RETA Breeze Jul-Aug 2025

This engine room is one of multiple engine rooms at Miller Poultry, Orland, Ind. It primarily consists of a HPR/Thermosyphen pressure vessel, a high temperature recirculator, and four GEA 400 GLX model compressors. Courtesy Henry Wilkins, Miller Poultry

UP-FRONT PSYCHROMETRIC CONCEPTS • Condensation will form on any surface that is at or below dew point com pared to the air temperature around it. This is the same principle explaining why a glass of tea sweats in humid weather. As air is cooled, the relative humidity of that air increases while the dew point remains the same. As the air temperature rises it holds more moisture, which is counter to what most people tend to think. The southeastern portion of the United States knows this all too well in summer months. There is a maximum amount of water vapor (measured in grains of water) for any given air temperature. When direct, natural-gas-fired heaters are used in MAUs or RMAUs, the burning of natural gas adds moisture to the air. Understanding basic plant construction and how to prevent heat and moisture intrusion, in addition to the above, will help minimize problems. In older plants, wall separation and roof leaks can become • • •

the bane of any refrigeration or mainte nance manager’s existence because these things can, and do, allow moisture and bacteria in the plant—ultimately at the risk of shutting the plant down until repairs can be made. The following information details a traditionally constructed harvesting facility. • Pre-cast or pre-stressed concrete “T” walls and ceilings. The exception to this may be in areas such as the holding shed, offal and any form of wastewater treatment. Some plants are just for harvesting while others are a combination of harvesting and further processing (partially or fully cooked products). o Each plant has its own unique requirements for design. • In general, the different areas of a harvesting plant consist of the following areas: o holding shed (usually separated from the harvesting plant itself); and o hanging pen. The hanging pen typically is an area with a lot of ventilation opportunities: • 

gas fired burners) and filter the incoming air to at least 10 µ. Other areas of the plant, such as deboning in a poultry plant, are refrigerated. This is typically accomplished with ceiling-hung evaporators, but as time passes, the use of refrigerated makeup air units (RMAU) is employed and comes with a minimum of using 5% outdoor air to help pressurize the building; these can be engineered to use more outside air if desired. This must work in conjunction with strategically placed exhaust fans. A common issue in food plants is to replace or even add equipment that requires exhaust fans without any consideration to plant air balance. It usually isn’t until temperature or condensation issues arise that brings this to attention and is most often blamed on a refrigeration problem. In plants that have any age on them, it is advisable to have a plant air-balance study performed to get a baseline and any recommendations that may come from that study. It only takes one exhaust fan installation to wreck the air balance of a plant. Correcting it typically takes far longer than it took to install the exhaust fan. Communication between departments can help prevent this.

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