With the large number of applications of centralized air conditioning systems, power demand has increased dramatically, resulting in a shortage of electricity during peak hours in some areas. In order to solve this problem, energy storage air conditioning technology has begun to receive attention. At present, the energy storage technology with more applications and relatively mature technology is the ice storage technology, but the ice storage technology can not completely solve the problem of indoor air dehumidification and air conditioning comfort in hot and humid areas. To this end, the author proposed an advanced energy storage air conditioning technology DDD variable mass energy conversion and storage technology, the technology has closed and open two types of work cycle. The main purpose of this study is to reveal the change law of energy conversion and storage process energy in the operation of open storage dehumidification air conditioning system, the solution parameters in the system and the working parameters of each equipment and the relationship between load and system running time.

1 system work cycle and process open energy storage dehumidification air conditioning system workflow as shown.

When using the full energy storage strategy, the working cycle and flow of the open storage dehumidification air conditioning system of the electric low valley control valve V4, V1 off, the solution pump sends a small amount of solution into the generator/condenser, and the auxiliary heater heats the solution. ; occurs / the pressure in the condenser rises to the design pressure, the heater stops working; the compressor starts, the solution pump pressurizes the solution in the solution tank again, and is heated by the solution heat exchanger to spray on the occurrence / condenser Outside the heat exchange tube bundle; the solution is heated to produce superheated steam, which is treated by humidification and cooling, and then enters the compressor; the compressed water vapor condenses in the heat exchange tube bundle, and the condensation heat is transmitted to the outside of the tube bundle as heat generation; most of the condensed water Enter the water storage tank; the solution of the occurrence/condenser is cooled by the heat exchanger and then flows back to the solution storage tank. As the above process proceeds, the mass of the solution in the solution storage tank gradually decreases, the concentration of the solution gradually increases, and the chemical potential of the solution increases.

When the concentration of the solution in the solution tank reaches the design value, the charging process ends and the compressor stops running, V4 is closed, and V1 is turned on.

When the energy is released, the water and the solution in the storage tank enter the evaporator and the absorber respectively; the generated water vapor enters the absorber and is absorbed by the solution; the solution of the absorber is pressurized by the recirculation pump and sent to the dehumidifier to absorb the water in the air. The dilute solution of the dehumidifier is split, and a part is circulated through the valve V3 and the concentrated solution from the solution storage tank to ensure that the dehumidifier has a suitable gas-liquid ratio, and the other part enters the solution storage tank; the cold water part of the evaporator enters the indoor The fan coil system bears the indoor cooling load, and the other part introduces the dehumidifying air conditioner to undertake the fresh air cooling and cooling load, thereby achieving the separate treatment of the sensible heat load and the latent heat load. As the above process proceeds, the mass of the solution in the solution storage tank gradually increases, the concentration of the solution gradually decreases, the chemical potential of the solution decreases, and the stored energy is converted into cooling capacity and dehumidification energy. After the release of energy, the excess water in the water storage tank is drained, and the system completes a working cycle for 24 hours.

Because the physical properties of the solution in the solution tank change with time, the parameters such as the operating characteristics and equipment load of the energy storage dehumidification air conditioning system also change with time. The system operation process is dynamic, and the numerical system is needed to carry out the system cyclic thermal process. Solve.

The working solutions of the open type energy storage dehumidification air conditioning system include lithium bromide, lithium chloride, calcium chloride and triethylene glycol, and they all have their own characteristics. In the field of solution dehumidification, lithium chloride aqueous solution has a relatively good working characteristic and is widely used. In this paper, an energy storage dehumidification air conditioning system using a lithium chloride aqueous solution as a working solution is studied.

2 dynamic mathematical model 2.1 modeling hypothesis Before establishing the dynamic mathematical model of the operation process of the open storage dehumidification air conditioning system, the system working process should be simplified as follows: 1) ignore the flow resistance of the fluid and the work of the pump; 2) Regardless of the boosting process at system startup; 3) neglecting the amount of liquid stored in the condenser/4; ignoring the heat capacity of each device in the system; 5) fully adiabatic the equipment in the system; 6) solution in the solution tank at any time The mass fraction and temperature distribution are uniform.

2. 2 Dynamic model establishment In order to facilitate the establishment of dynamic model, the energy storage system shown can be divided into several modules (the division of modules is relatively arbitrary, and a certain component in the energy storage system can be used as a module, or multiple As a module, the components are respectively established with mass and energy dynamic balance equations for each module, and then these equations are combined to solve the numerical solution.

