Thermostat & Outdoor Reset

Neil_5

Does the two go hand in hand? I have the Honeywell 3500? or maybe the 3200 that know how soon to turn on the heat based on the temp and time input. However, would different outdoor temp days affect the rate of rise sense by the stat as the water temp would change based on outdoor temp? Or pretty much the curve established by the outdoor reset would (for eg. in my case would take 90 mins to go from 68* to 72*) be the same no matter what the temp outdoor is?

Neil

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I THINK I know what you are asking. You are not asking about thermostats in general, but about doing setback and then intelligent recovery with a digital thermostat that has these features.

No, outdoor reset is not compatible with intelligent recovery. The reset curve should be set as low as possible for greatest efficiency, and this means the thermostat should be calling for heat almost all the time. This, in turn, means that if the thermostat goes off for the night, then in the morning the house won't heat back up.

You'll have to leave the themostat at a fixed temperature 24/7. But you'll save due to reset although you won't save due to setback. Don't expect much savings either way; the point of reset is comfort, steady even heating.

Unknown

actually, reset can result in quite substantial savings. we had a client put it in a high temp job, after it had been in operation for awhile, and did nothing else to the system. His fuel use dropped 20%. Of course climate may have contributed to some degree or other factors, but that was a big drop so it obviously helped noticeably.

Certainly enough to justify the cost of a reset controller!

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BillW@honeywell

I agree...

You should consider a FocusPro, our newest digital non-programmable stat. Just set it and leave it be, the reset system will do the rest, especially if it's one of our Aquatrol series. Thanks for asking about our products.

Neil_5

Chuckles:

Thanks for the feedback, I am not looking too much on the "savings" side as much as the comfort side. However I keep my house at 72*, BUT at nights we like to sleep with the room much cooler, 68*. For now I have been turning the Smart stat back at say 930pm and on at 72* at say 730am.

what would be my best approach to accomplish this?

So far for 3 weeks all has been well, except on mild days, I think the smart stat sees the house warmer and dont call for heat till almost 730am and when the heat do come on the water temp is lower due to the mild outdoor temp and thus the house does not meet my 72* by 730am. However on colder days the two (outdoor reset & smart stat) work great together.

Neil

Plumbob

The best way to accomplish this would be with a reset controller that has both indoor and outdoor temperature feedback. Tekmar makes them: look at their more fancy models. The reset controller will do the setback, and use the indoor reading to boost the water temperature temporarily for the recovery stage. You won't need a thermostat; in place of the thermostat you'll have a temperature sensor. And with these controllers you don't have to worry about setting the correct reset curve; it automatically corrcets the water temperature to keep the house warm without going higher than needed.

What we have instead is a TRV in the bedroom; the bedroom stays cool all day and night. That may or may not be what you want.

PS If your reset and smart stat work well together, it is because the reset curve is not set perfectly. The water temp is too high, so recovery is easy, but you are losing the advantages of reset.

Neil_5

Already have Model 256 Tekmar

So changing the outdoor reset is out.

TRV? temp XXX valve? I was thinking, leave the house at 72* all the time and turn off the valve in our room at night and back on in the morning, but thats to manual for a smart house I am have (automated lights/sensors etc)

I had to shift my curve a bit to combat the recovery time in the am, hence I went from ROOM setting of 70 to 77!

Maybe, I just setback from 72 to 70 and see how that works. Also was thinking of plumbing in a valve that I can control with my house automation for the one convector in my room. That way the house can remain at 72* and at say 7am, I turn that valve on thru my house controller .. hm-m--m-m-

I guess in a way I am creating a second zone eh?

Thanks one and all for all the feedback,
Neil

Neil_5

Was Also Thinking .....

That the Model 256 have a unocc setting, which pretty much is a n/o connection etc. So my wondering mind whats to know if this feature is there, the unit therefore goes into its own setback mode (when called for), how does it come out of this setback and boost its way out without a boost feature?

Maybe Jay@Tekmar can shed some light here for me please?

