Industrial-strength design: HVAC systems
Manufacturing and industrial facilities tackle heavy-duty projects during their day-to-day operations—so it makes sense that engineers working on such structures face a number of tough challenges. Engineers offer advice on how to achieve strong results in HVAC systems and to achieve sustainable, energy-efficient buildings.
Jerry Bauers, PE, NEBB Qualified Professional, National Program Executive, Outcome Construction Services, Kansas City, Mo.
Jason R. Gerke, PE, LEED AP BD+C, CxA, Mechanical and Plumbing Group Leader, GRAEF, Milwaukee
Mark O’Connell, PE, Manager of Facilities Engineering, Matrix Technologies Inc., Maumee, Ohio
CSE: What unique HVAC requirements do such structures have that you wouldn’t encounter on other structures?
Gerke: A manufacturing or industrial facility will typically have a large outside air requirement to offset the various exhaust systems throughout a plant. Energy-efficient design and placement of these make-up air systems will provide a benefit to the owner long after the design and construction team is gone. It is important to look for innovative ways to provide energy recovery in these systems, specify efficient fans/pumps, and ensure specified control systems are doing what they are supposed to do, i.e., commissioning.
O’Connell: Industrial environments have a wide range of HVAC requirements. Where commercial and retail facilities are focused on comfort cooling, an industrial facility may need explosion-proof ventilation in one area and a cleanroom environment in another. Process air streams may require large volumes of outside air, use specialized systems to clean the air, and maintain relative pressure zones. Such ancillary systems include dust-collection systems, scrubbers and laboratory hoods, and their control systems.
CSE: What changes in fans, variable frequency drives (VFDs), and other related equipment have you experienced?
O’Connell: Forward-curved fans are not being used as frequently because they do not meet energy code for larger volumes of air. Higher energy-efficiency requirements are being dictated by ASHRAE energy standards. VFDs are used more frequently than traditional starters, because the cost premium of using VFDs has diminished. Governmental regulation requires that refrigeration systems be more energy efficient and contribute less to the greenhouse effect. We see that industrial cooling needs are being met more frequently through ammonia as an alternative to more traditional refrigerants.
Gerke: Variable-speed drives are a standard in all current design practices. We have focused on using direct-drive fans whenever possible, and evaluating the performance of fan arrays whenever appropriate in air-handling units. There have been technology improvements with more widespread use of electronically commutated motors (ECM) and fan blade knowledge that have increased efficiency and created quieter moving parts.
CSE: Have you recently specified more alternative HVAC systems? This may include displacement ventilation, underfloor air distribution, chilled beams, etc.
O’Connell: Indoor air quality for systems that use great amounts of outside air are large users of energy for heating and cooling the air. As a result, we have used “flow-through ventilation” to provide comfort cooling to occupants before the air is exhausted through hoods.
CSE: Describe a challenging air-handling system you recently specified.
O’Connell: We are currently working on a project associated with the installation of two laboratories used in a chemical manufacturing facility. The laboratories are located on two separate floors and are designed to meet NFPA 45: Standard on Fire Protection for Laboratories Using Chemicals requirements. The project introduces 18 new lab hoods that require 100% diversity of use and 20 air changes per hour. This volume of air requires that a new HVAC air handler, re-heat equipment, and lab exhaust fans be installed on an elevated structure above the existing building. Design challenges include routing large-diameter ducts through existing building plenum spaces, and the balance of energy efficiency with human comfort.
CSE: Many aspects of structure sustainability (power, HVAC, maintenance, etc.) require building personnel to follow certain practices to be effective. What, if anything, can you as an engineer do to help increase chances of success in this area?
Gerke: Designing systems for the end user is an often-ignored task. It is important that basic items such as maintenance clearances for coil removal, motor removal, and future equipment replacement are observed during the design phase. However, there are other important points to remember during design that will impact the long-term use of the equipment and systems. A design engineer should remember to specify the same type of equipment whenever possible in a building, locate above-ceiling equipment in easy-to-access locations, and use the same equipment component configuration over and over instead of creating a design masterpiece in each location. It is important to remember that maintenance personnel can later be your friends and influence future work, or they can issue complaints that shed a backlight on your high-quality designs.