At any time τ, the mass dynamic equilibrium equation of the kth module is dmk(τ)dτ=∑dmk, i(τ)dτ-∑dmk, o(τ)dτ(1)0 =∑dmk, i(τ)dτξi (τ) - ∑dmk , o(τ)dτξo(τ)(2) Equation (1), where m is mass, kg; ξ is the mass fraction of LiCl; subscript i, o respectively means in and out The stream of the kth module interface.

The energy dynamic equilibrium equation of the kth module is d E(τ)dτ=∑d Q k , i(τ)dτ+∑dmk , i(τ)dτh k ,i(τ) -∑d Q k ,o( τ)dτ-∑dmk ,o(τ)dτh k ,o(τ)(3)

Where E is energy, kWh or MJ; Q is heat or cold, kWh or MJ; h is ç„“, kJ/kg.

The compressor power is N (τ) = dmw dτ + dm 1(τ)dτ< h 1(τ) - h 11(τ) > act = ( m wv + m 1)< h 1(τ) - h 11( τ) > isηis(4) where N is the power of the compressor, W; mw is the mass of water in the water storage tank, kg; m 1 is the mass of water in the humidifier, kg; h 1 and h 11 are compression respectively The ratio of the outlet of the machine to the inlet water vapor, kJ/kg;m wv is the mass flow rate of the steam generated/condenser, kg/s, equal to the mass flow mw of the condensate entering the water storage tank; m 1 is the injection The mass flow rate of the humidifier water, kg / s; η is the compressor efficiency; the subscript act refers to the actual process, and the is refers to the isentropic compression process.

The electric energy consumed by the compressor is W c(τ) = ∫τ0 d W c(τ)dτdτ=∫τ0 N (τ)dτ(5) The change in mass and energy of the solution or water in each tank is m ss ( τ) = m ss(τ) |τ= 0 +∫τ0 dm ss(τ)dτdτ(6)E ss(τ) = E ss(τ) |τ= 0 +∫τ0 d E ss(τ)dτdτ( 7) m ws(τ) = m ws(τ) |τ= 0 +∫τ0 dm ws(τ)dτdτ(8)E ws(τ) = E ws(τ) |τ= 0 +∫τ0 d E ws (τ)dτdτ(9) The subscript ss in the formulas (6) to (9) refers to a solution storage tank, and the ws refers to a water storage tank.

The heat transfer of the evaporator, absorber and water tank cooler is Q e(τ) = ∫τ0 d Q e(τ)dτdτ(10)Q ab(τ) =∫τ0 d Q ab(τ)dτdτ( 11) Q ws(τ) = ∫τ0 d Q ws(τ)dτdτ=∫τ0 cp , w(τ) < t 3(τ) - t 4 > dmw(τ)dτdτ(12) Equation (10)～( 12) cp, w is the specific pressure heat capacity of water, kJ/(kg °C); t 3 and t 4 are the condensate temperature entering the water storage tank and the outlet water temperature of the water storage tank respectively, °C; subscript e Evaporator, ab refers to the absorber. When the gas/liquid mass flow ratio is less than 2.3, the adiabatic dehumidification process can be approximated as an isothermal dehumidification process. Under the condition of small gas-liquid ratio, the fresh air treatment process can be regarded as the process of first isothermal dehumidification, followed by wet cooling and cooling.

The energy balance equation of the isotherm cooling and cooling process is d Q a(τ)dτ= < ha , i(τ) - ha , o(τ) > dma(τ)dτ- 2 500 < di(τ) - do(τ) > dma(τ)dτ(13) where d is the wet air moisture content, g/kg; subscript a refers to wet air.

At time τ, the energy brought into the system by the fresh air treatment process and the cooling capacity consumed by the isothermal cooling and cooling process are respectively E a(τ) = ∫τ0 < ha , i(τ) - ha , o(τ) > dma(τ) Dτdτ(14)Q a(τ) =∫τ0 d Q a(τ)dτdτ(15) The energy entering and leaving the system must be conserved. This is an important criterion for verifying whether the numerical simulation of the charge and discharge process is accurate, ie W c ( τ) + Q e(τ) + < E a(τ) - Q a(τ) > = E ss(τ) + E ws(τ) + Q ab(τ) + Q ws(τ)(16) needed It is noted that the heat released by the fresh air dehumidification process is finally discharged through the absorber, and the cooling amount consumed by the fresh air cooling and cooling process is provided by the evaporator, and the heat rejection Q a is included in the cooling capacity of the energy storage system.

3 The example is based on the dehumidification and air conditioning condition of office buildings in the high-humidity area of ​​southern China. The numerical simulation of the working process of the system during the operation of the full-scale energy storage strategy is carried out, and the operating parameters of the energy storage system under dehumidification air-conditioning conditions are obtained. The relationship of change. The energy storage dehumidification air conditioning system is as shown. The system treats the sensible heat and latent heat load of the building separately, that is, adopts an independent fresh air system without return air, and the wet load of the building is undertaken by the fresh air, which cuts off the transmission route of indoor bacteria.

