Air conditioning an open-plan office in Île-de-France: hot spots, draughts and employee complaints
L'équipe Proclimo
29 Oct 2026 - 09 min read
"We have a 420 m² floor in Issy-les-Moulineaux, 38 workstations, four ceiling cassettes and two ducted units. In July, the six people sitting along the glazed façade were at 29 °C; those in the middle were working in fleeces with a portable heater under the desk. The maintenance contractor came out three times and tells us the machines are working. And he's right: they are working."
That call comes to us from office managers, HR directors and small-business owners, in July as much as in January. And it is one of the rare cases where the diagnosis has nothing to do with a breakdown. On an office floor, the problem is almost never the installed capacity: it is the way that capacity is distributed, controlled and measured.
An open-plan office concentrates four constraints that a flat never faces: very uneven solar gains from one end of the floor to the other, enormous and variable internal gains (bodies, screens, lighting), movable partitions that shift with every reorganisation, and a human sensitivity to draughts that bears no relation to the average temperature displayed by a sensor.
This article describes what we actually find on office floors in Paris Rive Gauche, Issy, Montrouge, Saint-Denis, Nanterre and the business parks of Massy and Vélizy: why complaints are always asymmetrical, which corrections produce a real effect, and the budget ballpark figures for 2026.
Why an office floor cannot be cooled like a home
Internal gains matter as much as the sun
In a flat, occupancy is low and intermittent. On an office floor, it is massive and concentrated in the same hours.
The ballpark figures used in HVAC engineering practice, consistent with ADEME documents and CSTB guides on commercial buildings:
| Source of gain | Heat output (order of magnitude) |
|---|---|
| One person doing office work | 80 to 120 W |
| One computer workstation (PC + screen) | 80 to 200 W |
| A multifunction printer in use | 300 to 800 W in peaks |
| LED lighting | 6 to 10 W/m² |
| Older fluorescent lighting | 15 to 25 W/m² |
Across 38 workstations, people and machines alone already account for 6 to 10 kW of permanent gains from 9 a.m. to 6 p.m., before the sun even enters the equation. That is why a north-facing floor may need cooling in February while the empty meeting room next door is calling for heat.
This simultaneous demand for heating and cooling is the real issue in commercial premises. It almost never arises in housing, and it determines the type of system to install.
The façade creates two buildings in one
A floor with glazing on both sides is in reality two very different thermal zones:
- The perimeter zone (3 to 5 m from the glazing): subject to solar radiation, winter heat losses and rapid variations. In summer, unshaded south-facing glazing can contribute 300 to 500 W per m² of glazed area.
- The core zone: practically insensitive to outdoor conditions, driven solely by internal gains. It needs cooling almost all year round.
If both zones are controlled by the same sensor, only one of the two will be comfortable. Always. And since the return-air sensor is generally in the ceiling, in the middle of the floor, it is the perimeter zone that gets sacrificed.
The typical symptom: "the AC is running flat out, the people near the windows are hot, the ones in the middle are cold." That is not a contradiction, it is the signature of a zoning fault.
Employee complaints: what they really mean
In our experience, the feedback falls into four families, and each one has a distinct technical cause.
1. "I've got a cold draught on the back of my neck"
This is complaint number one, and it is almost never a question of temperature. In its dossiers on thermal conditions at work, the INRS points out that local discomfort (draughts, radiant asymmetry, cold feet) can make an environment unpleasant even when it is perfectly acceptable on average.
The usual benchmarks, drawn from commercial design practice:
- air velocity at occupant level: ideally below 0.20 m/s in summer, 0.15 m/s in winter;
- difference between supply air and room air: 8 to 11 °C maximum in cooling mode.
Concrete causes we find on site:
- a 4-way cassette installed directly above a workstation instead of a circulation area;
- deflectors stuck in the low position after someone adjusted them "to feel the cold better";
- a supply airflow left on high speed 24/7 because the remote control has been locked.
