0 Introduction
With the improvement of people's living standards, people have developed a strong interest in ice sports, both in the north and in the south. The construction of artificial ice rinks has broken the limitations of geography and time, and provided people with ice hockey, speed skating, figure skating, ice dance, popular entertainment skating and other ice activities. Artificial ice rinks can be divided into ice rinks and speed skating rinks for athletes' training and competitions, and public ice rinks for entertainment. The recreational ice rink air conditioning system is not only different from the large-scale competition ice rink, but also different from the general comfort air conditioner, and the initial investment in construction is high, and the operation energy consumption is large, so the design of the ice rink is worth studying.
1 Recreational Ice Rink Air Conditioning Features
1.1 Most of the general recreational ice rinks are set up in commercial recreational buildings, which are operated, maintained and managed by independent merchants. Since it is used for general purposes, the size can be arbitrarily determined, but most of them are built according to the size of the court that can be used for ice hockey games. Recreational ice rinks usually do not have large spectator seats, but only have some verandahs and public areas.
1.2 The general recreational ice rink has a large space, a large area of enclosure facing the outdoors, and sometimes a light-transmitting roof, and the load characteristics are complex.
1.3 There are three distinct temperature zones in the rink area: a low temperature of -4°C near the ice surface, a temperature of 10°C in the upright area of the skater and 20°C in the surrounding public area.
1.4 Solving the problems of fogging, roof and interior surface condensation, and anti-corrosion is a key part of the design of ice rink ventilation and air conditioning. Due to the influence of cold radiation, the calculation of anti-condensation in ice rinks is different from that of swimming pools, and it is difficult to directly use the existing formulas for accurate calculation, and numerical calculations are generally used for analysis.
2. Determination of interior design parameters
2.1 Temperature and humidity
For the dry bulb temperature and relative humidity of the air conditioning design in the ice rink, there are no relevant design specifications and technical measures in China, and only a few articles give recommended values. In the literature, it is recommended that the indoor temperature should not be too low, generally 24°C, and the relative humidity should not be too high. In other literature, it is suggested that the indoor temperature of the ice rink at a height of 1.2 m should be 20°C±2 °C, and the relative humidity should be 50% ±5%. The literature suggests that the air temperature and humidity in the ice rink should be strictly controlled, with the air temperature below 22°C and the relative humidity less than 60%. For example, some literature gives that the air temperature at a height of 1.5m in the ice rink is 6~12 °C, and the relative humidity is not more than 70%, and it is believed that this is both energy-saving and meets the requirements of use.
There is a big difference in the recommended values of the design parameters in the ice rink given by the domestic and foreign literatures. The design parameters of the ice rink given in the domestic literature are given with reference to the design parameters of the general comfort air-conditioned room, and the comfort requirements of the ice skaters in the ice rink are considered according to the general area, the temperature in the ice rink is low, and the heat supply is required in summer and winter to reach the design temperature, which produces a large amount of cold and heat to offset the energy consumption, while the comfort requirements of the skaters need to be explored, and the problems of condensation and fogging will be significantly aggravated under this design parameters. Foreign literatures basically do not control the temperature in the ice rink, and only slightly control the relative humidity. This may "sacrifice" the skater's need for temperature comfort (in fact, subsequent numerical calculations in this paper show that the comfort of the person is still within the acceptable range under this design condition), but it is good for preventing condensation and fogging, and is very energy-efficient.
In addition to meeting the comfort requirements of personnel, the temperature and humidity in the ice rink should also meet the requirements of anti-condensation, anti-corrosion, and anti-fogging. Some indoor parameters that are easy to cause fogging and structural decay and corrosion have been summarized in the literature, as shown in Table 1~3. In order to prevent the various components in the ice rink from being affected by condensation or fog, the relative humidity of the ice rink space needs to be strictly controlled.
2.2 Fresh air volume
Recreational ice rinks are generally built according to the size of the standard competition venue, and their sliding area is considered to be 1.5~2.8m2/person, and it will be very crowded when 1.5m2/person is taken. The per capita design fresh air volume can be taken according to Article 3.0.2 of the "Energy Conservation Design Standards for Public Buildings" (GB50189-2005, new edition 2015).
2.3 Wind speed
The wind speed in the personnel activity area needs to be strictly controlled, and excessive air supply speed will accelerate the melting of the ice surface and increase the burden on the ice-making system, generally, the wind speed should be about 0.2m/s. If the air supply of the nozzle is used, in order to control the wind speed in the area where the personnel are active, the air supply speed of the air supply outlet needs to be strictly calculated and determined. For the general upper air supply, the wind speed of the air supply outlet should generally not be greater than 2m/s.
