1. Greenhouse Heating Principles and Hardware

2. Important Heat Units Btu – British thermal unit – amount of heat required to raise 1 lb of water 1 ºF Btu – British thermal unit – amount of heat required to raise 1 lb of water 1 ºF Boiler horsepower – 33,475 Btu Boiler horsepower – 33,475 Btu Calorie – is the amount of heat required to raise 1 g of water 1 ºC Calorie – is the amount of heat required to raise 1 g of water 1 ºC 1 Kcal = 1000 cal = 3.968 Btu 1 Kcal = 1000 cal = 3.968 Btu 1 Joule =.239 cal =.00095 Btu 1 Joule =.239 cal =.00095 Btu 1 Watt = 1 J per second 1 Watt = 1 J per second

3. Heating Basics You must add heat at the rate it is lost You must add heat at the rate it is lost Heat is lost by: CONDUCTION, Infiltration, and Radiation Heat is lost by: CONDUCTION, Infiltration, and Radiation Many different factors play a role in the amount of heat that is lost (a few are listed here): Many different factors play a role in the amount of heat that is lost (a few are listed here): –Type of glazing –Frame material choices –Local climate

4. Glazing Heat Loss Worst – single layer of polyethylene film or single layer of glass Worst – single layer of polyethylene film or single layer of glass Best – 3 layer polycarbonate panels Best – 3 layer polycarbonate panels Double Layer of Poly with dead air space brings the heat loss down to.70 Units Double Layer of Poly with dead air space brings the heat loss down to.70 Units

5. Greenhouse Air Infiltration Varies with glazing material choice Varies with glazing material choice You must also consider the quality and age of the construction You must also consider the quality and age of the construction Variability among greenhouses is high Variability among greenhouses is high EXAMPLE: An older glass greenhouse may have air infiltration rates 8 times that of a new high quality double-layer plastic film covered house.

6. Types of Heating Systems Unit Heater Unit Heater Central Heat Central Heat Radiant Heat Radiant Heat Solar Heat Solar Heat

7. Important Heating Notes CH 2 O(s) + O 2 (g) -----> CO 2 (g) + H 2 O(g)

8. Unit Heaters Cost including installation labor is $0.50 - $1.00/ sq. ft. Cost including installation labor is $0.50 - $1.00/ sq. ft. More ideally suited for smaller greenhouses. More ideally suited for smaller greenhouses. As greenhouse operations get larger central heating systems become more economically feasible. As greenhouse operations get larger central heating systems become more economically feasible. Components Components –Fuel burner –Heat exchanger –Distribution –Controls

9. Unit Heaters Heat supplied as needed Heat supplied as needed Available in horizontal and vertical designs Available in horizontal and vertical designs Must have a constant supply of oxygen Must have a constant supply of oxygen Exhaust stack must be tall enough above the greenhouse roof to permit dissipation of the smoke without re-entry into the greenhouse. Exhaust stack must be tall enough above the greenhouse roof to permit dissipation of the smoke without re-entry into the greenhouse. Openings for fresh air must be provided for unit heaters---or else a heater can use up all the oxygen in a house quickly. Openings for fresh air must be provided for unit heaters---or else a heater can use up all the oxygen in a house quickly.

11. Common Fuels for Unit Heaters No. 2 oil No. 2 oil Kerosene Kerosene LP gas LP gas Natural gas Natural gas Many types of unit heaters can be refitted to burn a different type of fuel.

12. Unit Heaters You go outside to your doubly poly greenhouse early one winter morning and realize that the heater is off. You are naturally concerned about your Poinsettias as the Holidays are approaching. What should you do first? and Why?

