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why cycle rate and not anticipator?

I would like to ask why digital thermostats use "cycle rate" as the equivalent of "anticipation". In my mind the two things are not equivalent at all.

Anticipation is the "D" in PID control. For example, during recovery, the controller should look at how fast the house is warming up, and cut heat off earlier or later based on this. Any ten-cent microprocessor could be programmed to look at the warming rate, but I can't find any home thermostat with this feature. Cycling the heat on and off a fixed number of times an hour is not the fastest way to hit the target temperature.

If a thermostat has cycle rate set at 3, will the heat go off and on three times an hour, come hell or high water? Why? For steady state (not recovery), isn't it better to set a specific temperature swing and let the controller do what is needed to keep within that range? True anticipation and a "learning mode" will help do this efficiently. (Of course it would be nice to have a continuously variable heating rate, but that's not absolutely essential.)

Houses with radiators would benefit greatly from true anticipation, because the radiators continue to release heat for a long time after the circulators are turned off.

I'd be grateful for any clarifications.

Comments

  • carol_3
    carol_3 Member Posts: 397


    The purpose of the anticipator in non-electronic thermostats is to set cycle rate. When you match the anticipator setting to the amp draw of the load, you get about six cycles per hour. Five or six cph is the industry standard for "comfort" which means most people can't sense that the temperature changes, even though it fluctuates plus or minus a degree or so. This means that the equipment has the "opportunity" to come on every 10 minutes or so, and run as long as needed to reach set point.

    It's just as well that we're moving to cycle rate instead of anticipators because hardly anyone knew what an anticipator was, let alone how to set one!

    Here's something kind of funnt--18 years ago I got a top-end electronic thermostat returned on warranty. Scratched into the box was "Bad! Anticipator missing!" Well, yeh.
  • R. Kalia_6
    R. Kalia_6 Member Posts: 28


    > The purpose of the anticipator in non-electronic

    > thermostats is to set cycle rate.


    I am sorry, I know you have said this in previously published articles, but it's not correct. Indeed the anticipator in non-electronic thermostats affects the cycle rate, but it does not result in a fixed number of cycles per hour irrespective of conditions.

    The purpose of the anticipator is to anticipate, i.e. act a little before the set temperature is reached, based on current draw. In other words an anticipator causes the thermostat to adjust to the actual situation. Having a fixed number of cycles per hour is not responsive to the actual situation.

    For example, if the non-electronic anticipator is set to cause 6 cycles an hour, and I suddenly run the thermostat up 10F, the anticipator won't still cause the thermostat to cycle 6 times an hour, rather it will run till the temperature gets close to the new setpoint.

    It is easy to reproduce the behavior of a non-electronic anticipator using digital logic, but setting a fixed cycles/hr doesn't do it.
  • bob_50
    bob_50 Member Posts: 306
    anticipation is making me wait

    Rich, I think part of the problem is semantics. A non-electronic thermostat with "anticipation" doesn't really anticipate. About 45 years ago I read an engineering paper from Honeywell that explained "Timed Two Position Control" what the trade calls anticipation. Imagine a heat operated timer that consists of a power source, a temperature sencing element, a switch operated by the sencing element and an electric heater placed in close proximity to the sensing element. The temperature sensing element is maintained at a temperature above setpoint. The cycling rate and the ratio of on time to off time is dependant on heat input (I^2R) the differential of the switch and the rate of heat loss of the temperature sensing element. It doesn't really "anticipate". Set it on a table and watch it cycle. Carol is correct when she says the control Mfg. design for a cycling rate of about six CPH. Because of the non-linear heat loss rate of the sencing element the six CPH will occur only when the ambient is close to setpoint. As ambient drops below setpoint the ratio of on time to off time increases. Cph doesn't change much until the deviation is substantial but it will still cycle. Turn your system off, let the house cool to 35F and turn it back on. It will cycle before it reaches set point. I agree with you when you say electronic controls should have PID and auto-tune like industrial temperature controls. I think it's a cost issue. When I first started running service we used to carry a box of color coded carbon washers on the truck and a chart from honeywell, that was the only way to adjust "anticipators". bob
  • Chuckles_4
    Chuckles_4 Member Posts: 43


    Non-electronic anticipation just means that the effective setpoint is lowered when the poiler is running, due to the heat from the resistor, which lowers the setpoint.

