The problem with spreadsheet calculations
Most building services calculations still happen in spreadsheets. They work — up to a point. But spreadsheet calculations have three persistent problems that slow engineers down and introduce risk.
First, inputs are disconnected from context. A pipe sizing spreadsheet doesn't know which room the calculation is for, what the design flow temperature is, or which standard you're working to. You enter numbers, but the spreadsheet has no idea where they came from or whether they're still valid.
Second, there's no traceability. When a result appears in a cell, there's no structured record of which assumptions produced it. If a colleague opens the file six months later, they're reverse-engineering the logic from cell references and hoping nothing was overwritten.
Third, spreadsheets are easy to break. Insert a row in the wrong place, paste over a formula, or copy a sheet without checking the references — and you have silent errors that may not surface until a design review or, worse, on site.
How MEP Desk calculators work
Calculators in MEP Desk are designed to solve all three problems. Here's the typical workflow:
- Select a calculator. Choose from pipe sizing, duct sizing, ventilation rates, heat loss, heat gain, and other engineering calculations. Each calculator has a defined set of inputs and a clear methodology.
- Room context feeds in automatically. If you have an active room selected in your project, the calculator suggests relevant inputs based on the space type. An office will suggest different ventilation rates and occupancy densities than a server room or a kitchen.
- Accept defaults or override manually. Project-level assumptions — design temperatures, diversity factors, material properties — can be set once and applied across all calculations. Each input shows whether it was auto-filled from a default or entered manually.
- Results show full working. Every calculation output includes a breakdown of which inputs were used, their sources, and whether they were manual or auto-filled. There's no hidden logic.
- Save results to the project. Completed calculations are saved and linked to the room. They become part of the project record and can be included in exports.
Auto-run pipeline
For users on a paid plan, MEP Desk includes an auto-run calculation pipeline. When room data changes — for example, if you update the floor area or change the space type — any linked calculations can update automatically. This uses a centralised event bus that detects which inputs have changed and re-runs only the affected calculations. You still review and approve the results; the system handles the re-triggering so you don't have to remember which calculations depend on which values.
The assumptions system
MEP Desk lets you define project-level assumptions across six engineering disciplines: mechanical, electrical, public health, fire, acoustics, and sustainability. Each assumption is a named value — like an indoor design temperature or a minimum air change rate — that can be referenced by any calculator in the project.
The assumptions panel shows which calculators use each value, so when a value changes, you can see exactly what's affected. This is the single source of truth that spreadsheet workflows typically lack.
Traceability from output to source
Every calculation result in MEP Desk traces back through its inputs to the source data. If a pipe size was determined using a flow rate derived from a ventilation rate that came from a project assumption referencing CIBSE Guide B, that chain is visible. You can inspect any output and see exactly how it was derived — which is exactly what you'd want during a design review or an audit.