning characteristics and the microclimate properties of the areas maintained by particular systems of ventilation and air conditioning [7]. Some empirical and theoretical studies have shown that the circulation of air masses in isolated premises is largely due to outgoing flows thus in order to select an air distribution scheme special focus must be put on methods of supplying incoming air [3-6]. All of the above is indicative of the growing need for the following: development of a new air distribution scheme for air conditioning systems of ice arenas to improve their efficiency; a method of calculating the parameters of ice arena microclimates to assist in the design of air distribution according to a developed scheme; design of a mathematical description of the developed scheme to determine the parameters and operational modes of inlet and outlet devices. II. MATERIALS AND METHODS Existing methods of mathematical modeling of microclimate parameters in ice arenas are based on boundary conditions according to which the total area of the ice arena is divided into the ice field area and spectator seating. Systems to maintain the microclimate should be designed in such a way as to prevent air from coming from the ice field to the spectator seating, or vice versa. It is therefore possible to consider these areas in isolation. Fig. 1 shows the required air exchange in the ice field area with hybrid ventilation from the bottom to the top and from the top to the bottom. Due to architectural and planning features of artificial indoor ice arenas the incoming air can only be supplied from the top towards the maintained area by lateral or vertical flows. In the figure the inlet air is supplied from the upper area through air distributors 1 placed along the field and removed through the exhaust devices 3 placed over the ice. Fig. 1 Design of air distribution of an ice arena: 1. inlet air distributors; 2. air inlet devices fitted into the en- closure; 3. exhaust devices placed over the ice sur- face; 4. enclosure; 5. ice field; 6. pipeline exhaust placed in under floor ducts In the second case the inlet air is also supplied from the upper area, however it is removed using air inlet devices 2 placed in the immediate vicinity of the ice arena. The necessary amount of inlet air is determined via the condition of even filling of the ice surface by inlet flows. formula (1): The consumption of outside air [1] is given by the L q n, (1) where q is the health and safety standard of the fresh inlet air per one person training; n is the number of athletes and referees which is inadequate. In order to reduce energy consumption of ventilation and air conditioning systems inlet air is boosted by air recirculation. The parameters of air supplied by air conditioning systems are identified with a graph analytical method using ID-diagrams of air humidity, where determining the parameters of outdoor, indoor and removed air is crucial. (The ID-diagram of humid air con- nects graphically all the parameters that define the heat and humidity of the air. It features a built-in, oblique-angled coordinate system, which makes it easier to graphically con- struct the diagram. The diagram is divided by lines of con- stant values of enthalpy I = const and moisture content D = const. Thus it is termed an ID-diagram). In designing from the top to the top distribution of air to the outlet air, some of the heated air will be induced from the upper area of the ice arena with the amount of the moisture perceived by the removed air being 1 g/kg, thus the moisture content of the outlet air is given by the formula (2): d d 1, (2) where d is the moisture content in the removed air, g/kg; d is the moisture content at the ice surface, g/kg.

Melkumov, V. N., and S. V. Chuykin: Ventilation and Air Conditioning of Indoor Ice Arenas 141 Fig. 2 ID-diagrams of changes in the air parameters for warm season in designing the air distri-bution for the following schemes: (a) from the top to the top; (b) from the top to the bottom Fig. 4 ID-diagram of changes in air parameters in design of air distribution in the mixed scheme during the cold season Fig. 3 ID-diagrams of changes in air parameters during the cold season in designing air distribution according to the schemes: (a) from the top to the top; (b) from the top to the bottom In designing a from the top to the bottom air exchange, the parameters of the removed air correspond with the parameters of the air over the ice surface. A comparative analysis of the energy efficiency of both schemes, using the example of an ice arena in the city of Voronezh, shows that in designing a from the top to the bottom air exchange there is a considerable drop in energy consumption for cooling and heating of inlet air in its production during warm and cold seasons. This is accounted for by the fact that in removal of air from the area in the immediate vicinity of the ice surface, the temperature and moisture content are lower than the temperature and moisture content of the air removed from the upper parts of the premises. That is why the parameters of the mixing point change, thus saving cooling and heating energy. This is most pronounced in the from the top to the bottom scheme when compared with ID-diagrams of moist air as it is being treated in the inlet device for different air distribution schemes for warm and cold seasons as illustrated in Figs. 2 and 3. For design of air processing in the ID-diagram we begin with the application of points H, and and the parameters of outdoor, indoor and removed air (Figs. 2-4). Then points H and are connected. The resulting segment describes the process of mixing outdoor and recirculated air. The point of mixing C is found at the intersection of the segment H- with the line I y = const, determined by the formula (3): L I L I I, (3) L where L, L and L are the cost of recirculation, outdoor and supply air, respectively m 3 /h;, and are the density of the recirculation, outdoor and supply air, respectively, kg/m 3 ; I, I and I are the enthalpy of the recirculation, outdoor and supply air, respectively, kdj/kg. Point " " is located on the line d = const at a temperature determined by the formula (4): 3,6.. t t C L Q c Q n n p, (4)

