Session: 11-09-03: Modeling and Simulation Methods

Paper Number: 69509

Start Time: Wednesday, 05:00 PM

69509 - Closed Greenhouse Heating in an Arid Egyptian Winter Using Earth-Air Heat Exchangers 

Greenhouse agriculture is a commonly used means of plant cultivation in cold climates, whereby plant cultivation is enabled by maintaining an interior temperature that is warmer than the ambient exterior temperature. Closed greenhouses with minimal ventilation minimize the energy requirement for heating compared to open ventilated greenhouses. In this paper a closed greenhouse heating using Earth Air Heat Exchanger (EAHEs) is investigated during the winter season in an arid Egyptian climate. While the greenhouse interior temperature can be kept above the minimum for cultivation during the daytime, the temperature drops at night and heating is required. One renewable and sustainable heating strategy is storing the heat from solar energy during the day and using the stored energy to heat at night. Such systems involve the additional cost of solar collectors and a storage medium. Another strategy is relying on Geothermal energy through deep or shallow soil. At four meters depth, the soil temperature is warmer than the ambient air temperature during winter. That potential temperature difference can be exploited to provide heating to the greenhouse by using an EAHE.  A model of a closed greenhouse with EAHE heating is presented and simulations are performed using climate data of a representative day of the coldest month of the year (i.e. January) at the case study location, Hurghada, Egypt. A comparison is made between a closed greenhouse with and without EAHE heating. The simulation shows that without heating the greenhouse interior temperature drops below the minimum temperature for cultivation (20ºC) during the early and late hours of the day. Furthermore, at midday the temperature inside the greenhouse exceeded the maximum temperature for cultivation (30ºC). However, the simulations showed that by using five EAHE pipes operating in parallel enabled the greenhouse interior to be maintained at a temperature suitable for plant cultivation, cooling during the day and warming at night.  Aside from temperature, it is important to maintain the relative humidity inside a greenhouse within a range suitable for plant cultivation (50% to 80%), necessitating systems for humidifying and dehumidifying the internal air. By using five EAHE pipes in parallel, the variability in relative humidity was reduced from 35% to 15%, simplifying the control of the humidity within the greenhouse. Additional simulations show that the temperature and relative humidity in the greenhouse can be controlled throughout the winter period (November to February), demonstrating that the EAHE is a viable sustainable method for temperature and humidity regulation for a closed greenhouse in an arid Egyptian winter climate, without any requirement for additional heating.

Presenting Author: Anwar Hegazy University of Auckland

Authors:

Anwar Hegazy University of Auckland
Alison Subiantoro University of Auckland
Stuart Norris University of Auckland