Indirect evaporative cooling has the potential to significantly improve the natural environment. It follows from a significant reduction in electricity consumption in the hot period, and hence lower operating costs for cooling systems. This paper presents the current state of knowledge and research directions on dew point indirect evaporative cooling. It was found that researchers focus on the development of dew point indirect evaporative coolers (DPIEC) by improving its design, geometry, water distribution, and new porous materials implementation. To evaluate the performance of new types of DPIEC, different methods are used by the scientists. Finally, optimized devices are studied in terms of their performance in different systems, like hybrid and desiccant systems, considering different climate conditions. Potential directions of development of evaporative technologies were indicated, such as increasing the coefficient of performance of solid desiccant evaporative cooling systems, developing novel geometry, and efficient water distribution, including development of porous materials.

The aim of this study was to determine the suitability of a rainwater harvesting system to cover the water demand for indoor hydroponic lettuce cultivation located in Wrocław (Poland). The analysis was performed on the basis of the recorded rainfall in Wrocław in 2000–2019. The analyzed cultivation is located in a hall with an area of 300 m², where the lettuce is grown vertically by the hydroponic method. The calculations of the rainwater harvesting (RWH) system were carried out considering the selection of the tank capacity for the collected water. The operation of the water storage is simulated using a yield after spillage (YAS) algorithm. It was evident that the proposed system might be an auxiliary system that relieves the water supply network or supports other water recovery systems (e.g., the water vapor condensation in a cross-flow heat exchanger operating as an element of the air conditioning system, proposed in Part 1 of this study). The harvesting system for the selected vertical farming indoor hall covers an average of 35.9% of water needs and allows a saving of 146,510 L of water annually for the cultivation. An average water demand coverage increases up to 90.4%, which allows a saving of 340,300 L per year when the RWH system is combined with water recovery from exhaust air from the hall.

This paper presents the characteristics of the operation of the system for recovery of water from exhaust air in moderate climates in the years 2012–2019. The proposed system for water recovery uses the phenomenon of condensation in a cross-flow heat exchanger operating as an element of the air conditioning system. The parameters of exhaust air behind the heat exchanger have been determined using a mathematical model of the so-called black box. The mathematical model considers the risk of the cross-freezing of the heat exchanger. The calculations carried out for variable parameters of external air during the analyzed period confirm that the system allows to cover the demand for water for lettuce irrigation during the cold and transitional period, which is a major part of the year. It has been noted that the effectiveness of the system is very high (av. 67.12% per year) due to the specific parameters of the internal air in which the lettuce must be grown and the need for continuous air exchange in such facilities. This means that air is a stable source of water recovery, where the recovery rate depends on the parameters of external air.

In this study, two different indirect evaporative coolers operating with a desiccant wheel are compared theoretically: System A with the regenerative Maisotsenko Cycle (M-Cycle) unit and System B with the cross-flow M-cycle unit. Each system component performance was simulated using the original ε-NTU model. The influence of selected operational factors, such as inlet air temperature, humidity and regeneration air temperature for two system configurations was analysed and compared. It was established, that System B obtains higher cooling capacities and is more sensitive on ambient air humidity changes than System A.

In this study, a multi-stage regenerative-cross-flow dew-point evaporative cooler performance is analyzed and compared to the performance of a regenerative dew-point evaporative cooler. The most beneficial configuration of the proposed exchanger was established on the basis of its geometry and performance analysis using validated numerical models. For specific outlet air parameters, it was found that the multi-stage cooler with a working-to-primary air-flow ratio equal to 0.3 reaches 5.6% lower outlet air temperatures and 10.2% higher cooling capacity when compared to the regenerative unit. The proposed cooler provides lower outlet air temperatures for all average outdoor air parameters in selected locations, for both dry and humid outdoor air parameters (e.g., Denver (USA) and Izmir (Turkey)).

In this study, the application potential of desiccant cooling system with indirect evaporative precooling is analyzed for moderate climatic conditions. Wrocław (Poland) was selected as a representative city. On the base of summer season weather parameters different system running modes were proposed such as cooling and dehumidification mode (Mode 1) and only cooling mode (Mode 2). The average month Thermal and Electrical COP were established for selected climatic conditions. It was concluded that proposed system allows to cool the air without occurrence of condensation in Mode 2 with high average monthly electrical COP (COP_el = 62.2 in August). On the other hand when dehumidification is needed, system operates in Mode 1 and obtains relatively high average Thermal COP values (COP_th = 2.2).