Temperature integration and process-based humidity control in chrysanthemum

Abstract

Simulations in the authors’ previous studies have shown that a modified temperature integration regime with a 6-day averaging period and increased set-point flexibility was able to reduce annual energy consumption by up to 9% as compared to a regular temperature integration regime. The commonly applied fixed set-point for relative humidity (RH) of 80–85% strongly reduced the potential for energy saving with this regime. Therefore, a more flexible humidity control regime was developed. Simulations indicated that yearly energy consumption could be reduced by 18% as compared to a fixed set-point of 80% RH. By combining the two regimes (temperature integration and humidity control), it was predicted that the energy saving would be even greater. To test this prediction, the combined regimes were applied in two experiments with cut-flower chrysanthemum crops investigating the effect on plant development and growth. Different temperature bandwidths for temperature integration (±2, ±4, ±6 and ±8 °C) were also compared within the joint regime. Crop development was only delayed with the ±8 °C temperature bandwidth. The best regime with respect to plant development, growth, quality and energy saving (±6 °C temperature bandwidth) was compared in a spring experiment with a climate regime used in commercial practice. Energy consumption was 23.5% less with the joint regime. No negative consequences of high humidity were observed, but there was a strong increase in the dry weight of all plant organs. Total plant dry weight was 39% higher than in the regular regime. It can be concluded that energy saving and crop yield increase can be achieved simultaneously, although the dynamic temperature control has to be adjusted to the chrysanthemum developmental stage. The combined dynamic climate regime forms a promising basis for future climate controllers and is easily extendable to other greenhouse crops.