1、UFC 3-440-01 14 June 2002 Including change 1, December 2007 UNIFIED FACILITIES CRITERIA (UFC) ACTIVE SOLAR PREHEAT SYSTEMS APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-UFC 3-440-01 14 June 2002 I
2、ncluding change 1, December 2007 1UNIFIED FACILITIES CRITERIA (UFC) ACTIVE SOLAR PREHEAT SYSTEMS Any copyrighted material included in this UFC is identified at its point of use. Use of the copyrighted material apart from this UFC must have the permission of the copyright holder. U.S. ARMY CORPS OF E
3、NGINEERS (Preparing Activity) NAVAL FACILITIES ENGINEERING COMMAND AIR FORCE CIVIL ENGINEER SUPPORT AGENCY Record of Changes (changes are indicated by 1 . /1/) Change No. Date Location 1 Dec 2007 Page 2-2 add Para 2-5 and Page A-1 Provided by IHSNot for ResaleNo reproduction or networking permitted
4、without license from IHS-,-,-UFC 3-440-01 14 June 2002 Including change 1, December 2007 2FOREWORD 1 The Unified Facilities Criteria (UFC) system is prescribed by MIL-STD 3007 and provides planning, design, construction, sustainment, restoration, and modernization criteria, and applies to the Milita
5、ry Departments, the Defense Agencies, and the DoD Field Activities in accordance with USD(AT those having more heating degree days should use a 50 percent solution. This heating day criteria is provided as a suggested guideline only. It is up to the designer to take into account each locations parti
6、cular climate and freezing-day characteristics when determining whether a 30 or 50 percent solution should be used. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-UFC 3-440-01 14 June 2002 3-6 Figure 3-4. Flat-Plate Collector 3-4.1.2 Array Size. The
7、 first step in the system layout is to estimate collector array size (the actual array size cannot be determined until a specific collector is chosen for the detailed design). 3-4.1.3 Array Tilt Angle. The collector array tilt angle is defined to be the angle between the collector and the horizontal
8、, with 0 degrees being horizontal and 90 degrees being vertical. The proper tilt angle is a function of the time of year when the load occurs. For annual loads, such as service and process water heating, the widely accepted practice is to tilt the collectors to the value of the local latitude. If th
9、e load tends to have a seasonal variation, the tilt can be varied to favor the season. Examples include seasonal hot water requirements, space heating, and space cooling. If the collectors are tilted to the latitude angle plus 10 degrees, the energy output will be more evenly distributed over the en
10、tire year, although winter losses will tend to increase, due to lower outdoor temperatures. Tilting the array to the latitude minus 10 degrees favors summer energy output. It is not generally recommended to tilt the array any more than Provided by IHSNot for ResaleNo reproduction or networking permi
11、tted without license from IHS-,-,-UFC 3-440-01 14 June 2002 3-7 plus or minus 10 degrees from the site latitude. It should be noted that as the tilt angle increases, the minimum spacing between rows due to shading increases and larger roof area is required. 3-4.1.4 Array Azimuth Angle. The array azi
12、muth angle is defined to be the angle between the projection of the normal to the surface on a horizontal plane and the local meridian (north-south line). Zero degrees is defined as due south, a due west facing array is defined as plus 90 degrees, and a due east facing array is defined as minus 90 d
13、egrees (in the northern hemisphere). The optimal orientation requires the azimuth angle to be 0 degrees (due south) whenever possible, although deviations of plus or minus 20 degrees off of due south have a minimal effect on flat-plate system performance. 3-4.1.5 Collector Grouping. Internal-manifol
14、d collectors should be grouped into banks ranging from four to seven collectors each, with each bank containing the same number of collectors. Proper sizing of the collector banks is essential to maintaining uniform flow throughout the collector array. The maximum number of collectors that can be ba
15、nked together is a function of the maximum flow rate allowed in the plumbing, internal manifold and riser diameters, thermal expansion characteristics of the collector piping and absorber plate assembly, and the recommended flow rate of the particular collector chosen (usually given in gallons per m
16、inute (liters per second) per collector or gallons per minute per square feet (liters per second per square meter) of collector area). Thermal expansion problems are minimized by keeping the bank size less than eight collectors. 3-4.1.6 Minimum Array Row Spacing. The minimum row spacing must be calc
17、ulated for multi-row arrays. A general routine for north-south spacing of collector banks can be devised, based on a “no shading“ criterion for a particular time of year. The guidance presented assumes no shading of the array on the “worst“ solar day of the year (21 December, when the sun is lowest
