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Thermostat cycle settings for steam---is 1 cph ALWAYS the best choice?

Roddy
Roddy Member Posts: 59
While I know the vast majority of writers on this site (including me) are proponents of the one cycle per hour thermostat setting for steam, I remember a past discussion about alternatives...someone mentioned a stat that offered 2 cycles/hour as one of its options. Mine doesn't offer 2, but it does offer 3 and more (in addition to my chosen "1" for steam). Anyone who uses a setting of 2 or 3 out there / reading this? Any comments on your comfort level, fuel usage, etc. during various winter temperatures? I'm curious. Thanks in advance. Roddy

Comments

  • Jamie Hall
    Jamie Hall Member Posts: 17,025
    One and a half??? Seriously, it's a question of balancing letting the system run long enough (fewer cycles per hour) to get all the radiation hot when you need it (like today...) vs. limiting the temperature swing between cycles. There is no one right answer for every system.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Canucker
  • mikeg2015
    mikeg2015 Member Posts: 1,183
    At 1cph my system overshoots too much. There’s so much lag to detect the change in temp and so much momentum. In very cold weather the temp would drop too quick (drafty Victorian). Mine been running around 2 and seems to be a sweet spot. My Lennox S30 uses a combination of cycle rate and temp differential. I suspect it a full on pid control evaluating change in rate and adapting with time and temp as limits.
  • Roddy
    Roddy Member Posts: 59
    Thank you for that, Mikeg2015. I did some research...the Lennox S30 is pretty pricey, but if you use some of the other features, could very well be worth it. For me, my house, and my system, I leave the temperature at one setting ongoing; so, if I could find a more basic stat that has more CPH options than the standard 1, 3, etc., that could be of interest to me.
    Roddy
  • Jamie Hall
    Jamie Hall Member Posts: 17,025
    Your best bet is going to be the classic Honeywell T87A round. It still has anticipator, rather than cycles per hour, setting -- which means it is pretty well infinitely adjustable to what you want. Pretty close to bulletproof...
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
    Canucker
  • mikeg2015
    mikeg2015 Member Posts: 1,183
    Roddy said:

    Thank you for that, Mikeg2015. I did some research...the Lennox S30 is pretty pricey, but if you use some of the other features, could very well be worth it. For me, my house, and my system, I leave the temperature at one setting ongoing; so, if I could find a more basic stat that has more CPH options than the standard 1, 3, etc., that could be of interest to me.
    Roddy

    I only have it because i have a lennox heat pumps, downstairs is a communicating air handler so I can control a lot of features including airflow for different operating modes, humidifier, balance points, dehumidification, along with schedules (summer, spring/fall, winter, winter 2 (really cold). Gives me remove monitoring and I can set some parameters like balance points remotely.

    I would have probably just used a visionpro thermostat otherwise.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 10,235
    The # of cycle/per hour is different for every system. Too many cycles can waste energy. Too few and you get swings in temperature. A warm air system responds differently than steam.

    The correct way is to increase the cycles as much as possible. If you start getting temperature swings decrease the cycles just enough so temp swing isn't noticed
  • Solid_Fuel_Man
    Solid_Fuel_Man Member Posts: 2,304
    The focusPro 5000 has been my general stat of choice. Never had an issue with them and can be has in many stages heating and cooling etc. Cph 1-7 I think. I set most things to 1 or 2cph. Never had any complaints, and I use 1cph on all my zones in my own home with focusPro's as well.
    Serving Northern Maine HVAC & Controls. I burn wood, it smells good!
  • ChrisJ
    ChrisJ Member Posts: 11,966
    The rule I believe is the cph is allegedly what the thermostat should do at around 50% load as per something I found from Honeywell. So when warmer it'll do less and when colder it'll do more

    I just mentioned that because I feel it may help your decision.


    I don't feel any properly working steam system should be set to 1 cph. The problem is 3 is too much in my experience in warmer weather. 2 works great.

    My recommendation is buy one of the stats that does 2. I guess you could hunt down an old t87 but personally I wouldn't

    I've used both the th8000 series and now a Honeywell Prestige and both work very well and allow a lot of tweaking

    The Prestige is by far my favorite now but they don't come cheap. I'm using 3 wireless indoor sensors for averaging and their outdoor sensor and internet gateway and I think all of it set me back around $500. But I don't regret it.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
    Solid_Fuel_Man
  • Jamie Hall
    Jamie Hall Member Posts: 17,025
    I'll stick by my original comment: it depends. You are seeking a balance between getting the system up to something approaching an equilibrium (all radiators going at least somewhat) and yet not so long that you get excessive temperature swings. Where that equilibrium falls will depend on the size of the system and the personal feelings of the occupants -- and therefore will be different for every application.

    In other words, whatever works...

    If you don't need remote sensing and all the other bling, a properly adjusted mercury T87 is really hard to beat -- as has been pointed out in another thread. The mechanical T87's aren't bad, either -- they just don't last as long.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • SeymourCates
    SeymourCates Member Posts: 162
    @ChrisJ has it right.

    It does not depend on personal feelings or "whatever works". It depends strictly on the run time of the boiler. In warmer ambients, a cycle of once per hour is more than sufficient. The boiler might run for 10 minutes. Slightly cooler and the boiler will run for 15 minutes. When it gets colder, say below 30F, you might consider a cycle time of 45 minutes. The boiler still runs for 15 minutes. When it gets very cold, you might consider a cycle time of 30 minutes. The boiler still runs for 15 minutes. See the pattern?

    FWIW, a thermostat is not the ideal device to operate a steam system. A clock coupled with an outdoor sensor is what is preferred. The boiler runs for a programmed time depending on the selected cycle time and the outdoor temperature. A thermostat can never properly anticipate what will occur after it opens.
  • I use Honeywell FocusPro 6000 and it's set for 2 cph. Never had a problem with it and the temp swings aren't noticeable.
  • Jamie Hall
    Jamie Hall Member Posts: 17,025
    As a general rule, in control theory, a device should always be controlled by a sensor or sensors which are, in some way, connected to the output of the device or the demand on the device. I fail to see how a timer is connected to the space temperature. Perhaps I am missing something, and Mr. Coates could explain the relationship between space temperature or outside temperature and time?
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • ChrisJ
    ChrisJ Member Posts: 11,966
    > @Jamie Hall said:
    > As a general rule, in control theory, a device should always be controlled by a sensor or sensors which are, in some way, connected to the output of the device or the demand on the device. I fail to see how a timer is connected to the space temperature. Perhaps I am missing something, and Mr. Coates could explain the relationship between space temperature or outside temperature and time?

    The relationship between indoor and outdoor temperature and time? You can't be serious can you? ;)
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • Fred
    Fred Member Posts: 8,518
    edited December 2017
    @ChrisJ , @Jamie Hall didn't say "Indoor and Outdoor temp." He said "Indoor or outdoor temp" relative to time, as in a timer.