17. HAF (Horizontal Air Flow) Horizontal Airflow Horizontal Airflow Utilized to establish uniform temperatures in greenhouses Utilized to establish uniform temperatures in greenhouses For individual greenhouses – two rows of fans installed along the length of the greenhouse For individual greenhouses – two rows of fans installed along the length of the greenhouse Fans should be 2-3 feet above the plants Fans should be 2-3 feet above the plants For ridge and furrow fans should be installed along the center of the greenhouse For ridge and furrow fans should be installed along the center of the greenhouse

21. Central Heat Consists of one or more boilers in a central location (steam or water) Consists of one or more boilers in a central location (steam or water) Cost $2.50-$3.25 / sq. ft. of floor space Cost $2.50-$3.25 / sq. ft. of floor space Boilers can burn cheaper fuels than unit or radiant heaters Boilers can burn cheaper fuels than unit or radiant heaters Engineer Redundancy into the system whenever possible. Engineer Redundancy into the system whenever possible.

22. Suitable Boiler Fuels Wood Chips Wood Chips Logs Logs Coal Coal No. 4,5, and 6 fuel oil No. 4,5, and 6 fuel oil Many boilers can be retrofit to burn other fuels at a nominal cost.

23. Other Boiler Notes Hot water boilers most popular worldwide Hot water boilers most popular worldwide Temperature uniformity is greater than in steam systems Temperature uniformity is greater than in steam systems Larger reserve of heat Larger reserve of heat Due to lower operating temperatures you can place the pipes closer to the plants Due to lower operating temperatures you can place the pipes closer to the plants For some crops Boilers can also be a good source of CO 2 for greenhouse atmosphere enrichment. For some crops Boilers can also be a good source of CO 2 for greenhouse atmosphere enrichment.

30. Boiler Components FIREBOX – where fuel is burned FIREBOX – where fuel is burned Flue – provides a way for smoke, from the firebox, to vent to the outside air Flue – provides a way for smoke, from the firebox, to vent to the outside air Heat exchanger – network of tubes either filled with or surrounded by water. Heat exchanger – network of tubes either filled with or surrounded by water.

31. Heat Distribution Pipe size and quantity Pipe size and quantity –American greenhouse: 2” Fe pipe 180 F –Dutch greenhouse: 2” Fe pipe 203 F –Steam delivery: smaller pipe 215 F Amount of pipe necessary depends on greenhouse, crop, local climate, and type of pipe to be utilized Amount of pipe necessary depends on greenhouse, crop, local climate, and type of pipe to be utilized Tables 3-3 and 3-4 give you the info necessary to estimate pipe length once you have calculated the necessary total heat requirement for the greenhouse. Tables 3-3 and 3-4 give you the info necessary to estimate pipe length once you have calculated the necessary total heat requirement for the greenhouse.

34. Radiant Heater System May be cheaper to operate than unit heaters Emit infrared radiation May be cheaper to operate than unit heaters Emit infrared radiation Plants and other objects are heated first before the air, so air temperatures can be 5 to 10 ºF cooler than a conventional house Plants and other objects are heated first before the air, so air temperatures can be 5 to 10 ºF cooler than a conventional house Available in sizes from 20,000 to 120,000 Btu/hr Available in sizes from 20,000 to 120,000 Btu/hr

35. Radiant Heat Systems Place above plants in lines running along the length of the greenhouse Place above plants in lines running along the length of the greenhouse Can be spaced as far as 40 ft apart Composition of reflector is important Can be spaced as far as 40 ft apart Composition of reflector is important

36. Radiant Heat Advantages Newer systems do not emit visible red light Newer systems do not emit visible red light More efficient fuel combustion More efficient fuel combustion Cooler air temps reduce DF; why does this save you money? Cooler air temps reduce DF; why does this save you money? Only 25% electrical consumption of other systems. Only 25% electrical consumption of other systems.

37. Solar Heat Tax incentives for solar heating are gone, until this winter petroleum fuel product costs were low. Tax incentives for solar heating are gone, until this winter petroleum fuel product costs were low. There are commercial greenhouses with solar power – however some real costs may not have been included There are commercial greenhouses with solar power – however some real costs may not have been included Since fewer structures like this are built construction costs are generally higher. Since fewer structures like this are built construction costs are generally higher.

44. Bench Heating

45. Heating Calculations