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• Air temperature
• Moisture level
• Moisture condensation on surfaces
• Air temperature uniformity
• Air speed across animals
• Odor and gas concentration
• Airborne dust and disease organism level
• Combustion fumes from unvented heaters.

As the ventilating system exchanges air, it brings in oxygen to sustain life. It removes and dilutes harmful dust and gases, undesirable odors, and airborne disease organism and moisture.

Experience has shown that if a system moderates summer temperature extremes and controls winter moisture buildup, the ventilating rate is sufficient to provide for most needs. High odor levels from underfloor manure storage may require higher air exchange rates.

A properly operating ventilating system:

1. Brings fresh air into the building through planned openings.
2. Thoroughly mixes outside and inside air, picks up heat, moisture, and air contaminants, and lowers temperature, humidity, and contamination levels.
3. Exhausts moist, contaminated air from the building.

Failure to provide for any step of this process results in inadequate ventilation.

Heat Exchangers

Ventilation air-to-air heat exchangers are used in swine housing facilities to reduce supplemental heating cost and to preheat incoming fresh air. There is potential for heat exchanger use in some swine barns, since as much as 90% of the total heat loss from an insulated swine nursery facility occurs through the minimum ventilation air exchange. Heat exchangers recover a portion of this loss, depending upon design and maintenance. In addition to reducing fuel use, heat exchangers preheat the incoming ventilation air thereby reducing the potential for drafts on piglets and reducing frosting problems when air enters directly from outside. Heat exchangers also improve air distribution, because warmed inlet air will not drop as rapidly as cold inlet air.

Heat Recovery Process

In an air-to-air heat exchanger the heat recovery process is accomplished when warm, moist room air is moved past cold fresh inlet air, separated by a heat conducting plate or surface. Heat transfers across the plate because of the difference in temperature, often cooling room air to the dew point causing moisture condensation. While condensation releases large amounts of heat it also causes a need to drain water from the unit, and during extreme cold temperatures, the need for a defrost cycle to remove frozen condensate.

Heat is transferred through a solid surface thereby avoiding mixing of the two airflows. This is a very important characteristic when comparing heat exchangers to "blenders" devices that resemble heat exchangers. Blenders physically mix warm room air with cold fresh air a process, which under certain can create fogging unless additional supplemental heat is supplied to the barn.

Deciding on a Heat Exchanger

Factors such as: airflow rate, efficiency and initial cost of heat exchanger, plus fuel costs, size and number of pigs, and climate all influence the decision to use a heat exchanger in a swine housing facility. Estimates from a computer model at the University of Wisconsin suggest that fuel savings from a heat exchanger in swine farrowing or nursery facilities located in Wisconsin, will pay for the initial investment in a minimum of four to a maximum of ten years. Heat exchangers require periodic cleaning and more attention than most conventional ventilation systems.

Heat exchangers have two fans, one exhausting moist stale sir and one blowing fresh air into the barn. Heat exchangers, where the exhaust fan has slightly more capacity than the inlet fans are desirable, especially in remodeled facilities, since it is difficult to seal building shell leaks.

Summary

Benefits of air-to-air heat exchangers in swine facilities are preheating of the inlet air and reducing cold drafts while lowering energy costs and supplemental heat requirements. The feasibility of heat exchangers is highest in swine nurseries and farrowing barns, where warmer room temperatures are needed, drafts are a problem, and fewer animal numbers require supplemental heat. Other potential use of heat exchangers is in individually stalled gestation units, which in the upper-midwest also require supplemental heat.

Earth Tempering of Ventilation Air

Earth tempering of ventilation air for swine buildings has been considered because of the moderate fluctuations in soil temperatures at shallow depths. Depending on the season, incoming ventilation air is heated or cooled as it passes through a buried tube. The soil serves as a heat sink in the summer and as a heat source in the winter, thus giving almost year-round temperature modification. It has the potential to significantly reduce heating costs during winter and provide zone cooling during summer.

Soil Temperature

Soil temperature is one of the most important factors affecting design and performance of earth-tube heat exchanger systems. Soil temperatures vary with soil type, depth, moisture content, time of year, and geographic location.

The mean annual ground temperatures for various locations in the United States range from 49°F. in St. Paul, Minnesota, to 58°F. in Lexington, Kentucky, and from 52°F. in Ames, Iowa to 55°F. in Columbus, Ohio. The amount of temperature variation decreases as depth increases. For example, at a depth of 6 ft., the yearly variation of a typical clay soil can be expected to range from 11 degrees above to 11 below the mean annual ground temperature, or a total yearly variation of approximately 22 degrees. At a depth of 10 ft., this variation is reduced to plus or minus 6 degrees F. or a total variation of 12 degrees.