3. Anti-condensation design of the ice rink
3.1 Causes of condensation
Under the action of cold radiation on the ice surface, the temperature of the solid wall around the ice rink and the inner surface of the roof is low, once it is lower than the dew point temperature of the nearby air, it will cause water vapor condensation to adhere to the wall, which will not only corrode the wall material and form mold, but also form water droplets to fall in serious cases, affecting the smoothness and normal use of the ice surface. In addition, when the humid outside air enters the venue, the dew point temperature of the air inside the venue increases, which will also aggravate the condensation.
3.2 Measures to prevent condensation
At present, domestic and foreign measures to prevent condensation are mainly considered from two aspects: building materials and heated airflow.
1) Use low emissivity materials, such as aluminum foil, polished aluminum plate, FRP corrugated board, etc., as the surface material of the roof, so as to reduce the cold radiation of the ice to the roof, and at the same time maintain a high temperature (higher than the dew point temperature of the air in the field). These panels also play a role in improving the illumination in the field.
2) Heat the air to the roof to raise the surface temperature of the roof above the dew point of the surrounding air to prevent condensation, and the air supply is horizontally attached to the jet to form a layer of hot air at the top to avoid condensation on the roof.
3) Add a dehumidifier in the ice rink to reduce the humidity content of the air, thereby reducing the dew point temperature of the indoor air and reducing condensation.
4) On the premise of meeting the comfort requirements, try to reduce the temperature and relative humidity in the field, so as to reduce the dew point temperature and reduce the possibility of condensation.
For dehumidification, there are mainly the following methods: heating dehumidification, cooling dehumidification, solution dehumidification, solid dehumidifier dehumidification, dry dehumidification, etc., and the advantages and disadvantages of various dehumidification methods are shown in Table 4. In the ice rink air conditioner, because there is a low-temperature refrigerant can be used, cooling and dehumidification is convenient and economical, and it is widely used.
4. Anti-fog design
4.1 Causes of fogging
The fog over the artificial ice rink is mainly due to cold radiation and convective heat transfer on the ice rink. The air temperature near the ice surface is close to the ice temperature, but as the altitude increases, the air temperature rises rapidly until it is close to room temperature. The state point of the indoor air mixed with the ice air is in the fog area of the enthalpy-hygrogram, that is, fog can be formed, especially when the air does not flow. From the enthalpy and humidity diagram, it can be concluded that the higher the indoor air temperature, the greater the relative humidity, and the easier it is to form fog. According to the field measurements in the relevant literature, under the conditions of -4°C ice surface temperature, indoor air temperature 24°C, average air velocity of 0.2m/s and relative humidity of 80%, a weak fog with a fog particle radius of 7~15μm, a concentration of 100 pieces/cm3 and a sight distance of 15m will be formed over the ice rink after 8 h of cold radiation, and the fog layer height is about 4m. The formation time of the fog layer is 02:00~10:00.
4.2 Anti-fogging measures
According to the mechanism of fog formation, the defogging and dehumidification in the artificial ice rink can be summarized in the following ways.
1) Since the ice rink needs to introduce fresh air, as long as the fresh air system (which has been dehumidified) is used to supply air to the ice surface, the mixing of indoor air and the air near the ice surface is strengthened, so that the mixing point is close to the indoor air state, and it will be able to stay away from the fog area. In terms of airflow organization, it is advisable to choose the upward and downward return airflow mode, and the return air outlet is close to the ice rink. Because the volume of fog particles is larger than the volume of air molecules, it is easy to be carried away by the air flow, so the fog will overflow from the ice rink over the fence to the surrounding area, and then disappear by itself, so as to achieve the purpose of fogging. After the fog is removed, the air supply to the ice rink can be stopped, because the fog removal changes the air humidity in the ice rink, so there will be more than 8 h before the formation of the next fog layer, which can ensure a certain use time. After 8 hours, the ice surface can be trimmed by the ice surface dresser and then defogged, so that the ice rink can be fog-free. This approach can also reduce ventilation operating costs. It should also be noted that the average wind speed near the ice surface should not be too large, otherwise it will affect the cold load of the ice surface and cause changes in the ice surface temperature.
2) A dehumidifier is installed in the indoor ice rink area for local dehumidification treatment to reduce the dew point temperature in the indoor area. The dehumidifier can be cooled and dehumidified using the ice rink reflux solution.
3) For ice rinks with natural ventilation in the transitional season, pay attention to the temperature and humidity parameters of the outdoor air, and humid air cannot be directly introduced into the field.
5 Energy-saving measures for ice rinks
The initial investment in the construction of artificial ice rink is high, and the operation consumes a lot of electricity, and the energy consumption in the ice rink is mainly in two aspects: the ice rink refrigeration system and the ice rink dehumidification and air conditioning system.
