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New Lochinvar install. Primary Loop Delta T question

andymercuryandymercury Posts: 13Member
Just wanted to thank everyone here for all the great information posted on this site. I've been loitering around the site while installing a new boiler and the info I've found here has been invaluable.

I just finished an oil to gas conversion in my 2300 sq foot single level ranch. I installed a lochinvar KHN110....over sized....I know! Started with the recommendation of a friend who is a "Professional" and wanted me to install a KHN155. I knew it was more than I needed and went for the 110. After spending some time here I realized that I should have spent some more time researching! It does not seem to short cycle at all (still mild here in Rhode Island), just cruises around 15-30% depending on how many zones are calling, so i guess i will get by with it. I will post some pictures of the install for some constructive criticism!

I am in the process of fine tuning and dialing my outdoor reset back as far as possible.

The system is plumbed primary/secondary, zoned with circulators, 3 zones, baseboard radiators. I installed a Nimbus speed control for the boiler pump so that I could utilize the boilers ability to control the boiler pump speed using the 0-10v signal. The factory default setting for the boiler delta T is 20 degrees, and it maintains that 20 degrees perfectly. I was wondering if anyone had any recommendations for what delta T I should set. The only info I can find is from a lochinvar newsletter that basically says too much flow can cause erosion of the heat exchanger. Too low of flow can cause scaling of the heat exchanger.....though i'm not sure if this even pertains to the KHN Fire Tube boiler. I am also wondering if keeping the delta T lower might increase efficiency as the whole heat exchanger has a better chance of being in the condensing range.

Any input would be appreciated! Pics to follow (if i can figure out how)

Comments

  • andymercuryandymercury Posts: 13Member
    Here are some pics of the install. Any constructive criticism would be appreciated!
  • GordyGordy Posts: 8,209Member
    I would leave it until you get your outdoor reset dialed in. Seems to me it’s working great. What are your return temps? Was it determined you had more than enough baseboard to run lower supply temps?
  • andymercuryandymercury Posts: 13Member
    > @Gordy said:
    > I would leave it until you get your outdoor reset dialed in. Seems to me it’s working great. What are your return temps? Was it determined you had more than enough baseboard to run lower supply temps?

    I have not calculated output of all the baseboard. I have set a Max setpoint of 125 and had no problem satisfying the thermostats on a few 35 degree nights, which leads me to believe I can push it further. 1/3 of the house is regular baseboard and the rest is done with some kind of in-wall copper fin/tube radiators. Attached is a pic of my current temps (inlet should be a good indicator of system return temp). The firing rate is still settling down from a zone turning on
  • GordyGordy Posts: 8,209Member
    System side flow should be greater than boiler loop flow to achieve the lowest “possible” boiler return temps. However it’s limiting factor is the thermodynamics of the system side.

    When boiler flow is greater than system side flow you are sending back hotter return water to the boiler.

    So until you can get the reset curve to provide the lowest possible supply temps to the radiation yet provide the best comfort. You won’t be there yet. To early in the season yet.
  • GordyGordy Posts: 8,209Member
    Those are good condensing numbers. If you can go lower the better.
  • andymercuryandymercury Posts: 13Member
    > @Gordy said:
    > Those are good condensing numbers. If you can go lower the better.

    Great, thank you for the quick responses. I will continue to push the reset curve south and see how far I can go.

    Side note, just had my first Lochinvar repair. Found a small leaf in the venturi.....sounded like a helicopter taking off in my basement from the incorrect air/fuel mix. That was interesting.
  • NY_RobNY_Rob Posts: 1,156Member
    ^ the installer should have put 3" screens in the intake and exhaust terminations. If he didn't, you'll get more of the same over time.

  • NY_RobNY_Rob Posts: 1,156Member
    Here's my reset curve (1800 SQ ft house, Long Island) which has worked for two winters. I only had to adjust it last Jan when we had that week of single digit and zero deg days.




    Of course your's will be different, but it will give you an idea of what's possible. The goal with a mod-con is to keep the return temps below 130F as often as possible to enable condensing and high efficiency.


  • andymercuryandymercury Posts: 13Member
    > @NY_Rob said:
    > ^ the installer should have put 3" screens in the intake and exhaust terminations. If he didn't, you'll get more of the same over time.

    Thank you for the reset curve, that looks like a great starting point!

    I am the installer. I installed a vent termination kit and it has horizontal guards to keep debris out of the intake. I must have gotten a little carried away blowing leaves this weekend. Maybe I will fashion a better screen for it.....
  • andymercuryandymercury Posts: 13Member
    > @NY_Rob

    Any thoughts on primary Delta T as I have the ability to control it?
  • NY_RobNY_Rob Posts: 1,156Member
    edited November 6
    ^ only thing I can offer is to advise you to look at the condensing chart above and shoot for return water temps on the primary side that will keep you in condensing range. Once your RWT is over 130F you're not condensing.

    Nice workmanship on the install BTW!!
  • GordyGordy Posts: 8,209Member
    The emitters are in control of the boilers RWT. This is where to much radiation if there is such a thing becomes beneficial.

    You’ll probably seldom see the mid 90’s efficiency with baseboard maybe only for short periods in shoulder seasons

    unless you have a well designed radiant system that gets rwt down in the numbers from the chart Ny Rob posted.
  • andymercuryandymercury Posts: 13Member
    Thanks guys. Bear with me... I may be explaining myself incorrectly. I'm a marine technician, this is my first mod/con install.

    Ok so I understand that there is no changing RWT because the radiation in the house determines the Delta T of the system and therefore the RWT to the boiler (so long as the primary loop is flowing less than the secondary).

