Imagine being commissioned to create a laboratory in which the testing conditions are so sensitive the light from a single flashlight could ruin even the most carefully designed experiment.
These were the environmental control parameters that faced the Building Team for the National Institute of Standards & Technology's Advanced Measurement Laboratory in Gaithersburg, Md.
NIST required unprecedented levels of environmental stability for the 536,000-sf, five-wing lab facility, where scientists are engaged in measuring distances in increments smaller than the radius of an atom. The slightest variation in temperature, humidity, vibration, acoustics, air particulates, electromagnetic or radio frequency interference, or electrical power can skew the outcome of tests.
Executing this complex engineering feat were Building Team leader HDR Architecture, Alexandria, Va., and a joint venture of Gilford Corp., Beltsville, Md., and Clark Construction Group, Bethesda, Md., as GC. NIST's capital improvement facilities department served as CM on the $194 million project.
The building's mechanical system moves more than 2.5 million cubic feet of air per minute (enough to fill the Goodyear blimp every five seconds, according to HDR). Churning high volumes of air is key to maintaining tight tolerances for humidity, air cleanliness, and temperature, which could not exceed 0.01 degrees C in certain labs.
To minimize the vibration from the 300+ air changes per hour in the labs, the team designed a supply air system that distributes fresh air evenly through the entire ceiling.
Being able to precisely monitor and control the temperature within the labs was a bigger concern, according to Ahmad Soueid, principal and senior VP with HDR. The most advanced control systems on the market only allowed for control to 0.1 degrees C. A collaborative effort between NIST scientists, HDR engineers, and four different HVAC controls manufacturers led to the development of a new generation of controls with a tolerance of 0.001 degrees C. Unlike typical wall-mounted thermostats, these control systems permit temperature sensors to be located virtually anywhere within a room. In general labs, the thermostat is located near the sensitive equipment. In the high-accuracy labs, four separate sensors are mounted on the ceiling.
The most sensitive labs are located in two wings constructed 40 feet below grade to avoid the vibration waveforms that travel at and near the ground surface, as well as shaking induced by wind hitting the building. There, the labs sit on isolated concrete floor slabs supported by air springs to control vibration. Each slab is "tuned" to minimize the resonance effect from common frequencies and to balance equipment loads on the floor.
While other labs have achieved similar environmental control tolerances, none have integrated such a combination of control criteria into a single facility like the AML, says Soueid.