Delta T (ΔT) in HVAC Systems – Complete Explanation In HVAC, Delta T (ΔT) means: Difference between two temperatures Formula: ΔT=T1−T2 Where: ΔT = Temperature difference T₁ = First temperature T₂ = Second temperature Why Delta T is Important in HVAC Delta T tells us: • How much cooling or heating is happening • Whether equipment is working properly • Energy efficiency of system • Water flow and air flow condition • Coil performance • Chiller efficiency In HVAC mainly two Delta T are used: • Water Side Delta T • Air Side Delta T 1. Water Side Delta T (Chilled Water / Hot Water) This is the temperature difference between: • Supply water temperature • Return water temperature Usually used in: • Chillers • FCU • AHU • Heat exchangers Chilled Water Delta T In cooling system: • Chiller sends cold water → called CHWS (Chilled Water Supply) • Water absorbs room heat • Warm water returns → called CHWR (Chilled Water Return) Formula: ΔTwater = Treturn−Tsupply Example 1 – Normal ...
External Static Pressure (ESP) — zero ➜ hero Goal 📌 ESP = fan pressure needed to overcome all losses outside the unit casing. If the AHU has a return fan, compute Supply ESP and Return ESP separately. 1️⃣ Define the system • Airflow (Q) (m³/s). • Paths: supply to most remote diffuser, and return from farthest grille to unit. • What’s outside the unit: ducts, fittings, terminals, silencers, dampers, coils/filters in the duct, louvers. 2️⃣ Sketch the critical path 🧭 One‑line from fan discharge → last diffuser. Do the same back to the unit for return. The longest sum is the critical path. 3️⃣ Collect data • Duct sizes, lengths, number of fittings. • Device drops at design flow (Pa): filters, coils, VAVs, attenuators, grilles/diffusers, louvers. • Air properties: use ρ ≈ 1.2 kg/m³. • Conversions: 1 in.wg = 249 Pa. 4️⃣ Equations (plain text) • Area A = W × H (for round: A = πD²/4). • Velocity v = Q / A. • Velocity pressure q = 0.5 × ρ × v² (Pa). • Rectangular hydrauli...