What is Hvac: Definition and 50 Discussions

Heating, ventilation, and air conditioning (HVAC) 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).
HVAC is an important part of residential structures such as single family homes, apartment buildings, hotels and senior living facilities, medium to large industrial and office buildings such as skyscrapers and hospitals, vehicles such as cars, trains, airplanes, ships and submarines, and in marine environments, where safe and healthy building conditions are regulated with respect to temperature and humidity, using fresh air from outdoors.
Ventilating or ventilation (the "V" in HVAC) is the process of exchanging or replacing air in any space to provide high indoor air quality which involves temperature control, oxygen replenishment, and removal of moisture, odors, smoke, heat, dust, airborne bacteria, carbon dioxide, and other gases. Ventilation removes unpleasant smells and excessive moisture, introduces outside air, keeps interior building air circulating, and prevents stagnation of the interior air.
Ventilation often refers to the intentional delivery of the outside air to the building indoor environment. It is one of the most important factors for maintaining acceptable indoor air quality in buildings. Methods for ventilating a building are divided into mechanical/forced and natural types.

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  1. S

    HVAC The technician installed a new AC split without a vacuum pump

    Hello, The technician installed a new AC split without a vacuum pump. (Gree 24000 BTU Inverter) Should we drain the refrigerant, do vacuum, and refill the refrigerant? It is written in the AC manual that we should vacuum during installation. I read that air and humidity are harmful for the...
  2. UrbanFarmEngineer

    HVAC Electrical Issue: Current Leakage from Furnace

    Hey Everyone, I am not an electrical engineer I am a biochemmie and I am here for your help. I have been learning household wiring and troubleshooting electrical wiring problems in my house for the last few months and I am stumped on an HVAC issue and would really appreciate some insights from...
  3. DaveE

    Slow Cooker Recipes & HVAC Revolution

    Amazing info from a slow cooker recipes facebook group. If only Fleischmann & Pons had put a clay pot over their experiment... OTOH, they aren't exactly wrong.
  4. J

    Installing Motorized Dampers in Basement HVAC: Will It Work?

    I'm installing 4 motorized dampers in my basement HVAC, the motor on each unit is 24V drawing 6 watts at 0.25 Amps. I will be powering them from one 24V 40VA transformer. One temperature controller, that uses direct output and has a max output capacity of 10A, will be installed between the power...
  5. J

    I How is target superheat table generated for R22 HVAC system

    It seems the practice is to enter the table with evaporator air intake wetbulb temp and condenser ambient temp. I'm trying to understand the theory that translates these readings into the proper target superheat. Thanks
  6. T

    I HVAC dehumidifier energy wastage

    Hi. Anybody every wondered why we pay to run dehumidifiers in cold climates, when so much moisture could be condensed through the use of outside air temperature/transfer ..ie look at the condensation on your windows ! ...(summer months ...open a window or just circulate outside air). Of course...
  7. T

    HVAC engineering experts available?

    Anybody know an HVAC engineer or physicist? Curious about heat transfer
  8. B

    Chiller power consumption calculation

    Hello, If I am trying to calculate the heat removed from a chiller system through this formula on engineering toolbox.com: Does COP or efficiency of the equipment come into play with this calculation? For example if a chiller is fully loaded isn't it running more efficient for a watt/ton...
  9. B

    Simulate the temperature inside an aquarium tank

    there's a website to size an aquarium heater or chiller. This is just for learning purposes (not for fish) but I have modified these parameters from default to perform a load calculation on a 100 gallon glass tank... For the tank temperature range I set to be between 150-160 degree F. and a...
  10. P

    HVAC - Primary airflow temperatre

    Hi team, I am after some assistance. When I am amending the primary airflow temperature on diffusers from 22°C to 13°C, it is my opinion that all the Draught rating (DR) and comfort criteria calcs will all change as the air will become more dense. Is this correct?
  11. srinaath

    Arcing in electrical relay contacts due to different types of loads

    Arcing in a contact occurs due to open and close action of the switch. I am curious if the arc intensity depends on the type of load. For example the arcing (arc intensity) due to induction load will be greater than arcing due to resistive load?
  12. MacLaddy

    How can adjacent air be accounted for in fresh air exchanges for HVAC systems?

    Good morning folks. I have a question about fresh air in an HVAC system. The explanation I provide are a bit tedious, but the question is eventually asked towards the bottom. I am evaluating a negative air pressure room for a small medical laboratory. Using ASHRAE 170, I know this room needs to...
  13. Bat

    Engineering Is a Reynolds Number of 1914.2 Indicative of Turbulent Flow?

    1. Reynolds number = (Q/A/60) * (diameter) / (3.99 * 10^-5m^2/s) = 1914
  14. Emanuel Silva

    Pressure generated by a column of air

    Applying Bernoulli, Does the term ρ*g*h matters ? I am trying to select a fan
  15. G

    HVAC How to calculate pressure loss across a perforated and corrugated plate?

