RESULTS OF PRACTICAL EXPERIENCE OF HEATING A GREENHOUSE VIA SOLAR WATER HEATING COLLECTORS WITH VACUUM TUBES (IN KARSHI CITY CONDITIONS)

Аннотация

This article calculates the heat load required to maintain the internal temperature of the greenhouse and analyzes the possibilities of heating a greenhouse using solar water heating collectors with vacuum tubes under conditions of external temperature fluctuations. The article uses as a basis the model of a greenhouse with an area of 50 m², covered with glass. Keywords: greenhouse heating, solar energy, evacuated tube collector, solar water heater, alternative energy sources, practical experience results, thermal efficiency, environmentally friendly heating method, solar collector system, energy- saving technology. In Uzbekistan, year-round cultivation of vegetables and other products in greenhouses uses artificial heat sources. Compared to traditional fuels, the use of solar energy can reap environmental and economic benefits, especially through the use of vacuum tube solar collectors. https://scientific-jl.org/obr Выпуск журнала №-71 29 Часть–7_ июня–2025 ОБРАЗОВАНИЕ НАУКА И ИННОВАЦИОННЫЕ ИДЕИ В МИРЕ 2181- 3187 In winter, there is a need for an efficient source of heat to maintain a greenhouse microclimate. Solar energy is important as a renewable and cost-effective source. In order to determine the efficiency of vacuum tube solar water heating collectors under real conditions, an experiment was carried out in Karshi. Experience Conditions Date: February 22, 2025- Location: Karshi city, Kashkadarya region- System: vacuum collector with 20 pipes, capacity 200 liters- Time: from 09:00 to 15:30- Outside temperature: 6 °C → 23 °C- Water temperature: 20 °C → 51 °C- Solar radiation: 342 → 970 W/m² (mixed cloudy and sunny conditions) Table of experiments (main observations) Time External Water Solar temperature (°C) temperature (°C) radiation (W/m²) 9:00 6 20 342 9:30 7 22 480 10:00 8 25 627 10:30 9 28 729 11:00 10 30 645 11:30 13 33 860 12:00 17 35 820 12:30 18 38 650 13:00 18 39 400 13:30 18 42 650 14:00 20 44 845 14:30 23 49 970 15:00 22 50 560 15:30 21 51 710 https://scientific-jl.org/obr Выпуск журнала №-71 30 Часть–7_ июня–2025 ОБРАЗОВАНИЕ НАУКА И ИННОВАЦИОННЫЕ ИДЕИ В МИРЕ 2181- 3187 Calculation of energy harvest Thermal energy collected through water (during the whole experiment): Formula:Q = m · c · ΔTm = 200 kgc = 4186 J/kg·°CΔT = 51 - 20 = 31 °CQ = 200 × 4186 ×31 = 25,951,200 J ≈ 7210 Wh = 7.21 kWh Result: During the experiment, 7.21 kWh thermal energy was collected. Correlation with expected energy Average solar radiation: 745 W/m² Collector area: 2 m²Working time: 6.5 hours Q = 2 × 745 × 6.5 ≈ 9.67 kWh Actual: 7.21 kWhTheoretical maximum: 9.67 kWh Efficiency: (7.21 / 9.67) × 100 ≈ 74.6% Figure 1 Solar Water Heating Collectors with Vacuum Tube Calculation of greenhouse heat load Heat loss of a greenhouse is calculated by the following formula: https://scientific-jl.org/obr Выпуск журнала №-71 31 Часть–7_ июня–2025 ОБРАЗОВАНИЕ НАУКА И ИННОВАЦИОННЫЕ ИДЕИ В МИРЕ 2181- 3187 Q=U⋅A⋅ΔT here: Q is heat loss (W), U is the total coefficient of thermal conductivity (W/m²· K), A— heat-conducting level of the greenhouse (m²), ΔT is the temperature difference (K) between the inside and outside. Information: Greenhouse area: 50 m² Average height: 2.5 m → Volume ≈ 125 m³ Surface area (wall + roof): approx. 130 m² Glass (window) surface: 100% → U=5.7U = 5.7U=5.7 W/cu· K (U-value of a normal window) Internal temperature: +20 °C External temperature: from +5 °C to −5 °C Calculations: External ΔT temperature Q(W) (K) (°C) 5.7×130×15=111155.7 × 130 × 15 = +5 15 111155.7×130×15=11115 W 5.7×130×20=148205.7 × 130 × 20 = 0 20 148205.7×130×20=14820 W 5.7×130×25=185255.7 × 130 × 25 = −5 25 185255.7×130×25=18525 W Thus, when the outside temperature drops to −5 °C, the greenhouse heat load reaches 18.5 kW. https://scientific-jl.org/obr Выпуск журнала №-71 32 Часть–7_ июня–2025 ОБРАЗОВАНИЕ НАУКА И ИННОВАЦИОННЫЕ ИДЕИ В МИРЕ 2181- 3187 FIGURE 2: Solar Greenhouse Heat