Click here to Find a Contractor in your area.
Welcome! Here are the website rules, as well as some tips for using this forum.

If you've found help here, check back in to let us know how everything worked out.
It's a great way to thank those who helped you.
Need to contact us? Visit https://heatinghelp.com/contact-us/.

I hate outdoor setback

WellnessWellness Posts: 76Member
edited October 7 in THE MAIN WALL
I was looking at the responses to @dm9321287 recent post and the answers reminded me how much I hate boiler outdoor setback and integrated boiler controls in general. They may be helpful some instances, and help manufacturers meet government mandated efficiency targets, but my experience has been they are terrible in a few applications and contribute to short cycling, especially where a buffer tank is not used. So I have a question for the pros: if outdoor setback is so great, why is it not commonly used in AC cooling, especially since temperature swings in the summer are often greater than winter after or before a thunderstorm, for instance?

Comments

  • Jamie HallJamie Hall Posts: 10,852Member
    Outdoor setback on heating systems works -- and works well, if properly installed and set up with a modulating/condensing boiler -- because it allows the boiler to run more efficiently at lower temperatures. I and most will admit, happily, that if they are not installed and set up properly -- or used on equipment not designed to make use of setbacks, they can be a problem. The problem for AC is simple; air conditioning (and other such refrigeration devices, such as heat pumps) don't take kindly to being throttled back. They don't mind, however, turning on and off (at least in terms of efficiency; wear and tear on the motor for the compressor is another story) -- so there is no point to it.
    Jamie

    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.

    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • GWGW Posts: 3,439Member
    Ac does have a “variable compressor” or “inverter” technology, prevalent with mini split ac systems. Also common with higher end ducted systems. We install Carrier “Infinity” series, the 25VNA0 series, Cadillac of heat pumps

    But you’re right, regular systems cycle unless it’s hot and there’s and load. Air systems won’t cycle as badly as a low mass boiler (unless horrifically oversized)
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    www.wilsonph.com
    [email protected]
  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,650Member
    The vast majority of equipment I see hasn't been setup properly by the installer. For that matter most stuff isnt even piped correctly according to the manufacturer.

    It takes some time to do a proper heatloss and a radiation survey to determine a decent ballpark of outdoor reset. Then there is a good bit of playing with that number to get it dialed in, very few do it.

    Certain radiation like fin-tube isnt as well suited to reset, at least there isnt much room to drop temps if the structure has just enough fin-tube to meet heatloss, such as most modern homes.

    It works well with over radiated retrofits, and high mass cast iron or slabs.
    Serving Northern Maine HVAC, and Controls
  • flat_twinflat_twin Posts: 208Member
    "It works well with over radiated retrofits, and high mass cast iron or slabs."

    That's a very good description of our system and yes ODR works very well with such a system. When I put my hand on a radiator and barely feel any warmth and realize that's all it takes to heat the house it's like magic. The ODR settings were left by the installer at factory defaults but we did talk about optional settings so I read the manual and dialed it in myself over the last two heating seasons. Without several field visits by a tech, there's no way the ODR could be set as it is now.
  • ZmanZman Posts: 5,062Member
    Wellness said:

    I was looking at the responses to @dm9321287 recent post and the answers reminded me how much I hate boiler outdoor setback and integrated boiler controls in general. They may be helpful some instances, and help manufacturers meet government mandated efficiency targets, but my experience has been they are terrible in a few applications and contribute to short cycling, especically where a buffer tank is used. So I have a question for the pros: if outdoor setback is so great, why is it not commonly used in AC cooling, especially since temperature swings in the summer are often greater than winter after or before a thunderstorm, for instance?

    When you are heating or cooling just the air, there is very little mass at play so an outdoor reset is less important. It is used however in larger commercial chiller systems.

    Outdoor reset can increase short cycling due to the lowered output of the emitters. The buffer tank should have the opposite effect.

    If more designers would focus on the system's typical day rather then design day the HVAC world would be a far more efficient and comfortable place.

    No offense, but like another thing in life, if outdoor reset doesn't feel good, you are not doing it right. :D
    "If you can't explain it simply, you don't understand it well enough"
    Albert Einstein
  • WellnessWellness Posts: 76Member
    edited October 7
    @AC. Good point about variable compressors (as well as fan speed) I forgot about those. I'm still doubtful about outdoor setback, because it doesn't account at all at how fast or slow a house losses heat or what part of the house needs heat, only whether the outdoor temperature is rising or falling. My main point was the one noted by @Solid_Fuel_Man, ODS isn't suited to every type of radiant system and in my experience is most ideal for high mass ones.
  • TomSTomS Posts: 48Member
    So in moderate outdoor temperatures why would you want the boiler cycling at 100,000 Btu rather than at 20,000 Btu? As far as the statement as to how fast the home loses or gains heat this can be dialed into the controls to match your house. I will second the statement that if you are unhappy with setback it is not set up properly.
  • WellnessWellness Posts: 76Member
    edited October 7
    No I wouldn't want that. My heat loss example was aimed at underscoring the fact that ODS makes it hard to cope with those kind of differentials. The ideal solution would be to not have the boiler short cycling at all and that's how ODS mostly works in high mass applications. But copper finned tubing, without a buffer tank, works poorly with ODS. At least that's been my experience. But your mileage may vary.
  • John RuhnkeJohn Ruhnke Posts: 871Member
    Tekmar Controls has a nice system. They use outdoor reset with indoor feed back so you can get the best of both worlds.
    I am the walking Deadman
    Hydronics Designer
    Hydronics is the most comfortable and energy efficient HVAC system.
  • WellnessWellness Posts: 76Member
    @John Ruhnke. Yes I have cobbled together a system, using several 3rd party parts, that does something similar.
  • hot_rodhot_rod Posts: 11,773Member
    I think indoor feedback or indoor reset is critical. Just because outdoor temperature is dropping does not mean the building need more heat input or SWT temperature increase. Consider large changes in internal gains, end of day in an efficient home.

