"1975."Current research data indicate that active solar systems are not economical for livestock facilities if initial cost and heat production are the major considerations, But other economic factors, such as investment credit and tax incentives, may make systems feasible for some operations

Phillips, Richard E.

University of Missouri: MOspace

Sizing Solar Systems for Agriculture Richard E, Phillips Department of Agricultural Engineering College of Agriculture Current research data indicate that active solar systems are not economical for livestock facilities if initial cost and heat production are the major considerations, But other economic factors, such as investment credit and tax incen­tives, may make systems feasible for some operations, The successful solar system requires attention to design and construction, Failure to comply fully with accepted practice will result in poor system performance or failure. At the present time, three general uses of solar energy are feasible in livestock production, 1, Preheating ventilation air, 2, Supplementing water heating in floor heating systems, 3.	 Preheating water used for cleaning facilities or mixing feed, General procedures for system design. v Determine energy needs, V Estimate collectable solar energy. V Size the solar system, V Adjust size as necessary to achieve better energy use or minimum cost. Available Solar Energy The intensity of solar energy or solar radiation decreases as the distance from the sun increases, The sun is not at the center of the earth's orbit, so the earth's distance from the sun varies during the year, as does the intensity of the radiation reaching the earth. The average value, called the solar constant, for solar radiation reaching the outside of the earth's atmosphere is about 430 Btu per hour per square foot. The actual amount of solar energy available to collectors on the earth's surface depends on the time of day, the time of year, latitude, the collector tilt angle, and weather condi­tions. Clear day values for solar radiation at any location can be calculated using procedures outlined by the American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE). A more useful value for design, though, is the long-term average values taken from weather bureau records. These values take into account normal weather patterns as well as anticipated reflected radiation from surface snow cover. Values for Columbia, Missouri, are tabulated and illustrated in Figure I and Table 1. These values are acceptable for use in system design throughout the state of Missouri, Ventilation Preheat Systems, which partially warm outside air before it enters the livestock housing area, are effective in moduating daily temperature extremes and can offset some of the need for supplemental heat. These systems are most adaptable to swine farrowing and nursery buildings and to poultry brooding units, Proper use of thermal insulation can maintain desired temperatures in buildings designed for housing mature animals or for finishing. Ventilation preheat systems are most effective when installed with some type of thermal storage. Most systems can be expected to provide an energy equivalent to about 2 gallons of LP gas per square foot of collector per year, Analyzing your heat needs. An effective way to analyze heating needs for a building is to determine the requirements per degree of tempetature difference between the inside and outside. To calculate the conductive loss, Qc A R. Qc = Heat loss in Btu per hour A = Area of component R = R-value of component* *"R" stands for resistance and is a measure of a given material's ability to resist the flow of heat. "R" value is an additive property-2 inches will have twice the resistance of I inch, and total "R" will be the sum of existing insulation "R" and the "R" value of the building material in the particular section, 1975 Archive version -- See xtension.missouri.eduTable t. Solar radiation expected at the collector surface located in Missouri. Columbia, MO (39.0° North Latitude) Collector tilt angle Horizontal 4/12 Latitude Lat. + IS° Vertical Month (0°) (I8°) (39°) (54°) (90°) Average total daily radiation, Btu/day-fe January 651 912 1124 1210 1153 February 941 1209 1402 1459 1288 March 1316 1536 1644 1624 1252 April 1631 1729 1689 1563 988 May 2000 1993 1829 1612 873 June 2129 2053 1820 1563 788 July 2149 2084 1857 1599 807 August 1953 1981 1846 1645 914 September 1690 1857 1869 1762 1158 October 1203 1455 1597 1598 1256 November 840 1126 1337 1405 1249 December 590 839 1939 1119 1056 Besides wall, ceiling, window, and door components, also evaluate conductive heat loss for slab edges. Multiply the length of the slab edge (perimeter) in feet times a factor based on whether or not there is edge insulation. The factors are .83 for uninsulated slabs and .45 for slabs with edge insulation. When calculating the ventilation heat loss, the energy required to warm ventilation air per degree of temperature difference is Qv = 1.1 v. Qv = heat loss in Btu per hour V = ventilation rate in cubic feet per minute (use minimum rate). Example. Calculate the heat loss