The time of year when the ground temperature is at the extremes is also important in the design and performance of a system. Soil temperature fluctuations lag behind surface temperature changes due to the heat of the summer, but soil 10-12 feet deep may not reach its peak temperature until almost three months later. This thermal lag at the 10 ft. depth helps both the heating and cooling performance of these systems. During the winter, soil temperatures at this depth are at the fall season level, making the soil near the mean annual ground temperature, thus adding to the heating capabilities of a system. The reverse is true during the summer months, when the soil temperatures at the 10-12 ft. depth are spring like and can cool the ventilation air.

Soil types and moisture content also affect the ground temperature variation. Soils with increasing sand content tend to have larger temperature variations at deeper depths than clay soils. Soil moisture and ground water elevation also affect soil temperature. Seasonal temperature variation is larger in very moist soils as compared to very dry ones due to the increase in heat transfer through soils whose voids are filled with water.

System Design

The typical earth-tube tempering or heat exchanger system consists of a heat exchanger field, a collection duct/fan house, and a building air distribution system. Each of these portions must be adequately sized to insure proper performance.

Airflow Capacity. In general, much more air is required for summer ventilation than for winter. If zone cooling is used, the difference between the two rates is much less. For example, the recommended summer zone cooling rate for a sow and litter is 70 cu. ft. per minute (cfm) of uncooled air per farrowing crate, 50 cfm for evaporative cooled air, and 30 cfm for air-conditioned air. Air tempered by an earth-tube system should be somewhat cooler and dryer than evaporative cooled air (depending on climate), but for planning purposes use the 50 cfm per crate. During winter, the recommended cold weather ventilation rate is 20 cfm per crate. With the system designed for a capacity of 50 cfm per crate, there is an additional 30 cfm which can be used for mild weather room tempering as needed or it can be used to preheat the winter air of a compatible nearby nursery. Zone cooling is recommended over whole-room cooling because it is more cost effective, especially in the farrowing and gestation units.

Heat Exchanger Field Design.Both soil characteristics and tubing factors affect the design and performance of a system. Soil characteristics include soil type, moisture content, and water table elevation. Temperature levels for various soil types indicate the less favorable performance of sandy soils; so avoid these if possible. If sandy soils must be used, the number of lines, line lengths, and/or depth should be increased by 10 to 20% to offset this effect. Moisture content increases the heat transfer capability of the system. Therefore, a system installed in an area with a shallow water table should have the lines buried below the average yearly elevation of the water table for maximum performance. Such a system must be well sealed to minimize ground water seepage and additional pumping costs. construction should take place during periods of low water table to reduce the use of pumps and possibly unstable trench sides and bottom.

Air-tubing factors include diameter, length, depth of placement, and shape of the tube. Typically, non-perforated corrugated plastic drainage tubing is used because of its availability and cost. Small diameter tubing, such as the 3-, 4-, or 5-in. sizes, are impractical because of the large number of lines needed to provide enough air capacity for a typical system; thus the 8-, 10-, and 12-in. diameters are the most practical.

Layout. Several system layouts are possible including the wagon wheel (radial) of the lateral. Material and trenching costs are normally less for the wagon wheel pattern because no manifold lines are used; however, excavation can be difficult near the collection duct. Manifold lines must be much larger than lateral lines, and tubing materials and trenching are more expensive. However, a lateral system with a manifold may be the only option when surrounding buildings, roads, or fields limit the area available for installing the system. The spacing between lateral lines need not be uniform, but each lateral should be of equal length to keep the airflow equal. Laterals do not need to run straight, but abrupt turns should be avoided.

Placement. The tubing should be buried to a depth of 7-12 ft. depending on installation costs and geographic location. System thermal performance will be better with maximum depth. If installation costs are prohibitive, somewhat shallower depths may provide a more beneficial economic return.

Space lines at least 8-10 ft. apart to maximize soil heat storage and minimize the chance of tubing deflection and damage during construction.

At the outer end of the system, the tubes should curve up and extend 3 to 4 ft. above the soil surface to form the air inlet. Either rigid PVC pipe or corrugated plastic tubing can be used for the inlet risers; however, the tops should be screened to keep out debris and rodents and should be very visible to prevent damage from nearby machine traffic.

