Open Loop EWT and LWT delta is very small

Discussion in 'General Discussions' started by llaforest, Nov 11, 2013.

  1. llaforest

    llaforest Member

    It's funny, I couldn't see you post, I could only see that you quoted me but nothing else... Now I can see it. It's weird.

    Anyways your experience is very interesting for me! I my case, we installed a ½W resistor and placed it on lt1 sensor. It raises by 2-3F and it is enough to avoid LT1 lockout. I also plan to install a flow switch on water line. The compressor signal will go through it and when there is no flow, the compressor won't get energized. I don't know why they didn't try to monitor the flow, they have sensor to do it!

    That's about it, I would have liked to speak with a ClimateMaster engineer but I don't think they are interested...

    Thanks for your input hardchines, it help and it's reassuring!

    Cheers!
    Laurence.
     
  2. geoxne

    geoxne Active Member Forum Leader

    I am not sure what is going on here. It is my understanding that adding a resistor in series with a NTC thermistor will report a lower temperature than actual to the control board.

    Correct me if I am wrong.
     
  3. llaforest

    llaforest Member

    No it is much simpler than that: A 1W resistor produce 1W of heat. So when it is placed near the sensor, it falsifies the reading because the resistor is hot. In my case it gave me 2-3 degrees with the resistor I choose. The first one I tried was giving 15 degrees, so I hade to pick one with an higher resistance to reduce power dissipation.

    But I think I prefer the Hardchines solution. Given I know my temperatures, given that with a flow sensor the compressor won't start or will stop on no flow condition, there is no risk of freezing the coil. Not with that amount of moving water. So I will do the same he did and that's gonna be the end of it.
     
  4. hardchines

    hardchines Member Forum Leader

     
  5. hardchines

    hardchines Member Forum Leader

    Anything else to say hardhines? Now I understand this question, best of luck, I use flow gauges but do not have a interlock setup, but its would be good to have them interlocked, I have a visual very accurate flow gauge and control valve so I can adjust and watch the flow change as well as the EWT?LWT at the same time. I installed my water shut off solenoids on the output of the units to keep pressure on heat exchange , flow meters and all piping, helps to keep it all clean.
     
  6. llaforest

    llaforest Member

    So why is there a post only with my quote?

    I have also bought a shutoff solenoid because the modulating valve will stay open in case of power failure and this will empty my pressure tank. We use this water for domestic use and don't want to run out as soon as there is a power failure. My solenoid valve is normally closed without 24 volts. But can you explain why you put it after to keep pressure in the coil, I do not understand this logic but it seems interesting?

    I was thinking to put it before to avoid pressure hammer inside the coil when the solenoid cuts the flow... That was my logic. It would be connected on acc relay with the fan output to open before the modulating valve opens and close after modulating valve closes.
     
  7. hardchines

    hardchines Member Forum Leader

    OK lets see if what I did makes sense to you or anyone else, I have a set of sill cocks (hose bibs) on each unit one on entering water and one on exiting water, the hose connections are used to back flush the coil to clean it once a year. Water hammer is not all bad when it comes to a heat exchange coil, first, they are spring like and flex (vibrate) when they get hammered( its the condiment method) , its a good way to get settled material in the coil to break loose, most people use slow closing solenoids which reduce or eliminate hammer, I do not, I use ASCO commercial units that are mounted vertically to reduce sediment from landing on the seats inside them. I control the hammer effect by installing anti hammer devices on the hose bibs and leaving the valves open so I get some hammer.The solenoids are mounted on the exiting water to keep oxygen out of my components and help keep the iron in my water and out of my coils, I have cleaned the coils three times but it seams that my coils are staying very clean with out cleaning so I am going to a five year plan. The units have a solenoid control output, I use that low voltage output to energize a relay that sends 120volts to my solenoids. seems to work great, I use my domestic water system with a water pressure regulator this eliminates the fluctuating water pressure caused by the well pump cycling to a steady 25psi, this gives me a steady flow rate!
     
