1. “Greenhouse Guts” Lecture Series
Feb 17
“Greenhouse Guts” Lecture Series
Greenhouse Management & Floriculture
Agriculture Technology Department
Plymouth High School

2. TARGETS LECTURE: Glazings ACTIVITY:
To recognize and explain three kinds of equipment that can ventilate a greenhouse
To recognize and explain two kinds of equipment that can heat a greenhouse
To distinguish between the four types of greenhouse covering materials (glass, polycarbonate, polyvinyl chloride and polyethylene
LECTURE: Glazings
ACTIVITY:
Understand how the systems are used in the Plymouth HS Greenhouse
Understand how the computer controls the GH climate.
Discover the purposes of the head house

3. Covering (Glazing)
Glass Acrylic Polycorbonates Vinyl (polyvinyl cholride) Polyethylene (#1 used)

4. Factors to Consider when choosing a Glazing
G l a z I n g s
Factors to Consider when choosing a Glazing
Capital available
Desired energy savings
Crop(s) grown
Period of time the GH is in operation
Natural environmental conditions
Above 80% light transmission is good
u-value
ability of heat to move through the product
Lower value (more heat trapped)
High value (more heat is lost)
#/ft2/hour
Strength of Glazing
Dead loads
Snow
Live loads
Google: National GH Manufacturing Association
NGMA: building codes

5. Glass Thickness: - Single Strength: (SSB): 1/16”
- Double Strength (DSB): 1/8”
Light transmission: 90%
u-value = 1.13
Life Expectancy ???(no rocks through windows)
Cost: $ per ft2 (what does this all include?)
Light Transmission is not 100% because of the sash bars that hold the glass in place

6. Fiberglass Reinforced Polyester
Dimensions:
-51 ½” wide, up to 24’ long
Cost ($.85-$1.75/ft)
10-15 years life expectancy, UV light breaks down fibers, turning material yellow
u= 1.2
35% savings over glass
88% light transmission (diffuses light)
Surface deteriorates

7. Acrylics Trade names: Longevity: 10yr Holds 10-60 lbs/ft2
Exolite, Acrylite, Plexiglass, Lucite, Deglas
Holds lbs/ft2
Dimensions:
- 5/8” thick, ¼” flexible
Light transmission: 83%
Build houses E-W
Heat:
u=.56-.6
40-50% savings over glass
Longevity: 10yr
Guaranty 30yr
Growers still getting same light penetration, do not yellow
Snow load
Flammability: can burn
$2-$4/ft2
Tight GH (watch for condensation) Anti-condensation coating available.

8. B. Acrylics

9. Impact Modified Acrylic
Used a lot in the hail belts in the US
Multi-wall
85% light transmission
10x impact strength of acrylic (hail zones)
Like acrylic

10. Polycarbonates Tradenames: Fire: self-extinguishing
Exolite, Lexsaon, Tuffak, Polygal, Primex, cryoflex, qualex, Twin Wall
¼” thick to 5/8” thick
Width=48” Length= up to 32’ long sheets U=
(40-50% heat savings)
Good for 10yrs, light intensity, looses 1%/yr
Fire: self-extinguishing
Light: about 80% + 1% loss/yr
Snow: 25lbs/ft2
Cost: $1.35, $3, $4 per ft2
Coatings available
Anti-condensation
Acrylic for UV protection

11. Examples of glazing

12. Other coverings Plastic Films Vinyl (polyvinyl chloride)
2-8mils (.002” ”)
Vinyl (polyvinyl chloride)
8-12 mil
$$$
4-5yrs
Static electricity
ETFE (ethylene Tetraflouoroethylene)
Polyester
Durable for 7 yrs

13. Polyethylene # 1 Glazing Film used Single layer or Double layer
Heat Savings: dbl= 40%
Dbl: stability against wind
Cost $.06 to .09/ft2 (about $5/ft2 for entire house)
# 1 Glazing Film used
Life Expectancy 3-4 yrs
Tradenames: Visqueen 1504, Arco Tufflite
Single layer or Double layer
Light Transmission
67% double and 87% for single
Diffused light
u=1.1
¾” to 8” spacing of too big =air currents (2” is optimum)
.2 to .3 static pressure
6ml
4ml

14. Wednesday
Early Release
END OF TODAY