Greenhouse structures

Sally Drury examines the new cutting-edge GroDome research facility at the University of Warwick.

University of Warwick: School of Life Sciences’ phytobiology building developed for plant science and food security research is an ultra-modern sophisticated greenhouse facility - image: HW
University of Warwick: School of Life Sciences’ phytobiology building developed for plant science and food security research is an ultra-modern sophisticated greenhouse facility - image: HW

The first thing that you notice about the University of Warwick's central campus is that it is modern. It is not surprising then that when the School of Life Sciences wanted a phytobiology building, in which to conduct research into plant science and food security, what it got was an ultra-modern, sophisticated greenhouse with prep room and laboratory.

What might come as a surprise, however, is just how much commercial horticulture can learn from this state-of-the-art controlled-environment facility - especially when it comes to management. Believe it or not, the running cost per square metre of growth environment per day is around 12p - including supplementary lighting for 14 hours a day.

With land at a premium on the campus, the greenhouse sits on top of a building that houses a preparation area where seeds are sown, rows of growth cabinets and a laboratory with equipment for biochemical analysis. Upstairs, the greenhouse comprises growing chambers running off a central corridor.

The greenhouse is an 18m-wide Unigro GroDome - a contained greenhouse designed to offer exact environmental control. It is a low, curved structure built from 90mm-diameter curved steel with 7m-long sheets of polycarbonate. To enable cleaning of the cladding, a walkway has been provided on the roof and hard paving laid around the building for a cherry picker.

The greenhouse's squatness gives it an unusual appearance. A commercial glasshouse would normally be 3m taller to give a thermal buffer, but in this instance the curvature and deliberate low profile of the building actually help maintain the desired environments.

Inside the greenhouse, the central corridor is at positive pressure - you can feel the resistance as you open the door - so anything outside the corridor remains outside. The chambers are running at negative pressure, so anything inside the chambers remains inside. An air-handling unit adapts constantly to maintain the pressure balances and reduce the risk of cross pollination and cross contamination.

"What we have here is effectively a sealed box," explains Unigro research and development director Angus Padfield. "We are controlling the supply air, controlling the extract air and filtering both. We are always running at about 50 pascals negative air pressure, but when we pressure test and smoke test the chambers for potential leaks, we take them to about 250 pascals."

Chamber system

There are large, medium and small chambers, and they can be combined to make other sizes. "None of the partition walls are structural and the system in terms of programming has been set up so we can combine the chambers' operation," says Unigro managing director Keith Hamp.

"The very nature of research means that the scientists cannot be sure what they are going to want in five or 10 years' time, so we need to be able to offer something that is as flexible as possible, with the biggest range of parameters, but that runs economically,"

Each chamber is kitted out with roller container-benching. The incorporation of supplementary lighting, brought over from Wellesbourne, has meant fitting blinds to cancel the light pollution.

"Our cooling and heating is capable of dealing with the solar loading and thermal gains without blinds. The blinds are just there for light pollution. In the event of an emergency or a power failure, we have enough back-up power to bring the blinds up so the plants are protected," says Padfield.

The water supply is reverse osmosis to eliminate contaminants. To reduce potential pathogen habitats, thick pipework is used, so insulation materials are not required. All the chambers drain to a common point and the water is sucked out with an aqua vac and an autoclave. Each new batch of construction and equipment materials is tested for phytotoxicity before use.

As the greenhouse only has half the surface area that would normally be associated with a commercial glasshouse covering the same area, both losses and thermal gains are reduced. The strength of the steels - this greenhouse is built to industrial specifications for wind and snow loading - along with their spacing and lack of cross-bracing mean there is little structure to block incoming light and the insulating properties of the polycarbonate help reduce the heating demand. The building uses heat recovered from the university's combined heat and power plant. It is energy that might otherwise have been wasted.

The GroDome can control temperature between 35 degsC and 18 degsC regardless of external irradiance and any other external conditions, and it will hold the set temperature to within 1 degsC.

Temperature regulation

However, as anyone who has worked in a commercial greenhouse on a warm day will know, internal temperatures can rise dramatically. Just a little sunshine can make conditions unbearable and vents must be opened to release the heat. But that is not always convenient - especially when supplementing with CO2 and certainly not in a research situation where releases and contamination need to be zeroed.

The greenhouse at Warwick has no vents. Instead, it has fan coils running around the internal perimeter. This proves to be both a cost-effective and efficient way of cooling the house and maintaining the desired temperatures.

"When 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 Padfield.

To reduce the need for randomisation in experiments and ensure that plants on one side of the chamber are receiving the same conditions as those on the other, the environment must be constant and air movement has to be gentle. To achieve this, air is blown up the curvature of the structure. Being cooler, that air then drops down to the benches, cooling the whole area and then making its way back to the face of the fan coil.

"Air movement is often a parameter that is overlooked," adds Padfield. "Everybody always looks at light levels and temperature because they are things we can monitor, measure and actually control. What we should really be making sure is that we don't have a fluctuation of air movement across the area of more than 1m/sec. Scientists love it. It means the plants grow evenly. The way they act is different and morphology is so different compared to when they are subjected to greater movement."

The biggest surprise, and the biggest lesson we can take from the new structure, is the way the facility is operated. Clearly, this is no ordinary greenhouse, but how it is run is also different. A building-management system is used instead of a greenhouse-management solution, and it works well.

