significantly. Snow loads for collector racks are affected by local siting-whether they are in an exposed area where wind will readily blow snow off, or they are in a sheltered area where the snow is unlikely to be blown away.
Due to their filled weight, ICS and thermosyphon systems may be subjected to significant earthquake loads Consideration of earthquakes is specific to portions of California, as well as Hawaii, Puerto Rico, and the U.S. Virgin Islands. Evaluating the effects of these loads is complex and should involve professional engineering.
Wind loads are a critical consideration for tilted racks. The greater angle a collector is from the plane it is mounted on, the more impact wind loads will have. The magnitude of wind loads depends upon.
Wind speeds at the particular location.
The height at which the collector is mounted. A collector mounted on a 30-foot-high roof, for example, will experience greater wind loads than one mounted on a lower roof.
The collector exposure. Coastal homes that are unsheltered, for example, will have much greater wind loads than homes sheltered by large buildings or trees.
Wind-loading effects are exponentially related to the wind speed. A site with twice the wind speed of another will be subject to four times the wind force. Maps are available to assist designers with determining wind speed. In some cases, local authorities having jurisdiction will specify the design" ind speed.
Distributed versus concentrated loads. Many roof loads are considered distributed loads, which means they are spread out evenly over an area-like the roof sheathing, underlayment and roofing material. Wind and snow loads on the roof surface are also distributed loads. But when the wind or snow load is on the collector, it is exerted on the feet, becoming a concentrated load, which is applied to points on the roof structure.
Concentrated loads for flush-mounted collectors tend to have minimal impact on the stresses in the roof structure. When collectors are installed on tilt racks, the geometry of a tilt rack amplifies the impacts of the wind. The design of the mounting rack will have a significant effect on how large the concentrated loads will be on the roof structure.
Ground Mounted SWH Systems.
Likely, the best solar window at your site will determine whether your solar water heating(SWH) system is roof-mounted or ground mounted. Both have their advantages and disadvantages.
Since the ground-mount is independent of the roof, any concerns associated with the strength of the roof for supporting solar collectors are eliminated. Using a ground-mounted array also minimizes the safety risks associated with installing equipment on an elevated surface. Tilt racks are commonly used in ground mounted systems and provide the owner with an opportunity to install the collectors at an angle that best suits the application.
However, ground-mounted systems require their own foundation and are usually more expensive than roof-mounted SWH systems. Besides cost, there are other challenges associated with ground-mounted arrays. The type of soil in an area can have a huge impact on the stability of a new foundation. The presence of rock ledge may require drilling and pins to secure the foundation and clay may cause settling that could affect the integrity of the collector array. Additionally, ground-mounted arrays typically require burying pipe and can significantly increase the amount of piping needed between the collector array and the storage tank. This not only adds costs but also can affect performance by increasing heat loss in the system and potentially requiring more pumping power.
Rack Design
Racks are designed to transfer dead and environmental loads from the collectors to the roof structure. Hardware secures the collectors to the rack, the rack is attached to the building surface(usually the roof and the structure then carries the loads to the ground. SWH mounting kits are usually available from the collector manufacturer to match the collectors' frame. Most mounting kits use clamps that are inserted into frame extrusions, and proprietary mounting hardware. This is in contrast to most PV racks, which can be used with most modules.
Two types of tilt racks are common strut-type aluminum racks for flat-plate collectors and stainless-steel racks for evacuated-tube collectors. ICS units may also be installed o tilt racks, but these collectors are less prevalent in the U.S than flat-plate and evacuated-tube collectors.
Installing collectors in a landscape position can improve the aesthetics of the installation and reduce the wind loads the roof
Tilt or Parallel?
For aesthetics, it is often preferable to mount collectors at the same slope as the roof Parallel-mounted arrays are less conspicuous and also minimize the effects of wind on the collector array. But in systems where parallel mounting will dramatically impact system performance-for example when the roof pitch is too shallow, placing the collector at risk of summertime overheating and wintertime underperformance-tilt racks may be used. A tilt rack elevates the upper portion of the collector to increase the array's mounting angle. For further discussion about the impact of the collector tilt on system performance see"Site Assessment for Solar Water Heating Systems in HP159(homepower.com/159.64)
Aluminum for flat-plate collectors.
Several manufacturers offer a tilt rack that uses two struts one supports the upper portion of the collector, while the other supports the bottom portion. The upper strut is connected to legs attached to feet that are secured to the roof structure. The lower rail is attached directly to mounting feet without legs.
The distance between the rails depends upon the environmental loads and the strength of the collector frame. Loads can cause bending stresses, which also are affected by beefiness of the collector frame. Lighter, shallower frames will have more deflection(i.e., will bend more) and require more support than deeper frames. Longer cantilevers will increase the stresses in the collector frame, as will a large spacing between the rails. The allowable cantilever collector is less than the allowable span between the rails. For example SunEarth specifies a maximum cantilevered length that is 20% of the length of the collector while allowing the rails to be spaced at roughly 75% of the collector length.
