Whether you’re planning a new plant or are responsible for operating an existing one, it’s critical to have a strategy to ensure high HVAC performance and a healthy IAQ. A three-step process can help — identify the problem; gather the data and analyze, analyze, analyze; then arrive at a solution (using consultants, if necessary).
Start with an up-to-date plan view of the facility. Document the HVAC criteria each area requires, from the dock that receives raw material to the dock that ships finished products out the door. List each area on a spreadsheet and document its problems by asking a series of questions that will keep you from jumping to an incorrect conclusion or solution.
- Does the cleanliness of the air in the space (ordinary dirt as well as odors) indicate a contamination problem?
- Have the applicable ventilation codes changed lately? If so, identify and document.
- Has new production equipment, using new quantities of exhaust air, been installed in recent years?
- Is the HVAC in the office and other critical areas “positive” (more air supplied than exhausted) relative to the rest of the plant?
Check the governing ventilation codes and how they affect each part of the plant. Bear in mind that although the HVAC requirements for products and workers might be different, they must still coexist. One or the other will dominate the major portion of the plant. Some areas will become more critical than others as you seek quality of product, a clean, healthy facility and a performance-optimized HVAC system.
Color-code different building plan areas using pencils or CADD (the best way) and overlay a sketch of the HVAC systems. Identify clearly the requirements for each space as well as what actually exists. Keep a hard copy of this overall plan handy as you analyze each area. If necessary, seek help from technical societies or industry standards as to what constitutes good environmental criteria for your plant.
Understanding the relationship among different areas of your plant and the relative cleanliness and ventilation rates each requires might be a challenging task, but it’s essential to good performance and IAQ.
Check the ductwork and air distribution to determine if any HVAC systems are feeding conditioned air to multiple plant areas having different criteria. Look for overlap in areas being served. Don’t heat or cool large, vacant spaces where there is neither product nor workers. See if production can be isolated from areas that tend to contaminate air.
A plant cluttered with miscellaneous HVAC equipment probably started out with good centralized, customized air handlers designed to treat and distribute air for a certain production scheme. Through the years, as production changed, auxiliary heating and cooling became necessary. Budget-sensitive commercial equipment was probably added for certain small spaces. Collectively, this mass of equipment not only fails to do the industrial job, but eats into the plant’s energy efficiency and multiplies its maintenance requirements. Extraneous equipment represents another vehicle for dirt, moisture and pollution to enter the plant. In an effort to save energy, complicated controls might have been added. Bad decisions about air distribution could have exacerbated the energy problem.
Examine and document the physical condition of the HVAC equipment. Start a permanent log that lists the technical data and physical condition of each piece of equipment, including age and the area it serves. Look for equipment and systems serving areas in which performance requirements have changed. Ask if the equipment can do its job in a reliable and efficient manner or whether it should be replaced.
Review the humidity situation. Too much or too little can wreak havoc with your product, increase HVAC energy demand and never provide a comfortable environment. The same building, placed in a different part of the country, will present entirely different considerations. Dry winter environments typically plague the North. Excessive humidity during summer months is the enemy of production in the South. Likewise, your production process might be producing an excessively humid or dry environment anywhere in the plant.
Solutions will appear
Consider eliminating overlapping ductwork and replacing ductwork with industrial air diffusers or nozzles that throw large quantities of air long distances. If ductwork interferes with maintenance, another consideration might be fabric ductwork. When work is necessary, simply deflate the ductwork and pull the fabric aside like a shower curtain. The installation cost might be less than half the cost of using standard ductwork. The fabric is durable and easy to maintain. Both solutions reduce static pressure loss, save energy and help maintain HVAC exactly where you need it to be.
Test and balance the air systems. Most HVAC systems are badly out of balance within five years of installation. Hire a certified test and balance contractor to put your system in order after you finish your hardware and ductwork changes. You might be pleased to discover a lot of that auxiliary heating and cooling equipment can now be abandoned or used elsewhere as a result of good testing and balancing.
Bring the systems up to code and look for opportunities to reduce outside air. Erecting barriers around production areas might reduce required illumination, outside air ventilation and contamination immediately while improving control of critical temperature and humidity. Having smaller functional areas reduces the need for HVAC treatment.
