Finding efficiency

Like death and taxes, the need for energy to run a greenhouse operation — and its associated costs — are inevitable. What isn’t inevitable is how much you have to spend on your energy needs. Growers are finding innovative ways to reduce their energy usage. Learn how these growers have achieved savings.

Alternative fuels

In New Hampshire, where winter temperatures can be brutal, growers like Henry Huntington of Pleasant View Gardens know all about dealing with high energy costs. After doing what they could to save money with thermal blankets and paying close to $4 a gallon on No.2 heating oil, the company made the decision to invest in a biomass heating system.

“The natural gas infrastructure in New England is limited, especially in rural areas,” Huntington says. He adds that they pondered alternative sources for two years before deciding to switch to wood products.

Pleasant View spent $5 million dollars to convert to the new system, which feeds wood products into huge boilers. It paid for itself in a little less than five years, says Huntington. Another bonus is that they can source the wood products from within 50 miles of their business.

“It’s important [that] people understand what their fuel supply is and what the cost of it is going to be,” Huntington says.

He adds that there are some additional costs to heating with biomass that should be factored in, including the cost to utilize and maintain the system and equipment to feed the boilers. A biomass system may not be practical for smaller growers who start plants in February and March, rather than December and January like Pleasant View does.

Pleasant View still uses oil as a backup, but went from using about 600,000 gallons a year to around 25,000 gallons per year.

Thinking outside the box

Minnesota-based Bailey Nurseries has achieved some energy savings by implementing heat-saving strategies that don’t require a large capital expenditure. For example, Bailey Nurseries’ Production Manager Dave Gross says they’re doing a better job inflating the layers of their double poly, which they use exclusively to cover their houses.

They’ve also discovered energy savings by storing their ornamental plugs on seven-layer racks inside black poly greenhouses. Gross says this has helped them reduce heating costs during the frigid months of December through February.

“We have a 22-acre greenhouse facility here in Minnesota,” Gross says, who has been with Bailey for more than 35 years. “We have all natural gas forced air furnaces. In this range, the heaters that are installed have a capacity of 118 million btus. I’m happy to say we don’t ever get close to using all of them at once.”

Greenhouse coverings

It’s common knowledge that the “skin” on a greenhouse doesn’t provide much insulation, especially as night temperatures plunge. However, there are some coverings that work better than others at keeping the heat in and the cold temps out.

For instance, double polyethylene coverings are more efficient at conserving energy than a single layer of poly, reducing heating costs 50 percent over the latter, according to Debbie Remblence, sales director at the International Greenhouse Company in Danville, Ill. When air is forced between the layers, the poly becomes even more energy efficient.

It’s important [that] people understand what their fuel supply is and what the cost of it is going to be.”

– Henry Huntington, Pleasant View Gardens

“Single-layered polyethylene and polycarbonate offer the lowest heat retention and therefore the highest heat loss, which translates to higher energy costs,” Remblence says. She says that, in contrast, double-layered polyethylene (inflated with a fan) and multi-wall polycarbonates retain heat much better. There are even triple-wall and five-wall polycarbonates on the market, which Remblence says offers very high heat retention values, but at the expense of lower light transmission.

Neil is a horticulturist and freelance writer for the green industry, assisting businesses with advertising copy, blog posts, articles and other digital content. greenindustrywriter.com

Top 10 things a greenhouse grower can do to improve energy efficiency

Photo: Karen E. Varga

1. “Tighten up” the house

Many greenhouses have cracks and holes in the walls or roof that allow cold air to enter and warm air to escape. Your heating bill could be reduced by up to 10 percent by simply caulking and applying a foam insulation product. Metal posts and frames can also act as a conduit for heat to escape. Insulate pipes and posts where possible.

2. Add a thermal screen

Unfortunately, clear greenhouse coverings that offer peak sun into the greenhouse for growing healthy plants are also poor insulators. A grower can save 30 to 40 percent of heating costs by using thermal screens that can be drawn across the roof and walls of a greenhouse. In the summer they can be draped across the house to shade the plants inside.

3. Seal the fans

When ventilation fans are turned off, the louvers will automatically seal off the opening (at least, in theory). In reality, bent or malfunctioning louvers are all too common in greenhouses, along with drilled holes or gaps around the fan housing. Needless to say, this can cause a lot of cool air to come in, especially during the colder months. Have louvers repaired or replaced as necessary. Place foam insulation over the louver during the coldest winter months when fans aren’t being used.

4. Insulate the perimeter of the greenhouse

The bottom of the greenhouse along the perimeter of the house is notorious for heat loss. Cut down on heat escaping along sidewalls by installing insulation that begins at the height of the benches and extends into the soil by at least 1 foot. This could save up to 5 percent of energy costs.

5. Insulate the north wall

Because the north end of the greenhouse lets in such little light, it can be insulated like any other wall, even if only for the winter months. Reflective insulation panels installed on the inside of the greenhouse will reflect light toward the center of the house.

6. Replace ventilation fans with high efficiency models

Not all ventilation fans are created equal. If you opted for the cheaper ones when you were building your greenhouse, look into upgrading to more efficient fans. Larger fans are generally more efficient, but variations occur between models. Ask your dealer what the “ventilation efficiency ratio” is for a particular fan or look it up online.

7. Upgrade the lighting

It’s suggested that growers who have lights on for extended periods of time in the house do their homework and buy the most efficient lights that still provide enough illumination to work.

8. Clean the fans

Turn off the breaker to your fans and give them a good cleaning. This can save up to 20 percent on the cost of electricity to keep your fans running, plus help them to last longer.

9. Replace motors with properly sized, energy efficient models

Older houses might be operating with large, inefficient motors on ventilation and heating equipment, leading to additional energy costs for the grower. Have an electrician inspect the motors on your greenhouse equipment to determine if smaller, more efficient models can be used.

10. “Tune up” the control system

In the day-to-day rush of growing plants and filling orders, it’s easy to ignore greenhouse controls that do everything from open and close louvers to provide the right amount of fertilizer to your plants. Take the time after the rush is over to inspect all controls to see if they’re properly set to factory recommendations.

Source: Adapted from the Penn State Extension fact sheet titled “Top 10 Things a Greenhouse Grower Can Do to Improve Energy Efficiency” by D. Ciolkosz