Analysis of indoor environmental conditions and heat pump energy supply systems in indoor swimming pools
Graphical abstract
Research highlights
▶ Indoor swimming pools are studied based on human thermal comfort and energy saving. ▶ Construction and operating modes of a heat pump dehumidifier are analyzed. ▶ The heat pump dehumidifier can realize energy and cost savings in Shanghai.
Introduction
Indoor swimming pool is an important leisure and entertainment facility throughout the world. In order to provide a comfortable environment for the swimmers and protect the building enclosure structure, several important environmental parameters should be controlled in the indoor swimming pools, such as the space air and pool temperature, the relative humidity and air velocity over water surface. Thus, a lot of energy is needed for dehumidifying the moist indoor air, adjusting supply air temperature to meet indoor heating and cooling load, and heating pool water.
Nowadays quite a few indoor swimming pools are still using oil/gas fired boilers or electric heaters to maintain the pool temperature and conventional dehumidifiers to control humidity and condensation. Conventional dehumidifiers use a vapor compression cycle consisting of a refrigerant loop including an evaporator, compressor, condenser and expansion device. As indoor air is drawn through the evaporator, it is cooled to its wet-bulb temperature, thus the moisture in the air is condensed. The mixture of dehumidified air and outdoor fresh air then passes through the condenser coil to be heated before reintroduction into the room. Additional heater is needed for pool water heating, which consumed a great deal of energy.
There are relatively few studies on the energy saving issues of indoor swimming pools. The open-cycle absorption heat pump system was analyzed by Lazzarin and Longo [1], Johansson and Westerlund [2] and Westerlund and Dahl [3]. Compared with mechanical heat pump, the absorption system is operated by chemical dehumidification on the exhausted air of the swimming pool. Although considerable energy saving effect was demonstrated, the promotion of this technology was restricted by the product maturity and reliability. As for the mechanical heat pump dehumidifier, some applications and improvements were also conducted. The life cycle energy cost analysis of the heat pump used for heating pool water in a hotel swimming pool was studied by Lam and Chan [4]. Zhang et al. [5] incorporated a membrane-based total heat exchanger into a mechanical air dehumidification system with two air-cooled condensers in parallel. Another type of heat pump dehumidifier was introduced by Lee and Kung [6], which was also composed of two condensers in parallel, an air condenser for air supply heating and a water condenser for pool heating. However, these two heat pump dehumidifiers cannot absorb heat from outdoor air for indoor air and pool heating, which limited its application.
In response to this energy saving problem, a new heat pump dehumidifier with the ability of absorbing heat from outdoor air is proposed in this paper. Firstly, based on human thermal comfort analysis, this paper determines the space and pool temperature in indoor swimming pools under typical weather conditions. Subsequently, energy supply system based on the heat pump dehumidifier is analyzed. In addition, a case study in Shanghai is introduced, and operation regularities and economy of the energy supply system of the indoor swimming pool are discussed.
Section snippets
Indoor environmental conditions analysis
According to the provisions of China national standard [7], pool temperature of public swimming pool is 26–28 °C. However, there is no relevant regulation about the indoor swimming pool space temperature in other national standards. Only in a specification drawn up by China association for engineering construction standardization [8], it suggests that the space temperature should be set at least 2 °C higher than pool temperature. According to ASHRAE Handbook [9], for the recreational natatorium,
Heat and moisture gain analysis
Since the heat released by swimmers and sensible heat produced by pool water evaporation are both little, they could be neglected in the swimming pool energy model. Heat gain of the indoor space mainly results from heat transfer between indoor space and pool water, heat transmission between indoor and outdoor spaces through building envelope, and the introduction of outdoor fresh air and air infiltration into the indoor air space. According to system energy conservation, the indoor space heat
Calculation conditions and results discussion
A leisure centre indoor swimming pool in Shanghai is selected for this study. Physical conditions are shown in Table 5.
During operation on the typical days of different seasons, heat flow items of the indoor swimming pool have different characteristics, which are shown in Fig. 8. The setting values for indoor space temperature and pool water temperature are based on indoor environmental conditions analysis mentioned above. In Fig. 8(a)–(c), values of relative humidity in indoor space are all
Conclusions
Indoor environmental conditions, operating regularities of energy supply systems based on the heat pump dehumidifier, and economic analysis of an indoor swimming pool during business time in Shanghai are studied in this work. Some conclusions are obtained below:
- (1)
The indoor space temperature can be set at 28.2 °C, 29.8 °C, 27.8 °C and 28.6 °C respectively on a typical day of spring, summer, autumn and winter of a year based on thermal comfort and energy saving. Temperature difference between indoor
Acknowledgement
This work was supported by the National High Technology Research (Project Number 2007AA05Z220).
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