Heat Balance
Template (Excel)

A heat balance (or energy balance) is the process engineering deliverable that tabulates the heat duty transferred at every unit operation on the PFD: heat exchangers, heaters, coolers, reboilers, condensers, and fired heaters. For each duty it records hot-side and cold-side inlet and outlet temperatures, mass flows, specific heats, heat duty, LMTD, phase change behaviour, and utility type. Conservation of energy requires that for each node, total enthalpy-in plus heat added equals total enthalpy-out plus heat removed within project closure tolerance (typically 1%). The heat balance pairs with the material balance to form the HMB document.

At minimum: unit operation tag, PFD reference, hot-side and cold-side inlet and outlet stream numbers, inlet and outlet temperatures both sides, mass flows both sides, specific heat both sides, heat duty (kW or MMkcal/h), LMTD, phase change behaviour, and utility type. Add heat loss to ambient when the project tolerance is tight. Most EPC templates include a Design Case column flagging Normal / Start-up / Upset cases. The hot and cold stream tags must cross-reference the material balance template and the PFD standard reference for stream-numbering integrity.

Pathnovo, an engineering document intelligence platform, extracts heat exchanger tags and duty tables from PFDs and cross-references the corresponding heat and material balance sheets, exchanger datasheets, and simulation export files. The platform parses inlet and outlet conditions for both sides, calculates duty as m times Cp times deltaT (or extracts published duty from the simulation export), validates against project HMB closure tolerance, and flags any node with closure greater than 1%. Typical project turnaround is 48 hours for the initial batch with closure-tested output. See the P&ID and PFD extraction workflow for the full pipeline.

Downstream consumers: shell-and-tube exchanger thermal design per API 660 and TEMA uses duty, LMTD, and phase-change behaviour as primary inputs. Fired heater design per API 560 uses duty and process conditions. Utility load aggregation sums steam, cooling water, fuel gas, and refrigerant duties across all unit operations. Pinch analysis and heat integration studies use the heat balance to identify integration opportunities. Relief device sizing uses worst-case duty deviations per API 521. The heat balance is the master energy register that drives every downstream thermal sizing decision.

The material balance tabulates stream composition and mass flow (what is flowing). The heat balance tabulates duty and enthalpy change at each unit operation (how much energy is transferred). Together they form the Heat and Material Balance (HMB) document. Material balance closure is checked by mass-in equals mass-out at each node. Heat balance closure is checked by enthalpy-in plus heat added equals enthalpy-out plus heat removed at each node. Both must close to within project tolerance. See the material balance template for the mass register.

The exchanger row in the heat balance defines the design duty, hot and cold inlet and outlet temperatures, fluids, mass flows, and phase change behaviour. These are the primary inputs to API 660 thermal design (or its TEMA Class R / B / C variant). The design engineer uses them in HTRI Xchanger Suite or Aspen EDR to size the shell, tube count, tube length, baffle pitch, and area, then back-checks against the LMTD in the heat balance to confirm consistency. Any deviation triggers an HMB or datasheet update. See the datasheet template reference for the exchanger thermal datasheet structure.

Indian PSU refinery revamps (IOCL, BPCL, HPCL, MRPL, NRL) typically tie a new capacity case into an existing process train. The heat balance must show the existing-operating duty alongside the revamp design duty for every exchanger and fired heater on the revamp scope boundary. Tie-in exchanger duties are recomputed after revamp temperatures change. Existing fired heater duty is re-rated against new feed rates. Pathnovo handles the existing-versus-revamp dual case in the same Excel sheet with a Design Case column. See the Indian EPC compliance bundle for the integrated revamp deliverable structure.