Effects of Nonsteady Hot-water Greenhouse Heating on Heat Transfer and Microclimate

✍ Scribed by M. Teitel; A. Shklyar; I. Segal; M. Barak

• Publisher: Elsevier Science
• Year: 1996
• Tongue: English
• Weight: 266 KB
• Volume: 65
• Category: Article
• ISSN: 0021-8634
• DOI: 10.1006/jaer.1996.0103

✦ Synopsis

Hot-water tubes are used for heating in many agricultural buildings . Owing to the thermostatic control of the heating system , the tubes usually operate under non-steady-state conditions . Experiments were carried out to determine the ef fects of non-steady heating on the heat transfer coef ficients of the heating tubes , on the amount of energy supplied in the dif ferent phases of the heating cycle and on the temperature variation of the air and the crop . The experimental data show that the heat transfer coef ficients decreased during the cooling-down phase of the heating cycle . In addition , there was a continuous change in the ratio between the heat lost by convection and that lost by radiation from the outer surface of the tubes . At the beginning of the coolingdown phase , convection contributed more than radiation to the total heat loss , while towards the end of this phase radiation made a slightly larger contribution than convection . From energy calculations , it appears that approximately 60 -70% of the energy used was supplied to the greenhouse during the heating-up and quasi-steady heating phases ; the remainder was supplied during the cooling down of the tubes . Owing to the non-steady-state heating , the temperatures of the greenhouse air and crop varied in a cyclic manner with respect to time . These temperatures were closely correlated and the dif ference between them also changed in a cyclic manner .