Is there a programmable thermostat (for furnace) that allows the hysteresis to be changed from the front panel, using keys and display?
E.g. turn on at 65 degree and turn off at 66 degree
Or, maintain temp at 65 with X number of on/off cycle per hour
I have a 10 year old honeywell programmable thermostat. Although the hysteresis can be changed, it is done with a pair of screws on the back of the unit, and it is not continuously adjustable, just several predefined settings to choose from, and is hard to use (I can only guess what the current setting is since the screws have no indicators).
It worked fine for many years but last year, it started to cycle the furnace too frequently (felt like every few minutes). Using the screws in the back I changed to a less frequent setting, but it is too infrequent. There is no setting in -between.
I need something more flexible and easier to use. Any suggestions?
I just installed a Honeywell RTH7400 in my motorhome. It really works great. I was only using it for AC and Heat Pump. On the last trip, the Heat Pump was cycling too often so I checked the manual. They don't identify it as a cycling setting, but describe its settings for various types of heating systems. They only show a few numbers, however, all numbers from 1 to 9 affect the cycling. I adjusted mine to 5 and it seems perfect.
Hmmm, You are talking in terms of old mechanical 'stat. Digital programmable 'stat such as Honeywell Vision Pro series is VERY versatile. Just pick the right model for your application. I like 8000 series, often over kill but I like them a lot.
If you asked 99.9% of homeowners what hysteresis or deadband is they would give a blank stare. I've never seen a programmable stat that advertises a feature like that.
Hysteresis Vs. Deadband[edit] Deadband is different from hysteresis. With hysteresis there is no dead zon e, and so the output is always in one direction or another.[clarification n eeded] Devices with hysteresis have memory, in that previous system states dictate future states.[clarification needed] Examples of devices with hyste resis are single-mode thermostats and smoke alarms.
Thermostats[edit] Simple (single mode) thermostats exhibit hysteresis. The furnace in the bas ement of a house is adjusted automatically by the thermostat to be switched on as soon as the temperature at the thermostat falls to 18 °C, for exam ple, and the furnace is switched off by the thermostat as soon as the tempe rature at the thermostat reaches 22 °C. There is no temperature at which the house is not being heated or allowed to cool (furnace on or off).
A thermostat which sets a single temperature and automatically controls bot h heating and cooling systems without a mode change exhibits a deadband ran ge around the target temperature. The low end of the deadband is just above the temperature where the heating system turns on. The high end of the dea dband is just below the temperature where the air-conditioning system start s.
Alarms[edit] A smoke detector is also an example of hysteresis, not deadband. The smoke detector at the ceiling of the kitchen starts the alarm as soon as the leve l of smoke reaches a certain starting value, x, then the smoke detector sta ys in the alarm position until the level of smoke has been reduced to level y, after which the smoke detector is reset automatically to "normal". The hysteresis here is x minus y.
References[edit] Johnson, Curtis D. "Process Control Instrumentation Technology", Prentice H all (2002, 7th ed.) "Dead Band Plus Hysteresis Estimation with ValveLink Diagnostics". Product Bulletin. Fisher Controls International. October 2012. Retrieved 18 January 2013. Murty, D.V.S. (2009). Transducers & Instrumentation (2nd ed.). New Delhi: P rentice-Hall of India. pp. 15-16. ISBN 978-8120335691. Retrieved 18 January 2013. Postlethwaite, Bruce. "On-Off Control". Introduction to Process Control. De partment of Chemical and Process Engineering, University of Strathclyde. Re trieved 18 January 2013.
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