night set back

Vermonter_2

Since Honeywell recommended 13 degrees for so long, and you're planning on testing 15 anyway, have you considered testing 20? I think it would be an interesting and valuable data point that will show (unless the tests you're already planning show) if Honeywell's suggestion is the most efficient.

larry_39

Night set back

Two part question? Frist, what is the recomended set back? As I remember it is only 5 degrees bacause of the cost to heat up the area if it gets too low. And is that the same for steam? Example I have a school that is setting their t-stats down to 55 and in the morning heat the school up to 68 is this really cost affective or is it better to have them only set back to 5 degrees? Why?

carol_3

Honeywell's recommendation for years has been a max setback of 13 degrees. Don't know why that odd number, but I suspect the tests were done in Minnesota, so we can be confident that it works in the cold. The question on each application is can the equipment recover from the setback by the "wake" period. A reason for less setback with conventional recovery is that even though the air temp is at setpoint at the beginning of the "wake" period, all the surroundings (walls, floors, furniture) are still pretty much at the max setback temp. So the room will feel cold for awhile even though the air temp is warm.

Mike E_2

I'm working on measuring this currently. The system is a gas 93% forced air furnace in a preschool building that's part of my church. Occupied hours from 6am to 6pm at a temp of 69 degrees. I have hour meters that are counting the length of burner operation.

I already have data for the constant temperature, and the 5 degree setback. I am half way through the 10 degree setback, and then I'll try 15. When I have all the data collected in a couple of weeks I'll post the results.

So far the 5 degee setback uses considerably less gas than the constant temperature.

Michael

Mike E_2

I'll try 20 as well. I am letting the changed settings run for 7 days at a time. Thursdays are when I start a new temperature setting.

Michael

Tombig_2

Setback

Keep us posted inquiring minds want to know.

Weezbo

Our School....

had setback,,,we froze till noon and begged to open the windows by two o'clock...hey sure it Works especially when whoever is doing it doesn't have to Pay for the consequences.

when i was a child of three my mom always told me that criminals never consider the consequences...

so my question is...?

Gordy

variables

How are you taking into account external variables of the structure?

Gordy

Vermonter_2

Sounds more like a bad anticipator than a set-back problem [nt]

Bob Sweet

Im with Gordy

Those variables are what's really going to skew the results. Trying to make comparisons with varying conditions makes it hard to get any concrete numbers.




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Vermonter_2

Could you scale the data somehow?

Maybe compare BTUs vs. Heating Degree Day data to get BTU/HDD? Seems that would make the results more conclusive.

Gordy

recovery time

Weezbo is refering to the recovery time comming out of set back. While the air temperature may satisfiy the t- stat the temperature of all the hardware in the building is lagging this.

Vermonter_2

The cold hardware makes sense to me...

The cold hardware makes sense to me, that's why they had to wait until noon to get comfortable, but I don't see how it would explain the overshoot that makes everyone hot by 2.

Isn't it the anticipator's job to make sure the boiler quits before the room reaches temperature so the hot radiators will carry up to the t-stat setting?

Gordy

HDD

Actually HDD is some what of a comparision, but not concrete. HDD does not take into account solar influence, and wind. The longer you run your settings the more these variables will skew your findings.

You said there was a big difference in your initial set back results. If you ran the experiment for a week, and now intend to use a lower setback in the new week. How will you possibly compare the two results, unless weather conditions are IDENTICAL for the two periods.

It is far harder to find comparible consecutive weeks of weather than days. I applaude your curiosity in doing this...but to get good results in your findings you need to keep the variables as tight as possible. Otherwise conclusions are invalid data.


I would suggest going shorter durations, and looking ahead at the weather for comparble two day test windows.

There has been much discussion about this here, opinions vary. Speaking purley residential dwelling for me I don't bother.


Gordy

Gordy

Radiant

Remember most people here are into hydronics. I won't speak for Weezbo but he probably is refering to the "fly wheel effect" from a radiant concrete slab.

Gordy

Vermonter_2

Still Confused...

So the anticipator doesn't correct for the flywheel effect? I thought that was what it's there for.

Is this a case where the set-back is too great for the anticipator to compensate for? Is there a rule of thumb for set-back settings so this won't happen?

Gordy

anticipator

The fly wheel effect in high mass emitters. Basically once the t-stat gets satisfied the water in the concrete is still hot so it will keep radiating until it reaches equalibrium with its enviroment.

Then maybe the sun starts beating in through the windows about 2 ish when Weezbo is in math class on the south side of the building.

The slab is charged to get up to setpoint but now can't put on the brakes soon enough to compensate for the solar influence, thus over shooting the set point of the t-stat.


