Here is the detail that catches most procurement teams after the contract is signed: the multi-parameter LoRaWAN sensors that dominate the market carry a single electrochemical gas slot. That slot holds either an ozone cell or a formaldehyde cell — never both — and none of these devices measures carbon monoxide at all. So when a bid lands on your desk claiming one device covers "complete indoor air quality monitoring," the honest response is a question: which parameter did you quietly drop?
A complete indoor air quality specification covers eight measurements: carbon dioxide, carbon monoxide, PM2.5, PM10, temperature, relative humidity, total volatile organic compounds and ozone. The best multi-parameter devices cover seven. That arithmetic — eight required, seven available — is why any tender specifying the full set needs two devices per monitoring point, and why understanding the parameters individually matters more than comparing spec sheets side by side.
The eight parameters split into three functional groups, and each group answers a different compliance question.
If your specification names all eight parameters, the correct bid architecture is a multi-parameter device carrying the ozone cell (accuracy ±5% full scale) plus a dedicated carbon monoxide device at every monitoring point. There is no way around this with current hardware. A bid that prices one device per point has either excluded CO or excluded ozone, and the exclusion is rarely stated on page one.
Write your tender to force this into the open. Require bidders to map every specified parameter to a named device and a stated accuracy. Require a parameter-by-parameter compliance table, not a marketing paragraph. And require the bidder to state the service life of every electrochemical cell — because electrochemical ozone cells last two years, and a bid that omits replacement cells from the lifecycle cost has understated your five-year total by two full replacement cycles.
The planning rule that survives contact with real buildings: one sensor per 100 to 150 square metres within a single open zone, and every closed room gets its own point. A 3,000 m² open-plan floor needs 20 to 30 points; the six meeting rooms along its edge need six more, regardless of how small they are. Closed rooms have their own air exchange behaviour, their own occupancy patterns, and their own complaint history — averaging them into the open zone hides exactly the problems you bought the system to find.
One observation from deployments that spec documents never mention: mounting position moves your CO2 readings more than sensor accuracy does. A device mounted near a supply diffuser reads the incoming fresh air, not the occupied zone, and will report a compliant space while people three metres away sit in stale air. Breathing-zone height, away from diffusers, doors and direct sun on the temperature element — get this wrong and the ±50 ppm accuracy figure on the datasheet is irrelevant, because the sensor is accurately measuring the wrong air.
Tenders gain teeth when they reference specific frameworks rather than "applicable standards." Three do most of the work: ASHRAE 62.1 for ventilation rates and the CO2-based verification logic behind them; the WHO 2021 air quality guidelines for particulate thresholds; and your regional occupational health framework — in Abu Dhabi, for example, ADOSH-SF governs workplace exposure and gives HSE officers a named regulatory hook for the chemical-hazard parameters. Citing these by name in the tender means bidders must demonstrate their measurement ranges and accuracies actually support compliance reporting against those documents, not just data collection in general.
Accepting the two-device architecture creates a second-order problem: two data streams per point, possibly from two manufacturers, potentially reporting into two portals. Facility managers do not want two dashboards, and auditors want one export. This is where platform choice matters more than sensor brand. Vemco's VemSpace is sensor-agnostic by design — it combines devices from different manufacturers behind one dashboard, so the seven-parameter LoRaWAN unit and the separate CO device appear as a single monitoring point with a single compliance view. That also protects you at the two-year mark: when ozone cells need replacement, or when a better particulate sensor reaches the market, you swap hardware without rebuilding your reporting layer.
Air quality data becomes considerably more useful when paired with occupancy. A CO2 spike means one thing in a room holding thirty people and something entirely different in a room holding four — the first is normal load, the second is a ventilation fault. Where footfall counting runs alongside air quality on the same platform, that context is automatic. On counting accuracy, the honest numbers are these: a contractual minimum of 96%, typically 98–99% in practice where lighting, layout and visitor behaviour allow. Any vendor quoting a flat guaranteed figure above that is quoting best-case conditions as a promise.
If you are drafting an air quality tender or trying to reconcile competing bids that each claim full coverage, our team can review your parameter specification, point-count plan and lifecycle budget before it goes to market — including how VemSpace consolidates multi-vendor sensor fleets into one compliance dashboard. Get in touch at vemcogroup.com/contact-us and bring your floor plan; the point-count conversation is more useful with it on the table.