Investment in a postharvest building and its contents is one of the greatest long-term investments a grower/packer will make. Every aspect of postharvest facility must be well planned. To help start the design process, here are some ideas that can help new growers along the way.

A postharvest facility is an investment in quality maintenance. The level of sophistication of the facility is justified by both the amount and type of use. A facility that is used for direct retail sales to the consumer is quite different from a facility used for sales to wholesale buyers. A postharvest facility, unlike many other types of large capital expenditures, such as tractors and harvesters, is frequently subject to numerous alterations and additions. It is a mistake to assume that any building design is final because very few of these buildings remain as they were built originally.

Economic considerations, marketing opportunities, and many other external forces change the requirements of these structures. A facility with excessive and unused capacity makes little economic sense. However, all growers must plan for future expansion or alterations when they initially select a site and not years later when future expansions must necessarily work around that existing facility.

Postharvest facilities are expensive. The best advice for someone who plans to build a postharvest facility is to seek advice from many sources because one source will not have every answer. For those who are seeking design details, a good place to start is “Design Essentials for Refrigerated Storage Facilities, RP-1214” published by the American Society of Heating, Refrigeration and Air Conditioning Engineers, Inc.

Other good sources of information include local Cooperative Extension center specialists, postharvest engineers who work as consultants, building contractors, equipment manufacturers, environmental regulators, and land use experts. An especially valuable source of information is other grower/packers who may have built and used similar facilities. These experienced growers/packers have first-hand experience that can help novices avoid the most common mistakes. It will be helpful to ask these individuals what they would have done differently.

A postharvest facility for fresh produce must support a complex range of inter-related functions. In addition to being a building that protects fresh produce from environmental factors, which reduce quality, the building also houses the machinery, equipment, and the people needed for washing, sorting, packaging, and shipping produce. In a postharvest facility, many different tasks must be accomplished in the correct sequence and a timely manner. It is easy to think of the building as just a building, when in reality it is a cooling and handling facility surrounded by a building. Thus, the equipment design and layout are determined before the actual building.

Since a postharvest facility is essentially designed for material handling, the layout must accommodate the smooth flow of material into, through, and out of the facility. The spaces and all the equipment inside the facility dictate the shape, size, building materials, and the location of wiring, plumbing, and doors of the building. In general, the flow of material inside the building should be only in one direction. This means that the unprocessed products should enter through one side of the building and after processing, exit from the other side. This is especially critical in a washing and grading facility where food safety dictates separating dirty material from clean material.

No two postharvest facilities are exactly alike because each one is designed for a specific set of unique needs. The owners and operators of all facilities must be clear about the proposed function of the facility. It is wise to identify what problem the design is trying to solve, and to create clear statements about how the facility will be used for only cooling, cooling and storage, or also washing, sorting or packing; and for processing and storage, wholesale, retail, or some combination.

Throughput is the amount of material or items passing through a system or process. New owners of a postharvest handling facility must be clear about what type(s) of produce will be handled, how much of each (throughput) will move through the facility, and when will this occur. Each type of produce has its own unique requirements for temperature and relative humidity. These requirements can have a significant effect on the size and number of cooling rooms.

The engineer, builder, equipment supplier, and their client are a team. Good communications are essential to a successful relationship. As the technical expert, it is the job of the postharvest engineer to explain what is possible and what is not.

There are many regulatory rules and guidelines that can affect a postharvest facility. Land use and zoning, water use, waste disposal, food safety, worker safety, fire safety, environmental impact, and insurance obligations are just some of the areas that must be considered in the design and operation of a postharvest facility. Zoning rules vary considerably from place to place. Some jurisdictions consider a postharvest facility a farm building with few restrictions, although this has become the exception. Other jurisdictions may consider the postharvest facility an industrial building with numerous restrictions. The rules for facilities located inside a city limits may be far more restrictive than those in the rural areas of the county. Since there can be more than one regulatory agency with different and even conflicting rules, it is everyone’s job to know, interpret, and properly apply all the rules.

Even a modest postharvest handling facility can cost several hundred thousand dollars, while large, very complex facilities might cost tens of millions. With that much money at risk, financing agencies and their underwriters often impose additional restrictions and insurance to protect their investments.

Sufficient three-phase electrical power is one of the largest variable costs associated with a postharvest handling facility. Many of these facilities are located in rural areas that are some distance from three-phase lines. Power companies may require very high fees to extend the lines or long-term contracts as a condition for connecting. Before selecting a facility location, it is important to discuss the anticipated power demand with the local power company.

The availability of potable water in sufficient quantity is an important issue because postharvest cleaning and grading facilities use huge amounts of water. Large vegetable washing operations can consume as much as 40 thousand gallons of water per day. In rural areas, which may be far from county or city water systems, water must be pumped from wells on the property.

