I need advice on controls for my hot water/heating system.
I have a Rinnai “on demand” water heater doing both domestic hot water and radiant floor heat. I have isolated the DHW (domestic hot water) with a heat exchanger so that the radiant floor water does not come in contact with the DHW.
I have two radiant zones each with four loops. Each zone has a Taco 007 circulator pump which comes on when the thermostat calls for heat.
In order for the Rinnai heater to function properly, a primary loop is necessary. I have a Taco 0011 pump circulating water thru this loop. Each zone then pulls hot water from this loop. If I buy a Taco SR 503EXP relay, ($225) the primary loop pump will come on when either of the 007 cirulators start. Ok so far.
Now if I turn on any hot water tap, I will not get hot water unless the primary loop pump is operating to provide hot water to the heat exchanger. One solution is to leave this pump on constantly, but this is what I am trying to avoid.
I have installed a McDonnell Miller flow control switch ($205) on the cold water supply line to the heat exchanger. If water flows thru this flow control contacts will close and start a pump or whatever. If I connect this output from the flow control to the primary pump, the pump will start. However, what happens electrically if both the flow control and the SR 503 supply 120v to the Taco 0011 at the same time? Don’t I need a relay or something so that everything is compatible?
In general, my system works well. Right now I operate it manually. If I need heat or hot water, I turn on power to all three pumps. The two zone pumps will only come on when their respective thermostats call for heat. But as long as the primary pump is on, I get hot water from the tap because the primary loop runs thru the heat exchanger.
Any suggestions?
Bob
Replies
I'm curious, why did you run the domestic through the HE instead of the radiant?
Some taco relays have domestic priority features. you may be able to rig this up so domestic gets the heat when needed and the zone pumps are re-enabled when the domestic demand is done. (sorry for lack of specifics, this is my partner's end of things).
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The heat exchanger has limited heat transfer capabilities. The major heating load would be radiant heat, therefore, direct connection to the Rinnai. For example, with the heat exchanger I have ($250), I cannot do two showers at the same time, but since just my wife and I live here, it is not a problem.
For $500 or more I could get a bigger HE, but am on a budget. I guess putting the radiant thru the HE would work, it is just every diagram I have seen shows DHW thru the HE.
Your other comment is worth considering - I will see what I can come up with by shutting down the radiant while the DHW is being used.
Thanks,
Bob