Greenhouse Energy 



AHOT TOPIC ! 



Nancy E. Adams 



It seems that we are revisiting the 

 early 1980's again with the high 

 cost of fuel and the pressure this 

 exerts on running a profitable 

 greenhouse operation. Oil prices 

 have risen dramatically the past 

 few weeks and electricity rates are 

 expected to continue their upward 

 spiral. Howcan we better cope with 

 these changes and still manage an 

 efficient operation? Let's review 

 some possibilities. 



Glazing Options 



Many changes were made by 

 greenhouse operators in the 1980's 

 to improve greenhouse efficiency 

 without adversely affecting plant 

 growth. Oldleakyglasshouseswere 

 either replaced entirely or regl azed 

 with more improved versions of 

 glass, polycarbonates, acrylics, or 

 fiberglasses. Polyethylene films 

 became available, such as "Cloud 

 Nine", which were long lived and 

 were treated with infrared absor- 

 bent materials to reduce energy 

 losses. These surfaces allowed for 

 improved energy efficiency without 

 sacrificing solar radiation. 



Now that most of New Hampshire's 

 greenhouses are fairly tight from a 

 glazing standpoint, it's time to step 

 backandreassessother greenhouse 

 components. 



Ever wonder where your energy 

 dollar is spent? Figure 1 illus- 

 trates where the typical commercial 

 greenhouse operation spends its 

 energy dollar. Variations can be 

 expected due to the climate, condi- 

 tions of the structure and the crops 

 grown. Would you agree with these 

 figures? Energy costs alone some- 

 times exceed 20% of total green- 

 house production costs. 



Fuel choices 

 and cost comparisons 



Many growers have combustion 

 units that can bum more than one 



14 THE Plants MAN 



type of fuel. Before switching fuel 

 sources, consider not only the com- 

 parative cost of the alternative fuel 

 but also its availability and labor 

 requirements. The accompanying 

 table, figure 2 provides a fuel cost 

 comparison based on their heating 

 equivalent as expressed in dollars 

 per million Btu's. To use this chart, 

 draw a vertical line through the 

 price of the fuel being considered 

 to the Heating EquivalentCostline 

 on top and bottom. This line shows 

 the price per MBtu. For example, if 

 fuel oil costs $1.10 per gallon, the 

 equivalent fuel cost is approxi- 

 mately $10.80/MBtu.The same 

 heating equivalent for green wood 

 chi ps would cost $62/ton and for coal 

 about $148/ton. Does it make sense 

 for you to switch? 



Maintenance Suggestions 



1. Oil burner efficiency testing is 

 extremely important. A simple ten 

 minute test will help determine if 

 your unit is operating at optimum 

 efficiency. Adjustmentofthe burner 

 to obtain \%-2% greater efficiency 

 can significantly reduce fuel usage 

 over the heating season. For ex- 

 ample, a 2% increase in efficiency 

 in a 10 gallon per hour burner 

 that operates 3,300 hours from 

 September to May will save about 

 650 gallons of fuel. 



2. Cleaning fuel oil heaters will in- 

 volve removing soot from inside the 

 furnace. A 1/8" soot deposit can in- 

 crease fuel consumption as much at 

 10%. Wirebrush and vacuum or 

 cleansurfaceswithspecial cleaning 

 compounds. 



3. Ventilation systems should be 

 checked for worn belts, lubricated 

 bearings, and tight sealing louvers. 

 Good maintenance of the ventila- 

 tion system can save 10% to 20% of 

 fan energy use. 



4. Thermostat calibration can play 

 an important role in energy conser- 



vation. An inaccurate reading of 

 only a few degrees can result in lost 

 fuel. Forexample, when the outside 

 air temperature is 40 degrees F, a 

 greenhouse at 62 degrees F will use 

 10% more fuel than the same house 

 maintained at 60 degrees F. Sim- 

 ply aspirating thermostats will 

 greatly reduce the temperature 

 fluctuations experienced by ex- 

 posed, unshielded units. 



Additional Modifications 



1. Windbreaks constructed of a 

 mixtureofdeciduousandconiferous 

 trees or fencing can effectively cut 

 heat loss 5% to 10% below that of 

 an greenhouse located in an open 

 area. A well-planned windbreak 

 containing SCX' to 60%' open space 

 placed upwind of the prevailing 

 winter winds will reduce wind 

 velocities for 10 to 30 tree heights 

 downwind. 



2. Insulated 6" concrete foundation 

 walls with one inch of polystyrene 

 (R = 4.0) can reduce heat loss 

 through this surface by 75%. Insu- 

 lation can be installed either inside 

 oroutsidethegreenhousestructure. 



3. Horizontal aircirculationcreated 

 by small fans pi aced at set intervals 

 throughout the greenhouse can 

 more evenly distribute the warm 

 air and prevent temperature gradi- 

 ents. 



These are just a few suggestions to 

 consider as you look at your green- 

 house operation. Additional infor- 

 mation can be found in a booklet 

 entitled "Energy Conservation for 

 Commercial Greenhouses", pub- 

 lished by the Northeast Regional 

 Agricultural Engineering Service 

 and available from UNH Coopera- 

 tive Extension Publication Office 

 for $4.25. Call 862-2346 to receive 

 a copy. ^• 



Nancy E. Adams is an Agricultural 

 Extension Agent at tlie UNH 

 Rockingham County Cooperative 

 Extension. 