Wastewater is often very dirty with suspended solids and a high biological oxygen demand (BOD). Few county or municipal sewer systems are willing to accept this wastewater without significant pretreatment. The water may be considered an industrial wastewater when discharged to a municipal wastewater treatment plant or to surface waters in canals, creeks, or ponds. Land application of this material may be permitted, although a non-discharge permit may be required. Many postharvest operations have settling ponds and systems for applying the wastewater to adjacent fields. Facility owners may be required to obtain a wastewater discharge permit from the North Carolina Department of Environmental Quality.

Washing and sorting facilities generate a large waste stream. This waste cannot just be dumped out of sight and forgotten. Composting or field application is an alternative but owners of postharvest facilities must be knowledgeable about all restrictions. Thus, owners must develop a solid waste management plan that details the removal of all solid waste.

Every aspect of postharvest handling is concerned with food safety. Nothing can shutter a postharvest operation more quickly than being identified as the source of a serious outbreak. It is much easier to build food safety into the original design. Every aspect of the design, construction, and operation of a postharvest facility must focus on minimizing food safety risks. Owners of postharvest facilities need to have a thorough knowledge of Hazard Analysis Critical Control Points, which is an internationally recognized program for identifying and managing food safety risks.

Floors

A poured concrete floor on a well-packed grade of #57 stone is universal in postharvest buildings. In areas of heavy truck and fortlift traffic and loads, six in. of concrete with reinforcing mesh is customary. In light load areas such as offices, 4 in. of concrete is common. A 4 mil polyethylene sheet is used under the concrete as a vapor barrier. The concrete floors under refrigerated rooms have extruded foam polystyrene insulation positioned under the vapor barrier. The r–factor of extruded polystyrene is 5 per in. of thickness. The recommended thickness of the insulation under the concrete depends on the difference between the soil temperature and the intended temperature in the room. For most applications above freezing, 2 in. to 3 in. is sufficient.

The ground below the concrete floors in cold storage rooms that are kept well below freezing for long periods is subject to freezing. When soil freezes, it expands and can crack, buckle the floor, and damage the foundation. In these applications, the insulation may be as thick as 6 in. In floors under very cold rooms (below -20°F) and on heavily saturated soil, pipes with warm brine water or electrical resistance elements are positioned under the insulation to prevent ground freeze.

Concrete floors should be polished to a smooth finish for ease of cleaning. Cleanliness is paramount in any facility that is handling food products. Since food safety and good agricultural practices (GAP) dictate that equipment and floors be washed frequently, all floors should have drains or drain channels to safely remove wash water and spills.

Buildings

With the exception of small internal refrigerated rooms made of insulated SIP (stand in place) panels, most postharvest facilities are built with the internal support structure as shown in Figure 7-1. These structures are economical, simple to build, make maximum use of the enclosed space, and are easily insulated. Free spans up to 60 ft are common. Bay widths average about 30 ft but can vary depending with use. Eve heights up to 30 ft are common. When trying to enclose a certain volume, there is truth in the saying “It is cheaper to build up than out.”

Insulation

Frequently, a postharvest cooling facility might be cooling blueberries to 36°F when the ambient outside temperature may be 90°F. Without sufficient insulation in the floor, walls, and roof of the facility, much of the cooling capacity of the refrigeration will be wasted through the thin metal skin of the building. Since thin metal is a good conductor of heat, adding a layer of added insulation can resist heat transfer. Insulation can also act as a barrier that prevents the movement of moisture and blocks air infiltration. Metal buildings without roof insulation will sweat by collecting condensation on the underside at night. This moisture can damage the building as well as the contents.

Many types of insulation are used in refrigerated buildings. Some are relatively inexpensive on a square foot basis, although they may not be durable or may require extra labor to install which then makes them comparable in price to the more durable types. The common insulations found in most postharvest cooling facilities include:

Doors

Postharvest facilities typically have two types of doors: walk-in doors for pedestrian traffic and large, garage-like doors for the movement of materials. Walk-in doors are generally a standard size and design. The proper design and placement of the garage doors is an important aspect of facility design and operation.

Doors must allow for the smooth flow of material into and out of the facility, while also maintaining thermal and vapor seals between the refrigerated space and the outside. One of the major decisions associated with doors is selecting the proper size. The cost of a door is directly proportional to the size (see Figure 7-6). The wider and the taller the door, the greater the cost. The general rule is that doors should be 1 to 1½ times wider than the widest item that will enter the building. Most doors in postharvest facilities are at least 12 ft wide and at least 10 ft tall. In areas with two-way fork truck traffic, doors may be as much as 16 to 20 ft wide. For refrigerated facilities, as much as 10% of the operating cost can be attributed to cooling loss through doors. For example, a door that is 20 ft wide by 12 ft tall has an area of 240 sq ft. If left open for one minute, this size door can allow for the escape of more than 10,000 cubic ft of refrigerated air.