18、in the sky in the northern hemisphere) for the designated time period of 10 a.m. to 2 p.m. solar time. Most large-scale military solar systems are installed on low-slope flat roofs, and there are two possible cases to consider. The first is for a flat roof with enough space to locate the collector a
19、rray at one elevation. The second case is for a flat roof with too little space for the collector array. This requires the collector banks to be “stepped“, that is, each succeeding row of collectors must be elevated. This arrangement is necessary if the collector roof area required is larger than th
20、at available or if roof area costs are more expensive than elevated rack costs. The equations developed for minimum collector row spacing are presented graphically in Figure 3-5. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-UFC 3-440-01 14 June 20
21、02 3-8 Figure 3-5. Minimum Collector Row Spacing 3.4.1.6.1 Azimuth Orientations. The curves shown in Figure 3-5 are for collector azimuth orientations of plus or minus 20 degrees. For the due south orientation (0 degrees), the deviation from these results is less than 10 percent. Use of Figure 3-5 f
22、or due south orientations is thus slightly conservative. The effect of elevating the rear collector row (larger C/L values) shows a marked decrease in the minimum spacing (S/L). The flat roof, no elevation collector case is represented by the curves where C/L = 0. 3.4.1.6.2 Roof Pitch. Collectors ca
23、n also be mounted on pitched roofs. Often, when a solar energy system is to be added to a building, the roof is pitched and constructed such that the collectors could be mounted on the roof surface. This practice does not necessarily impose unreasonable constraints in the roof design, since there is
24、 some flexibility in the choice of collector tilt angle. If the roof cannot be pitched to allow flush mounting of the collectors, or if the tilt angle must be fixed, then the collectors can be raised at one end to give them the proper tilt. Figure 3-5 can be used to determine the spacing by includin
25、g the appropriate roof pitch with the height C. 3.4.1.6.3 Array Layouts and Estimated Roof Area Options. Collector array layouts and estimated roof area requirements for the system can be determined by using the estimated array size. For example, assume that 818 ft2(76 m2) of collector area is requi
26、red for a project located at 40 degrees N latitude. The number of collectors to install can be determined by dividing the calculated array area by the net aperture area of the collector. If a 4 by 8 foot (1219 by 2438 mm) collector with 31 ft2(2.9 m2) of net aperture area is to be used, the calculat
27、ion results in 26.4 collectors. Since 26 collectors cannot be divided evenly into banks of four, five, six, or seven, the designer must deviate from the calculated value by rounding to the next highest possibility result (i.e., 28 collectors). These units can be grouped into four banks of seven coll
28、ectors or Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-UFC 3-440-01 14 June 2002 3-9 seven banks of four collectors each. The length required for the collector banks is the width of the collectors plus connective piping. It is conservative to esti
29、mate 6 inches (152 mm) of connective piping between collectors, 3 ft (914 mm) between banks in the lateral dimension, and 4 ft (1219 mm) around the banks for personnel clearance. The bank widths are then estimated to be 31 ft (9449 mm) for the seven-collector bank and 17.5 ft (5334 mm) for the four-
30、collector bank. The distance required between collector rows can be found from Figure 3-5. For example, an 8 ft (2438 mm) collector at 40 degrees N latitude requires row spacing of about 2.5 times 8 ft (2438 mm), or 20 ft (6096 mm). The array layout should be determined by keeping in mind that the p
31、iping length should be minimized while geometric symmetry is maintained. This guidance results in a tendency for the banks to contain as many collectors as possible, and for the array layout to be rectangular in area with an even number of banks installed in multiple rows. Therefore, the case of fou
32、r banks with seven collectors each is the most preferred. A number of roof area dimensions should be proposed so the architect has some flexibility in determining the building orientation and dimensions. Figure 3-6 shows three possible collector array layouts for the 28-collector array. Similar cons
33、ideration can be given to the use of a 4 by 10 ft (1219 by 3048 mm) collector. The result would be 21 collectors (possibly rounded to 24 or 20), 25 ft (7620 mm) row spacing (if needed), and banks of seven, six, or five collectors respectively. 3-4.1.7 Array Support Structure. The support structure m
