The Energy Balance and Energy-Saving Measures in Greenhouse Tomato Cultivation

Abstract

Reliable and quick assessment of energy conservation measures in greenhouse cultivation supports growers in their operations. Such an overview should quantify the consequences of changes in energy flows for total energy consumption, amount and quality of production, and farm economy.Using tomato as an example crop, comprehensive energy balances were developed for a reference situation in The Netherlands. Solar radiation, primary and secondary heating circuits and CO 2 from the flue gasses of the heating system were quantified as energy sources. Energy use for air and leaf temperature increase, crop photosynthesis, crop transpiration, as well as energy losses through the roof, walls and ground surface were quantified. Subsequently, the effects of 11 energy conservation measures were computed. Consequences for gas consumption and production were simulated with a greenhouse and a crop growth model, respectively, consequences for quality were assessed on the basis of expert knowledge, and economic consequences were simulated with a cost-benefit model.For tomato, most energy was saved by increased insulation of the greenhouse cover (23% saving) and lowered temperature set point (16%), followed by increased set point for air relative humidity, screen gap control in steps, and temperature integration (all about 5%). Fresh tomato production fell in most cases, except in case of increased light transmission by the greenhouse cover. Energy use efficiency was defined as the amount of energy required to produce a certain quantity of fresh harvestable product. Energy-conservation aims to decrease the energy use efficiency. Greatest gains were reached through insulation (-20%), lowered temperature set point (-12%) and improved light transmission (-8%). Improved light transmission resulted in the strongest increase of the balance of yield and costs (€2.6, or 10%), followed by increase of RH set point, crop-based RH control, crop-based use of the energy screen, increased size of the thermal storage tank and reduction of crop transpiration (all less than €0.5).Although energy conservation reduces fuel costs, its implementation depends on the effects on production an overall economic profitability of the farm. Improved roof insulation, reduced temperature set point, screen gap control in steps, increase of the RH set point, temperature integration, and crop-based RH control are first candidates for (further) implementation. Other measures require prior technological advancements or fine-tuning. INTRODUCTIONGiven the high costs of energy and obligations imposed on national governments by the Kyoto protocol (UNFCCC, 1997), energy conservation in horticulture has become increasingly important. Reliable and quick assessment of measures to conserve energy supports growers in their operations, and policy makers in directing research funds. Energy conservation assessments require an overview of the most important energy flows and their consequences. Changes in energy flows may have consequences for the

Sensible use of primary energy in organic greenhouse production

“…The energy savings depend on the crop and the magnitude of temperature fluctuations allowed. The range of energy savings with TI, according to experiments and simulations, is 5-15% (Buwalda et al 1999;Körner and Challa, 2003;Elings et al 2005), with few effects on production.…”

“…Lowered day and night set points by 2 °C in a tomato crop resulted in a 16% energy saving but reduced annual production by 3.3% (Elings et al 2005).…”

“…In a certain extent, they can also be applied to organic greenhouse. Elings et al (2005) studied by simulations the impact of an increase of the relative air humidity (RH) set point from 85% to 90%. An increase in the RH set point reduced by 5% the use of energy while production was maintained, but the risk of botrytis increased.…”

Innovative Technologies for an Efficient Use of Energy

“…For a tomato crop, grown under Dutch conditions, a 10% higher greenhouse transmission was predicted to give an 8% improvement in efficiency (Elings et al, 2005). Further improvement of the greenhouse as an energy efficient solar collector is obtained by improving the light transmission of its structure and minimizing reflection losses through the modification of the roof slope.…”

“…using higher humidity set points (Elings et al, 2005); reducing the transpiration level of the crop, or dehumidification with heat recovery (Campen and Bot, 2002;Rousse et al, 2000).…”