He spent money, took risks and entrusted a lot of people with the future of his operation–people like Stephen Hamstra, executive vice president at GMB, who helped design the solar-geothermal energy system that should provide 80 percent of Elzinga’s heating needs. The GMB-designed system should cut down on Elzinga’s energy costs, as well, and significantly reduce the greenhouse’s carbon footprint.
“The geothermal hybrid is a new thing,” Hamstra says. “I’m not aware of a greenhouse that’s done it like this. We presented the concept in 2006 in a white paper at the International Ground Source Heat Pump Association (IGSHPA) annual meeting in Albany, N.Y., and there was a lot of favorable response.”
One Of A Kind
Elzinga was among the first to take notice, and he now has an impressive solar-geothermal system that includes 200 solar energy collectors, a 60,000-gallon insulated water tank and a heat exchanger that includes 26 miles of polypropylene tubing sunk in 200 wells that are each 300 feet deep.
The system uses Michigan’s year-round ground temperature to create hot water that’s stored in an above-ground tank and available for most of the greenhouse’s heating needs. In the summer, only a handful of heat is obviously needed in the building, yet available heat from the sun and air is abundant. So that excess heat is pumped into the ground and available to Elzinga the following winter.
Another part of the GMB design involves two air-handling units that sit outside the greenhouse.
“They’re basically fans and big radiator coils,” Hamstra says. “Each one moves 100,000 cubic feet of air per minute. If the air temperature (outside) is warmer than the soil temperature (underground) in the earth heat exchanger, we’ll turn on a pump and circulate cool water through those coils and blow warm air across the coils to also try to capture free solar energy and warm the soil.”
As reliable as Elzinga’s geothermal system is, the greenhouse can’t exclusively depend on heat from it year-round. Once cold temperatures arrive, high-efficiency boilers kick in to make up the difference that the heat pump cannot fill. And, if for some reason the geothermal system needs to be turned off, the boilers are capable of handling the heating load for the entire greenhouse.
Surprisingly, Elzinga is the first greenhouse GMB has ever served. The architectural and engineering company based in Holland, Mich., has mainly worked with the healthcare, corporate and education sectors. And, according to Hamstra, few of his peers have even thought much of having greenhouse growers as clients.
“It’s a huge market with a huge need, and the response is typically that the greenhouse market has been characterized by low-cost heating systems and that growers will put in the minimum to get by,” Hamstra says.
Elzinga’s vertical closed-loop system certainly bucks that trend, but the idea behind it is that the long-term benefits will eventually offset the costs upfront. Still, there’s more to geothermal heat systems in greenhouses than growers simply being open to invest in their futures now. Each greenhouse structure is unique, Hamstra says, and any system GMB installs is custom made.
At Elzinga, GMB was called on midway through the building process. But the earlier it could have been involved, the better, Hamstra says, because geothermal applications are functions of the greenhouse site.
If, for instance, GMB was involved with the Elzinga project at the start, it might have been able to put the bore field underneath the greenhouse itself. And that, among other applications, probably could have reduced the amount of area taken up by various parts of the system, too.
“We need some real estate to do this,” Hamstra says. “Talking to one grower who has a huge aquifer available and a big irrigation system with greenhouses and large open fields, a ground-water heat pump system is certainly a possibility. If you’ve got a good source of ground water, a good place to get rid of it after you’ve just pulled some heat out of it and no bacteria that will cause problems over time, it can work well.”
A geothermal system can also work well for a greenhouse, Hamstra says, if it collaborates with another building, particularly one that’s refrigerated. In a study conducted last year on a Meijer store in Michigan, GMB found that the store rejects nine times more heat each year than it needs.
Following the study, Hamstra did a computer simulation that gave the Meijer store a geothermal heat pump system, and he put the store side-by-side with Elzinga’s greenhouse. He then found that if Meijer’s waste heat was moved to the greenhouse, the size of Elzinga’s geothermal heat exchanger would drop in half in a virtual building simulation. He also concluded that the greenhouse could use that waste heat to significantly reduce the cost of operation while Meijer had a less-expensive way to lose its heat. “If you’ve got greenhouses that are next to some industrial process–plastic injection molding, even power plants–the waste stream from one industry could become the feedstock for the other industry,” Hamstra says.
As good as that scenario sounds, few growers are positioned right next door to buildings that can accommodate that amount of heat. But if growers are considering geothermal heat pumps for their greenhouses, Hamstra recommends that they consult engineers who’ve gone through the rigors of Certified GeoExchange Designer (CGD) training administered by IGSHPA. The investment is simply too much, he says, to rely on some run-of-the-mill heating company that’s conveniently located.
“I’ve heard reports, even in our area of West Michigan, of people who have applied geothermal pumps in greenhouses and the heat exchanger was way undersized,” Hamstra says. “They pulled the soil temperature down very quickly, and partway through the season it ceased to function.” If applied correctly, growers could see financial benefits for years to come. The benefits of such systems on the environment are big, too.
“Reducing our footprint by only moving energy instead of burning a fossil fuel to create heat is a significant one,” Hamstra says. “I think as an industry, growers have been looking for something to relieve them from these huge fuel bills.”