Digital Signage

On Videowalls: The Grunt Work

For More:
Part 1 - Direct View LEDs
Part 3 - Video Processing

Now that you’ve picked your monitors, it’s time to get serious about the implementation. Important decisions have to be made well ahead of the installation date.

Mounts

I was in a meeting at a Fortune 500 company to discuss a 100 LCD monitor wall installed in a system without a steel backing frame in order to save money. The installation team was on its fifth or sixth week of the installation with no projected completion date, and the team was worried this would become a regular occurrence on future, similar projects.

Adding a structural frame for all locations was decided, resulting in an unbudgeted cost addition well north of $100k for all projects. It was not a pleasant meeting. Yet, once the frame was installed, the monitor installation was reduced to under five days. A painful lesson was learned by the client: Frames are expensive but worth the expenditure.

High-definition, large-scale images require precise and repeatable mounting and alignment systems. Perhaps more importantly, they require the ability to remove and replace whichever monitor type you implement, and then to precisely align the monitors again after maintenance! Front service access generally requires some type of locking and pivoting system. Rear access is often easier, but requires significantly more real estate in square footage. More often than not, these mounts are custom designed and constructed, taking months from initial contact to installation to completion. Do not think a “trade show” frame weighted down by sandbags is acceptable in a permanent installation, and plan your project accordingly.

Beware of any consultant, manufacturer or integrator who tells you differently. The all-up weight of these walls is in the many-ton range; thus, they require a structural engineer-approved design and strong physical ties to the structure. Heaven help you if your videowall ever fell on a guest or employee.

HVAC

The good news is that today’s LCD monitors use less than half the power of their plasma predecessors.

The bad news is that they still use quite a bit of power and project significant heat into the room. One commonly used 24/7 WXGA LCD monitor specs out at 200 watts. Thus, 100 monitors use 20,000 watts, the equivalent of a 27-horsepower motor. For comparison, a first-generation Toyota Prius motor tipped the scales at 30 horsepower. In keeping with the comparisons from Part 1 last month:

Heat 1.0x (LCD panels) = 1.0x (LED Matrix) = 2.5x (LED Tiles)

Yet, even without knowing their heat rejection factor, the simple fact is that some of those LCD monitors have four internal fans each for a good reason: Much of their power ends up as heat. Potentially 68,000 BTU/hour is exhausted into the room just for the monitors. That’s six tons of air conditioning just for the monitors to maintain an existing temperature (you’ll want a bigger one in practice)!

LED Matrix heat output is similar to LCD panels. LED tile technology runs considerably hotter (one manufacturer’s cube is specified at 239 BTU/hour). Make sure to take this into account with your facility design.

Smart consultants and integrators work with the architect to build what is, in effect, a chimney effect surrounding the monitors. There should be a natural convection path for the exhaust heat from the monitors to exit the building. Hopefully that pathway does not include guests in it.

Design staff has to recognize that video technologies often also require a relative humidity of 20% and 80%. That may mean that, on a dry day, you will have to humidify the room, a feature not all HVAC systems include. On a wet one, you’ll have to dehumidify, a feature generally included in every system already.

Question 1: How Much Power?

Comparing power consumption between the three technologies is an important consideration. Unfortunately, there is no direct competitive information at the same light output from the manufacturers, so here is my best guess:

Power 1.0x (LCD panels) = 1.0x (LED Matrix) = 2.5x (LED Tiles)

Thus, given an equivalent-size wall at the same light output, LED tiles will expend more than twice the energy of either LCD monitors or LED matrix panels. At present energy rates, an efficient wall cost runs roughly $20k for power (not including HVAC), if run 18/7. An equivalent LED tile wall runs $50k in power alone, annually. It is unlikely electricity rates will be going down anytime soon.

Question 2: How many power outlets are required?

Although this seems an almost silly question, it helps to stop and do the math. More than likely, your 100 monitors will come with a hundred six-foot-long power cords. Some systems daisy chain, others don’t, and this will dictate the actual quantity and location of your outlets. Ideally, they will be close enough to the monitors, such that the outlets can be serviced. Each outlet location must be circuited to handle the appropriate current rating of the monitors. Again, the math dictates a number of circuits, and it is usually best to dedicate a separate panel board for the exclusive connection to the wall. There are typically other items in your system that will also require local power. Make sure to include those in your configuration early on, and coordinate your requirements with the facility electrical engineer.

Question 3: What of power & grounding?

Any professional large-scale video and audio system demands high-quality power and a quality technical ground. You will require a separate (likely K-13 or above rated) transformer if you are looking to isolate your AV system from other building systems, and provide surge protection, noise attenuation and a single point to terminate all your AV power grounds.

The grounding expectations are embodied in NEC Articles 800, 810, 820 and 830. If you find drawings not referencing these standards, find someone who does to work on your project.

Question 4: Should you use fiberoptic rather than copper for signal distribution?

Yes. Distributing your wall’s video content on fiber rather than copper might prove highly recommended. If you don’t, finding and breaking a ground loop may prove impossible. It is a relatively small investment relative to the rest of the system cost, and avoids an obvious long-term pitfall.

I’ll discuss processing next month in Part 3.

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