Revit MEP Tutorial-3
Revit MEP (HVAC GRD Placement & CFM Calculation Tuotorial-3)
Revit MEP is a very advanced tool to design HVAC systems So, Revit 2025 Is most Latest version. First, in this Tutorial of Revit MEP we calculate CFM manually for Revit MEP using ASHRAE Standards. Then, we Learn how we can place grills, registers, and diffusers at Revit MEP.
What is GRDs in HVAC systems?
In HVAC (Heating, Ventilation, and Air Conditioning), GRDs stands for Grills, Registers, and Diffusers. These components are central to the system, as they manage how air is dispersed into a room after it has been conditioned. They all work together for the system to operate properly by making sure that air does not stagnate in a room or building.
These components are important in controlling how the airflow produced by the HVAC machine is distributed throughout the building or room, ensuring comfort and good air quality. In this article, we will discuss these components in detail one by one:
Grills (Air Grilles)
A grill is a form of preventing an air vent from being blocked without restricting the flow of air. It lacks means to control the airflow such as dampers, screens or louvers; hence it has no moving components at all.
Purpose: Grills serve as an opening for air to flow into a space. They open and allow air to move, but do not control the amount of air going into a controlled area.
Design: Grill construction usually employs metal like steel, aluminum, or plastic. These parts are installable on walls, ceilings, and floors as long as there is a designated zone for the entrance or discharge of air from the HVAC system.
Functionality: Unlike grills, dampers and adjustable mechanism may block or limit filtration in registers. They can be used, however, in systems that do not need air control or need air control executed somewhere else. A case in point, grills are used in air return ducts where air is allowed to stream into the HVAC system for treatment.
Key Characteristics: An open square frame with no airflow control feature. Has no airflow control features. Found in place in return air ducts.
Registers
Like grills, registers also have an opening, but it is fitted with a shutter or adjustable air louvers that can change the air flow direction and restrict it to a certain extent so as to maximize or minimize the amount of air passing through the register.
Purpose: Registers are designed for allowing air to flow into a room while allowing a certain amount of control over the volume of air that is permitted to exit the room. The damper/louver system may also be manually set to limit the amount of air taking the stream or step the flow up to a certain level.
Design: Registers come up in a design where gratings are applied, but unlike grills, they are fitted with the adjustable means such as dampers or louvers which may stop the flow If air is a pressure. Thus the airflow direction and amplitude can be controlled.
Purpose: The registers are placed at the supply air ducts of the HVAC system. Registers usually are found in areas or spaces where fine-tuning the temperature or air supply in accordance with the controlled conditions is necessary.
Diffusers
In appliance, diffusers refers to devices used for the purpose of air diffusion. The air is evenly diffused across the room or space using diffusers and the appliance is most often installed at the mouth of the supply ducts where they are designed to diffuse air without causing drafts or hot/cold pockets of air.
Purpose: Armicrographia’s primary purpose is to perform air diffusion and therefore armicrographia cubs are created for the purpose of avoiding an unequally heated or cooled part of room. This helps in ensuring comfort in the area and aids in fulfilling the desired conditions.
Design: diffusers can be relatively square, round or rectangular. Most often, diffusers are constructed with a multi-directional air discharge which enhances the air circulation in the space and leads to increased comfort in the area. Air circulation diffusers and fans are built with adjustable vanes for controlling the direction of air flow.
Functionality: Most commonly, diffusers are placed in the ceiling or high wall areas so that they can be used to cover large areas with open airflow easily. Both residential and commercial HVAC systems make use of these appliances in open areas like offices or shops form where they are used to diffuse air at all times.
Main Features:
Helps maintain a room's temperature by distributing air uniformly.
Reduces the air hot or cold circulation in the room.
Most commonly fixed at the termination point of the supply duct.
Enhances the comfort level within the surrounding atmosphere.
Area Calculation
Select Space 1
in Revit 2025 click or Select the space 1
Area : 2485 Square Foot
Height : 8 foot
volume : 19880 CUFT
Space 1
Select Space 2
in Revit 2025 click or Select the space 2
Area : 2485 Square Foot
Height : 8 foot
volume : 19880 CUFT
Space 2
Select Space 3
in Revit 2025 click or Select the space 3
Area : 2803 Square Foot
Height : 8 foot
volume : 22424 CUFT
Space 3
CFM Calculation
Placement of Diffuser in Space 1
Space 1 is Domestic Room
As per ASHRAE Standards Air Changes per Hour (ACH) typically ranges between 4 to 6 ACH.
CFM=ACH × Room Volume/60
CFM = 5 x 19880 /60
CFM = 1656
if We Place 5 Diffusers then the CFM Value of each Diffuser is 332
Step 1
1-Select Air Terminal
2- Write Elevation of Space 8 feet
Step 2
1- Select Type of Diffuser
2 Writ Flow Rate
3 Calculate and Write Length and Width Diffuser
Recommended Velocity = 600FPM
Area of Diffuser=Q/V = 332 /600 =0.5533 SQFT= 0.5533x144 SQIN= 80 SQIN
so, 9x9 Diffuser
Step 3
Place 5 Diffuser in Space 1
Space 2
Space 2 is Exercise Room or gymnasium
ASHRAE's Standard 62.1, "Ventilation for Acceptable Indoor Air Quality," provides guidelines for ventilation rates in various indoor spaces. For gymnasiums, the standard recommends a minimum outdoor airflow rate of 0.18 cubic feet per minute (cfm) per square foot of floor area, plus an additional 7.5 cfm per person. This translates to approximately 4 to 6 air changes per hour (ACH), depending on occupancy and room dimensions.
CFM=ACH× Room Volume/60
CFM = 6 x 19880 /60
CFM = 1988
if We Place 6 Diffusers then the CFM Value of each Diffuser is 332
Area of Diffuser=Q/V = 332 /600 =0.5533 SQFT= 0.5533x144 SQIN= 80 SQIN
so, 9x9 Diffuser
Space 3
Space 3 is Domestic Room
As per ASHRAE Standards Air Changes per Hour (ACH) typically ranges between 4 to 6 ACH.
CFM=ACH × Room Volume/60
CFM = 5 x 22424 /60
CFM = 1868
if We Place 6 Diffusers then the CFM Value of each Diffuser is 312
Area of Diffuser=Q/V = 312 /600 =0.52 SQFT= 0.52 x144 SQIN= 74 SQIN
so, 9x8 Diffuser we select 9 x 9
