**1. Introduction**

In the case of group housing for calves, animals must be kept in a rather limited space, which may cause critically bad environment conditions, leading to the loss of livestock that, in some circumstances, attains 30% to 40%. Besides, it is associated with productivity reduction of 15% and with the growth of specific fodder consumption by 10% to 15% per product unit [1,2]. This is why, in conditions of intensive animal housing, major attention must be paid to maintaining the optimal microclimate (first of all, temperature and ARH).

Technical–economic studies show that, in case of group housing for calves (i.e., in boxes, preventive maintenance premises, cages, etc.), it is advisable to use storage-type electric units for air heating to serve as internal heat sources designed for small premises operating on the principle of convective heat exchange [3].

Applications of electric thermal storage (ETS) units in combination with energy generating installations in a net-zero multi-energy system, including those designed for farms, belong to the most effective solutions, as well. Such installations must be based mainly on various renewable energy sources (RES), first of all, solar- and wind-power installations for heat and water supply [4–8].

Simulation and tests on an electric thermal storage heating system with solid-state heat storage materials (SS-ETSHSM) using electric energy generated by coal combined heat and power (CHP) units [9] and wind, and solar power stations have been carried out [10,11]. ETS unit are charged during the minimum load period of the energy system. Then, this energy is transferred to the heat-carrier into the water-heating system with the help of 'air-water' heat-exchangers. Sun Y. et al. [9] investigated the characteristics of thermal processes and the regularities of temperature changes in different parts of the heating system occurring in the modes of charging and heat emission ETS under quantitative and qualitative regulation. Zhao H. et al. [10] investigated the heat transfer

**Citation:** Khimenko, A.; Tikhomirov, D.; Trunov, S.; Kuzmichev, A.; Bolshev, V.; Shepovalova, O. Electric Heating System with Thermal Storage Units and Ceiling Fans for Cattle-Breeding Farms. *Agriculture* **2022**, *12*, 1753. https://doi.org/ 10.3390/agriculture12111753

Academic Editor: Claudia Arcidiacono

Received: 15 September 2022 Accepted: 21 October 2022 Published: 23 October 2022

**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

characteristics of SS-ETSHSM. The thermal calculation method for key parameters of the electric heating system was proposed. Based on the experimental data, the amount of accumulated heat was calculated along with the heat-exchange coefficient, in air channels of various geometries. Amounts of thermal energy transferred from the heat-storage unit to the heated air were estimated as well. The perational effectiveness of ETS unit installations can be improved by a reasonable selection of the air channels number in ETS units, as well as by optimizing their shape and dimensions. Correctly defining the optimal values of air velocity, in channels, and location of air inlets and outlets is also important [11]. Xu G. et al. [12] developed a static-type ETS unit with a heat-storage phase change material (PCM) in which heat-exchange occurs in air channels, owing to natural convection. The proposed device is charged by the off-peak electricity. The dynamic process of the thermal state under a fully charging/discharging cycle of the device was tested. The amount of heat transferred in the air channels to the heated air and the heat given off by the ETS casing by natural convection and radiation were determined as a percentage.

Klymchuk et al. [13] considered various schemes of arrangement of tubular heating elements for the charging of heat storage cells. The temperature distribution over the cross-section of the thermal storage battery at the key points as a result of mathematical simulations was obtained. The obtained simulation results were tested on an experimental installation consisting of four heat storage cells during the charging and discharging of the thermal storage unit. The most effective arrangement of tubular heating elements was determined, allowing for maximum use of the volume of heat storage material. Dependences for determining the index and averaging coefficient of the heat flux were also found. An algorithm for defining the design parameters of the thermal storage depending on the heat supply system operating conditions was described by Klymchuk et al. [14] which made it possible to calculate the optimal position of the heating elements in the heat-storage core, their number, the thickness of the heat-storage layer, dimensions of the heat-storage core and the specific heat flux upon the heated surface. Beknazarian et al. [15] developed a method for selecting and optimizing the high-temperature thermal insulation that can be applied in ETS units.

