MEP Systems in a High-Rise Building ✅️ basically all the main technical systems inside a tall building. MEP = Mechanical + Electrical + Plumbing (plus Fire & Safety). 🔵 1. Mechanical System (HVAC / Cooling) 👉 Used for air conditioning & ventilation Cooling Towers (roof) → remove heat from building Chillers → make chilled water FCU / AHU / Air Handling Units → supply cool air Fan Coil Units → room cooling Ducting & air distribution 👉 Purpose: Cooling, ventilation, indoor comfort 🟡 2. Electrical System 👉 Power supply & distribution Transformers → voltage change UPS Room → backup for critical loads Switchboards / Panels Cable risers Lighting & sockets Generator → power backup 👉 Purpose: Provide electricity safely 🔴 3. Fire Fighting System 👉 Safety during fire Sprinklers Fire pumps Fire water tanks Hose reels & hydrants Fire alarm system 👉 Purpose: Detect + control fire 🔵 4. Plumbing System 👉 Water supply & drainage Overhead water tank Booster p...
Gul Bahar Shah
Gul Bahar Shah
VAV Box vs. CAV Box – What’s the Difference?
When a single AHU supplies multiple rooms, you need a way to control airflow and temperature independently for each space.
That’s where VAV Boxes and CAV Boxes come in.
->VAV Box (Variable Air Volume)
The core idea of a VAV box is simple:
It controls the airflow rate entering the space to maintain the desired temperature.
-> How It Works:
Airflow rate = Damper opening area × Air velocity
The damper modulates between minimum and maximum positions
It responds to signals from a thermostat or BMS
In some applications, a reheat coil is added to warm the air if the room becomes too cold
A sound attenuator may also be installed to reduce noise
📍 Typical Applications:
Offices, meeting rooms, hotel rooms, and any occupied spaces requiring precise temperature control.
-> CAV Box (Constant Air Volume)
Unlike VAV, a CAV box maintains a constant airflow rate, regardless of pressure variations in the duct system.
-> How It Works:
A pressure sensor monitors the duct pressure upstream of the damper
If pressure increases → the damper closes slightly
If pressure decreases → the damper opens
The goal: Keep airflow constant
A heating coil can also be added if needed
📍 Typical Applications:
Entrances, lobbies, corridors, restrooms, service areas, mechanical rooms, and greenhouses where consistent ventilation is more critical than precise temperature control.
💰 One additional advantage:
CAV boxes are generally more cost-effective than VAV boxes.
Important Notes:
1️⃣ Box vs. System
A CAV system maintains constant airflow from the AHU.
A VAV system varies airflow using a VFD/VSD based on the pressure difference between supply and return ducts.
If an AHU serves only one zone, a VAV box is typically unnecessary.
2️⃣ Why Use a CAV Box in a VAV System?
As VAV boxes modulate, they change the duct static pressure.
This affects the differential pressure sensor (DPS), which in turn adjusts the AHU fan speed.
However, some spaces require continuous, stable ventilation regardless of system fluctuations.
In such cases, a CAV box ensures constant airflow within a VAV system.
Conclusion
VAV Box = Flexibility & Precise Temperature Control
CAV Box = Stability & Consistent Ventilation
Both play essential roles in modern HVAC system design — and often complement each other.
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That’s where VAV Boxes and CAV Boxes come in.
->VAV Box (Variable Air Volume)
The core idea of a VAV box is simple:
It controls the airflow rate entering the space to maintain the desired temperature.
-> How It Works:
Airflow rate = Damper opening area × Air velocity
The damper modulates between minimum and maximum positions
It responds to signals from a thermostat or BMS
In some applications, a reheat coil is added to warm the air if the room becomes too cold
A sound attenuator may also be installed to reduce noise
📍 Typical Applications:
Offices, meeting rooms, hotel rooms, and any occupied spaces requiring precise temperature control.
-> CAV Box (Constant Air Volume)
Unlike VAV, a CAV box maintains a constant airflow rate, regardless of pressure variations in the duct system.
-> How It Works:
A pressure sensor monitors the duct pressure upstream of the damper
If pressure increases → the damper closes slightly
If pressure decreases → the damper opens
The goal: Keep airflow constant
A heating coil can also be added if needed
📍 Typical Applications:
Entrances, lobbies, corridors, restrooms, service areas, mechanical rooms, and greenhouses where consistent ventilation is more critical than precise temperature control.
💰 One additional advantage:
CAV boxes are generally more cost-effective than VAV boxes.
Important Notes:
1️⃣ Box vs. System
A CAV system maintains constant airflow from the AHU.
A VAV system varies airflow using a VFD/VSD based on the pressure difference between supply and return ducts.
If an AHU serves only one zone, a VAV box is typically unnecessary.
2️⃣ Why Use a CAV Box in a VAV System?
As VAV boxes modulate, they change the duct static pressure.
This affects the differential pressure sensor (DPS), which in turn adjusts the AHU fan speed.
However, some spaces require continuous, stable ventilation regardless of system fluctuations.
In such cases, a CAV box ensures constant airflow within a VAV system.
Conclusion
VAV Box = Flexibility & Precise Temperature Control
CAV Box = Stability & Consistent Ventilation
Both play essential roles in modern HVAC system design — and often complement each other.
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