# Learning Thermostat

Just installed my first Nest learning thermostat.  Really easy and affordable.  Check it out and let me know what you think:

http://www.nest.com/

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### Replies to This Discussion

I'd go with Michael Blasnik on this one. Tedkidd you strike me as sincere and knowledgeable on some aspects of HVAC but I sense that your understanding of energy is solely based on your experience and that you have no confidence in the laws of physics.  Frankly, that scares me.  Good auditors have field experience AND a solid understanding of the laws of physics.  You seem reliant on experience only.

Quoting from your response to Michael:

"Because setback saves energy in a tested home does not mean that energy is saved because of reduced delta losses through surfaces.  I assert this simplistic conclusion is seriously flawed. “

Your statement challenges not only Michael Blasnik but the equations that underlie your TREAT modeling software.  For your reference the equation for heat transfer across a surface is:

Heat loss by conduction (btu/hr.) = surface area (in sf) x delta T (between inside and outside in F) x (U-value)

Try this equation a few times with different temperatures inside and you will see that the closer to the indoor temp is to the outside temp the less heat is lost.  This is what a setback does, it lowers the indoor temp to be closer to the outside temp and energy is saved regardless of what the heating plant is.

“You just implied that shell retrofits are extraordinarily expensive and out of reach for most people.  Do you really want to perpetuate the myth that energy efficiency retrofits are extraordinarily expensive and financially unrewarding for the homeowner?”

That is not a myth, it is true quite often.  For example: you spend \$7000 that on air sealing and increasing the R-value of your attic from R19 to R50 and that only saves \$150/year (because you installed a new 95% AFUE boiler the same year and “eroded” some of the savings from the envelope upgrade).  Tedkidd do you account for the interactive affects of envelope improvements at the same time as equipment upgrades?   That’s a 47 year payback for your envelope improvement, financially unrewarding.

“Reorienting people at equipment replacement to consider adding envelope measures is hard enough without help like yours!!  I find it very disappointing that someone claiming to be an energy professional would make such discouraging statements.  In most leaky homes \$2000 worth of air sealing is the single best investment a homeowner can make.”

Someone claiming to be energy professional should just be concerned with telling the truth.  Publishing the data from past projects may not be not in alignment with the preferred propaganda but it is not “discouraging.”  If the data gathered on past projects is showing that not every project saves big then so be it.  I advocate that we publish the good with the bad - that is what will inspire people to have confidence in our profession.

I also suggest to you and others reading the book “The Home Energy Diet” by Paul Scheckel.   On page p.296 Paul goes through the steps of a simple energy model so you can understand the basics of energy modeling.  Everyone should understand the math behind energy models before they use them.  I know Michael Blasnik has some good information on the reliability of energy models but I am not going to get into that.  He says it better.

Hi John,

I have tremendous confidence in the laws of physics.  Also I've taken BA, Envelope, Heating Professional, and AC professional classes, done follow up interviews and energy tracking on a lot of improvement projects, and continue to take a lot of continuing education.  I think it's fair to suggest I have some building science background.

I don't have confidence that many people are actually crunching numbers, and suspect those who are  are making seriously flawed assumptions.  Assumptions are inherent to these calculations, and I think assumptions are being made by people who may lack depth of understanding.  Everybody seems to hide behind these words, "Laws of Physics".  Theory is fine, but can anyone back it up?  Please show-me-the-numbers?

Look people, houses are occupied by human beings.  Human beings HEAT houses so they can be COMFORTABLE.  Anybody can save money by FREEZING, and lots are doing it. Don't tell me how much you saved if you aren't experiencing the same level of comfort.  That's telling me a ruler is shorter than a yardstick, that you used less gas driving to Syracuse than you did driving to Boston.

Nobody is arguing that if you keep your thermostat at 65 instead of 70 all winter you will save energy.

"Yeah, no kidding."

Actually, tell me how much you are saving by freezing.  I bet you can't!  I bet it's "gobs".  Someone please help me.  Define "gobs" of money for me?

You MAY get arguments about whether the energy saved living 5 degrees colder will be significant.  In some houses it will be significant, and in some it won't.   You'll have to agree on the definition of significant  (Ie: for mine it appears not-I abandoned 64 for 67 a few years back and can't measure the cost difference on the head of a pin).  Typically the leakier houses will have more "significant" savings.