142 Journal of Technology, Vol. 32, No. 2 Table 1 Air parameters in the considered points in the organization of the air distribution for the scheme from the top to the top Nome of a point t, C, % d, g/kg I, kdj/kg, kg/m 3 Warm season 10 55 4,33 20,9 1,25 28,6 50 12,7 61,2 1,17 20,2 29 4,33 31,3 1,20 14,5 51 5,33 28,2 1,23 3,2 90 4,33 14,1 1,28 C' 18,1 54 7,1 35,9 1,21 Cold season 6 45 2,65 12,7 1,27-26 76 0,3-25,6 1,43 13,4 27 2,65 20,2 1,23 10,5 44 3,65 19,5 1,25-3,1 90 2,65 3,5 1,31 C' 6,1 52 3,1 13,9 1,26 Table 2 Air parameters in the considered points in the organization of the air distribution for the scheme from the top to the bottom Nome of a point t, C, % d, g/kg I, kdj/kg, kg/m 3 Warm season 10 55 4,33 20,9 1,25 28,6 50 12,7 61,2 1,17 20,2 29 4,33 31,3 1,20 10 55 4,33 20,9 1,25 3,2 90 4,33 14,1 1,28 C'' 12,5 60 5,4 26,2 1,25 Cold season 6 45 2,65 12,7 1,27-26 76 0,3-25,6 1,43 13,4 27 2,65 20,2 1,23 6 45 2,65 12,7 1,27 1,8 58 2,5 7,9 1,28 C'' 2,3 49 2,2 7,9 1,28 where Q. is the convective flow of heat from the air to the ice surface, Watts; Q. is heat output from people, Watts; t is required air temperature at the ice surface, ; is heat capacity of supply air, kdj/(kg C). Meanwhile the line - corresponds to the cooling of supply air at its convective heat exchange with the ice surface, and the segment - (the organization of the air exchange on the scheme from the top to the bottom parameters of the removed air will correspond to the parameters of the air above the ice surface) characterizes the process of changing the parameters of air at its removal. The next stage of processing of supplied air is its drying to the desired value of moisture content d n. This is done by cooling, which is characterized by the segment C-O. Point O is located at the intersection of the lines d = const and = 90%. In the final processing stage, the air is heated to a temperature t n, and the process of heating is characterized by

Melkumov, V. N., and S. V. Chuykin: Ventilation and Air Conditioning of Indoor Ice Arenas 143 the segment "O- ". The parameters of the air when processed for schemes "from the top to the top" and from the top to the bottom with climatic data characteristic for European Russia [5] are given in Tables 1 and 2. Fig. 2 shows changes in the parameters of the air of the inlet device and area of the ice field in designing of an air exchange according to the from the top to the top and from the top to the bottom schemes during the warm season. In this case the thermal energy for treating the inlet air does not depend on the chosen method of air distribution, which is not the case for the necessary cooling energy. As the supplied air is being dried, as characterized by the lines and, Fig. 2, in the cooling chamber, the energy is spent and the amount for analyzed schemes of air distribution is determined using the known formula (formula (5) and formula (6)) [8] applied for this case: ( t t ) 3600 ' 0 Q' L, (5) ( t t ) 3600 '' 0 Q'' L, (6) where Q x and Q x are amounts of cooling energy in the from the top to the top and from the top to the bottom air distribution schemes respectively, Watts; t and t are the temperatures of the air following the mixing in the from the top to the top and from the top to the bottom air distribution schemes respectively, ; t is the temperature of the air at the point,. For the from the top to the bottom air distribution scheme a lot of cooling energy is saved. This can be seen when comparing the value Q x (which corresponds to the cooling process of the supplied air C O in the inlet device from the scheme from the top to the top) with the value Q x (which corresponds to the cooling process of the supplied air C O in the inlet device from the scheme from the top to the bottom) in Fig. 2. This is the most significant finding for the operation of ice arenas all year round. A distinctive feature of the processing of air in the cold season are lower costs in the processing of outside air, as the moisture content decreases significantly as temperatures drop. In addition, our calculations suggest that cooling energy might not be needed at all, unlike from the top to the top air distribution where, in order to decrease moisture content following mixing, the air is cooled off, see Fig. 3. During the cold season when using the from the top to the bottom scheme, apart from saving cooling energy there is also a significant decrease in heat consumption for heat inlet air, as shown by formula (7): ( t t ''), Q L (7) 3600 This can be seen by comparing the value Q T (which corresponds to the heating process of the supplied air in the inlet device for the scheme from the top to the top) with the value Q T (which corresponds to the heating process of the supplied air in the inlet device for the scheme from the top to the bottom) in Fig. 3. From the above mentioned we conclude that the most viable energy-efficient air distribution scheme is from the top to the bottom as used in the construction of the Palavela, an ice arena in Turin, Italy. However it should be mentioned that in designing a from the top to the bottom air distribution