When the roof orientation is less than ideal, tilt racks can often be rotated 90° to allow for a wall-mounted array.
This aluminum tilt-up rack for flat-plate collectors(by SunEarth) makes the most of a shallow roof pitch.
Stainless steel for evacuated-tube collectors.
In contrast to flat-plate collectors, which can use the structure of the collector frame for bracing and support, evacuated-tube collectors rely strictly on the rack for structural support. Since stainless steel is stronger than aluminum, the thickness and size of an evacuated-tube rack tend to be thinner and smaller than those for a flat-plate collector. Racks for evacuated tubes require significantly more bracing-the manifold could easily be pushed sideways since the collector itself lacks the rigidity of a flat-plate collector. Diagonal bracing is required for evacuated-tube tilt racks.
An evacuated-tube collector is secured to the rack by clamping the manifold and the tube's mounting rail to a frame, which has two or three rails that run parallel to the tubes. The collector is tilted by using legs bolted to the mounting rails and attached to the roof via a foot or to another stainless steel section that connects to the bottom end of the mounting rail to form a triangle.
Evacuated-tube collectors often need cross-bracing, seen here through and behind the tubes.
Sealing Roof Attachments.
With the recent explosion of residential grid-tied PV systems numerous flashing products have been introduced to help waterproof roof attachment points. Many of these products are easy to integrate with parallel-mounted solar collectors.
However, using these products with tilt racks proves to be a greater challenge. Most mounting feet on tilt racks require two lag screws to resist the withdrawal forces that can occur at the rear foot. Though there are a number of mechanical flashing products on the market that utilize two lag screws, only a few integrate with selected tilt racks in the SWH industry. Heliodyne, for instance, utilizes the same flashing used on standard plumbing vents to mechanically flash the feet of its tilt racks. EcoFasten Solar's GF2 flashing and brackets provide another option for connecting the rear mounting feet of standard racks directly to the roof. There are a number of collector manufacturers that suggest waterproofing lag screw penetrations by applying a quality sealant to the threads and between the mounting foot and the roofing
Though some industry representatives claim that using sealant alone is a building code violation, there is a lot of ambiguity surrounding what is required for sealing penetrations. In many jurisdictions, if the roofing manufacturer specifies a method for sealing such penetrations, then the lag screw installation must conform to these specifications. In cases where the manufacturer doesn't specify these details or the roofing manufacturer is unknown, the building code specifies that the penetration must be flashed in a waterproof manner. This often means consulting with the original roofer, researching roofing best practices, and/ or referring to the rack manufacturer's installation instructions.
Seam clamps are often used when mounting collectors on standing-seam metal roofs. It is important to determine how the metal roof is attached to the roof structure to ensure that it can transfer the collector loads.
Attachment Points.
Lag screws are the most common method for attaching a collector rack to the roof. Other methods include using J-bolts that hook the underside of a rafter or roof truss. SWH racks m
