## Case Study
### The Integrated System  
The integrated air to water system works by means of a compression reverse cycle. Outdoor air is cooled below its dew point through a direct expansion evaporator, and condensed water is collected and sent to the water treatment unit. The main aim of the system is water production, but two secondary effects of the reverse cycle are considered for efficient use: fresh and dry airflow exiting after water condensation and heat coming from the condensation stage of the coolant. Therefore, the machine has been designed to collect the exiting fresh, dry airflow in a duct in order to deliver it to an air conditioning system, or directly to an indoor environment. Moreover, an alternative circuit to the air condenser employs a coolant-water plate fin heat exchanger to collect the heat flow for domestic water heating. The integrated system's working scheme is illustrated in Figure 5.  
This circuit was designed in order to be easily integrated in an existing system and to exploit all useful effects of the compression reverse cycle. Its effectiveness is related to the integration of the existing plant and to the real needs and use of those effects. As discussed in [9], these kinds of systems are particularly suited to hotels, as they generally require drinking water, heating (at least for domestic water), and air conditioning. Moreover, hotel needs can meaningfully affect the management of the municipality in terms of water and energy requirements, particularly if their occupancy rate is not constant and above all if they are located in places affected by water and energy issues [11]. Thus, significant energy and water savings for such a building can result in an economic advantage not only for hotel owners, but also an improvement for the whole community. The integrated system's design is based on previous research [9] and, in general, adopts the same scheme:  
* a cooling circuit, equipped with a screw compressor;
* an air treatment unit, provided with a heat recovery system;
* a condensed water treatment system. The plant of the previous design was scaled to about a one-quarter of its size: the compressor has a cooling capacity, in design conditions, of 100 kW, instead of 400 kW. Evaporation fans are sized in order to provide an average airflow of 8000 m\({}^{3}\)/h passing through the inlet section, which is fitted with pre filters G4 (90% \(\leq\) Am of ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) test for dust, in compliance with standard EN779:2012) and pocket filters F9 (95% \(\leq\) Em  
Figure 5: Scheme of the integrated system. of 0.4 \(\upmu\)m particles--minimum efficiency of 0.4 \(\upmu\)m particles of 70% in compliance with standard EN779:2012), as used in the previous design. An important difference from the previous design is that air-cooling is carried out by means of a direct evaporation of the coolant (R134a), and evaporating coils and heat recovery coils, as well as the condensation collector tank, are built with materials that are certified compatible for food and beverage contact. Fresh and dry air coming from the evaporation coil and the heat recovery system can be collected in a duct and, in turn, be delivered directly to zones which should be provided with primary air. Another difference from the previous design relates to the double circuit for coolant condensation. The first circuit links the compressor to a condenser coil, equipped with fans, which is cooled by means of outdoor air. The second circuit links the compressor to a plate fin heat exchanger. This coil is linked to the domestic water circuit and provides coolant condensation by means of domestic water heating. Its thermal power capacity is 120 kW. The condensed water treatment unit was designed in order to guarantee safety, healthiness and quality of the final product. Without treatment, water coming extracted from air is not safe nor suitable for human consumption [4].