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  1. #1
    Join Date
    Jul 2010
    Posts
    43

    waterfurnace desuperheater

    I have a two year old 3 ton envision that I love. But I have a question because I have read that the system should produce more hot water in the summer than in the winter. In mine the reverse is true. On a hot day where my system runs 20 hours and we don't use hot water the temperture in my tank will get to about 105 where as on a cold day it would be about 125. Is this normal or can anyone tell me anything to check? Thanks for any help anyone can give.

  2. #2
    Join Date
    Feb 2006
    Posts
    468
    Where are you?

    It is sometimes the case that more / hotter water is made in winter since heating operation is often characterized by higher compressor discharge pressure and temp.

    I'm near Jax, FL and despite it being a cooling dominated climate my winter peak desuperheater buffer tank temp has been 123, but in summer it rarely exceeds 110

  3. #3
    Join Date
    Jul 2010
    Posts
    43
    Thanks watercop I may not have a problem after all. I live in Virginia. I was confused because I had read that your unit should produce more in the summer than in the winter and I knew that was not true for me. My system is doing great my power bill was cut by 41% total and I didn't think that could happen I'm not complaining I just want to get all out of this system possible.

  4. #4
    Join Date
    Feb 2006
    Posts
    468
    Up in VA you may have entering water temps in the upper 50s or low 60s which makes for extremely efficient cooling performance. However, the system may be operating so efficiently that the compressor discharge temp isn't high enough to completely heat domestic water.

    Nevertheless you still can't lose if you plumb the desuper to its own buffer tank upstream of the main water heater. Even if it only heats incoming cold water from 60 to 90 or 95 you are still way ahead of having to pay to heat water all the way up from 60, and the recovered heat reduces the heat that has to be rejected elsewhere.

    Producing hot water in winter robs some space heating capacity, so the system tends to have to run a bit longer and will produce marginally cooler air. Desuper production in winter may be higher owing to both longer run times and CFM settings that result in higher compressor discharge temps in order to avoid "cold blow" off the registers.

    You are still ahead of the game in winter because the system makes hot water at a COP of 3-5, much better than most alternatives. Worst case you can disable the desuper pump during cold weather; some systems lock out the desuper pump if strips are active.

  5. #5
    Join Date
    Dec 2011
    Location
    USA
    Posts
    66
    My water furnace will heat my water for the whole family without any additional element heat when the outdoor ambient drops below 20 degrees. Nice extra.

  6. #6
    Join Date
    Mar 2008
    Posts
    279
    In the winter time i unplug my direct vent water heater and the geothermal makes more then enough hot water for the entire family. But in the summer time it i have to plug the water heater in since the geo don't run quite enough to make the hot water i need but it does a good job in the water heater not having to run as much. So if your in a colder climate enough nice hot water in the winter
    If you can not do it right, Why even do it at all?

  7. #7
    Join Date
    Dec 2011
    Location
    New Zealand
    Posts
    2,272
    There is a difference between energy and temperature. This is what you are seeing and this is how the sales promote performance.
    In summer you have more energy, than temperature, in winter you have more temperature than energy.
    Here is practical example (not quite technically correct) but will help you understand better.
    Get a flat Tyre, and an old fashioned hand pump. (hold one hand at the outlet of the pump)
    Start blowing up the Tyre
    You should see the tyre going up fast. the end of the pump is only warm.
    As the pressure builds, the rate the tyre enflates, slows, but the pump becomes much hotter. This is called compression ratio.
    Imagine the tyre had a big hole in it, you would be pumping like crazy lots of energy, but the pump end would not get hot.(just warm)
    If this end was you desuperheater, you could get hotter water without hole in the tyre, but you could heat more water to a lower temperature with the hole in the tyre. (but the water would never get hot)
    So in summer you have a lower compression ratio (lower temp)
    In winter you have a higher compression ratio (higher temp)
    I hope that makes sense!

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