Exergy optimization of parameters of a heat pump heating system

Abstract

Relevance: due to the fact that our country does not have its own production of heat pumps that meet modern world requirements, the Uzbek market offers products from foreign companies that produce similar equipment. At the same time, today the production of heat pumps in the world is subordinated, first of all, to the specific interests of the manufacturing countries (this refers not only to climatic features, but also to the level of applied construction technologies, architectural, planning and engineering solutions, the level of technology in the production of heat pump equipment, market needs and other factors). Therefore, the use of imported equipment and blind copying of foreign projects for the conditions of Uzbekistan can not only lead to suboptimal solutions. The feasibility of using heat pumps and the optimal modes of their operation for each specific facility can be determined only on the basis of completed thermodynamic and technical and economic calculations. Aim: to show the possibility of using the thermoeconomic method to optimize the operating modes of a steam compression heat pump unit operating in an autonomous heating system of a municipal facility. Methods: exergy analysis methods were used during development. When optimizing the parameters of heat pumps, the system of compiled equations was differentiated. Results: confirmed by calculation using the optimization model proposed on the basis of the exergy analysis method for the parameters of heat pumps when heating the premises of a building. An important advantage of the method is the accuracy of the thermodynamic calculation. Real calculations show that it is possible to take into account exergy losses during heat transfer through the elements of the system.

English abstract from the paper. The authors’ abstract, reproduced under CC BY-NC-ND 4.0.

Keywords

• heat pump
• exergy analysis
• thermoeconomic optimisation
• water-source heat pump
• heat exchangers
• Tashkent region

In plain English

The authors, of the Institute of Energy Problems and Tashkent State Technical University, build an exergy-economic (thermoeconomic) model of an autonomous heating system with a vapour-compression heat pump for a municipal building. The system has an electrically driven compressor, a condenser, an expansion valve, an evaporator, pumps for the low-grade and intermediate heat carriers, and a convective air heater with a fan. The model splits it into three zones and takes as its target function the variable part of the reduced cost of exergy: the electricity for the compressor, pumps and fan, and the depreciation and repair of each component.

Setting the derivatives of this cost to zero for six variables gives the conditions for the lowest cost. The variables are the temperature changes of the air, the intermediate heat carrier and the low-grade heat carrier, and the logarithmic temperature differences in the heater, condenser and evaporator. The worked example is a heat pump delivering 4 kW of heat, with outdoor air at −7 °C, a room at 18 °C, low-grade source water at 10 °C, R134 refrigerant with 5 °C of subcooling and 5 °C of superheat, electricity at 0.9 thousand sum per kWh and a heating season of 1,560.5 hours in Tashkent region.

Each cost curve has a clear minimum. For these conditions the authors recommend, for a heat pump using environmental heat, temperature differences of 4.5 °C in the evaporator, 5 °C in the condenser and 5.5 °C in the heating device. They conclude that the model gives an analytical way to set the design conditions and operating modes of any vapour-compression heat pump in this scheme.

How to cite

A. I. Anarbayev and M. A. Koroli (2024). Exergy optimization of parameters of a heat pump heating system. Energiya va resurs tejash muammolari (Problems of Energy and Sources Saving), No. 3, 2024, pp. 94–102. https://doi.org/10.5281/zenodo.14032812