HVAC Control Systems

The acronym HVAC stands for "heating, ventilating and air conditioning" sometimes is referred to as climate control and is particularly important in the design of medium to large industrial and office buildings where humidity and temperature must all be closely regulated while maintaining safe and healthy conditions within.

HVAC is based on the principle of thermodynamics, fluid, mechanics, and heat transfer, and on inventions and discoveries made by Michael Faraday, Willis Carrier, Reuben Trane, James Joule, William Rankine and many others. The invention of components of HVAC systems has gone hand-in-hand through time with the industrial revolution and new methods of modernization, higher efficiency and system controls.

The three functions of the HVAC are closely related. All seek to provide thermal comfort, acceptable indoor air quality, and reasonable installation, operation and maintenance low costs. These systems also provide ventilation, reduce air infiltration, and maintain pressure relationship between spaces. What's more, the HVAC system distributes and removes air from different spaces, this operation is known as room air distribution.

Main functions of the HVAC's:

There different types of heating system such as central heating, that is often used in cold climates, this system contains a boiler or heat pump to heat water, steam or air in a central location, such a furnace room or a mechanical room. This System requires ductwork or piping to distribute the heat and also needs radiators to transfer this heat to the air. The radiators may be mounted on walls or buried in the floor to give under-floor heat.

Boiler fed systems, all but the simplest systems have a pump to circulate the water the same ductwork can be use for air conditioning.

Heating can also be provide from electric or resistance heating using a filament that becomes hot when electricity is caused to pass through it. This type of heat can be found in electric baseboard heaters, portable electric heaters and supplemental heating pumps.

The invention of central heating is often credited to the ancient Romans, who installed a system of air ducts called "hypocaust" in the walls and floors of public and private villas.

Ventilating is the process of replacing air in any space to control temperature or remove dust, odor, smoke, heat and bacteria. Ventilation includes both the exchange of air to the outside as well as circulation of air within the building. It's one of the most important factors for maintaining acceptable indoor air quality.

There are different methods for ventilating a building:

Mechanical or forced ventilation is used to control indoor quality. Excess humidity, odors and contaminants often can be controlled via dilution or placement with outside air.

Kitchens and bathrooms typically have mechanical exhaust to control odors and sometimes humidity. Factors in the design of such systems include flow rate and noise level. If the ducting for the fans traverses unheated space, the ducting should be insulated as well to prevent condensation on the ducting. Direct drive fans are available for man applications and can reduce maintenance needs.

Ceiling fans and table/floor fans circulate air within a room for the purpose of reducing the perceived temperature because of the evaporation of perspiration of the skin of occupants. Because hot air rises, ceiling fans may be used to keep a room warmer in the winter by circulating the warm stratified air from the ceiling to the floor. Ceiling fans do not provide ventilation as defined as the introduction of outside air.

Natural ventilation is the ventilation of a building with outside air without the use of a fan or other mechanical system. It can be achieved with operable windows when the space to ventilate is small and the architecture permits. In more complex systems warm air in the building can be allowed to rise and flow out upper openings to the outside (stack effect) thus forcing cool outside air to be drawn into must be taken to ensure the occupants' comfort. In warm or humid months, in many climates, maintaining thermal comfort via solely natural ventilation may not be possible so conventional air conditioning systems are used as backups.

Air-conditioning and refrigeration are provided through the removal heat. The definition of cold is the absence of heat and all air conditioning systems work on this basic principle. Heat can be removed through the process of radiation, convection, and conduction using mediums such as water, air, ice and chemicals referred to as refrigerants. In order to remove heat from something, you simply need to provide a medium that is colder- this is how all air conditioning and refrigeration systems work.

An air conditioning system or standalone air conditioner, provides cooling, ventilation and humidity control for all part of a house or building. The refrigerant provides cooling through a process called the refrigeration cycle. The refrigeration cycle consists of four essential elements to create a cooling effect. A compressor provides compression for the system. This compression causes the cooling vapor to heat up. The compressed vapor is then cooled by heat exchange with the outside air, so that the vapor condenses to a fluid, in the condenser. The fluid is then pumped to the inside of the building, where it enters and evaporator. In this evaporator, small spray nozzles spray the cooling fluid into a chamber, where the pressure drops and the fluid evaporates. Since the evaporation absorbs or adds heat to the system. The vapor is then returned to the compressor. A metering device acts as a restriction in the system at the evaporator to ensure that the heat being absorbed by the system is absorbed at the proper rate.

Dehumidification in an air conditioning system is provided by evaporator. Since the evaporator operates at a temperature below dew point, moisture is collected at the evaporator. This moisture is collected at the button of the evaporator in a condensate pan and removed by piping it to a central drain or onto the ground outside.

Air-conditioned buildings often have sealed windows, because open windows would disrupt the attempts or the HVAC system to maintain constant indoor air conditions.