HVAC Actuator – Site Installation Update HVAC actuators are essential components in modern building systems, responsible for precise control of dampers and valves to regulate airflow and maintain optimal indoor environmental conditions. Proper installation and calibration of actuators ensure efficient system performance, improved energy management, and reliable operation within the HVAC network. As part of the ongoing HVAC works on site, the actuator installation and functional checks were carried out to ensure accurate damper control and seamless integration with the control panels Committed to delivering quality HVAC installations and ensuring efficient building services performance. hashtag Activate to view larger image, Activate to vi
Gul Bahar Shah
Gul Bahar Shah
FCU Coil and Duct Humidity (Moisture) & Water Condensation Problem
1. What is Condensation?
When a cold surface (like a coil, duct, or diffuser) temperature drops below the room’s dew point temperature, the moisture present in the air turns into water droplets.
This is called condensation or sweating.
Example:
If room dew point = 16°C
And duct surface temperature = 14°C
Then water droplets will definitely form.
2. How Does Condensation Occur in an FCU Coil?
✓. Normal Condition
Chilled water temperature in FCU coil = 7–12°C
Warm air passes over the coil
Moisture turns into water
Water collects in drain tray
Water goes out through drain pipe
This is normal operation.
What is FCU Coil Block Problem?
When the Fan Coil Unit (FCU) cooling coil gets blocked due to dust, dirt, sludge, or scale, airflow or water flow becomes disturbed.
Two Main Reasons for Blockage:
1. Air Side Blockage
Dust accumulates on coil fins
Filter becomes dirty
Airflow reduces
When Does the Problem Occur?
1. High Humidity
Too much fresh air coming from outside
Exhaust system not balanced
Doors opening frequently
Indoor humidity above 60%
More humidity = more sweating.
2. Very Low Supply Air Temperature
Chilled water temperature below 6°C
Supply air temperature below 10°C
In this case, duct surface temperature drops below dew point, and water appears on diffuser
3. Damaged Insulation
Torn duct insulation
Broken vapor barrier
FCU body not insulated
When warm humid air touches a cold surface, external sweating occurs.
4. Air Leakage
Gaps in plenum
Loose duct joints
Gaps around diffuser
Warm humid air enters and touches cold surface → condensation forms.
5. Drain Line Problem
Drain pipe choked
Wrong slope
No P-trap installed
Water will overflow and may damage the ceiling.
3. Special FCU Coil Problems
Low airflow → ice formation on coil
High velocity → water carries into duct
Dirty coil → uneven cooling
No P-trap → water stays inside
4. Where Does Duct Sweating Commonly Occur?
Above ceiling (plenum area)
Toilet area
Near kitchen
Basement
Near fresh air duct
High humidity locations
5. Simple Dew Point Example
Room temperature = 24°C
Humidity = 60%
Dew point ≈ 15–16°C
If duct surface temperature becomes 14°C,
sweating is confirmed.
✓ Chilled Water Control
Supply water = 7°C
Return water = 12°C
Maintain Delta T ≈ 5°C
✓ Proper Insulation
Use 25mm or 40mm insulation
Seal all joints properly
Maintain vapor barrier
Check aluminium cladding
✓ Drain System Check
Proper pipe slope
Install P-trap
Regular flushing
Avoid air lock
6. Quick Technician Checklist
✔ Check humidity
✔ Check supply air temperature
✔ Open and inspect insulation
✔ Check drain flow
✔ Perform smoke test for air leakage
7. Golden Rule
If surface temperature is above dew point → No sweating
If surface temperature is below dew point → Sweating will occur
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When a cold surface (like a coil, duct, or diffuser) temperature drops below the room’s dew point temperature, the moisture present in the air turns into water droplets.
This is called condensation or sweating.
Example:
If room dew point = 16°C
And duct surface temperature = 14°C
Then water droplets will definitely form.
2. How Does Condensation Occur in an FCU Coil?
✓. Normal Condition
Chilled water temperature in FCU coil = 7–12°C
Warm air passes over the coil
Moisture turns into water
Water collects in drain tray
Water goes out through drain pipe
This is normal operation.
What is FCU Coil Block Problem?
When the Fan Coil Unit (FCU) cooling coil gets blocked due to dust, dirt, sludge, or scale, airflow or water flow becomes disturbed.
Two Main Reasons for Blockage:
1. Air Side Blockage
Dust accumulates on coil fins
Filter becomes dirty
Airflow reduces
When Does the Problem Occur?
1. High Humidity
Too much fresh air coming from outside
Exhaust system not balanced
Doors opening frequently
Indoor humidity above 60%
More humidity = more sweating.
2. Very Low Supply Air Temperature
Chilled water temperature below 6°C
Supply air temperature below 10°C
In this case, duct surface temperature drops below dew point, and water appears on diffuser
3. Damaged Insulation
Torn duct insulation
Broken vapor barrier
FCU body not insulated
When warm humid air touches a cold surface, external sweating occurs.
4. Air Leakage
Gaps in plenum
Loose duct joints
Gaps around diffuser
Warm humid air enters and touches cold surface → condensation forms.
5. Drain Line Problem
Drain pipe choked
Wrong slope
No P-trap installed
Water will overflow and may damage the ceiling.
3. Special FCU Coil Problems
Low airflow → ice formation on coil
High velocity → water carries into duct
Dirty coil → uneven cooling
No P-trap → water stays inside
4. Where Does Duct Sweating Commonly Occur?
Above ceiling (plenum area)
Toilet area
Near kitchen
Basement
Near fresh air duct
High humidity locations
5. Simple Dew Point Example
Room temperature = 24°C
Humidity = 60%
Dew point ≈ 15–16°C
If duct surface temperature becomes 14°C,
sweating is confirmed.
✓ Chilled Water Control
Supply water = 7°C
Return water = 12°C
Maintain Delta T ≈ 5°C
✓ Proper Insulation
Use 25mm or 40mm insulation
Seal all joints properly
Maintain vapor barrier
Check aluminium cladding
✓ Drain System Check
Proper pipe slope
Install P-trap
Regular flushing
Avoid air lock
6. Quick Technician Checklist
✔ Check humidity
✔ Check supply air temperature
✔ Open and inspect insulation
✔ Check drain flow
✔ Perform smoke test for air leakage
7. Golden Rule
If surface temperature is above dew point → No sweating
If surface temperature is below dew point → Sweating will occur
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