"We try to run so many control strategies in order to run the building as cost-effectively as possible and we use a building-management system so it is infinitely expandable and infinitely controllable. We start with a blank sheet of paper and ask: 'What do you want to do?' Then we write every control strategy that goes in it," says Unigro commercial manager Nick White.

Cooling methods

With it being such a vital aspect, cooling can be performed by any of several methods - usually starting with the cheapest. Padfield points out: "The drier cooler located outside - just a big set of heat exchangers - that's the cheapest way to expel heat from the building. So, the first method of cooling is to drop our secondary cooling circuit, which is running a very high temperature, straight through the drier cooler and then straight back to the building. That's a very cheap way of doing it."

The next cheapest way of cooling the greenhouse is to use the university's absorption chiller. Padfield says: "A lot of the cooling is derived from the waste heat from the combined heat and power plant via an absorption chiller. When the heat demand for the university is low, instead of that heat being rejected through big chimneys and back into the sky, we take that heat, put it through an absorption chiller and use our cooling process from that waste heat."

The next cheapest way of doing it is to use Unigro's coolth tank. Sited below ground, the tank contains 50cu m of water and is cooled at night. "We use that next, but if we still don't have enough capacity, then we use the big electric chiller outside. It's is actually the client's chiller - we just hop on and use a bit of their capacity," says Padfield.

"The university has been very good in terms of cooling and heating infrastructure. They have been really flexible so we can use the big supplies required for the greenhouse and the controlled environment below. It does make it all very efficient."

Being a research facility, no one can afford any aspect of the control to fail. There is always a back-up - and then there is a back-up for the back-up. This is where building management plays an important role at the greenhouse.

"We are what you call N+2," says Padfield. "N+1 is if you have a pump running and it fails, you have a second pump. In many situations, because of the critical applications of cooling here, we are N+2. So if the pump fails we have a second pump and if that fails we still have another way of cooling the building. That is very important. So the building should be tremendously robust in terms of its operation.

"The thing that makes the client very content and reassured is that if everything goes wrong, under the ground there is 50cu m of very cold water. All we have to do is pump it up to the roof and run some fans. If there is enough power to do that, they know they are okay. If the big pump fails, or anything, there is still a back-up way of doing it."

Touchscreen control panels give easy access to the Trend Building Management System to control and adjust all the various environmental factors. Remote communication via the internet is also available for students, researchers and Unigro's engineers - each having a different level of access and control. It is simple to interface what is, in effect, complex control.

User interface

"The users are able to go to an interface with the building in a very simple way. It should be so self-explanatory that they don't even need an instruction manual - just the same as using an iPhone," says Padfield. "We are big fans of building-management systems because the only limitation is what you can think up. They are infinitely flexible and variable. That's our way of looking at the world."

Safety and security are built in to the system. As you would expect, alarms go off when a parameter is exceeded. Should it become critical, then the building will look after itself. If the building gets too hot, for example, the shading will automatically close, the alarms will go off and the system will default to a maximum cooling position.

Padfield is looking at schemes so that when the building is not in use, cooling, heating and electricity can be exported to local buildings. In commercial terms, that could mean a packhouse. "We can make that work in a most efficient way by having a heat-sink tank and a coolth tank below the building and moving the energy between the two," he adds. "It's an interesting system - looking at the building as an exporter of resources rather than a net consumer. That's something we are looking at the moment."

Outside the building, a standard 40ft shipping container houses all the services. It was set up and equipped at Unigro in Kent before being brought to site where it just needed "plumbing in and hooking up". Movements of actuators and valves and the running of pumps are under the control of the building-management system.

"When you bring all these together in one place it becomes rather complex but, as a building-management system, it is infinitely expandable," notes Padfield. "The control strategy is owned by the client and gives them complete access to the system. It doesn't make the client beholden to a licence agreement that they might have in a typical glasshouse arrangement."

What does it mean for the university, and more specifically for the School of Life Science? Deputy head Professor Brian Thomas is excited about the new facility. "Here we probably have one of the largest groups of plant scientists in the UK, working on a whole range of projects, and this will provide the facility to carry on their work," he says.

"The design of the building, and particularly because of the uniformity of control of the conditions, mean we can do quite large-scale work. It will give us much better-quality results and because of the energy efficiency of the building, it is much more cost-effective, so we get more work done on a particular grant. I am sure it will make a huge impact on the quality and amount of work we can do"

Earning income

In the future, Padfield would like to see facilities such as the one at Warwick take the opportunity to gain an income stream. He explains how it might work: "The grid can send you a signal asking you to reduce your electrical consumption. If you have a coolth tank under the building, all you have got to have is enough electricity to power the coolant up to your fan coil and you can keep your building cool.

"Providing you can go without supplementary lighting for a short period of time, you can dramatically reduce your energy use by 90 per cent and then the grid will pay you for all the time you have reduced your energy load. These contracts are worth considerable money. We have to think differently about the way we use energy. We are going to have a lot more brownouts in the future and a lot less reliable energy. So we say let's set the building up differently."

He continues: "The security of electricity is going to be a growing problem and I think a lot more people will be using combined heat and power - so they are burning gas and they are using the waste heat not just to heat their buildings but also to cool their buildings.

"I think for making a system that is absolutely contained more and more efficient and more and more economically sensible, we should really be on large scale looking at cooling buildings rather than spending a lot of money on venting, heating and CO2 generation."

It would seem that much of the technology employed in the University of Warwick GroDome is suitable for commercial-growing operations. With the running costs of 12p per day per square metre, it also sounds very attractive.

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