    Lighting, appliances, people, computers, pets all add energy to the space, and in some cases can over-heat a space when large occupancy changes are present.

    This is where tekmar as had it exactly correct from early on, ODR with indoor feedback and reset.

    It's a bit misleading to say outdoor temperature dictates heat emitter needs or output. That would be true if the heat emitters were installed on the outside of the home :)

    Heat emitters respond to the temperatures across them, SWT and average emitter temperature against ambient or air flow temperature across fins in baseboard of fan convectors.,
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • VoyagerVoyager Posts: 222Member
    I don’t understand the comments from @Wellness and even @hot_rod that outdoor temperature isn’t a significant factor in heat loss. It is one of the two biggest factors in heat loss, at least the ones we can control dynamically. We can’t easily control infiltration nor can we dynamically change R value or wall and roof area, so the only control opportunity left is based on deltaT.

    Any technology poorly installed or configured will not work as well as designed and may cause problems. That is not unique to ODR. As long as the boiler can operate at lower temps without damage (i.e. causing condensation in a boiler not designed for that), ODR will work well if configured properly.

    I don’t see how the emitter type makes a big difference here, but if specifics of a given situation are provided, then we can discuss that in more detail as to what might be going on.
  • John RuhnkeJohn Ruhnke Posts: 871Member
    @Voyager

    I do believe ODR works well and does a good job. I also believe that Tekmar has made a significant improvement and upgrade by adding its indoor feedback feature as Hot Rod described.
    I am the walking Deadman
    Hydronics Designer
    Hydronics is the most comfortable and energy efficient HVAC system.
  • Paul PolletsPaul Pollets Posts: 3,200Member
    I've never had problems with setting up the controls with ODR, whether using a Tekmar control or the integral Viessmann control. Most had an indoor sensor, but some, not. All of the systems were able to keep indoor temps to within 2 degrees of setpoint.
  • Mike_SheppardMike_Sheppard Posts: 575Member
    Don’t forget about latent heat with cooling. Set back too much and you won’t get rid of the humidity.

    I deal with a lot of chilled water. They’ll set it up on outdoor reset like the heating but if you raise the chilled water setpoint too far you lose your latent capacity.
    Never stop learning.
  • hot_rodhot_rod Posts: 11,773Member
    > @Voyager said:
    > I don’t understand the comments from @Wellness and even @hot_rod that outdoor temperature isn’t a significant factor in heat loss. It is one of the two biggest factors in heat loss, at least the ones we can control dynamically. We can’t easily control infiltration nor can we dynamically change R value or wall and roof area, so the only control opportunity left is based on deltaT.
    >
    > Any technology poorly installed or configured will not work as well as designed and may cause problems. That is not unique to ODR. As long as the boiler can operate at lower temps without damage (i.e. causing condensation in a boiler not designed for that), ODR will work well if configured properly.
    >
    > I don’t see how the emitter type makes a big difference here, but if specifics of a given situation are provided, then we can discuss that in more detail as to what might be going on.

    Not sure I stated that outdoor temperature isn’t a factor in heat loads or heat transfer from a space???

    My point is that Swt to a system, especially a high mass radiant may not need or want to change based on outdoor temperature feedback alone.

    Flywheel effect, energy stored in the mass and objects in the room, additional internal gains, and MRT should enter into the decision how or when to increase SWT to meet the load

    A fin tube or forced air system would be the opposite extreme perhaps where a response to outdoor temperature drop would reflect in indoor temperature drop and need to ramp up heat input or SWT quickly.

    Every building and expected use should be analyzed and an appropiate design specific to the job calculated. With available control options now, a comfortable, controllable system should always be obtainable.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • mikeg2015mikeg2015 Posts: 904Member
    Setback should match the turndown ratio of the boiler with the turndown output of the load. Meaning if min fire is 20% then a water temp should be used that results in approx 1/5th the radiation level.

    AC do not control to supply temperature. Their efficiency automatically improves in mild weather. Newer variable speed systems improve this further.

