Fuel-efficient production

There are a number of options to consider when trying to cut your glasshouse energy bills, writes Sally Drury.

How much more will you be paying for heating and lighting this winter? With prices soaring, many of us are wondering what to do.

What will happen to energy prices in the future is anyone's guess. There are so many global-impact issues that drive prices one way or the other.

What are the alternatives? In simplistic terms, growers have three choices. A few people will inevitably consider getting out of the business. Others will hope the current price peaks are temporary and hope they can ride out the storm, perhaps by changing crops or taking some simple energy-saving measures to help their situation. The third option is to invest in equipment that has the potential to reduce the cost of growing protected crops.

Whether the latter is a sensible option depends on your situation but also on what energy prices will do in the future. If this does turn out to be just a price spike and the cost of energy starts to fall, it will take longer to benefit from any investment. But it has to be said that gas and oil are becoming more expensive to find and extract. Then there is the fact that the UK is becoming a net importer of gas, and there is also the rising demand for energy from China. FEC Services technical director Tim Pratt thinks that, ultimately, investment could be the right way to go.

"If growers are looking to be in business for a long time, then investing now may well see a quick return on a substantial portion of that investment because we're in a high-energy-price zone.

"High prices make a lot of energy-saving measures attractive from a payback point of view. If prices drop a bit, the chances are growers will still be making savings," he explains.

There is also the issue of carbon footprints. If your agenda, or that of your customers, is concerned with reducing carbon footprints, then investment now in things like alternative-energy use could score points.

So what are the options?

1. Stabilise the price Consider longer fixed-term energy price contracts. It means you know what you are paying, now and for the length of the contract, giving stability, hence predictability. The peaks and troughs will be ironed out, so sometimes you will win and other times you will lose. And there will be a premium because the suppliers also have to guess what is happening in the market and where prices are going to go.

2. Reduce energy inputs Some crops could be grown at a lower temperature, although scheduling, yield and quality could be affected.

3. Reduce heat losses This is about good husbandry. Attention paid to boiler maintenance, calibration of monitoring and control systems, insulation of heat storage tanks and pipe work, replacing broken glass, repairing vents and keeping doors closed are simple but effective ways of saving energy.

A serious cause of energy wastage, especially in older houses, is air leakage through badly fitting joints and vents that will not shut properly. It is estimated that some growers could reduce heat demand by as much as 12 per cent per annum if attention is paid to these points.

Equally, pipe insulation can pay for itself very quickly. Poor-quality installation, damaged materials and water logging can all reduce potential savings. FEC Services has calculated that an external pipe without lagging can lose eight times the energy of an equivalent pipe lagged with 50mm of good-quality dry-insulating material.

4. Cladding and thermal screens Heat transmission losses in a glasshouse are high but they can be reduced by the installation of low-emissivity glass or double-skinned cladding materials, though subsequent energy savings may be at the expense of reduced light transmission.

The use of thermal screens in a glasshouse is, without a doubt, one of the best energy-saving measures. Research has shown screens can reduce the instantaneous heat loss from a greenhouse by up to 40 per cent, although realistically they can only be fitted to the more modern glasshouses and are easiest to fit to the Venlo type of house. Accurate controls are also essential; the Pyrgeometer from Hortimax measures the outgoing radiation at night and can connect to the computer to give accurate utilisation of screens.

While many growers have adopted the use of thermal screens in recent years, many more are missing out on an opportunity to save energy. FEC Services calculated the energy savings for a tomato grower considering thermal screens and found the costs of installation would be covered in 15 months in gas savings at today's prices.

The use of thermal screens is a tougher decision for ornamental growers, since they generally use less energy.

5. Temperature integration Research in the 1990s showed energy consumption could be reduced significantly by adopting temperature integration. Energy savings of up to 12 per cent (15 per cent on windy days) can be achieved, without adversely affecting crop performance, by allowing the heating setpoints to vary more widely but still maintaining the same average temperature. Solar gain is used to lift day temperatures by raising vent temperatures higher than normal. Heat losses are reduced by raising night temperatures under an efficient thermal screen.

Some growers have adopted temperature integration in its entirety. Others have adopted facets of it, such as trapping more solar heat by increasing the vent temperature when the humidity is good.

6. Boiler efficiency Newer boilers will be more efficient but when looking to replace an old one, match boiler capacity carefully to demand. For older boilers, consider refinements that provide quick paybacks through energy efficiency, such as fine-tuning combustion efficiency by adjusting the fuel/air mix parameters and boiler control. The use of multiple boilers can also give significant energy savings.