34、ust transmit the various loads incident upon the array to the building roof structure without overstressing it. The design must meet all code requirements and should be coordinated with, or reviewed by, a qualified structural engineer. At the system layout stage, the structural engineer or architect
35、 should have an idea about the building and roof type before the support structure is planned. Although steel has often been used for array structures, all systems designed under this guidance will be made from aluminum, to avoid the cost of applying and maintaining a protective finish. Although it
36、is difficult to generalize, experience has yielded some useful estimates about the weight and cost of large collector support structures. As a rough guideline for rack-type structures, the weight of the structure should be less than 5 lbs/ ft2(239 Pa) of collector area. The cost of the support struc
37、ture typically represents less than 15 to 20 percent of the total solar system cost. Any support structures falling outside of these guidelines could be considered inefficient from a cost versus performance view. It is expected that the support structure may be heavier and more costly in areas where
38、 design loads are higher or where stepped collector rows are required. Further, stepped arrays require elevated walkways for maintenance a personnel, which results in higher material and design costs. Provided by IHSNot for ResaleNo reproduction or networking permitted without license from IHS-,-,-U
39、FC 3-440-01 14 June 2002 3-10 Figure 3-6. Possible Array Configurations and Area 3-4.2 Storage Sub-System 3-4.2.1 Storage Tank Size. At the system layout stage, the storage tank volume and dimensions have a major impact on the design and location of the equipment room. Selection or specification of
40、the storage tank requires first determining the appropriate volume of the tank. The widely accepted practice for service water heating applications is to provide a storage tank volume of 1.5 to 2 gals per square foot (61.1 to 81.5 L per square meter) of collector area. Storage systems larger than th
41、is do not significantly increase the performance of the solar system, and the additional costs associated with larger storage are not justified. Storage systems smaller than this size can decrease system performance. The lower performance is due to relatively high storage temperatures, resulting in
42、lower solar collector efficiencies. Within these guidelines, the exact size of the storage tank is not critical to system performance and should be based upon available standard sizes. To provide proper stratification and to meet space requirements, vertical storage tanks are preferred. As tank size
43、 increases, space considerations and floor area become increasingly critical. When it becomes apparent that a single vertical tank is not possible, a horizontal tank or a series of vertical tanks will be necessary. Provided by IHSNot for ResaleNo reproduction or networking permitted without license
44、from IHS-,-,-UFC 3-440-01 14 June 2002 3-11 3-4.2.2 Storage Tank Location 3.4.2.2.1 Indoor Versus Outdoor. As with conventional energy systems, a solar system requires an equipment room to contain the heat exchanger, pumps, control system, and associated plumbing. If possible, the equipment room sho
45、uld be designed to house the solar storage tank. For retrofit situations where existing space does not permit the required tank volume, an outdoor location may be chosen. However, many factors discourage the location of storage tanks outside the building, such as a higher annual standby energy loss
46、(in most climates) and adverse environmental effects on the tank (including ultraviolet and moisture-based degradation). Solar storage tanks are not to be located underground. Underground tanks have had numerous problems, including leakage due to tank and ground shifting and thermal stresses; corros
47、ion due to the lack of cathodic protection; tanks surfacing due to buoyant forces while empty; and difficulty in retrieving and repairing sensors and instruments. 3.4.2.2.2 Tank Support and Floor Loads. Reinforced concrete pads and footings are often required to ensure that the weight of the tank do
48、es not endanger the structural integrity of the building. The design load calculation should take into account the estimated weight of the empty tank, the water to be stored in the tank, the insulation, and the tank support structure. The design load for the footing is also dependent on the type of
49、tank support used. 3-4.2.3 Legionnaires Disease. If a direct circulating system is supplying water for domestic use, ensure that water in the storage tank is heated to a minimum of 140 degrees F (60 degrees C) in order to avoid any potential source of Legionnaires disease. For additional information on Legionnaires disease refer to http:/www.efdlant.navfac