  8. AMI Contracting

    AMI Contracting A nice Van Morrison song Industry Professional Forum Leader

    Having the solenoid down stream of the heat pump is recommended by every manufacturer I know of. It makes sense as hardchines saya to keep hardness and other mineral suspended.
     
  9. llaforest

    llaforest Member

    Hello,

    I just realized that if I interlock the compressor stage 1 signal on the flow sensor, I will be stuck in a deadlock;
    Assume the system is off, the valve is closed, there is no flow. Then the thermostat sends the signal to start compressor and since there is no flow, the signal doesn't get through and the heat pump never start opening the valve because it never received the compressor input... I'm stuck there...

    I think I would need to interlock the compressor's 240V input directly to make sure that the heat pump always receives my request for compressor. I'm just wondering how it would react in the case I shut down the compressor myself, I assume the heat pump would fall in some error condition... There are all this 5 minutes delays between startup, all kind of logic I would prefer not interfere with... I just don't know if there is another signal I can switch... The logic is super simple, if there is no flow, the compressor should never start... But the valve should open nevertheless...

    Does anybody here knows what signal could be switched by my flow sensor other than the Stage1 input signal coming from thermostat?
     
    Last edited: Jan 7, 2014
  10. hardchines

    hardchines Member Forum Leader

    Simple, install a time delay relay , use the normally closed contact to show water flow when system is off (fake signal) this will allow system to start. After start the time delay relay energizes and the real flow circuit signal will use normally open contacts (which are now closed), if flow is lost your system will stop as before, every time the system shuts down, the relay resets, ten second delay should be more then enough.
     
    Last edited: Jan 7, 2014
  11. llaforest

    llaforest Member

    Thanks for the idea hardchines!! I just bought an Omron 2-30s ajustable delay relay that works on 24vac on Ebay! :) (Still don't understand how they can sell that for 6$ free shipping from China though! o_O)

    I think that should do the trick!
     
  12. hardchines

    hardchines Member Forum Leader


    Thank God for third world countries!
     
  13. llaforest

    llaforest Member

    Hello, just to let you all know, I had some advancement in my setup. :)

    I have the time delay relay that I tried to install. When I looked at where to hook up, I could see that on the DXM2 board, the CC and CCG terminal on upper right are the 24V signal that energizes the compressor relay. So I just connected my Flow Switch in intrelock on the CC terminal and voila, if I cut the flow, the compressor shuts off and the HVAC never know. I had it running like that for a while and it works fine.

    This brings me on my next problem! Because there is always something! :)

    When the HVAC has been stopped for a while, the water in the intake pipe that comes from outside is quite cold and the modulating valve behaves very poorly in that situation.
    In normal situation, I have 47F input water and I throw it out at 42F this with valve open to 75% and 5F delta T.
    In startup condition, I have 40F input water and the machine still tries to achieve 5F delta and throw out at 35F. To achieve that, the valve closes to 50%. So when the water is colder, the valve actually uses less water which is clearly a design error.

    Is there another solution except fixing the valve?
    Is there anybody that could configure modulating valve with minimum %? It's in the machine option but doesn't do anything when I choose ité

    In the Modulating Valve configuration menu on diag tool, there was originally there was 4 fields: Heat Delta T, Cool Delta T, Maximum Heat LWT, Minimum Cool LWT.
    A new field appeared recently and it is called Maximum Cool LWT just bellow the Minimum Cool LWT. It's always there now and it is set to 130F which makes sense.
    Sometime I can see like a glitch and Minimum Heat LWT field appears in top of Maximum Heat LWT. It never stays more than a second but enough so I could see it's set to 4F. If I could set this to let say 39F, then the modulating valve would ignore the delta and just keep the water volume when the water is cold...

    Is there anyone that was able to see these phantom menus I'm talking about?

    My last option is to disable all the vFlow but it was an expensive system that should work! Espacially since flow in heating and cooling is dramatically different.

    Thanks!
    Laurence.
     

Share This Page