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Author:
airdoug (SC)
We have an 80 gallon 6 element electric water heater in our building which has a recirc line and pump from furtherst point on hw line back to heater. The problem is with a mixing valve (watts 1 ") that is supposed to keep max temp from heater at 120 degrees.
Problem is that when recirc pump is running (controlled by L6006 at inlet to pump) and no water is being drawn out of system, "cold" water inlet to mixing valve ends up pulling the returned water from the recirc pump and can't temper the hot water inlet (140 degree water) to get a mixed temp of 120. No problems when using water, but when building is idle and recirc pump runs, water in lines gets hotter than 120.
How do I get cold water into system without drawing any hot water out of the system?
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Author:
hj
Connect the recirulation line to the cold water pipe ahead of the mixing valve. When it needs "cold" water it will open and the recirculated water, which by definition is colder than the hot water, will flow through it to reduce the temperature..
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Author:
Paul48 (CT)
To answer your question....you don't, but the way hj says, you'll only recirculate 120 degree water.I tried to post a link so it would be easier to visualize, but for whatever reason it won't let me. You have to think differently,you're not adding cold to maintain the set point, you're just not adding hot.
Edited 5 times.
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Author:
hj
He will circulate whatever the mixing valve is set for. The return water will seldom be at the valve setting so it will usually add a modicum of hot water to stabilize the temperature.
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Author:
airdoug (SC)
The problem is that I keep the hot water heater tank at 140 (any lower creates possibility of legionella, etc). When the recirc runs and water is drawn out of the tank through the hot water outlet, the water replacing it is the building water in the lines which will eventually get the hot water from the tank once it has completed its way back through the pump. The return line is piped into the cold water supply as close to the cold water inlet as possible. When the system is consuming water, cold "city" water will come into the cold inlet of the mixing valve and the valve does temper to 120. When there is no draw, there is no "cold city water" entering the cold water inlet - only the water returning from the recirc pump outlet and after a while this is at 120 degrees which is mixing with the hotter water from the tank. This causes the "mixed" temperature to be above 120.
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Author:
hj
The pump WILL create a "phantom" flow through the cold water inlet when the temperature is above the set point. Under extreme conditions, assuming the return water waa actually 120 degrees, the valve will close the hot water side and use ALL "cold water" which will be the temperature you desire. Any other condition, and the hot will be modulated to mix with the tempered water to give the desired output. BUT the pump has to return the water into the cold line ahead of the mixing valve.
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Author:
Paul48 (CT)
Search Caleffi Mixing Valves. They show what hj is talking about in their instructions. The return should come back to the cold of the mixing valve then the tank.
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Author:
mrmac (TX)
Put a check valve in the cold water line upstream of where the return line ties in.
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Author:
mrmac (TX)
Also, depending on the range of the mixing valve, you may need to tie the return line into the hot water supply of the valve. The manufacturer should be able to tell you how to pipe it.
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Author:
hj
That would just recirculate the hot water through the piping until it got cold. It would NOT draw any "hot" water out of the tank to maintain the temperature.
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