SBS - The Best Value in QMS software

Does a Lower Thermostat Setting really save Energy?

J
#1
Happy New Year everyone.....
I've had this thought bouncing around in my brain (retirement does that sometimes) and since it's kind of scientific in nature, I thought I'd toss it out here just for fun....

We all have heard the idea that turning down your thermostat is suppose to save energy. I will certainly agree that it can early in the heating season and as well as late in the season as the temperature changes - But I'm talking about in the the Dead of winter....When the average temperature difference between inside and outside is say 40 degrees F or more.

At this time, it seems to me that setting the thermostat on 78 would be no different than setting on 70. The house will lose heat at the same rate and the furnace kick off and on at approximately the same intervals. So the only real way to save energy in these months is to better insulate.

Now - the only thing that makes me wonder if I'm thinking right is this....Will a house lose heat faster or slower depending on the temperature differential inside to outside...(I'm sure it does)...but does the principle of "diminishing returns" kick on this wherein once the differential reaches a certain point the rate of heat loss will be fairly constant?

So - am I thinking right? Am I missing something? Am I still better off grabbing a sweater or not???

Peace
James
 
Elsmar Forum Sponsor

Michael_M

Trusted Information Resource
#2
This is a good question, where I live, it is averaging about 10?(f) at night and I have a programmable thermostat so at night (while sleeping) I have the temperature set to 65 and about 1 1/2 hours before the wife wakes up it 'should' move up to about 73. It seems that the interior temperature stays at about 69ish.

I am now going to set the thermostat to about 70 at night and hope that it moves up to about 73-74 when she gets up.
 

Miner

Forum Moderator
Staff member
Admin
#4
I am not an expert, but did well in Thermodynamics class. The rate of heat transfer is proportional to the difference in temperature between the inside and outside (as well as the thermal conductivity constant of the material and thickness of material), so it does make a difference.

How big of a difference will depend a lot on your insulation, air leakage, time spent at a lower temperature, days of sun and many more items. Here is a brief article at energy.gov.
 

Marc

Fully vaccinated are you?
Staff member
Admin
#5
<snip> How big of a difference will depend a lot on your insulation, air leakage, time spent at a lower temperature, days of sun and many more items. Here is a brief article at energy.gov.
Good summary, Miner. It's pretty much as I remember from physics in college years ago.

Having done the major refurb stuff on this house, I am somewhat "literate" with regard to the factors you mentioned. A few years ago I did 20" of insulation in the attic, replaced all windows with triple pane, gas filled windows, same with doors with windows and patio doors. Attached garage so I replaced the back door in it and the garage door its self with insulated steel ones. All external walls are insulated, but the house was built in 1967 so it's not nearly as well as most homes today are, but I can't do anything about wall insulation other than as I mention below I did put 3/4" pine on walls and ceiling. I'm not sure what the R rating for 3/4" pine is but I can tell the difference.

The key for homes is insulation - But - I can tell there is a significant difference if it is very windy outside so I know this house has a lot of gaps where the walls meet the attic. I did have cellulose blown in insulation done in the attic so that has somewhat been attenuated. It used to be that I could put my hand on any electrical outlet and feel cold air coming in if it was windy at all outside. Not so since I had the "blown in" insulation in the attic.

Another big factor is having done the living room and the hallways in 3/4" pine. It's about 15 F outside here and I don't have any heat turned on. I have baseboard heater in each room and each has it's own programmable thermostat. All of them are set to 50 F. The electronics I have as a whole run about 1500 watts (yup - I measure everything with a watt meter) and the master bathroom floor is heated but I don't really know how many watts it uses. In the last few years it has been rare that I have had to use any of the baseboard heaters. My biggest "problem" is in the summer when the AC has to pump out the heat from the electronics. But I put in an 18 SEER 30K BTU high efficiency ductless AC unit a few years back and that dropped my summer electric bills by about 1/2.

I do have a fireplace which is in the middle of the house. It used to be a fire would make a big difference - I would get pretty cold in here. But since I did the refurb I know I'll have to open the patio door because it will quickly warm up to 80 to 85 F inside, so fires these days are for the "fun" of having a fire.

