HVAC engineers

Pressure Switches and Pressure Transmitters two common devices used in process control and automation.  thought this comparison would be useful, especially for those working with DCS/PLC systems or new to instrumentation. Pressure Switch 1. Works like a simple ON/OFF switch. 2. Provides a digital signal (either ON or OFF). 3. Activates or deactivates an electrical contact when the pressure crosses a pre-set limit. 4. Used for basic control applications (e.g., turning pumps or compressors ON/OFF). 5. Suitable where only a threshold action is required, not continuous monitoring. Pressure Transmitter 1. A more advanced pressure-measuring device. 2. Continuously measures the actual pressure value. 3. Provides a continuous analog output signal (typically 4-20 mA or 0-10 V). 4. Used in process control systems like DCS, PLC, or SCADA. 5. Essential for applications needing accurate, real-time pressure data. In Short Pressure Switch Only indicates if pressure is too high or too low (ON/OFF)...

 Air Balancing - A Key Step for Efficient HVAC Performance! Air balancing is one of the most critical procedures in HVAC systems to ensure proper air distribution, occupant comfort, and energy efficiency. What is Air Balancing? Air balancing is the process of testing, adjusting, and balancing (TAB) the airflow in an HVAC system to ensure every room receives the right amount of conditioned air as per the design specifications. It is an essential step after system installation or major modifications. Why is Air Balancing Important? Ensures thermal comfort for occupants Improves indoor air quality Reduces energy wastage and operational costs Prolongs the life of HVAC equipment Achieves system performance as per design intent Detailed Procedure for Air Balancing 1 Pre-Commissioning Checks Verify that the HVAC system installation is complete. Ensure ductwork is sealed, filters are clean, and all dampers/valves are accessible. Confirm that the system is running at design conditions. 2 In...

TESTING & COMMISSIONING (T&C) OF HVAC CHILLER ✅ Pre-Commissioning Checks ✔ Verify chiller model, capacity, refrigerant, and installation as per approved drawings. ✔ Check foundation alignment, vibration isolators, and mounting bolts.  ✔ Confirm piping connections (CHW & Condenser Water) — flow direction, supports, flexible joints.  ✔ Ensure valves installed correctly: isolation, balancing, flow switch, drain, vent.  ✔ All electrical connections terminated — proper cable size, breaker, earthing, and isolator.  ✔ Sensor wiring & BMS points connected and tested.  ✔ Insulation completed and cladding sealed (especially outdoors). Flushing & Cleaning ⇒ Conduct chemical flushing of CHW & condenser lines:    Use biocide + scale remover.   Flush till water is clear.  ⇒ Post-flush: Passivation to protect pipe interiors.  ⇒ Hydrostatic pressure test as per code (usually 1.5x working pressure).  ⇒ Vent all air pocke...

  HVAC Design for Clean Rooms - Hospitals & Pharma 1. Clean Room Classifications (ISO & GMP)  Classification Max. Particles ≥0.5µm / m³ Typical Use ISO 5/ Class 100 3,520 OT, IV Room ISO 7/ Class 10,000 352,000 Compounding Area ISO 8/ Class 100,000 3,520,000 Packing Area 2. Air Changes Per Hour (ACH) Room Type Recommended ACH Operation Theater (OT) 20-25 ICU/NICU 15-20 Cleanrooms ISO 7 60-90 Cleanrooms ISO 8 15-20 Example: Room Volume = 5 m x 5 m x 3 m = 75 m³ ACH = 25 Airflow = (25 x 75)/60 = 31.25 CMM ≈ 1100 CFM 3. HEPA Filter Design HEPA Efficiency: ≥99.97% @ 0.3µm 1 HEPA filter (24"x 24") handles ~500 CFM OT needing 1000 CFM Use 2 filters 4. Room Pressure Differential Area Type Pressure Difference OT vs Corridor +10 to +15 Pa ICU vs Corridor +5 to +10 Pa Isolation Room -10 to-15 Pa 5. Laminar Airflow (LAF) Velocity: 90 ± 20 ft/min (0.45 ± 0.05 m/s) Area: ~9 ft x 6 ft above OT table 6. Humidity & Temperature Control Area Temp (°C) RH (%) OT 21-24 50-60 ICU / Pa...

