## 1 Introduction
The review shows that the recuperative exchanger was tested experimentally for moderate climate conditions as a device for heat recovery, and not for water recovery, and its further uses. It was found that during the cold and transitional period, the exchanger provided the parameters required in the room for most of the experiment. It is mainly related to the parameters of the outdoor air. In the case of indoor vertical farming facility, the possibility of using such a device for ventilation and water recovery was not analyzed previously. In such facilities, it is also necessary to compensate large amounts of transpired water from plants by removing the air from the hall and blowing dry outside air. Implementation of water recovery from an air system will be another advantage of indoor vertical plant cultivation, which are, e.g., increasing the effective arable area for crops by constructing a high-rise building with many levels on the same footprint of land, plant-growing conditions can be optimized to maximize yield by fine-tuning temperature, humidity, and lighting conditions [14]. It will increase the sustainability and the independence of the facility, enabling to work in a closed or partially closed loop. The aim of this study is to check the potential of water recovery from the exhausted air from the cultivation hall using the cross-flow plate heat exchanger. It needs to be underlined that plate heat exchangers are readily used in air conditioning systems because they have no moving parts, no additional power supply, and their operation is maintenance-free. Basically, the plate heat exchanger working in the air conditioning system allows reducing energy consumption and water may be recovered simultaneously. If the condense is not recovered it is poured out to the sewage system. In this paper it is found whether the amount of water recovered using a cross-flow heat exchanger is sufficient to irrigate the lettuce growing in the ventilated hall. A simplified paper conception is presented in Figure 1.  
The performance of the cross-flow heat exchanger, recovering water from the air removed from the indoor vertical farm facility placed in Wroclaw (Poland), was analyzed for the years 2012-2019. The diagram of the streams flowing through the exchanger is presented in Figure 2.  
The proposed exhaust air water recovery system works as follows. The ambient air is delivered into the hall after airflow treatment in an air handling unit (AHU) cooperating with a cross-flow exchanger (green lines in Figure 2). The cold air is heated (in winter months) in the exchanger, hence the plate of heat exchanger is lowered. When the plate temperature is lower than the dew point of the exhausted airflow (red lines in Figure 2), the condensation of water vapor takes place in the exhausted air channel. The condensate is removed from the exchanger, and transported to a storage tank (2 m\({}^{3}\)). Before the recovered water is used for watering the cultivation, it is pretreated by e.g., a water purification unit. When ambient air temperature is relatively high and no water is recovered or no water is available in the tank, the plants are supplied with tap water. The switching system is realized by switch over controller. The excess water collected in the tank can be discharged into the sewage system or can be used for other purposes than irrigation of the cultivation: e.g., cleaning purposes, flushing toilets.