Chapter 4

Greenhouse Heating

(book excerpts)

Heating is a major concern to commercial greenhouse operations. This is due primarily to the costs involved in the purchase and operation of heating equipment as well as the potentially disastrous effects of a poorly designed system can have on crop production. Many types of heating systems are available for use in greenhouses. Heating systems are usually classified as central or local. In a central system the boiler is located in a separate house outside the greenhouse and the heat is distributed to the greenhouses by a distribution system. In a local system the heat is released directly to the greenhouse space since the furnace and thus combustion are within the greenhouse space. There are four primary systems for greenhouse heating: (1) steam, (2) hot water, (3) hot air, and (4) infrared. Some systems cost less to buy or use less expensive fuels. Others may have a higher initial cost, but they are more efficient and cheaper to operate. Selecting the appropriate heating equipment depends partially on the type of fuel that is available. Suitable energy sources include natural gas, LP gas, fuel oil, wood, and electricity. The cost and availability of these sources will vary somewhat from one area to another. Greenhouse heater requirements depend upon the amount of heat loss from the structure. Heat loss from a greenhouse usually occurs by all four modes of heat transfer: conduction, convection, radiation, and infiltration all of which occur simultaneously. The heat demand for a greenhouse is normally calculated by combining all three losses as a coefficient in a heat loss equation.

Click on the following topics for more information on greenhouse heating.

Topics Within This Chapter:

  • Mechanisms of Greenhouse Heat Loss and Gain
  • Conduction
  • Convection
  • Radiation
  • Infiltration
  • Greenhouse Heating Requirements
  • Calculating Greenhouse Heat Load
  • Calculating Surface Area of Greenhouse
  • Calculating Temperature Difference (Δ)
  • Ascertain Heat Loss Coeffcient for Glazing Material
  • Calculating Total Greenhouse Heat Loss
  • Calculating Greenhouse Infiltration Rate
  • Greenhouse Unit Heaters
  • Types of Unit Heaters
  • Vented versus Unvented Unit Heaters
  • Vented Unit Heaters
  • Unvented Unit Heaters
  • Fresh-Air Vents
  • Greenhouse Central Heating Systems
  • Advantages and Disadvantages of Heating Plant Boilers
  • Types of Heating Plant Boilers
  • Firetube Boilers
  • Watertube Boilers
  • Condensing Boilers
  • Heat Distribution from a Boiler System
  • Pipe Network
  • Floor Heating Systems
  • Hot Water (Hydroponic) Unit Heaters
  • Greenhouse Infrared Heating Systems
  • Benefits of Infrared Heating
  • Types of Infrared Heaters
  • Air Distribution in Greenhouses
  • Horizontal Air Flow Fans
  • Shrouded versus Unshrouded Fans
  • Horizontal Air Flow Fans Capacity
  • Types of Horizontal Air Flow Fans
  • Placement of Horizontal Air Flow Fans
  • Polytube Systems
  • Heating with Polytubes
  • Calculating Size and Number of Holes for Polytubes
  • Greenhouse Thermal Curtains
  • Installation of Greenhouse Thermal Curtains
  • Gutter-to-Gutter Curtain System
  • Truss-to-Truss Curtain System
  • Greenhouse Curtain Support Systems
  • Opening and Closing of Thermal Curtains
  • Operation of Mechanical Drive Systems
  • Curtain Materials
  • Shade and Heat Retention
  • Blackout Curtains
  • Thermal Curtains Performing Multiple Functions
  • Types of Fuels for Greenhouses
  • Gaseous Fuels
  • Natural Gas
  • Propane
  • Fuel Oils
  • Biomass Fuels
  • Wood Pellets
  • Wood Chips
  • Comparing the Cost of Heating Fuels
  • Renewable Energy for Greenhouses
  • Solar Energy for Greenhouses
  • Active Solar Techniques
  • Passive Solar Techniques
  • Biomass Energy for Greenhouses
  • Biomass Boilers and Furnaces
  • Biomass System Design
  • Components of Biomass Systems
  • Geothermal Energy for Greenhouses
  • Wind Energy for Greenhouses