Stratification of the HVAC system works well in many plants. It involves bringing the air diffusers down to a level where treated air is needed. This allows adjustable-head industrial diffusers to produce a quality environment while avoiding air-conditioning the ceiling.
Adding a humidification system to a large air handler can waste energy and become a maintenance nightmare. It’s difficult to achieve the control you need at your product. Every “wet area” can become a farm for black mold.
Instead, consider spot humidification. This involves introducing vapor directly into the space itself or the final air distribution system ductwork. Humidify no more volume than necessary and make sure the humidifier system can be serviced and maintained easily. Humidification in a manufacturing plant is often better achieved with atomizing systems that infuse moisture directly into the space. It requires no energy, except for a small circulating pump. It may require more maintenance than what the manufacturer recommends, and leaking water needs to be a consideration. Installing indirect (steam-to-steam) systems in ductwork might be best for areas where steam- or water-side contamination of product compromises quality.
If the humidity is too high, dehumidification by means of refrigeration-based equipment is typically the first approach to consider. Unfortunately, ordinary direct-expansion refrigerants usually can’t control relative humidity (RH) below 40% to 45%. Super-cooling followed by reheat reduces the RH, but fails to remove moisture. For low humidity and controlled moisture removal, desiccant dehumidification is the best consideration. Desiccant-impregnated wheels mounted either in air handlers or total air systems are the mainstay of holding critical humidity levels. Commercial air-conditioning units, meant for human comfort, rarely meet the close tolerances of humidity in production plants.
Control other materials
More precise control over IAQ should include more efficient media filters or, in some areas, even HEPA filters. Standard 30% air filters in HVAC equipment protect cooling coils from dust, but that’s all. The production areas between dirty truck docks and clean rooms are often overlooked and can compromise IAQ seriously.
If the production line off-gasses volatile organic compounds or releases nitrogen, ethylene or other vapors, or if vehicle exhaust finds its way into the plant, look to modern gas-filtration to deal with it. These feature activated carbon filters for the heavier compounds and potassium permanganate filters for the lighter gases that bypass the carbon elements. Think of it as a light scrubber system.
Don’t overlook the static pressure and increased power requirement that filtration introduces. Balance the system with static pressure reductions elsewhere.
Installing more exhaust fans isn’t always the best solution if you don’t have sufficient makeup air to prevent the plant from going “negative.” Otherwise, you’ll find contaminated makeup air entering through cracks around doors windows, louvers and skylights, which increases your energy bills and pollutes the plant.
Review your HVAC maintenance records. Badly located equipment is difficult to maintain. Remember, equipment won’t remain efficient for long without a serious maintenance program. Maintenance on any air-moving device or energy converter (boilers, water heaters, chillers, humidifiers, fans, heat exchangers, unit heaters and coolers) requires that they remain clean, balanced and lubricated. Clean fan blades, condensate drain pans and coils regularly. Clean filters increase system performance because they improve equipment performance.
With the fundamental HVAC system elements, associated energy conservation measures and IAQ now documented and analyzed, it’s time to step back and look at the plant in a holistic manner. The changes required for interdependent HVAC systems have now become obvious:
- More localized humidification and dehumidification.
- Rebalance and realignment of air distribution.
- Tailored maintenance.
- Reduced space allocations.
- Specialized filtration.
- Spot cooling and spot heating.
- Reduced air-system static pressure.
- Operational changes.
A second look
Finally, develop and fine-tune a new sequence of operation for your HVAC systems. Eliminate or consolidate some of those auxiliary pieces of commercial HVAC equipment. Reuse waste heat from your process or building exhausts as an auxiliary heat source. Use waste heat from your refrigeration processes to heat water for reheat coils or domestic water.
Add auxiliary heating, cooling and humidification to air streams to satisfy the conditions at that point of use. It’s unnecessary to treat large volumes of air at the air handler when a particular area demands only a small fraction of the flow. Be comfortable with any solution and its financial payback. Extensive solutions might require the help of an outside consulting engineer or other expert.
Whether IAQ is addressed directly or in conjunction with increasing HVAC-system performance and energy conservation, the results should be the same. Both approaches to IAQ are interconnected and each relies on the other for success.
Eileen Duignan-Woods, P.E., is owner of E.D.W. Associates Inc., Rockville, Md. Contact her at [email protected] or (301) 230-1468.