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.
When designing TV production facilities, one of the major factors to consider is the type of ventilation system required for the comfortable, quiet and efficient operation of the facility.
TV production facilities can be uncomfortably warm, even hot. Studio lighting is by far the primary determinant of heat load in a production space. Even though other components, such as solar load and size of audience, may come into play with a street-front studio, nothing compares to the sheer immensity of watts-per-area devoted to production lighting.
The industry standard load for production spaces is 45W per square foot. A small studio may have a substantially larger load, because the net production area ratio is so much higher than in a larger studio. In large studios, you can theoretically lower this load to the range of 35W to 40W per square foot. However, this is impractical in reality, because air has to be delivered locally — at the area of production — in quantities that average 45W per square foot, and that could be anywhere in the studio.
Cooling is for people
Another factor that drives the design of a cooling system is physics — how heat is perceived by studio occupants, which is substantially different from what we are used to in a normal occupancy, such as an office or a home.
In a TV studio, heat is experienced as radiation from a set of lighting sources. This is radically different from convection, which is experienced as warm air.
By definition, radiation is the direct transport of energy through space via electromagnetic waves, light included. Convection is the transfer of heat by the actual movement of thermal energy in fluids (in this case, air).
Understanding these two methods of heat transfer is critical to designing a cooling system that is workable for the talent who use the studio space. It is from this knowledge that you decide on an ideal temperature for the studio, one that must be maintained while production is underway.
How cold should it be?
Some readers may be familiar with a phenomenon experienced by skiers. The temperature is cold (below freezing), yet they are exposed to full sun in the mountains, with the snow reflecting additional sunlight on them. It often feels warm, even though the skier may be wearing only a T-shirt. When the sun goes behind a cloud, it feels incredibly cold. The skier was experiencing heating by radiation, with little convection heating. Air is cold and holds little moisture at low temperatures; hence, there is very little matter to be heated by radiation.
This is the same effect your talent will experience, to a lesser degree, when working under the lights. So, how cold should it be? It should be cold enough that the talent doesn't sweat. An ideal temperature is at least 68° F for extended periods, but it is not unusual to find studio temperatures as much as 4° F lower. If there is an audience, those audience members can feel uncomfortably cold.
Calculating the cooling loads
The desired temperature of the studio when it is in operation is called the design temperature. The other important temperature is the discharge temperature at which air is discharged from the air diffuser. With these two temperatures in hand, and with the estimated load based on 45W per square foot, you can solve an equation for the required air volume by using the sensible heat formula. Typically, the entire load in a studio is sensible heat, which is heat in the form of thermal energy. Latent heat, the amount of energy in the form of heat released or absorbed by a substance during a phase transition, plays a negligible role in a typical studio design. The sensible heat formula is hs = 1.08 q Dt where:
- hs = sensible heat in BTU/hr;
- q = air volume flow in CFM;
- t = temperature difference in degrees Fahrenheit (delta in temperature between design and discharge temperatures); and
- 1.08 = a formula constant.
Or, as it is more commonly written, BTU/hr = 1.08 × CFM × Δt.
With an understanding of the variants (design and discharge temperature), once given a load, you can calculate scenarios to help better understand the implications of design temperature criteria decisions and system selection.
System selection issues
Every facility has a set of givens, each of which is critical in selecting a cooling solution for your studio. Here are some things to consider:
- When adding a studio to an existing facility, what type of infrastructure is already present for this project to tap into?
- Do I need a stand-alone system, or is there a chilled water system available?
- Is this studio part of a planned, new facility, where an overall cooling and redundancy strategy is to be considered?
- What is the initial cost of various system options when balanced with an operational cost analysis?
- What are the maintenance and reliability issues?
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