Looking for an adjustable dead time thermostat

[bobs409]

HELP!@@

I'm on day 3 now searching for a thermostat that will do what I want.

I would like one with a way to lengthen the dead time setting. Most of these out of the box are set to about 2-3 degree span so if I set it to 60, it will heat to 60, shut off and then kick back on again when it hits 57 or 58.

I'd like to set that longer to about 5 or more degrees. I've searched online so much my eyes feel like they are about to fall out!

I better explain why I want this. Overnight hours, I'd like to set to about 55 but I don't want the heater trying to maintain a constant 55. I'd prefer it heats to 55 and shuts off until temps drop to at least 50 or even more. That would make the heater run longer but fewer stops/starts.

It was suggested that a stat with an auto heat/cool feature might work for this. I'm a bit confused on that however. Would such a feature do what I am asking??


Thanks for any help,


Bob

 

[lilredex]

You are looking for a model with an adjustable "differential" like those old Honeywell, round ones have. You open the cover and there was a small lever to move it to a longer or shorter cycle.

http://inspectapedia.com/heat/Heat_Anticipator_Adust.htm

 

[pseudorealityx]

Why not just an programmable thermostat and have it maintain 60 during the day, and 50 at night?

 

[bobs409]

I'm trying to avoid the heater kicking on/off a lot. No need to have it kicking on every 2-3 degree in drop especially at night when I'm not in there. This will be easier on the equipment and possilby less fuel use.

Hoping to find a digital type that has this setting. I think they make such a thing but not easy to find it seems.

 

[Rockhead261]

Ecobee.

 

[LS6 Tommy]

I'm trying to avoid the heater kicking on/off a lot. No need to have it kicking on every 2-3 degree in drop especially at night when I'm not in there. This will be easier on the equipment and possilby less fuel use.

Hoping to find a digital type that has this setting. I think they make such a thing but not easy to find it seems.

Your existing T-stat is already programmed for the most efficient way to set back at night. You'll burn more fuel trying to catch up than you save by being "off" longer. No need to reinvent the wheel...

Tommy

 

[pseudorealityx]

I'm trying to avoid the heater kicking on/off a lot. No need to have it kicking on every 2-3 degree in drop especially at night when I'm not in there. This will be easier on the equipment and possilby less fuel use.

Hoping to find a digital type that has this setting. I think they make such a thing but not easy to find it seems.

That's what lowering your set point does automatically. As you decrease the delta T, the space temperature falls slower and slower as heat transfer are dependent on delta T.

HVAC equipment is designed to go through on/off cycles. As long as it's not excessive, you're fine. This stuff lasts decades with normal run times.

 

[bobs409]

Thanks Jeremy! That might just do the trick.

 

[Highbeam]

That dead time or differential you are referring to is called "hysteresis". You need a stat with adjustable hysteresis. Use that as a search term.

I could understand why you want what you want. Less cycles is easier on equipment than less, longer, cycles.

 

[404]

Your existing T-stat is already programmed for the most efficient way to set back at night. You'll burn more fuel trying to catch up than you save by being "off" longer. No need to reinvent the wheel...

Tommy

Yes.

Just like leaving light bulbs on all the time saves energy over turning them off and then having to heat up the filament again when they are turned back on...

Oh.. Wait...

Regards,
404

 

[dowmace]

Yes.

Just like leaving light bulbs on all the time saves energy over turning them off and then having to heat up the filament again when they are turned back on...

Oh.. Wait...

Regards,
404

That's not even remotely close of a comparison.

Cooling or heating has to raise or lower the temperature of a space. A lightbulb instantly lights the room.

 

[sourdough]

That's not even remotely close of a comparison.

Cooling or heating has to raise or lower the temperature of a space. A lightbulb instantly lights the room.

+1 unless you are referring to CFLs.

But that's a different forum, maybe.

