RHS Level 2 Certificate Week 12 – Understanding the control of the environment in protected structures
Learning objectives <ul><li>4.1 Describe the factors that affect light levels in protected structures, including shape of ...
Factors affecting light levels <ul><li>Site – needs an open site with no overhanging trees or shading buildings </li></ul>...
Light levels – shape of building <ul><li>Light will pass through a transparent material if it hits the surface at 90°.  Ot...
Light Levels – shape of building <ul><li>With a traditional straight sided greenhouse with a roof at about 30° light from ...
Light levels – shape of building <ul><li>With this Mansard greenhouse each pane of glass is at a slightly different angle....
Controlling light – blinds and shading <ul><li>Reducing light intensity within the greenhouse will protect plants from sco...
Controlling light – supplementary lighting <ul><li>The light source chosen must include PAR </li></ul><ul><li>Commonly use...
Controlling temperature - heating <ul><li>Possible sources of heat – electricity, paraffin or gas or use stored heat from ...
Controlling temperature - cooling <ul><li>Use of external shading – blinds or shade netting most effective, shading paint ...
Water - irrigation <ul><li>Methods – by hand using a can or hose; by capillary watering systems; by drip or spray watering...
Water – Relative Humidity <ul><li>A measure of the amount of water vapour in the air relative to the maximum it could hold...
Question sheet answers <ul><li>Shade the outside of the greenhouse, damp down in the morning or early afternoon, open the ...
Learning outcomes <ul><li>4.1 Describe the factors that affect light levels in protected structures, including shape of st...
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Rhs year 2 week 12 presentation

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Rhs year 2 week 12 presentation

  1. 1. RHS Level 2 Certificate Week 12 – Understanding the control of the environment in protected structures
  2. 2. Learning objectives <ul><li>4.1 Describe the factors that affect light levels in protected structures, including shape of structure; site factors; orientation; type and condition of cladding materials. </li></ul><ul><li>4.2 Describe how the temperature can be maintained in structures, including heating by gas, oil or electricity; heat distribution using circulating water and air; cooling by forced or natural ventilation; evaporation; and shading. </li></ul><ul><li>4.3 Describe methods of changing the relative humidity (RH) in a protected environment, including the effects of ‘damping down’, ventilation and temperature changes. </li></ul><ul><li>4.4 Describe manual and automated methods of irrigation, including the use of watering cans, hose pipes, capillary systems and ‘drip’ systems </li></ul><ul><li>4.5 Describe how light levels can be manipulated, by the use of supplementary lighting and shading, including blinds and shading paints. </li></ul>
  3. 3. Factors affecting light levels <ul><li>Site – needs an open site with no overhanging trees or shading buildings </li></ul><ul><li>Orientation – north/south gives even light distribution; east/west best for winter light </li></ul><ul><li>Glazing materials – compromise between light transmission and cost and insulation values. </li></ul><ul><li>Shape of building </li></ul><ul><li>Use of shading or supplementary lighting </li></ul>
  4. 4. Light levels – shape of building <ul><li>Light will pass through a transparent material if it hits the surface at 90°. Otherwise it will be reflected at a corresponding angle to the angle of incidence. </li></ul><ul><li>No material however is perfectly transparent so some light will always be reflected from impurities etc within the material. </li></ul><ul><li>The angle of the light changes with the season and the latitude. </li></ul><ul><li>So the angle of the roof and sides of the greenhouse can make a radical difference to the amount of light that passes through the glazing. </li></ul>
  5. 5. Light Levels – shape of building <ul><li>With a traditional straight sided greenhouse with a roof at about 30° light from a low sun (winter and spring) passes through the sides but is mainly reflected from the roof. </li></ul><ul><li>Dutch Light greenhouses have sloping slides which increase the light transmission but have the same issue with the roof </li></ul>
  6. 6. Light levels – shape of building <ul><li>With this Mansard greenhouse each pane of glass is at a slightly different angle. Whatever the time of year some part of the glass is at 90° to the light. This is very expensive to build. Poly-tunnels have a similar response to light. </li></ul>