    That's why it's called an anticipator: it stops the boiler early because the high-mass system will continue to heat for a while. This results in more precise temp control and makes the system cycle faster.

    But I don't understand why you say there would be any cycling when heating up from 35F. The resistor will make the thermostat think that the temperature is higher than 35K, but it won't think it's 70K! So the boiler will continue to run flat out until it gets to just under 70K.

    Whereas an electronic thermostat will go on and off six times an hour even though the room is cold. Is that right?

    PS You can't really do PID because the 'P' isn't there...unless the thermostat is allowed to mess with the reset temperature! But it's still possible to do the 'D' part using on/off. I know they say it's a cost issue, but microprocessor control is cheap these days . I think it's more of a product differentiation issue, they want to save the intelligent control for higher-priced industrial thermostats.
  • carol_3
    carol_3 Member Posts: 397


    I'm just amazed at what people know!
    Buster
  • R. Hayes
    R. Hayes Member Posts: 5
    Anticipator Vs. Heat Cycle Timer

    When I start my home steam heat on a cold morning, I set the thermostat to 65 and the boiler starts. After the steam gets to 1.5 psi, the boiler stops until the steam drops to .5 psi. Then the system keeps cycling (each complete cycle takes about 5 minutes) until the temperature gets to 65.

    My concern is that many of those 5 minute cycles are not necessary because all the radiators are hot and their vents are closed.

    I get the idea that one of those computer controlled thermostats would let me set the number of cycles per hour as the house heated up. Is this correct? Would I be able to have 15 or 20 minutes between cycles as the house heated instead of 5 minute cycles?

    My thermostat is a White-Rodgers 1F72-301 mechanical with an anticipator. I get the idea that the anticipator will not give me 15 or 20 minute cycles as the house heats up. Is this correct?

    Would I save heating costs with a programmable thermostat?
  • ttekushan_3
    ttekushan_3 Member Posts: 940
    control

    I'm going to sorely miss analog stats like the T87. I could tune the anticipator setting (albiet above gas valve current draw) to match the characteristics of individual steam heating systems. Once the heating system is cleaned and balanced, tuning the anticipator to the individual system creates minimum cycle times for good heat distribution. Occasionally the temp will overshoot the target temp after deep setbacks, but I've NEVER had anyone complain about that. Especially if i've solved cool room problems with tweaking the anticipator.

    Now we have one (or two) sizes fit all, and screw you if you can't afford a $1,000 electronic steam controller installation.

    Progress can and should be beneficial. But sometimes I think progress is used to reduce true consumer choice and force the purchase of very expensive options if you actually want good results.

    -Terry

    P.S. I've installed Tekmar 269's and Heat Timers. Great controls if you know how to set them up. True savings and flexibility. But frankly, the homeowner with the 1700 square foot house is forced to spend a lot more money for ROI than they needed to in the past. The feeling I get from the customer is that energy companies and heating equipment suppliers have called open season on the common homeowner.
    terry
  • R. Hayes
    R. Hayes Member Posts: 5
    Heater Cycles

    Maybe in my case I could have my buddies design a circuit that senses when the pressuretrol has shut down the boiler and then keeps the control circuit open for an adjustable range of 5 to 15 minutes before allowing the system to function as normal.

    Perhaps such a thing already exists.
  • Charles G.
    Charles G. Member Posts: 113
    Heat cycles

    Your heating cycles are not being determined by the t'stat; they're being determined by the pressuretrol. The t'stat is continuing its call for heat--one cycle.

    As for using programmable t'stats w/ steam, there's much debate about that. But since you're already setting back @ night, why not let a 'stat do the work for you?
  • Empire_2
    Empire_2 Member Posts: 2,343
    Timr Delay Relay

    Adjustable usually from .01 sec to 10 min or so. Delay on break than initiates the delay.

    Mike T.
  • Techman
    Techman Member Posts: 2,144
    heat anticipator

    The Carrier Infinity/Bryant Evolution control systems have seperate settings for cycle/anticipator!Also,its been my experince,that a non-electronic stat will NOT run full tilt until the room TEMP is satisfied,because of the anticipator.After set-back,with the room temp close to being satisfied ,the stat will cycle 1-2-3 times until the final called for temp is reached!
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