4 Responses to “Optimal System Thermodynamics”


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  1. Dear Dr. Ben,

    Once again I thank you for your very useful detail of drain back system. You’re right to make a huge effort to advertise the benefits of drain back system.
    My 30 years experience in the solar thermal system using glycol for the closed loop and the problem of lowering PH of glycol when there is a stagnation condition make me to appreciate your information.
    Drain back system is suitable for very cold and very hot climates too.
    To make our systems more reliable we have made a differential controller that appears faults on the display and voice alarm in case of system failure. The attached file shows you the most significant parameters of the controller. However a new design follows where the controller will be rail- mounted and the whole width will be as the width of three rail-mounted fuses namely 54 mm (2.12”). The controller later will be combined with an SMS telephone controller. The software is ready but I will be very grateful if you could suggest us some operations that have to be added too.

    Thank you again for your valuable information
    C. Oikonomidis
    Civil Engineer M.Eng.

  2. Dr. Ben

    I think you have done a good job of thinking up the major failures that could occur. You want to detect out of range values on the sensors (short and open circuits) and a stuck pump. However, determining when the pump is stuck can be tricky.

    You are using a high temperature reading on the collectors to indicated the pump is not pumping. There are several reasons the pump could not be pumping.

    1) the high limit temperature in the solar tank has been reached and the pump turned off
    2) the pump rotor is jammed
    3) the power wiring to the pump is open circuit because of a fault
    4) the power service to the building is off. In this case the whole controller is off and you can’t signal an alarm.

    So, the reasons the pump is not pumping are varied and one of them is a normal operating mode. You need a way to distinguish these different modes from each other.

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