1. Unit: The Physical Greenhouse
Heating
Unit: The Physical Greenhouse

2. Why is temperature important?
Temperature affects
Plant growth
Flower bud initiation
Crop quality
Operating costs

3. Relative Humidity Amt. of water vapor in the air
Amt. of water vapor the air can hold

4. To increase relative humidity, decrease temperature
To decrease relative humidity, increase temperature

5. Breathe in… Respiration Process whereby the plant uses its stored food
Intake of oxygen (mainly through the roots
O2 + C6H12O6  Energy + CO2 + H2O

6. Breathe out… Transpiration
The movement of water vapor through the stoma
A cooling system for the plant

7. If relative humidity is high…
The stomas close which impedes transpiration
The plant overheats

8. Photosynthesis The process whereby a plant makes food for itself
CO2 + H2O + light energy  C6H12O6 + O2

9. Light can affect… Flower bud initiation
Long day plant – begins to flower when days are longer than 12 hours

10. Short Day plant – begins to flower when days are shorter than 12 hours

11. Light can affect…
Greenhouse temperature

12. Carbon dioxide significantly above optimum & constant
Photosynthesis
Carbohydrate produced
Light intensity &
Carbon dioxide significantly
above optimum & constant
Temperature increase

13. Temperature increase
Carbohydrate metabolized
Respiration

14. Forms of Heat Loss Radiation Conduction Convection
From plants or other bodies in the greenhouse
Conduction
Heat transferred by physical contact
Convection
Movement of air within the greenhouse

15. Forms of Heat Loss Exfiltration Infiltration
Warm air escaping from the greenhouse
Infiltration
Air coming into the greenhouse

16. Infiltration, exfiltration, and conduction are affected by surface area.
Higher surface area = greater exfiltration, infiltration, and conduction loss

17. Energy Loss from Greenhouse

18. When is it necessary to heat?
Cold, cloudy days
Cool nights

19. Types of Heating Systems
Hot Water
Steam
Unit Heaters
Infrared Heaters

20. Hot Water Systems
Water is heated at a boiler and pumped through pipes around the greenhouse
Rising trend in modern greenhouses

21. Hot Water Systems
Heats through
Conduction
Convection
Radiation

22. Hot Water Systems Pipes can be placed: Along the sidewalls
Along or underneath the benches
Above the benches

23. Hot Water Systems Bottom Heat
Pipes placed beneath or along the benches
Can only provide ~40% of heat for a greenhouse

24. Hot Water Systems
Can reduce disease (soil dries faster and less condensation on the leaves)
Uniform temperatures

25. Pipe Placement

26. Steam Systems Similar to hot water
Water is heated by a boiler and the resulting steam flows through pipes throughout the greenhouse

27. Steam Systems
Same distribution system
Same heating principles

28. Steam vs. Hot Water Systems
Boiler must be at a higher temperature for steam
Steam is at a higher pressure
Steam cools faster than hot water.

29. Unit Heaters
Heat air within the unit and blow the air through the greenhouse
Can be further distrubuted by the circulation system in the greenhouse

30. Unit Heaters Units are inexpensive Operating costs are very high
Commonly used as a backup system

31. Unit Heates Possible problems Hot air on the plants
Uneven temperature distribution

32. Infrared Heaters Produce heat energy Energy absorbed by plants Note:
Infrared heater do not heat the air.

33. Infrared Heaters Placement Peak of the greenhouse
Well suited for very tall structures so energy radiates throughout the greenhouse

34. Infrared Heaters High installation costs Lower operating costs
No need to operate fans
Even heat distribution

35. Energy Curtains Pulling energy curtains can reduce heat loss at night
Blocks radiation and can reduce convection

36. Energy Curtains
Also used to provide shade during the day if temperature is too high
Reduce temperature