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Short Cycling of heating...

Dan_G
Dan_G Member Posts: 32
in Radiant Heating
I had adjusted my Munchkin 80M's boilers Outdoor Reset Curve to have a max temp of 150*F at 68*F outside temp - if I remember correctly. At night my T-stat is set for 66*F. It's been 17-32*F outside.



At night I've been noticing the t-stat switching on and off several times in a hour.



I'm not sure what to adjust to elongate the heating cycle.



Any advice?

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Comments

  • Zman
    Zman Member Posts: 7,610
    Questions

    Is the boiler cycling several times an hour or is the t-stat calling several times an hour?

    What type of radiators?

    What type of t-stat?

    Carl
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • PLUMMER
    PLUMMER Member Posts: 42
    How many stats or zones?

    What is the load. Is it possible the load is too small for the low fire on the munchkin? Lots of variables with not enough info.



    I've used small buffer tanks with munchkins and knights when micro zones are in the system. To fix this. 15kbtu is the low turn down on the 80.
  • Dan_G
    Dan_G Member Posts: 32
    response

    Carl,



    - T-stat is calling - I hear the internal relay clicking on and off a few times an hour at night.



    - Radiators are SlantFin 30 hot water baseboard.



    - T-stat is a older Honeywell digital programmable, don't have the model number on hand at the moment.



    Plummer,



    - The boiler runs 3 zones. One for the utility room that is off (supply/return valves are closed and t-stat is OFF), the room is always warm to begin with since both the boiler and hot water heater are in there.



    2nd zone is for the second floor, has it's one battery powered Honeywell digital non-programmable T-stat, about 822 sq. ft with 8' ceilings total from two interconnected rooms. All heated with more SlantFin 30 HWBB.



    1st zone with digital programmable Honeywell t-stat (located near in hallway that connects all beds/baths) is for the kitchen (300 sq. ft, 8' 5" ceiling), living room (~252 sq. ft., 8' 5" ceiling) and attached 3 beds, 2 baths and laundry room (~650 sq ft. with 7' ceilings), all heated with SlantFin 30 HWBB.



    The single story section of house contains the bedroom/bath/laundry rooms are all connected together by one hallway that then opens up to the living room that interconnects with the kitchen. The living room and kitchen are under the 2nd floor.



    The single story section of house was originally a 1950's bungalow. I believe the wall insulation is R19. The attic insulation is R19. I did air seal most of the attic, sans the hatch (I know, the biggest hole - just gotta get it done in summer).



    Let me know if you need more info and I'll try and figure it out.



    Thanks for all your help!

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  • Ironman
    Ironman Member Posts: 7,510
    edited February 2014
    Cycle Rate

    You need to go into the installer setup for the stats and set the cycle rate down to one per hour. They come from the factory set for 5 per hour to accommodate forced air systems.



    I would also have your reset curve set for 120* @ 68* outside and 180*@ design temp. If the heat doesn't keep up with those settings, bump up the 120* setting 5* each day until it does. Most likely, You shouldn't have to go above 130*.



    Don't use setback; it's contrary to the logic of a mod/con. You'll have better comfort and economy leaving the stats set at one temp. If you're doing it for sleeping at a cooler temp, then don't setback more than 4* and just dot it for that zone. Or, better yet, just leave that zone set cooler and close the dampers in the BB in your bedrooms if necessary.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Dan_G
    Dan_G Member Posts: 32
    bob...

    Bob,



    Never knew about that setting for the t-stats. I'll see how or if they can be adjusted. They ONLY control the boiler. I have no central air, just seasonally installed window AC units.



    So it seems like you're suggesting starting really low with the heating curve and moving it in positive increments from there. How do I determine if the heat is keeping up?



    I'm trying to grasp what the optimal boiler operation should be in order to maintain the called for temp by my t-stats. And then figure out how best to ascertain whether or not is it working as intended.



    I wish I had a way to monitor the boiler, t-stats, indoor and outdoor temps with logging software so I had hard data to be able to more quickly and accurately tweak things.

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  • Dan_G
    Dan_G Member Posts: 32
    edited February 2014
    nm

    nm

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  • Dan_G
    Dan_G Member Posts: 32
    edited February 2014
    setback?

    Bob,



    I read up on setback vs mod/con outdoor reset boiler functionality. It appears I need to adjust my understanding of how it all works together, but I'm slowly starting to get it. Will need to "teach" my fiance' too about how this works.



    We manually set it at 66*F for most of this winter day & night with occasional bumps to 68*-70*F on really frigid days (when it's below 30*F outside), and also usually run it at 66*F at night.



    My second floor t-stat is set to 66*F 24/7, unless we're working up there and then I usually set it to 68-70 so we don't have to wear sweat jackets to be comfortable.



