Greenhouse Production_ Heating and Air Flow

How many greenhouses does a unit heater provide heat to?

Only one greenhouse

What heating system uses steam or hot water for distribution of heat?

Central Heating system

How many greenhouses does a unit heater provide heat to?

Only one greenhouse

What heating system uses steam or hot water for distribution of heat?

Central Heating system

What heating system is more popular in larger greenhouse operations?

Central heating system

What heating system is better adapted for supplying bottom heat (bench heating)

Hot water system

What do we do with combustion gases from a heater? Why?

Combustion gases are vented to prevent accumulation of combustion fumes

In a polytube system a return plenum (duct) is used to reduce what? Where is it located?

Used to reduce cold spots. Located under the heater.

what does the 8 inch diameter fresh air intake pipe to the heater do?

Provides air for combustion

Where are most heating pipes located in a free standing greenhouse?

Along the side and end walls

When available, what is the most popular heating fuel in B.C for commercial greenhouses?

Natural Gas

In a greenhouse, where should thermostats be positioned? (4 points)

• At plant level for a representative reading.

• not in hot or cold spots

• protected from direct sunlight

• must be aspirated

Which greenhouse wall would more likely be covered with insolation for heat conservation?

North wall

What greenhouse covering would reduce the heating requirements the most?

Double layer polyethylene

What is greenhouse effect?

when structure covering allows solar light through but traps the heat energy

Why might shading compounds have an adverse effect on plant growth?

On cloudy days light levels will be too low for optimal photosynthesis

Shading compound is most easily removed from what greenhouse covering?

Glass

What is Ridge and side venting

A cooling method that takes advantage of natural convection currents. Hot air rises coll air pulled in

What are the disadvantages of ridge and side venting?

• heat loss from vents

• No suitable for gutter connected greenhouses

T or F- Ridge and side vents cool by flow convection

True

T or F- Ridge and side vents cool more effectively in gutter connected greenhouses than freestanding

False- Ridge and side venting is not suitable for gutter connected greenhouses

T or F- the operating cost of ridge and side vents is high

F- Ridge and side vents is naturally circulating. No fans= lower costs

T or F- Inlets should be positioned in the wall opposite of the exhaust fans

True

T or F- Under minimum ventilization, fesh air enters through the fan jet louvre (shutter)

True

WHat does inlet cooling pads do?

It reduces the temperature inside the greenhouse. It is used during hot days to help reduce the greenhouse temp lower than the temp outside.

What is greenhouse effect?

Light energy trapped inside a greenhouse

Exhaust fans in a greenhouse range should be no further apart than..?

16 to 20 feet part

T or F- There is less disturbance of the upper hot air in a gutter connected greenhouse range if the ventilating air flow is perpendicular to the gutters.

True

What are cooling pad commonly made out of?

Treated Cellulose

What is a key point to ensure fog systems succes?

Water quality. Water purity should be tested.

What is staged venting?

Exhaust fans that come on one, two or three at a time as required to maintain the desired air flow and temp reduction.

When do we use two- speed fans?

They are beneficial for cooling/dehumidification in the winter. They provide a two stage cooling control.

When are fan-jet intake louvers used? What season?

Fan-jet louvers are connected to poly-tube and allows fresh air to come in. This system is best for minimum venting during the winter. Exhaust fan runs on low and main intake louvers remain closed.

What are exhaust fans?

Most common way to cool greenhouse. THey expel hot air. Intake louvers must be open to allow cooler air to replace exhausted air.

What are three problems with excessive heat?

• Reduces workers efficiency

• increase in insect and disease

• reduced plant growth and quality due to excessive respiration

What is the combustion chamber?

The heat source (the flame)

What does the heat exchanger do?

The circulating air passes through it and the air is heated

What do intake louvers do?

Used to introduce fresh air into the greenhouse during the winter part of the fanjet system.

What does return air plenum do?

Pulls cool air from the greenhouse floor and thus will lesson the effect of cold spot beneath the heater.

What is the Flue stack?

It used to vent the combustion gas.

What kind of piping is used for hot water pipes in central heating?

Piping is usually steel lined, but PVC pipe or black poly pipe may be used.

WHat kind of piping is used for steam lines in central heating? Why is this less common?

Steam lines are pressurized, so they are always steel. Not as common as it is pricy for installation due to requiring a license.

What is the formula used to calculate heat requirements? WHat does each part stand for?

A x K x C

A: standard heat requirement based on a standard peak GH with 6:12 pitch

K: climate correction factor

C: construction correction factor

WHat is the formula for calculating CFM?

CFM= Length x Width x 8

What is the formula for calculating ventilation requirement?

CFM x E (elevation) x L (light) x T (temp)