Energy management in protected cropping: manipulation of glasshouse temperature
In this factsheet, Farm Energy Centre's Chris Plackett, and Steve Adams and Allen Langton from Warwick Horticultural Research International (HRI) highlight the energy savings that can be made through effective glasshouse temperature.
- Reducing the heating set-point by 1°C can typically save around 10–13% energy. However, account needs to be taken of the effects of lower temperature on crop timing, yield and quality. The approach may be best suited at present to ornamental spot crops such as poinsettias.
- Temperature Integration (TI) saves energy with little impact on yield and quality. In Basic TI, vent temperature is raised to gain energy ‘credits’ from solar gain, and these are ‘spent’ by lowering heating set-points at other times when energy use would have been high. Trials incorporating best-practice humidity control have given energy savings of 6–12%.
- Greater savings are provided by routinely incorporating a low day heating set-point, and preferentially heating the glasshouse at night under thermal screens (Extended TI). This gives savings in the winter months when there is little solar gain. Adverse effects on crop yield and quality can be overcome with good crop management.
- Regulating temperature on the basis of wind speed can save 5–10% energy in older houses without screens.
Using DROP may save up to 1.5–2% of energy and reduce the need for PGR treatment. The temperature is allowed to fall at dawn or before screens are removed, but is increased again several hours later so as to maintain the average 24 hour temperature.