HVAC for Cinemas and Auditoriums: Load, Fresh Air and Noise

A hall full of people is one of the most demanding spaces for an air-conditioning system. Hundreds of people sit still in a closed room, the load changes from almost nothing to full in minutes, and the audience expects to hear the film or the speaker without any noise from the ducts. This article explains what makes cinemas, theaters and auditoriums different and what to ask your designer and supplier.

People are the main load

In most offices the main loads are the building and equipment. In a hall, the audience dominates. As a rough guide, each seated person gives off on the order of 100 W of heat, part of it as sensible heat (which raises the air temperature) and part as latent heat (moisture). Lighting, projection and sound equipment add to this, and in cinemas the lights are low, so the people are almost the whole story. The load must be calculated for the real seat count and the real schedule, not copied from a general-purpose rule.

Fresh air and CO2

People also use up the fresh air. Design standards set a minimum amount of outdoor air per person plus an amount per square metre, and your local code decides which standard applies. The outdoor air must be cooled and dehumidified before it enters the hall, so for a full hall it can be a very large part of the total cooling load. Because the hall is often half empty, many designs use CO2 sensors to vary the fresh air with the actual number of people, which saves energy and keeps the air comfortable when the hall is full.

Humidity matters as much as temperature

A packed audience produces a lot of moisture. A system that controls only temperature can leave the hall feeling damp and stuffy. Check that the chosen equipment can remove enough moisture at the peak load, especially in humid climates.

Air distribution in a tiered hall

Cold air falls and warm air rises, and a hall with a sloped or stepped floor makes this worse. Two approaches are common: supplying air from diffusers high in the room, or supplying low-velocity air from under or near the seats and extracting it at a high level. The aim is the same in both: even temperature across all rows, with no draughts on the people in the first few rows. Ask the designer how the airflow will be checked for the actual seating layout.

Noise

A hall needs a low background noise level, so ducts must run at low air velocity, with silencers where needed, and the fans, chillers and compressors must be isolated from the building structure so vibration does not carry into the room. Ask what noise level the design is aiming for, and have it written into the specification.

Part-load operation

A hall is full only part of the time, so the HVAC system runs at partial load most of the day. Equipment that is efficient at part load, such as multiple chillers that start and stop in stages or inverter-driven units, will use less energy than a single large unit that cycles on and off. This is where a good control system pays back; see our guide to HVAC controls and BMS integration.

Which system fits a hall?

• Central air handling units with a chiller: the usual choice for larger halls, because it gives good control of fresh air, humidity and noise. See AHU and chiller systems and our comparison of air-cooled and water-cooled chillers.
• VRF: works well for foyers, offices and smaller rooms, but the large fresh-air and humidity load of a hall usually needs a dedicated outdoor-air unit alongside it. See VRF or chiller.
• Packaged rooftop units: a compact choice for small halls where plant-room space is limited.

Information to give your supplier

Send the seat count, the schedule of use, the hall's size and the design conditions, plus your noise target and the fresh-air standard. Our checklist for requesting an HVAC or chiller quote lists the rest.

Summary

A hall's HVAC design depends on its audience, fresh air, humidity, air distribution and noise, and on how it behaves at part load. Treat these as requirements from the beginning, not as problems to fix after the seats are installed. See the HVAC systems we supply, try the HVAC engineering advisor, or request a quote for your hall. If you are also planning the seating, read our guide to choosing cinema and amphitheater seating.