HVAC

HEAT VENTILATION AND AIR CONDITIONING

IMPORTANT TERMS
DUCT
A TUBE OR PASSAGEWAY IN A BUILDING OR MACHINE FOR AIR, LIQUIDS AND CABLES ETC.
DAMPER
A DAMPER IS A VALVE ,VANES OR PLATE THAT STOPS OR REGULATES THE FLOW OF AIR INSIDE A DUCT, CHIMNEY, VAV BOX, AIR HANDLER OR OTHER HANDLING EQUIPMENT.
A DAMPER MAY BE USED TO CUT OFF CENTRAL AIR CONDITIONING TO AN UN-USED ROOM OR TO REGULATE IT FOR ROOM BY ROOM TEMPERATURE AND CLIMATE CONTROL.
FIRE DAMPER
FIRE DAMPER ARE PASSIVE FIRE PROTECTION PRODUCTS USED IN HEATING, VENTILATION AND AIR CONDITIONING, DUCTS TO PREVENT THE SPREAD OF FIRE- RESISTANCE RATED WALLS AND FLOORS.
VAV  (VARIABLE AIR VOLUME )
VAV IS A TYPE OF HVAC SYSTEM. VAV SYSTEM VARY THE AIR FLOW AT A CONSTANT TEMPERATURE.
CAV (CONSTANT AIR VOLUME )
CAV SUPPLY A CONSTANT AIR FLOW AT A VARIABLE TEMPERATURE.
LOUVER
A LOUVER IS A WINDOW BLIND OR SHUTTER WITH HORIZONTAL SLOTS THAT ARE ANGLED TO ADMIT LIGHT AND AIR BUT TO KEEP OUT RAIN, DIRECT SUNSHINE AND NOISE. THE ANGLE OF SLOTS MAY BE ADJUSTABLE OR FIXED.
PLENUM
IN BUILDING CONSTRUCTION A SEPARATE SPACE PROVIDED FOR AIR CIRCULATION FOR HVAC AND TYPICALLY PROVIDED IN THE SPACE BETWEEN THE STRUCTURAL CEILING AND A DROP DOWN CEILING.
BTU ( BRITISH THERMAL UNIT)
ONE BTU IS THE ENERGY REQUIRED TO RAISED ONE POUND OF WATER TO ONE DEGREE FAHRENHEIT. 
1 POUND = 0.453592 KG
1 KG = 2.20462 POUNDS
CHILLER 
A DEVICE WHICH REMOVES HEAT FROM A LIQUID VIA A VAPOR- COMPRESSION OR ABSORBS ION REFRIGERATION CYCLE.
THIS COOLED LIQUID FLOWS THROUGH PIPES IN A BUILDING PASSES THROUGH COILS IN AIR HANDLER. COOLING AND USUALLY DEHUMIDIFYING THE AIR IN THE BUILDING. CHILLER CAN BE EITHER AIR OR WATER COOLED.
PSYCHOMETRIC
THE STUDY OF THE BEHAVIOR OF AIR WATER- VAPOR MIXTURES. WATER PLAY AN IMPORTANT ROLE IN ENERGY TRANSFER AND HUMAN COMFORT IN HVAC DESIGN.

Principles of HVAC System

The following factors determine the capacity of HVAC system.

1. Heating: The amount of thermal energy that needs to be added to the space.
2. Cooling: Thermal energy will sometimes need to be removed from a particular space in order to bring the temperature down.
3. Humidifying: The process of increasing the relative humidity through the addition of water vapor into the system.
4. Dehumidifying: Process of removing water vapor from the given space.
5. Cleaning: Purifying the air by the removal of dust, smoke, pollen and other pollutants.
6. Air Movement: Ensuring that there is movement of air to keep the inhabitants comfortable

A chart known as the Psychometric chart is very useful in understanding how these different factors interact with each other. This chart is integral in performing the calculations that determine the type of system required.
Removal of Heat form an HVAC system:
There are many methods to remove heat form a building. It is a common misconception that air conditioners are the only option. A heat pump can also be used which offers many advantages to a traditional AC. The different types of ACs that can be used are direct expansion, chilled water, split and window.
Components of an HVAC system
There are three main components to any HVAC system. These are the air handler, heating & cooling system and the heat exchanger. A furnace of some sort is usually used as the basic heating component. The air conditioning system will be slightly more advanced with a number of smaller sub-components.
Heat exchangers come in a number of different types and models. The design depends on the application of the heat exchanger. The basic functioning is that of exchanging heat between two fluids without their mixing.
The refrigerants
The refrigerant gas is the most important part of an air conditioning system. Most ACs work on the principles of compression and expansion of the refrigerant. The gas becomes very cold when it is compressed. Then it is sprayed on to the walls of the heat exchanger. R-12 is the primary refrigerant used in air conditioning. Recently though it is being phased out in favor of the R-34a.
This is just a basic overview of the many different components of a HVAC system. As you can imagine, the subject goes into far more depth and detail. However this should be a good starting point for any aspiring engineer.