Two of the best ways to reduce the loss of cooling at doors is the use of hanging vinyl strips and remote controlled door openers. The clear vinyl strips hang in place when the door is either open or closed (Figure 7-7). The strips provide good visibility and allow the passage of both pedestrians and fork trucks with a minimum of cooling loss even when the door is open. Clear vinyl strips can pay for themselves in one or two years.

Finally, another area of energy loss occurs around door seals. All door seals should be made from good quality, wear-resistant material that can withstand heavy use and all need to be checked periodically for cracks and leaks.

1. Rigid board insulation. This is available in standard thicknesses (1 to 2 in.) and may be clad or unclad on one or both sides with a plastic or metal skin. This insulation can be purchased in sheets of up to 4 ft wide and 24 ft long that are relatively easy to install. The clad sheets have a neat, clean appearance and may be cleaned as necessary (Figure 7-2). The foam can be either expanded or extruded polystyrene, polyisocyanurate, polyurethane, or phenolic (phenol formaldehyde). Board insulation of clad rigid fiberglass is also common. One issue with all board insulation is the sealing of joints. Typically, a joint seal strip with an “H” cross section is used along with a suitable adhesive. Edges can also be caulked or taped to prevent air leakage.
2. Roll fiberglass insulation. Many manufacturers offer rolled plastic film clad fiberglass as a standard low-cost insulation. This material is easy to install during construction and is adequate for many applications. However, there are negatives with this insulation. The thin plastic film cladding is easily torn and cannot endure being wet. The fiberglass attracts nesting birds and rodents. One of the major disadvantages is that this type of insulation is severely compressed between the roof sheeting, the wall panels, and the purlins and girts, which provide structural support. This allows for significant heat transfer at these points, as shown in Figure 7-3.
3. Foam in Place Insulation. Foam in place or sprayed on is produced from a mixture of phenol formaldehyde and other additives. This insulation offers the advantage of rapid installation, the ability to vary thickness as needed, and a seal against infiltration. The major disadvantage is that some formulations use an acid catalyst that in the presence of water or high humidity can cause severe corrosion of the metal structural components and sheeting panels. The corrosion takes place out of sight at the interface of the metal and insulation and may not be evident until significant damage has already occurred, as shown in Figure 7-4. Selecting the proper insulation is an important design decision and should be done with consideration of both the short and long-term costs. Since the cost per square ft for insulation can vary over quite a range, selecting the lowest cost alternative may prove costly in the long term. A significant amount of the operating cost of a postharvest facility is electrical power used by the refrigeration system. High-quality insulation in appropriate amounts can pay for itself several times over, and is clearly a good investment. Insulation of any type can be easily damaged. To protect the insulation and to add a more washable surface, it has become common to use metal sheeting to protect the insulation from mechanical damage. The sheeting typically runs from the floor level up to about 8 ft as shown in Figure 7-5.

Figure 7-1. Typical steel building showing internal support structure.

Source: M. Boyette.

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Figure 7-1. Typical steel building showing internal support structure.

Source: M. Boyette.

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Figure 7-2. Postharvest facility under construction. Notice the 30 ft sheets of foil clad rigid foam insulation in foreground.

Source: M. Boyette.

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Figure 7-2. Postharvest facility under construction. Notice the 30 ft sheets of foil clad rigid foam insulation in foreground.

Source: M. Boyette.

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Figure 7-3. Fiberglass insulation compressed above purlins.

Source: M. Boyette; courtesy of Buck Steel.

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Figure 7-3. Fiberglass insulation compressed above purlins.

Source: M. Boyette; courtesy of Buck Steel.

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Figure 7-4. Severe corrosion failure with sprayed on phenol formaldehyde insulation after 25 years of service.

Source: M. Boyette.

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Figure 7-4. Severe corrosion failure with sprayed on phenol formaldehyde insulation after 25 years of service.

Source: M. Boyette.

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Figure 7-5. Metal sheeting installed at floor level to protect insulation from mechanical damage.

Source: M. Boyette.

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Figure 7-5. Metal sheeting installed at floor level to protect insulation from mechanical damage.

Source: M. Boyette.

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Figure 7-6. A 24 ft wide by 12 ft tall, insulated rollup door in a large postharvest facility.

Source: M. Boyette.

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Figure 7-6. A 24 ft wide by 12 ft tall, insulated rollup door in a large postharvest facility.

Source: M. Boyette.

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Figure 7-7. Clear vinyl strip curtains reduce loss of cooling. The controls for the remote door opener are mounted on the fork truck. The driver can operate the door from the seat of the fork truck, which minimizes the time the door is open.

Source: M. Boyette.

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Figure 7-7. Clear vinyl strip curtains reduce loss of cooling. The controls for the remote door opener are mounted on the fork truck. The driver can operate the door from the seat of the fork truck, which minimizes the time the door is open.

Source: M. Boyette.

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