- Energy Saving
Energy management in protected cropping: good housekeeping
In this factsheet, Farm Energy Centre's Chris Plackett, and Steve Adams and Allen Langton from Warwick Horticultural Research International (HRI) highlight the benefits of good housekeeping — the first essential step in achieving efficient energy management.
- Energy saving in protected cropping starts with good housekeeping. Regular equipment maintenance, and making essential repairs without delay can reduce energy use by up to 10% for little or no capital outlay.
- It is helpful to have someone in the organisation with specific responsibility for energy issues. Staff training in energy matters can be very beneficial.
- Energy use data, preferably using sub-metering, should be assessed at least once each week. This will give a detailed insight into factors affecting energy use. Ideally, energy data should be compared alongside greenhouse climate data, weather data and cropping information. If possible, benchmark performance against that of other growers.
- Degree day analysis is a simple, but effective technique that is useful in studying comparative energy use (between years, glasshouse units, growers etc).
- Control equipment including measuring boxes, outside weather stations and CO2 sensors should be regularly maintained and calibrated. A measuring box that reads 0.5°C low can increase the annual greenhouse energy cost by around £5,000/ha.
- Single glazing is still the preferred option for greenhouse cladding, and thermal screens generally provide a better option for reducing heat loss than double glazing.
- Air leakage can account for 5–30% of instantaneous greenhouse heating demand, and energy efficiency can be improved in older structures by sealing the gaps between panes of glass, and by fitting seals to greenhouse doors and ventilators. Gaps around pipe, cable or duct entry points also need to be sealed, and damaged panes of glass replaced as soon as possible.
- Windbreaks will reduce heat loss from the greenhouse, particularly under windy conditions and when internal energy screens are not in use. However, care needs to be taken to prevent associated shading effects.
- The glass should be kept clean, inside and out. In tomato production, a 10% increase in light transmission has been predicted to result in a 2% reduction in energy use and an 8% improvement in energy use efficiency.
- Boiler upgrading has considerable energy-saving potential. The most efficient designs of boilers with condenser units can achieve seasonal efficiencies close to 90%. This compares to around 80% for modern boilers without a condenser, and less than 70% for older boilers (20+ years old).
- It can be more energy-efficient to install a number of smaller, localised heating systems rather than a single, large central boiler. This will improve boiler use efficiency and reduce energy transmission losses.
- Air heaters have some advantages over piped hot-water heating systems. However, heat distribution can be very uneven.
Insulation applied to pipes, flanges and hot water valves, the boiler casing and the heat store will typically reduce heat losses from them by more than 90%, with a payback period that is typically less than two years.