MEP Engineer’s Diary

MEP Engineer’s Diary Real MEP engineering knowledge | HVAC | Plumbing | Electrical | Site experience & design tips.

AC Motor vs DC Motor – What’s the Difference?⚡ AC Motor• Runs on Alternating Current• Used in fans, compressors, pumps• ...
15/03/2026

AC Motor vs DC Motor – What’s the Difference?

⚡ AC Motor
• Runs on Alternating Current
• Used in fans, compressors, pumps
• Low maintenance

🔋 DC Motor
• Runs on Direct Current
• Speed control is easier
• Used in small devices & electronics

In HVAC systems, AC motors are commonly used for fans and compressors.









14/03/2026

Cutting HVAC copper pipes using an oxy-acetylene gas torch 🔥🔧
Precision work for refrigerant piping installation.

🔧 3-Phase Kitchen Exhaust Fan Electrical ConnectionIn commercial kitchens such as hotels and restaurants, kitchen exhaus...
14/03/2026

🔧 3-Phase Kitchen Exhaust Fan Electrical Connection

In commercial kitchens such as hotels and restaurants, kitchen exhaust fans play a critical role in removing heat, smoke, oil vapour, and odors generated during cooking. Most of these exhaust systems use three-phase motors to handle large air volumes efficiently.

⚡ Power Supply
A typical kitchen exhaust fan operates on:
• 400V, 3-Phase power supply
• Cable type: 4 Core cable (L1, L2, L3, Earth)

🔌 Standard Electrical Connection
The electrical connection normally follows this sequence:

Distribution Board (DB)
⬇
MCB / MCCB (Circuit Protection)
⬇
Local Isolator Switch
⬇
Contactor
⬇
Overload Relay (Motor Protection)
⬇
Kitchen Exhaust Fan Motor

This arrangement protects the motor from short circuits, overload, and electrical faults.

🛠 Motor Terminal Connection
Inside the motor terminal box, the connection is usually:
• L1 → U
• L2 → V
• L3 → W
• Earth → Motor Body

Most exhaust fan motors are connected in Delta (Δ) configuration for normal operation.

🔄 Fan Rotation Check
After wiring, always check the fan rotation direction.
The fan must rotate in the correct direction to properly exhaust air through the duct system.

If the rotation is wrong:
➡️ Swap any two phases (for example L1 and L2).

📌 Important Installation Tips
✔ Install a weatherproof isolator near the fan for maintenance.
✔ Ensure proper earthing for safety.
✔ Use appropriate cable size based on motor power.
✔ Verify fan rotation before commissioning.

Proper installation of the kitchen exhaust system ensures efficient ventilation, improved air quality, and safe kitchen operation.

⸻

⚙️ MEP Engineer’s Diary
Sharing practical HVAC and MEP knowledge for engineers and technicians.

13/03/2026

🔥 Oxygen–Acetylene Brazing in HVAC

In HVAC installations, copper pipes are joined using an oxygen and acetylene torch. This process creates a strong and leak-free joint that can handle high refrigerant pressure.

The torch produces a high-temperature flame (around 3000°C) which melts the brazing rod and bonds the copper pipes together.

✅ Commonly used for:
• VRF / VRV systems
• Split AC installations
• Chiller pipe connections

A proper brazing technique ensures strong joints, no refrigerant leakage, and long system life.

👷‍♂️ Every strong HVAC system starts with a perfect copper joint.

#

12/03/2026

Understanding HVAC copper pipe sizes is very important for proper refrigerant flow and system efficiency. 🔧❄️
Here are some common copper pipe sizes used in HVAC and VRF systems.

HVAC Copper Pipe Soldering Procedure 🔧In HVAC systems, copper pipe soldering (or brazing) is a very important step. Prop...
12/03/2026

HVAC Copper Pipe Soldering Procedure 🔧

In HVAC systems, copper pipe soldering (or brazing) is a very important step. Proper soldering ensures there are no refrigerant leaks and the system operates efficiently.

Here is the basic procedure technicians follow on site:

1️⃣ Cut the Copper Pipe
Use a pipe cutter to cut the copper pipe straight and clean.

2️⃣ Deburring
Remove the sharp edges inside the pipe using a deburring tool. This prevents damage to the refrigerant flow.

3️⃣ Clean the Pipe Surface
Clean the pipe and fitting using sand cloth or a wire brush. The surface must be shiny and free from dirt or oxidation.

4️⃣ Apply Flux (If Soldering)
Flux helps the solder flow properly and prevents oxidation during heating.

5️⃣ Assemble the Joint
Insert the copper pipe into the fitting properly before heating.

6️⃣ Heat the Joint
Use a gas torch to heat the joint evenly. Heat the fitting first, not directly the solder rod.

7️⃣ Apply the Solder/Brazing Rod
Touch the solder rod to the heated joint. The heat will melt it and allow it to flow into the gap.

8️⃣ Cooling and Cleaning
Allow the joint to cool naturally. Clean any excess flux or residue.

✅ A properly soldered joint will be strong, leak-free, and long-lasting.


❓ HVAC Quiz Time!Every HVAC engineer works with AHU systems, but do you know this basic question?👉 What is the main func...
12/03/2026

❓ HVAC Quiz Time!

Every HVAC engineer works with AHU systems, but do you know this basic question?

👉 What is the main function of an AHU fan?

Drop your answer in the comments and let’s see who really understands HVAC systems! 👇

💡 I will reveal the correct answer in the next post.


❄️ Difference Between VRF AHU and Chiller AHUIn HVAC systems, Air Handling Units (AHU) are used to distribute conditione...
11/03/2026

❄️ Difference Between VRF AHU and Chiller AHU

In HVAC systems, Air Handling Units (AHU) are used to distribute conditioned air to buildings. But the cooling source can be different. The two common types are VRF AHU and Chiller AHU.

🔹 VRF AHU
A VRF AHU is connected directly to a VRF outdoor unit using refrigerant copper pipes.
The cooling is produced by refrigerant flowing through an EEV kit (Electronic Expansion Valve) and cooling the air coil.

✔ Uses refrigerant (R410A / R32)
✔ Connected with copper pipes
✔ Good for hotels, offices, and medium-size buildings
✔ Easy installation compared to chilled water systems

🔹 Chiller AHU
A Chiller AHU works with a chilled water system.
Cold water from the chiller plant flows through the AHU cooling coil and removes heat from the air.

✔ Uses chilled water instead of refrigerant
✔ Connected with CHW supply and return pipes
✔ Used in large buildings, malls, airports, and hospitals
✔ Suitable for centralized cooling systems

⚙️ Simple Comparison

• VRF AHU → Cooling by Refrigerant
• Chiller AHU → Cooling by Chilled Water

Both systems are widely used in modern HVAC depending on the building size, energy efficiency, and system design.

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