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Full HVAC Calculation – Building Level (Professional Approach)

Gul Bahar Shah
  Full HVAC Calculation – Building Level (Professional Approach) Designing an HVAC system is not just about equipment selection — it’s about engineering accuracy. This visual summarizes a complete workflow used in real projects: 🔹 Heating Load Calculation Q = A × K × ΔT 🔹 Cooling Load Estimation 100–180 W/m² (practical method) 🔹 Flow Rate Calculation * Heating: 0.043 m³/h per kW * Cooling: 0.172 m³/h per kW 🔹 Pipe Sizing (Hydronic Systems) Based on flow rate, not area 🔹 System Selection * Split (<10 kW) * VRF (10–50 kW) * Chiller (>50 kW) 🔹 Pump Calculation Flow + Head loss 🔹 Air Side (CFM Calculation) 1 kW ≈ 400 CFM 📊 Example: 500 m² office building Cooling load = 70 kW Flow = 12 m³/h Pipe size = DN50 👉 A good HVAC design = Accurate Load + Correct Flow + Proper Pipe Sizing
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HRV vs ERV

Gul Bahar Shah

 HRV vs ERV

Many engineers treat HRV and ERV as interchangeable. They’re not. Choosing the wrong one doesn’t just affect efficiency… it can damage indoor air quality control, especially in humid climates. First — The Real Difference HRV (Heat Recovery Ventilator) Transfers: Sensible heat only (temperature). Does NOT transfer: Moisture (latent heat) ERV (Energy Recovery Ventilator) Transfers: Sensible heat (temperature). Latent heat (moisture). What this means in real operation HRV: * Brings in fresh air * Keeps humidity control separate * Safer for critical environments ERV: * Reduces cooling/heating load * Transfers humidity between air streams * Improves energy efficiency Where engineers get it wrong (field reality) Mistake #1: Using ERV in high humidity + poor maintenance ERV wheels can: * Transfer moisture * Transfer contaminants (if not properly maintained) In hospitals or labs, this is a risk, not a benefit. Mistake #2: Ignoring latent load Using HRV in humid climates (like Gulf / coastal regions): * Outdoor air brings high moisture * HVAC system becomes overloaded Result: * Low ΔT * High energy consumption * Comfort issues Mistake #3: Thinking energy recovery = always good Not always. In some systems: * Energy recovery conflicts with air hygiene requirements * Especially in: * Operating Rooms * Isolation Rooms * Cleanrooms Sometimes no recovery is the correct design Quick Selection Logic (Real Engineering Approach) Use HRV when: * You need strict air separation * Humidity must be controlled independently * Healthcare / labs / cleanrooms Use ERV when: * Energy efficiency is priority * Comfort applications (offices, malls, hotels) * Humidity transfer is acceptable Hidden Point Most Don’t Talk About ERV effectiveness drops if: * Wheel leakage exists * Purge section is missing * Pressure balance is wrong So your “high efficiency system” becomes: Cross-contamination path. Uncontrolled moisture transfer. Field Insight If you see: * Unexpected humidity increase * Odor transfer between zones Don’t blame AHU immediately… Check the ERV wheel leakage and pressure balance first

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