    While installing the boiler I found that it had the capability of controlling the speed of the primary circ. using a 0-10v signal produced by the boiler. Because I cant seem to leave well enough alone, I decided to try and find a way to control the supplied grundfos 15-58 circ. with that signal. I stumbled across a thread here mentioning this speed control being used with a 007 circulator

    http://controlresources.com/ac-fan-control-ac-motor-control-smartfan-nimbus/

    I ordered one up and installed it.

    Before installing the control, the boiler would maintain SWT just by modulating the firing rate of the boiler, and obviously the circ speed remained constant (I ran the 15-58 on medium speed). Standard operating procedure i suppose.

    Now that the control is installed, the boiler adjusts both the firing rate AND the speed of the circulator. It is able to maintain both the desired Delta T across the heat exchanger AND the system temperature almost perfectly (look at my picture of the temps above. I have a target Delta T set at 20* ).

    The RWT is a given, it cannot be changed with the speed of the boiler circ. So it is decreasing the speed of the circ. and increasing the outlet temp in order to meet the requested SWT. It works GREAT!......but is it necessary??

    Question is.....Why is Lochinvar giving me the option to control the circulator and ultimately the heat exchanger Delta T? There must be some benefit. I can change the "target delta T" setting and it will follow suit. How do I determine the correct target setting? There must be something I'm missing

    Any thoughts?
  • GordyGordy Posts: 8,209Member
    edited November 7
    Firing rate, and boiler delta t is better managed when the flow rate is coupled with the firing rate. It keeps modulation from hunting when the circ speed is fixed.
  • GordyGordy Posts: 8,209Member
    To maintain a fixed delta across the HX something has to give when three variables are in play. Boilers firing rate, return water temp, and flow rate.

    Since return water temp will be at the mercy of the emitter tightly controlled by ODR, and is not a constant through out the heating call other than the supply temp. Then the other variables back in the boiler loop are the firing rate, return water temp from the heating loop, and flow rate of the boiler loop.

  • GordyGordy Posts: 8,209Member
    Are you sure it is the KHN?
  • andymercuryandymercury Posts: 13Member
    > @Gordy said:
    > Are you sure it is the KHN?
  • GordyGordy Posts: 8,209Member
    edited November 7
    Hmm can’t seem to find a manual for KHN online on lochinvars website even. It is discontinued . However I think in your manual max delta is 35 degrees in the boiler loop? So I wouldn’t go more than that if you want to play with it. That is a watertube boiler.

    In order to get a wider delta you decrease pump speed. If the modulation can’t go low enough you will probably cycle off hi limit due to low flow rate. Right now with a 20 delta you are 15-30% modulation so you might have a little room to go lower. Key is to have nice long cycles to reach setpoint with out hitting high limit.

    But like I said earlier until you dial in the reset curve, and get some real heating weather your fiddling for nothing. It could take an entire season to dial in the reset curve.

    Ultimately with a proper curve the thermostat becomes nothing more than a high limit device for internal, and external gains the reset is completely in the drivers seat.
  • andymercuryandymercury Posts: 13Member
    Gordy said:

    Hmm can’t seem to find a manual for KHN online on lochinvars website even. It is discontinued . However I think in your manual max delta is 35 degrees in the boiler loop? So I wouldn’t go more than that if you want to play with it. That is a watertube boiler.

    The KHN was just discontinued on Sept 21st. It is a fire tube boiler

    https://s3.amazonaws.com/s3.supplyhouse.com/product_files/Lochinvar-KHN110-Brochure.pdf


  • andymercuryandymercury Posts: 13Member
    Gordy said:


    In order to get a wider delta you decrease pump speed. If the modulation can’t go low enough you will probably cycle off hi limit due to low flow rate. Right now with a 20 delta you are 15-30% modulation so you might have a little room to go lower. Key is to have nice long cycles to reach setpoint with out hitting high limit.

    But like I said earlier until you dial in the reset curve, and get some real heating weather your fiddling for nothing. It could take an entire season to dial in the reset curve.

    Ultimately with a proper curve the thermostat becomes nothing more than a high limit device for internal, and external gains the reset is completely in the drivers seat.

    So it seems as though you would favor a wider Delta so long as I don't hit high limit.

    Clearly it seems I need to spend some more time with my ODR during some colder weather and try to get as close to a constant running condition as possible.

    Is there any chance that maybe I am assbackward, and a higher flow rate with a super low Delta (like I had before playing with circ.) would be favorable as it would keep the entire heat exchanger closer to condensing range?
  • GordyGordy Posts: 8,209Member
    edited November 7
    Okay found it, this page should be in your I/O manual. Pay close attention to the MINIMUM flow rate at low and high fire.
  • GordyGordy Posts: 8,209Member
  • andymercuryandymercury Posts: 13Member
    Got it, Thank you for all your time and help Gordy.

    Looks like I am over complicating a pretty simple system!

    I will have to figure out how to determine the minimum flow rate of my primary loop....with an aftermarket speed controller, and with a pump that has no data relating to the voltage applied vs gpm output.

    Maybe I should just pull it off and set the darn 15-58 to setting 2 lol
  • GordyGordy Posts: 8,209Member
    All you really need to pay attention to is the delta. If you get higher than 35 at low fire your probably not getting the minimum flow rate, and it may lock out.

    If you can hold 35 at high, and low fire it's as good as it gets in my opinion, but that all depends what the emitters will let you have :)

    Sounds like you have a good thing going the way you have it. Time will tell as the heating season progresses
  • GordyGordy Posts: 8,209Member
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