Apricus Solar Water Heating System Installation and Operation ...

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Apricus Solar Collector Installation & Operation Manual - USA- Roof flashing, if in direct contact with copper pipe- Soldering material must be rated to more than 480°F (250°C) within 24” linear from collector header- Washers or seals used in any quick-connect, compression or threaded fittings etc.- Heat transfer fluidsApricus solar collectors will not be damaged by thermal shock.b) High Temperature Controller Setting: Some controllers may have a high temperature setting which willprevent the pump from operating when the collector is above a certain limit. This function is mostcommonly used with drain-back systems as circulating water through the collector when hot would causelarge volumes of steam (depending on pressure setting) resulting in a pressure increases and potentialdumping of water/steam from the drain-back tank.c) Low Temperature Limits: The low temperature limits of all components in the system must be knownand cannot be exceeded. In every climate region, all materials exposed to winter freezing conditions mustbe able to withstand such conditions. This is particularly important for any synthetic materials, such asplastics or rubbers that may become brittle when extremely cold. The following are examples ofcomponents that should be able to withstand the coldest conditions experienced in the installation location:- High-point ball valve (used for auto-air vent during system charging)- Pipe insulation (either high temp EPDM or fiberglass)- Roof flashing, if in direct contact with copper pipe- Washers or seals used in any quick-connect, compression or threaded fittings etc.- Heat transfer fluids, if closed loop- Rubber/plastic components on solar collectors, particularly if they are structural.Apricus uses silicone rubber components which are able to maintain good flexibility even during freezingconditions.d) Ultraviolet (UV) degradation: Any components installed outside must be able to withstand UV radiationwithout significant degradation. Color fading is common, but cracking, peeling and other severe degradationshould not occur during the design-life of any component in the system.e) Structural Loads: Components must be able to withstand environmental forces such as wind loading,snow loading, rain and hail. They must also be securely and positively fastened to the structure.- Wind loading refer to section 3.13.- Snow loading refer to section 3.14.- Hail refer to section 3.16.3.11. Fluid Expansiona) Thermal Expansion of Water: Water can expand in volume by up to 2% from cold to hot in a solarthermal system. In the past, most water heaters utilized the cold supply inlet as a vessel to accept thisincrease in fluid volume; in other words, they literally pushed the excess volume backward against incomingwater pressure. Many codes now require back-flow prevention devices that prohibit this method. In thesecases, an expansion tank is necessary to accept increased fluid volume, otherwise the T/P Valve willdischarge frequently. If there is already an expansion tank present, you will need to install another one or alarger one, as necessary. For example, a direct flow system with an 80 gallon tank and 2 gallons in the solarloop needs between 1.5-2 Gallons of additional volume. The expansion tank needs to be able to accept thatamount of fluid. If no back-flow device is present, a potable expansion tank should not be necessary.b) Expansion Tank (potable AND direct flow): Direct flow systems AND closed systems that have a checkvalve or back-flow preventer on the incoming cold potable supply must have an expansion tank installed toaccept the potable water’s thermal expansion. The expansion tank must be potable water rated and sized toaccept the maximum thermal expansion possible for the entire volume of water heated in any and all thetanks in the system. Contact the expansion tank manufacturer to confirm, which model is necessary giventhe system fluid type, fluid volume, pressure and operating temperature range.c) Expansion Tank (closed loop): For closed loop systems, an appropriately-sized, expansion tank mustbe installed in the solar loop to accept the heat transfer fluid’s thermal expansion. The expansion tank mustCopyright 2011 – Apricus Inc Doc: A7-05.4.1.4-PB-1.9 Page 28 of 126
Apricus Solar Collector Installation & Operation Manual - USAbe sized to accept the maximum fluid expansion possible for the specific heat transfer fluid and rated foruse with it (without corrosion). Contact the expansion tank manufacturer to confirm which model isnecessary, given the system fluid type, fluid volume, pressure and operating temperature range. Heattransfer fluids, such as propylene glycol have a higher expansion coefficient than water, but given the smallvolume of fluid in most residential closed loops (domestic system only, max 90 tubes) the standard Apricusexpansion tank is adequate.d) Steam Formation: When steam forms, the volume it occupies is much greater than water. Atatmospheric pressure, 1 gallon of water can expand to occupy 223 ft3 (1L of water = 1.673 m3). Underpressure, steam can be compressed into a much smaller space. At 50 psi, a common operating pressurefor the collector during a period of stagnation, the volume that steam would occupy is around half its volumeat atmospheric pressure (around 104 ft3 per gallon (0.885 m3 per Liter).In the solar collector, when the fluid temperature exceeds about 290°F (145°C) water (or water in a glycolmix) will form steam in the header. The entire fluid contents of the header, DO NOT form steam, whichwould result in nearly 10.5 G (40 L) of additional volume, far beyond the capacity of the expansion tank.Instead, the capacity of the header and pipe in very close proximity fill with steam, an expansion volume ofabout 0.26 G (1 L) per AP-30 collector. Only a very small volume of water is actually turning to steam,about 0.067 fl.oz (2 ml). This steam will quickly clear the header of fluid by pushing the fluid down the returnline, since there is a check valve in or after the pump on the Supply (Feed) Line. The standard 4.7Gexpansion tank provided with the closed loop pump station or a similarly-sized expansion tank on a directflow system will be able to accept this volume.3.12. Heat Exchangers3.12.1. Internal Coil Heat Exchangersa) Coil Design: Indirect tanks normally use coil heat exchangers to facilitate heattransfer between solar/boiler heated fluid and the water in the tank. Most tanksuse large diameter (1” or larger) coils that are designed for the high flow ratesand high delta-t common in a boiler system. Unfortunately, the ideal for solarcollector efficiency is low flow rates and low delta-t levels. Large coils requirehigher solar collector temperatures in order to achieve sufficient heat transferrates.Apricus recommends that you select a tank with a coil heat exchanger that is !”diameter or multiple smaller diameter pipes designed specifically for solar.Alternatively, an external, brazed-plate heat exchanger that has been specificallydesigned for solar can be used with most storage tanks.b) Closed Loop Fluid Volume: When calculating the closed loop fluid volume,remember to include the volume in the coil, which should be listed on the tank’sproduct specification sheet. In Canada, CSA requires that the fluid volume of the solar system not exceed10% of the volume of the storage tank.c) Single vs Dual Wall: If the local area requires a dual wall heat exchanger Apricus recommends avoidingthe use of a coil heat exchanger as the efficiency will be lower than desirable. Choose a dual wall brazedplate heat exchanger instead (see 3.12.2). When using a single wall heat exchanger the solar loop pressureshould be less than the potable water pressure.Copyright 2011 – Apricus Inc Doc: A7-05.4.1.4-PB-1.9 Page 29 of 126
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