Glasshouse technology

Precise control and accurate monitoring are essential for optimum greenhouse crops, Sally Drury notes.

Glasshouses: environment will ultimately determine overall yield and quality of crops
Glasshouses: environment will ultimately determine overall yield and quality of crops

Aiming for perfect, profit-guaranteed crops, we heat greenhouses, vent them, light them and adjust the humidity in them. We water the plants, provide automatic shading, apply nutrients and adjust CO2 levels. But none of this is any good unless we have precise control and accurate monitoring in place.

The greenhouse environment will ultimately determine the overall yield and quality of a crop. Great strides are made year by year through improved hardware and software. Now environmental process computer manufacturer Priva has taken a radical step by putting the plant itself at the heart of the controls in a system it calls Priva TopCrop.

CMW Horticulture sales director Ian Metcalfe says: "In trials of Priva TopCrop carried out at the Dutch Demo Nursery last year, cucumber yields were boosted significantly, so this new system promises to be the biggest breakthrough in climate control since the introduction of greenhouse computers."

Simple principle

Like all good ideas, the principle of Priva TopCrop is simple. If the plant is always in the ideal environment, it will develop at its maximum potential. Priva says it can now ascertain whether or not the environment is ideal for its purpose by monitoring plant activity, disease pressure and water uptake. Plant activity is measured by recording the plant's water balance (the relationship between transpiration, cooling and water uptake) through the take-up, transport and transpiration of irrigation water.

Monitoring water balance, and therefore plant activity, is achieved by making infrared measurements above ground, tracking plant temperature at three different heights. Priva claims successful results at commercial nurseries with tomatoes, roses and chrysanthemum, as well as the cucumber trial.

A new user interface is also launched for the front end of Priva TopCrop, ensuring that growers can always check plant activity quickly and easily, and make changes if necessary with the minimum of fuss. As far as Priva is concerned, this reduces the chances of errors, and with fewer mistakes better quality and production will follow.

Priva TopCrop is expected to be available commercially later this year and CMW plans to run a number of grower workshops to introduce the system to customers.

Product development

Electronic & Technical Services (E&TS) has also been working hard developing and enhancing products to help propagators, as well as growers, improve efficiency and quality. Among the most talked about of these in recent years is the Evaposensor range.

Launched onto the market in 2011 and winning several awards for innovation, it was developed by scientist Richard Harrison-Murray and consultant Chris Burgess. It is based around evapotranspiration - a measure of water use by a crop, combining evaporation directly from the soil and or pots and transpiration from the plants themselves.

Evapotransporation varies with weather, especially solar radiation, humidity, air speed and temperature. But it is important to know how much water a crop is using so decisions can be made as to when to irrigate. Accurate measurements are important not only because water is a precious commodity but because accurate irrigation can help to prevent crop damage, improve crop quality, reduce water bills and meet regulatory requirements for water-use efficiency.

Physical model

The Evaposensor is a physical model of a transpiring leaf and gives a continuous electrical output proportional to the rate of evaporation. "This makes it ideal for the control of mist or fog to protect cuttings during rooting," says E&TS founder John Walker. Horticultural Development Company project HNS 159 demonstrated the benefits for propagators in rooting success and ease of management. Current users include Boningale Nursery.

By integrating the output over time, the Evaposensor can be used to estimate ETref for scheduling irrigation. The latest addition to E&TS range of products is the Eii MK1.3 EvapoIrrigation Interface+. This automatically adjusts irrigation frequency according to weather conditions, so that water applied matches crop requirements, saving water and improving plant quality.

"Particularly appropriate for small to medium-sized enterprises, the EvapoIrrigation Interface+ is uncomplicated, grower-friendly and takes the guesswork out of deciding when to irrigate," says Walker. "The key feature of the Eii is its ability to integrate evaporation rate over time. It triggers irrigation when accumulated evaporation reaches a user adjustable target value."

It extends the EvapoSensing range by storing the starts that would occur during the day in those problematic areas where wetting would be a concern for personnel or to the general public. "Simplicity is the key," Walker maintains. "The Interface+ unit will store starts over a period, normally during daylight hours, to be accessed at a time convenient to the grower."

A new player in the market is NP Controls. A division of the plastic-clad structure manufacturer NP Structures, it provides a one-stop shop and brings together a collection of products that includes fans, benching and automation controllers. Drawn from selected manufacturers around the world, products include LEDs by Valoya, AGAM dehumidifiers and iGrow 800 and iGrow 1400 controllers.

