Your SlideShare is downloading. ×
Rhs year 2 week 12 presentation
Rhs year 2 week 12 presentation
Rhs year 2 week 12 presentation
Rhs year 2 week 12 presentation
Rhs year 2 week 12 presentation
Rhs year 2 week 12 presentation
Rhs year 2 week 12 presentation
Rhs year 2 week 12 presentation
Rhs year 2 week 12 presentation
Rhs year 2 week 12 presentation
Rhs year 2 week 12 presentation
Rhs year 2 week 12 presentation
Rhs year 2 week 12 presentation
Rhs year 2 week 12 presentation
Upcoming SlideShare
Loading in...5
×

Thanks for flagging this SlideShare!

Oops! An error has occurred.

×
Saving this for later? Get the SlideShare app to save on your phone or tablet. Read anywhere, anytime – even offline.
Text the download link to your phone
Standard text messaging rates apply

Rhs year 2 week 12 presentation

3,581

Published on

Published in: Education
0 Comments
3 Likes
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total Views
3,581
On Slideshare
0
From Embeds
0
Number of Embeds
0
Actions
Shares
0
Downloads
93
Comments
0
Likes
3
Embeds 0
No embeds

Report content
Flagged as inappropriate Flag as inappropriate
Flag as inappropriate

Select your reason for flagging this presentation as inappropriate.

Cancel
No notes for slide

Transcript

  • 1. RHS Level 2 Certificate Week 12 – Understanding the control of the environment in protected structures
  • 2. Learning objectives
    • 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.
    • 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.
    • 4.3 Describe methods of changing the relative humidity (RH) in a protected environment, including the effects of ‘damping down’, ventilation and temperature changes.
    • 4.4 Describe manual and automated methods of irrigation, including the use of watering cans, hose pipes, capillary systems and ‘drip’ systems
    • 4.5 Describe how light levels can be manipulated, by the use of supplementary lighting and shading, including blinds and shading paints.
  • 3. Factors affecting light levels
    • Site – needs an open site with no overhanging trees or shading buildings
    • Orientation – north/south gives even light distribution; east/west best for winter light
    • Glazing materials – compromise between light transmission and cost and insulation values.
    • Shape of building
    • Use of shading or supplementary lighting
  • 4. Light levels – shape of building
    • 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.
    • No material however is perfectly transparent so some light will always be reflected from impurities etc within the material.
    • The angle of the light changes with the season and the latitude.
    • 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.
  • 5. Light Levels – shape of building
    • 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.
    • Dutch Light greenhouses have sloping slides which increase the light transmission but have the same issue with the roof
  • 6. Light levels – shape of building
    • 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.
  • 7. Controlling light – blinds and shading
    • 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’.
    • Materials used include blinds (external or internal), shading paint and shade netting.
    • External shading is most effective at reducing temperature.
    • Factors to be considered include cost, life span, work involved and ease of adjustment.
  • 8. Controlling light – supplementary lighting
    • The light source chosen must include PAR
    • Commonly used are High Pressure Sodium and compact fluorescent lights.
    • HPS generates heat and is more expensive to run but gives more light than compact fluorescent lights.
    • 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.
  • 9. Controlling temperature - heating
    • Possible sources of heat – electricity, paraffin or gas or use stored heat from the sun.
    • Electricity is cheaper than gas or paraffin and more controllable but expensive to install.
    • Gas and paraffin are less controllable and produce condensation but are cheaper than electricity.
    • Solar thermal can buffer temperatures in a cool greenhouse but a very elaborate set up would be needed for any greater level of heating.
    • Insulation is vital to avoid wasting heat.
  • 10. Controlling temperature - cooling
    • Use of external shading – blinds or shade netting most effective, shading paint has some effect
    • 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.
    • Ventilation – natural or forced. Hot air moves upwards and draws cool after it. Top and bottom vents must be open for natural ventilation.
  • 11. Water - irrigation
    • Methods – by hand using a can or hose; by capillary watering systems; by drip or spray watering systems.
    • Aim is to maintain water content of the growing media at the ideal level.
    • Drip or spray systems can be automated and easily adjusted to conditions.
    • Capillary systems can look after themselves while you go away for a few days.
    • Hand watering allows precise control and plant monitoring.
  • 12. Water – Relative Humidity
    • A measure of the amount of water vapour in the air relative to the maximum it could hold; this varies according to the temperature.
    • Ideal levels vary according to the plant and its maturity.
    • Relative Humidity can be increased by misting or damping down and reduced by ventilation .
  • 13. Question sheet answers
    • 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.
    • Blinds allow easy adjustment on cloudy days and provide good reduction of temperature on hot days.
    • It removes the need for daily watering and increases humidity in hot weather
    • Benefits: precise amounts applied, plants are checked daily. Limitations: hard work in large areas and needs someone to do it.
    • Because light is reflected back through the glass by the inside surface of the water droplets.
  • 14. Learning outcomes
    • 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.
    • 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.
    • 4.3 Describe methods of changing the relative humidity (RH) in a protected environment, including the effects of ‘damping down’, ventilation and temperature changes.
    • 4.4 Describe manual and automated methods of irrigation, including the use of watering cans, hose pipes, capillary systems and ‘drip’ systems
    • 4.5 Describe how light levels can be manipulated, by the use of supplementary lighting and shading, including blinds and shading paints.

×