Foster continued
between two plates, typically three-eighths to three-fourths apart with one plate grounded and one plate charged positively.The positively charged particle is pushed away from the positively charged plate and attracted to a negatively, or grounded plate. These devices are very effective as long as they are cleaned regularly. Most have automatic wash systems. However, since the wash down produces grease laden waste, a grease trap is usually required by code. A supply of hot water in volume, detergent supply tank and dosing system is also required.The ESP control panel, detergent dispenser and the grease trap need to be factored into the space requirements for a complete system. In addition to automatic cleaning, another benefit of ESP systems is that they have a very low-pressure drop and can be used with solid fuel cooking like wood-fired pizza ovens or grills. The benefits of having a lower-pressure drop (0.15” vs. up to 3.75”) for a multi-stage filter unit means smaller fan motors and less fan energy. When an ESP becomes clogged, its ability to abate smoke and odor suffers, but the fan will continue to exhaust, avoiding kitchen shut downs. Optimal performance requires routine maintenance. Even with automatic cleaning, the ESP still requires manual cleaning on a periodic basis, depending on the cooking volume and type. It’s best to contract an outside service company to perform this task to keep the system run-
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Figure 2
ning at peak performance. It’s also important to provide full access to all parts of the ESP system for routine service and parts/replacement repair.Too often ESP systems are installed above drop ceilings or over walk-in coolers where access is challenging and service is hard to perform. A system that is out of sight and can’t be monitored by management is less likely to receive the necessary maintenance—and when it does, it costs more money. Multi-Stage Filtration (Bag Filter) These devices (see Diagram 2) use a series of increasingly fine filters to collect the material in the exhaust. The first stage is a two-inch or four-inch pleated filter, the second stage is a deep bag filter, and the final stage is either a HEPA or a 95 percent DOP filter @ 0.3 microns. On the positive side, these filters are simple and lower in initial cost, and there is no support equipment required, such as detergent dispensing, grease traps, or hot water supplies. However, the negative is the high-pressure drop (up to 3.75”) of the filters (bigger fan motors and more fan energy), coupled with the fact that as the filters load up, they will reduce the air flow through the system. These devices typically have sensors to indicate at the control panel when the filter needs to be changed. If the filters aren’t replaced in some of these systems,the entire exhaust system will shut down and the kitchen will be out of service.This leads to three other big negatives in using multi-stage filters for heavy-cooking applications (vs. ESP systems): • The cost of the filter replacements can be quite high and continues through the life of the project. • A frequent need to change the filters often requires building a catwalk or a grating around the unit or locating it on a floor slab in a dedicated room or space. • Bag filters and the high-efficiency final filters are not commonly stocked like furnace filters or replacement water filters. If you run out of replacement filters on a Friday evening, it’s possible you may be shut down for an entire weekend. Lastly, maintaining adequate backup filter stock adds to space requirements and becomes another operating cost for the system. Considering these and other issues, it often makes sense to continued on page 24