Complex services like air conditioning and ground/air source heating involve more than basic services. Air conditioning fully controls temperature, humidity, air cleanliness and fresh/recycled air balance using refrigeration principles. It compresses a refrigerant fluid to raise its temperature, then cools it to lower the temperature and dehumidify air before reheating it. Ground source heating exchanges heat with underground pipes, while air source uses outdoor air but works less efficiently in cold weather. Both primarily warm buildings and may require backup heating in very cold conditions.

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
3a: Warm compressed fluid is
cooled back down to ambient Heat vented
temperature by extracting heat in to the
a cooling tower. environment
1: Fluid at
ambient 5: Cold compressed
temperature fluid used to cool
internal environment
2: Fluid compressed 4: Compressed fluid, now at
and its temperature ambient temperature,
rises (done by a expands through a valve and
pump) cools to a lower temperature

7. Systems are closed loops
Heat vented
to the
environment
Compressor External Expansion
pump cooling tower valve
Internal air blown over Fluid is piped through
cold pipes, cooling the an internal heat
air and warming the exchanger and back to
fluid in the pipe compressor pump

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 Air for use in the building
much greater than with blows over the low
just a gas. 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”
summer
winter
Reverse the refrigerant flow, reverse the heating and cooling

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
Reversible compressor
Reversible
• In the winter: lake cooled, expansion
building heated valve
• In summer: lake heated
building cooled

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.