But when you calculate an 8 hour setback, are you assuming the house is actually colder for 8 hours?  FAIL!!!  That's your first significant calculation error.    Even on the coldest day, even an average house may not get "back" for more than an hour or two.  Over a season of much less than worse case conditions, what "setback" are you actually achieving?  Even a horrifically crappy house the air doesn't instantly cool to setback (much less the mass), and the crappy one will have to start recovery sooner.

Then you have to overheat the house to bring it back.  (Cold furniture will cause occupants to require higher air temperatures than warmer furniture.)  You may think there is beef there?  I ask "where?"

Has anyone done any calculations, or is this all hiding behind words without depth?  Can someone please share with me these "laws of physics" calculations and tie them to cases of proven money savings?  Give me an example of annual BTU savings in either your area or mine.  Show me where the theory proves out.  TRACK.  Show me the money!  Show me the beef!

So what is your modeled savings if you take your "theory" to the real world?

Somebody please share with us some savings you have measured using setback strategy.  Never measured?  Oh.  What a surprise...

Ted-

Never measured?  i don't think so...

When you declare the laws of physics or thermodynamics wrong then it should be up to you to provide some evidence to support your beliefs.  But I'll give you the benefit of the doubt.  I certainly agree that energy models are often wrong because they make poor assumptions or ignore some key interactions, but you'd be hard pressed to come up with a model that shows no decrease in heating loads when you reduce the in /out temperature difference.

If you are skeptical of modeled savings, then how about some measured results? I've done many large scale studies comparing actual energy use data from before and after retrofits over the past 25 years. A number of these studies have included programmable thermostats as a measure.

One retrofit program in particular that I've studied many times over the past 15 years is a low cost weatherization program in Philadelphia that serves low income gas heated households.  I was able to quickly dig up 7 evaluations I've done of that program.  All homes in the program receive some low cost measures during the energy audit and about two thirds of these homes also get a programmable thermostat installed.  Some homes receive additional work such as insulation and other larger measures.  The savings from thermostats were assessed in a couple of different ways but I'll show the lower-end savings numbers from those assessments -- a comparison of savings in homes that got thermostats vs. those that did not, and just for homes that received no major insulation or HVAC measures. This table shows the study year, the number of homes that were evaluated and received thermostats, the gas savings in therms/yr and the percent savings.

Year   #     Savings  Save%

1998  603     81      5.0%

1999  689     71     5.9%

2001  1092   79     5.2%

2003  1081   81     6.2%

2005  576    137    6.9%

2006   387    162   8.2%

2008  189    145    7.2%

These are some pretty large scale studies -- many hundreds of homes -- and the incremental savings  averaged 5%-8% of total gas use in all 6 studies -- all based on actual gas bill reductions.  In every  study, the bill savings paid for the thermostat in less than 1 winter.  There are very few retrofits with such a solid track record of savings.

If you don't like these, you could check out another billing analysis study -- this one done by RLW Analytics for Gas Networks in 2007 -- they found thermostat savings of 6.8% in a sample of 415 homes in New England (not low income).

You should also consider that in all of these studies there were certainly homes that ended up not using the setback or homes that practiced setback before getting the thermostat and so the savings here are already diluted by these factors.  Therefore the savings in homes that did not practice setback before and now use the thermostat properly are almost certainly much larger than the 5%-8% savings found here.  In addition, these percent savings are percent of total gas use and not just heating use, and so the percent of heating load saved is a couple of percent larger.

Nonsense is doing weatherization work, then claiming setback thermostats and "thermodynamics" are the cause of savings.

Nonsense is installing a setback thermostat with no tracking or monitoring, and claiming the thermostat and thermodynamics are the reason for the savings.

Nonsense is seeing a result and not wanting a better understanding of why.  Being pedestrian enough to accept the simplest possible answer.  Claiming that savings occurs because the house is colder is about as sophisticated as saying "because".

Nonsense is the belief that a 90% efficient furnace delivers heat 90% efficiently and an 80% efficient furnace delivers heat 80% efficiently, no matter what conditions or heat call length it receives.

