Unit 2.6: Greenhouses

Learning Objectives

  • Understand how heat is lost or escapes from a greenhouse.
  • Discuss which types of glazing have the lowest heat loss.
  • Describe equipment that can be used to conserve heat.
  • Describe different types of heating systems and their efficiencies.
  • Discuss management strategies that can reduce heating costs without affecting plant growth.

Introduction

Greenhouses make it possible to grow warmer season crops in cooler climates or to force plant production outside of the normal growing season. In northern climates, energy used for heating greenhouses is a major expense – typically the third highest cost in greenhouse production. Despite increasing energy costs, greenhouse managers, in many cases, have been slow to adopt energy efficient technologies that can greatly reduce the energy costs of heating or cooling greenhouses (possibly due to the higher up-front investment costs). Today there are many types of heaters and boilers that have efficiencies of greater than 90 percent, which can replace older equipment that may have efficiencies of less than 60 percent. Thermal curtains can reduce nighttime heating costs by 30 percent and, depending on the type of material used, can double as shade curtains to aid in summer cooling. Using a positive day-night temperature differential (DIF) a higher daytime temperature and lower night temperature — can save 3 percent in energy costs for every 1°F of temperature difference compared to using the save setpoint temperature for day and night time periods. The glazing materials (coverings) on greenhouses used in cold climates should have a double layer to provide the best compromise between heat retention and light transmission.

The following units will discuss options for reducing energy costs in greenhouse production.