A fan should be located between the underground tubing system and the building air distribution system. Size this fan to deliver the desired airflows against 3/8 to «-in static pressure. Usually, a two-speed fan would be best, with the maximum volume matched to the summer zone cooling rate and the smaller volume matched to the winter continuous ventilation rate. Tightly seal the collection duct and all connections to prevent short circuiting of air from outside directly into the duct, thus bypassing the tubing system.

Building Air Distribution System. The distribution system for the earth-tempered air consists of a fan, main duct or ducts, and downspouts (or drop ducts) located as needed for each animal. In a farrowing house, locate a downspout above each individual crate with the airstream directed at the sow's head. The downspout should be located as close to the animal's head as possible to make full use of the cooled air.


If spouts are within the animals' reach, they should be made pig-proof. Include dampers in the downspouts to close individual lines when crates are empty and to adjust airflow if needed.

For winter operation, earth-tempered air can be routed through an existing room air distribution system, through room make-up air heaters, or the summer downspouts can be removed and tempered air can be introduced into rooms via the distribution duct openings along the room ceiling.

System Costs

Major costs encountered when installing an earth-tube heat exchanger system include: excavation, tubing, fan, and the interior distribution system. Cost will vary with the depth of installation, excavation method, layout, and site constraints. Obtain cost estimates for the specific site, layout, and desired depth before selecting a final design. Total costs for an average system should range from $2.75 to $3.50.

Performance Data

Several functioning systems have been monitored in Illinois during the past few years, including systems designed according to the guidelines presented here.

Summer and winter performance curves for a 30-crate farrowing facility located near Springfield, Illinois, are shown in Figures 12 to 13. The system consists of five 12-in. lines, each 260 ft. long, buried about 10 ft. deep.

The outside temperature for a three-day period in August 1981 varied from 60 to 92°F. The earth-tempered air temperatures ranged from 64 to 69°F. The average sensible cooling effect during the three-day period was equivalent to 20,773 Btu/hr. The temperature of the outside air during the three-day period in January 1982 varied from +20 to -19°F., whereas the earth-tube output temperature was steady at 46 to 48°F., a maximum temperature increase of 67 degrees. The earth-tube heat exchanger provided about 40% of the heating required during the winter of 1981-82 by delivering tempered air at the approximate rate of 920 cfm.

Economic Payback

As with other alternative energy systems (solar and heat exchangers), tempering of ventilation air by earth-tubes is not free. Since the costs and returns vary considerably for earth-tube systems, a rigorous economic analysis would be both difficult and lengthy. However, to give some indication of economic payback for a system, the following example is provided, using the performance data and costs given above, plus estimated returns an expenses.

The "heating" performance was recorded of a system in Illinois over three days in January from a 30-crate farrowing barn. A relatively constant exhaust air temperature from the earth-tubes at 48°F. was indicated over this period. If one assumes this same temperature over the entire heating season (will probably be greater in the fall and less toward spring), then the amount of energy recovered per heating month can be found using the following relationship:

Q = 1.1 x 920 cfm x (To -T) x 24 x (number of days in month)
where
Q = Btu/month
T0 = temperature exiting tubing (48øF. for our example)
T = average monthly outside temperature

Using average monthly temperature for central Illinois during the heating season (November through March), a total of 61.5 million Btu's of energy would be recovered. If this total is divided by 75,000 Btu's (amount of usable energy per gallon of L. P. gas) then this is the energy contained in 820 gal. of propane. At 75 cents per gallon, a total of $615 would be saved per year. Since a larger fan (« h.p.) is needed in this system than with conventional ventilation, a total of $100 (2,000 kwh x 5 cents/kwh) should be subtracted from $615 for a net return of approximately $500 per year from heating.

Estimating the cooling benefits during the summer is much more difficult than calculating heat savings. It would be unfair not to consider the returns from cooling, especially when comparing the earth-tube system with solar units and air-to-air heat exchangers. Some animal scientists have estimated that 1 extra pig per liter occurs if a summer cooling system is used, because of reduced sow heat stress, more efficient sow milk production, and faster breeding. If that assumption is used in our example, then 30 extra pigs per farrowing would result for a total of 60 extra pigs (assume 2 farrowings per summer). If an estimated value of $15/extra pig is assumed, this results in a return of $900 due to cooling. Adding this amount to the annual estimated heat savings ($500), a total return of $1,400 per year results.

