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Thermostat option?

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lolar
lolar Member Posts: 5
Is there an thermostatic control that notices when the interior temp is dropping ( when the interior temp is above the set point) and turns the boiler on a couple degrees before the set point is reached.

I ask because the boiler in my building takes a good hour to get the rads hot and I experience 7 degree temperature swings. Thermostat calls for heat, interior temp ends up 4 degrees over set point, interior cools, thermostat calls for heat at set point but by the time the radiators heat up, the interior temp is 3 degrees below set point of thermostat.

It is an old, single story brick 1,400 sqft storefront building with closed loop cast iron radiator heat. Open floor plan. Mains are 2” and mostly insulated in the basement. The boiler seems appropriately sized- based on online heat loss calculators and in its relationship to the outputs of the radiators. Also, in the coldest weather, it has no problem keeping the interior warm. I set the thermostat 3 degrees cooler overnight.

All the radiators heat up nicely, it’s just the wide interior temp cycling that is uncomfortable. I end up trying to catch when the interior temp is starting to fall and bumping up the thermostat at that time to get a head start on the heating cycle. And then turning it down once the rads are warm.
The problem feels less extreme in very cold weather because the radiators stay warm between thermostat call cycles.

It’s a nearly 30 yr old ng Burnham, 68k btu. I can’t believe it is still running.

Is this a symptom of an undersized boiler or ...? Is there a thermostat control that would help?

Thanks.
Btw, this forum has been a great resource for me- it’s answered a lot questions I’ve had about radiator sizing, expansion tanks and pumping away.

Lloyd
Chicago

Comments

  • hmlj
    hmlj Member Posts: 10
    edited November 2017
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    I'm new around here, but an hour seem like a long time for the radiators to get hot. Is your air venting adequate?

    Edit: whoops, didn't realize I had ventured from Strictly Steam into the wild.
  • lolar
    lolar Member Posts: 5
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    Air venting- referring to air in the system?
    The system has an air separator and the rads are bled and quiet.
  • JUGHNE
    JUGHNE Member Posts: 11,075
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    Hot water system.
    What model of tstat do you have?
    If old, it may have a heat anticipator adjustment that shuts off heat before overheating. If so move it to the opposite end of where it is now. Some of them have failed, if you have one and move it that far something should change. If not time for new.
  • lolar
    lolar Member Posts: 5
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    It’s a newer sensi, that I got for the WiFi feature. My understanding of the anticipator feature is that it helps to reduce the amount the interior temp overshoots the thermostat set point. I’m looking for a way to reduce the 3 degrees that the interior temp goes below the set point because it takes an hour to heat the rads.
  • Jamie Hall
    Jamie Hall Member Posts: 23,433
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    You may be out of luck. Without an anticipator -- or a smart thermostat which can "learn" how long it takes to heat things up, and how much warmer it will get after it turns off -- the problem is going to be there.

    You could try setting it for more cycles per hour, if it has that feature.

    Were the setup mine, I'd go for an outdoor reset on the boiler, and try to keep the thing running at a constant interior temperature, with the boiler running at just the right temperature to keep it there.

    Setbacks on a slow responding system like that are almost always more trouble than they are worth.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Solid_Fuel_Man
  • JUGHNE
    JUGHNE Member Posts: 11,075
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    Some newer wifi controls have issues with hot water systems with high mass emitters.
    Someone else here may pick this ball up and run with it.
  • lolar
    lolar Member Posts: 5
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    Jamie, I’ve heard about outdoor resets, but aren’t clear on what they do. Can you give me a thumbnail sketch?

    Also, are they applicable on older boilers? Do they require a new boiler control setup?

    Regarding more cycles per hour- that would be consequence of an anticipator or is it determined by a separate control?

    It sounds like there are established systems for dealing with overshooting the set point of a tstat but nothing for turning the boiler on before the room cools to the set point. Is this because reducing the overshooting also minimizes the overcooling because there are more cycles per hour and the average temp of the water in the system stays higher?

    Jughne, yes, that’s a good way to characterize the system- high mass. With high thermal inertia relative to the boiler size.
  • Jamie Hall
    Jamie Hall Member Posts: 23,433
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    Basically what an outdoor reset control does is change the set water temperature of the boiler so that the heat emitted from the radiation matches -- one hopes -- the heat lost by the building. Properly set up, the circulation never stops and the radiation adjusts slowly to the required heat loss. It works best on the newer modulating boilers, as it changes the firing rate of the boiler at the same time so that -- within a rather wide range -- the boiler never turns off either. In your case, the aquastat (which would now be controlled through the outdoor reset) will still cycle the boiler on and off to maintain the desired temperature range.

    And yes, it would require some new controls -- and someone knowledgeable to set it up (try "Find a Contractor" on this web site).

    And it is not compatible with setbacks. Setbacks (such as your 3 degrees cooler at night) have been the subject of considerable debate over the years, and the general conclusion is that they save little, if any, energy in a high mass system -- such as most steam systems, or your high mass radiator system (or radiant systems...). They are just dandy for forced air, and that's about it.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Solid_Fuel_Man
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,646
    edited November 2017
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    Jamie is spot on, as usual. I bet you'll see at least 10% drop in fuel consumption with outdoor reset and constant or near constant circulation.

    To get the reset dialed in you may have to fiddle with it and wait a few days. Trial and error will get it dialed in to a set it and forget it system.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • lolar
    lolar Member Posts: 5
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    Jamie, thanks for the explanation- I understand the idea now. I wasn’t aware of the option to control the water temp as a way to modulate the temperature of the living spaces.Good to hear it would be applicable on an older boiler.

    I’d like to investigate the possibility of installing it myself- partly because I enjoy learning about things and doing the maintenance myself as well as a way to save money. Is there a manufacturer or control system you recommend? Are there any articles or books on the control systems that would be applicable?

    How do I determine what the lowest temp the return water can be that won’t damage the boiler?

    If this is a problem set beyond the reach of a skilled diy’er, let me know. I’m in the trades myself (millworker) and understand the value of an experienced and trained professional.

    Lloyd