7. Decentralising On modern, large-scale production sites it is common for heating to be produced by large, centralised, fossil-fuel-fired boilers with associated long, and sometimes inefficient, hot-water distribution systems. It is thought that the situation could be improved by the installation of a number of smaller, localised heating systems. This allows the heating of specific production areas when necessary and reduces energy losses from pipe work.

8. Heat stores These allow you to store excess heat as hot water in a large tank for use at other times when heat demand is high. Stores must be the correct size and adequately insulated.

9. Efficient lighting This includes the use of more efficient lighting equipment and improved reflector design.

10. Alternative energy source This is the big issue. Alternative sources include waste heat, waste incineration (waste directives apply), biomass, biofuels, anaerobic digestion, geothermal energy, solar and wind power.

Cornerways Nursery at British Sugar's Wissington plant in Norfolk, and John Baarda's tomato nursery close to Terra Nitrogen's Billingham site, are prime examples of the use of waste heat in horticulture. But for most, such an opportunity is rare and would mean relocating the business.

A current HDC project took "closed greenhouse" technology into consideration when looking into the effects of blowing air through the crop with ducts and fans. The technique is likely to give more effective heat per pound spent but would also open up opportunities for growers to use low-grade heat - basically lower-temperature water than you might normally use, say 50 degsC instead of 90 degsC - and increase the possibility of linking with industry.

Heating dominates energy use in protected cropping and currently is largely by gas or petroleum products. The use of biomass and waste products to generate energy for heating glasshouses was recorded as "negligible" in 2005.

The usefulness of biomass as an alternative energy source depends on location, but increases in fossil-fuel energy costs have renewed the interest in its use for glasshouse heating, either directly or to power a combined heat and power (CHP) unit for electricity generation.

"Biomass is site-specific," says Pratt. "If you are next door to a woodland management scheme and have a stack of woodchips readily available, or if surrounded by straw-producing arable farms, then transport costs will be low."

In addition to security of supply, the quality of the biomass is also paramount as it affects the calorific value. Biomass also needs investment and, depending on the size and degree of complexity, can range from £100,000 for a relatively simple system to £500,000 for an automated system capable of burning a variety of fuels.

There are a lot of factors to consider when deciding whether energy-saving measures or a major capital investment programme for alternative or renewable energy is more suitable for you.

You need to look at capital and installation costs; there may be planning and infrastructure costs, as well as the costs of maintenance and the fuel. These need weighing against savings and grants, and the return from any energy sold. There are also environmental considerations, such as savings in CO2 emissions or potential for pollution. If only we knew what the price of gas and oil would be in the future.


- Protected cropping uses a great deal of energy for heat and lighting. It is estimated (according to Defra report Direct Energy Use in Agriculture - Opportunities for Reducing Fossil Fuel Inputs) that as much as 26 per cent of the direct energy use in the whole of agriculture is consumed by the protected crops sector.

- Glasshouses use around 95 per cent of the energy in horticultural production.

- Some 97 per cent of the energy used in tomato production is for heating and lighting, with organic and on-the-vine specialist types incurring the greatest burden.

- It is estimated that some growers could reduce heat demand by as much as 12 per cent per annum if joints, vents and doors were fitted and worked properly.

- An external pipe without lagging can lose eight times the energy of an equivalent pipe lagged with 50mm of good-quality dry-insulating material.

- Research has shown screens can reduce the instantaneous heat loss from a greenhouse by up to 40 per cent.

- Energy savings of up to 12 per cent (15 per cent on windy days) can be achieved through temperature integration.

Benson Heating 01547 528534
Bridge Greenhouses 01775 821191
Calor Gas 01926 330088
Cambridge Glasshouse Co 01430 449440
Elan Dragonair 023 9237 6451
Gavita AS 00 47 33 43 80 80
Glen Farrow UK 01775 722327
Hortech Systems 01406 426513
Hortilux Schreder BV 00 31 174 286628
Hortimax 01482 668676
Hortisystems 01798 815815
LS Systems 01772 815080
Manco Energy 01430 828660
Priva 01684 293081
Radiant Services 01902 494266
RiteAir Heaters 01803 522146
Talbott's Biomass Energy 01785 213366
Thermobile 024 7635 7960
Thermoforce 01900 823231
Tomtech 01945 700553
Tube Heat 0121 779 5253
FEC Services undertakes research and consultancy work and can be
contacted on 024 7669 6512.

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