    My 3rd zone, in my utility room is complete off, t-stat is off, and the plumbing circuit valves for the supply/return are in the off position.



    I will check the settings for my curve and re-post them here. Then will adjust my curve as per your suggestions and see how that goes - and leave the t-stats alone! :)

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  • Dan_G
    Dan_G Member Posts: 32
    edited February 2014
    i remember something!

    I seem to now remember setting my reset curve to:



    150*F at 5*F outdoor temp (i'm pretty sure this is what I set)



    95*F at 68*F outdoor temp (turned this down from 180*F)



    I'll double check when I get home.

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  • Ironman
    Ironman Member Posts: 7,510
    Backwards

    That's backwards.

    180*@ 5* outside; 120*@ 68* outside.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Dan_G
    Dan_G Member Posts: 32
    got it..

    Bob,



    Got it. So why are we increasing my water temp from 150* to 180*? I thought the idea was to lower the temp curve to increase efficiency and maximize run times?

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  • Ironman
    Ironman Member Posts: 7,510
    Water temp

    If 150* will heat your house when it's 5* outside, then that's what you should use.



    BB heaters are rated at 180* water. They should be sized based on AVERAGE water temp of 170* max (180* supply, 160* return).



    If you using 150* supply on the coldest night of the year, that means your AVERAGE water temp will probably be 140* unless the system is over pumped. At 140*, the output of BB is half what it is at 180*.



    That means you would need twice as much lineal footage of BB to get the same output as if the supply water was 180*. Unless the BB radiation was intentionally over-sized to allow for a 150* supply, you'll probably need 180* when it's 5* outside.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Dan_G
    Dan_G Member Posts: 32
    understand

    Bob,



    I understand now.



    I guess at some point it would be prudent to do a room-by-room heat loss and figure out the load and whether or not the BB and/or boiler is properly sized.

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  • Dan_G
    Dan_G Member Posts: 32
    Home...

    Here's the setting for my boiler outdoor reset curve:



    Warm water shut off 66F



    Min outside design temp 13F



    Design supply water temp at min design outside temp 160F



    Max outside design temp 60F



    Design supply water temp at max outside temp 95F



    Lowest temp for central heating 68F



    Central heating differential 30*



    So based on that, and my t-stats switching on frequently for 66F, what should I start adjusting?

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  • Ironman
    Ironman Member Posts: 7,510
    Reset curve settings

    Without a heat loss calculation, emitter sizes, piping and circ sizes, its not possible to give you a precise answer.



    Does the system heat the house sufficiently when it's 5* outside? If so, then 160* water at 5* is sufficient. If not, you need to set it higher and for 5* outside! not 13*.



    95* on the other end is almost negligible for BB unless it's low temp BB. I'd raise that to about 120* at 65* outside.



    Again, just some general guidelines. You can experiment by raising, lowering and stretching the difference between the two. When you reach a place where the heat won't keep up, you know you've gone too far. Take it 5* at a time and give it a day or two of relatively cold weather to see how each increment effects the house.



    But, get your t'stats programmed correctly first.
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • Dan_G
    Dan_G Member Posts: 32
    t-stats

    Bob, noted on the curve adjustments. I'll experiment with your suggested revisions over the next several days. I did notice that the HWBB output specs do substantially drop off below 120* supply. Do you think I need to adjust the differential setting at all?



    Ironically, it's not supposed to warm up outside =\



    Last night I did adjust two of my three t-stats - will get the last one tonight.



    They were both set for 5 CPH, I changed them to 1 CPH.



    One for the main living area (Honeywell Pro 4000) is set for "Gas, Oil or electric heat with air conditioning". The alternate setting is for a "Heat pump (5 minute compressor time off in heating and cooling". Also Adaptive Intelligent Recovery is "On". Fan operation switch is set for "gas or Oil" as opposed to "Electric or Heat Pump".



    The second one (Honeywell FocusPro 5000 for my 2nd floor work area/office is set for "Heat only (2-wire, 3 wire zone valves [Series 20], and normally open zone valves)



    Let me know if you think I should further adjust any of these settings.

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  • Dan_G
    Dan_G Member Posts: 32
    didn't save original setup

    I worked on programming my boiler's heating curve last night. First, I determined that the settings I thought I had saved the first time, I didn't. So the boiler has been running with default settings since I installed the outdoor reset sensor months ago =\



    Max Supply Temp was at 210F



    I changed it to 180F, and moved the low supply temp up from 95F to 120F.



    Also changed the boiler disable temp, max outdoor temp, and low temp for central heating to 66F (if it's 66F outside, we more than likely don't need any heat running).



    I double checked that I actually saved the settings this time - all good.



    I'll see how this goes...

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