Now the day is over everyone goes home the t-stat gets set back again after the slab finally settled into its sweet spot.

The next morning the cycle starts all over again. That is why its not a good idea to set back a radiant concrete slab on a daily bases.

There are controls to minimize this in this day, and age. Outdoor reset, indoor reset, slab sensors are some examples, but when Weezbo was a tot...Well I will let him expand on this.

Gordy

Dave_4

Hydronic heating and night setback, and other things

The more we understand building physics and thermal storage, the better off we'll be. Night setback can work well in a high mass structure with a light mass heating element. It won't work well, or at all, in a low mass structure with a high mass heating element (radiant slabs, cast iron radiators etc.). For example- a wood frame house, no matter how well it's insulated, is still a light mass structure and will not store very much heat in the walls, floors or ceilings. If you have a radiant slab (gypcrete, anything more than 1.5" of conrcrete topping), you have a high mass heating element that will take a long time to cool off, and a long time to heat up again, while the light mass structure gains and loses heat at a much different (faster) rate.

With high mass hydronic heating elements it's more energy efficient to use a more or less constant circulation with variable temperature control system during peak heating periods, and maybe go to an intermittent circulation control during spring/fall conditions.

Anticipators for high mass heating elements need to have a temperature sensor on, or in the heating element to act as a feedback point to the room thermostat to start modulating the heating flow (or heating water temperature) down as the emitter gets up to temperature, before the room overheats. Most simple controls for home heating systems just use a time setting, or a deadband setting to start cutting the heat flow back as the room setpoint is reached. These need a bit of tuning to match the heating system type with the building heat loss rate characteristics.

carol_3

Too much setback costs you in comfort and in fuel for the temp overshoot.
When the heat takes a long time getting up to temperature coming out of setback, you either set back too far and the walls, floors and furniture got too cold to overcome quickly , or there's a window open.:)
When the temperature overshoots the setpoint, it's usually because the equipment has been running long and hard and just like a hard-running racer, can't stop on a dime (or a degree mark).
The anticipator controls cycle rate. That means it determines how many times per hour the equipment has an opportunity to come on. If it's set to match the amp draw of the load (example a Honeywell V8043 zone valve is .32A) you get six cycles per hour. If the anticipator is set at 1.2 times the amp draw, you get three cycles per hour. When the equipment can't reach setpoint in one cycle, it just keeps running.

Gordy

Thats why

> Too much setback costs you in comfort and in

> fuel for the temp overshoot. When the heat

> takes a long time getting up to temperature

> coming out of setback, you either set back too

> far and the walls, floors and furniture got too

> cold to overcome quickly , or there's a window

> open.:) When the temperature overshoots the

> setpoint, it's usually because the equipment has

> been running long and hard and just like a

> hard-running racer, can't stop on a dime (or a

> degree mark). The anticipator controls cycle

> rate. That means it determines how many times

> per hour the equipment has an opportunity to come

> on. If it's set to match the amp draw of the

> load (example a Honeywell V8043 zone valve is

> .32A) you get six cycles per hour. If the

> anticipator is set at 1.2 times the amp draw, you

> get three cycles per hour. When the equipment

> can't reach setpoint in one cycle, it just keeps

> running.

Gordy

Thats why

I don't bother. Our home enviroment is one of where one temp sleeping verses living space satisfies all who live here. No one is gone long enough during the day to let the home cool down 5* then come out of set back to warm back up when everyone returns home.

In my mind steady state efficency applies here some what. Unless of course you won't be in the home for extended periods.

Gordy

Weezbo

Thank you.

set back should be step ramped down..and up.

something needs to take into account the sensible heat gain and the occupancy levels..activity ,i can attest ,has very specific effects upon room environmental conditions also....

room sensors and t stats do not seem entirely sufficient even in this day and age...i tend to think that each day is a new day and as such has sufficient evil therein.

with more computerized control systems becoming available i am seeing in my minds eye a day when there are predictive rather than reactive control strategies....

[Deleted User]

Kinda important to

differentiate building uses, as well as emitters & construction, when discussing temp set back. We have installed control systems in schools, church/school combos, & older office buildings.

Deep set backs of 20-25* for long periods (weekends) are cost effective. Even overnite, when temp seldom reaches max set back, saves over the entire heating season. Keys are controls w/ 7 day multiple programming, & variable ramping of temp drop & rise. We've used Heat-Timer HWR (water)& MPC (steam).

Numbers? Of those we tracked, minus 9-22%. HDD conpensated, not. With large inputs, a little savings goes a long way.

My home set back? 4*. Why? That's what the wife is comfortable with. That is also what we program into our multi-family Tekmars.