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?
Let's start by looking at some air-conditioning system basics. (See Figure 1.) All air-conditioning is based on a fan blowing air through a coil. Either a refrigerant or water is used in a closed system to absorb the heat from the air moving through the cooling coil. This cools the air at the discharge side of the coil. The heat absorbed by the refrigerant or water is carried through piping to a condenser section, where it releases the captured heat and can begin the cycle again. Some systems use water mixtures as the medium for the heat transfer, but only rarely would they be considered as a solution. Refrigerant is the most commonly used method.
There are two basic types of systems that use refrigerant: direct expansion (DX) systems and chiller systems. DX systems use an evaporator that is in direct contact with the air stream, making the cooling coil of the air supply and the evaporator of the refrigeration loop one and the same. (See Figure 2.) In a chiller system, chilled water is produced and used as a medium to transfer the heat from air side (fans in the building) to chillers — and then to the outdoors for heat rejection.
Types of DX systems
DX systems are typically divided into unitary or split systems. Unitary systems comprise all the components of a refrigeration loop, including controls, in one unit. A split system separates a portion for installation inside the building (fan, cooling coil and filter), with the condenser and compressor located outdoors, connected by refrigerant piping. Unitary DX systems can be indoors or roof-mounted, often with a bottom discharge right into the building.
Unitary indoor DX systems are typically too small to make them viable candidates for a TV studio application, unless it is an extremely small project where a mechanical room with a large amount of louver space is available. A commercial split system allows all of the air-handling equipment to be installed indoors, resulting in many benefits:
- Air-handling units (AHUs) will be in an air-conditioned space, protected from the elements and temperature fluctuations.
- Maintenance for filters and belts is easier and therefore more likely to occur.
- Most studios require at least two AHUs. This means AHUs must be joined by ductwork so that units can share one distribution system. This is more difficult to do outdoors.
- No ductwork should ever be exposed to the elements and the deterioration that those elements cause. All exterior ductwork must be waterproofed, insulated and maintained.
DX and chiller systems
Chillers are more efficient than DX systems and can be either water-cooled or air-cooled. (See Figures 3 and 4, next page.) Water-cooled chillers are often used for large systems (500 tons where 1 ton = 12,000 BTU/hr) and require a cooling tower. Air-cooled chillers are flexible, modular systems that can be used where installation of a cooling tower is not feasible. In a chiller-based system, whether air-cooled or water-cooled, the air handler is indoors and, therefore, shares the benefits mentioned above.
Keep in mind that the air discharge temperature of a chiller-cooled system is typically 55 degrees, and for a DX system it's 60 degrees. However, the discharge temperature of a DX system can drop as low as 48 degrees when the compressors first turn on. These fluctuations, coupled with the normally higher discharge temperature, make a DX system less efficient and less comfortable for studio occupants.
Even so, DX systems are especially popular for one-time projects, because of their lower initial cost and relatively simple maintenance. Large facilities or those built from scratch and consuming more than 100 cooling tons mean higher energy consumption. In such cases, larger ductwork will be required. Always insist on a professional analysis.
Redundancy
Production facilities can be mission-critical, meaning the air-conditioning system must work in some capacity during an equipment failure, or they can be noncritical, where content is created on a flexible schedule. Each broadcaster has to identify the facilities' performance criteria with the aid of a consulting team in order to set the HVAC design criteria.
There are several levels of redundancy to consider. Complete redundancy requires at least two AHUs and related power, along with other system components. Depending on the selected system, other needed components may include pumps, chillers and other single-point-of-failure candidates.
Other levels of redundancy may be considered based on the importance of the TV studio as a key component in the content creation food chain. It is often economically desirable to include built-in redundancy for maintenance and unit replacement because even if it's not a mission-critical space, you can't be without a studio for long periods.
When air-conditioning a studio, the cost for air distribution largely remains a constant where redundancy issues are considered. Usually it takes multiple units to cool a studio, lessening the chance that the studio will be without cooling at any given time.
Typically, plan for three units with capacities so that, in case one unit fails, the other two can fulfill the cooling requirements. For example, a cooling requirement of 100 tons can be satisfied with the use of three 50-ton units. This provides 50 percent redundancy. If one HVAC unit fails while another is in maintenance, only 50 percent of the load can be served. The additional cost is primarily in the units themselves. The incremental cost is based on the risk tolerance, which defines the number and capacity of units.
