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Hysteresis

Smidge69
Community Member

Hi, the hysteresis setting on my Nest is ridiculous. The room is swinging through 2 degrees C  (as measured by an independent temperature sensor) between on and off which is totally unacceptable from a comfort point of view. I have had a Netatmo for many years and it managed to maintain a 0.3C variance. There are many posts about this problem but no solution seems to have been made public. My Nest will be being removed at this rate - its close to useless!! 

6 REPLIES 6

Wellcraft19
Community Member

In my view, that is a good swing in order to reduce the risk for short cycling. But the 'swing band' (or more correctly  'hysteresis') should be adjustable. Easy firmware fix.

Are you listening Google???

gt_
Community Member

I am thinking of buying a nest v3, how exactly does its 1oC hysteresis work?

For example, if I set it to 21oC, will it turn on at 20 and heat it to 21 OR will it turn on at 20 and heat it to 22?

Thanks for any help.

Wellcraft19
Community Member

I think that is what is being debated here - and the fact that Google still has not made the hysteresis ('swing band') adjustable.

But in a general case, you set temp to 20C, furnace would likely run until temp is closer to 21C (by the thermostat) and then not turn on again until it has reached something like closer to 19C.

Too narrow of a band, especially combined with a too large furnace (common in the US), results in short cycling. Furnace turns on and temperature by the thermostat quickly reaches its shut off point. But dwelling hasn't been heated, and just by simple air movement (the warm air quickly cools down, is denser and falls) also drops the temperature at the thermostat, triggering a demand for heat again.

Part from properly dimensioning the furnace, on the small side which is really hard as the environment it operates in varies so much, only way to get around this is to have: 1) adjustable hysteresis, 2) an adjustable timer (like once turned on and off, furnace cannot start until 30 min has elapsed).

Should note that this is also truly much more of an issue for forced air systems than anything. Most of the are 'digital'; On or Off. If you have hydronic heating, as an example, the thermostat does not control the furnace or boiler. Furnace/boiler is controlled by the temperature in the energy storage (water), and the thermostat either controls the distribution of water (circulation pump on/off, or adjusting a shunt valve to regulate the outgoing water temperature). In this setting, furnace/boiler will run until the water has reached a certain temperature, regardless what the inside temperature is. 'Heat' will then be taken from this 'energy storage' (which might only be good for 30 min to 1 hour, or can be good for several days if having a large accumulator tank), but the upside is that when the furnace/boiler runs, it runs. And when it's off, it's really off. For a long time.

Personally, I hate the forced air systems, but they are prevalent in the US because they are cheap, simple, and they do easily provide support for for A/C as well. With the accelerated proliferation of mini-splits, that is finally starting to change, but I'd love also to see more hydronic heating systems. Nothing is more comfortable than large areas that are 'mildly' warm (wall mou8nted radiators or  entire floors) versus a very hot small area (heat exchanger in a furnace, a baseboard heater, fan driven or just natural convection). The latter works great to dry out the already dry winter season air and promote all types of health issues (in addition to what the ducting in a forced air system already is responsible for).

Jeff
Community Specialist
Community Specialist

Hi all,

 

I notice that activity slowed down here but I wanted to check in and see if anyone here was still looking for some input on things. If you're still looking for some help or have additional questions, please let me know.

 

Thanks,

Jeff

Jeff
Community Specialist
Community Specialist

Hi everyone,

Just one quick final check in here since activity has slowed down. We'll be locking the thread in the next 24 hours, but if you still need help, I would be happy to keep it open. If there's more we can do, just let me know.

Thanks,
Jeff

Smidge69
Community Member

I guess the original question has never really been addressed. Why ia the hysteresis band so wide as to be really uncomfortable, and why cant google make it adjustable as different heating systems will have different cycling issues or none.