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Honeywell TH8110U1003 strange behavior

Alex265Alex265 Member Posts: 41
Hello,

I bought a new thermostat, and it behaves differently from my old thermostat (also Honeywell, older model). I'm trying to understand whether this is an intended behavior or a bug. I have a steam heat, and I set the cph to 2, but I feel this is not related to the problem.

So, I'm using the old thermostat as a control thermometer, it's located right on top of the new thermostat but is not wired. I observe the following.

Let's say both thermostats show 62. The schedule calls for 65, so the new thermostat calls for heat, boiler kicks in. After 15 minutes radiators start to fell warm, and the temperature display on both thermostats starts to go up. In 5-10 minutes both thermostats show 65. Here is the strange behavior, Instead of turning off, the new thermostat continues running for another 20 minutes, all this time showing 65 as if temperature stays the same. The old thermstat at the same time goes up to 68 which seems absolutely natural and sure feels right. After this additional 20 minutes (that were not required at all), the new thermostat goes off, and only then its displayed temperature slowly goes up the 68 - the same that the old thermostat shows.

Can anyone explain to me what is happening? This does not seem like the new thermostat is 'learning', or does it? For me it looks like it significantly overshoots by working extra 20 minutes, but does not really know about it, as it thinks that all this 20 minutes the temperature is still 65.

Thank you and best regards.

 

Comments

  • Tim McElwainTim McElwain Member Posts: 4,389
    Go to

    [url=http://www.customer.honeywell.com]www.customer.honeywell.com and type in model number of your thermostat and everything about it is listed there.



    Your thermostat has the following however which will explain its behaviour.



    Special features

    Auto Changeover: When set to Auto, the thermostat automatically selects heating or cooling depending on the indoor temperature.When set to Auto, the thermostat automatically selects heating or cooling depending on the indoor temperature.

    Adaptive Intelligent Recovery: This feature allows the thermostat to "learn" how long the furnace and air conditioner take to reach programmed temperature settings, so the temperature is reached at the time you set. For example: Set the Wake time to 6 am, and the temperature to 70°. The heat will come on before 6 am, so the tempera6 am, so the temperature is 70° by the time you wake at 6. The message "Recovery" is displayed when the system is activated before a scheduled time period.This feature allows the thermostat to "learn" how long the furnace and air conditioner take to reach programmed temperature settings, so the temperature is reached at the time you set. For example: Set the Wake time to 6 am, and the temperature to 70°. The heat will come on before 6 am, so the tempera6 am, so the temperature is 70° by the time you wake at 6. The message "Recovery" is displayed when the system is activated before a scheduled time period.

    Compressor Protection: This feature forces the compressor to wait a few minutes before restarting, to prevent equipment damage. During the wait time, the message "Wait" is displayed on screen.This feature forces the compressor to wait a few minutes before restarting, to prevent equipment damage. During the wait time, the message "Wait" is displayed on screen.
  • Alex265Alex265 Member Posts: 41
    Honeywell TH8110U1003 strange behavior

    Thank you for your reply. As I tried to figure this out myself, I read the documentation and do know about these features. Auto Changeover and Compressor protection are not applicable to my case as I have the Heat Only 2-wire setup.



    Adaptive Intelligent Recovery feature does look relevant to my problem, but to me it looks like it is malfunctioning, and I'm trying to understand whether it does or not. Keeping the heat on for 20 minutes showing the same temperature does not seem right to me, as the temperature just cannot be the same because the radiators are hot. The control thermometer does show the temperature increase. The control thermometer is located right next to the thermostat.
  • Alex265Alex265 Member Posts: 41
    edited November 2009
    Honeywell TH8110U1003 strange behavior

    Just a thought - the only explanation of this phenomenon I can think of is that CPH setting works like temperature swing setting on some other thermostats, i.e. the thermostat does not stop before the temperature reaches (set temperature) + (temp swing setting). For example, my CPH setting 2 may be equal to swing temperature setting of 2F. If so, and if my set temperature is 65F, the thermostat will start when the temperature goes down to 63F, and then work until the temperature reaches 67F. There go the extra 20 minutes of  "on" time! And I would be fine with this theory, if not for one circumstance - Why does the thermostat show the constant 65F during those 20 minutes, and only then, after it stops, goes up to 67F (or even 68F because of the heat inertia)?