for a 20-sow farrowing house ventilated a minimum rate of 20 cubic feet per minute per sow. The building is 24 x 60 x 8 feet and is insulated with R=24 in ceiling and R= 13 in sidewall. There are two exterior doors with R = 2.5, and the perimeter slab is insulated. Conductive loss: Wall 2(8 x 24 + 8 x 60) 10313 Ceiling 24 x 60 L4 60 Doors 42 13 17 Perimeter 2(24 + 60) x. .45 76 Conductive total 256 Ventilation loss: 20 x 20 x 1.1 440 Building total 696 Btu per hour Once you have determined heat loss per degree of J Table 2. Expected average outside temperatures for Missouri locations. Month Columbia Kansas City St. Joseph St. Louis Springfield January 30 32 27 32 34 February 34 36 31 35 37 March 42 43 40 42 44 April 55 55 54 57 57 May 64 65 65 66 65 June 73 74 74 75 74 July 77 79 78 79 78 August 76 77 77 77 77 September. 68 69 68 70 69 October 57 58 56 57 58 November 43 45 41 44 45 December 34 36 31 35 37 1975 III Table 3. Sensible heat production for farm animals. Species and size Btu per hour Dairy Adult per 1000 lbs. 2900 6 to 12-month calf 675 Poultry 10 to 20-lbs. turkey per lb. 3.5 5-week-old broiler per lb. 7.5 Mature hen per lb. 3.2 Sheep Adult with fleece per lb. 2.0 Adult without fleece per lb. 3.8 Swine Sow and litter 600 50-lb. pig 620 100-lb. pig 310 ISO-lb. pig 400 200-lb. pig 460 250-lb. pig 520 Figure 1. Columbia, MO. N ­-= >0­~ 2000 I---+--_f--+--~~:+----_____j ;;, §. Z o fi 1500 I-....".,.L..f-Hr....-----f==~--:..:+~~~_____jQ ~ a: a: ~ ..J o en ~ Collector Tilt ~ w 500 ~ I---+------f-----+----'-_____j a: w ~ OL--::-L-_I--l..._I--l..._I--l..._L..--l...----'L..-...J Jan Feb Mar Apr May Jun Jul Aug Sept Oct Nov Dec I I I I I I I I I I I I I Angle temperature difference, you are in a position to evaluate total energy needs for the building. (See Tables 2 and 3.) Total need = (Building total per degrees temperature difference x temperature difference) - animal heat produc­tion. Because sensible heat production (see Table 3) varies throughout the day (normally, it's highest during daylight hours when outside temperature is highest), you need to apply an adjustment factor to average production in order to arrive at values for total heat needed, so the results are more nearly in line with actual performance. Use an adjustment of .50. Example. Calculate the required daily supplemental heat for the farrowing house in our example. It is located in St. Joseph and is operated at a temperature of 60°F. Find heat needs for all months when it is required. The general equation will be Qtot = ((696 x (60 - To» -.5 Qs) x 24. To = Average outside temperature (Table 2) Qs = Sensible heat production (Table 3) = 20 x 600 = 12,000 Btu per hour 24 = Hours per day Setting up a table sometimes helps in the analysis. (See Table 4). Table 4. Sample analysis. Month Temperture difference Btu per day January 60 - 27 407,200 February 60 - 31 340,400 March 60 - 40 190,000 November 60 - 41 173,400 December 60 - 31 340,400 Estimating collectable solar energy. Table I tells how much energy you might expect to strike a solar collector. It does not tell how much it will capture. Collector efficiency and orientation gives us these values. Since ventilation preheat has highest demands during winter, a vertically oriented collector is frequently selected. Ventilation preheat units generally operate at efficiencies of .40 to .50 when equipped with some type of storage. An efficiency of .45 and a vertical orientation result in the following estimates of solar availability for those months: January 1153 x.45 518 Btu per ft2 February 1288 x .45 579 Btu per ft2 March 1252 x .45 563 Btu per ft2 November 1249 x.45 562 Btu per ft2 December 1046 x .45 470 Btu per ft2 If you wanted to try a different orientation or year-round collection, you could make similar calculations . Sizing the collector system. Two general procedures are used to determine an initial size for the collector. The first involves the physical constraints of the facility. For example, if a vertical sidewall collector is chosen, the practical size 1975 Table 5. Heat supplied and energy needs in Btu. Heat supplied by collectors Month Daily heat needs 1 re 302 re 480 re January 407,200 518 156,400 248,600 February 340,400 579 174,900 277,900 March 190,000 563 170,000 270,200 April 444 134,000 213,100 May 392 118,400 188,200 June 354 106,900 169,900 July 363 109,600 174,200 August 4Ll 124,100 197,300 September 521 157,300 250,100 October 565 170,630 271,200 November 173,400 562 169,700 269,800 December 340,400 470 141,900 225,600 will be limited by the available south-facing wall area. It turns out that this is a fairly accurate estimate of size for ventilation preheat. The second method involves the use of some proportaion of need during a particular month. Typically, December or January are chosen and the percentage value of 40 to 50 is used. Higher percentage values result in large amounts of unusable heat being collected during spring and fall months. Use a percentage of 50 and apply it to the December needs for the farrowing house. Solar Need = .50 x 340,400 = 170,200 Btu per day. A vertical collector can be expected