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Two stage ODR curve

Leon82
Leon82 Member Posts: 684
Hello
So I have my whn055 with fin tube base board running and have had only 25-50 degree weather to play with the ODR curve and have gotten it to run continuously up to about 40-45 degrees without the thermostat ending the call for heat.

The curve becomes too cold above 45 and the boiler reaches the setpoint. sadly the sh1 reset curve is linear so I had the bright idea to run from the relay end switch to both the sh1 and sh2 contacts. I then programed the sh2 curve almost flat from about 100-105. My goal was for the sh2 setpoint to gain priority because it was a higher temp than the sh1 curve. as it gets colder the sh1 would take over as its steeper curve was a higher temp.

Last night I set it to 40-68 odr temp and 105-100 degree water. it had priority. this morning it was snowing but the odr sensor was reporting 37 degrees and sh2 still had priority. so after work I raised the sh2 to 45-68 and 100-95 degree water. after the control rebooted sh1 regained priority. now I just need to play with it until the intersection is where I want it.

I attached a picture incase I rambled in my post.

The house remains comfortable even with 105 degree water running thru the baseboards.

Am I putting too much thought into this?

Comments

  • njtommy
    njtommy Member Posts: 1,105
    @Gordy
    I'm sure he would be more then able to help you.
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
    Interesting… why not simply raise the supply temp for your "high" outdoor temp and keep the low outdoor temp setting the same. As in, set it: 6* ODT = 135 supply and 67* ODT = 100 supply (if I read your number right). Should be almost the same curve, maybe slightly higher at certain ODTs.

    Raising the supply temp won't increase run times, as emitters will output more BTUs at higher temps. In addition the boiler already has a differential setting, where it can go +/- 10* from set-point (default).

    When the boiler is meeting set-point and shutting down (set-point + differential), usually that means the heat-loss of the building is less than the MIN modulation/fire rate of the boiler (~11k in the case of the WHN055).

    To set ODR:

    Turn thermostat full up (80*) and let it run and stabilize at a indoor temp. Then take note of the ODT and IDT. Make small adjustments to the curve (based on the most recent ODT). Lower the curve to lower the IDT. This take a while, might take a whole season (to test at all ODTs).

    After your satisfied with consistent IDTs, adjust both ends of the curve up a few degrees. Done. Now the thermostat will simply act as a high-limit switch (set it back down to desired IDT).
  • Leon82
    Leon82 Member Posts: 684
    edited February 2016
    I suppose my goal was for at the 50 to 68 degree outdoor temp it would function as a conventional system and heat to 100 and turn off instead of try to heat water to 90 or 80 degrees.

    For example right now the boiler has been running since 4 pm when I adjusted it and has been steady at 69 degrees in side so I was hesitant to mess with the low temp curve. It has been about 35 degrees out now. Current curve has been good from 45 to 25 degrees sofar. I haven't had any colder days yet. I was afraid it may shift the curve a little too much
  • Gordy
    Gordy Member Posts: 9,514
    What you are doing is counter productive to efficiency of the boiler.
    While higher efficiency is gained in condensing. More efficiency is gained the lower the RWT goes down.

    I'm not sure of the goal you are trying to achieve here?

    When you say the boiler is to cold at milder outdoor temps what is meant? The rooms to cold?

    The most efficient boiler is one that is off.

    A properly set ODR curve which may take an entire heating season if outdoor temps do not cooperate. should not make what you are doing necessary.

    Remember the low end modulation on the 55. Trying to force longer boiler run times when the heatloss does not need it is not helping efficiency. There will be a point that the 11k will be to much output and the boiler hits high limit.

    Some ramblings after 1/2 cup of joe.

    Did you do your heat loss? What is it?

    What percent modulation are you at with milder temps?

  • Leon82
    Leon82 Member Posts: 684
    edited February 2016
    I meant it is calling for about 90 degree water.

    Right now its 23 degrees outside and the boiler is at 40 percent with a water temp at 120 degrees.

    I was at about 35k loss with an uninsulated basement using my gas bill. The slant fin app reported 45k but I'm told it is usually 20% high.

    The thermostat called for heat for about 30 seconds one day wile I was downstairs so I have been trying to get it to modulate continusly.

    I could just set it to 100 and let the boiler turn off I just wasn't trusting the Thermostat to not act crazy. I have since stuffed the hole behind them with insulation to stop possible drafts.

    From what I've read letting it run continuous was good. If its better to let it i can change it. shut off during mild weather

    At about 45 degrees it hits 20%
  • Leon82
    Leon82 Member Posts: 684
    The internet got me paranoid with short cycling
  • Gordy
    Gordy Member Posts: 9,514

    Understand that is a goal that requires the boiler to match the heatloss precisely at both ends of the heatloss. Not always possible. The limiting factor is the low end modulation. Sooner or later as outdoor temps climb your heatloss is below the 11k of the boiler.