Neil

Plumbob

A TRV is a thermostatic radiator valve, it replaces your regular valve and automatically holds a fixed temp (as long as the desired temp is lower that the temp achievable with the valve wide open). In our case, we have the TRV set low, because we don't mind if the bedroom is cool all day. You can also get programmable TRVs.

A Tekmar 256 (their basic model) will do setback but not boost, so coming out of setback will take forever if the curve is properly set. It's a Catch-22; either it won't come out of setback fast enough, or the reset curve is too high.

Einsiedler_2

un occ

you need a switch on un-occ & com terminals.

this could be a manual switch or a 032 timer (or similar)

EIN

Plumbob

You can just wire a cheap thermostat to it, using the thermostat as a timer---for occupied periods set 90F so the relay is always closed, and for the setback periods set 50F so the relay is always open.

Neil_5

EIN:

That I am familiar with switching the 256 to go into un occ mode. I am wondering if when comming out of the setback (un occ mode) if the 256 will reponsd different that when its turned off via the smart stat.

Zoning is a much better way, however, with my 1955 monoflo system, that can get expensive.

Thanks for all the input, back to the drawing board for me to figure this out.

Have a Happy Thanksgiving One and All,
Neil

Neil_5

Think you have it backwards

Chuckles:

For occ, its open and unocc its contact closure. That is not a problem as I can wired an x10 relay to the timer input of the 256 and have the contact close from 9pm to 7am, except as you said, comming out of setback with a good curve will take forever UNLESS comming out of setback from the 256 itself is different that comming out of setback from a Stat?

Neil_5

What about ......

Attaching a relay to the 256 boiler out as an overide and having that relay connected to a timer (or in my case my home x10 control) and use that as the boost feature for the early AM hours to come out of setback.

In that way, say the boiler temp should be at 150F per the curve, but that is too low of a temp to bring the house out of setback, then with the overide via the relay, the boiler will continue to fire to its aquastat limit and not the limit of 150F set by the 256.

Its my version of the boost feature on my model 256.

Neil

Plumbob

Sweet. A programmable thermostat can be used for this too. (Personally I have found X10 to be only 99% reliable and this is not good enough for critical components like HVAC.)

When you sell, make sure this is documented or removed!

Neil_5

Prog. Stat for Relay

Now that' even cleaner package Say at 630 am you set the prog. stat to say 90* and at 9am at 50*, this would overide the 256 during that time and can be adjusted very easily for the next owner vs. my home control which will go with me.

Ahh the mind was active today, thanks again for your inputs and ideas.

Neil

hydronicsmike

ANSWER

Setback through the 256 Control, using the UnOcc Sw and COM terminals, will cause the Control to switch from a Occ (Day-time) Heating Curve to an UnOcc (Night-time/Setback) Heating Curve. If a Heating Curve is setup correctly, technically, the Control should provide you with the right water temperature to be able to maintain continuous circulation (as long as the Boiler Minimum Setting is not in the way) while maintaining your desired Air Temperature.

Now lets use an examples. If you would like to maintain an Indoor Temperature during the Day of 70°F, based on a given Outdoor Temperatrue, the Control may provide you with a water temperatrue of 160°F (that would be required based on current Outdoor Temp) to your Baseboard, resulting in continuous circulation and steady air temperature. When you do night setback, your desired air temperature may only be 65°F and if you provide a dry-contact closure to the COM and UnOcc terminals, the Control would shift the Heating Curve down to a preset loaction based on the Controls settings, resulting in lowering the water temperature provided to the same baseboard during the same outdoor condition to maybe (lets say...) 150°F. The lower water temperature naturally dropps off the the indoor air temperature.


