Unit: The Physical Greenhouse Heating Unit: The Physical Greenhouse

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

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

To increase relative humidity, decrease temperature To decrease relative humidity, increase temperature

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

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

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

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

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

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

Light can affect… Greenhouse temperature

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

Temperature increase Carbohydrate metabolized Respiration

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

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

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

Energy Loss from Greenhouse

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

Types of Heating Systems Hot Water Steam Unit Heaters Infrared Heaters

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

Hot Water Systems Heats through Conduction Convection Radiation

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

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

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

Pipe Placement

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

Steam Systems Same distribution system Same heating principles

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.

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

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

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

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

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

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

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

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