Designing Air Conditioning for Open-Plan Offices



How to Design Air Conditioning for Open-Plan Offices: A Complete Engineering Guide

Open-plan offices are now the standard layout for UK businesses.
They offer flexibility, collaboration, and high workspace density — but they also create serious HVAC challenges.

Large open areas experience:

• uneven temperatures

• drafts

• inconsistent airflow

• high heat loads

• acoustic sensitivity

• varied occupancy

This detailed guide explains how to design air conditioning for open-plan offices using correct airflow engineering, zoning, diffuser placement, and VRF technologies.

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1. Why Open-Plan Offices Are Hard to Cool

The absence of walls means:

• air spreads unpredictably

• heat loads shift rapidly

• sunlight affects large zones

• airflow often concentrates in one area

• temperature differences reach 3–5°C

Without proper HVAC engineering, some employees freeze while others feel hot.

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2. Best HVAC Systems for Open-Plan Offices

A) VRF Systems — The Most Effective Option

VRF provides:

• smooth modulation

• multiple indoor units

• precise zoning

• excellent energy efficiency

• compatibility with cassettes and ducted units

Perfect for large floors with 20–200 employees.

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B) Cassette Units — Ideal Airflow Pattern

4-way cassettes deliver 360° airflow.

They are ideal because:

• air spreads evenly

• downward throw is balanced

• they cover wide zones

• noise level is low

• they fit perfectly into suspended ceilings

For optimal mixing: use multiple smaller cassettes instead of one large unit.

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C) Ducted Systems — Premium Option for Hidden Aesthetics

Ducted indoor units provide:

• almost invisible installation

• quiet operation

• controlled airflow distribution

• ability to serve multiple diffusers

Used in premium offices and corporate HQs.

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3. Airflow Design Principles for Open-Plan Offices

A) Distribute airflow evenly

Do NOT position diffusers only in the centre of the room.

Correct layout:

• grid pattern

• equal distance between diffusers

• supply and return airflow separated

B) Avoid direct air blowing on desks

Direct drafts cause complaints and discomfort.

C) Maintain low air velocity

Optimal velocity: 0.18–0.25 m/s

D) Use multiple supply diffusers

This ensures uniform cooling throughout the workspace.

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4. Zoning Strategies

Open-plan offices still need zoning to prevent temperature conflicts.

Recommended zones:

• central workspace

• perimeter zone (nearest to windows)

• meeting rooms

• breakout areas

• printing/copy zones

Each zone requires:

• dedicated thermostat

• separated airflow

• individual control

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5. Managing Solar Heat Gain

Windows dramatically affect temperature.

HVAC engineers must consider:

• west-facing afternoon heat

• morning glare

• heat transfer through glazing

• shading systems

Solution: create solar zones with extra cooling.

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6. Ventilation in Open-Plan Offices

Large offices often fail because of poor ventilation, not poor cooling.

Fresh air supply prevents:

• CO₂ buildup

• afternoon fatigue

• stuffiness

• temperature rise

Ideal systems:

• MVHR

• HRV

• dedicated fresh air ducting

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7. Noise Control Matters

In open offices, noise spreads easily.

Use:

• low-noise VRF units

• insulated ducting

• anti-vibration hangers

• separated return plenum

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8. Smart Controls Improve Efficiency

Smart thermostats and sensors:

• regulate heating/cooling cycles

• prevent overcooling

• adjust ventilation

• track occupancy patterns

• prevent “hot afternoons” issue

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Conclusion

Open-plan offices require a carefully engineered HVAC system that combines zoning, VRF control, proper diffuser layout, and balanced ventilation.

Following these principles creates a comfortable, productive work environment with stable temperature all day long.