Performance of Solar-Assisted Modified-Open-Front Swine Nurseries

Performance data of two modified-open-front non-mechanically ventilated swine nurseries have shown that solar energy can be effectively utilized to maintain a productive environment within the animal space during cold weather (temperatures as low as —26°C ( — 15 °F). The nurseries feature a monoslope roof design and passive collector panels that also function as warm weather ventilation panels. An active solar-heating system uses a ground-level collector operated in conjunction with an in-floor solar heat distribution and storage system. The nurseries were designed to handle pigs weighing from 7 to 23 kg (15 to 50 lb). An average of 19% of the solar energy incident on the collector was transferred to the floor surface during the heating seasons from October 1980 to January 1982. Season "heating" costs were approximately 1.0% of the estimated cost to heat the nursery by conventional means. INTRODUCTION Weaning of pigs at 3 to 5 weeks of age (3.5 to 9.1 kg (8 to 20 lb)) has created a need for nursery facilities capable of providing a suitable environment for young pigs. These small pigs require air temperatures ranging from 27 to 35 °C (80 to 95 °F) depending upon pen design and air velocities through the sleeping/feeding area. The most common technique for achieving these temperatures has been to heat the entire volume inside the building (whole-building heating) and maintain air temperatures within the range necessary for young pigs. With few exceptions these buildings have also been mechanically ventilated, relying upon electricallypowered fans to achieve air movement through the facility. Whole-building heating and mechanical ventilation make operation of these nurseries energy intensive. Facilities not as energy intensive can be used. Hovers, Article was submitted for publication in October, 1987; reviewed and approved for publication by the Structures and Environment Division of ASAE in March, 1988. Paper published as Journal Series No. 8457, Nebraska Agricultural Research Division. The authors are: G. R. BODMAN, Associate Professor and Extension Agricultural Engineer, University of Nebraska; M. F. KOCHER, Assistant Professor, Agricultural Engineering, University of Arkansas; and J. A. DeSHAZER, Professor, Agricultural Engineering, University of Nebraska. Acknowledgment: Appreciation is expressed to Art and Doug Paus, Fairfield, NE and Ross Larson, Ceresco, NE, cooperating producers; Nebraska Agricultural Research Division, U.S. Dept. of Agriculture and Nebraska Energy Office for their financial support of this project. infrared heating, and floor heating can be used to provide the proper thermal environment in the pigs' sleeping area. The remainder of the pen space does not need to meet the same thermal requirements since pigs do not need a prolonged stay in this secondary environment (feeding and dunging areas). The air temperature in this secondary environment can be allowed to drop below normal nursery air temperatures (Curtis, 1981; Shelton and Brumm, 1986). Similarly, temperatures outside the pen can be much lower. The result is a reduction in heat energy required by the nursery. Providing several micro-environments within the pig zone decreases the need for exacting ventilation control, since effective temperatures in the secondary environment may vary outside those required for optimum comfort by the nursery pigs. Non-mechanical ventilation systems, i.e., achieving airflow without fans, can meet the environmental needs for nurseries with several micro-environments. Non-mechanical ventilation further reduces energy usage since electricity to power ventilation fans is not required. This paper describes the performance and economies of solar assisted modified-open-front (MOF) swine nurseries that use different micro-environments and nonmechanical ventilation. The original unit based on this design has been operating continuously since October 1979. DESCRIPTION OF FACILITIES Building Based on previous studies at the University of Nebraska involving the use of solar energy in swine confinement buildings (DeShazer et al., 1976, 1980; Bodman et al., 1978, 1980, 1981) the nursery discussed in this paper may be considered a "third generation'' design. The original Nebraska Solar MOF Nursery (Fig. 1) is on a working farm owned and managed by Alvin Paus and Sons (Art and Doug). The Paus farm is located near Fairfield in south central Nebraska (40° 24 'N, 98° 11 ' W). The building measures 35.4 x 7.0 m (116 x 23 ft) and encloses 22 pens plus an equipment area. Design capacity for the building is 550 pigs weighing between 7 and 23 kg (15 and 50 lb). Operation of the building began in October 1979. A second Nebraska Solar MOF Nursery was built on the farm of Ross Larson near Ceresco in east central Nebraska (41° 8'N, 96° 40'W) (Fig. 2). The nursery measures 18.3 x 7.0 m (60 x 23 ft) and is subdivided into 12 pens. Design capacity of the unit was 300 pigs ranging from 4 to 23 kg (9 to 50 lb). Operation of the facility began in September 1981. Results from this unit are used to supplement findings from the Paus nursery. All results Vol. 5(2):June 1989 207 Fig. 1—The first Nebraska solar MOF nursery (Paus 550-head capacity). Fig. 2—The Larson 300-pig Nebraska MOF solar nursery. discussed in the following paragraphs are from