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The use of solar energy as a potential alternative source to ensure the heat supply to energy-efficient houses was explored. We have performed preliminary theoretical analysis of energy indicators for the combined heat supplying system when a solar window is used as part of the enclosure for an energy efficient house. In order to enhance operational effectiveness of the studied plant relative to existing solar collectors and to improve it in the structural aspect, the stratification of a heat carrier in the tank-accumulator of the combined heat supply system with a solar window was calculated.The study of operational efficiency of the experimental setup for using solar energy was carried out under the mode of circulation and gravitational motion of the heat carrier by the intensity of radiation of the solar energy simulator on the system of 600 W/m2 and 900 W/m2. Water was used as a heat carrier.We have analyzed changes in temperature of the heat carrier in the solar collector and in the tank-accumulator of the proposed combined solar heat supply system with a solar window as part of the external enclosure of an energy-efficient house.It was established that the heat carrier temperature under the circulation mode reached 26.5 °C. We have also presented comparative field, laboratory, and theoretical calculations of the average temperature of the heat carrier in the tank-accumulator under the mode of the heat carrier gravitation motion under various conditions.Efficiency of the experimental setup was calculated. The dynamics of change in efficiency of the solar heat supply system with a solar window were described. Efficiency was ≈55 % under the mode of heat carrier circulation for heat energy accumulation in the tank-accumulator, depending on heating duration. Under the mode of gravitational motion of the heat carrier, we calculated efficiency for the design of a solar window only, which was 53 %, Досліджено використання сонячної енергії як потенційного альтернативного джерела для забезпечення теплопостачанням енергоефективних будинків. Проведено попередній теоретичний аналіз енергетичних показників комбінованої системи теплопостачання за використання геліовікна як частини огородження енергоефективного будинку. З метою підвищення ефективності роботи досліджуваної установки відносно існуючих сонячних колекторів та покращення її в конструктивному аспекті, було розраховано стратифікацію теплоносія в баку-акумуляторі комбінованої системи теплопостачання із геліовікном.Дослідження ефективності роботи експериментальної установки в системі для використання сонячної енергії проводили в режимі руху циркуляції та гравітації теплоносія за інтенсивності випромінювання імітатора сонячної енергії на систему 600 Вт/м2 та 900 Вт/м2. Як теплоносій використовували воду.Проаналізовано зміну температури теплоносія в сонячному колекторі та в баку-акумуляторі запропонованої комбінованої системи сонячного теплопостачання із геліовікном як частини зовнішнього захисту енергоефективного будинку.Встановлено, що температура теплоносія в режимі циркуляції досягала 26,5 °С. Крім цього, наведено порівняльні натурні, лабораторні та теоретичні розрахунки усередненої температури теплоносія в баку-акумуляторі в режимі руху гравітації теплоносія за різних умов.Було розраховано коефіцієнт корисної дії експериментальної установки. Описано динаміку зміни коефіцієнта корисної дії системи сонячного теплопостачання із геліовікном. У режимі руху циркуляції теплоносія за накопиченням теплової енергії в баку-акумуляторі, залежно від часу нагріву, ККД становив ≈55 %. В режимі руху гравітації теплоносія було обраховано коефіцієнт корисної дії лише конструкції геліовікна, що становив 53 %, Исследовано использование солнечной энергии как потенциального альтернативного источника для обеспечения теплоснабжением энергоэффективных домов. Проведен предварительный теоретический анализ энергетических показателей комбинированной системы теплоснабжения за использование гелиоокна как части ограждения энергоэффективного дома. С целью повышения эффективности работы исследуемой установки относительно существующих солнечных коллекторов и улучшения ее в конструктивном аспекте было рассчитано стратификацию теплоносителя в баке-аккумуляторе комбинированной системы теплоснабжения с гелиоокном.Исследование эффективности работы экспериментальной установки в системе для использования солнечной энергии проводились в режиме движения циркуляции и гравитации теплоносителя по интенсивности излучения имитатора солнечной энергии на систему 600 Вт/м2 и 900 Вт/м2. В качестве теплоносителя использовали воду.Проанализировано изменение температуры теплоносителя в солнечном коллекторе и баке-аккумуляторе предложенной комбинированной системы солнечного теплоснабжения с гелиоокном как части внешней защиты энергоэффективного дома.Установлено, что температура теплоносителя в режиме циркуляции достигала 26,5 °С. Кроме этого, приведены сравнительные натурные, лабораторные и теоретические расчеты усредненной температуры теплоносителя в баке-аккумуляторе в режиме движения гравитации теплоносителя при различных условиях.Был рассчитан коэффициент полезного действия экспериментальной установки. Описана динамика изменения коэффициента полезного действия системы солнечного теплоснабжения с гелиоокном. В режиме движения циркуляции теплоносителя по накоплению тепловой энергии в баке-аккумуляторе, в зависимости от времени нагрева, КПД составлял ≈55 %. В режиме движения гравитации теплоносителя был подсчитан коэффициент полезного действия лишь конструкции гелиоокна, который составил 53 %

