Another question about T-stat setbacks

[bolsen]

Once again I find myself questioning whether or not to set-back temperature at night. Although I find the cooler temperature more comfortable at night, I question the energy efficiency of this. Plus, the furnace kicking into high wakes me up every morning. (very irritating)
We have the carrier infinity system, including, the infinity control, 58 MVP080. Daytime setting is 72, nightime, 66.

I realize that I may be saving gas but what about hydro? The furnace needs to run in high for a couple of hours or more to recover. I just received my 2 month hydro bill, and after the warmest January on record, (live in Toronto, Ontario), I used nearly 1000 KWH more than last year! Last year I did'nt set back and furnace never kicked into high.

Everyone always talks about fuel efficiency but what about the hydro?

[mayguy]

I honestly don't know about Carrier's stat, but does it learn and slowly brings the temp up in the home?

When mine recoverys in the morning on the Honywell, it don't bring 2nd stage on all the time.. just once in awhile.

[cem-bsee]

so, bring temp back up in steps, such that 2nd stage not kick in--
experiment!

[thorton]

Originally posted by bolsen
Once again I find myself questioning whether or not to set-back temperature at night. Although I find the cooler temperature more comfortable at night, I question the energy efficiency of this. Plus, the furnace kicking into high wakes me up every morning. (very irritating)
We have the carrier infinity system, including, the infinity control, 58 MVP080. Daytime setting is 72, nightime, 66.

I realize that I may be saving gas but what about hydro? The furnace needs to run in high for a couple of hours or more to recover. I just received my 2 month hydro bill, and after the warmest January on record, (live in Toronto, Ontario), I used nearly 1000 KWH more than last year! Last year I did'nt set back and furnace never kicked into high.

Everyone always talks about fuel efficiency but what about the hydro?

Hi: I'm from Kingston, Ontario! I have a heat pump and a electric variable speed fan coil. I have the Carrier Thermidistat, too! You do not state which thermistat you have but I have to assume you have the "Thermidistat" also. If you do, there is a 4 section DIP switch within the "Thermidistat Control" which must be properly set by the installer. It is easiest to set these 4 swithces before the "Thermidistat Control" is mounted to the wall. Although, it can still be done by opening the front half from the back half to expose these DIP switches. Switch # 3 is the one you need to set to SMART recovery, rather then conventional recovery. This setting will facilitate your set-up temperature in 1 degree increments and keep your furnace from kicking into high, thus keeping the noise down.

I sure hope this helps. If you do indeed have this particular Thermidistat, please feel free to ask me any questions about it as I know it like the back of my hand.

Thorton

[theredbaron]

I wish someone could let me know what is the most efficient way to run t-stat.

Gas co. and elec. co. say no set back is the most efficient because recovery time eats up savings of set back time.

T-stat manufacturers say 10deg set back is the most efficient.

Customers ask me all the time.

Used a temp/humidity recorder at my house over a register. Set t-stat back 4 deg during day and @ night on the first day. 10 deg next day, and no set back the next.

added up run times and found 4 deg was best by 20 min total run time.

10 deg set back ran for 3 1/2 hours to recover

all three days at around 10 deg ODT.

only one test but interesting.

anyone know of any other ways of determining this?

[odcman]

I think you only really do setback for comfort. It's nice to have a cooler room to sleep in, but that's about it.

Setback makes sense from the engineering physics perspective. The cooler the house. the less the differential is between the house and the outdoors, and the less heat you lose. So any time you can take advantage of that, you will save money. But consider when you setback. At night, when you setback, the furnace may not run for a couple of hours before it starts to regulate again in conventional houses. But the whole house and all its mass are cooling off to the cold nightime temps and then you have to heat that all up in the morning before the sun comes up on the furnace hi setting which is usually not as efficient as the low setting. When you set back during the day, you have some solar load and the outside of your building envelope stays warm. It's easier and faster to recover from that on the low setting.

If you have a condensing boiler, the additional heat to recover from setback is costing you money since the AFUE drops at high loads (when the return temps go up).

If you have a super insulated house like we do (21 inches from the stone outside face to the drywall inner face, ICF construction) then we don't even get much of a setback. During the last cold spell (which was December !) we would setback 5 F at night, but the house would never cool off that far from it's 70F daytime temp. 68 is about as low as it went turning off the boiler at 8 pm and back on for the 2 hour recovery at 4 am even at 10F outside temps. So we only setback to sleep better, I doubt there is much energy efficiency.

Of course thermostat manufacturers want you to buy programmable thermostats, so they say setback is better. It is, but it's a small difference. Few % really.

With A/C it makes much more sense. You use a higher temp during the day when it's hot and then you use a lower temp when it cools off at night and the A/C works less hard. With a boiler/furnace it's the opposite. The heating unit has to work really hard to warm you up in the morning while the temps are usually still at their nightime low.

