Study of the Distribution of Air Temperature in a Greenhouse Heated by Air to Air Heat Pump

Abstract

The temperature distribution inside the experimental greenhouse heated by air to air heat pumps and its impact on the growth and productivity of tomato plants were studied. Experimental greenhouse located at SIA Rītausma facility in South-East Latvia.Two commercially available regular air to air heat‑pumps with a combined heat power of 10 kW were used. To measure the temperature distribution, 18 temperature sensors with solar radiation shields at different heights and positions among the plants were installed. Additional 4 temperature sensors were used to measure the air flow temperature at the heating elements. Reference air temperature was measured at an industrial production facility heated by a common gas heating system.Temperature was found to be homogenous within 1 °C. Observed temperatures were up to 4 °C lower than set on the control unit of the heat pump. This discrepancy was compensated by higher set values for the controlling unit. As research showed the temperature stability was better than at the water-heated industrial facility at time slots when the sun was suddenly cleared from clouds.The cooling of the experimental greenhouse by air conditioning during summer time was rather challenging for the tomato plants and productivity. 23% of plant stems died until the end of the season and the yield was 50% lower than in the reference greenhouse. The energy efficiency compared to the industrial facility was approx. 8 times better and the estimated CO2 emissions were 8-16 times smaller compared to gas heating. There were no increases of heating costs determined.Further studies are needed to optimize the heating parameters and reach the desired greenhouse productivity.

Use of accumulated solar thermal energy in greenhouse for extending vegetation period of crop plants

“…In order to record and store the temperature and humidity measurement data, a system (Postgre SQL) has been arranged for monitoring and control of the modes, as well as for evaluation of the efficiency of thermal energy accumulation [14]. The measurement system (Fig.…”

“…The pipe system was used to transfer warm air from the greenhouse to the thermal mass for storage and, when necessary, to transfer the stored heat from the thermal mass back to the greenhouse. The PostgreSQL system used in the previous study [14] was applied to monitor the thermal energy storage parameters and to record and store the data. The aim of the work is to find the possibilities and usefulness of thermal energy storage DOI: 10.22616/ERDev.2023.22.TF128 629 and recovery in a greenhouse with a thermal mass, as well as the possibilities of extending the vegetation period of the plants in such greenhouse.…”

Análisis sobre la actividad científica referente a las estrategias de climatización pasiva usada en invernaderos: Parte 2: análisis técnico

“…Así mismo, se identificó que la implementación de bombas de calor aire-aire para la refrigeración en verano en invernaderos pequeños, afecta a las plantas debido a escapes de aire a bajas temperaturas, aproximadamente 8°C, emitidos durante las horas de la tarde que siguieron a los días cálidos, evidenciando daños del 23% de los tallos y obteniendo rendimientos inferiores al 50% con respecto al invernadero enfriado con ventilación natural con ventanas en el techo (Auce et al, 2021).…”

Impact of Environmental Factors on Indoor Air Temperature in Gas-Fired Radiant Heated Cultivated Structures

“…Practical horticulture is only feasible when creating favourable temperature and humidity conditions within cultivation structures throughout the entire cold period of the year. To achieve this, various heating systems are employed in winter greenhouses and conservatories, including water (or steam), air, combined water or steam and gas-air systems [9][10][11][12][13][14][15]. The heating of cultivation structures can also be accomplished through the use of electrical energy.…”

“…The heating of cultivation structures can also be accomplished through the use of electrical energy. In addition to the mentioned traditional heating systems, alternative methods for providing thermal comfort to cultivation structures are organized, such as through heat pumps [1,15] or solar collectors (solar greenhouses) [2,6,[10][11][12][13][14]. Currently, for several reasons [3]: artificial source of infrared radiation; the absence of the need for a boiler installation, thermal networks, and related engineering equipment; automation of the technological process; even distribution of thermal energy on the soil surface; possible application of carbon dioxide (CO2) for plant fertilization, obtained from fuel combustion products when using gas infrared emitters -gas radiant heating systems are of significant interest in agriculture [16][17][18][19][20][21][22][23][24][25].…”