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Re: Desuperheaters
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Posted by Robert Gammon on Thursday, 24 April 2008, at 10:22 a.m.,
in response to Re: Desuperheaters, posted by Phil
If you look at the heat exchanger calculations at flatplate dot com, you can see that increasing the flow rate increases the total btu transferred. Granted the temperature of the water out to the DHW will drop, so this is also a LOSING game for keeping the DHW tank at or above 120F.
I am NOT arguing that ANYONE should try to exceed 0.4GPM/ton thru their desuperheaters. Desuperheaters need to be used with buffer tanks, particularly so if the primary heater is gas fired.
All I am suggesting here is that there is MERIT to what the DOE says about desuperheaters. Scaling IS a problem with desuperheaters. We all need to be aware of the issue and be prepared to deal with it in our systems.
This is an issue of lesser importance for you with your w-w hydronic heat pump. The load side is connected open loop and as such is subject to scaling and reduction of thermal transfer efficiency. The heat exchanger area is much larger on the primary load side than it is on a desuperheater, so the plating effect will take longer to develop.
Have you drained your DHW tank on a regular basis to purge the mineral rocks that plate out and settle to the bottom? Have you checked the anodes in the DHW tank to see that they are still working?
I had a modest 9-10 grains of hardness in my water. I drained the tank about every other year, and it still failed in under 9 years due to filling up with rocks (internal pressure on the tank from rocks cracked the liner, rust developed, and heater efficiency dropped). Added a water softener and the next one lasted over 15 years and so far as I know, is still in service.
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