From plants to plant
People and plants are both more productive in a controlled environment — and Priva’s expertise with both cross-fertilises.A company that specialises in controlling the environment in buildings and in huge greenhouses covering several tens of hectares to grow tomatoes, flowers and other crops may seem an unlikely combination. But such is Dutch company Priva, whose business started nearly 50 years ago in 1959 heating greenhouses, progressed to controlling the environment in them and then into the controls for buildings occupied by people 25 years ago. Bob van Randeraat, the company’s chief technology officer, says, ‘If you know how to treat a plant, you know how to read a human being.’ Plants such as tomatoes require temperatures to be controlled to ±0.1 K or they will grow too rapidly or too slowly. It is also important to control relative humidity. If RH is too low, the plant will not evaporate water and be unable to take on food. If the RH is too low, the plant will lose water too quickly and become distressed. In normal greenhouses, controlling temperature and relative humidity is a challenging task. Opening the roof to bring down the temperature reduces the relative humidity, which then has to be increased by injecting water. In cold weather, the crop will evaporate water and increase the RH. Carbon dioxide is a third factor, since it is essential for the growth of plants. A carbon-dioxide concentration of 800 ppm is consistent with good production — but opening the roof to cool the interior reduces the carbon-dioxide concentration, leading to a move to closed greenhouses cooled using ground water. The need to control the environment in greenhouses is driven by the need for a good yield and the fact that energy is the biggest single cost, ahead of labour. Priva is working with major greenhouse growers to control heating systems that use boilers by day to heat the greenhouse and deliver carbon dioxide into the atmosphere and also to charge thermal storage for heating it by night when carbon dioxide is not required. Let’s get back to the easier task of controlling buildings — as demonstrated by Priva’s new headquarters building. Meiny Prins, managing director of Priva, explains that the building is designed to be a showpiece of sustainability and demonstrate the importance of the Priva control systems in delivering that objective. The 8200 m2 building has two wings either side of a central ‘street’. The BMS manages the natural ventilation in this atrium by opening skylights in the roof and high-level windows at the end using experience gained in the operation of greenhouses. The new building has been flexibly designed to enable it to have a long life. Meiny Prins explains, ‘A building can exist for a hundred years, but be destroyed after 30 because it cannot be adapted to new uses. To provide just that kind of flexibility, Priva’s new headquarters is divided into 11 units that could be rented individually by small companies or, even, transformed into apartments. The necessary control flexibility is provided by 952 individual Comforte controllers above the ceiling, enabling a new wall to be installed anywhere or for a whole wing to be fully open plant. No fossil fuels are used, and there are no boilers or chillers. Heat pumps provide cooling and heating by rejecting heat into the ground via a borehole when cooling is required and drawing heat from the ground via a separate borehole 80 m away when heating is required.
Controlled sustainability — Priva’s new headquarters in The Netherlands with (inset) managing director Meiny Prins who masterminded this development
In due course, over a couple of years, ‘bubbles’ of hot and cold water will have been built up so that heating and cooling can be provided more efficiently. It is expected that the temperature of the cold bubble will be about 5°C and the hot bubble 23°C. Because water moves from one borehole to the other, flows must be accurately monitored. Flows must be in balance over a 2-year period and reported to the authorities. Up to 437 kW of heating can be provided and up to 465 kW of cooling. Previous experience with underground thermal energy storage has shown that energy consumption can be reduced by 40 to 80%. The same technique is also being applied to closed greenhouses to provide heating and cooling, without having to admit outside air and disturb the carbon-dioxide balance. Central plant in the headquarters building is controlled by Comprix HX controllers. Last summer ambient temperatures reached over 35°C, but the chilled-beam installation enable the internal office temperatures to be maintained at 24°C. Meiny Prins summarises, ‘The building is a true representation of the Priva organisation — open, flexible and innovative.’ In the UK Priva Building Intelligence has been working with a partner network since 2004. The original group of 20 partners has now expanded to 29. The company has completed over 800 projects in the UK, and the aim of managing director Anders Norén is to pass further increases in business activity through the existing partner network rather than appoint more partners. Last year alone saw a 60% increase in the number of projects. UK projects include all types of buildings — both new and refurbished. They include the refurbishment of over 20 Tesco stores and some 20 M&S stores, both new and refurbishments. One benefit of Priva’s approach that Anders Norén highlights is that in retrofit projects all existing cabling can be reused. He also tells us that on completion of a project, engineering source files are lodged with the client, so the client is not locked into any Priva partner but can subsequently with any partner of his choice. Other projects include the European headquarters of Chevron in Aberdeen, Learning Tree International in London, schools, student accommodation, hotels and the London Underground ticket hall at Kings Cross St Pancras. The control of buildings and greenhouses are both substantial business to Priva, in the ratio 60/40, respectively. Bob van Randeraat summarises Priva’s principal driver as the art of having control. ‘Failure to control a building leads to discomfort, and failure in a greenhouse loses production,’ he says.