Now, when we reverse this action and go from UnOcc to Occ (Night-time to Day-time), then the connection bewteen the COM and UnOCC Sw terminals is removed and the Control will go back to the OCC Heating Curve and bring your water back up to 160°F. That 160°F is the right water temperature to maintain your space at 70°F, but to recover a room temp from 65°F back to 70°F, this water temperatrue may not be high enough to give you a "speedy" recovery. To overcome the time delay in recovery, most of the more sophisticated Controls have a Boost feature. The Boost feature causes the Control to shift the Heating Curve above the normal Occ Heating Curve for a limited amount of time resulting in a higher water temperatrue being delivered to your baseboard in order to make up the air temperatre dufference quicker. In this example, this water temperature may now be 170°F instead of the normal 160°F.

Anyways, make a long story short, the 256 doesn't have this Boost feature and therefore I would suggest to use a setback thermostat with "Early or Optimum Start" that simply changes it's setpoint within. Don't even use the UnOcc feature in the 256. A smart thermostat, such as the 500 Series Stats or the nice Honeywell Stats that Bill keeps talking about would be suitable. Then the thermostat can figure out how much sooner to turn on a zone to have it back at your desired setpoint at your desired Occ start time.

The truth is, you can't expect a low cost item to perform high end results.

If you want to do setback efficiently with the speediest recovery while being realistic, you need to use a Control System that considers both Indoor and Outdoor Temperature. As the time goes on and more people get into the radiant, more people will (in my opinion) pay more attention to those things. Comfort (no temperature swings, expansion noises), Energy Consumption and ideal Indoor Air Temperature Control will work best if both, Indoor and Outdoor Temperatures are considered.

hydronicsmike

Very good replies to this already, but here is mine

Setback through the 256 Control, using the UnOcc Sw and COM terminals, will cause the Control to switch from a Occ (Day-time) Heating Curve to an UnOcc (Night-time/Setback) Heating Curve. If a Heating Curve is setup correctly, technically, the Control should provide you with the right water temperature to be able to maintain continuous circulation (as long as the Boiler Minimum Setting is not in the way) while maintaining your desired Air Temperature.

Now lets use an example. If you would like to maintain an Indoor Temperature during the Day of 70°F, based on a given Outdoor Temperature, the Control may provide you with a water temperature of 160°F (that would be required based on current Outdoor Temp) to your Baseboard, resulting in continuous circulation (ideally) and steady air temperature. When you do night setback, your desired air temperature may only be 65°F and if you provide a dry-contact closure to the COM and UnOcc terminals, the Control would shift the Heating Curve down to a preset location based on the Controls settings, resulting in lowering the water temperature provided to the same baseboard during the same outdoor condition to maybe (lets say...) 150°F. The lower water temperature naturally dropps off the the indoor air temperature.


Now, when we reverse this action and go from UnOcc to Occ (Night-time to Day-time), then the connection between the COM and UnOCC Sw terminals is removed and the Control will go back to the OCC Heating Curve and bring your water back up to 160°F. That 160°F is the right water temperature to maintain your space at 70°F, but to recover a room temp from 65°F back to 70°F, this water temperature may not be high enough to give you a "speedy" recovery. To overcome the time delay in recovery, most of the more sophisticated Controls have a Boost feature. The Boost feature causes the Control to shift the Heating Curve above the normal Occ Heating Curve for a limited amount of time resulting in a higher water temperature being delivered to your baseboard in order to make up the air temperature difference quicker. In this example, this water temperature may now be 170°F instead of the normal 160°F.

Anyways, make a long story short, the 256 doesn't have this Boost feature and therefore I would suggest to use a setback thermostat with "Early or Optimum Start" that simply changes it's setpoint within. Don't even use the UnOcc feature in the 256. A smart thermostat, such as the 500 Series Stats or the nice Honeywell Stats that Bill keeps talking about would be suitable. Then the thermostat can figure out how much sooner to turn on a zone to have it back at your desired setpoint at your desired Occ start time.

The truth is, you can't expect a low cost item to perform high end results.

