Staying warm

When the greenhouse temperature alarm rings at 2 a.m. on a cold winter night, it’s a good possibility that your heater is not getting fuel. I know growers that have spent many cold nights trying to keep heaters working.

There are a few things you can do to get a more peaceful sleep.

Fuel oil

Fuel oil thickens as the temperature drops and may even get sluggish below freezing. This is caused by the congealing of the paraffin. Warm oil will improve atomization and increase efficiency due to smaller droplet size. Outside tanks are subject to weather extremes. Several things can be done.

• Insulate the tank and supply lines. Some growers have had good success covering the tank with a clear polyethylene shelter. This allows the oil in the tank to warm up from the sun during the day.
• Add methanol to the oil to reduce the viscosity. This is usually done by the fuel supplier for winter deliveries.
• Increasing the oil pressure to 140 psi and reducing the nozzle by one size will vaporize the oil droplets to ignite easier.
• Single pipe delivery systems reduce oil flow and allow oil to be warmed in the pump.
• Add a fuel oil pre-heater. By setting the pump to operate continuously, the oil is heated and flows easier. Pre-heaters are usually electric and consume about 100-150 watts.
• Move the tank inside the greenhouse. Although it may take up growing space, it will keep the oil at room temperature.
   

The cleaner the fuel, the fewer problems that occur from plugged filters and nozzles.

• Check and replace fuel filters regularly.
• Check fuel in the tanks for water, mold and black sludge. These occur from moisture condensation, microbial growth and fuel breakdown due to heat in the tank. The tank may have to be cleaned.
• Install a fuel catalyst reformer that creates smaller particles that burn cleaner. This can increase efficiency by at least 10 percent.
  
   

Propane

Due to the availability of high efficiency condensing boilers and unit heaters, propane use for heating greenhouses is increasing. Propane heating units have less maintenance due to cleaner fuel. The following should be considered:

• Cold weather can affect supply in above ground tanks. Volatilization and pressure decrease with lower temperatures. The liquid propane is changed to a gas by heat from the sun, so an above ground tanks should not be insulated. A plastic shelter over the tank can provide some additional heat and cold protection. An alternative is to install a buried tank that will increase volatilization due to the constant heat from the ground. Some growers have ducted heat to the tank shelter through the wall of the greenhouse.
• Install larger tanks. With small tanks, gas may be removed faster than the liquid can be heated and volatilized. This may result in moisture condensing on the tank surface creating insulation that further reduces the conversion to a gas.
• Remove snow from around the tank so that it gathers heat from the sun.
• In cold weather keep the tank at least ? full. Propane volume decreases and becomes more dense as the temperature falls.
• Clogged burner nozzles or a plugged regulator can also restrict gas flow. These need to be serviced on a regular schedule.

Bartok is a regular contributor to Greenhouse Management and an agricultural engineer and emeritus extension professor at the University of Connecticut. He is an author, consultant and a certified technical service provider doing greenhouse energy audits for USDA grant programs in New England.

Have a question? You can write John at jbartok@rcn.com.