The fixes are often very inexpensive: reposition the louvres, fit deflectors for air conditioning vents on cassettes blowing onto a desk, put the fan back to auto speed, or move two workstations. Before committing to any works, a simple hot-wire anemometer held at shoulder height settles the argument in ten minutes.
2. "It's 26 °C but we're stifling"
Here, the culprit is humidity or air renewal, not temperature. A densely occupied floor whose air handling unit is running at minimum airflow to "save energy" accumulates CO₂ and water vapour.
The reference thresholds:
- comfortable relative humidity: 40 to 60 %;
- CO₂ concentration: ANSES and the Haut Conseil de la santé publique consider that above 800 to 1,000 ppm, ventilation is insufficient for the level of occupancy.
A CO2 sensor for the office placed in the core zone for a week immediately puts hard numbers on the issue and saves months of discussion. When the curve climbs to 1,400 ppm by 11 a.m. and drops back at lunchtime, it is not the air conditioning that needs changing: it is the fresh-air flow rate. We set out this interplay between cooling and ventilation in our article on the respective roles of air conditioning and mechanical ventilation against humidity.
3. "It smells stale on Monday morning"
That is the characteristic smell of a fouled heat exchanger or a condensate tray left standing over the weekend, when ventilation is switched off. On an office floor it is also a question of image: a candidate visiting your premises on a Monday morning will remember it.
The remedy is professional cleaning and disinfection, not an air freshener. The mechanism is exactly the same as in a home: we described it in our article on musty, sewage or vinegar smells coming out of an air conditioner.
4. "Everyone fiddles with their own settings"
On floors with multiple remote controls, we regularly find three units in cooling mode at 19 °C and one in heating mode at 25 °C in the same volume. The result: machines fighting each other, an electricity bill through the roof and general discomfort.
What the regulations say in 2026
Three sets of rules frame the subject, on the employer side and on the operating side.
The French Labour Code sets no maximum temperature for offices. It does, however, require the employer (articles L. 4121-1 et seq.) to assess risks and take the necessary measures, and since the decree of 27 June 2025 on the prevention of heat-related risks it imposes reinforced obligations during intense heat episodes: assessment, adaptation of work organisation, provision of water, information for employees. We detailed these obligations in our article on the heat decree and employers' new obligations.
Decree 2020-912 requires annual servicing of air conditioning systems and reversible heat pumps with a capacity between 4 and 70 kW, by a professional, with a certificate issued. On a floor fitted with several split units and cassettes, that threshold is easily reached.
The BACS decree requires commercial buildings whose HVAC systems exceed 70 kW to have a building automation and control system. That is precisely the tool that solves the zoning problems described above: we covered it in our article on class A building management systems now mandatory in commercial buildings.
Finally, the order of 22 July 2022 on temperature setpoints in premises sets 26 °C as the lower cooling setpoint during the summer period in commercial buildings — a value that is comfortable when properly applied with a good air velocity, and unbearable when poorly applied with air blowing directly onto occupants.
The corrections that genuinely work
Level 1: the settings (€0 to €800)
This is where you have to start, and in 40 % of the floors we audit, it is enough to make the complaints go away.
- Lock the setpoints within a narrow range (for example 24-26 °C in cooling, 19-21 °C in heating) and remove the individual remote controls.
- Put the fans back into automatic mode.
- Redirect the deflectors away from workstations.
- Move the return-air sensor or use a remote wall-mounted sensor in a representative zone.
- Set the time clocks to actual occupancy hours, including pre-cooling.
Level 2: deal with the façade before the machine (€1,500 to €12,000)
On a south- or west-facing floor, no system will win against unshaded glazing. Solar gains have to be stopped outside, not inside.
- External blinds or adjustable brise-soleil: the most effective solution, but often subject to the landlord's and the building owners' association's approval.
- Solar window film applied internally: 50 to 75 % solar rejection depending on the product, installed in a single day on an average floor, reversible at the end of the lease. It is very often the best efficiency-to-constraint ratio in leased offices.
- Internal blinds with technical fabric: useful against glare, considerably less effective thermally.