We have improved a procedure for calculating the kinetic and energy parameters of the convection fruit drying process in a solar drying plant, based on which it is possible to analyze enhancement in the effectiveness of the technological process of drying and to reduce the cost of energy resources through solar energy. We have examined the kinetics, dynamics and intensity of fruit drying in a solar drying plant, in particular for apples cut in slices with a thickness of 8 mm, treated with a sugar solution, exposed to blanching, and without treatment. We have determined such kinetic characteristics of the process: duration of drying the apples treated with a solution of sugar or exposed to blanching was 27 hours, without treatment ‒ 33 hours. In this case, the intensity of drying apples with a moisture content from 2.89 to 0.24 kg wet/kg of dry matter is 1.57÷0.18 kg/(m 2 ·s). We have established the effect of energy parameters on the technological parameters of a heat carrier and the plant’s efficiency. Specifically, over a single drying cycle from 1.5 m 2 of the air collector’s surface, a solar drying plant consumed solar radiation energy in the range from 723 to 800 W/m 2 . It has been established that this energy was converted into heat energy (2,368.2 kJ), absorbed by a heat carrier (1,984.9 kJ) and used to heat the product (836.3 kJ) and moisture evaporation (756.7 kJ), with a part absorbed by the heat accumulator (356.9 kJ). We have determined the efficiency of a solar drying plant, which ranged from 23 to 60 % depending on a change in the density of solar energy arrival, which ranged in the morning period (from 7:00 to 10:00) from 456 to 965 W/m 2 and in the evening period (from 17:00 to 20:00) from 734 to 223 W/m 2 . The results obtained could be used in the development and improvement of technical means for drying fruit, to enhance the technological and energy efficiency of the process

We developed a new design of an air solar collector made in the form of an inseparable power unit, which includes a frame with heat-insulated walls, single glazing and a selective surface on its bottom. We defined a number of generalizing dependences for the determination of thermal efficiency of an air solar collector, namely, an influence of the mass air flow q a on a temperature difference of the heat-transfer agent t o and insulation E, on heat productivity q and the efficiency η of the solar collector. Based on the experimental data, we obtained linear regression dependencies of the average daily ambient temperature t eat on energy illumination E and the average temperature of the heat-transfer agent carrier t aat of the average daily ambient temperature t eat . We verified the adequacy of the results of theoretical and experimental studies. We established that we achieve the maximum values of the efficiency of the solar collector η ‒ from 65 to 80.6 % at a temperature of the outlet flow of the heat-transfer agent t o from 30 to 60 °C and mass air flow, q a from 170 to 190 m 3 /h. We determined that an increase in the level of insulation E from 100 to 1,000 W/m 2 makes it possible to increase heating productivity of the collector q from 320 to 1,260 W and the temperature of the heat-transfer agent at the collector outlet t o from 10 to 60 °C. We can use the obtained results in development and improvement of technical means for drying fruits, for improvement of technological and energy efficiency of the process.

We developed a new design of an air solar collector for a fruit dryer including double glazing and a selective surface made of a thin metal substrate with inlet and outlet openings on its bottom. We established that it is necessary to use a glass with a heat-reflecting coating of a solid K-glass type with a radiation coefficient e=0.1...0.15 for a double-glazing substrate. This makes it possible to obtain the widest possible spectrum of direct sunlight rays that irradiate a surface of an absorbing plate and reduces a diffuse component of radiation, which ensures an increase in efficiency of a solar collector. We determined regularities of the influence of a change in flow speed of a heat-transfer agent, a temperature drop, and radiation intensity on power of a solar collector. We developed a model of heat exchange processes occurring in an air solar collector. We presented the methodology for estimation of heat loss of an air solar collector with passive use of solar energy. We established that energy illumination E, which is from 377 to 1,223 W/m 2 , affects heat output of an air collector Q=117...480 W significantly. We established that a use of a non-selective absorbing surface in an air solar collector with a low insolation level E=377 W/m 2 makes it possible to increase efficiency by η=70.7 % more for selective, and at a large energy illumination of E=1,000 W/m 2 , on the contrary small η=54.6 %. This makes it possible to explain how redistribution of the ratio of the maximum current thermal power (N SC =48.8...100 W) and efficiency of an air solar collector occurs. One can use the obtained results in development and improvement of technical means for fruit drying to improve technological and energy efficiency of the process.