5.1 Energy saving of refrigeration system
The main energy consumption in an ice rink is the ice-making system, where the chiller generates a large amount of condensation heat during the ice-making process, which is usually discharged from the cooling tower to the outside. At the same time, there are many occasions that need to be heated in the ice rink (such as end reheating, whole ice heating, etc.). If these two aspects are combined, it will be an energy-saving measure to recover the condensation heat generated by the ice machine and supply it to the parts that need to be heated. In addition, direct cooling and dehumidification with the ice rink reflux solution is also an energy-saving measure, as no additional refrigeration equipment is required, which saves initial investment and operating costs. Figure 1 shows the process diagram.
5.2 Energy saving of air conditioning system
When the outdoor fresh air is sent into the ice rink space through dehumidification treatment, the air in the ice rink needs to be discharged in order to maintain a certain slight positive pressure of the ice rink, and the energy recovery of the low-temperature air to be discharged can be used as a pretreatment for the fresh air. The schematic diagram of the air treatment process is shown in Figure 2.
6 Project examples
6.1 Project Introduction
An ice rink is an entertainment ice rink, located on the 7th floor of a large shopping mall in Shanghai, spanning 7~9 floors until the top floor, with a net height of nearly 20m in the ice rink, and the 1st floor is the general service desk, mainly for ticketing, shoe change and other areas. The 2~3rd floor is a sightseeing corridor, and the surrounding area of the corridor is a dining and entertainment venue. The ice rink is operated by a professional company and is responsible for the design and construction of the entire ice rink ice making system. The ice rink model is shown in Figure 3.
6.2 Determination of indoor parameters and air-conditioning methods
In the empty state (i.e., without any air conditioning measures), CFD simulations were carried out on the model in summer, winter and transition seasons to obtain PMV and PPD in the ice rink in different seasons, as shown in Figure 3.
ISO7730 recommended value for PMV, PPD index is: PPD<10%, PMV = - 0.5~0.5. "Design Code for Heating, Ventilation and Air Conditioning" (GB50019-2003) The recommended values for PMV and PPD indicators are: PPD ≤27%, -1≤PMV≤1. It can be seen that ISO7730 relatively strict requirements for human comfort are relatively strict.
From the CFD calculation results (see Figure 4~8), it can be concluded that the temperature of the skater's somal zone at 1.5m from the ice surface is 7~16°C, and the relative humidity is about 60% without turning on the air conditioner.
It can be calculated that the PPD in summer is between 5.1%~7.4% and the PMV value is between -0.4~- 0.1, the PPD in winter is between 5.6%~9.1% and the PMV value is between 0.2~0.4, and the PPD in the transition season is between 7.0%~9.1% and the PMV value is between -0.4~0.3. It can be seen that regardless of winter, summer or transition season, PMV and PPD indicators can basically meet the requirements of ISO7730. It can be seen that there is no need for air conditioning in the ice rink, and the proportion of skaters who are dissatisfied with the thermal environment of the ice rink when skating on the ice in the appropriate clothing for each season is quite small. This result is in good agreement with the recommended indoor parameter values in foreign ice rink design guidelines. As for the fresh air required by the personnel, it is only necessary to process the fresh air sent into the room to the air status point in the ice rink (the state point in the ice rink in each season can be calculated by CFD).
6.3 Anti-condensation analysis and calculation
The calculation results of the temperature, humidity field and roof wall temperature in the ice rink area can be obtained through model calculation, and then the possibility of condensation at the same time under different room parameters under each seasonal condition can be analyzed by comparing the dew point temperature of each wall surface (roof and surrounding cloister ceiling) and the air dew point temperature near it (which can be calculated by the obtained dry bulb temperature and relative humidity).
In summer, due to the influence of outdoor temperature, the inner wall of the roof above the ice rink has a higher wall temperature, coupled with the double influence of cold radiation on the ice surface below, the design day wall temperature is about 18.2~20.1 °C, and the temperature and relative humidity near the wall are 18.4 °C, 65%, and the dew point temperature is 11.7 °C, which will not produce condensation.
In winter, although the temperature of the roof wall is 5.5~6.7 °C, the air temperature near the wall is 6.5 °C, the relative humidity is 75%, and the dew point temperature is 2.4 °C, and there will be no condensation.
In the transition season, the wall temperature is 8.6~9.6 °C, the air temperature near the wall is 9.3 °C, the relative humidity is 45%, and the dew point temperature is -2 °C, and there will be no condensation.
