Air conditioning for open-plan offices

Why open-plan offices are harder to cool than cellular ones

In a cellular office, each room has its own load and its own unit, so problems stay contained. In open-plan space, heat from solar gain on one side of the floor, from a bank of printers or a server cupboard, and from simple occupancy density near meeting pods all mix together in one shared volume of air. A single point of measurement, like a thermostat by the door, rarely reflects what's happening at the far end of the floor.

Desk layout changes also outlive the original air conditioning design. An office fitted out for 40 desks that later squeezes in 55 through hot-desking will find the original cooling capacity was never designed for that occupancy, even if nothing else about the space changed.

Zoning: the single biggest factor in open-plan comfort

Splitting an open floor into two or three independently controlled zones, each with its own indoor units, allows the glazed south side to run harder than the shaded north side without either area being sacrificed to a compromise setting. Zoning is usually achieved with multiple cassette units or a multi-split arrangement, each set responding to its own local conditions rather than one thermostat trying to represent the whole floor.

Zoning also solves the recurring workplace argument over who controls the thermostat. Give each zone its own control, ideally somewhere central and out of reach of the person who sits directly under the nearest vent, and most day-to-day complaints disappear on their own.

Dealing with glazing gains

Large glazed frontages, common in modern office buildings and business parks, can add a substantial cooling load on sunny afternoons that has nothing to do with occupancy. Solar film, internal blinds or external shading all reduce the load reaching the room before it becomes something the air conditioning has to work against.

Where glazing can't be treated, for example in listed or leased buildings with restrictions on external changes, the cooling design needs to account for that load directly rather than assume a standard office heat gain figure. This is exactly the kind of detail a proper site survey picks up that a rough online cost estimate never will.

Cassette layout for even coverage

• Ceiling cassettes throwing air in four directions generally give more even coverage across open floor plates than a row of wall units all facing one way.
• Space cassettes to avoid overlapping cold zones near desks directly beneath them and dead zones between units.
• Keep return air paths clear of partitions, storage and printer stations that can starve a cassette of the air it needs to recirculate properly.
• Position controllers away from direct airflow paths so temperature readings aren't skewed by a nearby vent.

Managing complaints once the system is in

Even a well-designed system generates the odd complaint, usually from people directly under a vent or furthest from one. Having a facilities contact who can adjust louvre direction, fan speed or zone setpoints without calling an engineer for every tweak resolves most of these quickly. Where complaints persist despite reasonable adjustment, it's often a sign the original zoning needs revisiting rather than something wrong with individual desks.

If your open-plan office is stuck with hot desks by the window and a queue of complaints every summer, it's worth having someone look at the zoning rather than just adding another portable unit. Get in touch for a free quote and site survey, and we'll assess how the space is actually being used before recommending a layout.