The costs of the above 1,500 cfm earth-tube system is estimated at $4,500, when using the $3/cfm figure discussed earlier (1,500 cfm x $3 cfm). The simple payback period, which excludes fuel price increases and interest, would be between three and four years. Consideration of L.P. gas (propane) price increases would reduce payback with the inclusion of high interest rates would extend them considerably.

As is apparent from the above example, the economic feasibility of an earth-tube system should be thoroughly investigated before beginning construction. While the heat savings can be calculated accurately, one should also give adequate weight (or value) to the estimated cooling benefits. Solar systems and heat exchangers provide no summer cooling while mechanical air conditioning has proved to be too costly. Earth tempering of ventilation air may be the least-cost alternative for providing tempered air during all time of the year.

Solar Heat

Solar energy is one energy source that is abundant and inexhaustible. Energy conservation is a reason to consider solar heat from swine buildings. Money must be spent to insulate a building before solar heating can be effective. Also, check the winter ventilation rate to prevent overventilating, wasting much valuable heat.

The Amount of Solar Energy Available

The energy available on a solar collector surface depends on the time of day, the time of year, the weather, the latitude(location) of the collector site and the collector's tilt angle. In the Midwestern United States at noon on a sunny day in winter, the amount of solar energy striking a south-facing surface at a right angle is about 300 Btu/hr./sq.ft. of collector or 88 watts/sq.ft. Fixed solar collectors receive the most energy if they face south, but deviations up to 15ø from due south make little difference in total energy received. At 40ø north latitude, a vertical south-facing wall receives the most energy during October through February, and considerably less the remainder of the year. A horizontal surface receives the most energy during the summer but the least during the winter. Normally, a tilt angle of the latitude plus 15ø, or an angle of 55ø at 40ø north latitude, will give the maximum heating during the winter heating season as shown in Figure 1. A standard roof slope of 4/12 (18.4ø) receives considerably less solar radiation during the normal heating season than either a vertical wall or the 55ø sloped collector. The minimum tilt angel for regions with high snowfall is about 55-60ø so the snow will slide off.

Solar Economics

Will solar energy be economical for your swine building? It depends, for many things affect the economics of solar energy. Wide ranges in these factors can mean that he solar energy saved may be worth ten to twenty times as much for one producer as it is for another.

To reach a reasonable decision on a solar system you need to know several things:

• How much solar energy is available in your location?
• How many months can you use solar?
• How much of your fuel will a solar system replace?
• What is the cost and expected life of the solar system?
• What percent of the available solar energy will the system collect and use?
• What are the interest rate, operating and maintenance costs?

Types of Solar Heating Systems

Two types of systems are used to collect solar energy for swine buildings - passive and active.

Passive solar heating occurs when radiation passes through glass or fiberglass windows and is absorbed by the objects it strikes (walls, floor, pen partitions and animals). This absorbed energy in turn warms the environment. The amount of heat buildup on a sunny day may be sufficient to meet the pigs' needs during the daylight hours, but these same windows also allow heat to escape at night. During winter, the sun shines only about 6-8 hr. a day, allowing heat to escape during the remaining 16-18 hr. The results can be drastic cycling of air temperatures and excessive moisture condensation on the window surfaces during cold weather. Considerable improvement results if an insulated curtain or door is used to cover the windows when here is little or no solar heat gain.

Passive solar heating can best be used in open-front buildings. It is necessary to sue a roof overhand (usually roof extension) or some other covering to shade shout-facing windows in summer and still permit the sun to penetrate in winter. Normally, to provide complete shading in July in the Midwest, the overhang should be equal to about 1/3 the vertical distance from the overhang to the bottom of the window.

Active solar systems require facilities and equipment for collecting, transferring and often storing solar energy. This allows solar energy to be collected at one location and moved by fans or pumps for use or storage in another location.

An active system may also allow for dual use of a collector. For example, the heat from a collector could be used to help heat the ventilation air of a farrowing house during winter, while in the fall the heat could be transferred to a nearby grain bin for drying grain. Using a collector for more than one purpose helps justify cost.

The most feasible application of solar collectors would be with farrowing and nursery buildings because considerable supplemental heat is usually required in these buildings to maintain a uniform temperature in cold weather. Usually no supplemental heat is used in growing-finishing and sow buildings.

Summary for Solar Planning

Weatherize and insulate the building you plan to heat to proper standards before spending money on a solar heating system.