The work addresses the issue of solving a scientific-applied task on the substantiation of operation modes of the solar fruit dryer in order to improve energy efficiency of the technological process of fruit drying for small amounts of fruit processed at private farms. We have explored the use of solar energy for fruit drying at the latitude of the location of Rivne oblast, Ukraine, which has the average annual solar radiation power of the order of 3.41 kW∙h/m 2 per daylight. This makes it possible to receive from 1.5 to 2.3 kW∙h of energy per day from the air collector area of 1 m 2 . The series of analytical and experimental studies that we conducted has confirmed the possibility for a significant intensification of the process of fruit drying in the solar dryer. Compared with modern convective drying devices, the specific energy consumption when drying the fruit in the solar dryer is reduced by 3…3.7 MJ/kg. The degree of intensification grows by 3.3…12 times compared to drying devices of the mine and tunnel types. Such results were achieved by implementing the proposed design of a flat mirror concentrator, to enhance the slanting fluxes of morning and evening sun irradiation, and a heat accumulator, based on pebbles, for accumulating at night the excessive heat from the reserve source of energy. It was established that regardless of a blanching technique for fruit raw materials, the duration of drying in the solar dryer varies depending on physical parameters of the environment. In the process of drying, the experiments were carried out at a temperature of 289.15…333.15 K, and the duration of drying was from 50 to 74 hours. We have analyzed the effect of operational parameters on a change in the chemical indicators and quality of the dried fruit. Specifically, the content of vitamin C, which was 5.2 mg/% for pear, and 4.3 mg/% for apple. The acidity was 0.29 % for pear, and 0.46 % for apple. The content of dry nutrients was 87.5 % for pear, and 85.9 % for apple. The sugar content of fruit raw materials was 59.36 % for pear, and 57.8 % for apple.

We proposed a generalized procedure of convective fruit drying, which takes into account comprehensive combination of thermal-physical and physical-chemical properties of fruit with their kinematic heat and mass exchange characteristics. We developed a mathematical model of heat, moisture and mass exchange for convective fruit drying, which considers moisture-yielding velocity of the dried material in the operation zone of the heat carrier under conditions of diffusion process of moisture transfer in the dried material. The given model allows us to determine heat and mass exchange characteristics and intensity of the drying process. We proposed the systems of differential equations of heat and moisture transfer in the process of convective fruit drying for parabolic and uniformed original distribution of temperature and moisture content. As a result of the solution of a system of differential equations, we obtained appropriate dependences to determine the energy of bound moisture, moisture content on the surface and in the center of the material, difference of moisture content between the surface and central layers, as well as critical moisture content. The obtained results may be used when predicting the heat and mass exchange processes, for improvement of technology and equipment for fruit drying in the solar dryer, for increasing technological and energy efficiency of the process.

A new design of a solar dryer for drying fruits is proposed, which includes the use of a flat mirror concentrator to enhance the flow of slant morning and evening sunlight, and a thermal accumulator based on pebble for accumulating over night time the excess heat from the reserve source of energy. This makes it possible to increase economic efficiency of the drying process by 20 %, to reduce energy consumption by 15 %, specific energy consumption by 10 %, direct operating costs by 5 %, electricity consumption by 3,4 kW·h, or 12384 kJ of thermal energy, by using solar energy. We improved a technique of the substantiation of economic efficiency of the developed solar dryer, the basis of which is a simplified mechanism for calculating direct operating costs, economic effect and payback period of the machine depending on the fluctuation of prices for electricity and dried products, linked to a specific territory of the location of a personal peasant farm. The results that were obtained can be used when developing and improving technical means of drying fruits, to improve technological, energy, biological and economic efficiency of the process.