How to Read HVAC Drawings 3: Air Conditioning System


I learned to read different kinds of HVAC drawings through years of working in the HVAC industry. I thought if junior engineers are able to know how to read HVAC drawings earlier, they are able to come out with a better HVAC system. So, I decided to create a course with a series of posts to explain how to read HVAC drawings.

In this course, I have 5 posts on how to read HVAC drawings. These 5 posts are:

  1. Title block & symbols
  2. Ventilation system
  3. Air conditioning system
  4. Control panel diagram
  5. Section, schematic & elevation drawings

In this post, you’ll learn how to read the common symbols, shapes and acronyms used in the air conditioning system drawing. Although the ductwork used for air conditioners is similar to the ductwork used for ventilation fans, it has a few important designs to consider for air conditioning.

Navigation Guide

I’ll be zooming in to different sections of an office floor ducted air conditioning shop drawing for the explanation. So, you can refer to the below full drawing to navigate around.


Equipment Tag Name and Details

Similar to ventilation fans, air conditioning units also have a tag name and a few details written on shop drawings. Details included in the drawing are as follow:

Tag name > Brand > Model > Cooling Capacity > Airflow > Static Pressure > Weight

However, if the drawing is too congested, some of the details may be excluded. In the above drawing, the most important tag name, capacity and airflow are included only.

The tag name follows the same principle covered in the previous course about the ventilation system. Every major piece of equipment should have a tag name including control panels.

AHU stands for air handling unit while FCU stands for fan coil unit. If CHW is added before AHU/FCU, the whole thing stands for chilled water fan coil unit.

Common acronyms used for air conditioners are as follow:

AcronymDescription
AHUAir Handling Unit
FCUFan Coil Unit
CHWChilled Water
CWCondenser Water
IDUIndoor Unit
ODUOutdoor Unit
CHWPChilled Water Pump
CWPCondenser Water Pump
VRVVariable Refrigerant Volume
VRFVariable Refrigerant Flow (same as VRV)
Acronyms for Air Conditioners

The unit of measurement for cooling capacity is mostly btu/hr or British Thermal Unit per Hour. However, some people prefer to use other units of measurements.

Basically, there are only 4 units of measurements for cooling capacity:

  • btu/hr or BTU = British Thermal Unit per Hour
  • RT or Ton = Refrigeration Ton (1 RT is 12,000 btu/hr)
  • kW = kilo Watt (1 kW is 3,412 btu/hr)
  • HP = horsepower (1 HP is ~9000 btu/hr)

Including the equipment dimension and weight is very handy if you have sufficient space in the drawing. Installers need the dimension and weight when handling the logistic and positioning of the equipment.

Notice that the control panel has an additional “above ceiling” indicating that it should be installed above the ceiling rather than below the ceiling. At the same time, it is assumed that you know to put a ceiling manhole under the control panel for service and maintenance.

Rigid Duct, Fittings and Flexible Duct

Similarly, the duct size, duct reducer and guide vane are being drawn the same way as the ductwork of the ventilation system. However, there are a few new terms used in the air conditioning system.

Common acronyms used for the air conditioning system:

AcronymDescription
SASupply Air
RAReturn Air
SADSupply Air Duct
RADReturn Air Duct
FADFresh Air Duct
Acronyms for Air Conditioning Duct

Flexible ducts are drawn in the shape shown in the above drawing. If a rigid duct is drawn very close to a grille without a flexible duct, it means that NO flexible duct is used but only rigid ducts.

For the air conditioning duct, the duct sizes indicated are excluding the duct insulation. Hence, if you are determining anything related to how much the duct occupied the space, you need to refer and add the insulation thickness on top of the duct size indicated in the drawing unless otherwise specified.

Supply Air Diffusers and Return Air Grilles

If you look closely, some grilles are attached to a flexible duct while some grilles don’t. Those grilles that have a flexible duct attached are supply air diffusers. Grilles without a flexible duct are return air grilles.

Some of the common acronyms used for grilles are:

  • SAG = Supply Air Grille
  • SAD = Supply Air Diffuser
  • RAG = Return Air Grille

Based on the layout of the supply air diffusers and return air grilles in the above drawing, we know that this system is designed to use the entire ceiling as a return air plenum space for the air handling unit.

Furthermore, there is an entire stretch of ceiling return plenum opening near the exterior wall to allow cold air to return back to the air handling unit, moving through the space above the ceiling. At the same time, the cold air also returns back to the air handling unit via the return air grilles.

Dampers and VAVs

Dampers used for air conditioning system is the same as the ventilation system. Here, we have a VAV or Variable Air Volume which is a box that controls the amount of supply air to a particular space.

Typically, VAVs required straight duct clearance (about 600mm) in the front and back. As you can see in the above drawing, sufficient space is allowed before putting the VAV.

Tags beside the VAV such as C2, G2 and A2 are just a name given to each type of VAV for us to read better and avoid installing the wrong one since VAVs look more or less the same from the outside.

Duct Internal Insulation

From the above drawing, you can see that there is a dotted line drawn inside air conditioning ducts. The dotted line starts from the air conditioner and covers only a small section of the duct.

These indicate that insulations are needed inside the duct. Duct internal insulation is required to reduce the noise transmitted from air conditioners to the office space through the duct.

Chilled Water and Condensate Pipes

Air conditioning pipes can be drawn in several forms. The most common one is the dotted line as shown in the above drawing. Lines with circles are often used for condensate pipes. Nevertheless, there is no fixed rule and you can always refer back to the legend to confirm.

Control Panel and Thermostat

Most control panels are drawn as shown in the above drawing. Some people may not color half of the rectangular but they are generally shaped as a rectangular box with a diagonal line. As for thermostats, they always have the word “T” whether is inside a circle or a square.

In the above drawing, each thermostat corresponds to one VAV. Hence, there are many thermostats shown in the drawing. Typically, there is only one thermostat for one air conditioner.

Ceiling Manholes

I would suggest everyone to include square-shaped ceiling manholes in their shop drawings where necessary. Many times, people miss out on ceiling manholes. Later, they have arguments due to heavy variation orders from the ceiling contractor. Sometimes, the arguments end up with ceiling manholes get voided, causing a lot of problems for future maintenance.

Design Engineer Starter Pack

Many junior engineers often don’t get enough support from their seniors, managers and bosses. Back when I was a fresh graduate, I had no idea what I was doing. I wish someone had given me guides especially on design work.

Hence, I started to work on some gsheet/excel calculators, diagrams and charts and then, I packaged them together to create the Design Engineer Starter Pack (click to view details) to help Junior Design Engineers with their HVAC design work.

I think it will be great if you have it. So, I encourage you to check it out.

Yu Chang Zhen

Yu was working in the air conditioning industry for the past 7 years, covering from design to installation and maintenance. Yu wish to share all the things he learned with the people around the world.

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