These days this house pretty much stays at about 75 degrees in the living room but gets down to 67 in the back bedroom when it's in the teens or below and is windy outside.

@JRKH - If you're setting the thermostat low at night and the place doesn't warm up quickly in the morning you're probably looking at poor insulation and/or a heating unit (especially heat pumps) which just doesn't have the power/output to make the change quickly. But, the main aspect in the winter is the heat output. Before I did the rehab it would get pretty cold in here, but I could turn on the baseboard heater in any given room and within 15 minutes the air it that room was at the set temperature.

NOTE: My house is an 1100 sq ft single story on a concrete slab so it's pretty cheap to operate anyway.

I'd almost bet you have a heat pump with a small electric coil "booster" for when it goes below the lowest outdoor temperature at which the heat pump will operate.
 
Last edited by a moderator:

BradM

Staff member
Admin
#6
Here is a pretty reasonable explanation:

http://energy.gov/energysaver/articles/thermostats-and-control-systems

A common misconception associated with thermostats is that a furnace works harder than normal to warm the space back to a comfortable temperature after the thermostat has been set back, resulting in little or no savings. In fact, as soon as your house drops below its normal temperature, it will lose energy to the surrounding environment more slowly. The lower the interior temperature, the slower the heat loss. So the longer your house remains at the lower temperature, the more energy you save, because your house has lost less energy than it would have at the higher temperature. The same concept applies to raising your thermostat setting in the summer -- a higher interior temperature will slow the flow of heat into your house, saving energy on air conditioning.
 

Wes Bucey

Prophet of Profit
#7
FWIW:Building managers project energy usage based on "degree days" (the difference between outside temperature and the temperature to be maintained inside (regardless of heating or cooling.)) In some of the high rises downtown, the spread between sunny side of a building and shady side requires zoned HVAC. I agree with Marc: wind makes a difference in "vacuum" effect of sucking heated/cooled air out of poorly sealed buildings, but can actually blow away heated air from solar radiation on outside building surfaces. We may not be as well insulated as Marc's, but a new roof and thermal windows resulted in a significant drop in HVAC costs over the last two years, mostly by reducing leakage of heated air (snow takes a lot longer time to melt off the roof, adding a further insulating blanket.)
 

Marc

Fully vaccinated are you?
Staff member
Admin
#8
Here is a pretty reasonable explanation: <snip>
Thing is, everything in the house has mass. As the house cools down inside the walls and ceiling are the first to transfer heat out. Objects in the house act as heat sinks which release heat as the air in the house and the walls and ceiling cool.

So - When you wake up and turn the temperature up (or the thermostat does so) the air heats first. If you have a powerful heat source this can happen quickly. As it does the air starts to transfer heat to the objects inside the house that lost heat as the house cooled which typically takes a while so the heat source has to work "harder" to get everything inside up to the same temperature.

Back when I used to travel I would set the thermostats at 50 F when I left. I would usually be gone a week to 3 weeks. When I came back everything in the house had equalized to about 50 F so to get it back to "normal" (~70 to 75 F) took quite a while. I had a kerosene heater at the time which I would light when I got home and burn for a few hours because it was very fast at heating the air and back then kerosene was cheap. Depending on the outside temperature it took a few hours before objects inside the house would equalize with the air temperature. The baseboard heaters put out a lot of heat but adding that kerosene heater made a big difference until everything inside absorbed heat to the point where it was near equilibrium with the air.

The opposite was true in the summer, obviously. I would set the AC to 85 F when I left. When I got home it took several hours for the AC to pump out the heat which had built up in the objects in the house. Actually it took longer because the slab would hold and radiate heat until it reached equilibrium, but that part wasn't as noticeable.

As Minor pointed out: "The rate of heat transfer is proportional to the difference in temperature between the inside and outside (as well as the thermal conductivity constant of the material and thickness of material)" which applies mostly to the walls, floor and ceiling.

It is true that the rate of heat transfer decreases as inside and outside temperatures come closer together and vice versa. When they are at equilibrium there is no heat transfer.

