Although HVAC is executed in individual buildings or other enclosed spaces (like NORAD's underground headquarters), the equipment involved is in some cases an extension of a larger district heating (DH) or district cooling (DC) network, or a combined DHC network. In such cases, the operating and maintenance aspects are simplified and metering becomes necessary to bill for the energy that is consumed, and in some cases energy that is returned to the larger system. For example, at a given time one building may be utilizing chilled water for air conditioning and the warm water it returns may be used in another building for heating, or for the overall heating-portion of the DHC network (likely with energy added to boost the temperature).[4][5][6]
Heating, ventilation, and air conditioning (HVAC[1]) is the technology of indoor and vehicular environmental comfort. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation, as HVAC&R or HVACR or "ventilation" is dropped, as in HACR (as in the designation of HACR-rated circuit breakers).
Indoor Fan Motor -- Indoor fans circulate the air from your house and through the system. Age and dust buildup are the two biggest contributing factors to their failure. When they are starting to fail they will often make noise. Failure of the fan will result in no heating or cooling, and if it is not repaired soon, it can cause other components to fail.
My heat pump/hvac system is not blowing cold air anymore, got checked out was told compressor broken. was told it cost  almost the same to repair/replace they recommend whole system. It's the same company that installed it 18 years ago, telling me that system is old and it will cost $9-10k for new system, because furnace has to be replaced with new hvac. what to do, need answers thanks????
Without proper ventilation, carbon monoxide can be lethal at concentrations of 1000 ppm (0.1%). However, at several hundred ppm, carbon monoxide exposure induces headaches, fatigue, nausea, and vomiting. Carbon monoxide binds with hemoglobin in the blood, forming carboxyhemoglobin, reducing the blood's ability to transport oxygen. The primary health concerns associated with carbon monoxide exposure are its cardiovascular and neurobehavioral effects. Carbon monoxide can cause atherosclerosis (the hardening of arteries) and can also trigger heart attacks. Neurologically, carbon monoxide exposure reduces hand to eye coordination, vigilance, and continuous performance. It can also affect time discrimination.[15]
HVAC equipment is estimated to last about 15 to 20 years. Yet over the years, parts go out and need to be repaired. Heat sensors, exchangers, and ducts can become worn out. Air conditioning motors may need repairing from time to time. For repairs to your heating and air conditioning systems, and even general maintenance, let HomeAdvisor help. Enter your zip code and let us connect you with prescreened HVAC repair services near you.