## 1 Introduction
For instance, water is recovered from humidified air in greenhouses in hot climate conditions. [PERSON] and [PERSON] [16] developed and validated experimentally a steady-state model of a seawater condenser working in a greenhouse in Oman. The model determines the outlet air parameters such as temperature and humidity, the outlet seawater temperature, and the condensation rate. [PERSON] et al. [17] investigated the water vapor evaporation from the saline in the greenhouse space and water vapor condensation. The condensate is collected for irrigation of plants. The authors gave some recommendations for system design to enhance the condenser performance and to allow recovering more water from the air. Another topic widely researched by scientists is the condensate recovery from air handling units. The review by [PERSON] [18] summarizes the current state of knowledge. [PERSON] [19] proposed the water recovery from the air handling unit (AHU) used for the air treatment. The analysis is performed for the laboratory building which needs to be ventilated by 100% of the fresh outdoor air. On the basis of meteorological data and psychometric relationships the amount of condensate was predicted. [PERSON] and [PERSON] [20] analyzed the potential of water recovery from the several AHUs operating in hot and humid climates. The captured condensate is reused for precooling the air in another AHU and making up for water losses in the cooling tower. It is found that recovered water allows to perform the energy savings of approximately 10% and compensate cooling tower water demand over 50%. [PERSON] et al. [21] compared nine scenarios of different possibilities of water reuse in commercial buildings in two locations (San Francisco and Washington) using OpenLCA version 1.7.2 software. They considered a rainwater harvesting system and air-condensate harvesting system and the system based on a combination of the two mentioned. [PERSON] et al. [18] reviewed the progress in research and development of an air-conditioning condensate recovery. In this study the various research directions on condensate production and management of the condensate are presented. The quality and quantity of condensate for different locations and air conditioning systems are summarized. At certain air parameters, recuperative heat exchangers used in air conditioning systems operate under condensation conditions. Therefore, use of a counter-flow or cross-flow heat exchanger in the air handling unit enables to recover the water condensed from the exhaust air. In case of low external air temperatures, frost or ice may appear in the exchanger. Frosting of recuperation exchangers must therefore be taken into account when carrying out water recovery analyses using this type of equipment. [PERSON] et al. [22] analyzed the performance of the cross flow membrane based heat and mass exchanger under the condensation and frost formation conditions. To obtain the desired results the mathematical model was developed and validated on the base of the literature data. [PERSON] et al. [23] established the frosting limits for plate heat and mass exchanger using a mathematical model verified for this purpose. They confirmed that the air flow rate has a significant impact on frosting limits. The threshold outdoor air temperatures for cross-flow and counter-flow heat exchangers were established respectively by [PERSON] et al. [24] and [PERSON] et al. [25]. The authors created mathematical models that consider various variants of heat and mass transfer that may occur in plate heat exchangers. Using the mathematical models, the operation of the exchangers was analyzed for various parameters of the exhaust and outdoor air. In greenhouses, it is necessary to dehumidify the air, it was confirmed by a comprehensive review of this field of science [26] ([PERSON] et al.). For these purposes, the authors propose several solutions e.g., natural ventilation systems, sorption systems, heat pumps, etc.