How to lower your greenhouse energy bill

With increasing fuel and electricity costs, growers are installing equipment and technology to help conserve energy and make operations more efficient. Once energy conservation measures are in place, new systems may require maintenance, something that is often overlooked.

Regular inspections and maintenance are vital to ensure that systems and structures are at peak performance and that growers are getting the full benefit of their investment. These steps, which don’t require much labor, can prevent systems from breaking down and becoming an expensive fix.

Air leaks

Air leaks are typically found around doors, shutters, vents, baseboards, broken glass or tears in plastic glazing. Doors especially get a lot of use and abuse, and even tiny gaps can waste resources and increase utility costs.

For example, for a greenhouse that is heated 180 days with an insulated steel door, tight seal, thermal break and insulated sill, the estimated savings in fuel use from replacing a door with a 3/32-inch gap around the perimeter is about 60 gallons of fuel oil, 90 gallons of propane or 80 ccf of natural gas. Payback at today’s fuel prices is one to two years.

Fan shutters can also lose a lot of heat. A 48-inch fan shutter that fails to close properly and leaves 1-inch gaps allows about 23,000 Btu of heat to escape each hour. Straightening bent or broken blades and lubricating hinge points is important. Placing removable insulation board over the shutters not needed during the winter will reduce heat loss as well.

Wind gusts and wear on the rack and pinion drive may knock vents out of alignment. A gap between the vent and frame is like a chimney that pulls heated air out of the greenhouse. It’s important to perform a visual check and adjust the pinion so it can close tightly. Adding an endwall seal for roll-up sidewalls can reduce infiltration losses.

HAF fan inspection

Growers seldom look up at their HAF fans, which help make greenhouse heating and cooling more effective by improving air circulation. If they are spinning, they must be OK. But dust and dirt buildup on the guards, blades and motor can reduce performance by as much as 30%. It slows the speed and creates turbulent airflow. Cleaning and spraying with a furniture polish will slow this buildup.

Energy screen maintenance

Gaps around the edges of energy screens can create a “chimney effect,” where temperatures are warmer above the screen than within the growing area. Check the edge seal to be sure it’s tight, and fill any gaps with foam. Each fall, service the cable system before the heating season begins. Tighten the cables so the screen does not sag, adjust the limit switches so that the screen closes against the stops, and lubricate wear points, universal joints and the gear motor drive.

Heating system efficiency test

A simple 10-minute test can result in significant fuel savings. Each time a furnace or boiler is serviced, be sure the technician measures the flue gas temperature and carbon dioxide content, smoke level and draft reading over the fire. Adjusting the air to the burner can reduce carbon buildup on heat exchangers and lower exhaust flue gas temperature. When tested regularly, technicians can detect problems earlier.

Environmental control sensors

Thermostats and sensors should be cleaned several times a year. Blow off dust with compressed air. Check for accuracy by placing sensors in an ice bath or by comparing them to an accurate digital thermometer. Be sure that the sun shield is in place and that sensors are close to the plants near the center of the growing area.

An endwall thermostat location only senses the temperature at the wall. Aspiration of the sensors can reduce the differential between the high and low setting by several degrees. For every 1 °F lower a greenhouse temperature can be maintained, fuel use can be reduced by 3%.

Light fixtures

Maintaining light fixtures will increase light and save electricity. This includes turning off the power and vacuuming and wiping the dust and dirt from each bulb, reflector and housing. Also check for adequate ventilation, tight electrical connections and cracked lenses.

Energy is a large cost in the production of plants, and both fuel and electricity prices have been increasing. Maintaining your equipment helps extend its lifespan and will pay off with lower energy bills.