This paper analyses two different models (methods) used for determination of water consumption in residential buildings. For this purpose, some basic sanitation facilities were implemented in the models as typical household equipment. As there is a big variety of sanitary solutions available, in order to achieve a significant reduction in water consumption, a novel classification of faucets (taps and mixers) is proposed. This classification also allows for the assessment of energy efficiency ratings of sanitary appliances. On the basis of this classification, water savings resulting from the use of faucets with different water efficiency ratios were determined. Depending on the type of faucet, it is possible to achieve more than 50% water savings, as well as a significant reduction in energy demand for heating and pumping water to customers. The paper also discusses the equations used to determine the energy demand for domestic hot-water preparation and its pumping to consumers. The results of the energy consumption calculations for the above-mentioned purposes were determined per person.

This study discusses the use of a membrane module for semi-direct evaporative air cooling. A cross-flow membrane module was used to carry out this air treatment process. For such a flow, it was proposed to describe and solve the heat and mass transfer model as a one-dimensional problem. The mathematical model was used to determine the moisture content and air temperature at the outlet from the module and the temperature of the circulating water. Results obtained using the proposed model are in good agreement with the experimental data. The relative error for the air temperature at the module outlet did not exceed 0.5%. For the moisture content, the relative error did not exceed 4%. For the circulating water temperature, the relative error did not exceed 0.6%. This paper also discusses the heating efficiency of the evaporative cooling process. Methods for determining the unit cooling indicator and the energy efficiency ratio are also proposed.

This study explores the integration of greywater recovery systems (GRSs) within single-family buildings across European countries. The analysis evaluates the impacts of these systems from multiple perspectives: potable water conservation, economic feasibility, energy consumption, and environmental impact. Employing life cycle cost (LCC) and net present value (NPV) analyses, the research assesses the economic viability of these systems compared to standard water installations. Positive NPV is observed in countries such as Belgium, Germany, Denmark, Finland, and Norway, according to the base scenario. Additionally, the implementation of subsidies can enhance economic incentives for adopting GRSs by reducing the payback period (PBP). Significant findings include reductions in potable water demand by up to 43.0%, and energy savings of up to 42.6% are also observed with the use of GRSs. Additionally, notably lower carbon dioxide emissions (CDEs) were reported, with reductions being directly proportional to the decreases in energy use. This holistic approach aims to establish frameworks for decision-making processes, emphasizing that economic and environmental aspects are mutually complementary and significant.