Impact of Heat Pump-Driven Liquid Desiccant Dehumidification on the Energy Performance of an Evaporative Cooling-Assisted Air Conditioning System

Abstract

The main objective of this research is to investigate the energy performance enhancement obtained by applying a heat pump to a liquid desiccant and indirect and direct evaporative cooling-assisted 100% outdoor air system (LD-IDECOAS). In conventional LD-IDECOAS operation, the boiler providing regeneration heat to the weak desiccant solution consumes most of the energy. In order to reduce the regeneration energy consumption in the LD-IDECOAS, a heat pump-integrated LD-IDECOAS (HPLD-IDECOAS) is suggested in this research. The heat pump reclaims waste heat from the absorber side of the system, and delivers the reclaimed heat to the regenerator side. Detailed energy simulations for both the LD-IDECOAS and HPLD-IDECOAS were conducted to analyze the energy saving potentiality of the proposed system over the conventional LD-IDECOAS. In both systems, it was assumed that a packed-bed type liquid desiccant unit with an aqueous solution of lithium chloride (LiCl) was used. In the proposed system, a heat pump with R-134a refrigerant was adopted. The results show that the proposed system was able to provide a 33% reduction in annual primary energy consumption compared with the conventional LD-IDECOAS. This significantly enhanced energy performance was mainly obtained through an 83% reduction in the gas energy consumed for regeneration of the desiccant solution in the proposed system by applying the heat pump.

Energy Performance Comparison between Two Liquid Desiccant and Evaporative Cooling-Assisted Air Conditioning Systems

“…The LD system used in this study has an integrated HP as the heat source, according to the feasibility demonstrated by existing research [6][7][8][9]. The HP has both a condenser and an evaporator, which can simultaneously satisfy the heating and cooling demand of the LD solution.…”

“…Thus, the CC and the HC of the solution in the LD system are connected to the evaporator side and the condenser side of the HP, respectively, which simplify the operation and the package. Furthermore, the heat pump-integrated liquid desiccant system (HPLD) shows an energy saving potential, compared to the use of a low-quality heat source (e.g., solar energy) and a water-side cooling tower [6,22,28,29]. Moreover, the LD system used a 40% lithium chloride (LiCl) solution as a working desiccant solution.…”

“…The heat demand for solution cooling (Q cooling ) and heating (Q heating ) could be estimated using the values of the mass flow rate of the desiccant solution ( . m sol ), the specific heat capacity (C p sol ), and the solution temperature difference between the inlet and outlet side of the HC and the CC in the LD system, as shown in Equations (6) and 7.…”

“…This study used a variable-speed compressor-controlled HP in cooling mode. The assumed HP was used as a solution-solution (water to water) HP [6,39]. The cooling capacity of the HP could be calculated using Equation 12, proposed by Energy Plus [35].…”

“…The heat pump (HP) has a benefit that it can provide solution heating and cooling at the same time through the condenser and evaporator parts, which allows a more compact system size. Moreover, existing studies show that HPs have been widely researched in terms of their high efficiency [6][7][8][9].…”