    The plate is in inclined position in a chamber where the air flows from bottom to top.
  16. T

    Do vacuum Ironing boards cause negative pressure in my Space

    Hey, I'm designing an HVAC system for a laundry building. I have vacuum equipment (Vacuum press and Vacuum Ironing boards ) in the space which have a vacuum outlet the is taken outside the building through individual ducts. When all machines are operational, 877 l/s of hot air and moisture would...
  17. M

    Motor fan pulley sizing for HVAC

    Hi Everyone! I designed a motor fan system pulley system. So, basically, the motor is of 15 kw with a driver pulley of 7" dia. And through a v-belt I attached a backward curved fan with a 10" dia pulley on the shaft. My fan shaft power is 13.24 kw. This selection was given to me by the software...
  18. srinaath

    Definite purpose and general purpose contactors

    I came across a contactor catalog saying "Definite purpose". Then tried to figure out the types of contactor. Came across definite purpose and general purpose. What is meant by definite purpose contactor and general purpose contactor? On what basis can i choose definite purpose?
  19. MacLaddy

    Pressure loss in an HVAC system

    I'm working on my first engineering project in the real-world and I'm hitting a bit of a snag. It's regarding pressure loss analysis in an HVAC system. We have a system that is capable of providing a maximum of 2.0-in.wg pressure at the air handler, but we are finding very little air movement at...
  20. M

    Phase of refrigerant crossing heat exchanger devices

    When a refrigerant crosses a heat exchanger device or has some heat added into it, like condenser/evaporator or boiler/cooling tower, does the phase always change? If that's so, why? Or do we need to check if the temperature is above or under the boiling point?
  21. mechlite

    Possible Air Conditioning System?

    Hello everyone! Summer is coming and instead of buying a $200-$400 air conditioner, I'd figure I could try a DIY version. I came up with a schematic (attached below) and how I think it would work. I feel like I'm missing something blatantly obvious that will make it not feasible. Wondering if...
  22. S

    Pressure/temperature question about HVAC

    I have been reading about hvac and have a question. I downloaded a neat app where you can input the refrigerant type, (say r22) and the low side pressure as well as the suction line temp, and it will give you the superheat of the refrigerant. Is there a way to figure out if a person installed a...
  23. M

    What do you think about conditioning the outdoor air?

    What do you think about conditioning the outdoor air? Is it impossible? Is it useless? Is there any research about it?
  24. Claude_mar

    Predicting internal temperature with or without HVAC

    Hi, how to predict indoor temperature with or without HVAC? I have the internal temperature's value, the external temperature's value and the temperature of HVAC's air output. I want two function, one with HVAC on and other with mode off. Hp: start time 0, end time Tend. Tend has values from 0...
  25. J

    Understanding HVAC Superheat: Common Issues with Calculating Target Levels

    I was trying to calculate my target superheat when I ran into a bit of a problem. My indoor return wetbulb temperature is 60F and the outdoor ambient condenser temp is 90F. These figures apparently don't compute in a calculator application or a chart. With 60F wetbulb, the charts and...
  26. A

    Electrical Efficiency Calculations HVAC

    Hi, I am trying to do a comparison of electrical efficiencies between 2 HVAC compressors but struggling to find formulas or calculations to figure it out. Can anyone help me?
  27. T

    Bank Strong room (Vault) special HVAC requirements

    Hey, I'm designing the HVAC system for a bank. What are the special cooling and ventilation requirements that go into the bank(specifically the vault ventilation) and where can i find resources regarding the subject. Thanks in advance.
  28. srinaath

    What is constant flow system in air condioning (HVAC)?

    I am an electrical guy, i can't understand the concept of constant flow system...and how temperature is controlled in room by Air conditioner...thanks
  29. P

    How to reduce RH of air from evaporative cooler?

    Hi guys! I'm new here and this is my first post! I'm a fresh engineering graduate and I'm facing a dilemma. I'm currently in charge of a project. We intend to use an evaporative air cooler for a carbonated soft drink filling line. The flow of air intake is as follows: evaporative cooler -->...
  30. gauss44

    Home Improvement Project & PV=nRT

    I live in an attic apartment and have been suffering a problem lately. Convection seems to be pushing (nasty kitchen smelling) air up to my apartment from my neighbors who live below me in the same building. This nasty air current primarily seems to be coming from a specific crawl space inside...
  31. T

    Preferred HVAC system for small laboratories

    What are the preferred systems that are typically used to condition small to medium sized labs.I've read that terminal reheat CAV systems are preffered .Why is this?
  32. T

    Laboratory HVAC Design Inquiries

    I'm doing a university project on HVAC design of a laboratory(Agricultural Products).I'm having trouble verifying whether I have understood what I have researched correctly This is what I have understood from what I've read.First I would calculate the cooling/heating loads as I would have from...
  33. EVriderDK

    HVAC: Calculating enthelpy change after humidification

    - Without chart! I know I can bring up my molliers chart and use that enthalpy scale and draw a line and all that, but I want to know how to calculate it, and I cannot find any formula. Right now I have a problem where I only have the absolute moisture content before the humidifyer at w=0.0057...
  34. A

    HVAC /generator service mechanic should I pursue an electrical or mech

    I have been doing HVAC for 15 years and generators for the last 3. I'm 37 and will be working full time as I go to school. I'm wondering though where I should focus my major yet I do have lots of time. Since I'm only taking 2 classes this semester to get my feet wet. An English writing class and...
  35. S

    How Does HVAC Control Humidity in Pharmaceutical Production?