 

[JCByrd24]

Set back thermostats save money and what the OP is trying to do will as well. It is completely a myth and physically (like physics) impossible that you will use more fuel "trying to catch up". First, heat transfer is directly related to delta T, the temperature difference between the indoors and outdoors. Thus, by lowering the t-stat at night, you lower the temperature differential and heat transfer. In the morning when the t-stat kicks back on yes you will have to raise the temp of the space and contents, but in doing so you will likely run the heat source at it's most efficient, which is constantly running. Not to mention, when the thermostat first goes down at night you won't use any fuel for a while. Almost all heaters have standby losses when not running or at the very least take warming up themselves. Large heaters have more of both of these, which is why if you google it you will find the importance of getting the right size heater to avoid short cycling and efficiency loss. This is why modulating and cold start boilers exist, and also why electric heat is 100% efficient (no connection to outside the box for heat to escape through). There is only one reason not to set back and that is if the size of the system and outside temperature mean it doesn't recover quickly enough for the occupants to be comfortable in a timely manner.This is a possibility if the system is sized properly, so the balance must be found and setbacks may not be able to be as extreme during extreme weather.

The case of a larger swing or hysteresis is less cut and dried if the temperature differential is assumed to be the same on average. However, given an oversized heater providing the same amount of BTU/hr, it will both be on stand by more and cycling more than a more appropriately sized heater and therefore have more loss in either standby loss (boilers hot water loosing to chimney) or warming up (Big Maxx style heater warming up before fan kicks on). In the case of the OP I believe he's taking about a Big Maxx, so any startup from cold iron that is eliminated is money saved.

 

[Charles (in GA)]

That dead time or differential you are referring to is called "hysteresis". You need a stat with adjustable hysteresis. Use that as a search term.

I could understand why you want what you want. Less cycles is easier on equipment than less, longer, cycles.

The round Honeywell thermostat calls this an anticipator, thats the little lever you slide.

I think you will find that a temp change of two or three degrees in a house takes a long time. Digital thermostats have very tight on/off differentials, One White Rodgers digital I tried has only about 0.7° with a jumper that you can cut to extend this to slightly over one degree. Really good digitals seem to have ways of limiting the number of times per hour the unit cycles. They use a fixed on/off spread and this cycle limiter to achieve what the anticipator does.

Honeywell makes(ed?) a round digital, model T8775C the 1005 being a heat/cool single cycle, and the 1009 being a oil and gas heat only. They have several DIP switches on the back to set the max number of cycles per hour at 3-5-7-9 or something like that. They are easily found on Ebay.

I finally bought a round Honeywell mercury thermostat. I have it set on a spread of about 2½°F and for the shop oil heater, this works great. The house has a heat pump system, I don't really care how often it cycles, I just want a constant temp. I reset it in the spring and again in the fall, otherwise never touch it. I have a old rectangular Honeywell/Temp-A-Trol mercury thermostat.

Charles

 

[404]

That's not even remotely close of a comparison.

Cooling or heating has to raise or lower the temperature of a space. A lightbulb instantly lights the room.

The principle is the same but the time scale is different.. plus I was being a smart ***.

Let's agree that the closer the outside temp and the inside house temps are to each other the less heat the house loses. And that the less heat it loses the less energy it takes to keep it at the chosen temp.

Let's say the outside temp is 49 degrees.
Now over a period of a week, have the house temp up to 70 for one day, and set it back to 50 for the other 6 days. The heating system uses more heat for only the one day, the other 6 days much less. This is a really long time scale, opposite of the light bulb example.

Regards,
404

 

[LS6 Tommy]

The round Honeywell thermostat calls this an anticipator, thats the little lever you slide.

Charles

Heat anticipators adjust the heat cycle to eliminate big swings in room temp, like overshoot. They're not meant to be used as a deadband adjustment.

Tommy

 

[burhead]

Pexsupply.com sells a control called a electronic temp control. It could be used like a stat. It has a differential setting of 1-30 and it comes in several voltage configurations 24,120 and 220. Very simple device. Give it voltage and then there is a set of NO/NC contacts. I am using these on my radiant floor as I was having problems with it short cycling. They are accurate , simple and inexpensive.

 

[bazar01]

HELP!@@

I'm on day 3 now searching for a thermostat that will do what I want.

I would like one with a way to lengthen the dead time setting. Most of these out of the box are set to about 2-3 degree span so if I set it to 60, it will heat to 60, shut off and then kick back on again when it hits 57 or 58.

I'd like to set that longer to about 5 or more degrees. I've searched online so much my eyes feel like they are about to fall out!

I better explain why I want this. Overnight hours, I'd like to set to about 55 but I don't want the heater trying to maintain a constant 55. I'd prefer it heats to 55 and shuts off until temps drop to at least 50 or even more. That would make the heater run longer but fewer stops/starts.

It was suggested that a stat with an auto heat/cool feature might work for this. I'm a bit confused on that however. Would such a feature do what I am asking??


