Energy-Independent Heating System with Improved Energy Efficiency for Agricultural Premises

Abstract

Introduction. The article is concerned with increasing the efficiency of energy-independent heat supply systems in agriculture through using a heat recovery unit with a thermomechanical energy converter. The most promising is a thermomechanical energy converter with a thermodynamic cycle of periodic action to drive a diaphragm pump. For heaters and boilers, the use of pulsating mode of the heat carrier has a double effect: it increases heat transfer and reduces the formation of deposits on the heat transfer surfaces. Materials and Methods. Using the thermodynamic method and the possibilities of impulse technologies, a thermodynamic cycle and a device of periodic action were proposed. In this device, three thermodynamic processes are sequentially implemented: isochoric heating and evaporation of the working substance, adiabatic performance of work, and isobaric condensation. Thermodynamic cycles are constructed for five known working substances (R11; R21; R113; R114; R123) on lgP-h thermodynamic state diagrams and their parameters at characteristic points are calculated. Results. There has been performed frequency matching of the thermal-mechanical converter with the hydraulic parameters of the heat source and heat-consuming unit. Such matching was based on the frequency responses. To describe the hydrodynamics of the heat supply system, a system of differential equations with constant coefficients was used, which was solved using the Laplace transformation. A rational frequency of oscillations of the heat carrier flow was determined within the range of 1.38–2.76 rad/s. Discussion and Conclusion. A scheme of a heat supply system with the independent connection of the heat-consuming unit to a heat source is proposed. On the example of a heat source with a power of 100 kW, graphical dependences of the heat source minimum pressures on the change in the consumption of a heat carrier and the active hydraulic resistance of the heat network are obtained. An algorithm for determining the power increment from the use of a heat exchanger with a thermomechanical converter is proposed. It has been determined that the efficiency of the heat recovery unit will be higher for low-power boilers.