Greenhouse HeatingGreenhouse Heating

Principles and HardwarePrinciples and Hardware

Important Heat UnitsImportant Heat Units

Btu – British thermal unit – amount of heatBtu – British thermal unit – amount of heatrequired to raise 1 lb of water 1 ºFrequired to raise 1 lb of water 1 ºF

Boiler horsepower – 33,475 BtuBoiler horsepower – 33,475 Btu Calorie – is the amount of heat required to Calorie – is the amount of heat required to

raiseraise1 g of water 1 ºC1 g of water 1 ºC

1 Kcal = 1000 cal = 3.968 Btu1 Kcal = 1000 cal = 3.968 Btu 1 Joule = .239 cal = .00095 Btu1 Joule = .239 cal = .00095 Btu 1 Watt = 1 J per second1 Watt = 1 J per second

Heating BasicsHeating Basics

You must add heat at the You must add heat at the rate it is lostrate it is lost

Heat is lost by: Heat is lost by: CONDUCTIONCONDUCTION, Infiltration, , Infiltration, and Radiationand Radiation

Many different factors play Many different factors play a role in the amounta role in the amountof heat that is lost (a few of heat that is lost (a few are listed here):are listed here):– Type of glazingType of glazing– Frame material choicesFrame material choices– Local climateLocal climate

Glazing Heat LossGlazing Heat Loss

Worst – single layer Worst – single layer of polyethylene film of polyethylene film or single layer of or single layer of glassglass

Best – 3 layer Best – 3 layer polycarbonate polycarbonate panelspanels

Double Layer of Poly Double Layer of Poly with dead air space with dead air space brings the heat loss brings the heat loss down to .70 Unitsdown to .70 Units

Ffthr

Btu

2

Greenhouse Air Greenhouse Air InfiltrationInfiltration

Varies with glazing material choiceVaries with glazing material choice You must also consider the quality and age ofYou must also consider the quality and age of

the constructionthe construction Variability among greenhouses is highVariability among greenhouses is high

EXAMPLE:  EXAMPLE:  An older glass greenhouse mayAn older glass greenhouse mayhave air infiltration rates 8 times that of a newhave air infiltration rates 8 times that of a newhigh quality double-layer plastic film coveredhigh quality double-layer plastic film coveredhouse.house.

Types of Heating Types of Heating SystemsSystems

Unit HeaterUnit Heater Central Central

HeatHeat Radiant Radiant

HeatHeat Solar HeatSolar Heat

Important Heating NotesImportant Heating Notes

CH2O(s) + O2(g) -----> CO2(g) + H2O(g)

Unit HeatersUnit Heaters

Cost including installation labor is $0.50 - Cost including installation labor is $0.50 - $1.00/$1.00/sq. ft.sq. ft.

More ideally suited for smaller greenhouses.More ideally suited for smaller greenhouses. As greenhouse operations get larger centralAs greenhouse operations get larger central

heating systems become more economicallyheating systems become more economicallyfeasible.feasible.

ComponentsComponents– Fuel burnerFuel burner– Heat exchangerHeat exchanger– DistributionDistribution– ControlsControls

Unit HeatersUnit Heaters

Heat supplied as neededHeat supplied as needed Available in horizontal and vertical designsAvailable in horizontal and vertical designs Must have a constant supply of oxygenMust have a constant supply of oxygen Exhaust stack must be tall enough above theExhaust stack must be tall enough above the

greenhouse roof to permit dissipation of thegreenhouse roof to permit dissipation of thesmoke without re-entry into the greenhouse.smoke without re-entry into the greenhouse.

Openings for fresh air must be provided for Openings for fresh air must be provided for unit heaters---or else a heater can use up all unit heaters---or else a heater can use up all the oxygen in a house quickly.the oxygen in a house quickly.

Common FuelsCommon Fuelsfor Unit Heatersfor Unit Heaters

No. 2 oilNo. 2 oil KeroseneKerosene LP gasLP gas Natural gasNatural gas

Many types of unit heaters can be Many types of unit heaters can be refitted to burn a different type of fuel.refitted to burn a different type of fuel.

