Analysis of Air Heating in Winter in Underground Heat Exchangers and in Water Bodies During Water Freezing on Submerged Pipes
Keywords:Heat flow, Heat exchanger, Ventilation systems, Heat supply systems, Thermal resistance, Linear density, Air heating, Heat of crystallization, Heat generating equipment
Background. Air heating in winter in the ambient temperatures range below -5 °С is possible both by the heat of the soil and by the heat of the phase transition of water to ice. Heated air reduces energy consumption in ventilation systems and heat pumps such as air–water and air–air during peak loads on the heating system, which reduces the installed capacity of the heat-generating equipment.
Objective. The aim of the paper is determination of the influence of air velocity (flow rate) on the desired length of pipes at a constant value of the diameter of the channel with air, as well as determination of thermal resistances and linear heat flux density with a comparison of the processes of soil cooling and water crystallization.
Methods. Air with a temperature below -5 °С is passed through elements of the natural environment for use in ventilation systems, heat pumps, and in the buffer zones of buildings during the frost period. The lower the air temperature, the greater the economic and energy efficiency.
Results. The calculated analysis of the effect of air velocity (flow rate) on the required length of pipes embedded in the ground and submerged in water subject to a phase transition of water to ice was carried out. It is shown that the required length of the ground heat exchanger is strongly influenced by the mode of operation (continuous operation without interruptions or operation with interruptions). To heat the air from -10 to -3 °С, depending on the air speed in the ground heat exchangers, the needed length of the pipes should be 1.5–2 times longer because the thermal resistance of the soil is greater than that of ice and the ice thickness is lower than that of the cooled soil, due to the high heat value of water crystallization. At high speeds, the linear density of the heat flux reaches 40–60 W/m2.
Conclusions. When placing a channel in the form of a pipe in the ground or in water, it is possible to pre-heat the frosty air during peak loads on heating systems, which makes it possible to reduce the installed power of the heat-generating equipment. The technology of water freezing during air heating has significant advantages, especially when operating in annual mode.
I.I. Pukhovoy, “Pukhovoy’s building heating system”, RU Patent 1388665, June 21, 1993.
I.I. Pukhovoy, “Building heating system without heat pump using natural cold water”, Promyshlennaya Teplotekhnika, no. 1-3, pp. 57–61, 1992.
I.I. Pukhovoy, “Space heating without a heat pump and utilizing naturally-cold water”, Heat Transfer Res., vol. 26, no. 4, pp. 572–575, 1993.
I.I. Pukhovoy et al., “Analysis of heat supply schemes with two heat pumps and the use of ventilation emissions and air heated by the heat of water crystallization”, Vidnovliuvana Energetyka, no. 4, pp. 28–35, 2014.
P. Hollmuller. Utilisation des echangeurs air/sol pour le chauffage et rafraichissement des batiments [Online]. Available: http://www.unige.ch/cyberdocuments/theses2002/HollmullerP/these.html. DOI: 10.13097/archive-ouverte/unige:147
I.I. Pukhovoy, “Freezing of water in cylindrical plastic containers and heat flows obtained for heating the air with the heat of crystallization”, Vidnovliuvana Energetyka, no. 4, pp. 43–46, 2007.
I.I. Pukhovoy et al., “Heat of crystallization of water for heating of air in channels with ice edges”, in Proc. Х Int. Conf. Modern Problems of Scientific Support of Power Engineering, Kyiv, Ukraine, April 17–20, 2012, p. 186.
I.I. Pukhovoy et al., “Method of heating and cooling the air by natural environment”, UA Patent 103185, Dec. 10, 2015.
Copyright (c) 2018 Igor Sikorsky Kyiv Polytechnic Institute
This work is licensed under a Creative Commons Attribution 4.0 International License.Authors who publish with this journal agree to the following terms:
- Authors retain copyright and grant the journal right of first publication with the work simultaneously licensed under CC BY 4.0 that allows others to share the work with an acknowledgement of the work's authorship and initial publication in this journal.
- Authors are able to enter into separate, additional contractual arrangements for the non-exclusive distribution of the journal's published version of the work (e.g., post it to an institutional repository or publish it in a book), with an acknowledgement of its initial publication in this journal.
- Authors are permitted and encouraged to post their work online (e.g., in institutional repositories or on their website) prior to and during the submission process, as it can lead to productive exchanges, as well as earlier and greater citation of published work