Thanks for any help,


Bob

The only way to get longer run times is to properly size a single stage unit. The second other way to get longer run times is to get a properly sized two stage system. If first stage of a 2-stage unit runs at 60% capacity, rather than 100% all the time with a single stage unit, then it will achieve longer run time.
The third, which is the most efficient is a variable speed compressor unit in the case of a heat pump or variable burner control to achieve low fire conditions on low demand situations.

 

[larry_g]

http://www.instrumart.com/products/29942/watlow-ez-zone-pm-express-controller

Have you considered a temperature controller vs a thermostat? Most of these have programmable setpoints for on and off.

lg
no neat sig line

 

[rlitman]

That dead time or differential you are referring to is called "hysteresis". You need a stat with adjustable hysteresis. Use that as a search term.

I could understand why you want what you want. Less cycles is easier on equipment than less, longer, cycles.

This.

My digital Honeywell thermostats have a programming mode (hidden deep in the manual) where you can change this value with a cryptic set of button presses.

 

[sourdough]

Heat anticipators adjust the heat cycle to eliminate big swings in room temp, like overshoot. They're not meant to be used as a deadband adjustment.

Tommy

True dat, but it is a matter of semantics explaining the difference.

I have a digital t-stat operating a Coleman downdraft modular home propane furnace. We have been experiencing much colder than normal temps (16* lows and 40* highs) for the past week. Not to take away from the majority of states whom have had record low temps in the same period.

Our normal protocol is to set the t-stat from 68* day setpoint to 65* night setpoint when my wife finishes watching TV around 11 PM (I go to bed much earlier because sitcoms hold no interest for me).

I do not like setting the time programming on the digital t-stat for certain hours/temps because it never coincides with the real-world temps outdoors.

I normally awake around 4 AM and sleep lightly from 2 AM onward. I am aware if the furnace kicks on during this period and it usually does not unless we are in the mid-teens or below. It's a 2100' ranch house and when I adjust the t-stat upon awakening the furnace is able to raise the house temp from 65* to 68* in little over an hour, and the t-stat shows a 69* temp upon shutoff.

I have been a fan of night setback for decades while working for a mega-million-square-footage hospital as a HVAC/Building Controls tech. It might make sense there, but for domestic purposes I find it not the case. If one has a dead-band of 2* on the t-stat it works well as the forced-air plenum has sufficient time to heat before the blower comes on and I have altered the time for the blower to shut off to 180 seconds (factory set at 120 seconds) after the burner stops, robbing it of all the possible heat I can get.

 

[LS6 Tommy]

I get your scenario, Sourdough. I was only explaining the "normal" use of the anticipator.

Tommy

 

[bobs409]

Ok, I'm stumped! I bought one of the on make timers that Jeremy mentioned and it didn't seem to work so I sent it back thinking it was just defective. Just got another one and it is doing the same thing. Both were sending full power right through all the time, no delay at all in any position of the dial.

I even tested it with a volt meter and it was sending out the exact voltage I put in.

Now I can't believe I'm asking this but am I wiring it wrong? lol I put this in between the white wire that sends power from the stat. There are only 2 terminals.

When will this hell be over!

 

[bobs409]

Also, anyone that has a digital thermostat with an adjustable dead time, please share the make/model so perhaps I can solve my situation that way.

 

[sourdough]

Also, anyone that has a digital thermostat with an adjustable dead time, please share the make/model so perhaps I can solve my situation that way.

Mine is this:

http://www.amazon.com/dp/B003N5HG4C/?tag=atomicindus08-20

It is seven years old and has an adjustable deadband 1*-3*. The default setting is 2* IIRC.

IMO, it is spendy even by Amazon prices.

I have purchased a much cheaper/different brand (Honeywell) unit from Home Depot that will work just as well for my 1* deadband requirements if this unit fails. It has worked well so far.

Jim

 

[PT Doc]

My Honeywell has programmability for the change in temp that I want before have system kicks on.

 

[bobs409]

Thanks Jeremy, I'll have to check this out and get back to you with the readings.

 

[bobs409]

Success! I decided to just snip that wire, plug it back in and skip the ohm meter. I set it for 2 minutes and sure enough, it took 2 minutes before the heater kicked on! I guess the Big Max heaters are sensitive as you mentioned.

This is going to be a great way to "fine tune" my heater.

Many thanks Jeremy, this is just what I needed.