Army Research Laboratory Uses CHP and MeeFog Humidification to Cut Energy and O&M CostsClean Rooms
The Army Research Laboratory in Adelphi, Maryland had been using a boiler to provide hot water as well as steam humidification to two clean rooms. A MeeFog system was installed to provide humidification to both clean rooms, at a much lower cost and with less maintenance than the boiler.
The Army Research Laboratory in Adelphi, Maryland had been using a boiler to provide hot water as well as steam humidification to two clean rooms. It recently installed a combined heat and power system in its central utility plant, but the hot water generated was not hot enough to provide needed humidification.
A Meefog system was installed to provide humidification to both clean rooms, at a much lower cost and with less maintenance than the boiler.
To save energy costs, the ARL retrofitted the central utility plant with a Combined Heat and Power (CHP) Cogeneration system. The existing high temperature hot water generator and the existing chiller were removed and two 1.1 MW Waukesha natural gas reciprocating combustion engines were installed.
There was one problem that had to be resolved before switching over to the CHP system. The old High Temperature Hot Water (HTWH) system operated at 400°, which was hot enough to produce steam to humidify the Zahl Building clean rooms. The CHP hot water system operates at 250°, hot enough for process water, but not enough for steam humidification. The boilers could be kept on line to provide the necessary steam, but it would be expensive to run them just to humidify the labs, slashing the savings the ESPC was supposed to produce.
To address this issue Ameresco and the ARL opted to go with a MeeFog humidification system from Mee Industries, Inc. of Irwindale, California. The MeeFog system uses a high pressure pump to direct water to an array of impaction pin nozzles in the air handler. These nozzles atomize the water into billions of droplets which quickly evaporate in the air stream, raising the humidity to the desired level. Although clean rooms originally used media type evaporative coolers, Bradford says that the MeeFog system is different in that it breaks the water into such tiny droplets that the surface to volume ratio of the water is high enough to allow rapid evaporation, even during the winter.
“The MeeFog system presents a lot more surface area of water to the air, which makes it easier to evaporate,” says Bradford. “It is much more difficult to get the air to absorb the water from a media evaporative humidifier.”
Mee provided the ARL with two MeeFog systems. For Makeup Air Unit (MAU) 1, there was a 5 HP duplex pump with a backup (N+1) providing 1,512 lbs. of moisture per hour. For MAU-2, is a 3 HP duplex pump system (also N+1) providing 739 lbs./hr. The MeeFog systems use water from the lab’s deionized water system and so a section of the each air handler needed to be lined with stainless steel.
“Deionized water was used because the clean rooms need to have very clean water put in the air,” says Bradford. “If we did put a lot of calcium or phosphates into the air, it would Load up the HEPA filters pretty quickly.”
With the new Meefog systems in place, the ARL was able to cap off the steam lines and shut down the boiler. Although the CHP plant just came online in mid-year, they estimate FY 2012 savings of $127,000. The Meefog systems went on line more than a year earlier and it has proved to be a lot less expensive to operate and maintain than the steam humidifiers.
“The boilers are old and tired, they have failed or are failing, and they are quite expensive to keep running. From an O&M standpoint, we prefer the MeeFog system.”— Tom Bradford, Chief of the ARL’s Engineering Division
Location: Adelphi , MD, USA
Air Handling Units: 60,000 CFM
(100% outside air)
Mee’s scope of work: Supply of fog pump skid, staging valves, nozzle manifolds, mist eliminators. Supervision of startup.
Fog System Design
MeeFog nozzle count: 140
Square footage: 155,000
Humidification capacity: 2,250 #/hr
Max gpm/hp: 4 gpm @ 3 hp
Humidification stages: 3