X. INCREASING TEMPERATURE - HEATING A. Heating system requirements –Optimum inside temperature –Uniform temperature –Prevent hot air on plants –Low cost –Fuel available –Automated

Energy Loss from Greenhouse

B. Heating terminology –refer to physical principles C. Factors affecting heating –Q = Qc + Qi –Qc = U x A x (t i -t o ) –Qi =.018 x V x N x (t i -t o ) Q - heat loss Qc - conduction & radiation heat loss Qi - infiltration heat loss U - heat transfer coef. A - area of coverings ti-to - inside set pt – coldest temp

1.House surface area vs volume –Surface area –Reducing surface area lower eaves ridge and furrow shape of house perimeter & surface area correlated 2.Temperature differential –(t i -t o )

3. Covering: Number of layers Heat transfer coeffieicnt –2 layers 40% less energy than 1 –3 layers 16% less energy than 2 4. Types of coverings Heat transfer coefficient 5. Air leakage Tight house vs loose house Leaks around fans, doors, vents Thermal radiation

6. Side walls Heat transfer coefficient 7. Structure - conductional heat loss 8% more loss through metal than wood Frame on double layer not exposed to outside 8. Wind Sweep away boundary layer

D. Sources of heat 1. Fossil fuels –Major: CoalNatural gas OilPropane –Minor: Wood chips Straw WheatSawdust 2. Electricity

3. Other possible sources Generating plants Natural gas compression stations Ethanol plants Geothermal –hot springs –ground water –underground caverns

Greenhouse heat: Gas from Landfill

Mine Air Heated Greenhouse

E. Types of Heating Systems –hydronic –forced air –Infrared 1. Hydronic - water or steam a. heating process –conduction –convection –radiation

b. Steam vs hot water –boiler –steam higher pressure –steam cools faster

c. boiler fuel - gas, coal, propane operation and maintenance manual or automatic control

d. distribution system 1)sidewalls, under benches, above benches 2) circulate air natural forced convection 3) finned pipe 2/3 along side wall, 1/3 under benches

Greenhouse Heat: Hot water or steam

2.Forced Air - Unit Heater a.Types hot water or steam –boiler required fuel fired unit heaters –Fuel burned in house –Air distribution forced convection electricity

b.distributing heat from unit heaters –Polytube –Heater fan and HAF c. problems arising from heat distribution –Hot air on plants –Uneven temperatures –Incomplete combustion CH3-CH2-CH2- + O > CO2 + H2O + (CH2- Ch2, CO, SO2) –Remedy 1 sq in/2000BTU/hr for air inlet

3. Infrared Heater a. Principles Energy not absorbed by air Leaves, etc., absorb energy –Increase in temp. Air warmed –conduction - leaves, etc., to air –convection - air rises b. Possible less condensation Plants warmer than air at night –Air up to 7 deg cooler Other systems - plants cooler than air at night –Radiation heat loss –Transpiration

Infrared Heating

c. Energy savings 30-70% Fuel combustion 90% Less temperature differential –Air up to 7 deg cooler –Less energy loss Do not use circulation fans –Less electricity Installation cost higher

4.Bottom heat Can provide 25-50% of heat during winter a. Root system warmer b. Natural air currents c. Water small rubber tubes on bench or floor Finned pipe under bench Plastic pipe in floor d. Electricity Resistance coil

e. Advantages Uniform temperature Crop time reduced Reduced disease –Root rot- soil dries faster –Foliar - leaves warm less condensation Crop uniformity Compact plants Zone flexibility

Bottom Heating Bottom heating: tube placement

Bottom heating: Biotherm (tube)

F. Special Heating Needs 1. Propagation Warm bottom temperatures Cable, pad, pipe under bench 2. Sterilization/pasteurization Steam best if available

G. Using Less Energy 1. Conservation Seal cracks Burner efficiency Insulation - side walls, north wall Double layer movable curtains Foam between polyethylene Styrene beads

2. Management practices Optimum space utilization –progressive spacing –movable benches –grow under benches –hanging baskets Reduce container size Improved varieties –faster production –cooler temp. requirements

2. Management practices (cont) Supplemental lighting CO 2 increase Reduce crop losses Reduce night temperature

Reduce Energy Use: Management Practices

Reduce Energy Use: Use space more efficiently

Supplemental heating: collect and store solar radiation