A number of years back I came to the conclusion that for short periods of time (<24 hours) it makes the most sense to keep the inside of the house at a set temperature. I definitely could be (and probably are) wrong, but that is my thought.

When I did the AC here the AC people recommended a 20K BTU (~2 tons) unit. I went for a 30K because I remembered the days when I would get home and it would take 2 to 3 hours for the house to "cool down" inside. I wanted an over sized unit so that within an hour the house would be comfortable. That is also why I chose a ductless AC system - No ducts and surrounding insulation to have to cool down (the duct work here is in the attic, but I sealed all the ducts off when I had this unit put in).

Anyway - These are just some of my thoughts. I am sure some will disagree and they may be right. I know a lot of people told me baseboard heat was "inefficient", but taken as a whole - No moving parts, for example - Baseboard heat it quite efficient (especially in contrast to a heat pump). :2cents:
 

BradM

Staff member
Admin
#9
Good points, Marc. :agree1:

House heating/ cooling is opposite to industrial furnaces and such. In the industrial setting, I am interested more in the heating of the mass in the furnace; not the air surrounding it. Yes the air temperature matters as it transfers the heat. But the monitoring/ recording probe needs to be intimate/close to the product being heated.

With house heating, I am monitoring (and are interested in) the air temperature. I want the room air to be 76?F, and are largely unconcerned whether the entertainment cabinet is 76?F. But most definitely the temperature of the mass in the room (furniture, walls, etc.) have to be heated also, as they absorb the heat.

Like the link suggests one will use less energy bringing the "cold" room up to temperature that leaving it on all day. Because leaving it on all day, it will have lost multiple "packets" of energy to be replaced. Where if it is left off all day then turned on, it only has one "packet" of energy to replace.

I would think if the unit is undersized, it's going to run almost constantly just to keep up during the day. So if it gets turned off during the day, it will never obtain a desired temperature in the evening.

I'm pretty sure "packets" is not a technical, engineering word. :tg:
 

Statistical Steven

Statistician
Staff member
Super Moderator
#10
Also remember that due to factors such as insulation, the true delta between the outside and inside temperature is much smaller than theoretical. For example, if you shut off the furnance on a very cold day, the temperature inside the house does not equal the temperature outside. I personally shut off the thermostat before I leave to work in the morning and bring the temperature back up till bed time, then lower it to sleep. Not sure if I am saving a penny or a dollar though :)
 
