1、 Plastic Pipe in Solar Heating Systems TN-14/2016 Foreword This report was developed and published with the technical help and financial support of the members of the PPI (Plastics Pipe Institute, Inc.). The members have shown their interest in quality products by assisting independent standards-mak
2、ing and user organizations in the development of standards, and also by developing reports on an industry-wide basis to help engineers, code officials, specifying groups and users. The purpose of this technical note is to provide general information on plastic pipe used in solar heating systems. Thi
3、s report has been prepared by PPI as a service for the industry. The information in this report is offered in good faith and believed to be accurate at the time of its preparation, but is offered “as is” without any express or implied warranty, including WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
4、 A PARTICULAR PURPOSE. Any reference to or testing of a particular proprietary product should not be construed as an endorsement by PPI, which does not endorse the proprietary products or processes of any manufacturer. The information in this report is offered for consideration by industry members i
5、n fulfilling their own compliance responsibilities. PPI assumes no responsibility for compliance with applicable laws and regulations. PPI intends to revise this report from time to time, in response to comments and suggestion from users of the report. Please send suggestions for improvements to the
6、 address below. Information on other publications can be obtained by contacting PPI directly or visiting the PPI web site. The Plastics Pipe Institute, Inc. www.plasticpipe.org This technical note was first issued in July 2001 and revised in April 2016. PLASTIC PIPE IN SOLAR HEATING SYSTEMS 1.0 Obje
7、ctive This report describes, in a simplified manner, the technologies used in the solar heating industry; the limitation, if any, of plastic piping in each; and includes reference sections on recommendations to cope successfully with those limitations. 2.0 History The use of thermal solar energy was
8、 virtually nonexistent 45 years ago, but has grown to become a significant industry in the United States. Most solar applications are geographically concentrated in the states of California, Arizona, New Mexico, Colorado, Hawaii and Florida, although the technology is effective in all US states. Sol
9、ar heating (also known as thermal solar) systems range in size and complexity. The very simplest consist of nothing more than a black pipe or tubing lying in the sun connected to a swimming pool circulating pump. More complex systems consist of highly engineered collectors with one or more layers of
10、 glazing plus piping, pumps and controls for temperature and pressure. These systems frequently involve heat transfer fluids other than water, heat storage tanks and heat exchangers. For the purposes of this report, all subsequent references to plastic pipe apply only to the piping outside of the co
11、llectors themselves unless otherwise stated. Plastic piping can play a major role in this application. See Table 1 for a list of materials with elevated temperature capabilities. Plastic pipings combination of flexibility, relatively high temperature properties, and resistance to freeze damage and c
12、orrosion are major advantages for this end-use. There are, however, precautions that should be taken to prevent misapplication. 3.0 Collector Technologies The most significant use of solar heating has been for residential and commercial swimming pools, followed by domestic hot water and space heatin
13、g. Solar collectors are classified according to their water discharge temperatures: low temperature, medium temperature and high temperature. Low temperature systems generally operate at a temperature of 110 F (43C) and have a maximum stagnation temperature of 180 F (82C). Medium temperature collect
14、ors typically have discharge temperatures of 180-200 F (82 - 93C) but can generate stagnation temperatures of up to 280 F (154C) or more for several hours. High temperature collectors routinely operate at temperatures of at least 210 F (99C) and can generate stagnation temperatures of more than 400
15、F (204C). High temperature collectors operate above the capabilities of the materials in this document. There are several different plastic pipe materials that may be used directly with low temperature collectors with no special precautions. In addition, much plastic piping is being used extensively
16、 inside unglazed collectors where operating temperatures rarely exceed 110 F (43C) on a frequent basis. To protect against ultraviolet exposure damage and to increase efficiency, plastic piping for use in collector panels should contain a minimum of 2% carbon black of proper particle size and with g
17、ood dispersion as well as contain antioxidants. Check with the pipe manufacturer to be sure the pipe is suitable for long term exposure to sunlight. Plastic piping should not be used in systems with high temperature collectors including evacuated tube or concentrating types because of the extreme te
18、mperatures they can reach. Medium temperature collectors constitute the largest segment of the market. These glazed collectors are used in domestic hot water and space heating systems. Depending on the type of collector and system design, some special precautions should be taken. The major types of
19、medium temperature systems are described in the following paragraphs along with appropriate precautions. Medium temperature systems are either “passive” or ”active”. Passive solar systems use no pumps, controls or mechanical equipment to transport the heated water. The integral collector storage (IC
20、S) is a passive design which uses a tank or tube assembly absorber in an insulated metal case which is covered with a glazing material, usually glass. The absorber is painted flat black or coated with a “selective” material to increase solar energy absorption. Another type of passive solar heater is
21、 called “thermosiphon.” In this design a storage tank is mounted above the solar collector on the roof surface. All passive solar water heaters operate by the same principle; when a hot water tap is turned on in the building, cold water from the city water supply flows through the solar collector fi
22、rst and is pre-heated before entering the conventional gas, oil or electric water heater thereby considerably reducing or even eliminating consumption of fossil fuel energy. Because of the large volume of water in the collector, passive solar systems are not subject to high stagnation temperatures.