    Am I complicating things?



    If this theory is true, then what I could try is to set the CPH to 3, and see if this will reduce the temperature swing. If so, that 20 extra minutes will turn into shorter time.



    Sorry if all this sounds ridiculuos, I'm not a professional.
  • matthewjmatthewj Member Posts: 6
    is the wall cold?

    I have never used one of those stats with a steam system, but we did have some issues where a customer used deep setback and they would overshoot.  I believe that the wall temperature affects those thermostats - we installed a piece of 1/4" thick cork between the wall and the stat and it helped quite a bit.
  • MEKMEK Member Posts: 15
    CPH = Cycles Per Hour

    I'm not sure if you resolved your issue yet, but I just looked up the manual for my Honeywell CT2700 thermostat and it allows me to adjust the CPH calling it "Cycles Per Hour". To me, this doesn't sound like it relates to a degree temperature tolerance.



    I am thinking about changing my setting according to their table. For steam they recommend 1 cph. Right now, my system cycles more often although it hasn't been that cold out yet to require longer cycles. Anybody know about this setting and what is best for steam boiler efficiency?
  • Jean-David BeyerJean-David Beyer Member Posts: 2,665
    wall temperature affects those thermostats

    I have a thermostat that claims it is influenced both by the air temperature and the wall temperature. They consider it an advantage. I think they may be right, but it would be good to know the proportion of the measurement from the wall and the proportion from the air. And how the entire system is designed.



    I have read that your perception of the temperature is related to the amount of body heat absorbed by the environment. A lot of this is absorbed by radiation from the body to the surrounding walls, floor, ceiling, furniture, ... . So it seems to me that having some of the thermostat reading coming from the wall could be a good idea. This may be especially true for spaces heated by radiant heat sources.



    I have a building (I do not own it, but am in charge of heating) that is heated by forced hot air. Basically, it has two rooms. One has no water in it. The other does. It has two zones. In the zone where there is no water, we allow the setback to drop the room to 40F when the building is not in use. In the other room, with water, we do not allow it to go below 50F. The walls are plaster on top of very heavy wood beams. All the space between the beams is filled with brick. The building is normally unused 6 days a week. It takes many hours to recover from that kind of setback. And the thermostat responds mainly to air temperature, so it feels cold even when the air temperature satisfies the thermostat because the walls remain cold. I think the thing to do is to have an adjustment to the thermostat to control the ratio of air temperature to wall temperature, but I am fairly sure there are no such thermostats. Even if there were, they would surely be adjusted incorrectly.
  • Alex265Alex265 Member Posts: 41
    It's all about the formula

    The thermostat has a built-in algorithm by which it calculates and adjusts on/off times. The algorithm's behavior is determined by a number of coefficients, some hard-coded (like outside temperature on VisionPro), some adjustable - like CPH on most thermostats, or, on VisionPro - temperature correction setting. Obviously, my old thermostat used slightly different algorithm than my new thermostat, so even with the same values of the coefficients, the behaviour was different. However, I did come to like my new VisionPro better and decided to stay with it.



    As for your question, lower values of CPH are in general recommended for steam heat system, many sources say it should be 1 or 2. However, this does depend on each particular house (size, insulation of walls, insulation of steam pipes, living patterns of inhabitants like tolerance to chilly air and so on :)), thermostat - what algorithm it uses, and also on temperature outside, so I would say that value of 3 (or even 4) is not unthinkable for steam system - it can provide more comfort for the same or just a little more money than hard temperature swings of CPH = 1.
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