significantly. Snow loads for collector racks are affected by local siting-whether they are in an exposed area where wind will readily blow snow off, or they are in a sheltered area where the snow is unlikely to be blown away. Due to their filled weight, ICS and thermosyphon systems may be subjected to significant earthquake loads Consideration of earthquakes is specific to portions of California, as well as Hawaii, Puerto Rico, and the U.S. Virgin Islands. Evaluating the effects of these loads is complex and should involve professional engineering. Wind loads are a critical consideration for tilted racks. The greater angle a collector is from the plane it is mounted on, the more impact wind loads will have. The magnitude of wind loads depends upon. Wind speeds at the particular location. The height at which the collector is mounted. A collector mounted on a 30-foot-high roof, for example, will experience greater wind loads than one mounted on a lower roof. The collector exposure. Coastal homes that are unsheltered, for example, will have much greater wind loads than homes sheltered by large buildings or trees. Wind-loading effects are exponentially related to the wind speed. A site with twice the wind speed of another will be subject to four times the wind force. Maps are available to assist designers with determining wind speed. In some cases, local authorities having jurisdiction will specify the design" ind speed.Distributed versus concentrated loads. Many roof loads are considered distributed loads, which means they are spread out evenly over an area-like the roof sheathing, underlayment and roofing material. Wind and snow loads on the roof surface are also distributed loads. But when the wind or snow load is on the collector, it is exerted on the feet, becoming a concentrated load, which is applied to points on the roof structure. Concentrated loads for flush-mounted collectors tend to have minimal impact on the stresses in the roof structure. When collectors are installed on tilt racks, the geometry of a tilt rack amplifies the impacts of the wind. The design of the mounting rack will have a significant effect on how large the concentrated loads will be on the roof structure.Ground Mounted SWH Systems.Likely, the best solar window at your site will determine whether your solar water heating(SWH) system is roof-mounted or ground mounted. Both have their advantages and disadvantages. Since the ground-mount is independent of the roof, any concerns associated with the strength of the roof for supporting solar collectors are eliminated. Using a ground-mounted array also minimizes the safety risks associated with installing equipment on an elevated surface. Tilt racks are commonly used in ground mounted systems and provide the owner with an opportunity to install the collectors at an angle that best suits the application. อย่างไรก็ตาม ระบบติดดินต้องมูลนิธิของตนเอง และมักจะแพงกว่าระบบ SWH ติดหลังคา นอกจากต้นทุน มีความท้าทายอื่น ๆ ที่เกี่ยวข้องกับอาร์เรย์ที่ติดพื้นดิน ชนิดของดินในพื้นที่สามารถมีผลกระทบมากกับความมั่นคงของมูลนิธิใหม่ ของหินหิ้งอาจเจาะและหมุดเพื่อมูลนิธิ และดินอาจทำให้เกิดตะกอนที่อาจมีผลต่อความสมบูรณ์ของอาร์เรย์เก็บ นอกจากนี้ เรย์ติดพื้นดินโดยทั่วไปต้อง burying ท่อ และสามารถเพิ่มจำนวนท่อที่จำเป็นระหว่างการเก็บอาร์เรย์และถัง นี้ไม่เพียงแต่เพิ่มต้นทุน แต่ยัง สามารถส่งผลกระทบต่อประสิทธิภาพการทำงาน โดยเพิ่มการสูญเสียความร้อนในระบบ และอาจต้องใช้สูบน้ำพลังงานออกแบบชั้นวาง ชั้นถูกออกแบบมาเพื่อถ่ายโอนโหลดตาย และสิ่งแวดล้อมจากการสะสมโครงสร้างหลังคา ฮาร์ดแวร์ยึดสะสมเพื่อชั้น ชั้นแนบกับพื้นผิวอาคาร (ปกติหลังคาและโครงสร้างแล้วนำโหลดไปพื้นดิน ชุดติดตั้ง SWH มีปกติจากผู้ผลิตเก็บให้ตรงกับกรอบของสะสม ชุดติดตั้งที่ส่วนใหญ่ใช้ clamps ที่มีแทรกเฟรม extrusions และฟทร์แวร์ติดตั้งฮาร์ดแวร์ อยู่ตรงข้ามส่วนใหญ่วิศวกรรมชั้น ซึ่งสามารถใช้กับโมดูลส่วนใหญ่ ชนิดสองชั้นเอียงเป็นชั้นอลูมิเนียมชนิดป๋อนี้ทั่วไปสำหรับการสะสมแผ่นแบนและราวเหล็กสเตนเลสสำหรับสะสมหลอดอพยพ หน่วย ICS อาจ o ติดตั้งเอียงราว แต่เหล่านี้สะสมอยู่น้อยที่แพร่หลายในอเมริกาที่กว่าสะสม จานแบน และ หลอดอพยพ ติดตั้งสะสมในตำแหน่งแนวนอนสามารถปรับปรุงความสวยงามของการติดตั้ง และลดโหลดลมหลังคาเอียง หรือแบบขนาน สำหรับความสวยงาม ได้บ่อยกว่าการกำหนดเป็นอาร์เรย์พร้อมติดตั้งหลังคามีน้อยเป้า และยัง ลดผลกระทบของลมในอาร์เรย์เก็บสะสมที่ความลาดชันเดียวกัน แต่ ในระบบที่ติดตั้งแบบขนานจะอย่างมากส่งผลกระทบต่อประสิทธิภาพของระบบ-เช่น เมื่อระดับหลังคาจะเกินตื้น การเก็บรวบรวมการเสี่ยงจ้าชั้นเอียง underperformance ร้อนและฤดูอาจจะใช้ได้ ชั้นเอียงยกระดับส่วนบนของตัวเก็บรวบรวมเพื่อเพิ่มมุมการติดตั้งของอาร์เรย์ เพิ่มเติมสนทนาเกี่ยวกับผลกระทบของการเอียงตัวเก็บรวบรวมในประสิทธิภาพของระบบการ "ประเมินไซต์สำหรับระบบพลังงานแสงอาทิตย์น้ำร้อนใน HP159(homepower.com/159.64)อลูมิเนียมสำหรับสะสมแผ่นแบน ผู้ผลิตต่าง