Thread starter Similar threads Forum Replies Date
S Why does Cpm only have a lower bound from Minitab? Using Minitab Software 7
M Does the scope of ISO 9001:2015 applies to tenders, pricing and sales department of a medical devices distributor? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 3
K Why does load cell supplier requires force verification General Measurement Device and Calibration Topics 3
M Does C=0 strictly mean 1 bad, all bad, all the time? ISO 13485:2016 - Medical Device Quality Management Systems 6
C Does a medical device active (zinc oxide) needs BPR registration in EU? Other ISO and International Standards and European Regulations 1
D Does Risk Management apply to re-labeler (MDR) EU Medical Device Regulations 1
Ed Panek Does this FDA Requirement Apply to international (not USA) distributors for USA based manufacturing companies? 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 0
S Does anyone have a checklist to prepare for ISO 13485, Stage I audit? ISO 13485:2016 - Medical Device Quality Management Systems 1
S Does a refurbished product required a new UDI? US Food and Drug Administration (FDA) 3
D Change to labelling - does it require a new 510(k)? US Food and Drug Administration (FDA) 5
M What does "constantly" mean ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 13
N Does anyone use SGS for ISO 13485 / CE certification Registrars and Notified Bodies 0
G Does FDA allows remote approvals of quality documentation. Is there any specific guidance on signing any quality records remotely? Document Control Systems, Procedures, Forms and Templates 1
B Does FDA Registration QSR need to cover non-medical devices for contract repackager? US Food and Drug Administration (FDA) 1
lanley liao Does all of the suppliers need to integrated into the supplier list qualified of the company? Oil and Gas Industry Standards and Regulations 2
0 To which part of 13485 does this refer? ISO 13485:2016 - Medical Device Quality Management Systems 3
A Medical Device Contract Manufacturer - Does the CM need to register with FDA? 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 3
J Records Control - Does each individual record need to be numbered? Records and Data - Quality, Legal and Other Evidence 2
lanley liao Does the customer`s trademark belong to customer-supplied property? Oil and Gas Industry Standards and Regulations 2
H How does a gas turbine work on diesel fuel? Oil and Gas Industry Standards and Regulations 12
G What does performance specification include? US Food and Drug Administration (FDA) 1
W Where does a coatings and paint company fall in IATF? IATF 16949 - Automotive Quality Systems Standard 5
A How much does a complete biocompatibility test package cost? Other ISO and International Standards and European Regulations 1
B Does anybody know how to get older versions of Minitab to work in Windows 10? Quality Tools, Improvement and Analysis 9
M Does the ISO 9001:2015 standard require a disaster recovery plan or emergency response plan ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 16
C Does an accessory need an IFU if it use is discussed in the Parent device IFU? 21 CFR Part 820 - US FDA Quality System Regulations (QSR) 5
S How long does it take to register a product with MHRA? UK Medical Device Regulations 8
M Quality Manual - Where does Revision History Section go? Document Control Systems, Procedures, Forms and Templates 8
U Does *anyone* know a lab that will test to EN 455-4 Medical Gloves shelf life determination? EU Medical Device Regulations 1
A Brexit When does the UK responsible person need to be in place? UK Medical Device Regulations 10
M How does IEC-60601-1 apply to a non-medical device in the patient vicinity? IEC 60601 - Medical Electrical Equipment Safety Standards Series 1
N Does anyone have experience of GB/T 34986-2017? China Medical Device Regulations 1
Z Does anyone have experience with EN ISO 17664 ? IEC 62366 - Medical Device Usability Engineering 9
F Does anyone have an ESD quality/cooler talk to share? Training - Internal, External, Online and Distance Learning 4
A What does this line from MDCG 2020-3 (MDR art. 120 substantial change) mean to you? EU Medical Device Regulations 4
D Change Approval Requirements - Does every change need formal customer approval? Design and Development of Products and Processes 17
T What does AS9100 mean when it says you must establish a process to do X? AS9100, IAQG, NADCAP and Aerospace related Standards and Requirements 24
L Does a backdate form format can be changed if wrong revision is used? Document Control Systems, Procedures, Forms and Templates 8
B General Motors and Honda Alliance - What does this mean to suppliers? IATF 16949 - Automotive Quality Systems Standard 3
C ISO 13485 :2016 - CAPA - Does every CAPA need to be checked by regulations? ISO 13485:2016 - Medical Device Quality Management Systems 9
A Does ISO 9001:2015 cover all the requirements of ISO 10012:2003? ISO 9000, ISO 9001, and ISO 9004 Quality Management Systems Standards 6
N FDA UDI - Label vs. Labeling - Does the insert need to include UDI? Other US Medical Device Regulations 1
A Does anyone have a checklist of API Spec 650 13th Edition? Oil and Gas Industry Standards and Regulations 0
D Does Manufacture can submit CE mark application under MDD with NB for his New product after May 2020? EU Medical Device Regulations 3
A What does this sentence "this symbol shall be used in the orientation shown" mean in ISO 780:2015? Other Medical Device Related Standards 4
L Turkish Requirements - Does the Software need to be translated? CE Marking (Conformité Européene) / CB Scheme 2
R Where does IATF 16949 address Process mapping? IATF 16949 - Automotive Quality Systems Standard 3
J Does Pakistan Medical Device Import License allows parallel import? Other Medical Device Regulations World-Wide 0
BeaBea Interesting Discussion Where Does Marketing/ Advertisement of Products fit in to ISO 9001? Process Maps, Process Mapping and Turtle Diagrams 39
P Does anyone have a API Q1 Documentation Package? Quality Management System (QMS) Manuals 1

Similar threads

Top Bottom