Complex services
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Complex services Presentation Transcript

  • 1. Complex services Air conditioning and Ground source/air source heating
  • 2. Complex services • Services beyond the basic – Basic drainage, electrics, heating and water supply covered in level 1 – This section will look at more complex ideas of internal climate control • There is more to services than this – High voltage power supply – Lifts and escalators – Telecommunication installation – Etc, etc
  • 3. Air Conditioning Creating an desired internal climate
  • 4. Air conditioning • Air conditioning goes beyond basic ventilation and warming of the air • Fully air conditioned means that all of the following are controlled – Air temperature (high or low) – Humidity – Air cleanliness – Balancing recycled and fresh air. • Much of this depends on an ability to lower air temperature
  • 5. How to lower temperature • Lowering the temperature of air requires exploitation of basic physical principles. – When a fluid is compressed, its temperature rises. – Conversely, when a fluid expands, its temperature falls. – Air is cooled by exploiting these factors in a three stage process
  • 6. Simple cooling of a fluid 1: Fluid at ambient temperature 2: Fluid compressed and its temperature rises (done by a pump) 3a: Warm compressed fluid is cooled back down to ambient temperature by extracting heat in a cooling tower. 4: Compressed fluid, now at ambient temperature, expands through a valve and cools to a lower temperature 5: Cold compressed fluid used to cool internal environment Heat vented to the environment
  • 7. Systems are closed loops Fluid is piped through an internal heat exchanger and back to compressor pump Internal air blown over cold pipes, cooling the air and warming the fluid in the pipe Compressor pump Expansion valve External cooling tower Heat vented to the environment
  • 8. Refrigeration in practice • A refrigerant fluid is used. • When compressed at room temp it liquefies • When it expands at atmospheric pressure it it becomes a gas • The heating and cooling effects are much greater than with just a gas. Air for use in the building blows over the low pressure, chilled pipes and is cooled
  • 9. Cooling the compressed refrigerant in a cooling tower Typical commercial cooling towers. Hot, compressed refrigerant is cooled by blowing air and dripping cold water over the hot pipes. Evaporation cools them down and the cooled compressed refrigerant passes to the expansion valve, where it cools right down
  • 10. How to dry the air • Air is dried by over cooling – The air temperature is lowered by refrigeration until it falls below the local dew point – Moisture condenses out onto cooling coils and is channelled away. – The dried air is then heated up to the desired temperature.
  • 11. How to clean the air • Air can be cleaned in a number of ways – Mechanical filters: these work, but have to be maintained and will increase the power needed for the fans – Water scrubbing: spraying fine water droplets through the incoming air stream will remove dust, but the air will then need to be dried (see previous) – Electrostatic cleaning: the air passes through a highly charged wire mesh, which charges solid particles in the air. These are then attracted to oppositely charged metal plates, which will have to be cleaned regularly.
  • 12. But what does it all cost? • Air conditioning is staggeringly energy expensive – Pre-heat (in case exterior air is below freezing): energy needed – Scrub/filter: energy needed – Over-chill to dry: energy needed – Reheat to desired temperature: energy needed – Pump the air through the system: energy needed • In addition, the best refrigerant fluids are: – ammonia (poisonous) – CFC gases, which have destroyed the ozone layer – “Safe” alternatives are now used, but for 50 years we thought CFCs were safe…
  • 13. Environmental heating Reversing the cooling process
  • 14. Air conditioner or “Heat pump” Reverse the refrigerant flow, reverse the heating and cooling summer winter
  • 15. Ground source heat pumps, the theory • Pipes in ground full of water + antifreeze which is pumped around loops • Ground is at a constant +10oC so warms water in winter, cools it in summer • “Refrigerator” in house concentrates this heat to warm the house.
  • 16. Heat pump in practice: Cotswold water park visitor centre • In the winter: lake cooled, building heated • In summer: lake heated building cooled Reversible compressor Reversible expansion valve
  • 17. Air source heat pumps • Extract heat from external air • Low quantity of heat in air, especially in the winter • External coils will be chilled very cold, which can lead to pipe frosting problems
  • 18. Limitations of environmental heating • Both systems only warm rather than heat the building • Back-up heating may be needed in very cold weather • Capital cost of ground source very high • Electrical power consumed • Both work best with high insulation levels, but then so do all systems • Possibly high insulation plus small gas boiler makes most cost effective system.