Temperature control

Temperature control is also vital for quality plant production. At Warwick University, the Life Sciences department demands accurate and precise monitoring and control of temperature and other factors as it conducts experiments into plant science and food security. The department now has a new GroDome. Designed and constructed by Unigro, the facility is effectively a sealed box so the supply of air, heating, cooling, lighting and irrigation all has to be controlled.

As with any greenhouse, cooling the inside in summer is vital. With no vents to open, this is achieved by fan coils running around the internal perimeter. This proves to be a cost-effective and efficient way of cooling the house and maintaining the desired temperature.

"We are cooling the chamber. The water used is only just colder than the air temperature and the way we get the efficiency out of the fan coolers is by moving a large volume of air," says Unigro research and development director Angus Padfield. The air is gently blown up the curvature of the greenhouse roof and, being cooler, it then drops down to the benches, cooling the whole area.

With cooling being such a vital aspect, it can be performed in several ways. The first, and the cheapest, is to use a drier cooler. The second method is using the university's absorption chiller. If more capacity is needed there is a coolth tank. Temperatures, regardless of external irradiance, can be held within 1 degsC of a required setting between 18 degsC and 35 degsC.

Being a research facility, no one can afford any aspect of the control to fail. "We are what you call N+2," explains Padfield. "N+1 is if you have a pump running and it fails, you have a second pump. Because of the critical applications of cooling here, we are N+2. So if the second pump fails we still have another way of cooling the building."

Management of the individual chambers within the GroDome is by a Trend Building Management System rather than a greenhouse solution. "We are big fans of building management systems because the only limitation is what you can think up," says Padfield.

The system is infinitely expandable and controllable. Touchscreen control panels give easy access to adjust all the environmental factors. Remote communication via the internet is also available at various levels for students, researchers and Unigro engineers.

A lesson learned from the Warwick project is that control is crucial to plant development - and ultimately to crop quality. While the engineering may be complex, the controls must be simple to avoid costly errors.

Encouraging renewable heating

Like the Feed-In Tarrif for renewable electricity, the Renewable Heat Incentive (RHI) is aimed at increasing heat generated from renewable sources. One of the largest production costs of any grower is energy, so those needing to heat should look at the incentive.

The RHI is a Government commitment to long-term financial support, paying a fixed amount per kilowatt-hour of heat produced over a 20-year period and adjusted each year for inflation. Main interest lies in biomass boilers and heat pumps. Solid-fuel biomass boilers, such as woodchip boilers, produce hot water at the same temperature as a traditional gasor oil-fuelled boiler so are easily integrated into existing heating systems.

For more information about biomass boilers and the RHI, see The project is delivered by Farm Energy Centre on behalf of the Horticultural Development Company.

Energy news: heating and hot water

After installing a 10kW solar panel system to produce 10 per cent of its electricity needs, streptocarpus specialist Dibleys Nurseries has installed two 290kW woodchip boilers to heat its biggest glasshouses and offices - and reduce its dependence on oil heating.

In Chorley, Lancashire, family-run Pole Green Nurseries has replaced its coal-fired energy system with a more effective and cost-saving Schmid 900kW UTSE biomass boiler and walking-floor fuel store installed by Imperative Energy.

At the Four Oaks Trade Show in Macclesfield next month, Mainline Energy is showing Guntamatic and ETA biomass boilers. "With efficiencies over 90 per cent and the ability to burn a wide range of readily available fuels, biomass boilers are a realistic option when it comes to supplying heating and hot water," says company spokesperson Claire Robinson.

The systems supplied by the firm will burn wood pellets, woodchips, logs, energy grains and Miscanthus.

Bridge Biomass Solutions: 01775 821191
Energy Innovations UK: 01728 635761
Imperative Energy: 0845 205 5575
Mainline Energy: 01283 222112
Manco Energy: 01430 828660
Mercia Energy: 01788 842377

Suppliers of control and monitoring equipment include:
Access Irrigation: 01788 823811
Boiler Spares (NW): 0161 477 1946
Bridge Greenhouses: 01775 821191
Brinkman UK: 01482 842123
CambridgeHOK: 01430 449440
CMW Horticulture: 01430 422222
Climate Controls: 01481 263860
Contrel: 01787 881292
Delta-T: 01638 742922
Electronic & Technical Services: 0151 645 8491
HBS Design: 01482 679344
Horticultural Solutions: 01482 665449
Hortilux Schreder: 00 31 174 28 6628
Hortimax: 01482 668676
Hortisystems UK: 01798 815815
JD Ultrasonics: 01924 378448
Mitchell Technical Services: 01202 892402
NP Structures: 01282 873120
Polybuild: 01903 892333
Priva UK: 01923 813480
Rite Air Heating & Equipment: 01803 522146
Tomtech: 01945 700553
Unigro: 01474 573850

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