TV production spaces: ventilation systems
Jan 1, 2009 12:00 PM, By Antonio Argibay, AIA
Stay cool by selecting the right air-conditioning system for your facility.
Custom plaque-type diffusers are common in TV studios and in other acoustical applications, because the discharge opening is concealed either with a circular or square plaque that allows the air to flow out the sides. Typically, the top of the plaque has a cone or pyramid to deflect the air horizontally.
They are only effective where the pattern of distribution is not critical, such as in small studios. In larger studios, they are ineffective in getting the air down to where it is needed. The result has been a genre of solutions called elephant trunks, which are flexible canvas ducts terminated with a plaque diffuser. Using a system of ropes and pulleys, the elephant trunks can be located at the height and location where air is needed.
Nozzle-type diffusers are the preferred way to push air down through the stratified, hot layer before it loses too much cooling ability. They are built effective at delivering high volumes, without turbulence and its accompanying noise.
Other issues regarding cooling studios
You will notice that this article concentrates on the supply and return of air from the ceiling. This is largely because TV studios, by definition, should be designed to be as flexible as possible. Placing diffusers on the walls is an ineffective way to deliver air in the huge volume that a studio needs. Even placing return registers on the walls is something that has to be examined carefully, as doing so may create a situation in which the registers will be covered with scenery or a cyclorama curtain. If a wall area has a space where a return can be installed without compromising the studio's future flexibility, it should be located close to floor level, where using up to 25 percent of the air volume can substantially help airflow.
Ideally, air in a studio should be provided from the floor to maximize the advantage of convection, which allows warm air to rise. This method of removing heat is called thermal displacement. The quantities of air required, the fact that studio floor construction is many times isolated and that the studio floor surface is needed for scenic elements, such as rugs, all conspire to make this approach impractical.
Final observations
Audience studios have code requirements for smoke evacuation/purging. Consider the use of fans, because, depending on how the studio purges smoke and other special effects, you can use them separately from the ventilation and cooling system.
Taking care on important decisions regarding issues like selecting the type of fan for the air-conditioning unit will save time and money. The use of duct silencers and attenuators has been omitted here, largely because a well-planned project should not need them. If the acoustical consultant finds that, due to certain conditions in the project, duct silencers and attenuators must be specified, make sure the acoustical consultant carefully coordinates the selection and placement, because duct attenuators are frequently the source of noise caused by their turbulence.
It is important to have an acoustical consultant involved in the design and specification of any studio air-conditioning system. It is equally important that the architect, as the leader of the project, understand the issues involved so that, in coordination with the mechanical engineer, a balanced and practical design solution will be developed for your project.
Antonio Argibay, AIA, is a principal of Meridian Design.
Sizing ductwork
Regardless of the type of cooling system, it has to be delivered to the studio via ductwork. The size of the ductwork is mandated by the air volume necessary to cool the TV studio space and by the air velocities required to meet acoustical or noise criteria (NC).
Let's consider this by looking at an example:
- Find the CFM required to cool a 10,000sq-ft studio.
- Find the load expressed in BTU/hr (1W = 3.41 BTU/hr), where 10,000sq-ft × 45W = 1,534,500 BTU/hr.
- Provide the DT (delta in temperature between design and discharge temperature), assuming a chiller-based air temperature of 55° F and a design temperature of 68° F. The answer is 13° F.
- Apply the sensible heat formula (BTU/hr = 1.08 × CFM × Dt).
If CFM = 1,534,500 BTU/hr/1.08/13° F, the CFM is 109,294. - If it is a DX system, the Dt would decrease by 5° F, making it 8° F (the difference between 60° F and 68°F because of the higher discharge temperature). So if CFM = 1,534,500 BTU/hr /1.08/ 8° F, the CFM is 177,604.
Notice the increase of almost 40 percent between the two systems in the amount of CFM required to cool the space, given that the design temperature remains the same. The cooling ton stays the same in both, as 1 ton of cooling = 12,000 BTU/hr, or, in this case, 128 cooling tons.
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