    Cycling becomes an issue then. Things that compound this are zones. Is your system one zone, or multiple?

    Tightness of the structure. Even at lo load temps of you rapidly lose btus the boiler will try to replace them.

    Poor thermostat location effected by drafts, solar,and any other cool, ar warm loads in its vicinity.

    Tight thermostat swing adjustment.
  • Gordy
    Gordy Member Posts: 9,514
    Once you get the curve set then you can play with ramp settings. To prolong certain stages of modulation to prevent short cycling.
    SWEI
  • Leon82
    Leon82 Member Posts: 684
    It is 2 zones, the bedroom zone is too small to use all the 11k at low water temps. But the current curve has allowed the large zone to run continuous and the bedroom zone turns itself on and off.

    They are the Honeywell programmable but I have set them on hold.
  • Gordy
    Gordy Member Posts: 9,514
    Well short cycling is going to be a monkey on your back with a zoned low load system.
  • Leon82
    Leon82 Member Posts: 684
    edited February 2016
    I set the anticyling to the max of 10 min.

    That was my thought behind the 2 curves. Mild weather heat with 100 degree water and cycle the boiler.

    When it gets cold the steeper curve will allow the boiler to run continuous and modulate.

    If it is not efficient this way I have no problem changing my approach.

    My design temp is 7 degrees
  • Leon82
    Leon82 Member Posts: 684
    I originally tied both zones together so they would both run at the same time.

    This caused the bedroom to get too hot. So I removed the jumper in the switching relay.
  • Leon82
    Leon82 Member Posts: 684
    I knew that would be an issue going in. I was planning to equalize them in the off season.

    I was originally going to combine them on one but would have been a major job for the winter
  • Gordy
    Gordy Member Posts: 9,514
    Can you combine zones, and throttle flow to the zone that is to warm?
  • Leon82
    Leon82 Member Posts: 684
    I can. they are viridian pumps so I can speed the water up to reduce the delta T and re attach the jumper in the switching relay.

    As of now it hasn't been a problem because the large zone always runs equal to the heat loss.

    But if it were opposite I know I would have issues
  • Gordy
    Gordy Member Posts: 9,514
    Increase delta to the zone that is overheating. In other words slow the flow.
  • Leon82
    Leon82 Member Posts: 684
    edited February 2016
    ok, thanks

    With fintube Is it better to run constantly modulating( if outside temp allows) or for the boiler to run say once an hour?
  • Gordy
    Gordy Member Posts: 9,514
    What ever keeps the room comfortable. Don't sacrifice your comfort level to accommodate the boilers behavior.

    You can try holding modulation steps for extended periods also. See if you can find the sweet spot.
  • Leon82
    Leon82 Member Posts: 684
    OK thanks
  • Gordy
    Gordy Member Posts: 9,514
    The right way to go about it is get the reset curve setup. When that is not getting it start changing ramp settings. Doing a little of this and that with out a baseline makes things difficult.
  • Leon82
    Leon82 Member Posts: 684
    We have had from 25 to 45 weather so I cant do much until we get some cold nights, if they ever come. the current curve has been good, but mat need tweaking at 0 degrees.

    I happened to notice the 50 degree weather issue and realized it will be impossible to modulate and the boiler has to cycle.
    Gordy
  • Leon82
    Leon82 Member Posts: 684
    We had a cold spell with -10 degree temps and the house stayed between 66 and 68. I increased the min water temp to 110 and it was a lot more stable and would modulate even at 50 degrees outside. I replaced the thermostat with a Robert shaw 5110 with a temp differential of 2 and now there are no more nuisance calls for heat. So now I am pretty happy with its performance.

    I have one question with its modulation strategy. I noticed when it had 140 as the set temp it would run up to about 150 and ramp down to 130 then ramp back up. I just wanted to make sure that's normal. I am using the system sensor.
    njtommy
  • bmwpowere36m3
    bmwpowere36m3 Member Posts: 512
    Yes, setpoint +/- differential
  • njtommy
    njtommy Member Posts: 1,105
    What did you find for a max supply water temp on the -10 degree day?
  • Leon82
    Leon82 Member Posts: 684
    The highest setpoint in () I saw was 145 and it would run up to 156 and ramp down. The odr is set to 140 at 7 deg. I have about 95 ft of fin tube.
  • njtommy
    njtommy Member Posts: 1,105
    Thats good hopefully that kept your return temps low enough for the boiler to keep condensing.
  • Leon82
    Leon82 Member Posts: 684
    Probably not at -10 but at 20 yes