Desuperheater Direct Load Hookup

Discussion in 'General Discussions' started by GeoBelk, Nov 21, 2019.

  1. GeoBelk

    GeoBelk New Member

    Question on efficiencies with a two-tank domestic hot water desuperheater configuration.

    I've seen a couple piping diagrams with buffer tanks (here and here). I'm curious if a direct-load configuration (discussion here) would benefit a Desuperheater similarly to a standard heating load. Since the DSH runs when the heating load is called, the intermittent cycling should be a factor, right?

    For ease of discussion, I've attached a few diagrams and given them names.
    Direct Load - A configuration from the Buffer Bypass thread, John Siegenthaler's article, and other sources.
    Partial Direct Load - Prioritizes hot water at the top of the tank, the HWH pulls from near it's input
    Indirect Load - the recommended buffer tank configuration from the two linked sources above.

    DSH_Direct.PNG DSH_Partial_Direct.PNG DSH_Indirect.PNG
    For context, I'm a DIY-er planning my install using hot water heaters as buffer tanks (no dip tubes). This forum has been a huge help. I've really appreciated combing through it to learn for the past few months.

  2. ChrisJ

    ChrisJ Active Member Forum Leader

    Here is my DIY-er take on this.

    Direct Load: During a call for hot water the incoming cold water is around 50*F, as it passes through the DSH, the low capacity of the DSH will not raise the temp much. Cold water will be going directly to the finish tank during hot water draws (showers ect).
    GeoBelk likes this.
  3. GeoBelk

    GeoBelk New Member

    That's a great point. I'd not considered that the direct load in those example systems basically have no input and output.
    As John mentions under the 'Keep it Close' section, the hydraulic separation between the load and heat source should be more than between the load and the buffer. In the case of a DSH, the water entering on the DSH loop makes that difficult.
    The Partial Direct Load diagram keeps the load and source hydraulically separate. I can't seem to decide whether the direction of DSH flow matters in the Partial Direct example.

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