07/05/2020
INTRODUCTION TO HVAC
HVAC means heating, ventilation and air conditioning system. This system is designed to provide thermal comfort and acceptable indoor air quality. HVAC is subdiscipline of mechanical engineering. This system works on following principles.
Thermodynamics
Fluid mechanics
Heat transfer
Refrigeration
It is the essential part of modern buildings, shops, apartments, hotels, hospitals and industrial areas also. Besides this, it is used in ships, trains, airplanes, cars and submarines etc. there are many types of HVAC system to provide building comforts. Mostly, we use central air-conditioning systems for large buildings and some packaged type units for small usage.
Heating:
Heating is required in relatively cold areas where room temperature remains near freezing point or below. Heat generation system contains boiler, electric heater, heat pump or furnace. Heat pumps are gaining more popularity in cooler climates. They extract heat from cooler area to hot area.
Ventilation:
Ventilation means change/ replace of air in specific time to control air temperature, moisture, odors and contaminants. The best example of ventilation is kitchen exhausts. They control odors, humidity sometimes. In this designing, the basic factor is air flow rate. In common practice, 150 cubic feet per minute (CFM) is sufficient for washroom exhaust and 500 to 1000 CFM for home kitchen.
Air conditioning:
This is generally considered cooling. This is correct but this also means control of humidity factor and odors by filter usage. Normally heat is removed form conditioned space to provide habitable room temperature. The conditioned space it kept air-tight to control wastage of energy. In normal cases air pressure is kept positive so that air could flow outside by door and window holes. This is compulsory for human beings. In some cases, air pressure is kept negative especially in hospital dialysis theatres.
American society of heating refrigeration and air conditioning ASHRAE(https://www.ashrae.org/), is an international institute which provides standards of HVAC. There are many more institutes that regulate these standards, but most commonly ASHRAE is used for constriction of air conditioning plants.
