Part2Lecture1-3 - HRT 221 GREENHOUSE STRUCTURES AND...

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Fall 2002 Biernbaum, MSU HRT 221, pg 25 HRT 221 GREENHOUSE STRUCTURES AND MANAGEMENT PART II --GASES AND TEMPERATURE Gases in the greenhouse carbon dioxide, oxygen, water vapor Temperatures for plant growth What is "heat" and how is it measured? --VENTILATION Temperature control Humidity control Carbon dioxide levels Passive venting Forced or active venting (calculations) --EVAPORATIVE COOLING Advantages of evaporative cooling Principles of adiabatic (evaporative) cooling Calculations and system design --HEATING Calculating heat requirements Methods of heating central systems - steam, hot water localized systems - forced air, radiant heaters Selection of a fuel source Emergency heaters and generators --CIRCULATION Overhead unit heaters with fans, or fan jets Overhead units with perforated convection tubes Horizontal air flow (HAF) --TEMPERATURE CONTROL SYSTEMS Types of hardware Concepts of Staging --ENERGY CONSERVATION IN GREENHOUSES Low, medium and high cost methods Carbon dioxide fertilization
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Fall 2002 Biernbaum, MSU HRT 221, pg 26 Part II - Introduction (Lecture 1) Now that we know something about the structure and light levels in the greenhouse, we need to learn how to maintain the desired temperature and conditions for optimal plant growth and quality. The Greenhouse Environment LIGHT TEMPERATURE GASES (CO 2 , O 2 , H 2 O vapor) FERTILIZER ROOT MEDIA WATER We have talked mainly about light. The lectures for the next three weeks will cover the control of the greenhouse atmosphere. (Water, media and fertilizer will follow.) The greenhouse is subject to the extremes of summer heat and winter cold. There is little or no insulation or buffering capacity and the temperature can change dramatically, dependent on the level of sunlight. The atmosphere must also contain the proper amounts of water vapor, carbon dioxide, and oxygen. Our basic goal is to provide conditions which allow photosynthesis and respiration to proceed so that our plants grow, and that the plants look good and are marketable. Photosynthesis Respiration
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Fall 2002 Biernbaum, MSU HRT 221, pg 27 Temperature (Nelson, pages 409-418 ? 5 th edition) Temperature is a measure of the relative hotness or coldness of an object. Temperature is also a measure of the heat energy present. Temperature controls the rate of many biological reactions. Reactions are slower at lower temperature, faster at warmer temperatures. Examples of important reactions in the plant controlled by temperature are photosynthesis, respiration, water use and transpiration. Temperature can also have an important effect on the morphology or appearance of the plant and flowering. Temperature effects on rate of development: The temperature coefficient or Q 10 is the rate of change with a 10 degree centigrade change in temperature. It is usually close to 2, which means the rate of the reaction will double with a 10 degree centigrade change. Comparison of temperatures in Fahrenheit and Centigrade:
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Part2Lecture1-3 - HRT 221 GREENHOUSE STRUCTURES AND...

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