  HVAC MEP Thumb Rules & Formulas (With Examples) 1. Heat Load Calculation  Formula: Q = Area (sq.ft) x Heat Load Factor (BTU/hr per sq.ft) Example: 500 sq.ft office: Q = 500 x 30 = 15,000 BTU/hr TR = 1.25 2. CFM Calculation Formula: CFM = Sensible Heat (BTU/hr) / (1.08 x Delta T) Example: 12,000 BTU/hr, Delta T = 20°F CFM = 556 3. AHU/FCU Sizing Rule: 1 TR = 400 CFM 2 TR Airflow = 800 CFM 4. Duct Sizing Velocity Limits: Main: 1400-1800 FPM 800 CFM @ 1000 FPM 0.8 sq.ft 14"x10" 5. Chilled Water Flow Rate Formula: GPM = BTU/hr / (500 x Delta T) Example: 24,000 BTU/hr GPM = 4.8 6. Pipe Sizing 1" pipe: 8-12 GPM 2" pipe: 30-40 GPM 35 GPM Use 2" 7. Chiller Sizing Formula: TR = BTU/hr / 12,000 Example: 60,000 BTU/hr → 5 TR 8. Cooling Tower Sizing Rule: Heat Rejection = 1.25 x Load 10 TR → Tower = 12.5 TR 9. Pump Head Calculation Formula: Power (kW) = (Q x H x 9.81) / (Efficiency x 1000) Example: Q = 5 L/s, H = 20 m, Efficiency = 0.75 Power 1.31 kW 10. Fresh Air Re...

  VALVES USED IN A CHILLER SYSTEM AND THE TYPICAL VALVE PACKAGE 1.Chilled Water Side Valves ⇒Isolation valve (manual/electric actuated). ⇒ Installed on CHW supply and return lines.  ⇒ Used to isolate chiller for maintenance. 2. Balancing Valve (Manual or Automatic)  ⇒ Ensures correct flow rate to/from chiller.  ⇒ Helps maintain Delta T and proper flow distribution.  ⇒ Located after evaporator outlet (return line). 3. Differential Pressure Bypass Valve (if 2-way valves in system)  ⇒ Prevents excess pressure build-up when terminals shut.  ⇒ Maintains flow through chiller. 4. Flow Switch  ⇒ Senses chilled water flow across evaporator.  ⇒ Safety interlock: trips chiller if flow is lost.  ⇒ Usually paddle type or electronic. 5. Air Vent Valve (Manual or Automatic)  ⇒ Removes air pockets.  ⇒ Placed at high points of piping and chiller headers. 6. Drain Valve  ⇒ For flushing, cleaning, and maintenance.  ⇒ Located at low poin...

CHILLER CONTROL PARAMETERS 1.Chilled Water Supply Temperature (CHW Supply Temp) ⇒ Setpoint usually 6–7°C.  ⇒ Maintained by controlling compressor operation and refrigerant flow.  ⇒ Impacts building cooling efficiency directly. 2.Chilled Water Return Temperature (CHW Return Temp)  ⇒ Normally around 12–14°C from building side.  ⇒ Indicates cooling load — higher return temp = higher demand. 3.Delta T (Temp Difference)  ⇒ CHW Return – CHW Supply. Ideal: 6–8°C.  ⇒ Lower delta T = flow too high or load too low.  ⇒ Important for energy optimization and sizing. 4.Chilled Water Flow Rate  ⇒ Must meet minimum flow for evaporator (to avoid freezing).  ⇒ Controlled by VFD pumps, 2-way valves, or bypass lines.  ⇒ Flow switch protects evaporator from dry run. 5.Evaporator Pressure & Temperature   ⇒ Used to monitor refrigerant evaporation process.  ⇒ Sudden drop = low refrigerant or blocked flow.  ⇒ Used to trip chiller on low pressu...