In this example, the roof above the ice rink is a sandwich space, and the boundary conditions for the simulation calculation are also selected according to this, so it is concluded that the wall temperature in winter is 5.5~6.7°C, and radiative heat transfer plays a leading role.
However, if the roof above the ice rink is a general insulated roof, the wall temperature of the roof may be lower than the dew point temperature near it due to the low outdoor temperature and the dominant heat conduction, so it is generally recommended to set up a mezzanine roof or heat the roof to increase the temperature of the inner surface of the roof without condensation for the sake of insurance. CFD calculations can also be made according to the actual situation of the project, and corresponding measures can be taken after obtaining relatively accurate data (whether it is possible to condensate). The results of the comparison of the surrounding areas are shown in Table 5.
From the results of condensation analysis in Table 5, it can be seen that for the first floor area of the surrounding area, in order to ensure that the room is free of condensation, the relative humidity should not be higher than 55% when the design temperature is 24~25°C in summer. Condensation is almost non-condensation in winter. When the design temperature is 20°C during the transition season, the indoor relative humidity should not be greater than 50% in order to prevent condensation. For the 2nd and 3rd floors of the surrounding area, in order to ensure that the room is free of condensation, the relative humidity should not be higher than 60% when the design temperature is 24~25°C in summer. Condensation is almost non-condensation in winter. When the design temperature is 20°C during the transition season, the indoor relative humidity should not be greater than 50% to prevent condensation.
For the large space ice rink, the roof of the ice rink is far away from the ice surface, the radiation angle coefficient is correspondingly small, and the radiation heat exchange is reduced, and because the roof material is made of low emissivity material (aluminum foil), the radiation heat transfer is further reduced, so the roof receives less cold radiation from the ice surface, and the temperature of the roof wall is not lower. The corridor area around the ice rink, due to its proximity to the ice surface and the general material of the ceiling, receives greater cold radiation from the ice surface, and the temperature of the ceiling is very low, which is particularly easy to condensate.
6.4 Determination of parameters in the ice rink
1) Ice rink area
From the simulation results of summer, winter and transition season, it can be seen that there is no need to add an air conditioning system in the ice rink area, as long as the required fresh air is processed to the indoor state point to ensure the comfort of personnel, and the roof of the ice rink will not condense dew.
2) Surrounding area
In order to prevent the occurrence of condensation, the interior design parameters are determined as follows: dry bulb temperature 24 °C and relative humidity 55% in summer, 18 °C dry bulb temperature and 55% relative humidity (not controlled) in winter, and no more than 50% relative humidity in the transition season.
7 Conclusion
Building a well-functioning ice rink requires the concerted efforts of all relevant professions.
7.1 Requirements for the Architectural Profession
1) First of all, the construction profession should make a full demonstration when determining the location of the ice rink, and in terms of use effect and energy saving, it is best to place the ice rink in an enclosed space to minimize the impact of the external environment. Some rinks have glass roofs above them, and the condensation protection design for this purpose is too energy-intensive to cost.
2) The roof above the ice rink and the surrounding walls should be well insulated, and the roofing material above should be low-emissivity materials.
3) There are no facilities within 6 m above the ice surface, otherwise it will condense and condense due to cold radiation on the ice surface, resulting in mildew. The height above 6m is relatively difficult to condense due to the weakening of the cold radiation energy on the ice surface, but the specific project still needs to be calculated before conclusions can be drawn.
4) The fence around the ice rink is very important because it can effectively block the cold radiation of the ice rink into the surrounding space.
7.2 Requirements for Air Conditioning Major
1) Due to the considerable influence of radiative heat transfer in the ice rink, it is necessary to calculate the radiative heat transfer when designing the air conditioning of the ice rink. Hand calculations are usually not possible, and calculations using CFD simulation software can guide the design later.
2) The air temperature in the ice rink can be left uncontrolled, but the relative humidity should be controlled at less than 60%.
3) Corridors on all floors (especially those on the same floor as the ice rink) Because the cold radiation on the ice surface is the strongest, and the dew point temperature in the corridor is high, there is a high possibility of condensation, and it is necessary to effectively control it.
4) The air supply outlet in the ice rink should not be directly hit by the ice surface, and the wind speed of the air conditioning air supply outlet directly facing the ice rink should be 2m/s smaller, otherwise the ice surface will be easy to melt.
5) In some areas (such as severe cold areas), in order to prevent condensation on the roof, the ice rink can be directly air-conditioned with outdoor low temperature and dry air in winter, or the outdoor air can be heated to 30°C and sent into the air above the ice rink to form a hot air layer. In summer, outdoor air is injected horizontally through the air supply outlet directly through the fresh air unit (usually without a heat exchange coil), forming a layer of hot air in the upper part of the roof to avoid roof condensation.