Apricus Solar Water Heating System Installation and Operation ...

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