scheme during the cold season for providing the specified moisture parameters of the inlet air it might be necessary to fit an extra watering section in the inlet device, which will cause construction and operation costs to rise. Conversely if the indoor air of an ice field gradually dries out it will compromise ice quality. Degradation of ice characteristics following drying of the indoor air is due to both condensation and sublimation (evaporation) of moisture off the field surface with moisture content of the air over the ice intensifying sublimation as it decreases. Based on the difference between temperatures at the boundary of the phases of the ice with a negative temperature it is inevitable that there is a thin film of water produced whose thickness depends on the temperature of the air and ice. Since the friction coefficient of skates on ice is directly proportionate to the properties of the ice, this film that facilitates skidding is a major consideration for sporting events held in indoor ice arenas. The thickness of the water film increases with increasing air or ice temperature and vice versa. Ice is suitable for skating on at thicknesses ranging from 25 to 50 mm. Greater than this value will result in increased costs to maintain a constant temperature of the ice surface, because with every 10 mm increase in ice thickness it is necessary to lower the refrigerant temperature by 1. The ice surface obtained by this technology has a layered structure with relatively small, isolated crystals which do not penetrate into the overlying layers. In addition, humidity influences the development of a sub-layer of water between the ice and air of an ice arena. Therefore if the moisture content of the indoor air drops considerably, sublimation might

144 Journal of Technology, Vol. 32, No. 2 cause complete evaporation of water off of the ice. Hence during a long period of operation of air conditioning systems the moisture content of the indoor air of an ice arena becomes unacceptably low and extra processing by an inlet flow is necessary for from the top to the bottom air distribution. This can be avoided using multi-step mixing of indoor and recalculated air with different parameters. For that it is necessary to develop a new scheme for air distribution of air conditioning systems of an ice field which will include all the advantages of existing methods of air distribution. III. RESULTS AND DISCUSSIONS The above mentioned multi-step mixing of outside and recalculated air with different parameters can be performed using individualized selection of recalculated air from the upper and lower areas of an ice arena. An optimal flow is best achieved from the upper area through air distributors placed at an angle along the longer sides of the ice field due to the architectural and technological properties of these venues. We term the suggested method of air distribution mixed as shown in Fig. 1. The indoor air is removed from the lower area with exhaust devices fitted into the enclosure. The air from the upper area of the ice arena is removed with a similar from the top to the top scheme through air inlet devices placed over the ice. We investigated special features of modes of changing the air parameters in the inlet device and area of an ice field using an ID-diagram of the condition of moist air using graphic analytical calculations. The original data for the graphic analytical calculations of air processing are the parameters for indoor, outdoor and recalculated air as well as volumetric and mass consumption parameters. During the cold season, at the initial stage for the inlet device there is a two-step mixing of outside and recalculated air with recalculated air being supplied at the first and second stages of mixing which is removed from the lower and upper parts of the premises respectively. The processing of the air in the inlet device, characteristic for a developed mixed scheme of air distribution, including twostage mixing and heating, is presented in Fig. 4. Similarly to the previously given example, design of air processing using ID-diagrams begins with drawing of the points, and whose parameters correspond with those of outdoor, indoor and extracted air (Fig. 4). The points characterizing the parameters of the airflows being mixed are then brought together. At the initial stage of mixing these will be and. The resulting line characterizes mixing of the outdoor and recalculated air at the initial stage. The mixing point 1 is at the intersection of the line - with the line I 1 = const where I 1 is given by the formula (8): I 1 G 1I 1 G I. (8) G 1 Here G 1, G and G 1 represent mass consumption of recalculated air at the initial stage and of outdoor air and following the mixing respectively, kg/h; I 1 are enthalpies of the recalculated air at the initial stage respectively, kj/kg. Air consumption following the mixing G 1 is the sum of the consumption of recalculated air at the initial stage G 1 and consumption of outdoor air G. At the second stage mixing is characterized by the line 1- and the mixing point 2 is at the intersection of the line 1- with the line I 2 = const where I 2 is given by the formula (9): I 2 G I G I 2 2 1 1 G c2. Here G 2, G 2 are mass consumptions of recalculated air at the second stage and air following the second mixing respectively, kg/h; I 2 are enthalpies of the recalculated air at the second stage of mixing, kj/kg. As for the first and second stage of recirculation the air is collected from the lower and upper parts of the premises, their parameters are determined by those of the air at points and respectively. The consumption of the air following the second