Swimming pools are used around the world for recreational, rehabilitation and physical activity. From an energy and environmental standpoint, grey water as a waste thermal potential of swimming pools is a valuable heat source produced continuously in extensive, measurable and large quantities. The main objective of this article is to analyse the feasibility of proposed grey water heat recovery (GWHR) system from the showers and backwater from swimming pool filters for an indoor pool located in recreation centre in Poland. Analysis, calculations and results were obtained and discussions of water and energy consumption were carried out for the mentioned indoor swimming pool on the basis of real measurements case study for water flow rate, water temperature in swimming pools and showers. The results ensure a significant potential of energy savings by using the proposed GWHR system, which allows to reduce the energy demand by 34% up to 67% for pool water preheating and domestic hot water (DHW). The environmental impact of proposed GWHR system was analysed and calculated by using Common Air Quality Index. Environmental results are illustrated and discussed specially for the reduction of CO₂, NO_X, SO_X emissions and dust and ensure a significant reduction of these pollutants in range of 34% to 48%.

The paper examines the variability of long-wave radiation fluxes in two contrasting types of urban active surfaces - grassy surface and surface without plants (bare soil) in Wrocław (Poland) within a 12-year period (August 2007-July 2019). The study used net radiation and heat balance formulas to calculate the share of individual radiation fluxes in these balances, and then utilized the Stefan-Boltzmann formula to calculate the effective temperatures of researched surfaces. The analysis showed the temporal variability of these fluxes against the background of weather and climatic conditions and in relation to the variability of short-wave radiation fluxes. The role of long-wave radiation fluxes in forming net radiation was examined in detail to show the buffering role of vegetation surfaces regarding the variability of solar radiation fluxes and their heat effects. The mean monthly values of outgoing long-wave radiation fluxes change from 309.0 W·m^-2 for bare soil, 309.8 W·m^-2 for grassy surface, and 288.8 W·m^-2 for downward atmospheric radiation to respectively 435.8, 425.0 and 369.4 W·m^-2 in July. The coefficient of variability for long-wave radiation daily fluxes are approximately one order of magnitude lower than for the short-wave radiation. The differences between values of long-wave radiation fluxes for bare soil and grassy surfaces vary from slight negative values in winter to relatively sizable positive values during the vegetation period (March-October). The weakening of the buffering effect for grassy surface and how air temperature then changes considerably compared to the effective temperature of the active surfaces were explained using the dry summer period of August 2015 as example. The obtained results are important, as they provide empirical arguments for urban planning to extend plant areas' share in big cities as well as to introduce there a friendly environmental system of irrigation in these areas using renewable solar energy.

A hybrid air conditioning system, which is composed of a novel gravity-assisted heat pipe (GAHP)-based indirect evaporative cooler (IEC) and direct expansion (DX) cooling coil, is proposed and investigated here. After developing a mathematical model to describe the performance of the GAHP-based IEC, the hybrid system is evaluated during the cooling design day for providing thermal comfort for an office building in Poland. The results are obtained and compared with the combination of a rotary heat exchanger (RHE) and DX cooling coil as the conventional hybrid system. The comparison is performed by analyzing cooling capacity, electricity consumption, and coefficient of performance profiles, which describe the technical, energy, and efficiency aspects, respectively. The results show that the GAHP-based IEC hybrid system is able to enhance the energy performance significantly compared to the conventional one. The proposed hybrid HVAC system improves COP by 39.2% and reduces electricity consumption by 45.0%, according to the design-day of 24 August and the outdoor temperature of 30 °C. As a result, the total operating cost for the assumed cooling season is reduced by 51.7%.

Currently there is increasing interest in using surface water bodies as renewable energy sources for year around or seasonal heating and cooling applications e.g. heat pumps. This paper presents the statistical analysis of average water temperature and the flow rate of the Oder River. Linear regression analysis was carried out on the base of ten years (2005–2014) diurnal water temperatures measurements data. The results determine the relation between average air temperature in Wroclaw and Oder river water average temperature for two analysed locations. The Pearson's r correlation coefficients were determined. Additionally, the variability of water flow rates from 2008–2010 in the annual cycle were illustrated. The article proposes the conceptual framework for surface water bodies technical aspects. This proposition is the first step for wider analysis in order to identify the thermal potential of the Oder river water as heat source for heat pumps.