The air volume of the air-conditioned building is 12 760 m 3 / h, and the amount of fresh air is reduced after 19:00. On the design day, the outdoor temperature ranged from 27 to 35 ° C and the average relative humidity was 75%. The fresh air temperature after treatment was 25 ° C and the relative humidity was 45%. The design day is indicated by the total air conditioning load, fresh air load, outdoor temperature and cooling water temperature. The system evaporating temperature is 7 ° C, the solution heat exchanger cold end temperature difference is 10 ° C, the pressure is 40 kPa, the compressor isentropic efficiency is 60 %, absorption

The outlet temperature is 5 °C higher than the cooling water inlet temperature. Set the gas-liquid ratio in the dehumidifier to 1. 36. The system charging time is 10 h (22:00 to 8:00), no air conditioning load during the charging period; the release time is 14 h (8:00 to 22: 00).

4 Numerical simulation results and analysis After numerical simulation, the parameters of the solution or water in the two tanks are designed as follows: ξss(τ) |τ= 0 = 0. 387 0 , m ss(τ)|τ = 0 = 28 123 kg (V ss | max = 22. 43 m 3) , t ss(τ)|τ = 0 = 33. 3°C, m ws(τ) |τ= 0 = 0 kg.

The change in the mass and energy of the solution or water in each tank during the charging and discharging process of the system is shown in Fig. 5. The mass of the solution in the tank of the charging process is gradually reduced, and the energy is gradually increased; while the mass and energy in the water tank are increased. The water temperature of the water storage tank is kept constant (28 ° C), so the increase in energy is only due to the increase in mass.

The change of solution energy in the solution storage tank is affected by two factors. First, the concentration of the solution in the storage tank changes its chemical potential, which causes the potential of the solution to change. Second, the temperature of the solution changes, so that the sensible energy of the solution changes.

The change in mass and energy in the tank during the energy release process is exactly the opposite of the charging process. The mass and energy of the solution or water in each tank during the charging and discharging process changes with time as shown in the solution tank and the LiCl mass fraction as a function of time. In the recharge process, the water in the storage tank is continuously reduced, and the mass fraction of LiCl is continuously increased, and the maximum is reached at the end of the charging, which is 50.2%. The reason for the increase in the temperature of the solution in the storage tank is that the temperature of the concentrated solution of the solution heat exchanger is 10 ° C higher than the temperature of the solution in the storage tank, and the heat is taken into the storage tank by the concentrated solution and accumulated, so that the temperature of the solution in the storage tank rises.

During the charging and releasing process, the temperature of the solution in the solution tank and the mass fraction of LiCl change with time. The parameters in each tank are: m ss |τ= 10 h = 21 680 kg , ξss(τ) |τ= 10 h = 0. 502 ,t ss(τ) |τ= 10 h = 63. 8°C, m ws(τ) |τ= 10 h = 6 443 kg (V ws | max = 6. 57 m 3). At the end of the release process, the solution parameters in the solution reservoir are restored to the value at the start of charging. The amount of water remaining in the water storage tank is m ws(τ) |τ = 14 h = 1 960 kg, and this part of the water is drained.

During the charging process, the LiCl concentration in the solution tank gradually increases, and the temperature rises continuously, resulting in an increase in the compressor outlet pressure (pc) and temperature. When the compressor suction pressure is constant (pg = 40 kPa), the compressor compression ratio (Γ = pc / pg) increases. In order to avoid excessive compressor discharge temperature, wet compression is adopted. During the simulation calculation, the water vapor at the outlet of the compressor is always saturated. To meet this condition, the water flow rate (m 1) injected into the humidifier can be adjusted to change the wet steam dryness. The gradual decrease in the water vapor dryness of the humidifier from 0. 849 7 kg / s, the water vapor dryness of the humidifier is gradually reduced from 0. 849. To 0. 816. Since the mass flow rate and compression ratio of the inhaled wet steam increase with the charging time, the power (N) required for the compressor also gradually increases, increasing from the beginning of charging at 147.9 kW. To the end of 192.9 kW.

The compressor stops working as the charge time changes. The system relies on the potential of the solution stored in the solution tank to complete the refrigeration and dehumidification work. The change of heat load of each heat exchange device with time in the process of energy release is shown in Fig. 9.

The absorber not only bears the load from the evaporator, but also bears the load of the heat exchanger from the heat exchange equipment except the release process of Fig. 9 with time, and the heat load is large. Compared with the latent heat load of the dehumidification process, the cold load required for fresh air cooling after dehumidification is small. The maximum latent heat load of the dehumidification process is 152.1 kW, and the maximum cooling load required for fresh air cooling is 42.79 kW. The evaporator load includes the indoor air conditioning load and the fresh air cooling load.