    Homework Statement A pharmaceutical company operating a tabletting facility in Puerto Rico requires stringent environmental control set at 20°C and 40%RH in order to provide consistent high quality production. The HVAC system is designed to cope with outdoor tropical conditions of 30°C and 90%...
  36. MacLaddy

    Energy calculation for HVAC systems

    I've been asked to approximate a dollar amount for heating and cooling an occupied tenant space in a commercial office building. We've looked into installing a temporary gauge on each unit to give us a good approximation, but the cost to gauge up all the electrical and gas was beyond the scope...
  37. E

    Should i go for power engineering or excel my career in hvac.

    i m going to be a mechanical engineer this year :smile: ,In my third academic year i studied a subject named as steam generation and steam turbine..that subject is awesome ..since i have strong background of thermodynamics i liked it very much and got highest marks.its my final year now..and i m...
  38. B

    HVAC in a welding/machine shop

    Hiya I need to spec up a ventilation system for a small welding and machine shop. The area will have ten welders, one large vertical machining centre, a bunch of small machine tools and things like air compressors, heat treatment, small(ish) cranes and air compressors etc. My question is...
  39. V

    Questions for all of you HVAC massters,

    Questions for all of you HVAC massters, please help:) Hi, I would like to know couple of things ?:) 1. With U shaped manometer attached to the surface of the pipe we are measuring static pressure drop? Pressure exerted by the water on the surface of that pipe? Am i right ? 2. Is that...
  40. J

    Can misting systems improve HVAC efficiency?

    Hi Guys, I'm fairly new here, but I can't solve my problem (or I did but than I found a miracle) I'm trying to optimize a HVAC system, especially for dry and hot areas. Now I was thinking about the use of a misting system in front of the condensor as done by for instance these guys...
  41. F

    What are the key considerations for designing a chilled water system?

    Hi. Im a post graduate student but worked in the HVAC industry for almost 3 years but mostly done refrigeration and VRV systems which i designed etc... Had done some minor chilled water system designs but never got to the construction phase. Have a couple of questions and looking for some...
  42. P

    Understanding HVAC Dampers and Flow Rates

    Hello guys, I recently got an internship at a engineering consultant firm doing HVAC work. I am kinda confuse on one thing. How does HVAC dampers work? I have always learned in school the continuity equation Q=AV=AV , Q = the volumetric flow rate A = the cross sectional area of flow V...
  43. J

    Engineering How to Transition from an Application Engineer HVAC to an HVAC Design Engineer?

    I got a job as an Application Engineer HVAC.My duties include assisting the sales team,preparing tenders and conducting selection of AHU's.Please tell me the steps i have to take inorder to become an HVAC design Engineer.
  44. P

    HVAC - help designing dehumidification system

    Hi, I am trying to design a "dehumidification system" for my home; I use quotes because this not really much of system, I am simply deciding what rating of a portable dehumidifier to buy! This is my first real world HVAC application and I wanted to know if what I am doing really makes sense...
  45. A

    HVAC Calculation: Learn About CFM, BTU/HR, TMBH & SMBH

    Dear all I am working in MEP field but no experience so I need your helps how find out an area cfm calculation and what is the ton of Ac given, what is the power how to find this calculation .. BTU/HR - British Thermal Unit /Hr...
  46. D

    Where can I find resources for becoming an HVAC engineer?

    Hey all, I am beginning my first job out of college this coming January. I will be working for an architectural/engineering firm as an entry level mechanical engineer designing HVAC systems. I have interned with them for two summers so the company is not completely foreign to me. However, I'd...
  47. JaredJames

    What Can I Expect in an HVAC Industrial Placement?

    Right, not sure where this should go exactly but feel free to re-locate if necessary. I'm starting a placement as a student engineer in July with a company which specializes in HVAC for industry. I am currently doing a degree in Aerospace Engineering (BEng Hons). Basically, all I want to...
  48. Moonbear

    Shivering with the thermostat set to 75 F HVAC question

    This question occurs to me from time to time, but I never remember to ask it. When HVAC systems are designed, does anyone bother to take into account "wind chill factor?" I've been feeling about ready to freeze to death in my office for quite some time, in spite of the thermostat being set for...
  49. G

    Can Tracking Degree Days Help Improve Energy Efficiency for HVAC Systems?

    As I fine tune our VAV HVAC system (506,000 sq.ft. facility), we'd like to determine the effectiveness of our adjustments over time. As we both heat and cool portions of the building at the same time (electric VAV reheat), we need to apply degree days to the analysis. How is that done...
  50. Cyrus

    Thermo -- Airflow Analysis for Heating Ducts in an HVAC system

    2-48) The 60-W fan of a central heating system is to circulate air through the ducts. The analysis of the flow shows that the fan needs to raise the pressure of air by 50Pa to maintain flow. The fan is located in a horizontal flow section where the diameter is 30cm at both inlet and outlet...