This is the fourth of an open ended series of articles detailing the design and construction experiences of the Hensley Field Operations Center, a facility currently seeking LEED certification.

---

In a previous article, I discussed the aesthetic reasoning of the raised floor at Hensley Field. But, the true capabilities of this system only become apparent when the mechanical and electrical systems underneath it are designed efficiently.  

CHURN - it’s a word that every facility manager fears. Churn is the never ending modification of administrative workstations and cubicles. Down-sizing, up-sizing, re-org’s, new technology – these all require modification of the modular furniture. More importantly, the location of the electrical and sometime mechanical systems also has to be modified. Industry average is that a workspace will require modification every two years. Believe me – I’ve lived this nightmare - I work in a building with 1100 other occupants. Even in times of economic depression, people are relocating.  

So, let’s start with the electrical/data distribution. Data is the backbone of our industry. 30 years ago, it was uncommon to need a phone at every desk. Now, it’s the exact opposite. And with more and more devices requiring network capabilities, data use will continue to grow. To accommodate this, we started with a centrally located data distribution area. We physically located this room as close as possible to the raised floor area to minimize cable length. This data room is also quite large – it is not a converted janitor closet! The data racks in this room lead to a central raceway, which runs through the wall and under the floor. This raceway runs through the center as the space, and acts as a spine from which data can be distributed throughout the space. Electrical is routed in the same method.  

From the raceway, data and electrical branch off to the raised floor boxes. These boxes sit flush in the floor, and feed the individual cubicle locations. Normally, this is where you see the most change, where a box has to move a couple feet in any direction. You can accommodate this by using 8’ whips on the boxes themselves, and laying out the boxes on 10’-12’ centers. The whips allow you to easily relocate a box one or two tiles away without having to re-work electrical conduit. 

We made a special point to select raised floor boxes that have quick-connects on the backs of them. This allows a non-electrician to safely disconnect/reconnect the electrical when the box needs to be relocated. This also allows you to only remove the floor tiles where needed, instead of every tile between those points.  

Air distribution follows a similar principle. Once again, the mechanical rooms are located as close as possible to the area, in order to minimize duct runs. There is a short length of duct running from the air handler overhead into a chase that then feeds down to the floor. From here, air is dispersed into the under-floor area, which acts as a large plenum. This plenum is pressurized and air tight, which turns it into a large continuous air duct. From here, a VAV box/grill can be located at any point for air diffusion.  

There are several other benefits that go with under-floor air distribution. First, the air can be discharged at a higher temperature while keeping the same cooling parameters. With a diffuser in the ceiling, cool air passes through a large volume of hot air before it gets to the user. This layer of hot air is a result of both hot air from the space rising and being re-circulated through the returns and also from the heat generated from the lighting fixtures. The end result is that when the cool air reaches the user, it has already been warmed by several degrees.  

Now, flip the system. By discharging cool air at the floor level, you eliminate the need to compensate for the cooling that is lost when discharging from the ceiling. Less cooling means less tons of AC required, which results in smaller (and less expensive) HVAC systems. A nice side effect of this type of system is that indoor air quality is improved, as contaminants in the air are lifted straight up and into the returns – the conditioned air does not mix with the unconditioned air as it is discharged.  

With both air diffusers and raised floor boxes being able to change at will, this space has a high degree of flexibility. At the same time, the future cost of reconfigurations is reduced. No longer is an electrician required for a simple relocation of a floor box, nor is a mechanic needed to re-route duct runs for a simple relocation of an air diffuser. As the furniture changes, all the support systems can change with it.