Tender documents
The bill of quantities a data center tender actually needs
A bill of quantities exists to make bids comparable. Most of the trouble on a data center package comes from items that were never in the bill at all — and from quantities that no longer match the drawings they came from.
What a BOQ is for
One purpose, and it is worth being blunt about it: every bidder prices the same scope. When the bill is complete and unambiguous, the lowest number is the lowest price. When it is not, the lowest number is whoever read it most optimistically — and the difference reappears later as a variation.
That gives two tests for any line item. Can a contractor price it without asking a question? And if two contractors price it differently, is that a genuine commercial difference or a difference in what they assumed?
Structure: by discipline, then by system
Group so an estimator can find things and a technical reviewer can check coverage. On a data center package that means discipline first, because the specialists pricing it are different people.
| Section | Typically covers | Common unit |
|---|---|---|
| MV & transformation | RMU, switchgear, transformers, MV cable | Item / m |
| Generation | Sets, day tanks, bulk fuel, exhaust, acoustic treatment | Item |
| LV distribution | Main boards, ATS, bus ties, sub-boards, MCC | Item |
| UPS & stored energy | Modules, battery strings, racks, bypass panels | Item / string |
| DC plant | Rectifiers, DC boards, batteries | Item |
| Critical distribution | PDU, RPP, busway, rack feeds | Item / m |
| Cabling & containment | Power and earth cable by size, tray, ladder, basket | m |
| Mechanical | Chillers, CRAH, in-row, CDU, pumps, dry coolers, pipework | Item / m |
| White space | Cabinets, containment, perforated tiles, floor, leak detection | Item / m² |
| Safety & ancillary | EPO, SPD, PFC, harmonic filters, earthing, fire systems | Item |
| Testing & commissioning | Factory tests, site tests, IST, load bank hire | Item / day |
What gets left out
These are the omissions that turn into variations. None are exotic; all are easy to forget because they are not equipment on a schedule.
- Load bank hire and the fuel to run it. Integrated systems testing on a facility of any size is days of full-load running. It is a real cost and it belongs in the bill, not in a note.
- The house load. Lighting, small power, lifts, comfort cooling, fire pumps and BMS are not critical load, but they are on the same distribution and somebody has to build them.
- Earthing and bonding as a system rather than a line in the cable section — the mesh, the bonding conductors, the connections to the building steel.
- Spares and strategic holdings the operator will require at handover.
- Phasing costs on a live site. Out-of-hours working, temporary supplies, temporary cooling and the method statements to support them. On a brownfield job this is a substantial figure and it is invisible on the drawings.
- Making good where existing plant is removed.
The re-keying problem
The quantities come from the drawings. Almost always, somebody counts them by hand and types them into a spreadsheet. From that moment the bill and the design are two documents that agree only by continued effort.
Then the design is revised — as it always is. A board is added, a feeder re-routed, a cooling unit moved. The drawing is reissued. Whether the bill follows depends on whether someone remembered, had time, and knew which lines were affected.
A quantity that no longer matches the drawing is worse than a missing one. A missing item is found at tender review, when somebody asks. A wrong quantity is priced, awarded, and discovered on site — by which point it is a claim rather than a question.
The structural fix is to generate the bill from the model that produces the drawings, so the two cannot disagree. Every item counted from the single line and the floor layout, grouped by discipline, re-issued whenever the design is.
Making bids comparable
- Describe by performance, not by part number, unless there is a compatibility reason. Naming a manufacturer without an equivalence clause narrows the field and rarely improves the price.
- State the redundancy in the item, not only on the drawing. “UPS 500 kVA” and “UPS 500 kVA, N+1, four required” are priced differently by different bidders reading the same drawing.
- Separate supply from install where the client may free-issue equipment.
- Give a provisional sum for the genuinely unknown rather than leaving it out. Everyone prices a provisional sum the same way; nobody prices a gap the same way.
- Reference the specification clause on each item, so the requirement travels with the quantity.
Counted from the design, not typed from it
Data Center Simulator produces the bill of quantities from the same model as the single line and the floor layout — every item counted, grouped by discipline, with quantities that cannot drift from the drawing. It prints on the same letterhead as the design report, ready to issue with the tender.
Download the demo See the documents it produces