23、Thus, plastic piping can be used throughout, including a hook-up directly to the collector system. Active type solar systems utilize a pump to move heat transfer fluids through the collector. Some utilize swimming pool or potable water as the heat transfer fluid (open systems) while others typically
24、 use a non-toxic solution of propylene glycol and water to prevent freezing (closed systems). Heat is transferred from the heat transfer fluid to potable water by means of a heat exchanger in the solar storage tank or heat exchanger/pump appliance. All piping must comply with the local plumbing or m
25、echanical codes. Hydrocarbon oil or silicone oils are used in high temperature solar systems and are generally not recommended for use with plastic pipe. Note: Because there are many heat transfer fluid types available, the fluid selected must be approved as being suitable by the plastic pipe manufa
26、cturer. Active type, medium temperature collectors can limit or disqualify the use of plastic piping as stagnation temperatures can exceed 280F (138C) as mentioned earlier. Under no circumstances should any plastic piping be used inside the collector or in the system where it will be exposed to such
27、 high temperatures unless that particular plastic pipe has been qualified for that temperature of service. 4.0 Customer Characteristics and Distribution Channels In general, solar collector manufacturers do not provide piping for the system. The installer most likely will purchase the piping from a
28、local plumbing supply wholesaler or solar supply house. Installers are usually plumbers, but in some regions solar specialists provide installation services. Installation should be performed by knowledgeable, licensed contractors. The installation requires knowledge of carpentry to provide roof supp
29、ort or mounting, electricity to install the control system (where applicable), and plumbing to install the piping system and to tie in to the swimming pool or storage tank or the existing domestic water supply. Always be sure the installation meets the requirements of the local building, plumbing an
30、d mechanical codes. As the solar energy industry matures, the swimming pool industry and plumbers are recognizing thermal solar energy as an opportunity to expand business by becoming installers in addition to the solar specialists. 5.0 Space Heating Because of the relatively low fluid temperatures
31、used in radiant floor heating (110-140 F/ 43-60C), the heated fluid for these systems can be derived from the medium temperature solar systems . For these reasons, many radiant heating systems installed today use solar collectors as the primary heating source. Baseboard hydronic heating requires hig
32、her temperatures (typically 180 F/82 C) to be effective, as does a water-to-air heat exchanger located in the plenum of a forced air system. Features and Benefits of Plastic Piping Feature Benefit Ease of Installation, Cost Savings Minimizing the overall cost of solar heating systems is necessary to
33、 make them viable alternatives and to expand customer acceptance. Flexibility Since most solar systems are installed after the building construction is completed, the flexibility and ease of joining plastic piping systems are a big advantage. In addition, there is no need to use a soldering or brazi
34、ng torch in an attic full of combustible materials as otherwise might be required for metal piping systems. High Temperature Resistance For continuous use, thermoplastic pipe must be suitable for high temperature environments. The following materials and composite structures are listed in PPI TR4 wi
35、th elevated temperature capabilities. PE 140 F (60 C) CPVC 180 F (82 C) PA 180 F (82 C) PE-RT 180 F (82 C) PEX 200 F (93 C) PEX-AL-PEX 200 F (93 C) PE-AL-PE 140 F (60C) PERT-AL-PERT 200 F (93C) PVDF 200 F (93 C) In addition to materials listed in PPI TR-4, there are other materials whose manufacture
36、rs recommend them for elevated temperature applications. PP 180 F (82 C) PB 180 F (82 C) PFA 212 F (100 C) The materials listed above are by generic name only. It is necessary that the user verify with the manufacturer that a particular pipe compound is properly formulated (stabilized) to withstand prolonged elevated temperatures. Pressure ratings at elevated temperatures are reduced from the 73 F (23 C) pressure ratings. Consult with the manufacturer for pressure ratings above 73 F (23 C).