The principle is the same as the one we set out for homes in our article on the synergy between insulation and air conditioning.
Level 3: re-zone the installation (€4,000 to €25,000)
When adjustments are not enough, you have to physically separate what is thermally different.
- Moving from a multi-split "everything on one remote" setup to separate groups for the perimeter and the core of the floor.
- Adding motorised dampers to an existing ducted network, with sensors per zone.
- On large floors, heat recovery systems capable of heating a meeting room while cooling the core of the floor.
- Reworking the ductwork: extending a duct, adding diffusers, reducing supply velocities.
For meeting rooms, often the worst spaces on a floor (12 people in 20 m² with no window), we recommend a dedicated unit with an occupancy sensor: it is the only way to avoid the fridge/sauna alternation.
Level 4: replacement (from €12,000 for an average floor)
Replacement is justified when the installation runs on R410A, when breakdowns keep recurring and when the very architecture of the network rules out any zoning. The decision criteria are the same as for an ageing home system: we laid them out in our article on deciding whether to repair or replace an air conditioner over ten years old.
The human side: get the facts before arbitrating
The difficulty with an open-plan office is that there is no temperature that suits everyone. Research on thermal comfort shows that even in a perfectly compliant environment, a proportion of occupants always remain dissatisfied.
What works, in the companies we support:
- Measure before debating. Three or four connected thermometer-hygrometers spread across the floor, logged over two weeks, eliminate most of the arguments. Differences of 4 to 6 °C between two zones show up in black and white.
- Publish the setpoint. A floor where the rule is written down ("25 °C in summer, fan on auto, centralised remote controls") generates far fewer conflicts than one where everybody assumes their neighbour has been tampering with the settings.
- Handle individual cases individually. An exposed workstation that cannot be moved is dealt with using a blind, a relocated diffuser, or failing that a quiet desk fan — infinitely cheaper and less contentious than lowering the general setpoint by 2 °C.
- Keep records of interventions. The maintenance logbook and annual certificates also serve, in the event of a dispute with an employee or a landlord, to demonstrate that the installation is being properly maintained.
2026 budget ballpark figures
| Service | Range observed in Île-de-France |
|---|---|
| Comfort audit of an office floor (measurements + report) | €450 to €1,200 |
| Reworking the settings and centralising the controls | €300 to €1,500 |
| Cleaning and disinfecting 4 to 6 cassettes | €600 to €1,400 |
| Annual maintenance contract, 300 to 500 m² floor | €700 to €2,000/year |
| Solar film on 40 m² of glazing | €1,800 to €3,500 |
| Adding motorised dampers and zone sensors | €3,000 to €9,000 |
| Dedicated unit for a meeting room | €2,500 to €5,000 |
These ranges assume normal access to the ceilings and work carried out during the day. Evening or weekend works, common in order to avoid shutting down operations, generally add 30 to 50 % to the labour cost.
What we look at during a site visit
For a manager who wants to prepare for the visit, here are the points that determine the diagnosis:
- an up-to-date workstation layout plan, with façade orientations;
- the type and area of the glazing, and any existing solar shading;
- make, model and year of the indoor and outdoor units, and the refrigerant used;
- the exact position of the diffusers relative to the workstations;
- sensor locations and a list of control points;
- whether mechanical ventilation exists and whether the fresh-air flow rate can be measured;
- breakdown history and the most recent maintenance certificates;
- lease clauses covering equipment and the façade.
With this information, an audit takes half a day and leads to a prioritised plan: first what is free, then what pays for itself, and last what is heavy-duty.
In summary
An uncomfortable open-plan office is almost never undersized: it is badly zoned, badly ventilated at the diffusers, or badly ventilated overall. The right sequence is to measure, correct the settings and the air supply, protect the façade, and only then re-zone or replace. In that order, spending stays under control and complaints subside quickly.
If your office floor combines zones at 29 °C with employees in fleeces, a comfort audit is the most cost-effective starting point. Our technicians work throughout Paris and the whole of Île-de-France: book an appointment online or use our contact form to describe your setup.
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