| Collectors, Part 1 |
 |
 |
|
Batch Collectors, or Integrated Collector Storage (ICS) Devices In these systems, the hot-water storage tank is the solar absorber. The tank is painted black or has a special coating and is mounted in an insulated box, usually about 6 inches deep, that has glass on one side. Cold water is piped to the bottom of the tank. Sun shines through the glass, heats up on the black surface, and warms the water inside the tank. Warmed water is taken from the top of the tank when a hot faucet is opened and cold water again moves into the tank. Some are single large tanks (30 gallons or more), and others use several metal tubes plumbed in a series. Single tanks are usually made of steel. Tubes are usually made of copper. Tube-type tanks perform better because more surface area is exposed, but they also cool off more quickly at night. ICS tanks can reach temperatures as high as 180 F on a warm sunny day, and half that on a warm cloudy day. There are some disadvantages to batch collectors. They are extremely heavy when full and must be mounted on sturdy structures (a reinforced roof or on the ground). When mounted the collectors must be tilted so they will drain properly. Batch heaters are good to use in climates that do not freeze. They can be used in seasonal homes during the warm months, but must be drained before it freezes. Flat Plate Collectors (FPCs) Flat plate collector heaters are the most commonly used throughout the world. They are durable and effective, and they shed snow and ice. FPCs are shallow, rectangular boxes, usually 4 feet by 8 feet by 4 to 6 inches, consisting of a strong frame, glass on the front of the collector, and a solid back. Just beneath the glass is an absorber plate with copper pipe manifolds that run across the top and bottom of the collector inside the frame. Smaller riser tubes are welded perpendicular along the manifold, spaced about 4 to 5 inches apart. A flat copper fin is welded or soldered to a riser to transfer heat from the fin to the tube. The fin is painted or coated with a special material to maximize absorption. FPCs need a strong mount (usually aluminum) to withstand high winds. All components of the collector must be made of compatible metals to reduce corrosion. Low-iron, low-glare tempered glass is commonly used for glazing FPCs. A rubberized gasket along the edge of the frame ensures a proper seal and protects the frame. Evacuated Tube Collectors (ETCs) In an ETC an annealed glass vacuum tube surrounds each individual pipe or absorber plate. The vacuum allows higher temperatures to develop. Some types have the tube connected to a manifold so water circulates through the tube. Other tubes contain a special fluid that evaporates and rises to a heat exchanger. When it cools off, it condenses and falls back into the tube. Still other tubes have a metal rod attached to the absorber and protruding from the tube for insertion into a manifold where circulating water picks up the heat. The disadvantages of ETCs include the fact that they can generate temperatures above boiling (causing scald injuries and system-pressure hazards). These problems can be mitigated by oversizing the storage tank, undersizing the collector, or by using a drain-back system (see below). The tubes are very fragile, and the collectors do not shed snow and ice well. |
Discuss this item on the forums. (0 posts)