Southland Industries Engineering: Carl R. Darnall Army Medical Center Replacement
New construction at a hospital/health care facility.
Engineering firm: Southland Industries Engineering
2014 MEP Giants rank: 81
Project: Carl R. Darnall Army Medical Center Replacement
Address: FT. Hood, Texas, U.S.
Building type: Hospital/health care facility
Project type: New construction
Engineering services: HVAC/mechanical, energy/sustainability, and plumbing/piping
Project timeline: 12/1/2010 to 11/30/2014
MEP/FP budget: $4,600,000
There were many significant engineering challenges in providing the design for the 940,000-sq-ft military replacement health care facility for the U.S. Army in Fort Hood, Texas. First of these challenges was providing the ability to deliver and maintain the required amount of outdoor air while meeting the request for porposal’s (RFP) energy reduction goals. This can be difficult with a conventional recirculating (mixed air) system coupled with the Unified Facility
Criteria (UFC) mandated outdoor requirements, which, in many cases, are more stringent than ASHRAE. Once the main central system was selected, the next hurdle was laying out the systems within a buildingwide integrated building system (IBS — interstitial space). The IBS is used to route all the main MEP systems for the facility, from the associated mechanical spaces out to the rooms in which they serve via a walkable interstitial space with UFC outlined goals for maintenance accessibility, modularity, and limiting impacts to the occupied spaces for future renovations. As with most of today’s engineering efforts, there is an overlying focus on sustainability. Energy and water conservation were key focal points for the client and can be challenging for hospital facilities, which are known to be heavy users of both. The project location in central Texas is susceptible to droughts, so water use reduction was a major focus for the design team. The trio of heavy domestic water use common with hospitals, a large project site irrigation demand, and the need for a water-cooled central plant to meet energy goals provided large consumption demands the team would have to work through to reduce water usage. On the energy front, the team had to work in concert with the architectural and electrical engineering counterparts to find solutions to overcome strict UFC lighting requirements and the hot and humid climate, while providing adequate fenestration for views and daylighting to provide a positive healing atmosphere for the hospital’s patients. This required the design team to consider proven technologies along with thinking outside the box for creative ways to meet the project energy goals. Managing all the potential energy conservation measures versus the cost, and doing so quickly as not to hold up the design, proved to be a formidable task for a project of this size and magnitude. From start to finish, the design of this facility was a huge test for the design team, offering many challenges including system selection, MEP infrastructure coordination, and sustainability objectives bound around rigorous project criteria. The team had to sharpen their pencils to deliver the ultimate goal of the client for this world-class facility.
To meet the challenge of energy conservation and exceed the minimum outdoor air requirements for the facility, a 100% direct outdoor air system (DOAS) with energy recovery wheels was used. This provides superior indoor air quality by continuously exceeding the minimum outdoor air rates required by the UFC and ASHRAE, while mitigating airborne infection concerns from recirculation of air. It also maximizes system flexibility for future renovations with the capability to achieve all UFC or ASHRAE ventilation requirements for any space type without modifications. Together with appropriately selected energy recovery devices, the DOAS system still meets the energy conservation goals of the project including LEED, EPAct, and EISA. To tackle the unique challenge of routing all
the MEP systems while maintaining accessible pathways to equipment, the design team turned to a BIM solution. Using Revit and Navisworks as BIM tools, the design team was able to integrate accessible walkways to over 1,300 terminal units by modeling the access aisles, equipment, and associated clearances, along with the MEP infrastructure to balance energy efficiency with maintainability. Using fly through and clash detection features also allowed the team to clearly communicate the design intent to the client and to facilitate coordination with other trades. To minimize water usage, the team used several strategies to meet project goals. Low-flow plumbing fixtures, where allowed by the UFC, were used projectwide. A condensate collection system was implemented to harvest cooling coil condensate from the large central air handling units that then reused the recovered water for cooling tower makeup. Additionally, a chemical-free condenser water treatment system was used that allows over 1 million gal annually of cooling tower blowdown water to be used for site irrigation. Many key strategies were implemented to maximize energy conservation. Heat recovery chillers were used to preheat the domestic and heating hot water systems, and they were sized to meet the facility’s wintertime low load to allow the main chillers and cooling towers to be shut down during those times. A variable grease exhaust system was used on the large commercial kitchen areas to match the exhaust and energy intensive makeup airflows to the actual cooking demand. The main data center was incorporated with hot aisle containment integrated into the server cabinets allowing for higher water side and air side temperature differentials across the coil to save pumping and fan energy. To enhance occupant comfort and reduce energy use compared to an all-air system, a radiant cooling and heating system was employed to handle the entire solar, occupant, and lighting loads for the project’s 30,000-sq-ft atrium that includes two-story glazing. The in-house energy modeling team continually evaluated these measures along with low-wattage lighting, exterior sun shading, and high-efficiency glazing throughout the design process to find the right balance of efficiency and cost for the owner.