HVAC Design

Heating and cooling system design, including Allison's hilarious description of the vapor compression cycle for air conditioning.


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The technology for indoor environmental control is referred to as H-V-A-C or (H-vac÷ which stands for Heating, Ventilating and Air Conditioning. Typically, large modern buildings like office towers have heating systems that use boilers to heat water which is then distributed by pipes around the building to radiators that transfer the heat to the air. Smaller buildings and homes typically have what¦s known as a (forced air system÷ , where a furnace heats air that is then distributed throughout the house through a series of air ducts. In warmer weather, these same ducts can be used to distribute air that¦s been cooled by a central air conditioner.

Most air conditioning systems work by a process engineers call a (Vapour-compression refrigeration cycle.÷ A fluid with unique thermodynamic properties called a (refrigerant÷ is forced through a powered compressor as a gas. The refrigerant exits the compressor as a high-pressure, superheated gas. It passes through a condenser that removes the heat from the refrigerant causing it to condense into liquid. This condensed, liquid refrigerant then travels through an expansion valve where it goes through a sudden pressure drop. This drop in pressure causes the liquid refrigerant to instantly vaporize and, because of the thermodynamic properties of the refrigerant, this rapid expansion also causes a drop in temperature. This low-temperature gas refrigerant then passes through an evaporator where it comes into contact with the high-temperature room air. Heat is exchanged; the room air cools down and the refrigerant heats up. The warm, gas refrigerant is then fed back into the compressor to complete the cycle.

Engineers are now faced with the challenge of finding ways to make air conditioning systems more energy-efficient. One energy-saving design is a solar powered air conditioner that uses solar energy to power the motors and fans. The GreenCore Air system is powered by 170-Watt solar panel and can be used entirely off the grid or as a solar/battery hybrid.