[yossarian]

We have a Carrier MVB furnace and an Infinity zone system, with an Infinity stat. I am pretty sure that the temperature rises in increments during the early morning to go from its setback point (62 or 63) to its morning setting (68).

[deejoe]

The question ;"should I set back or if I do ,how much".?
This can only be absolutely verified by actually keeping track of the burner's "on" times in a 24 hour period without any set back.
Then, with a similar outside temperature 24 hour period,with a setback,keep track of the burners "on" times.
Note; every home has its various differences, including the equipment, duct design,orientation,tightness,etc, etc, so a certain amount of setback may be a real savings for one home but not for another.
I have had the time (retired) and have run these "setback tests periodically several times and have ascertained that my best set back is 4 degrees from midnite to 7 am (7 hrs) I keep the T stat at 72 F all day and then the setback kicks (68) in while asleep.
In my case of keeping track, the burner "on" time was at least 20 minutes less per day.
It does'nt seem like much, but over a month of similar weather it amounts to approx 600 mintes (10 hours)
I have tried going with a 8 degree setback, but found the "make-up" time increased so much as to not realize any significant savings.
Like I said, every case is different. The sure way is to check out the burner's "on" times.
The "key part"(but not difficult in the winter) in the test is to get 2 somewhat similar temperature days,and then you will know for sure, if in your case, if setbacks really save.
Good luck.

[Edited by deejoe on 02-18-2006 at 06:24 PM]

[odcman]

I'd agree. It's really a comfort thing. Assuming you have a 60000 btu furnace, that 600 mins is 586 cu ft of gas, which is about 16.6 cu meters, which is about 8 bucks including all taxes and tranportation charges under my current gas contract. That will buy my morning's TIm Hortons coffee for a week.

[fortressofcomfort]

Low vs high fire operate at roughly the same efficiency. I believe any efficiency in burner output is offset by the increase in blower current.
It may be the blower speed on high is too fast. Shouldn't be waking you up in the morning. How loud is it?

[cn]

1. Similar to leaving your car running all night.
This consumes more gasoline than #2 below.

versus

2. Shut the car at night and restart in the morning to warm it up.
This consumes less (pro), but it is unpleasant in the morning when getting in the car(con).


According to this study, SETTING back thermostat saves you some money (not much but it does save money). It pays for itself in one year.

http://epics.ecn.purdue.edu/hfh/sub%.../heo/index.htm


cn

[Special-K]

Rules of thumb for gas furnace setback.

Heat- only use a slight setback at night, maybe 2-3 degrees. Setback during the daytime hours if you're not at home makes more sense.

A/C- Setback at night will save energy but may not be comfortable. Setback during the day is good but only 5 degrees or so. One thing to consider is how well the A/C will recover, many are sized so marginally they won't recover in time when coming on in the afternoon heat.

Drop some $$$ and get a high end programmable stat or don't bother. Get the units with smart recovery. You tell the stat when you want the home to be at temp and it decides when to come on depending on how much ground it has to make up and it's experiance with the unit it's controlling.

Heat pumps-different animal. Using a setback can actually increase your energy usage from bringing in the strips to recover. Use only a slight setback in heat mode and use a thermostat that is smart enough to attempt recovery on first stage only.

So many factors at play on this issue. Muti-stage equipment can change the rules as can certain types of construction, geo-thermal units, your schedule, etc. No one set of rules will work for all cases.

Clear as mud????

[cdn hvac]

I have the MVB 80-14 with Infinity Controler and am very happy with it. Live in Toronto Ontario.

I tried the set back at night only to be awoken by high stage heating early in the mornings.

I should have got the 80-12 smaller blower would have worked well I just went with that 14 for cooling needs.I did want the 80-20 !! glad I didnt put that in!

I'v read the carrier manual and cannot see any heating blower adjustments only cooling.

The furnace can be set to run on low stage heating only in the advance menu in the Infinity Controler T-stat.

I'v since stopped using the set back and just keep the house at 22C'. Fan on cont' low with humidifier operating with furnace fan. Heating and humidity are Perfect!!

I just cant wait to install my TDB-36 2 speed carrier AC thats sitting in my garage! Common Spring!

Its my understanding that setting the stat back at night only saves you $30 to $50 a year? (Heating)

[Advanced Response]

The size of the blower whether 1400cfm, 1200cfm etc has nothing to do with the high speed heating airflow.. If the second stage airflow is waking you up either you are a light sleeper or the velocity of the airflow for the 2/stage is high due to a undersized ductsystem or the unit is too large for the home or atleast the ducts..Load calculation??? Duct calculation???

A variable speed motor will try to move the correct cfm whether or not the ductwork will carry it, if duct can not carry the cfm it can make the velocity of the air thru the duct to become too high which can lead to objectionable airflow noise...

If you have a infinity control the TESP can be checked to see if it is running too high at that cfm..

