Complex services

Complex services

Air conditioning and

Ground source/air source heating

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

Air Conditioning

Creating an desired internal climate

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

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

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

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

Expansionvalve

External cooling tower

Heat vented to the environment

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

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

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.

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.

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…

Environmental heating

Reversing the cooling process

Air conditioner or “Heat pump”

Reverse the refrigerant flow, reverse the heating and cooling

summer

winter

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.

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

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

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.