| Nursery maximizes energy value through efficiency projects |
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A bottom heat system heats this greenhouse at Harts Nursery.
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It’s not cheap to heat 167 greenhouses during an Oregon winter, and this winter’s cold temperatures drove heating costs especially high. “We were looking at a six-figure energy bill for March alone,” said Doug Hart of Harts Nursery in Jefferson.
But it could have been much worse without Harts’ aggressive efforts to increase energy efficiency over the past few years. The nursery is gradually converting to high-efficiency heating of its houses, and has implemented several other projects.
Chris Guntermann of Horticultural Services Inc has worked with the nursery to install several energy efficiency measures and emphasizes, “It’s often much cheaper to install efficiency measures than it is to put in a renewable energy system. In addition, if you first reduce your energy demand, then any renewable system you install can be sized to match that smaller energy demand.”
The nursery began exploring energy projects about four years ago by meeting with the Energy Trust of Oregon, an organization that provides cash incentives for certain efficiency measures. The nursery received funding for a professional energy audit. “The audit identified 8 to 10 items that we could do,” explains John Becker, Maintenance and Electrical Manager for Harts Nursery. “One of the items was using bottom heat in the greenhouses. We decided that’s where we wanted to go.”
The nursery began using bottom heat in its propagation greenhouse. During the heating system installation, the nursery replaced two boilers with two high-efficiency condensing boilers. The new boilers heat water that flows through finned tubing under the benches in the propagation greenhouse. Heat goes directly to plants and plant roots where it is needed, rather than rising to the greenhouse ceiling.
The nursery has also switched to in-floor heating in several greenhouses using microtubing that circulates hot water, and is in the process of converting more. As part of the current project, they are also installing two thermostats in each converted greenhouse, along with outdoor sensors. “The outdoor sensors help the heating system anticipate temperature changes,” explains Becker. “It will tell the heating system to begin warming the greenhouse before it can even cool down.”
The nursery received several incentives to help cover the cost of the greenhouse efficiency improvements. The Energy Trust of Oregon has provided incentives for the heating system conversion. The system qualified for Oregon’s Business Energy Tax Credit, which is available for a variety of energy efficiency and renewable projects. Also, Harts successfully applied through a competitive process for a USDA Rural Development Energy Efficiency Grant.
Harts has also made some simpler energy upgrades in some other greenhouses. Even if these houses are eventually converted to bottom heat, the energy upgrades are worth it because they pay back so quickly. “I replaced the old thermostats in these houses,” Becker explains. “The old ones were very inaccurate and the unit heaters would turn on and off over a wide temperature range.”
He replaced them with inexpensive programmable thermostats. “These thermostats have four daily settings. We saved $6 to $9 per day per greenhouse heating with these thermostats. The payback period was 8 to 9 days.”
Other improvements included putting sliding doors on greenhouses to minimize air leaks, and adding weatherstripping along the doors and greenhouse bases.
During the summer, irrigation is a significant energy demand for the nursery, and they have taken steps to reduce that use as well. “We’ve put in about 35 miles of drip tape,” explains Becker. “It reduces the amount of water we use by 50 gallons per minute per greenhouse, so it has reduced pumping costs. We can also fertilizer through the drip tape, so it saves us fertilizer, and we know we’re getting the water and fertilizer directly to the product.”
The nursery irrigates from two wells using two pumps. Both pumps are equipped with variable speed drives. The variable speed drives ensure that the pumps only operate at the speed necessary to maintain pressure, rather than running at full speed all the time.
“Each of the fog pumps in the greenhouses have variable speed drives on them too,” Becker explains. The variable speed drives also start and stop pumps and motors slowly, extending their life.
With Harts’ electric and natural gas utilities both requesting rate increases in the coming months, their efficiency measures will pay back faster than ever. John Becker emphasizes that they will continue to search for efficiency opportunities. “We are evaluating every possible opportunity to maximize the value of the energy we use.”
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