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Author Topic: DHW loop switching  (Read 2570 times)

Chicken farmer

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DHW loop switching
« on: August 16, 2015, 02:33:56 PM »

I'm planning on using a Taco zone controller from Menards with priority function. My DHW loop is simply a boiler side loop through a 40 plate HX and the potable side heats the feed ("cold") side to the water heater. My question is: What are you guys using to sense load when the DHW is turned on? Some kind of thermo couple on the discharge side of the potable side of HX? Maybe a flow switch? Just curious....

Farmer......
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30 yrs burning wood - new to the boiler scene
Midwestern Ohio

slimjim

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Re: DHW loop switching
« Reply #1 on: August 16, 2015, 02:38:43 PM »

Try to draw out what you want to do to help those of us that are challenged with descriptions to understand
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Wood boiler sales, service and installation for the Northeastern USA.

Chicken farmer

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Re: DHW loop switching
« Reply #2 on: August 16, 2015, 07:06:00 PM »

Let me try one more description. When some one in the house turns on the hot water, cold potable water starts travelling through the plate HX to feed the water heater. My question is this: what is available at reasonable cost to monitor the potable water flow so the boiler side circ pump can be turned on at that time (or zone valve, I haven't decided yet). I have a back ground in industrial controls, so I'm familiar with many different types of flow monitoring sensors. But everything is industrial and very expensive.
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30 yrs burning wood - new to the boiler scene
Midwestern Ohio

slimjim

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Re: DHW loop switching
« Reply #3 on: August 17, 2015, 02:53:57 AM »

Ok, I think I have it now. Are you using another flat plate to heat the oil boiler and if so are you running that loop circ constantly? If so this is what we typically do to heat the domestic, it can also be done off the wood boiler loop but provisions should be made to clean the plate exchanger periodically.
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Wood boiler sales, service and installation for the Northeastern USA.

Chicken farmer

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Re: DHW loop switching
« Reply #4 on: August 17, 2015, 02:04:16 PM »

Well, leave it to Slim to go above and beyond. My system is very simple. Currently I only have one loop. From the boiler to a water to air HX and back, with only one circ pump. I don't have any back up water heat. I might add a tankless heater to the system eventually, but not for awhile. I had it in my head to do something similar to what you drawn up. I was just toying with some different ideas on how to monitor flow. Maybe I should get a touch screen and design my own control............hmmmmmm
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30 yrs burning wood - new to the boiler scene
Midwestern Ohio

RSI

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Re: DHW loop switching
« Reply #5 on: August 17, 2015, 04:26:34 PM »

Is it possible to just let the pump run 24/7? If not, I would try to go with controlling it off the temperature instead of actual flow. If you go off flow and it sits long enough for the water to cool in the underground pipe then it will take a while to get hot water.

What size pump do you have? If you can't have the water flowing all the time, would it work to use a Groundfos Alpha Pump and a zone valve to stop the flow? A very small bypass (or if the zone valve type allows, drill a hole in it) would let enough water through to keep hot water up to the plate. An Alpha pump would automatically adjust to a low flow rate when the valve closed.
I would put the temp sensor on the domestic water inlet pipe. That should get the fastest response to water being turned on and should get hot fairly quick after the domestic water stops flowing.
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Chicken farmer

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Re: DHW loop switching
« Reply #6 on: August 17, 2015, 07:11:05 PM »

RSI - My main loop pump between the boiler and house would, and does, run all the time. I was just thinking about putting the DHW HX in it's own zone. Just because, no real need. I will probably just put in series in the the main loop and call it a day..
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30 yrs burning wood - new to the boiler scene
Midwestern Ohio

RSI

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Re: DHW loop switching
« Reply #7 on: August 17, 2015, 10:19:39 PM »

Oh, ok that makes more sense now.

If you do it, I think a temperature sensor is the best way to control it.

A 40 plate shouldn't add much restriction in the main loop though and would keep the system much simpler.
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