ๆ มีชั้นเอียงที่ใช้สองอยู่หนึ่งสนับสนุนส่วนบนของตัวเก็บรวบรวม ในขณะที่อื่น ๆ สนับสนุนส่วนล่าง ป๋อนี้ด้านบนเชื่อมต่อกับขากับเท้าที่ปลอดภัยให้กับโครงสร้างหลังคา รางล่างแนบกับเท้าไม่ มีขาติดตั้งโดยตรง ระยะห่างระหว่างรางขึ้นอยู่กับโหลดสิ่งแวดล้อมและความแข็งแรงของเฟรมตัวเก็บรวบรวม โหลดอาจทำให้เครียดดัด ซึ่งยัง ได้รับผลกระทบ โดย beefiness ของเฟรมตัวเก็บรวบรวม เฟรมเบา เด็กเล็ก ๆ สามารถจะมี deflection เพิ่มเติม (เช่น จะงอขึ้น) และต้องการการสนับสนุนเพิ่มเติมกว่าเฟรมที่ลึก Cantilevers อีกต่อไปจะเพิ่มความเครียดในการเก็บรวบรวมเฟรม เช่นช่องว่างขนาดใหญ่ระหว่างรถไฟ เก็บ cantilever ที่ใช้จะน้อยกว่าช่วงที่ใช้ระหว่างรถไฟ ตัวอย่าง SunEarth ระบุความยาว cantilevered สูงสุดที่ 20% ของความยาวของตัวเก็บรวบรวมขณะให้รางจะถูกเว้นวรรคประมาณ 75% ของความยาวตัวเก็บรวบรวมเมื่อวางแนวหลังคาน้อยกว่าห้อง ชั้นวางเอียงมักจะได้หมุน 90 องศาเพื่อให้แถวที่ติดผนังชั้นนี้เอียงขึ้นอลูมิเนียมสำหรับสะสมจานแบน (โดย SunEarth) ให้มากที่สุดของสนามหลังคาตื้น เหล็กกล้าไร้สนิมสำหรับสะสมหลอดอพยพ ตรงข้ามจานแบนสะสม ซึ่งสามารถใช้โครงสร้างของตัวเก็บรวบรวมเฟรมสำหรับ bracing และสนับสนุน สะสมหลอดอพยพพึ่งอย่างเคร่งครัดชั้นสำหรับการสนับสนุนโครงสร้าง เนื่องจากเหล็กกล้าไร้สนิมแข็งแกร่งกว่าอลูมิเนียม ความหนาและขนาดของชั้นมีหลอดอพยพมักจะบาง และเล็กกว่าสำหรับเก็บจานแบน ชั้นสำหรับใช้หลอดสุญญากาศมากอเนกมาก bracing อาจได้มีการผลักดันด้านข้างตั้งแต่เก็บตัวขาดความแข็งแกร่งของเก็บจานแบนได้ Bracing เส้นทแยงมุมจะต้องเอียงหลอดอพยพราวAn evacuated-tube collector is secured to the rack by clamping the manifold and the tube's mounting rail to a frame, which has two or three rails that run parallel to the tubes. The collector is tilted by using legs bolted to the mounting rails and attached to the roof via a foot or to another stainless steel section that connects to the bottom end of the mounting rail to form a triangle. Evacuated-tube collectors often need cross-bracing, seen here through and behind the tubes.Sealing Roof Attachments.With the recent explosion of residential grid-tied PV systems numerous flashing products have been introduced to help waterproof roof attachment points. Many of these products are easy to integrate with parallel-mounted solar collectors.However, using these products with tilt racks proves to be a greater challenge. Most mounting feet on tilt racks require two lag screws to resist the withdrawal forces that can occur at the rear foot. Though there are a number of mechanical flashing products on the market that utilize two lag screws, only a few integrate with selected tilt racks in the SWH industry. Heliodyne, for instance, utilizes the same flashing used on standard plumbing vents to mechanically flash the feet of its tilt racks. EcoFasten Solar's GF2 flashing and brackets provide another option for connecting the rear mounting feet of standard racks directly to the roof. There are a number of collector manufacturers that suggest waterproofing lag screw penetrations by applying a quality sealant to the threads and between the mounting foot and the roofingThough some industry representatives claim that using sealant alone is a building code violation, there is a lot of ambiguity surrounding what is required for sealing penetrations. In many jurisdictions, if the roofing manufacturer specifies a method for sealing such penetrations, then the lag screw installation must conform to these specifications. In cases where the manufacturer doesn't specify these details or the roofing manufacturer is unknown, the building code specifies that the penetration must be flashed in a waterproof manner. This often means consulting with the original roofer, researching roofing best practices, and/ or referring to the rack manufacturer's installation instructions.Seam clamps are often used when mounting collectors on standing-seam metal roofs. It is important to determine how the metal roof is attached to the roof structure to ensure that it can transfer the collector loads. Attachment Points. Lag screws are the most common method for attaching a collector rack to the roof. Other methods include using J-bolts that hook the underside of a rafter or roof truss. SWH racks m
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