Theoretical studies of the heat-storage core thermal state of the dynamic-type ETS units were performed by Janssen et al. [16], for both heat charging and heat emission operation modes. Three-dimension models for the heat-exchange processes were developed and the calculations for the non-stationary temperature field were carried out using the finite element method.

When selecting a reasonable method of heat and air distribution in premises, one must consider the requirements for providing the specified air–thermal conditions in work areas where calves are kept, including those of cages.

Various design options for inflow-exhaust ventilation installations and systems, can be implemented enabling solutions for the following assigned tasks, to a significant degree: providing natural ventilation, conventional air distribution equipment (air-ducts for uniform air distribution); sputtering heads, inflow exhaust installations of AHU type), ejection-axifugal air terminal units, conventional air distribution units, etc. [17]. Also, in order to improve the energy efficiency of heat supply systems when using the heat of low-potential energy sources and environmental protection, it is possible to use heat pumps with an eco-friendly refrigerants such as CO2 [18,19].

However, in such systems, non-homogeneous air temperature distribution with the height takes place. Warm air, having lower volumetric density, tends to concentrate directly under the ceiling, thus forming an airlock. On the other hand, cold and excessively wet air is accumulated in the lower layers where young stock is located, creating unfavorable conditions for animals. Air velocity in the area where calves are located should not exceed 0.3 m/s, during the cold and period of the year [20].

Based on the results of experimental studies, Bodrov [21] developed a method for defining the required value of the heat transfer resistance, for unheated livestock premises depending on the individual biological characteristics of the particular animal type. Methods for calculating the natural ventilation, on an annual basis, were developed as well.

We assume that the maintenance and energy-related parameters of heat- and airdistribution installations and systems can be improved substantially by application of ceiling fans. Such fans, installed in addition to the conventional heating equipment, ensure effective air circulation (within the permissible air velocity range, in areas where animals are located). As a result, the air temperature distribution becomes more uniform with the height, thus reducing the heat energy loss through the enclosing structures and increasing the heat-exchange coefficient of heating devices. The ceiling fan speed control function makes it possible to maintain its specified performance and, consequently, the air flow velocity. Fans can be mounted in any area of premises making it possible to produce their effect on the animals locally depending on their age and physical status.

A ceiling fan installed in the upper area of the premises draws in air from above and directs the fan-twisted air jets having an internal vortex core towards the floor. These air jets reach the ceiling in form of an overlapping flux that gets spread over the premises and moves towards the walls, penetrating the areas where animals are kept.

In these conditions, the required air mobility is provided, and warm air is supplied to the space where animals are located, including in zones under the cages, thus insuring temperature equalization along the vertical axis. This technical solution makes it possible to reduce the required heating system capacity and to save considerable amounts of energy.

Shah et al. [22] reported the results of a technical-economic effectiveness evaluation, for various ceiling fan options, having optimized fan blade design and for wider application of DC electric motors. Babich et al. [23] developed and verified a three-dimensional timedependent implicit model of the standard ceiling fan by simulation results comparison with the experimental data. Present et al. [24] analyzed the results of the ceiling fans practical application, in commercial premises. Liu et al. [25] and Raftery et al. [26] carried out a series of experimental studies of air velocity fields formed with the use of the ceiling fans, in enclosed areas. Based on the results of experimental data, parameters were specified that, to a major extent, defined the air flow rate in premises, for the case when the ceiling fans operate. Li W. et al. [27] have carried out numerical simulations and experimental studies of air conditioning system and ceiling fans combined operation. Application of a ceiling fan made it possible to reduce the density of airborne participates by more than 20% in the area of the human breathing zone, owing to a better dispersion of airborne participates over the premises. Omrani et al. [28] have performed an incisive analysis of the ceiling fan effects on the microclimate, i.e., air flow rate, thermal acceptability and air quality and energy consumption. It was pointed out that the thermal acceptability and air the flow rate belong to the most extensively studied parameters. Major attention was paid to the air quality and electric energy consumption. Besides, that analysis has brought to light the gap in our knowledge concerning the specifics of natural ventilation and ceiling fans combined operation including their influence on the air quality, in premises, which is vitally important during pandemic periods.