  7. 7. Controlling light – blinds and shading <ul><li>Reducing light intensity within the greenhouse will protect plants from scorching and may reduce temperature. Black out shading can also be used to create artificial ‘night’. </li></ul><ul><li>Materials used include blinds (external or internal), shading paint and shade netting. </li></ul><ul><li>External shading is most effective at reducing temperature. </li></ul><ul><li>Factors to be considered include cost, life span, work involved and ease of adjustment. </li></ul>
  8. 8. Controlling light – supplementary lighting <ul><li>The light source chosen must include PAR </li></ul><ul><li>Commonly used are High Pressure Sodium and compact fluorescent lights. </li></ul><ul><li>HPS generates heat and is more expensive to run but gives more light than compact fluorescent lights. </li></ul><ul><li>Artificial lighting can be used to add to existing day light in winter and/or to extend the ‘day’ to mimic light conditions at other times of year. </li></ul>
  9. 9. Controlling temperature - heating <ul><li>Possible sources of heat – electricity, paraffin or gas or use stored heat from the sun. </li></ul><ul><li>Electricity is cheaper than gas or paraffin and more controllable but expensive to install. </li></ul><ul><li>Gas and paraffin are less controllable and produce condensation but are cheaper than electricity. </li></ul><ul><li>Solar thermal can buffer temperatures in a cool greenhouse but a very elaborate set up would be needed for any greater level of heating. </li></ul><ul><li>Insulation is vital to avoid wasting heat. </li></ul>
  10. 10. Controlling temperature - cooling <ul><li>Use of external shading – blinds or shade netting most effective, shading paint has some effect </li></ul><ul><li>Evaporation of water – ‘damping down’. Energy used to turn the liquid to gas is taken from the heat in the air or in the greenhouse floor etc. </li></ul><ul><li>Ventilation – natural or forced. Hot air moves upwards and draws cool after it. Top and bottom vents must be open for natural ventilation. </li></ul>
  11. 11. Water - irrigation <ul><li>Methods – by hand using a can or hose; by capillary watering systems; by drip or spray watering systems. </li></ul><ul><li>Aim is to maintain water content of the growing media at the ideal level. </li></ul><ul><li>Drip or spray systems can be automated and easily adjusted to conditions. </li></ul><ul><li>Capillary systems can look after themselves while you go away for a few days. </li></ul><ul><li>Hand watering allows precise control and plant monitoring. </li></ul>
  12. 12. Water – Relative Humidity <ul><li>A measure of the amount of water vapour in the air relative to the maximum it could hold; this varies according to the temperature. </li></ul><ul><li>Ideal levels vary according to the plant and its maturity. </li></ul><ul><li>Relative Humidity can be increased by misting or damping down and reduced by ventilation . </li></ul>
  13. 13. Question sheet answers <ul><li>Shade the outside of the greenhouse, damp down in the morning or early afternoon, open the side and top ventilators in the morning and close at night. </li></ul><ul><li>Blinds allow easy adjustment on cloudy days and provide good reduction of temperature on hot days. </li></ul><ul><li>It removes the need for daily watering and increases humidity in hot weather </li></ul><ul><li>Benefits: precise amounts applied, plants are checked daily. Limitations: hard work in large areas and needs someone to do it. </li></ul><ul><li>Because light is reflected back through the glass by the inside surface of the water droplets. </li></ul>
  14. 14. Learning outcomes <ul><li>4.1 Describe the factors that affect light levels in protected structures, including shape of structure; site factors; orientation; type and condition of cladding materials. </li></ul><ul><li>4.2 Describe how the temperature can be maintained in structures, including heating by gas, oil or electricity; heat distribution using circulating water and air; cooling by forced or natural ventilation; evaporation; and shading. </li></ul><ul><li>4.3 Describe methods of changing the relative humidity (RH) in a protected environment, including the effects of ‘damping down’, ventilation and temperature changes. </li></ul><ul><li>4.4 Describe manual and automated methods of irrigation, including the use of watering cans, hose pipes, capillary systems and ‘drip’ systems </li></ul><ul><li>4.5 Describe how light levels can be manipulated, by the use of supplementary lighting and shading, including blinds and shading paints. </li></ul>
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