Chiller & Boiler Pump Location – Upstream or Downstream? Let’s Settle This Debate One of the recurring questions I hear from engineers, operators, and even contractors on site is: 👉 “Should pumps be located upstream or downstream of chillers and boilers?” At first glance, it feels like a simple “rule-of-thumb” answer. But in reality, it’s a nuanced design decision guided by hydronic principles, ASHRAE handbooks, and equipment manufacturer limits. Let’s break it down 👇 🌡️ Chilled Water Systems Low- to Mid-Rise Buildings: Pumps are often placed upstream of the chiller evaporator (on the return side). ✅ Benefits: Pump heat is absorbed by the chiller, positive NPSH margin, and evaporator stays flooded. 🔎 Backed by: Trane Engineers Newsletter & ASHRAE guidance. High-Rise or Pressure-Limited Plants: Pumps are placed downstream of the chiller evaporator (on the supply side). ✅ Benefits: Prevents adding pump head across the chiller tubes (protects pressure rating). ❌ Drawback...
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...