Greenhouse Heating Requirements

1. Greenhouse Heating Requirements Greenhouse Management

2. The “Greenhouse Effect” • On a sunny day, light easily passes through the greenhouse glazing. • Objects inside the greenhouse begin to warm up. • The energy absorbed by these objects is re-radiated as heat. • This heat is “trapped” inside the greenhouse, raising the greenhouse temperature.

3. Greenhouse Heat Loss • Both sunlight and greenhouse heaters warm up the inside of the greenhouse. • Eventually this heat is lost and escapes the greenhouse.

4. Greenhouse Heat Loss • There are 3 different ways that heat can be lost from a greenhouse: • Conduction • Air Leakage • Radiation

5. Conduction • The movement of heat through solid objects that are touching each other. • For example, roof trusses to glazing.

6. Air Leakage • The loss of warm air through openings in the greenhouse frame. • For example, heat loss around doors and exhaust fans.

7. Radiation • Transfer of heat between objects that are not in contact with each other. • For example, the radiation of heat from floor or benches to glazing.

8. Btu’s • Heat is measured in Btu’s (British Thermal Units). • One Btu is the amount of heat required to raise the temperature of one pound of water one degree Fahrenheit.

9. CalculatingHeating Requirements • The heating requirements of a greenhouse can be determined using the following formula: • H = (k) (a) (t1 - t2) • H = heat required in Btu’s per hour. • k = heat transfer coefficient for the glazing. • a = exposed surface area of the glazing in square feet. • t1 = desired inside temperature in degrees F. • t2 = outside temperature in degrees F.

10. Heat Loss Coefficients

11. Fuel Costs • The price of natural gas and other heating fuels continually changes. • This type of information will be supplied.

12. The End