to supply 562 Btu/ft2 . Thus, size = 170,200/562 = 302 square foot collector. Using energy. Collector size may be adjusted upward or downward depending on the designer's concept of how much energy is used versus how much energy is wasted during warmer parts of the year. Estimate this by plotting energy needs for the building and potential energy supplied by the solar system. (See Figure 2.) Example. Use the 20-sow farrowing house and two sizes of collectors. One will be 302 feet squared as already determined. The other will be the entire south wall or 8 x 60 = 480 feet squared. See Table 5 for this data. Supplemental Heating of Water Solar-heated water can be used to supplement conven­tional water heaters or boilers used to provide creep heat. The most commonly used system uses the solar collector to heat a water storage tank (about 3 gallons of water storage per square foot of collector). Whenever storage temperature is above the desired water circulation temperature, water is drawn from storage and circulated through the heating loop. If storage temperatures are below desired levels, the storage is bypassed and the conventional heater takes over. Because these solar systems operate at temperatures considerably above outside air temperatures, they generally Ventilation Preheat System .J50r--------------------~ TOial building need~ ~ o ffi 250 0.. ~ ~ 200 o o:= 150 --­100 50 10 lit.:! Month Figure 2. Heat required by example farrowing house versus heat supplied by two different sized solar collector walls. have lower collection efficiency. Values of.2 to .25 appearto be good for design purposes. Determining heat needs. Most floor slabs are designed for operation at surface temperatures of 95 degrees F. According to ASHRAE, heat transfer upward from a horizontal-heated surface can be calculated by multiplying the temperature difference between floor and room by 1.63 to obtain heat loss in Btu per hour per feet squared of surface. In actual practice, animals will be lying on some portion of the floor area, and this will reduce heat loss. If you assume 60 percent of the heated space as unoccupied, you will have reasonable heat loss values. During winter months, inside temperature can be used for the calculation. During warmer months, use average outside temperatures as the room temperature value. Example. The 20-sow farrowing house has 40 creep areas, each of which are 18 x 60 inches or 7.5 square feet. Determine the daily heat needs for each month of the year. 1975 -----Daily Btu	 = 40 x 7.5 ft2 x .6 use x 24 hours x Sizing the collector system. Physical constraints of temperature difference the facility may also limit the collector size with these = 4320 x temperature difference. systems. However, this is not usually the case, and systems See Table 5 for creep heat needs. Table 6. Creep heat needs. Month Temperature difference Btu per day January 95-60 151,200 February 95-60 151,200 March 95-60 151,200 April 95-60 151,200 May 95-65 129,600 June 95-74 90,700 July 95-78 73,400 August 95-77 77,700 September 95-68 116,600 October 95-60 151,200 November 95-60 151,200 December 95-60 151,200 Estimating collectable solar energy. See same section under Ventilation Preheat. The desirable tilt angle for year-around use is approxi­mately equal to latitude + 15 degrees. Using these values and an expected year-around efficiency of .20, you will obtain the following expectations for the sample water collector. See Table 7. Table 7. Expected output from water collector tilted at latitude +15° - Missouri (Efficiency = .20). Month Btu Per Day January 242 February 290 March 325 April 310 M~ 3W June 310 July 320 August 330 September 350 October 320 November 280 December 220 are sized based on a percentage of heat supplied. Start by using a value of 50 percent of December needs. 151,200 x .50 343 l'S· ExampIe. lze = 200 = square teet. Most agricultural collectors come in 40-square foot modules; thus, you would select nine units or a total of 360 square feet. Using energy. See the same section under Ventilation Preheat. Table 8 shows the tabulation for the 360 = square foot collector. Creep Heat Solar Supplement 180,-------------------------, HEAT NEEDED 150 ~ 120 C a: w 0.. ::l 90 l- SOLAR POTENTIAL ID § ~60 30 10 II 12 MONTH Figure 3. Heat required for example creep area versus heat supplied by 360 square foot collector. Domestic or Service Water Heating Water-based coliectors can be effectively used to heat or preheat water for residential use, equipment cleanup, or mixing of liquid feeds. Although it is possible to heat water to nonnal service temperature (140 degrees F) with a solar Table 8. Energy use for th~300 square foot collector. Month Creep heat needed BTU per day 151,200 Fepruary 151,200 March 151,200 April 151,200 May 129,600 June 90,700 July 73,400 August 77,700 September \16,600 October 151,200 November 151,200 December 151,200 January Solar potential BTU per day 87,120 104,400 117,000 111,600 115,200 1U,6oo .11"5,200 1181800 126,000 115,200 100,800 79,200 1975 

Sizing solar systems for agriculture (1982)

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