    Reset is used in chilled water to a point. You stil need to dehumidify as mentioned in most climates.
  • VoyagerVoyager Posts: 222Member
    @hot_rod I was going only but this statement “ It's a bit misleading to say outdoor temperature dictates heat emitter needs or output. That would be true if the heat emitters were installed on the outside of the home.” Outdoor temp is a key variable in what the emitter output needs to be. That was my only point. Whether that output energy comes from the boiler quickly or from thermal mass is another question, but the outdoor temp is a key variable, probably the key variable, in what the emitter output needs to be at a given time.
  • WellnessWellness Posts: 76Member
    edited October 9
    So your ODS determines that 20,000 BTUH is sufficient to heat your house on a cool, but mild fall or spring day. And that would work, all other things being equal. But first kid leaves house, letting in cool air and lowering the front room temp by 2 degrees. Second kid leaves 5 minutes later, room drops another 2 degrees. Boiler won't ramp up because nothing outside has changed and the indoor thermostat had already been calling for heat to maintain room temperature with a 20,00 boiler BTU supply. As @HodRod observed "It's a bit misleading to say outdoor temperature dictates heat emitter needs or output."
  • hot_rodhot_rod Posts: 11,773Member
    if the heat emitter us within the conditioned envelop it’s output and response is directly related to the conditions surrounding it, regardless of the type of emitter

    No doubt outdoor conditions effect the loss from the space but the heat emitter doesn’t know or see that condition it can only respond to the condition around it

    My concern is ramping up Swt when it is not needed or required based only on outdoor temperature And of course wind and solar gain would play into the load requirement
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • JohnNYJohnNY Posts: 2,324Member


    It works well with over radiated retrofits, and high mass cast iron or slabs.

    Truest statement on the subject ever made.
    I'm heating a 6-story school in Brooklyn with 137°F water on the coldest days of the year for about a decade now. Most days, the water temperature is around 108°F.
    If I had fin tubes or convectors in that building instead of the original giant cast iron rads that in place, it would be a VERY different story.

    For installations, troubleshooting, and private consulting services, find John "JohnNY" Cataneo here at :
    "72°F Mechanical, LLC"
    Or email John at [email protected]
    John is a professional Master Plumber, licensed by The Department of Buildings of The City of New York, and works extensively in NYC while consulting for clients in and out of state.
  • WellnessWellness Posts: 76Member
    @JohnNY. Exactly! But if you are running copper finned baseboard at 180 degrees, I don't see anything but problems with ODS unless you use a buffer tank, and even then, the ODS curve often has to be set very aggressive.
  • Jean-David BeyerJean-David Beyer Posts: 2,632Member
    My point is that Swt to a system, especially a high mass radiant may not need or want to change based on outdoor temperature feedback alone.


    In my experience as a homeowner with a radiant slab at grade, the improvement in comfort with outdoor reset is desirable. My old boiler did not have any reset and pumped a constant SWT whenever there was a call for heat. An it always rapid cycled (60 seconds off, 90 seconds on, or something like that). That old GE boiler was tough. And the indoor temperature had large (+|- 4F sometimes) temperature swings because when the thermostat was satisfied, the slab was pretty hot and continued to heat the house, when it was not needed, for several hours or more. Similarly, when the temperature got below the set-point, the boiler went on and started heating the slab, but the temperature of the house continued to drop until the slab got up to temperature again.

    Now with outdoor reset, the boiler supplies water at just over the temperature needed to maintain the desired temperature, so the thermostat calls for heat many hours at a time. I wish it would do that all the time, but the boiler will not modulate down far enough. Now it holds the indoor temperature +|- 1F.

    So my system is controlled by outdoor reset all the time. Only when it gets to the top of the set-point range does the thermostat take over and stop the call for heat.
  • hot_rodhot_rod Posts: 11,773Member
    Use delta Ts Colorado weather for example. 60 daytime, boiler supplying maybe 80 to a slab

    Temperature drops 30 degrees quickly odr control has boiler ramp to 120f or higher regardless

    Next day by 10 am temperature returns to 60

    Isn’t it possible the slab had enough stored energy that it did not need the large SWT increase

    An indoor feedback and modulation function would prevent slab overshooting
    Energy efficient homes compound the issue, although those homes may not be a good match for high mass radiant to begin with.
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • hot_rodhot_rod Posts: 11,773Member
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    The magic is in hydronics, and hydronics is in me
  • Solid_Fuel_ManSolid_Fuel_Man Posts: 1,650Member
    Those who dont like outdoor reset, seem, to have fin-tube or hot air.

    Referring back to my original statement about mass.

    Indoor feedback from something like Tekmar's house controls of which I've installed several, work exceeding well. Now you have two real-world inputs. Not just outdoor temperatures and a closed contact for a heat call.

    @Wellness the scenario you describe with kids opening the door sequentially and the subsequent lowering of room temp describes a low-mass system with the reset set too low. Weil Mclain (that I know of) has a boost function in their boilers that after a heat call of sufficient time the boiler will boost the SWT to overcome the "lag" if the reset is set too aggressively, such as a windy day, lots of door openings etc. This is kind of a bandaid compared to indoor and outdoor reset.
    Serving Northern Maine HVAC, and Controls
Sign In or Register to comment.

Welcome

It looks like you're new here. If you want to get involved, click one of these buttons!