Apricus Solar Water Heating System Installation and Operation ...

Apricus Solar Collector Installation & Operation Manual - USA3.6. Stagnation and Overheating3.6.1. What is Stagnation?a) Stagnation: Stagnation refers to the condition that occurs whenever the pump stops running. This couldbe due to pump failure, power outage or most commonly, as the result of a max tank temperature protectionfeature setting on the controller. During stagnation, the collector, unable to actively dump heat, will continueto rise in temperature until the heat loss from the collector and piping equals the heat being absorbed. Instrong sunlight with high ambient temperatures, the collector will reach a peak stagnation temperatures ofabout 428°F (220°C), if dry (decommissioned system or drain-back), and a lower level of 320°F (160oC), ifthe piping and collectors contain fluid (as in pressurized systems).b) Consider High Temperatures: Components that may be exposed to the high temperatures such asvalves, plumbing or insulation should be suitably rated. Heat will not migrate downward to the tank becauseheat rises. but when the pump turns ON, a batch of super hot water may be delivered to the tank. Althoughthat will only last a minute or so, it should be considered when sourcing materials for the piping on thereturn line to tank.3.6.2. System Pressure & Boiling Temperaturea) Boiling Temperatures: The boiling temperature of water (or other fluid) is directly related to the pressureof the system. Water will boil at a higher temperature, the more pressure it under. This is a very importantconcept, as the pressure of the system can greatly influence the operation and reliability. Generally, a higherpressure is better (within reasonable limits).The table below provides pressures and corresponding boiling temperatures for water. These will beslightly higher for 50/50% glycol mixes, which on average have a boiling point of 220°F (104°C) at sea level(i.e.1 atmosphere of pressure) versus pure water at 212°F (100°C).PRESSURE and H2O BOILING POINTPSI oF kPaoC14.5 212 101 10028 247 203 12043.5 271 304 13358 289 405 14372.5 304 507 15187 317 608 158b) Different Fluids: In a closed loop system using a heat transfer fluid, the properties will be different thanplain water. The Solar Hi-temp heat transfer fluid manufactured by J.C.Whitlam does not boil until 468°F(242oC) at 1 Atmosphere and will never boil when used in an Apricus solar water heating system, as long aspressure above atmospheric is maintained. Other heat transfer fluids will behave in a similar fashion. Seethe section on heat transfer fluids for more information.c) Pressure Loss with Height: Even though a system might be a closed loop and pressurized, there isalways some pressure loss caused by height. This is extremely important to understand when deciding thesystem pressure. The loss of pressure is about 0.5 psi per vertical foot. This means that while the pressureat the pump station may be 40 psi, a vertical rise of 50 ft will result in only 14.5 psi at the collector, which isthe same as atmospheric pressure. A low system pressure can result in bubbles (vapor) forming within theheat transfer fluid due to a lowered fluid boiling temperature. These bubbles will collect in the high points inthe solar loop piping, especially within the collector itself and can result in air locks that the pump may notbe able to overcome, resulting in no flow and then stagnation.During other periods of stagnation, the pressure in the system will rise, especially if there is any steamformation, but the same vertical loss still applies, so while the pressure may increase from 40 to 60 psi atthe pump station, the collector with a 40’ vertical height will only be about 40 psi.d) Flash Point: The flash point of a fluid is the lowest temperature at which vaporization can occur to form amixture in air that can be ignited. Propylene glycol has no measurable flash point in concentrations lessCopyright 2011 – Apricus Inc Doc: A7-05.4.1.4-PB-1.9 Page 22 of 126