Texas WaterFurnace Water to Water Unit - tank temp monitoring issues

Discussion in 'Maintenance and Troubleshooting' started by Bill Petrey, Aug 3, 2018.

  1. Bill Petrey

    Bill Petrey New Member

    I have a WaterFurnace Model: NSW025G10HCSS0DA water to water unit and I have in interconnected to three 200 gallon tanks. My problem is that the unit comes with two sensors, the first monitors the input line going into the water-to-water unit, and the second is supposed to go on the tank. That's fine for a single tank system, but I have three tanks and until the sensor monitored tank triggers the unit to start up, the other tanks cool down without triggering the unit to start up. I need to find a way to monitor the temperature in all three tanks so if any tank drops below set point, it triggers the unit to turn on and circulate and heat the water in all three tanks. Is there a workaround for this problem? Can sensors be wired in series? Is there a sensor gateway product that could connect all three, but send only the lowest temp info to the unit? During normal, everyday usage, the tanks cooling don't create a problem, but when we had a house full of relatives over the holidays, the issue came to light.

    Any help would be appreciated. My vendor is also researching it, but I wanted to ask other sources.
     
  2. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Have a pump on a switch that circulates all the tank water so they are a consistent temperature. Turn on when 3 tank demand is required.
     
  3. Bill Petrey

    Bill Petrey New Member

    Chris,
    Thanks for the tip. I forgot to mention that these tanks are glass insulated and in separate areas of the house serving different rooms. Therefore all three tanks are used all the time. They are circulated by 6 pumps once the WTW unit is on , and when circulated, they do hold water of similar temperature I assume, but can't measure to be sure. I just know it gets swished around all three tanks. I also forgot to mention that I think the problem is related to the cold water inputs feeding into each tank rapidly cooling down the unmonitored tanks. Once the WTW system kicks on, the tanks heat up and regulate. The problem is getting the system to turn on if ANY tank cools below set point. I even thought about installing a smaller fourth tank that only had a cold input, no output, and the in/out circulation pipes, and put the sensor on that tank since it should be the coldest tank of the group, then shut off the cold inputs to the other tanks. My only concern is will the pumps block the flow of water running through the circulation pipes if they're off? If so, having a cold input removed from the tank wouldn't work. Sorry if I'm rambling. Thanks again for your help.
     
  4. urthbuoy

    urthbuoy Well-Known Member Industry Professional Forum Leader

    Well you could coordinate the 3 calls with using relays. There are multiple pull 1 throw relays on the market. That's a simple solution. Do you have three separate circulators to go with those 3 separate tanks?

    For a plumbing fix, it would probably be best to draw out your setup.
     
  5. geoxne

    geoxne Active Member Forum Leader

    I assume you are using the communicating Waterfurnace HydroStat controller on your NSW025 with the advanced control board. Correct me if I am wrong. The HydroStat is a unitary controller. It can control one HP, one load pump, one tank temperature. The HydroStat senses the tank temperature, when it falls below setpoint the load pump will turn on periodically for a certain time. After that sample period, if the LEWT (load entering water temperature) is below setpoint minus differential the HP will turn on to satisfy.

    Your installation is most unusual with 3 tanks (piped in parallel? with different loads at different times?), 6 pumps (controlled by what?). All which normally requires the control system to be designed before the system is piped. OK, with that being said, let's try to work with what you have.

    Multiple thermistor sensors can be wired in a series/parallel circuit to provide an average temperature but the number of sensors must be the square of an integer ie. 4,9,16,25.... You would have to figure the best place for the fourth sensor. An example of 4 is shown here-
    http://zenhvac.com/averaging-thermistors/
    However, I do not believe that will help you much. One tank may fall significantly more than the others and that tanks sensor will only carry a 25% weight. Also, if you do not have a way to divert HP load flow only to the tank that needs it, the tanks already heated will mix down in temperature while raising the LEWT. You already paid to get the satisfied tanks to setpoint. Much like a bypass on a WtoA HP, this makes the HP work harder than it has to and lowers COP.

    I believe for this system to work efficiently and as intended, you must design a control system that senses tank temps individually and diverts load flow to the tanks that needs it, while maintaining proper load flow. As Chris has mention this can be done with 24v controls, aquastats, relays and well thought out control logic.
     
  6. Bill Petrey

    Bill Petrey New Member

    Chris:
    No the circulation system for the three tanks is one output line and one input line going into each tank then circulating into the heat pump. It's all one loop spread around the house that goes from tank to tank to tank to HP then back to the tanks. I agree, I need to go up in the attic and map this thing out. Yes, I am using the HydroStat controller. And the tanks are piped in series, entering at bottom of each tank and exiting at top. The middle tank is "T'd off the input and output circulation so it's not completely series, but the two tanks on the ends are. The pumps are turned on when the HP turns on to circulate the water.
     
  7. Bill Petrey

    Bill Petrey New Member

    Sorry, I need to correct myself, it is parallel, not series. I was thinking they should be piped in series.
     

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