Abstract
The effect of considering cultivar differences in stomatal conductance (g s ) on relative air humidity (RH)-related energy demand was addressed. We conducted six experiments in order to study the variation in evapotranspiration (ET c ) of six pot rose cultivars, investigate the underlying processes and parameterise a g s -based ET c model. Several levels of crop ET c were realised by adjusting the growth environment. The commonly applied Ball–Woodrow–Berry g s -sub-model (BWB-model) in ET c models was validated under greenhouse conditions, and showed a close agreement between simulated and measured ET c . The validated model was incorporated into a greenhouse simulator. A scenario simulation study showed that selecting low-g s cultivars reduces energy demand (≤5.75%), depending on the RH set point. However, the BWB-model showed poor prediction quality at RH lower than 60% and a good fit at higher RH. Therefore, an attempt was made to improve model prediction: the in situ -obtained data were employed to adapt and extend either the BWB-model, or the Liu-extension with substrate water potential (Ψ; BWB-Liu-model). Both models were extended with stomatal density (D s ) or pore area. Although the modified BWB-Liu-model (considering D s ) allowed higher accuracy (R 2 = 0.59), as compared to the basic version (R 2 = 0.31), the typical lack of Ψ prediction in greenhouse models may be problematic for implementation into real-time climate control. The current study lays the basis for the development of cultivar specific cultivation strategies as well as improving the g s sub-model for dynamic climate conditions under low RH using model-based control systems. • Relative air humidity control is a key but costly aspect of greenhouse climate. • Accurate estimation of evapotranspiration (ET c ) is essential for relative air humidity regulation. • Six pot rose cultivars and several cultivation regimes were used. • ET c estimation was improved using cultivar-specific stomatal conductance parameters. • The use of low-stomatal conductance cultivars secures energy saving (2.5–5.75%).
Highlights
Climate-controlled greenhouses are high energy-consuming facilities, especially in hot or cold regions (Bot, 2001; Vanthoor, 2011, p. 307)
Since the crop itself is a major driver of relative air humidity (RH) via crop evapotranspiration (ETc), its accurate estimation is essential for greenhouse climate control
We focus on the variability of ETc and gs in selected rose cultivars with similar external appearance, aiming to show the effect of cultivar specific BWB-model parameters on prediction quality and effect in model application to predictive greenhouse climate control
Summary
Climate-controlled greenhouses are high energy-consuming facilities, especially in hot or cold regions (Bot, 2001; Vanthoor, 2011, p. 307). Since the early 1990's, energy demand has been reduced by the introduction of crop directed climate control regimes with dynamic temperature boundaries Aaslyng et al, 2003; Ko€rner & Challa, 2003a) These exploit the naturally-occurring diurnal temperature fluctuations without the need for heating to a fixed temperature, achieving up to 18% savings in energy use for heating in e.g. Dutch climate conditions (Ko€rner et al, 2004). The energy needed for dehumidification (by heating) increases when RH is adjusted to lower levels. Despite great efforts devoted to the development of more efficient dehumidification methods, reducing RH to a secure level ( 85%) remains rather costly, accounting for about 20% of annual energy demand in Northern European climates (Ko€rner & Van Straten, 2008). Since the crop itself is a major driver of RH via crop evapotranspiration (ETc), its accurate estimation is essential for greenhouse climate control
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