Increasing energy costs make conservation and efficient use of facilities an important part of today’s greenhouse operation. New greenhouse designs, better glazing, improved heating and ventilating equipment and new management systems should be included when upgrading or adding on. With typical annual energy usage being 75% for heating, 15% for electricity and 10% for vehicles, efforts and resources should be put where the greatest savings can be realized. Many improvements have a payback of less than two years.
Reduce Air Leaks
- Keep doors closed – use door closer or springs.
- Weatherstrip doors, vents and fan openings. Close gap around the flue pipe penetration.
- Lubricate fan shutters frequently so that they close tight. A partially open louver may allow several air changes per hour. For example, a 48” fan louver that fails to close properly leaving 1” gaps, allows 23,000 Btu/hr of heat to escape costing $0.92 if you are burning $4.00/gallon fuel oil. Shut off some fans during the winter and cover openings with insulation board or film plastic to reduce infiltration of air.
- Repair broken glass or holes in the plastic covering. Seal holes around the foundation.
- Line sidewalls and endwalls of greenhouse inside with poly or bubble wrap to achieve the double wall effect. Install double or triple wall polycarbonate structured sheets to reduce heat loss.
- Use poly with an infrared inhibitor on the inner layer for 15% savings. Payback is 2-3 months.
- Add a single or double layer of plastic over older glasshouses to reduce infiltration and heat loss by 50%.
Energy Conserving Screen
- Install a retractable thermal screen overhead and on sidewalls for 20%-50% savings. Cost is $1.50 – $4.00/sq ft. Payback is 1-3 years. A double screen will save an additional 10 – 15%. Tight closures should be maintained where curtains meet sidewalls, framing or gutters. Heat and water lines should be insulated or located below the screen.
Foundation and Sidewall Insulation
- Insulate the Perimeter foundation – place 1-2” polyurethane or polystyrene insulation board to 24” below ground to reduce heat loss. This can increase the soil temperature near the sidewall as much as 10 degrees during the winter.
- Insulate the kneewall or sidewall to bench height. Use 1” to 2” of insulation board or double bubble wrap with aluminum foil faces. Applying 2” of foam insulation to a 3’ high kneewall on a 28’ x 100’ greenhouse will save about 400 gallons of fuel oil/year.
- Insulate behind sidewall heat pipes – Use aluminum faced building paper or insulation board behind to radiant heat back into the growing area. Leave air space next to wall to prevent frost damage to wall.
- Locate new greenhouses in sheltered areas to reduce wind-induced heat loss if this does not reduce light.
- Install windbreaks on the North and Northwest sides of the greenhouse. The windbreak can be a double row of conifer trees or plastic snow fence.
- Increase space utilization to 80% – 90% with peninsular or movable benches.
- Install multi-level racks for crops that don’t require high light levels.
- Grow a crop of hanging baskets on overhead rails or truss-mounted conveyor system.
- A roll-out tray system can double growing space. Plants are moved outside on rails during the day.
Efficient Heating System
- Convert oil fired heat to high-efficiency natural gas or propane – gas units are available with 90% + efficiency as compared to typical oil units with 75 – 80% efficiency.
- Installation of floor or under-bench heat will allow air temperature to be set 5º – 10ºF lower.
- Yearly maintenance – Check boiler, burner and backup systems to make sure they are operating at peak efficiency. Have furnaces cleaned and adjusted and an efficiency test run before heating season. A 2% increase in efficiency for a 30’ x 150’ greenhouse will save about 200 gallons of fuel oil.
- Clean heating pipes and other radiation surfaces frequently.
- Check accuracy of thermostats – correcting a reading that is 2ºF high will save $100-$200.
- Install electronic thermostats or controllers with a +/-1°F accuracy. Potential yearly savings of 750 gallons of fuel oil in a 30’ x 100’ greenhouse when changing from a mechanical to an electronic control.
- Aspirate thermostats or sensors for more uniform temperature control. Differential between on and off can be reduced as much as 6ºF.
- Install horizontal air flow (HAF) fans to get more uniform temperature in the growing area and reduce disease potential.
- Insulate distribution pipes in areas where heat is not required.
- Check and repair leaks in valves, steam traps and pipes. Install barometric dampers on oil-fired furnace flue pipes for a savings of 5 – 15%.
Efficient Cooling System
- Build a new greenhouse with vents or an open-roof design to eliminate the need for fans.
- Install roll-up or guillotine sides to reduce the need for fan ventilation.
- Use shading to reduce the need for mechanical cooling.
- Install evaporative cooling to get better temperature control during the summer.
- Select fans that meet AMCA standards and have a Ventilation Efficiency Ratio greater than 15.
- Use the largest diameter fan with the smallest motor that meets ventilation requirements.
- Keep doors closed when fans are operating. Locate intake louvers to give uniform cooling.
- Motorize intake and fan shutters to opening from wind pressure differences.
- Have wiring system inspected for overloading, corroded parts and faulty insulation.
- Replace 3 hp or larger motors with high efficiency ones to reduce electric consumption by 2-5%.
- Check for proper belt tension and alignment on motors.
- Replace incandescent bulbs with compact fluorescent or HID bulbs. Save 2/3rds on electricity. Change T-12 fluorescent fixtures to T-5 or T-8.
- Install motion detectors to control security lights so they are not on all the time.
Trucks and Tractors
- Regularly scheduled tune-ups can save 10% on fuel usage. Keep tires properly inflated.
- Avoid lengthy idling. Idling can consume 15-20% of the fuel used.
- Train drivers in truck operation. The difference between the poorest and best drivers is 30% savings.
- Locate hot water tanks as close as possible to the largest and most frequent use. Insulate the tank and pipes.
- Heat water to the lowest temperature needed, usually 120ºF is adequate.
- Stage water pumps so that they do not all turn on at the same time. Operate irrigation system at minimum pressure needed.
- Use pipe size large enough to supply necessary water at minimum friction loss.
- Eliminate water leaks – A dripping faucet at 60 drops/min. will waste 113 gallons/month.
- Insulate pump houses – floor, walls and ceiling with 6” insulation board.
- Lower night temperature – Fuel consumption is reduced 3% for each 1ºF night temperature is lowered.
- Delay starting the greenhouse by a week or more. Build a germination/growth chamber to start seedlings.
- Keep growing areas full at all times.
John W. Bartok, Jr., Extension Professor Emeritus & Agricultural Engineer, Department of Natural Resources and the Environment, University of Connecticut, Storrs CT – Updated 2013.