stage of mixing should correspond to the necessary consumption of the inlet air supplied to the premises. In addition the moisture content of the air following the second mixing should be maximally approximated to that of the inlet air, i.e., d c2 d n. The ratio of the amount of the recalculated air supplied at the first and second stage of mixing is determined by a method of sequential approximation with our calculations showing that during the initial approximation the consumption of the air should be 70% of the total amount of recalculated air. As a result of mixing at the first stage the outdoor air is heated and wetted as in Fig. 4, which is characterized by the line - ( 1 ). After that the air enters the second stage of mixing where the moisture content is increased to as high as is required, which is characterized by the line 1-. Following the second stage of mixing the inlet air is heated in a radiator (process 1- ) and delivered into the premises. The necessary amount of heat to treat the inlet air during the cold season is given by the formula (10): ( t t 2), Q L (10) 3600 (9)

Melkumov, V. N., and S. V. Chuykin: Ventilation and Air Conditioning of Indoor Ice Arenas 145 Fig. 5 Diagram of required heat expenditure for processing air in inlet device for cold season depending on air distribution scheme In Fig. 4 the line - characterizes cooling of the inlet air as a result of convective heat exchange with the surface of the ice field. For example we determined the required amount of heat energy for various schemes in the cold season. For this, we substituted the values of, t, t, which are typical for from the top to the top schemes and from the top to the bottom schemes, from Tables 1 and 2 in the Formula (7). The consumption of supplied air we take as equal to17,000 m 3 /h. Thus, the consumption of heat energy under the from the top to the top scheme will be about 96 kw, and under the from the top to the bottom scheme it will be about 68 kw. For our developed scheme, in addition to the mentioned parameters, it is necessary to know the temperature at the point of mixing in the second stage, which is 3.4 in this case. Then, from the formula (10) it follows that the heat consumption will be about 59 kw. The calculations (with climatic parameters characteristic for European Russia) show that in designing air distribution during the cold season in the mixed scheme there is a significant saving of thermal energy, around 15% in Fig. 5. During the warm season, in treating inlet air the major considerations drying of outdoor air and reduction of its temperature. The mixed scheme is thus more efficient, making from the top to the bottom air distribution the most viable option. Fig. 2(b) indicates that if this type of air exchange scheme is employed, after entering the mixing chamber inlet air should be dried until it reaches the moisture content at point by cooling off (process - ). At the final stage the air is heated to the temperature at point (process - ) and supplied into the premises where as a result of interaction with the ice field surface it cools off, which is characterized by process -. IV. CONCLUSIONS In this study we present a newly developed mixed scheme of air distribution for air conditioning systems of ice fields that differs from existing schemes due to multi-stage mixing of outdoor and recalculated air, removed from the upper and lower parts of the maintained area of the premises. It follows from the diagram that in the implementation of air distribution in the cold season with the proposed mixed scheme energy costs for air processing are reduced by 15%. At the same time the use of this type of scheme during the warm season increases energy and heat consumption. Therefore during yearly operation of an ice arena, to reduce energy consumption air conditioning of the arena during the warm and cold seasons must be performed according to different schemes. i.e., during the cold season when the arena is used heavily, it is recommended that air distribution should be performed as set forth in the paper using the mixed scheme. During the warm season air exchange should adopt the existing from the top to the bottom scheme. Therefore in order to optimize operation ventilation and air conditioning systems a necessary consideration in the design process is to provide a way to switch between air distribution modes. In addition it should be remembered that the main drawback of the developed mixed scheme of air distribution is that the main air ducts of the recirculation system of the first stage are laid in underground conduits, so a careful study of pipeline routes in the design of ventilation and air-conditioning would be required. REFERENCES 1. Melkumov, V. N., and S. V. Chuykin. 2013. Organization of Air Distribution of Covered Multipurpose Ice Rinks. Scientific Herald of the Voronezh State University of Architecture and Civil Engineering. Construction and Architecture (3): 17-28. 2. Chen, Q., K. Lee, S. Mazumdar, S. Poussou, L. Wang, M. Wang, and Z. Zhang. 2010. Ventilation Performance Prediction for Buildings: Model Assessment. Building and Environment 45 (2): 295-303. doi: 10.1016/ j.buildenv.2009.06.008. 3. Mel'kumov, V. N., A. V. Loboda, and S. V. Chuykin. 2015. Mathematical Modelling of Air Streams in Large Spaces. Scientific Herald of the Voronezh State University of Architecture and Civil Engineering. Construction and Architecture (1): 15-24. 4. Anisimov, S. M. 2012. The Solution of the Problem of Turbulent Transfer of Momentum, Heat and Scalar in the Volume of the Ice Arena Bowl. Bulletin of Civil Engineers 34 (5): 149-155.

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