Performance analysis of the latest solution heat r

Performance analysis of new solution heat recovery fresh air fan

1 introduction

in the field of air conditioning, in addition to the hot and humid environment, indoor air quality has also attracted more and more attention []. Outdoor fresh air is significantly better than indoor return air in eliminating indoor CO2 and VOC and diluting indoor bacteria that may exist. However, considering the operation energy consumption of fresh air fan, the increase of fresh air volume is restricted. The total heat recovery method is an effective method to reduce the energy consumption of fresh air treatment, but the rotating wheel type, which can not give full play to the advantages of this kind of experimental machine, the plate fin type and other total heat recovery devices can not avoid the cross pollution of fresh air and indoor exhaust air. In order to solve the contradiction between improving indoor air quality and reducing the energy consumption of fresh air treatment, a solution heat recovery fresh air fan is proposed. This form of fresh air fan has a high total heat recovery efficiency, and the solution has the effect of sterilization and dust removal [], which can avoid the cross contamination of fresh air and indoor exhaust air

there are many ways of heat recovery type fresh air fan with solution as the circulating medium: literature [4] proposed a fresh air fan driven by electric energy, which is composed of a solution total heat collector and a small capacity refrigeration cycle. Many domestic scientific research institutions and colleges and universities have carried out fatigue design. In summer, the refrigerating capacity of the evaporator in the refrigeration cycle is used to cool the solution to enhance its dehumidification capacity, The heat discharged from the condenser is used for the concentration and regeneration of the solution; During winter operation, the four-way valve can be used to realize the mutual conversion of evaporator and condenser, so that the cooler works under the working condition of heat pump, and the fresh air is heated and humidified. Literature [5] proposed a solution heat recovery fresh air fan driven by 90 C hot water. In summer, the cooling capacity of indoor exhaust evaporative cooling is recovered by the plate heat exchanger to cool the solution and enhance its dehumidification capacity. The dehumidified fresh air is further cooled by 15~18 C cold water and then sent indoors; In winter, through the conversion of the working condition of the fresh air fan, it can operate in the full heat recovery mode. The humidified fresh air is further heated by high-temperature hot water and then sent indoors. The solution heat recovery type fresh air fan proposed in this paper is composed of a solution total heat recovery device and a single-stage spray module with plate heat exchanger temperature regulation. Hot water is the main driving source. In summer, 15~18 C cold water is used to adjust the solution temperature entering the single-stage spray module and enhance its dehumidification capacity. Compared with literature [5], the concentration of circulating solution is reduced, and 60 C hot water can be used to meet the requirements of solution regeneration; In winter, hot water at 40~50 C is used to adjust the temperature of the solution entering the single-stage spray module to enhance its humidification capacity

This paper introduces the working principle of the new solution heat recovery type fresh air fan, analyzes the annual operation energy consumption on this basis, and compares the operation energy consumption with the conventional fresh air fan, the solution heat recovery type fresh air fan proposed in literature [4] and literature [5] respectively

2 working principle of fresh air fan

see Figure 1 for the working principle of fresh air fan. The water distribution valve is closed and the solution valve is open. The fresh air fan is composed of two parts: on the left of the dotted line is a solution type total heat recovery device [4] (there are three levels in the figure), and on the right of the dotted line is a single-stage spray module. The outdoor fresh air first passes through the total heat recovery device to recover the energy of the indoor exhaust air, and then is sent to the air-conditioned room after further treatment by the single-stage spray module. In summer, in order to enhance the dehumidification ability of the solution, the cooling treatment process of the solution is realized by the chilled water before the solution enters the single-stage sprinkler. As the dehumidification task is undertaken by the solution system, the water temperature of the chilled water is higher than the water temperature requirements of conventional condensation dehumidification, and the evaporation temperature and coefficient of performance of the refrigerator are significantly increased. The concentration of the solution flowing out of the fresh air fan decreases, and it needs to be concentrated and regenerated before it can be reused. The fresh air fan shown in Figure 1 uses 60 C hot water as the regeneration heat source of the solution. The structure of the regenerator is similar to that of the spray module. See Figure 2. The system is equipped with solution regenerator and air regenerator to preheat the dilute solution and regeneration air entering the regenerator respectively, so as to reduce the energy consumption of the system. In the building, the centralized regeneration method can be adopted to uniformly enter the dilute solution from each fresh air fan into the regenerator shown in Figure 2 to realize the centralized concentration and regeneration of the solution. See Figure 3A for the state changes of fresh air and indoor exhaust air in the fresh air fan (see Figure 1 for the state number), and the cold water temperature entering the single-stage spray module plate heat exchanger is 16 C. Where A1 is the fresh air state, A5 is the air supply state, R1 is the indoor state, and R4 is the exhaust state. A1~a2~a3~a4 is the state change process of fresh air in the solution total heat recovery device, and a4~a5 is the state change through the single-stage spray module; R1~r4 are the state changes of exhaust air in the solution total heat recovery device. In winter, the regenerator stops running, and the solution only circulates in their respective fresh air fans, as shown in Figure 1, in which the water make-up valve is open and the solution valve is closed. In Figure 1, the left side of the dotted line is still a solution type total heat recovery device, and the right side of the dotted line is a single-stage spray module. Before entering the single-stage spray module, the solution is heated by hot water through the plate heat exchanger, so as to enhance its humidification capacity. The 4.5t rotating plate mold has 4 mold cavities. Since the surface vapor pressure of the solution is higher than the partial pressure of the water vapor of the treated fresh air, water in the solution constantly enters the air. A water replenishment device is set in the system to maintain the concentration of the solution in the single-stage spray module. The state change process of outdoor fresh air and indoor exhaust air in the fresh air fan is shown in Figure 3B, and the state number is shown in Figure 1. The temperature of hot water entering the single-stage spray module plate heat exchanger is 40 C

3 evaluation method of fresh air fan performance

3.1 the energy consumed by fresh air fan in summer

includes two parts: one is the electricity consumed by the refrigerating machine to prepare chilled water, EAIR, and the other is the heating amount required for solution concentration and regeneration, qhot. The performance of the fresh air fan can be described by the electrical performance coefficient ecop and the thermal performance coefficient TCOP [6]. The definitions of the two coefficients are as follows:

(1)

(2)

, where qair is the cooling capacity obtained by the fresh air, and its calculation method is shown in formula (3). HW and hsend are the enthalpy of the fresh air and indoor exhaust air respectively. Ecop can be rewritten into the form of formula (4), where R is the ratio of the cooling capacity provided by cold water in the fresh air fan to the cooling capacity obtained by fresh air, and COPR is the performance coefficient of the refrigerator

(3)

(4)

3.2 the energy consumed by the fresh air fan in winter is: the heat required to heat the solution with hot water qhot. The performance of the fresh air fan is described by the thermal performance coefficient TCOP, and the specific expression is shown in formula (5)

(5)

a. summer