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Old 05-21-2013, 07:46 PM   #1
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Solar Hot Water Tempering


My engineers are having difficulty in finding a solution to a problem arising from a solar hot water system. For reasons beyond our control the solar hot water tank which is being plumbed as a pre-heat is going to be set to a max. temp of 180deg.F per IRC. The domestic water heater cannot receive higher than 140deg.F water per IRC. The dilemma is a tempering system that can work with an hot inlet of a varying temperature of 55deg.F through 180deg.F. while ensuring 100% that the water leaving the valve will be 140deg.F. max. Do any of you here have solar experience? The consensus amongst the engineering team is that in solar applications, if the 180deg.F max storage is chosen then it should be in an indirect domestic water heating application only. Trying to introduce the potential 180deg.F water directly to the DHW supply is practically impossible due to the 40deg.F variable (140-180) that needs tempering and all valves currently available (to our knowledge) do not operate with such a broad range...Is the consensus correct? Does this valve (single unit or assembly) exist? Help...

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Old 05-21-2013, 10:10 PM   #2
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Solar Hot Water Tempering


A diagram of the system would help for starters.

AFAIK, there is no such assembly that will regulate it the way you're describing. It sounds like you need some kind of a buffer tank, but it's hard to say without seeing how it's set up.

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Old 05-21-2013, 10:14 PM   #3
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Mixing valve with an aqua stat if i understand you correctly, expensive to operate,
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Old 05-22-2013, 08:20 AM   #4
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Solar Hot Water Tempering


The tank on the right is the domestic electric heater. The tank on the right is the solar storage tank. The electric heater can be brought to 140degF (shown at 110degF) but would require another tempering valve after the tank. The real issue we have is the mixing valve shown. The 180deg.F tank is installed and plumbed and set for 180deg.F The glycol is in a closed loop system as shown. The 180deg.F tank is filled with domestic water at whatever temperature the solar provides up to a max of 180deg.F. We are leaning towards the solar tank needing to be setup as an indirect to have a max. of 140F to allow for direct injection into the domestic tank, but this is met with great resistance from the solar provider. An expensive solution would be a good solution as we can justify, monetarily, why the solar tank should be at 140F. Trouble is, we don't know how to best temper a tank that has a wide varying temperature since it is only recovered by the sun. We have not found any tempering valves that have greater than a 2degF+/- functional range.

p.s. The tank volumes may seem lop sided because I removed some of the other equipment which is part of it all as they would only serve to make the drawing smaller (harder to read) and add more information than is really necessary for my question.
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Last edited by AGWhitehouse; 06-19-2013 at 02:59 PM.
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Old 05-22-2013, 06:50 PM   #5
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Solar Hot Water Tempering


http://media.wattswater.com/1915905.pdf

Says it can do up tp 200 F on hot inlet.

I would suggest sitting your outlet to 120-130

If what gets to the residence is a huge concern add another one above the domestic HWT.
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Old 05-22-2013, 10:35 PM   #6
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Who designed this system, cant see the specifics on the drawings but the solar storage tank is drawn and piped as an exchanger ?

i haven't fooled with solar since the 80s installed hundreds of systems here in south Florida, cant understand why the variances in temp according to your code? what you may need is a heat dump package for the excess temp.
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Old 08-22-2013, 08:20 PM   #7
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Solar Hot Water Tempering


There are tempering valves that will operate in the range you are looking for. Not cheap, but they are available. The reason the domestic water heater has that temp limit is because the dip tube for the cold water supply is plastic. I've seen them melted off if high temp water runs in them for too long. One solution might be to pull out the dip-tube, and make one out of stainless steel...it should not be that tough...they are a simple shape and standard diameter. Then, you could allow any temp water the solar would produce (and it will have a hard time making 180F water, unless the collector array is oversized) and run it right into the domestic water heater. Put in a tempering valve to limit the final water temp.
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Old 08-22-2013, 09:02 PM   #8
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Threads a little on the old side
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Old 08-22-2013, 09:09 PM   #9
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Yeah...but it's for the benefit of someone else who might have the same type of question. Plus, I need to make a number of posts before I get off "probation".

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