• Roof Slopes
  • Gothic or peaked roofs with slopes of 6-12 inch pitch (6 inches of rise for every 12 inches of horizontal) will allow condensation to run off, reducing reduction in light levels caused by condensation on the glazing. Sloped roofs also aid in reducing the snow accumulation on greenhouse roofs.
• Glass Greenhouses
  • Glass greenhouses inherently have more infiltration because of the larger number of joints. Covering glass greenhouses with a single or double layer of polyethylene film reduces infiltration and heat loss. The cover can be installed permanently or just during the winter months. Reducing infiltration can lead to increased humidity levels and a rapid depletion of carbon dioxide. Mechanical ventilation may be needed to control humidity and can be used to replace the carbon dioxide. If additional carbon dioxide is needed, it can supplied by purchasing compressed carbon dioxide or using a special natural gas or propane burner to enrich the air. The light levels will be reduced by 18% because of the poly films which needs to be taken into accounted in an economic analysis. A double poly cover can reduce heat losses by up to 50%.
• Side Wall Height
  • Adding a foot or two to the sidewall heights to a greenhouse increases heat loss by only about 5% but gives room for hanging basket and may allow room for night curtains to be used.
• Gutter Connected Greenhouses
  • Six 30 foot by 100 foot individual greenhouses with 10 foot sidewalls have 37% more surface area than a gutter connected greenhouse covering the same growing area. If individual growing rooms are needed, poly wall dividers can be installed between bays so there are different heating zones. It is also easier to take advantage of a centralized heating system with a gutter connected greenhouses.
• Site Location
  • Choose a sheltered site to reduce wind induced infiltration heat losses as long as it doesn’t reduce lighting levels.
• Natural Ventilation
  • Greenhouses with roof vents or opening roofs and side wall vents can take advantage of thermal buoyancy for cooling. The air temperature at crop level should be no more than 5ºF above the ambient air temperature in a well designed system. Each vent should be 15-20% of the floor area and the sidewall vents should be equal in area to the ridge vent. Some ventilation fans may be need even in a greenhouse that can be naturally ventilated when only a little cooling is needed or the cold outside air could cause damage to plants.

 

If you have questions about the information on this site, please contact
Scott Sanford, Distinguished Outreach Specialist, University of Wisconsin, sasanford@wisc.edu.