Nonsense is taking an incredibly complex system of interactions and attaching a hyper-simplistic cause to the savings.

Nonsense is taking behaviors that worked in the day of the typewriter and single stage grossly over sized furnace on corn crib homes and carrying it forward 40 years, through huge changes in building science, computer, and equipment technology, and thinking it's a great strategy today.

Nonsense is people who don't recognize times change or recognize "because we've always done it this way" is EXACTLY the answer that should be challenged.

I contend that more savings are likely due to the fact that you get long run cycles from over sized, otherwise short cycling equipment than they are to the fact you're losing 400 fewer btu a day through surfaces.  If that is true, start picking away at the rest, if you're man enough.

True proof of savings is logging temperature.  Unfortunately really digging into the why is likely to shift paradigms and make people uncomfortable.

Ted-

"True proof of savings is logging temperatures" ? really -- I thought true proof of savings is measuring energy use before and after in large scale studies.  Isn't it energy savings we are after -- it seems like measuring energy use is kind of key to that.  I've got the data on thousands of homes -- you have what exactly?

Just to clarify, in case you didn't read carefully, the savings I listed from those multiple evaluations are not the total savings found in the homes that got low cost weatherization plus thermostats -- they are how much larger the savings were in those homes compared to hundreds of homes that got just the minor weatherization nut no thermostat. For example, the 2001 savings of 79 therms was actually based on 99 therms saved in the homes that got minor weatherization plus thermostat compared to 20 therms saved in homes that got just minor weatherization.

If you think the savings are from longer cycles during recovery you'd be wrong, but it still wouldn't change the fact that the setback produced savings.

If you don't believe that heat loss is related to delta T then you are even more clueless than your long winded, insulting, and off-base replies indicate. It seems pretty clear that neither physics nor data will get through to you so you can continue your rants on your own.

Michael,

Thanks for the data on setbacks.  Very useful.

Ted,

Seems like the data we need that might convince you is if we take combustion out of the equation.  What if we showed that setbacks worked in homes heated only by electric heat?  There would be no cycling losses to confuse the issue.  I'll admit I don't personally have the data for that but if we put out a call someone may.

Jon - Yes that might be very useful!  We would also want to know insulation and air leakage levels, and we would want to define what is statistically significant.

(Finally someone who can think outside the box!  A questioning soul, someone who's not a blind follower, who's favorite word is not "Baaaaahhhh.")

Michael,

Behind Jon I say, thank you.  This is the first anyone has provided ANYTHING at all wrt setback.

When I did financial planning for people there was the 'theoretical" approach and the more human approach.  The best theoretical design, if followed, was the way to achieve greatest success.  Unfortunately it never succeeded because it didn't consider how people think and behave.  It didn't fit into the way real people in the real world live, so it wasn't implemented for long.
Then there was what I liked to refer to as "human nature" approach.
When I designed recognizing human nature, the psychology of the situation, the client succeeded.  Those plans are still in place today and are significant wealth for people who otherwise might have very little.
Mass psychology is not recognized for its critical importance.  It seems so simple, design so perception of pain is much much less than perception of reward.
Proponents of setback are coming out hard against me, but until recently (Thank you again Michael) all they've shown up with is rhetoric.  Only recently has one provided summarized results of a Weatherization study.  He's claiming a "documented" 5% savings.
For me, 5% of total consumption (not just heat) would mean less than \$50 a year.  Do you think it would be fair to say this savings is so small as to be a rounding error?  Could it be results stolen from other measures performed at the same time but under credited?  Could it potentially be attributed to a more educated homeowner post weatherization (I.e: not spinning stat to 90f to "Heat Up", or opening windows when they get overheated?)  Could it be because maximum set point is 70 instead of 74?  And really, is 5% meaningful? Would an UNBIASED statistician even find those results statistically significant?
Further challenge is that people may go from comfortable to uncomfortable for a short while, but thats not apples to apples.  And worse, I don't think those savings stick year over year.  So those "savings," if achieved by sacrificing, are not really savings nor are they permanent.
For me a big un/underrecognized issue:  The public resists efficiency because they see it as sacrifice, and feel they are already maxed out.  We "sell" them on these thermostats, they live less comfortably, and their savings taste like tofu.
We need to change that perspective. People need to know they can be more comfortable and use less energy, sometimes at no true economic cost (savings pays for improvement).  I saw some of my clients at a party Saturday, their year is up and this is what they report to me.
Once "more comfort, less energy" becomes part of public consciousness, once we get rid of the idea that setting thermostats colder is the approach to meaningful energy savings, things will accelerate forward.

