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50 Medical Construction & Design | M AY/ J U N E 2017 | MCDM AG.COM BY GAYLON RICHARDSON The healthcare setting is one of the most challenging and high-stakes environments for testing and balancing a heating, ventilating and air-conditioning system. At its basic level, the purpose of test and balance is to ensure the facility's HVAC system provides maximum oc- cupant comfort at the minimum energy cost possible. However, accomplishing this in the healthcare environment is any- thing but a simple task. To assist in this process, The Associated Air Balance Council, a nonprofi t association, recently released its 7th Edition of The National Standards for Total System Balance. The document refl ects the latest advancements in the test and balance industry and contains a new chapter: "Testing and Balancing Health Care Facilities." The following are key con- cepts to keep in mind when it involves testing and balancing healthcare HVAC systems. A more detailed overview is avail- able in the new AABC standards document. Pressurization is fundamental Room pressurization is a fun- damental HVAC concept in any public or commercial space. In the healthcare setting it takes on added urgency to prevent the spread of airborne hazards and protect patients and staff from germs. The AABC Standards concur with the prevailing standards and requirements. The National Institutes of Health Biosafety Level 3 Laboratory Certifi cation Requirements establish that the control pressure between pressurized rooms and the adjacent spaces be .05" WC and alarm at .03" WC4. WC is water column inch, the standard unit of measure for small pressure diff erentials. The ANSI/ASHRAE/ASHE Standard 170-2008, Ventilation of Health Care Facilities, requires that the minimum pressure diff erential must be at least .01" WC. In all areas that require pressurization, the stan- dards suggest the supply and return and/or exhaust sys- tems incorporate 100 percent pressure-independent terminal boxes. When return or exhaust terminals are used, it is recom- mended to protect against lint buildup at each grille. Evaluating building pressurization With all systems operating, the building pressurization should be evaluated. To accomplish this, the test and balance en- gineer must develop a sched- ule to identify if all fl oors are designed for positive pressure and update the document us- ing actual exhaust and outside airfl ows per fl oor. Testing the pressurization should be done on a calm day with no wind. The TBE should identify if any fl oors have excessive out- side airfl ow or exhaust airfl ow creating diff erential pressures referenced to the exterior to be greater or less than the recommended .05" WC. If vari- ous fl oors indicate excessive outside air or exhaust air, they should be documented and the TBE will provide the data to the design engineer for review. Important considerations in building pressurization include: > Duct leakage: Leaks can create room pressure problems, causing an imbalance between supply and return airfl ows that can increase or decrease the outside air requirements Total HVAC system balance in healthcare facilities T ta l HVAC t b a l a i MANY BENEFITS ONE OBJECTIVE,