Indirect Hot Water Tank

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  #1  
Old 04-07-16, 06:10 AM
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Indirect Hot Water Tank

After 14 years, my indirect water heater has finally called it quits. I am having a professional install a new one in a day or so. It is a 50 gallon Bradford Indirect Tank. I always thought the water inside the tank circulated by the pump through the boiler and back was how everything heated up. From the diagram, I see there are coils for the supply and return, whereby the heated water runs back and forth through the supply coil and heats up the surrounding water. I am assuming the coils are made of a material which gets very hot to heat up the surrounding water. Temperature on the boiler stops at around 180 and starts up at 160 (20 degree difference).

We now have a 40 gallon, which is increasing to a 50 gallon tank. In the past, I have had to keep the thermostat at the highest setting to ensure that we do not run out of hot water for showers. Anything lower than this would require waiting 20-30 minutes before there was enough hot water. Then again children take 20 minute showers.

The real question I have is at what temperature range is the water at all the time (minimum and maximum)? Is this an efficient system?

The thermostat wire from the tank goes to a control board. The board is wired in with an aqua-stat on the boiler and a circulator pump.

I am just curious at this point trying to understand my system a little better. Thank you.

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  #2  
Old 04-08-16, 09:38 AM
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A major short coming of this system is using one pump for both heating zones and hot water tank. The hot water tank should have a separate pump controlled by smaller deltaT.

The temperature you keep the water tank at is widely variable. For safety, especially with kids I would install a Hot Water Extender Tempering Valve.

I have a similar system and use a digital PID controller with 1 F delta T with set point of 113F.

If you are interested in a more efficient setup as part of this replacement consider adding a $150 Outdoor Reset unit. Keeping the boiler at 180F year round is not efficient. Yes, the boiler water temp will effect response time but the difference between 140F and 180F should not be that significant.
 
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Old 04-09-16, 07:03 AM
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I do have separate pumps for each zone. One smaller pump for the holding tank. One for the first floor, another for the second floor and lastly one for the radiant heating.

Unfortunately the tank is now leaking a very small amount of water from the thermostat area. Good news is Bradford will pay for 2 hours labor @ $60 to repair the area.

Thank you for your help!
 
  #4  
Old 04-09-16, 07:29 PM
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Not shown on diagrams #3 and #4 is what controls temperate for boiler and circulator for water tank. Usually each would have a separate "aquastat" controller.

You say "Temperature on the boiler stops at around 180 and starts up at 160 (20 degree difference)". That sounds like an aquastat on the boiler.

Am not sure what "thermostat" is in other quote "I have had to keep the thermostat at the highest setting to ensure that we do not run out of hot water for showers."

As I said in my original post a low deltaT temp control setting for water tank makes for faster response. When someone opens a hot water faucet, cold replacement water coming into the tank starts the circulator. A deltaT of 10F or 20F results in longer lag.
 
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Old 04-10-16, 09:31 AM
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Thank you for all your help.
 
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