This objectional airflow noise can also happen in cooling if the cooling cfm needed is the same or high than the cfm needed for the high speed heating..

As stated the TESP need to be checked and if too high, the ductwork needs to be checked and upgrades are needed to lower the TESP to an acceptable level which will also make the airflow go thru the ducts at the appropriate velocity, this will allow the unit to be as quiet as possible..

Also when the TESP is high the VS will ramp up to a high rpm which will cut any savings advertised with a VS,, this may also lead to premature VS failure..

I hope some of this info may help..
Goodluck
J

P.s. A totally correct TESP would be .5 at the highest cfm the system will operate at.. However, I have found that these unit are still quiet in most instances if the TESP is below .7, anything over that the airflow starts to get alittle noisy..


[Edited by Advanced Response on 02-19-2006 at 12:16 AM]

[odcman]

Originally posted by fortressofcomfort
Low vs high fire operate at roughly the same efficiency. I believe any efficiency in burner output is offset by the increase in blower current.

Yes, that's what I meant. It's not the gas efficiency, but the total furnace effficiency that changes. Power required by a blower motor goes up as the cube of the cfm requirement.

In our Lifebreath air handler, we only ever run the EC motor on low and it uses 60W at 350 cfm during heating season. It uses 1.4kW at times during the cooling season.

So if you have a second stage that blows hard and long, that 1.4kW is going to bite you in the pocket book. If you have a PSC motor, then you aren't getting the low speed savings you'd get from an ECM motor, but it is less. Typically 400 W at 400 cfm comparing Carrier specs with and without ECM motors.

[odcman]

Originally posted by k_fridge
Rules of thumb for gas furnace setback.


Clear as mud????

Actually, really clear. And makes sense too. SImilar reasoning to my earlier post, but you have give some good guidelines for setbacks.

Thanks

[deejoe]

Originally posted by odcman
I'd agree. It's really a comfort thing. Assuming you have a 60000 btu furnace, that 600 mins is 586 cu ft of gas, which is about 16.6 cu meters, which is about 8 bucks including all taxes and tranportation charges under my current gas contract. That will buy my morning's TIm Hortons coffee for a week.

**********************************************
the set back savings for me are; oil fired,70K, .65 nozzle, saves approx = 10 hrs @.65 = 6.5 gals. = 30 ltrs of oil @ .80 = $24. per month.
not too shabby,eh,? and that's with only a 4 degree set-back for only 7 hours per day.

[cdn hvac]

I tested the system using the Infinity Controler checkout.Filter is dynamic 16x25 and is clean. A-coil has not been installed and I have a large by-pass humidifier.
House is 2800 sqft not including fully finished basement.

Plenum 19.5"x 19.5"x46"
1 PTO 16"x20" into 8"x27" Y-Branch , Two Branchs are 8"x16"
Return air drop 14"x23"x75" with round boot.
Ruturn air duct 10"x22" and only 65" long.
2 8"x30" r/a grills main level
2 8"x14" r/a grills second level
1 6" round r/a in bsement
19 heating ducts 5" and 6" including the 5 in the basment.
Carrier MVB-80-14

Low Heat
air flow : 669
inducer rpm : 2140
blower rpm : 492
static press : 0.17

High Heat
air flow : 1331
inducer rpm : 3390
blower rpm : 945
static press : 0.56

How do these numbers look? Any idea why high heat fan or just high fan is loud?

[cem-bsee]

the sp being 3.25x more jumps out!

[Advanced Response]

cd,

You stated your high speed heating is moving 1331 cfm at .56 static sound good but you also stated your airconditioning a-coil has not been installed.. This concerns me.. The a-coil will probably have a pressure drop of .2,, give or take.. This will make your static pressure higher..

It sounds like you need to have your a-coil installed and see what the static pressure will be.. But it will definately be higher.. I hope you have no larger than a 3ton a/c system needed..

Your ductwork needs to be evaluated to see what needs to be changed to make it compliant with noise considerations..

You need a tech familiar with manual D and static pressure measurements.. It could be your return drop is the wrong size or your main extended plenum is too small or transitions are too retrictive,,,etc.. Need to have a tech that can measure return static and supply static separately so it can be determined where your greatest problems are..

It may be possible to remedy your situation with minor ductwork changes or all may need to be corrected if possible.. As stated only a quality hvac tech that is well versed in Manual D will be able to advise you in person after taking measurement..

You are really going to have higher TESP once the A/c coil is installed if I am understanding you correctly that currently you have no a-coil installed in your plenum..

Search some of my previos post to see what your tech needs to check if ductwork changes are needed.. I typed a long enuough reply..

Goodluck
J

Sorry, CDN, no disrespect meant.. I did not realize you are in hvac.. My appologies.. Check out Manual D and Check out NCI... It will help with more understanding or Sign up as a Pro and post any questions in the pro forum and you will get more answers..

[Edited by Advanced Response on 02-19-2006 at 08:10 PM]