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GEO-THERMAL HEATING AND COOLING IN ‘CLOSED GREENHOUSE’ CONCEPT

In 'closed greenhouse' concept

Written by David Schmidt   
Considerable input savings may be possible, along with improved yields and reduced disease pressures. The results, which come from only one year of testing and one year of growing, are “very promising,” according to one expert.

Open your mind, close your greenhouse, and reap the rewards in energy savings, reduced water usage, less disease and increased yields.

Greenhouse consultants Hubert Timmenga, of Vancouver, and Peter Klapwijk, of The Netherlands, brought the emerging concept to B.C. greenhouse growers at the Pacific Agriculture Show in Abbotsford.

The pair described Dutch research agency Innogrow’s patented “GeslotenKas” closed greenhouse system, Timmenga detailing scientific theory and performance data and Klapwijk providing production information.
Closed systems collect and store energy from the sun without releasing it into the environment. According to Innogrow, they provide “climate control” instead of “climate management” through geo-thermal heating and cooling.

Geo-thermal heating/cooling is becoming common in homes. A closed-loop version is being developed for the NASA Mars program and Agriculture and Agri-food Canada is using an open-loop version at the Pacific Agriculture Research Centre in Agassiz. The first commercial-scale Innogrow system was built for the 5.4 hectare Themato greenhouse in Holland in 2004. Two of Themato’s eight bays were “sealed” and are now being heated and cooled geo-thermally using an open-loop system.

“The system is set up for energy savings,” Timmenga says. Covering 27 per cent of its production area resulted in 36 per cent energy savings in just the first year.

The system is set up to maintain a 22ºC daytime and 18ºC night time temperature at 85 per cent relative humidity. During the day, hot air collected in overhead hanging gutters is pulled through by a high-volume air conditioner (HVAC) and cooled with a heat exchanger. Water stripped from the air is saved for recirculation while carbon dioxide is added to the cool air being sent back though the greenhouse via perforated plastic pipe located at the base of the plants.

At night, the system is reversed. Cold air is pulled from the hanging gutters and heated by the HVAC/heat exchanger. The heated air is then sent back into the greenhouse through the perforated pipe.

The water for the heat exchanger is maintained separately. While small amounts of hot and cold water are kept in storage tanks (another installation uses ditches instead of tanks), the primary reservoirs consist of “storage bubbles” in the aquifer below the greenhouse.

“You need about a hectare of storage for each hectare of closed greenhouse,” Timmenga explained.
The bubbles are accessed by “warm” and “cold” wells. Water temperature is about 6ºC in the “cold” bubble and about 18ºC in the “warm” well.

Provided the right cooling system is in place, Klapwijk said not opening vents makes it easier to control humidity and temperature in a greenhouse. It also means the ventilation comes from below instead of above the plant, a critical element which provides better horizontal and vertical distribution of both temperature and CO2 and should lead to better quality and production.

Themato has shown natural gas savings of over 30 per cent in the total greenhouse. The closed section has shown water savings of over 40 per cent, a 65 per cent saving in CO2  and a 20 per cent increase in yields.

Klapwijk calls the results, which come from only one year of testing and one year of growing, “very promising.” He stresses the system is so new, “we don’t yet know the borderlines of the growing process,” saying further research is need to determine optimum plant numbers and optimum conditions for different varieties and different crops. “This can only improve as we gain more experience.”

Timmenga reminded growers the system is very expensive to install. A typical Dutch greenhouse costs $40-65/square metre to build and would cost another $75-125 to retrofit to the closed system. He notes growers building a new house could save some costs by eliminating vent windows. Since the system requires much more electric power, growers must consider the potential future costs of both electricity and natural gas. It also requires an outside source of CO2 . If the open section of the greenhouse uses a natural gas boiler, that can provide the CO2 .

Nor is it clear if the system will work for B.C. greenhouse growers. Timmenga notes no one knows what the impact of saltwater in Delta aquifers (where most vegetable greenhouses are located) may be on the system. The aquifers in Surrey and Abbotsford have good groundwater, but are heavily used and hot water pumped into the aquifer could be pulled in by a neighbour’s drinking well. The Chilliwack aquifer also has good groundwater, but moves at a rate of 200 metres/year compared to the aquifer Themata uses which only moves at 50 metres/year.

“Heat will move as the aquifer moves,” he says. That means cold and warm bubbles have to be located far enough apart not to impact each other. “This is something which needs to be investigated thoroughly.”
Regulator issues are another concern. Themato extracts 200,000 cubic metres of water/year for its system and that requires a permit. There is no assurance provincial or local environmental authorities would even issue a permit.

Nevertheless, Klapwijk urges growers to consider it. “Maybe you can wait a few years but you will lose out on the experience.”

David Schmidt is a freelance writer and photographer in British Columbia.