the Paus nursery unless otherwise noted. The nurseries were constructed with insulated sidewalls (RSI 2.3 to 2.6 (R13 to 15) and ceilings (RSI 3.3 to 3.8 (R19 to 22)). A polyethylene vapor barrier was placed between the insulation and inside finish materials to assist in controlling movement of water vapor into the walls and ceiling. A 3:12 single-slope roof and inside ceiling enhance air movement (and ventilation) by natural convection. A shallow (10 cm (4 in.)) open gutter provides a dunging area for the pigs. Tanks equipped with dosing siphons periodically provide water to remove manure from the gutters. Effluent is discharged to a lagoon. Individual pens are 1.5 x 6.1 m (5 x 20 ft) and extend from the service alley along the south side to the north wall. Pen width is center-to-center of precast 10 cm (4 in.) concrete partitions. Pen length includes the 0.9 m (3 ft) open flush gutter. The pen arrangement, proceeding from north to south, is, sleeping area, feeding area, and dunging area. Feeders are positioned 0.6 to 0.9 m (2 to 3 ft) north of the edge of the gutter (Fig. 3). A plywood hover (1.3 cm x 1.2 x 2.4 m (1/2 in. x 4 ft x 8 ft)) was installed over the sleeping area (north end of pens). Hover height varies from pen to pen and is adjusted to be 15.2 to 30.5 cm (6 to 12 in.) above the pigs. The south walls are stud-frame to a height of Fig. 3—Schematic of the solar MOF nursery cross-section. approximately 1 m (3 ft, 4 in.) above grade. In the Paus facility, openable acrylic windows (1.8 x 2.4 m (6 x 8 ft)) above the stud-frame section of the south wall serve as a passive solar collector and ventilation panels. Larson substitued insulated openable panels for the lower half and fixed fiberglass reinforced plastic passive panels for the upper half of the south wall. A 5 cm (2 in.) wide ventilation air outlet runs the full length of the building above the passive windows. The north wall is insulated concrete sandwich panels (RSI 2.1 (R 12)) to a height of 0.8 m (2.5 ft) above grade (Fig. 3). The remainder of the north wall consists of 0.6 m (2 ft) high insulated panels in a stud framework. These panels run the full length of the building and can be opened during warm weather for increased ventilation. In-Floor Heat The sleeping area micro-environment along the rear third of the building consists of in-floor heat and hovers. The in-floor heat is provided by an active solar collector using air as a heat transfer fluid. Air in the closed loop heating system passes from the collector through an InFloor Heat Distribution and Storage (IFHDS) system before returning to the collector (Fig. 4). The 1 m (3 ft., 4 in.) high flat plate active collector is tilted 60 deg above horizontal and positioned at ground level across the front of the building. Air flow is achieved via a centrifugal fan which "pushes" air through the IFHDS system at the designed rate of 37 mhm(2 cfm/ft) of collector surface. The collectors have two Tedlar® * glazings and dd&xk brown pre-painted ribbed steel roofing sheet absorber plate. A 5 cm (2 in.) layer of high temperature fiberglass insulation is positioned behind the absorber plate to limit heat losses. Painted wood was used to construct the *Mention of trade names is for informational purposes only. No endorsement of listed products or discrimination against other products by the University of Nebraska is intended. Fig. 4—Schematic of the horizontal closed-loop in-floor heat distribution-storage system. 208 APPLIED ENGINEERING in AGRICULTURE resultant storage mass is approximately 0.6 to 0.7 mm~ (2 to 2.3 ftVft) of active collector surface — providing a thermal storage capacity of approximately 1700 k J C 0 " ^ 2 (84 Btu/F°/ft). The IFHDS system is insulated to RSI 0.7 to 0.9 (R4 to 5) by extruded polyisocyanurate foam insulation on the sides and bottom. Equivalent insulation is directly beneath the concrete floor within the feeding area. A 4 mil polyethylene vapor barrier is placed at the insulationsoil interface to limit moisture migration. SYSTEM PERFORMANCE Building The solar-assist features of both Nebraska Solar MOF Nurseries have provided most of the required heating energy (Table 1). Manual adjustment of ventilation panels has not been a drawback since it gave the producers cause to visit the facility at least twice daily, a desirable management regimen. Manual adjustment was found to be necessary in the Paus nursery because condensation on the aluminum sash and frames of the translucent ventilation/passive collector panels freezes during cold weather. Lack of sensitivity on the part of mechanical drive mechanisms for automatic operation would have resulted in damage to the panels. Air quality was deemed excellent. The maximum gas concentrations measured during the winter were: H2S = 0 ppm and NH3 = 5 ppm. A recording hygrothermograph with monthly calibration with a sling TABLE 1. Thermal Performance Results for the Solar MOF Nursery (PAUS) potal active solar heat transferred to IFHDS System, GJ (10 Btu) kvg. daily radiation incident on active pollectorf MJ/m . day (Btu/ft.day) kvg. daily active solar heat input to IFHDS system, MJ/m (Btu/ft) pollector area.day kvg. temperature under paver, °C (°F) kvg. inside temperature, °C (°F) kvg. outside temperature, °C (°F) kctive solar energy transferred to the floor surface, percent Heat supplied by solar, percent 1980