If you want to do setback efficiently with the speediest recovery while being realistic, you need to use a Control System that considers both Indoor and Outdoor Temperature and have the Heating Curve shifted automatically. As the time goes on and more people get into the radiant, more people will (in my opinion) pay more attention to those things. Comfort (no temperature swings, expansion noises), Energy Consumption and ideal Indoor Air Temperature Control will work best if both, Indoor and Outdoor Temperatures are considered. You will hear more and more about what we call “Indoor Temperature Feedback”. Not can it only deal with the Night setback better, it also minimizes the troubles we see in systems with thermal heat gains.

A Thermostat and a Reset Control never communicate and a Reset Control can only operate based on Outdoor Temp, as the Control has no idea whats actually going on in the space. All it knows, is that there is a call for heat (Thermostat contact closes) or there is no call for heat (Thermostat contact opens). It never knows how much or how little you need. Indoor Temperature Feedback is done with RTU Systems that communicate with a Reset Control and the Control always knows what is required where and compensates for any given situation.

Of course, never hesitate to contact tekmar Controls for more info. 250-545-7749, www.tekmarcontrols.com.

Mike

jerry scharf_2

I disagree

There are interactions between the thermostat and the outdoor reset. It's not to say it doesn't work, but you have to be very careful.

I believe it is wrong to set the outdoor reset as close to the heating demand as possible. This serves to reduce the "control authority" of the thermostat. The thermostat should always be the thing that controls the temperature of the room, not the outdoor reset. If there is an uxexpected demand in the room, I consider it a controls failure to not be able to heat the room to desired temperature under any situation above design temperature.

As for savings, you didn't mention either you type of boiler or your type of emitter. You could save a small amount or a large amount depending on these. The savings for setback are more modest than the best case outdoor reset savings, but it's predictable based on the aggregate insulation level of the house. With the best emitter/boiler combination (low temperature radiant and a modulating/condensing boiler) the savings on outdoor reset can be quite good.

For my personal opinion, outdoor reset is better than nothing, but it's certainly not the ideal. Having a control system that integrates the maximum amount of information will produce the best results. If you know that the system is going to come out of setback or it's a windy day and you have more infiltration loss, the boiler temps should go up to cover.

jerry

Brian Macdonald_4

thermostat and reset

Here's how I am managing the same issue in my home with a gravity conversion system. Works great from the comfort end. Can't say what it is doing to efficiency, yet. I am tracking gas use per degree day and hope to decipher that riddle by the end of the month.

The current experiment is a two stage thermostat where the second stage bypasses the reset. Eliminates reset during recovery only (or other higher than usual heat needs, like a really cold windy day.). The second stage wire from the t-stat energizes a relay that takes the outdoor reset out of the loop.

My motivation for setback is the same as yours: nightime comfort. Warning - cooler bedroom temps can cause snuggly wives!

Good Luck.

Brian Macdonald

hydronicsmike

Great way to approach this Brian.

Good thinking.

Neil_5

Good Solution

That's another way to go as well ... well I was playing with my system over the last 5 days, one of things I hate about the AM recovery, lets say you recover from 68 to 72*, the house at 72* does not feel the same if you may, as a house that was at 72* for say the last 4 hrs. vs at 72* the last 45 mins. I prefer the comfort overall.

So my plan so far is to leave the house at 70* during the night and turn off the convector in our room, and with the smart stat, wake up to 72* this way I find the house is cozy and furniture etc are all warm and NOT now comming from 68 to 72* and have that lag.

Now I have to find an automatic means to turn off the bedroom convector at night and on when I wake up .. ahh laziness.

Based on this I now set the curve to be more pratical to the above and not to recover from setback.

Thanks everyone!!

Neil

Neil_5

Second Option

Was also thinking that to keep things simple, why not have a two stage thermostat like OP suggested, and use the second stage to close the unOCC input on the 256, however, set the ROOM higher thus shifting the curve to use a higher water temp and have this input used ONLY to come out of setback?

Mike T., Swampeast MO

"the house at 72* does not feel the same if you may, as a house that was at 72* for say the last 4 hrs. vs at 72* the last 45 mins."

That's because you've mainly only raised the air temperature, not the mean radiant temperature. It takes a lot longer to raise the temperature of the objects in the space.