Is your Air Conditioner not cooling properly?

Many factors can cause your air conditioning system to resist cooling your rooms, but these are the most common:

 Improper Installation

Was your air conditioning system recently installed yet it isn’t cooling as it should be? If so, your AC may have been installed incorrectly, or the unit could be too big or too small for your home.

Solution: It is important to get a second HVAC team out to look at your system because the first group did not do something correctly.

Unmaintained Condenser Unit

One of the most overlooked aspects of AC maintenance is taking care of the condenser outside. Your condenser needs to have good airflow at all times…but it’s outside. That means that weeds and grass are always growing around it.

Solution: First, be sure to regularly maintain the lawn (or nature) around your condenser. You will want to use a weed wacker and keep the growth clear of the equipment so it can work at its best.

Even if there’s no grass around the condenser, keep in mind that this piece of machinery is sitting outside all day, it’s still getting dirty. If there are trees around your condenser, debris may fall from above inside the casing of the condenser.

If you haven’t cleaned out your condenser in over a year, this could be the cause of your AC not cooling.

 Insufficient Airflow

If there isn’t enough air coming through your vents, then it doesn’t matter how cold your AC makes the air — you’ll just never feel cooler! How do you know if there’s enough air blowing?

Solution: You can get a lighter and hold it up in the direct flow of air from the vent. You’ll want to do this across your entire home, making sure that the vents furthest away from the HVAC unit also have good air flow.

What should you do if the airflow is too low? First, check your air filter. If it’s dirty, replace the air filter and repeat this test. If you still aren’t getting the results you want, it may be time to contact an HVAC company to perform a duct cleaning for you and to examine your AC’s fan for any potential problems.In one room, start with the flame close to the vent and move progressively farther away until it stops wavering. You should be able to make it to the opposite end of the room from the vent and still have an effect on the flame  especially in rooms close to the HVAC unit. The flame is less likely to waver across a room that is far away from the unit, but ideally, you would still be able to make it to the other side.

 Electrical Issues

Sometimes a breaker can be tripped, but it doesn’t flip into the “OFF” position.

Solution: You can look for the breakers (there are usually two or three) labeled something along the lines of HVAC, AC, Air Conditioner, Condenser or Compressor. Flip them off, then back on again and see if this gets your AC working properly.

Thermostat Issues

Another common, but difficult to spot issue is a problem with the thermostat.

The batteries could die, the circuitry inside can malfunction, and a host of other failures can happen to a thermostat without drawing a lot of attention. It’s not as dramatic as some sudden clanging noise or grinding.

Is the face of your thermostat blank? That’s one telltale sign that something inside has malfunctioned.

Solution: You can try to change the batteries yourself and see if this remedies your problem. If it doesn’t, a licensed HVAC professional can further troubleshoot this issue for you.

Sometimes the inside electrical board can be replaced, other times the repair involves installing a new thermostat. Even if you consider yourself fairly handy, you should have a licensed HVAC professional install a thermostat for you due to the nature of the wiring being tied to your AC unit.

This could especially be your problem if you are dealing with a home with multiple conditioning zones.

 Frozen Air Handler

If none of these solutions have taken care of your AC’s cooling problem, look behind your air filter inside the unit’s evaporator coils.

Are they frozen?

It sounds a little weird, but yes, if your AC is frozen it will cause the air to be too hot. The ice will block the air inside of your home from coming into contact with the refrigerant of the evaporator coils, preventing the air from being cooled and also preventing your AC from dehumidifying the air.

Solution: If your AC is frozen, turn it off. You’ll need to allow it about 24 hours to defrost and dry out before you attempt to use it again (sorry if this happened to you in the summer!).

Going through the above steps, you would have already resolved most of the common reasons for an AC freeze. An additional step you could take to try to remedy an AC freeze is to look at the evaporator coils after they are defrosted. Are they dirty?

If they are dirty, try cleaning them.

Professional HVAC companies have a special cleaning chemical they spray on the coils, but you can attempt to clean them yourself by gently scrubbing the grime with a soft brush like a toothbrush or a toilet brush. You want to be careful not to bend the fins or the coils at all.

If the grime isn’t coming off, you can attempt to use some water to loosen the grime as well.

If you’re not making much progress, you’ll want to get an HVAC technician out to service your unit right away for a more thorough cleaning.

 Low Refrigerant

One of the main causes of your AC not cooling is a low refrigerant level. Refrigerant is necessary to produce cool air.

Solution: A licensed HVAC professional will have the proper equipment to measure the levels inside of your unit, and a method to properly dispose of the used refrigerant.