A domestic hot water (DHW) system has been modernized in a multi-family house, located in the southeastern part of Poland, inhabited by 105 people. The existing heating system (2 gas boilers) was extended by a solar system consisting of 32 evacuated tube collectors with a heat pipe (the absorber area: 38.72 m2). On the basis of the system performance data, the ecological effect of the modernization, expressed in avoided CO2 emission, was estimated. The use of the solar thermal system allows CO2 emissions to be reduced up to 4.4 Mg annually. When analyzing the environmental effects of the application of the solar system, the production cycle of the most material-consuming components, namely: DHW storage tank and solar collectors, was taken into account. To further reduce CO2 emission, a photovoltaic installation (PV), supplying electric power to the pump-control system of the solar thermal system has been proposed. In the Matlab computing environment, based on the solar installation measurement data and the data of the total radiation intensity measurement, the area of photovoltaic panels and battery capacity has been optimized. It has been shown that the photovoltaic panel of approx. 1.8 m2 and 12 V battery capacity of approx. 21 Ah gives the greatest ecological effects in the form of the lowest CO2 emission. If a photovoltaic system was added it could reduce emissions by up to an additional 160 kg per year. The above calculations take also emissions resulting from the production of PV panels and batteries into account.

The present work involved an extensive outdoor performance testing program of a solar water heating system that consists of four evacuated tube solar collectors incorporating four wickless heat pipes integrated to a storage tank. Tests were conducted under the weather conditions of Baghdad, Iraq. The heat pipes were of 22 mm diameter, 1800 mm evaporator length and 200 mm condenser length. Three heat pipe working fluids were employed, ethanol, methanol, and acetone at an inventory of 50% by volume of the heat pipe evaporator sections. The system was tested outdoors with various load conditions. Results showed that the system performance was not sensitive to the type of heat pipe working fluid employed here. Improved overall efficiency of the solar system was obtained with hot water withdrawal (load conditions) by 14%. A theoretical analysis was formulated for the solar system performance using an energy balance based iterative electrical analogy formulation to compare the experimental temperature behavior and energy output with theoretical predictions. Good agreement of 8% was obtained between theoretical and experimental values.