HVAC engineers

Scroll compressors Scroll compressors (also called spiral compressors) are positive-displacement machines widely used in HVAC, refrigeration and heat-pump systems. They contain two interleaved spiral scrolls one fixed and one orbiting that trap and squeeze refrigerant vapor. As the motor-driven orbiting scroll moves eccentrically (off-center) around the fixed scroll, it continuously traps and pushes refrigerant toward the center at rising pressure. This smooth, pulseless compression (with no metal-on-metal contact) makes scroll units compact, quiet and highly reliable. In the cutaway image you can clearly see the key parts. The orbiting scroll (bolted to the shaft) nests inside the fixed scroll. Surrounding the shaft is the stator (stationary motor coils) and rotor - together they drive the orbiting scroll. Refrigerant enters at the low-pressure suction port, gets caught in the spiral pockets between the scrolls, and is compressed as those pockets shrink toward the center. The high-pre...

METERS AND GAGES PART 1-GENERAL 1.1 RELATED DOCUMENTS A. Drawings and general provisions of the Contract, including Conditions of Contract and Division 1 Specification Sections, apply to this Section. 1.2 SUMMARY A. This Section includes meters and gages for mechanical systems and water meters installed outside the building. B. Related Sections include the following: 1. Division 2 Section "Water Distribution" for water meters outside the building. 2. Division 13 Sections for fire-pump flow-measuring systems. 3. Division 15 Section "Fuel Gas Piping" for gas meters. 4. Mechanical equipment Sections that specify meters and gages as part of factory-fabricated equipment. C. Utility-Furnished Products: Water meters shall be furnished by the contractor to site, ready for installation. Where install exposed to weather conditions, meters and gauges shall be corrosion resistant. 1.3 SUBMITTALS A. Product Data: Include scale range, ratings, and calibrated performance curves fo...

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...