TK> For me, 5% of total consumption (not just heat) would mean less than \$50 a year.  Do you think it would be fair to say this savings is so small as to be a rounding error?

MB>  No -- they are not rounding error.  The savings of 5%-8% (funny how you selected the lowest of the 7 results) are certainly significant.  If you think they aren't, then you shouldn't care for most retrofits, since taken individually many of them save <10%.  For these customers, the average bills savings were generally \$150 per year or more (Philadelphia has high gas rates and these customers have high use).

TK>Could it be results stolen from other measures performed at the sametime but under credited?

MB> Not really - the other measures only saved a small fraction of this impact in homes that did not get thermostats and the savings from homes that got just those other measures has been subtracted.

TK> Could it potentially be attributed to a more educated homeowner post weatherization (I.e: not spinning stat to 90f to "Heat Up", or opening windows when they get overheated?)

MB> No -- not unless you think the installation of the thermostat gave them education that other people did not get because we are comparing them to other customers who got the same audits and same other minor measures.

TK> And really, is 5% meaningful? Would an UNBIASED statistician even find those results statistically significant?

MB> Yes -- any competent statistician would have found those results and they were always statistically significant by a wide margin.  The t-statistics on the difference in means was typically ranging from 4 - 5 and when incorporated into a regression analysis, the estimated thermostat savings typically increased above these estimates and the t-statistics were often 6-7.  These results indicate that random chance is not a credible explanation for the findings (p-value of no savings <.0001).  If you think the size of these savings aren't worthwhile, then you might also want to rethink many other common retrofit measures that produce comparable savings.  The fact that programmable thermostats are so inexpensive makes them incredibly cost-effective in homes that want them and use them. In terms of being UNBIASED, when I performed the first evaluations I was very surprised by how large the savings were for thermostats.  I checked the results repeatedly because the savings were larger than I had expected since I had assumed that many more people would over-ride them.

I would not advocate for making people uncomfortable -- but I don't really worry much about that because it is easy enough for people to change the settings. If it weren't changeable, the savings would be larger than the 5%-8% found.

How about it auditors?  Does anyone have any data  showing changes in electical consumption from one year to the next by using a  thermostat setback with electric heat?   It would be helpful in this conversation and good info for all of us.  Thanks.

For people in the SF Bay Area, Nest is giving a technical seminar at our Lab on December 9.  These are open to the public, but you need to contact the Coordinator (see link) to get a gate pass.  Not sure if there will be a dial-in number; ask the Coordinator if you're interested in that.

Nest doesn't do dual fuel. Mew owners report little benefit if one person is home manually changing the temp. It looks nice, though!

I've found setback thermostats to be VERY effective when combined with Time of use Electricity rates. In the summer our rate is 4.5 cents per KWH except for 2-7pm weekdays. 2-7pm weekdays the rate goes to 23 cents. Having the thermostat set for 72 during off peak and 78 during peak saves a considerable amount on the COST of energy. I have a smart meter and the ability to monitor power consumption and cost in 15 minute increments online. So yes, programmable stats really can save money.

In winter we set the heat at 68 and leave it. I agree there isn't significant savings to be had w/o experiencing comfort issues. My wife is a stat at home mom, but if there was nobody home the programmable stat would be set for significant setback in the day. We're running 'legacy equipment' that is significantly oversized. I can't justify replacing a working 12 SEER A/C unit and 80% furnace that's 12 years old strictly from an energy savings standpoint. When it does die, it will be getting significantly downsized.

Agreed that properly sized equipment is more effective at reducing energy bills than setback thermostats, especially when the attached ductwork most often is undersized for the larger systems. I wonder how much of the oversized equipments capacity is actually delivered into the house...

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