Unit HeatersUnit Heaters

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

HAF (Horizontal Air HAF (Horizontal Air Flow)Flow)

Horizontal AirflowHorizontal Airflow Utilized to establish uniform temperatures in Utilized to establish uniform temperatures in

greenhouses greenhouses For individual greenhouses – two rows of fans For individual greenhouses – two rows of fans

installed along the length of the greenhouse 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 For ridge and furrow fans should be installed

along the center of the greenhousealong the center of the greenhouse

Central HeatCentral Heat

Consists of one or more boilers in a Consists of one or more boilers in a central location (steam or water)central location (steam or water)

Cost $2.50-$3.25 / sq. ft. of floor spaceCost $2.50-$3.25 / sq. ft. of floor space Boilers can burn cheaper fuels than Boilers can burn cheaper fuels than

unit orunit orradiant heatersradiant heaters

Engineer Redundancy into the system Engineer Redundancy into the system whenever possible.whenever possible.

Suitable Boiler FuelsSuitable Boiler Fuels

Wood ChipsWood Chips LogsLogs CoalCoal No. 4,5, and 6 fuel oilNo. 4,5, and 6 fuel oil

Many boilers can be retrofit to burn Many boilers can be retrofit to burn other fuels at a nominal cost.other fuels at a nominal cost.

Other Boiler NotesOther Boiler Notes

Hot water boilers most popular worldwideHot water boilers most popular worldwide Temperature uniformity is greater than in Temperature uniformity is greater than in

steam systemssteam systems Larger reserve of heatLarger reserve of heat Due to lower operating temperatures you Due to lower operating temperatures you

can place the pipes closer to the plantscan place the pipes closer to the plants For some crops Boilers can also be a For some crops Boilers can also be a

good source of COgood source of CO22 for greenhouse for greenhouse atmosphere enrichment.atmosphere enrichment.

Boiler ComponentsBoiler Components

FIREBOX – where fuel is burnedFIREBOX – where fuel is burned Flue – provides a way for smoke, Flue – provides a way for smoke,

from thefrom thefirebox, to vent to the outside airfirebox, to vent to the outside air

Heat exchanger – network of tubes Heat exchanger – network of tubes either filled with or surrounded by either filled with or surrounded by water.water.

Heat DistributionHeat Distribution

Pipe size and quantityPipe size and quantity– American greenhouse: 2” Fe pipe 180 FAmerican greenhouse: 2” Fe pipe 180 F– Dutch greenhouse: 2” Fe pipe 203 FDutch greenhouse: 2” Fe pipe 203 F– Steam delivery: smaller pipe 215 FSteam delivery: smaller pipe 215 F

Amount of pipe necessary depends on Amount of pipe necessary depends on greenhouse, crop, local climate, and type greenhouse, crop, local climate, and type of pipe to be utilizedof pipe to be utilized

Tables 3-3 and 3-4 give you the info Tables 3-3 and 3-4 give you the info necessary to estimate pipe length once necessary to estimate pipe length once you have calculated the necessary total you have calculated the necessary total heat requirement for the greenhouse.heat requirement for the greenhouse.

Radiant Heater SystemRadiant Heater System

May be cheaper to operate than unit heatersMay be cheaper to operate than unit heaters•Emit infrared radiation•Emit infrared radiation

Plants and other objects are heated first Plants and other objects are heated first beforebeforethe air, so air temperatures can be 5 to 10 ºFthe air, so air temperatures can be 5 to 10 ºFcooler than a conventional housecooler than a conventional house

Available in sizes from 20,000 to 120,000 Available in sizes from 20,000 to 120,000 Btu/hrBtu/hr

Radiant Heat SystemsRadiant Heat Systems

Place above Place above plants in lines plants in lines running along running along the length of the length of the greenhousethe greenhouse

Can be spaced Can be spaced as far as 40 ft as far as 40 ft apart apart Composition of Composition of reflector is reflector is importantimportant

Radiant Heat Radiant Heat AdvantagesAdvantages

Newer systems do not emit visible red Newer systems do not emit visible red lightlight

More efficient fuel combustionMore efficient fuel combustion Cooler air temps reduce DF; why does this Cooler air temps reduce DF; why does this

savesaveyou money?you money?

Only 25% electrical consumption of otherOnly 25% electrical consumption of othersystems.systems.

Solar HeatSolar Heat

Tax incentives for solar heating are gone, Tax incentives for solar heating are gone, until this winter petroleum fuel product until this winter petroleum fuel product costs were low.costs were low.

There are commercial greenhouses with There are commercial greenhouses with solar power – however some real costs solar power – however some real costs may not have been includedmay not have been included

Since fewer structures like this are built Since fewer structures like this are built construction costs are generally higher.construction costs are generally higher.

Bench HeatingBench Heating

Heating CalculationsHeating Calculations