Optimisation of Co2 and Temperature in Terms of Crop Growth and Energy Use

Abstract

In current greenhouse climate control, temperature set points follow a pre-set trajectory based on absolute or solar time parameters, adapted only to instantaneous and daily radiation. CO 2 is supplied during a well defined period of the day until a maximum concentration is reached. However, the rate of CO 2 supply is strongly limited by the heat demand, since flue gases are the most commonly used source of CO 2 . Interactions between effects of light, temperature and CO 2 concentration on photosynthesis and crop growth are usually not taken into account. This study aims to make more efficient use of temperature and CO 2 by developing an optimised climate control system in which temperature and CO 2 are deployed such that energy use is minimised while maintaining crop production. Firstly, the diurnal temperature course resulting in a predefined daily mean value was optimised while minimising the heat demand. Most of the time, this resulted in higher day temperatures and lower night temperatures. Secondly, using the heat storage tank, the partitioning of the CO 2 associated with the daily heat demand was optimised, aimed at maximised photosynthesis. Simulation results showed that in the optimised climate control system 7% less energy was used and 2.5% more production was realised than in a standard climate. Testing the optimised climate control in a greenhouse experiment showed that in a sweet pepper crop 6% more energy could be conserved compared to that in the standard climate with similar production levels and fruit quality between the climate control treatments. INTRODUCTIONIn view of the Kyoto protocol (1997), Dutch horticulture and government have agreed to improve the energy efficiency by 65% in 2010 compared to 1980. Energy efficiency can either be enhanced through an increase in production or a reduction in absolute energy consumption. The latter implies that the availability of CO 2 from flue gases associated with the heating demand of greenhouses will be reduced. Hence, an efficient use of CO 2 is getting more important. At present, the greenhouse climate is commonly controlled by rather rigid set points for heating and ventilation. Climate control systems are set to limit temperature fluctuations, resulting in high ventilation rates when the sun is shining and in heating during the night. However, several studies have shown that most horticultural crops tolerate temporary deviations from the temperature set point, as long as the average temperature over 24 hours is kept constant (Bakker and Van Uffelen, 1988;Rijsdijk and Vogelezang, 2000). This so-called temperature integration allows heating to be shifted to times when the heat loss is low, thereby reducing the energy use (Körner and Challa, 2003a). Allowing the day time temperatures to increase, enables average 24 h temperature to be obtained at lower night temperatures. The decreased ventilation rates during the day result in higher CO 2 concentrations that can be realised with a certain rate of CO 2 supply, thereby increasing photosynthes...

An overview of climate and crop yield in closed greenhouses

“…During sunny periods, ventilation for cooling prevents high air humidity. With an increasing ventilation rate, CO 2 dosing becomes less efficient in maintaining the greenhouse CO 2 concentration above ambient conditions (Dieleman et al, 2005;Bakker et al, 1995). Ironically, it is under such conditions of high irradiation and high temperature where crop photosynthesis would benefit most from increased CO 2 concentrations (Morison and Lawlor, 1999).…”

Energy Saving in Greenhouses: Optimal Use of Climate Conditions and Crop Management

“…To make more efficient use of temperature and CO 2 , an optimised climate control system was developed in which temperature and CO 2 were deployed such that energy use was minimised while maintaining crop production (Dieleman et al, 2005a). Firstly, the diurnal temperature course resulting in a predefined daily mean value was optimised while minimising the heat demand, based on the principles of temperature integration.…”

“…A modelling study with sweet pepper showed that this optimised control system reduced the energy use by 6% compared to a commercial cropping system, which was experimentally verified. The subsequent optimization of CO 2 supply, based on an algorithm that weighed the positive effect of CO 2 on production against the CO 2 loss by ventilation resulted in a simulated 2.5% higher production (Dieleman et al, 2005a).…”

Timing of a Short-Term Reduction in Temperature and Irradiance Affects Growth and Flowering of Four Annual Bedding Plants

“…Many growers maintain static air temperature set points, independent of ambient weather conditions outside [10]. Allowing the greenhouse temperature to rise above the desired mean daily temperature (MDT) when heating demand is low and fall below the desired MDT when heating demand is high, but maintain the same MDT, is another strategy to reduce energy use [11].…”