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There is a new note on HTP Elite Piping instructions.

OldSkool Member Posts: 18
This summer I am going to finally fix the boiler piping on our home here.  As I read the HTP Elite piping instructions/suggestions I see a new note (among others) that I have not seen in any of my pre-work for this project.  The note starts as follows:

 <strong>  5.</strong>  <strong> System flow (secondary loop) should be greater than the boiler primary loop flow.</strong>  

My installation here is actually a Munchkin 140M, and the Vision 1 drawings do not have such a note, but just trying to learn, does anybody have any idea what in the heck are they talking about?   Proper primary/secondary hydraulic separation should make the various loops in a system unaware of flow differences, right?  Am I perhaps missing something?   Page 23 of the attached HTP Manual is included for context.



  • Mark Eatherton
    Mark Eatherton Member Posts: 5,840
    In and ideal world....

    System flow would ALWAYS be greater than boiler flow... in an ideal world.

    In the REAL world, during the shoulder seasons, there will be many times that the system flow is less than the boiler flow. This is due to the use of zone valves.

    In order to guarantee that the system loop flows more than the boiler loop, an oversized pump and a pressure activated bypass will have to be used.

    I suspect that they are worried about the flow in the tweener tees running backwards. In reality, the intelligent control logic on that boiler will know well in advance that the load has decreased, and will dial the burner back as far as it can go.

    For example, if the boiler pump is running 8 GPM (30 degree delta T), and the system pump is moving 10 GPM, then the flow stays in a forward moving condition between the two closely spaced tees at 2 GPM. But if zones shut down, and the system flow drops to 3 GPM, then the flow between the tees will be 5 GPM in a backwards direction in relation to the normal system flow.

    Seems kind of like a silly request to me, because in reality, the only time that "ideal" condition will occur, is at design condition, which only occurs for about 2 % of the time here in Denver.

    I wouldn't sweat it too much. Provided that the boiler is not grossly oversized, it won't make much difference.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
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