Tempcontrol-cons-CO2

Tempcontrol-cons-CO2 - Environmental Management Temperature...

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Environmental Management – Temperature and Gasses _____________________________________________________ Outline – Part II Ventilation Factors influencing amount of required ventilation Passive Ventilation Active Ventilation; calculating fan requirements Evaporative cooling; calculating pad and pump size Heating Methods of heat loss and calculating heat loss Central (boilers) Unit heaters Circulation Temperature Control and Monitoring Systems Energy Conservation Carbon Dioxide Fertilization
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Environmental Management – Temperature and Gasses _____________________________________________________ What Level of Control is Needed? If our goal is to keep the greenhouse at 70F average daily temperature (ADT), we also need to consider how much variation in temperature are we willing to allow to save our equipment? Set point 70F with plus or minus 1 degree variation or plus or minus 4 degrees variation? Exact control, equipment works harder Less control, equipment works less (and lasts longer)
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Environmental Management – Temperature and Gasses _____________________________________________________ Heating and Cooling Setpoint If we want to maintain a given temperature, we normally have a separate heating and cooling setpoint which also can be either close together or further appart. 70F ADT as goal – 68 heating, 72 cooling 70F ADT as goal – 65 heating, 75 cooling The difference between the heating and cooling set point where no equipment works is called the dead band. The larger the dead band, the less the equipment works.
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Environmental Management – Temperature and Gasses _____________________________________________________ Temperature Management The strategy used in a commercial production greenhouse usually requires less precision than that used in a research greenhouse. Relates to equipment longevity Also depends on what is available for controlling the temperature – thermostats or an environmental control computer.
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Environmental Management – Temperature and Gasses _____________________________________________________ Temperature Cycling 66 67 68 69 0 1 02 03 04 05 06 0 Time (min) Ai r T em per atu re (F ) Heat on Heat on Heat off Heat off The frequency of temperature cycling increases as greenhouse size decreases Dead band – temp where no action is taken
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Environmental Management – Temperature and Gasses _____________________________________________________ Greenhouse Temperature Control Thermostats Single-zone controllers Climate-control computers
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Environmental Management – Temperature and Gasses _____________________________________________________ Thermostats
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This note was uploaded on 07/25/2008 for the course HRT 221 taught by Professor Biernbaum during the Fall '04 term at Michigan State University.

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Tempcontrol-cons-CO2 - Environmental Management Temperature...

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