The mass flow rate of the solution through the various control and recirculation pumps over time is shown as a function of the release process. Through control valve V1

The mass flow rate of the release process flowing through the control valve and the recirculation pump changes with time and the solution mass flow of V2 has the same relationship with time, and is similar to the change rule of the total hourly total load of the air conditioner. The flow difference between the two is the solution. Total water flow absorbed. At the beginning of the release phase, the total air conditioning load is low due to the high LiCl mass fraction in the solution tank, and the mass flow rate through the V2 control valve is small. As the process of energy release progresses, the mass fraction of LiCl in the solution tank gradually decreases and the total load of the air conditioner gradually increases. The mass flow rate of the solution through the V2 control valve increases rapidly. The reason is that when the air conditioning load is gradually increased, it is required. More concentrated solution to absorb water vapor from the evaporator. By 16:00, the total air conditioning load began to decrease, although the LiCl mass fraction in the solution tank solution had decreased, but the mass flow rate through the V2 control valve also began to decrease. Therefore, it can be known from numerical simulation that the air conditioning load has a greater influence on the flow rate of the solution flowing through each control valve. In the simulation calculation, the mass flow rate of the absorber outlet solution is limited by the gas-liquid ratio in the dehumidifier, and the flow rate does not change much (the fresh air flow rate decreases after 19:00, and the flow rate of the solution entering the dehumidifier also decreases).

The absorber inlet solution mass flow is equal to the absorber outlet mass flow minus the water flow into the evaporator. The water flow is much smaller than the mass flow of the solution. Therefore, the mass flow rate of the inlet solution of the absorber is similar to that of the outlet mass flow, and is equal to the mass flow rate of the solution through V2 and V3. Therefore, the mass flow rate of the reflux solution passing through the control valve V3 is exactly opposite to the mass flow rate of the solution passing through the control valve V2.

5 System COP and effective energy storage density The open-loop energy storage dehumidification air conditioning system has a cyclic CO P of CO P = ∑Q e + ∑ ( E a - Q a) ∑ W c = 2. 55 energy storage density is an evaluation of the energy storage system Another important indicator can be used as a measure of the volume utilization of an energy storage system.

Define the effective volume storage density as the ratio of the system output energy to the total volume of the tank, ie SD = 0185 (Q e + E a - Q a) | ss V ss | max + V ws | max = 0185 (Q e + E a - Q a) | ss m ssρss max + m wsρws max = 130. 4 kWh/ m 3 = 469. 6 MJ/ m 3 The coefficient in the formula is 0.85. It is necessary to expand the tank in consideration of the influence of temperature and pressure on the liquid. Leave a certain space; V ss | max and V ws | max are the calculated volume of the tank at the maximum liquid storage; (Q e + E a - Q a) | ss is the energy conversion output of the system storage The cold energy and the latent heat of dehumidification.

6 Conclusions The full-energy storage strategy is used to operate the open-type energy storage dehumidification air conditioner. The compressor operates at night during the low-power period, converting the nighttime rich electric energy into the chemical potential energy of the working solution and storing it; during the daytime peak hours, the compressor does not Working, the system relies on the chemical potential of the solution stored in the solution storage tank to complete the purpose of cooling and dehumidification, and can well play the role of peak clipping and valley filling.

The energy storage principle, operation mode and cycle heat calculation of the energy storage dehumidification air conditioning system are completely different from conventional energy storage air conditioners, which can not only alleviate the contradiction of peak power consumption, but also has the following characteristics: 1) Water as refrigerant, OD P And GW P are 0, no damage to the environment; 2) compressor suction pressure is independent of evaporation pressure, can reduce the size of steam compressor by increasing the pressure; 3) stored energy can be converted into cold The building air conditioner can be converted into dehumidification latent heat for fresh air dehumidification treatment; 4) the system storage tank has simple structure and high effective energy storage density; 5) the temperature of the system output cold water and the cold water output of the refrigeration unit in the general centralized air conditioning system The same temperature makes it easier to transform an ordinary air conditioning system into an energy storage air conditioning system without changing the air conditioning piping and end systems that are expensive and difficult to retrofit.

The analysis of numerical simulation results in this paper is of great help to understand the working characteristics of open-type energy storage dehumidification air conditioning systems. These calculation results are also the basic data of energy storage system design, equipment selection or design, operation control, and technical economic evaluation. As a new energy conversion and storage technology, its working characteristics are completely different from other energy storage technologies. The technology not only can cut the peak load and fill the electric load, but also has high energy conversion efficiency and large solvent effective energy storage density, and has good development and application prospects.

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