Abstract
This publication discusses technologies and equipment used for
root-zone heating, a greenhouse production method that focuses on
providing an optimum root temperature by distributing heat to bench
and floor growing systems.
This publication
contains references to enclosures which are available in hard
copy only. Please call our toll free number to receive a copy at
1-800-346-9140. |
Table of Contents
Root Zone Heating
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 include
geothermal, solar, wood, thermal biomass (heat from compost or brushwood
piles), and co-generation. 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 hot water system to produce
chrysanthemum and tomato crops. (1)
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. (2)
High-temperature EPDM tubing was a revolutionary achievement in
the development of floor-heating 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, greenhouses were fitted with permanent floor-heating systems
featuring PVC piping buried in the floor biomass. While PVC piping
is low-tech in comparison to 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 gas water
heaters 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. (3)
Three concepts have
been integrated to develop low-cost greenhouse stuctures
and enviornment control systems: (1) the
air-inflated double-layer polyethylene greenhouse; (2)
movable thermal insulation for greenhouses; and (3)
root-zone heating systems for production greenhouses. |
As a note of interest, the Department of Bioresource Engineering
at Cook College, Rutgers University (famous for these innovative
greenhouse engineering achievements such as floor heating) ceased
to exist in the year 2000, primarily due to retirements among its
faculty. The remaining faculty, as well as the horticultural engineering
program, are now part of the Department of Plant Biology and Pathology
at Cook College, Rutgers University. (4) Of
special interest are the Web archives for the Horticultural
Engineering newsletter and the CCEA Newsletter. (5)
Root-zone heating systems work well with any low-temperature (90–110°
F) hot water system. Possibilities include geothermal water, waste
water from power plants and cogeneration facilities, and solar-
or compost-heated water.
In addition to this resource packet on root-zone heating, there
are two related ATTRA publications on the topic of greenhouse heating:
The enclosed items provide further details and resources on root-zone
heating. Of special interest is the informative summary by John
W. Bartok, Jr., “Designing a Root Zone Heating System,”
in the Connecticut Greenhouse Newsletter.
For suppliers of tubing, radiant heat tape, and related root-zone
heating equipment, see the enclosed article from Greenhouse Management & Production, “A Look at: Root Zone Heating.” For
a comprehensive list of products and suppliers that support the
nursery and greenhouse industries, see The Green Beam Web site; it
will include updated contact information for the companies listed
in the aforementioned article.
The Green Beam
www.greenbeam.com/
The Green Beam Web site is maintained by Branch-Smith Publishing—publisher
of NMPro, GMPro, Garden Center Merchandising
and Management, and Garden Center Products and
Supplies. It is an online version of the comprehensive
Buyer’s Guide Directory published in these trade magazines.
Back to top
References
-
Sachs, R.M. et al. 1992. Plant
response and energy savings for bench-top heated greenhouses.
Scientia Horticulturae. Vol. 49, No. 1–2. p. 135–146.
-
Whitcomb, Carl E., Charlie Gray,
and Billy Cavanaugh. 1985. A floor heating top ventilating system
for quonset greenhouses. p. 4–10. In: Nursery Research Field
Day. Research Report P-872. Agricultural Experiment Station,
Oklahoma State University.
-
CCEA Newsletter. 2000. Outstanding
agricultural achievement of the 20th century. The Center for Controlled
Environment Agriculture, Rutgers University. Vol. 9, No. 3 & 4.
-
Department of Plant Biology and
Pathology
Cook College Campus Rutgers University
20 Ag Extension Way
New Brunswick, NJ 08901-8500
732-932-9753
Note: A related publication from Rutgers University is Environmental
Control of Greenhouses, Publication E-213. Contact the Department
of Plant Biology and Pathology to obtain a copy.
-
Horticultural Engineering Websites
at Cook College, Rutgers University:
Horticultural Engineering Center for Controlled Environment Agriculture
Horticultural
Engineering Newsletters, Rutgers University
Includes:
Horticultural Engineering
CEA Newsletters and
Center for Controlled Environment
Agriculture Newsletters
Back to top
Enclosures
Bartok, John W., Jr. 1994. Designing a root zone heating system.
Connecticut Greenhouse Newsletter. December 1994–January 1995.
No. 183. p. 11–17.
Bartok, John W., Jr. 1995. Root zone heating options. Greenhouse
Management & Production. August. p. 80–81.
Brugger, Michael, and Randall Zondag. 1989. Be astute—heat
your roots. Greenhouse Grower. December. p. 28, 31.
Hopkins, Matthew T. 1994. The bottom line on heating. Greenhouse
Grower. December. p. 26, 28, 30.
McLean, Jennifer. 1995. A look at: Root zone heating. Greenhouse
Management & Production. August. p. 53–54, 59.
Pyle, Kathleen. 1994. Revisiting root zone heating. GrowerTalks.
April. p. 22, 24, 26.
Roberts, William J. 1996. Soil Heating Systems for Greenhouse Production.
Rutgers University Cooperative Extension, E-208. 16 p.
Back to top
Further Reading
This Further Reading
section contains literature citations to additional articles and experiment
station bulletin reports we have identified through research.
They are listed here for reference, in case you wish to follow
this topic in more detail. A local librarian can help you
obtain photocopies of agricultural literature through the
Inter-Library Loan program. |
Bartok, J.W. and R.A. Aldrich. 1984. Low cost solar collectors
for greenhouse water heating. Acta Horticulturae. Vol. 148. p. 771–774.
Brugger, M.F. 1984. Some applications of floor heating in commercial
Ohio greenhouses. Acta Horticulturae. Vol. 148. p. 115–118.
Elston, Rob. 1991. A look at: Root-zone heating systems. Greenhouse
Manager. December. p. 83–84.
Gent, Martin and Vincent Malerba. 1994. Soil heating made simple.
American Vegetable Grower. August. p. 38–39.
Roberts, Bill. 1991. Soil heating improves transplant production.
American Vegetable Grower. November. p. 40–42.
Roberts, W.J. et al. 1985. Energy Conservation for Commercial Greenhouses.
NRAES–3. Northeast Regional Agricultural Engineering Service,
Cornell University. p. 27-30.
Whitcomb, Carl E., Charlie Gray, and Billy Cavanaugh. 1984. The
“ideal” greenhouse for propagation. p. 4–8. In:
Nursery Research Field Day. Research Report P–855. Agricultural
Experiment Station, Oklahoma State University.
Whitcomb, Carl E., Charlie Gray, and Billy Cavanaugh. 1985. A floor
heating top ventilating system for quonset greenhouses. p. 4–10.
In: Nursery Research Field Day. Research Report P-872. Agricultural
Experiment Station, Oklahoma State University.
Back to top
Web Resources
Greenhouse Condensation Control: Bottom Heating and Between-row Heating
Ohio State University
Midwest Renewable Energy Association
Solar
Hydronic Radiant Floor Heating Systems—Fact Sheet (PDF
/ 280 K)
Liquid-Based Active Solar Heating
Office of Energy Efficiency and Renewable Energy,
Root Zone Heating for Greenhouse Crops
By Steve Diver
NCAT Agriculture Specialist
Paul Williams and Richard Earles, Editors
Cole Loeffler, HTML Production
CT 164
Slot 196
Back to top |