Acoustical issues
If all of the other studio noise issues have been eliminated by adequate acoustical isolation via walls, doors and ceilings, then the air-conditioning system becomes the primary source of noise in a studio. It may be noise from air moving in the ductwork, or it may be airborne noise generated by turbulence at different points in the ductwork.
Cooling system noise can be diminished by placing mechanical systems an adequate distance from the first discharge outlet in the studio. This is typically 75ft. By using a lined discharge plenum of 2in (typically) and continuously lined ductwork to the discharge point most of the system noise will be absorbed prior to entering the space.
Noise generated by air turbulence can be diminished with turning vanes mounted in the ductwork, by placing balancing dampers as far as possible from the discharge and by decreasing the velocity of the air. Of these three options, the last two are the most difficult to satisfy, as they require careful design, fabrication and a thorough examination of potential problem areas. An acoustical consultant should be able to establish general design criteria.
Return air openings must exceed the supply surface area by about 10 percent and do not require direct ducting. Generally, return air is removed from the space through a transfer duct that is fully lined with 1in of duct liner and has two 90-degree turns to trap sound. To remove the air from the ceiling cavity, install a duct directly tied to the unit that penetrates the sound-isolated wall construction.
Many studios are designed for a 20-25 noise criteria (NC). To achieve this kind of sound performance, ductwork air velocities must be carefully controlled. Air delivered to a studio should not exceed 750ft per minute in the primary duct, 450ft per minute in branch ductwork and 300ft per minute or less at the studio diffuser. Selecting the air diffuser is also important. Be sure to consider both acoustical performance as well as its air distribution pattern.
Air distribution for different studio heights
Content creation spaces vary widely, both in area and in height. This requires that the strategies for ventilating them adjust according to the physical characteristics of the space. Spaces are divided into three primary categories, according to their height.
First are small studios approximately 13ft to 18ft in height, where the lighting grid is installed as high as possible. In these studios, the supply diffusers and the returns are on the same plane as the ceiling and located a short distance from the luminaries. This will provide even supply air coverage throughout the studio and remove it in clusters through returns located near the perimeter, where the heat load is less.
Even though it is common for air-conditioning to distribute air in a wide pattern along the ceiling in studios, it's necessary to get through the layer of hot luminaries to cool the occupants. A heavy mass of cold air, falling uniformly in the center of the space, will push warmer air to the perimeter, where it can be exhausted by convection through the return ducts.
The second category of studio are those in the 18ft to 25ft height range. These are medium-sized spaces in which the lighting plane is about 3ft below the ceiling. At this height, and with this gap between the lighting and the hard ceiling, there is a significant stratification layer. This is a layer of hot air created by the heat rising from the lighting instruments, which acts as a barrier to air flowing from the diffusers. A conventional method of distributing air (with a strong horizontal pattern) will simply result in the cooling being provided at the same height as the lighting, with little reaching the floor.
Therefore, use a diffuser that can focus the airflow downward and at an angle, creating a cone of cool air above the head level of the occupants. Use a checkerboard diffuser layout pattern, with some returns mixed into the pattern. The distance between the supply diffusers, the angle of the diffuser blades and the height above the heads of occupants must be planned so that there is overlap in coverage.
The third type of studios are those 25ft or greater in height, where the gap between the lighting plane and the ceiling is 6ft or greater. With so much available cavity in the ceiling above the lighting plane, the stratification layer can be exploited even more.
In this case, follow the same diffuser layout as in the plan above for the medium-sized studio. This entails providing a checkerboard pattern, creating overlapping cones of cold air and mixing in returns. Additionally, the diffusers should be installed about 6ft below the ceiling, where the returns are installed, to take full advantage of stratification. This also helps avoid having to supply air through the stratification layer. Carefully plan your cross-section so the heights of all the elements in the studio and the horizontal spacing coincide to provide the required coverage.
Types of diffusers
It is important that diffusers be selected with acoustical performance, as well as air distribution, in mind. In small studios, a diffuser and proper neck sizing should be based primarily on acoustical performance. In many cases, it is feasible to use standard products, whereas in others, you will find the ceiling so crowded with ductwork that custom diffusers may be required.
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.