Position a solar collector so it faces south with an east-west axis. Generally, the most efficient slope for a collector for winter heating can be found by adding 15ø to the location's latitude. In most cases the simplest and least costly construction would be to use the south vertical wall, which has a favorable angle to the winter sun.

Avoid placing a collector behind objects that could block the sunlight. Remember small trees grow large and may eventually shade a collector.

Provide a minimum of 1 sq. ft. of collector for every 1-4 cu. ft./min/ (cfm) of ventilating air to be heated. Higher airflows reduce the temperature rise but improve collector efficiency.

Use clear fiberglass with a coating to protect the cover from ultraviolet light. If a grade recommended for solar use is not available, a use a good greenhouse grade. A 15-yr. written warranty for greenhouse use is a good indication of quality. However, most suppliers today will not guarantee greenhouse-grade fiberglass for solar-collector use.

When installing a fiberglass collector, it is a good idea to use hex-head, self-tapping screws with rubber gaskets to seal the air leaks. Pre-drill all holes in fiberglass, even when self-tapping screws are used. This avoids shattering of the fiberglass. Drill the holes slightly larger than the screws or nails to allow for expansion and contraction. A bit of silicone caulking over the top of the head after tightening down the screws will prevent leaks. Do not fasten too tightly. Screws are easier to remove than nails if the fiberglass must be replaced or dismantled for repairs or modification.

Seal the collector against air leaks with silicone caulking or equivalent product. One tube of silicone caulking covers 75-100 linear ft. Seal the sides of the collector with sealer strips that have ben preformed to the shape of the fiberglass sheet.

Screen the air inlets to make them bird- and rodent-proof and shield them so snow will not be drawn into them. Use 1/4-in. x 1/4 in. hardware cloth, not fly screen. Clean the screened area periodically or when necessary so the inlets do not become clogged with dirt or debris.

Use a black absorption surface to collect the solar energy. You can spray almost any material with flat black paint. There are also selective surface black paints available which are designed specifically for solar collectors; but regular flat black pain performs reasonably well. Selective surface paints are expensive and it is more feasible to use them on the more expensive collectors.

Avoid large pressure drops by allowing 1 sq. ft. of duct area for every 500-600 cfm of ventilating air. This will result in a maximum velocity of 500-600 ft./min. Since grain drying systems use more powerful fans than livestock buildings, you can go up to 1000 ft./min. (1 sq. ft. of duct area / 100 cfm of air). Keep the total static pressure below 1/2 in. of water (1/4 in. is better). Greater pressure drops reduce fan performance.

Insulate the back and sides of the collector with high temperature fiberglass (do not use fiberglass with organic binder) or polyurethane insulation. Polystyrene is not recommended by manufacturers for use at temperatures over 165° F.

Ventilate the collector in the summer when you are not using it by providing openings that will allow air to flow through it. A small fan can also be installed. The stagnation of air in a collector can result in temperatures over 200° F inside the collectors. Extended exposure to temperatures over 200° F will damage the fiberglass glazing and may weaken the structural members of the building.

Fluorescent Light

A switch from incandescent bulbs to replacement fluorescent U-Tube units can reduce energy needed for lighting by 75%.

In a 40,000 bird broiler house the switch would save 17,600 kWh a year at 9&Mac221; a kWh, that amounts to over $1500 a year.

In a 15,000 bird laying house, the energy savings would be over 5000 Kwh a year for a dollar savings of over $400.

In a 15,000 turkey building, the energy savings would be 281 Kwh for each 10 hours of light provided or a dollar saving of $2.50 for each hour of lighting.

In a 10 sow farrowing room, the energy savings would amount to 270 kWh a year or about $24 a year.

Dairy Water Heating with Heat Recovery

When milk is cooled on the farm, the heat removed from the milk was once released to the air. With a proper design some of this heat was utilized to help heat the milk house in winter. A more efficient use is to install a heat recovery unit to hear or pre-heat water that is used in cleaning milking equipment. Water must be heated year around so this system saves energy every day.

A study in New York State indicated that the energy saved by using a heat recovery unit was about 100 kWh per corn per year.

Energy Efficient Fan Motors
Recent testing of ventilation fans at the University of Illinois has shown significant differences in the energy efficiencies. Results for a 36" fan indicate an average of 13.4 cfm/watt with a range of 8.3 to 17.4 cfm/watt.

The cost to operate the most efficient fans for 120 days at 10&Mac221; a kWh electricity is about $150 compared to about $300 for the inefficient fans.

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