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Continuously increasing energy prices, as well as the increasing number of legal stipulations, bring to the attention of scientists the necessity of finding solutions for energy saving by using different heat sources. According to the EU Action Plan, the highest potential of energy savings (27-30% until 2020) will be applied to the existing buildings. Under the circumstances of environmental issues, research on the use of secondary energy resources is of great interest, being a concern in the context of sustainable development. The aim of the present paper is to accumulate knowledge on how a drain water heat recovery unit using a heat pipe heat exchanger performs under different drain water flow profile scenarios. Researching how the intermittent behaviour of the drain water influences the performance for this type of system is important because it gives insight on how the system will perform in a real life situation. In this paper the authors investigated the performance of a heat recovery unit, from drain water heat recovery. Investigation of the heat recovery unit performance shows that the heat pipe has the capability to recover more than 30% of the available heat in the drain water, at the flow rates investigated (0.3 ÷ 0.5 m 3 /hour). The application of the presented solution shows that a heat recovery system of this type has the possibility to recover a large portion of the available heat if it has been achieved in those buildings where the hot water consumption is higher (housing complexes, university campus, hotels, swimming pool, sport and leisure, hospital/healthcare, restaurants, laundry, pharmaceutical manufacturing).

This paper presents a research on ways to reduce waste and to diminish sound pollution by recovery of fir sawdust and recycled rubber granules and use in making sound absorbing composite materials. Four materials were prepared using raw materials (fir sawdust and recycled rubber granules) in various percentages, and polyurethane binder. Materials mechanical and acoustic properties were characterized, proving these materials have useful properties. Materials acoustic performance was compared with performance of materials existing on the market: glass wool and flexible polyurethane foam. Sound absorption coefficient was experimentally determined by impedance tube method, in a frequency range of 100-3200 Hz. Results show that composite materials made from waste are superior to existing materials, with regard to acoustic performance, particularly at frequencies below 1600 Hz. Sound absorption coefficient measured for material made with sawdust and 30% polyurethane binder reached a minimum value of 0.65 in the large frequency range of 300-3150 Hz, and a maximum value of 0.979 at the frequency of 2000 Hz.

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The problem of global warming and the reduction of energy consumption have led to an evolutionary progress of research directed towards finding as many solutions as possible to these environmental issues. Firstly, this paper presents the background information on the role of wastewater as a source of heat for the future. Next, the paper includes the analysis elements that define a system for recovering thermal energy from wastewater. The main objective was to identify the parameters that determine the heat transfer. It has started from a conceptual model of the technological system that involves inputs and outputs characterized by technological, physical-chemical, measurable or imposed properties. In the second part this paper presents a numerical model elaborated for the analysis and simulation of the main physical processes, the mass and heat transfer, which underlie the operation of the heat pipe heat exchangers (HPHE). The numerical simulation of heat and mass transfer in the HPHE is computed by using Delphi 7 solver program. This program contained a series of sub-programs for the meshing of the field occupied by the HPHE, another subprogram for solving the meshing equations and the third for post processing. The design of HPHE is the key to provide a heat exchanger system to work proficient as expected. Finally, the result is used to optimize and improving heat recovery systems of the increasing demand for energy efficiency in residential buildings or industry.