Greenhouse Solar Hydronic "Root Zone" Heating
Greenhouse Solar Hydronic Heating or root-zone heating is a greenhouse production method that focuses on an optimum root temperature by distributing heat to bench and floor growing systems. It is an appropriate technology in the sense that it promotes energy conservation in modern greenhouse production. To warm roots, hot water is distributed through EPDM rubber tubing (also known as hydronic thermal tubing) or PVC piping laid out in a looping pattern. Though modern greenhouses typically use natural gas or fuel oil to heat water, alternative energy sources like solar thermal are one of the best economical alternatives long term. The benefits to plant growth from root-zone heating systems are well documented.
Energy savings are a distinct advantage. Simply put, research has shown that root zone temperatures are more critical to plant growth than leaf temperatures. By maintaining an optimum root zone temperature, greenhouse air temperatures can be lowered 15° F. Researchers in California determined that bench-top heating systems used only half the energy required by a perimeter hotwater system to produce chrysanthemum and tomato crops.
Floor heating is ideal for crops grown directly on the floor such as bedding plants, containerized ornamentals, and bag-cultured vegetables as well as greenhouse vegetables grown directly in the soil. With a cool-season crop (lettuce, spinach, Asian leaf vegetables), supplemental air heating may not even be required in a floor-heated greenhouse. A typical temperature pattern for a two foot-tall crop in February with an outside temperature of 10° F would be a floor temperature of 74°F, a canopy temperature of 55° F, and a temperature of 48° F four feet above the ground. Root-zone heating systems work excellent with any low-temperature (90-110° F) solar hot water system.
High-temperature EPDM tubing was a revolutionary achievement in the development of floorheating systems, and in addition to its use in greenhouses, hydronic tubing has spurred the adoption of radiant floor heating in homes and office buildings. Prior to EPDM tubing, greenhouseswere fitted with permanent floor-heating systems featuring PVC piping buried in the floor biomass. While PVC piping is low-tech in comparison to EPDM hydronic tubing, this system design is still employed in many greenhouses today. Regardless, tubes or pipes are usually laid out on 12" to 18" centers, embedded in porous concrete, gravel, or sand. Hot water from a water heater or from an alternative fuel source such as solar hot water collectors located outside the greenhouse is circulated through the pipes, warming the greenhouse floor.
Rutgers University initiated research into soil heating systems in the mid-1970s. Soil Heating Systems for Greenhouses Production, a 16-page leaflet from Rutgers Cooperative Extension, is enclosed for your information. It provides a summary of floor heating systems; materials that can be used for piping; system design; floor construction; warm water supply; environmental control; and bench heating options.
In the year 2000, the Horticultural Engineering program at Rutgers University was recognized by ASAE American Society of Agricultural Engineers as one of the five outstanding achievements in agricultural engineering for the 20th century.
"Credits go to ATTRA publication written by Steve Diver in 2002 for his extensive research."
Energy savings are a distinct advantage. Simply put, research has shown that root zone temperatures are more critical to plant growth than leaf temperatures. By maintaining an optimum root zone temperature, greenhouse air temperatures can be lowered 15° F. Researchers in California determined that bench-top heating systems used only half the energy required by a perimeter hotwater system to produce chrysanthemum and tomato crops.
Floor heating is ideal for crops grown directly on the floor such as bedding plants, containerized ornamentals, and bag-cultured vegetables as well as greenhouse vegetables grown directly in the soil. With a cool-season crop (lettuce, spinach, Asian leaf vegetables), supplemental air heating may not even be required in a floor-heated greenhouse. A typical temperature pattern for a two foot-tall crop in February with an outside temperature of 10° F would be a floor temperature of 74°F, a canopy temperature of 55° F, and a temperature of 48° F four feet above the ground. Root-zone heating systems work excellent with any low-temperature (90-110° F) solar hot water system.
High-temperature EPDM tubing was a revolutionary achievement in the development of floorheating systems, and in addition to its use in greenhouses, hydronic tubing has spurred the adoption of radiant floor heating in homes and office buildings. Prior to EPDM tubing, greenhouseswere fitted with permanent floor-heating systems featuring PVC piping buried in the floor biomass. While PVC piping is low-tech in comparison to EPDM hydronic tubing, this system design is still employed in many greenhouses today. Regardless, tubes or pipes are usually laid out on 12" to 18" centers, embedded in porous concrete, gravel, or sand. Hot water from a water heater or from an alternative fuel source such as solar hot water collectors located outside the greenhouse is circulated through the pipes, warming the greenhouse floor.
Rutgers University initiated research into soil heating systems in the mid-1970s. Soil Heating Systems for Greenhouses Production, a 16-page leaflet from Rutgers Cooperative Extension, is enclosed for your information. It provides a summary of floor heating systems; materials that can be used for piping; system design; floor construction; warm water supply; environmental control; and bench heating options.
In the year 2000, the Horticultural Engineering program at Rutgers University was recognized by ASAE American Society of Agricultural Engineers as one of the five outstanding achievements in agricultural engineering for the 20th century.
"Credits go to ATTRA publication written by Steve Diver in 2002 for his extensive research."
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