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thermostat with adjustable hysteresis?



 
 
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  #1  
Old October 15th 08, 02:19 PM posted to alt.home.repair
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Posts: 5
Default thermostat with adjustable hysteresis?

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?


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  #2  
Old October 15th 08, 02:43 PM posted to alt.home.repair
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Posts: 4,505
Default thermostat with adjustable hysteresis?

On Oct 15, 8:19*am, "david" wrote:
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?



Check out the Honeywell VisionPro series. They have lots of
programming options.
  #3  
Old October 15th 08, 02:48 PM posted to alt.home.repair
external usenet poster
 
Posts: 4,938
Default thermostat with adjustable hysteresis?

On Oct 15, 7:43*am, wrote:
On Oct 15, 8:19*am, "david" wrote:





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?


Check out the Honeywell VisionPro series. * They have lots of
programming options.- Hide quoted text -

- Show quoted text -


I have a old cheap Lux that does that, but Honywell is quality and I
bet will offer all you could ever want in features.
  #4  
Old October 15th 08, 03:19 PM posted to alt.home.repair
external usenet poster
 
Posts: 932
Default thermostat with adjustable hysteresis?

david wrote:
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.
  #5  
Old October 15th 08, 05:13 PM posted to alt.home.repair
external usenet poster
 
Posts: 5,144
Default thermostat with adjustable hysteresis?

david wrote:
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?


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.
  #6  
Old October 15th 08, 05:52 PM posted to alt.home.repair
MLD
external usenet poster
 
Posts: 280
Default thermostat with adjustable hysteresis?


"david" wrote in message ...
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?

Not to get picky, but "dead band" is what you really mean, not hysteresis.

  #7  
Old October 16th 08, 03:38 AM posted to alt.home.repair
external usenet poster
 
Posts: 6,163
Default thermostat with adjustable hysteresis?


"david" wrote in message ...
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 need something more flexible and easier to use. Any suggestions?


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.


  #8  
Old October 16th 08, 05:23 PM posted to alt.home.repair
z
external usenet poster
 
Posts: 707
Default thermostat with adjustable hysteresis?

On Oct 15, 9:38*pm, "Ed Pawlowski" wrote:
"david" wrote in ...
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 need something more flexible and easier to use. Any suggestions?


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.


yeah, and that's probably something that the average homeowner
shouldn't be allowed to adjust unless you want to give the customer
service people headaches.
like the OP says, that generally seems to be an internal adjustment,
rather than front panel, since it's something that doesn't usually
need to be adjusted too often.
  #9  
Old April 7th 14, 01:25 AM posted to alt.home.repair
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Posts: 1
Default thermostat with adjustable hysteresis?


Not to get picky, but "dead band" is what you really mean, not hysteresis..


http://en.wikipedia.org/wiki/Deadband

Hysteresis Vs. Deadband[edit]
Deadband is different from hysteresis. With hysteresis there is no dead zone, and so the output is always in one direction or another.[clarification needed] Devices with hysteresis have memory, in that previous system states dictate future states.[clarification needed] Examples of devices with hysteresis are single-mode thermostats and smoke alarms.

Thermostats[edit]
Simple (single mode) thermostats exhibit hysteresis. The furnace in the basement 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 example, and the furnace is switched off by the thermostat as soon as the temperature 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 both heating and cooling systems without a mode change exhibits a deadband range 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 deadband is just below the temperature where the air-conditioning system starts.

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 level of smoke reaches a certain starting value, x, then the smoke detector stays 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 Hall (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: Prentice-Hall of India. pp. 15-16. ISBN 978-8120335691. Retrieved 18 January 2013.
Postlethwaite, Bruce. "On-Off Control". Introduction to Process Control. Department of Chemical and Process Engineering, University of Strathclyde. Retrieved 18 January 2013.
  #10  
Old April 7th 14, 08:13 PM
Senior Member
 
First recorded activity by DIYBanter: Aug 2012
Posts: 2,490
Default

David:

Look on your thermostat set up instructions for something called "heat anticipation" or the "heat anticipator" setting.

Every thermostat, even the old Honeywell mercury bulb thermostats had a heat anticipator built into them. Basically, a heat anticipator is nothing more than a small 24 VAC adjustable electric heater that's positioned right beside the bimetallic spring. It's job is to generate heat whenever the thermostat is calling for heat to fool the thermostat into thinking the room is warmer than it actually is, and thereby shut the heat off earlier than it otherwise would.

The reason you need a heat anticipator is many. The most obvious one is that normally the thermostat is centrally located in the heated space, but the radiators or electric heaters are located around the perimeter of the room, usually under windows. So, by the time the temperature in the center of the heated space reaches the thermostat's set temperature, the temperature everywhere else is higher than the set temperature. To avoid this, the thermostat's heat anticipator heats the bimetallic spring to shut the call for heat off earlier than it otherwise would, thereby preventing that overshoot.

Also, different heating systems work differently. With electric heat, as soon as you shut off the power to the electric heaters, that's the end of the heat. With hot water heating, however, once those cast iron baseboard radiators get filled with water at 190 deg. F, they're going to keep convecting warm air into the room for a long time after the thermostat stops calling for heat. Ditto for steam heat; once you get those heavy cast iron radiators hot, they keep convecting warm air into the room regardless of what the thermostat is doing. So, different kinds of heating systems need different heat anticipator settings to minimize the amount of temperature overshoot and thereby provide comfortable heating.

Now, on a standard round Honeywell mercury switch thermostat, the heat anticipator is adjusted by sliding a pointer one way or the other. It's very likely that all that's wrong with your existing thermostat is that it's heat anticipator setting has been turned up way too high so that the anticipator produces way too much heat and thereby shuts the call for heat way too early. Then, if the room is cold, the thermostat cools down quickly and very soon starts calling for heat again, only to have the heat anticipator warm up the bimetallic spring in a minute or two, causing the thermostat to shut off the furnace or boiler again. That is, rapid cycling as you're experiencing.

It is the heat anticipator setting of the thermostat that determines how frequently your furnace or boiler cycles on and off. Too high a heat anticipator setting will result in the anticipator producing too much heat and the resulting rapid cycling of the heating system with the heating system undershooting the thermostat set temperature each time. Too low a heat anticipator setting results in the furnace or boiler running for longer each time it fires and the heating system overshooting the thermostat set temperature.

Too many people have difficulty with thermostats because they don't understand the function of the anticipator. They're constantly turning the heat up and down on the thermostat when really they just need to adjust the anticipator.

I'd just download the information that came with your old thermostat off the manufacturer's web site and find out where the heat anticipator is and how to adjust it. Get on the manufacturer's web site, find out their 1-800 tech support phone number and those guys should be able to guide you to where you can find the original literature that came with your thermostat.

Last edited by nestork : April 7th 14 at 08:21 PM.
 




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