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GUEST POST: The Case Against High Thermostat Setbacks

 

This article in the Energy Vanguard Blog is a guest post by Ted Kidd, whom I know through LinkedIn and Home Energy Pros. If you've interacted with Ted, you know that he's nothing if not passionate, especially on the topic of setbacks and heating and cooling equipment that can change its capacity to match the loads. I don't agree with what he says below and have posted my response in our first Point/Counterpoint series here. He makes a couple of good points, though, and his article is worth the read.

 

The Case Against High Thermostat Setbacks

Particularly in Hi Mass (i) Situations

By Ted Kidd, Energy Efficiency Specialists ©2011

thermostat setback heating and cooling energy savingsSetback Strategy is an energy conservation strategy of programming your thermostat to drop 8 or more degrees for 8 or more hours a day. Often people would setback during the day when they were at work then at night when they slept.

Setback strategy developed in the 70’s as a result of the energy crisis, and technological advances in HVAC controls. The benefits of this now aged strategy are assumed to be a prescription for energy savings in a broad range of heating applications. In order to understand why this strategy may not be effective today it is important to understand why this energy saving “trick” was effective 40 years ago.

The rationale behind programmable or setback thermostats was essentially that if you turned the thermostat down, you used less energy. While this may make sense if you go away for a few days, for shorter periods (which vary depending on the house) the cost of reheating may negate any savings. Without measuring before and after there is no way of know what, if anything, setback is saving, so people simply implemented these strategies and hoped they were saving energy.

Setback on a daily basis made more sense 40 years ago due to a combination of factors that are not applicable in modern homes. The average home of 40 years ago had a tremendously leaky shell (ii). Leaky ductwork magnifies these shell air losses. A nearly complete lack of insulation was the norm, so any heat created quickly left the home. These poor building conditions all contributed to savings from setback.

There are 2 sides to this energy thing. One is the heat lost side; the other is replacing what is lost. The common assumption was that setback savings was from reduced furnace run time. But surprisingly the primary savings from setback probably came from the ability of oversized, inefficient equipment to dramatically improve delivery efficiency during 2 long daily recovery periods. In other words, savings came from much more efficient creation of the energy delivered to the house, not from miniscule reduction in losses from the house. Let’s explore this idea.

Every time a large, heavy furnace comes on from a cold state it operates really inefficiently until it reaches design-operating temperatures, which may take 5-10 minutes. Add to this that the ductwork needs to be warmed up uniformly before it can effectively deliver heat evenly to rooms. If this equipment only runs for a few minutes before the thermostat is satisfied, the equipment never reaches efficient operating range and rooms often experience temperature imbalance.

Before setback, equipment would run full speed for a short period, then shut down, run, then shut down again, and so on. Setback allowed two significantly increased run-times which provided a huge portion of the household’s daily heat generation requirement. Delivering this heat in large blocks dramatically reduced daily short cycling and allowed an increase in the percentage of heat actually reaching living spaces versus going up the flue. Coming off setback the furnace would run continuously to warm the house up. When going into setback it would be off for a significant time rather than short cycling (iii). This left intermittent cycling for only a short time in between.

Automobile Analogies

Imagine driving an automobile 100 miles a day. This old automobile gets 5-mpg city and 20-mpg highway. Setback is akin to planning your route so that 80 daily miles are on the highway instead of none. In other words, the savings from setback was due to much more effective route planning (delivery of heat) rather than from reduction in losses due to a miniscule temperature reduction.

There has been a paradigm shiftthermostat setback heating and cooling energy savings window in all the components of comfort and the old “rules” should be thrown out the window.

Instead of only driving 110 mph or shut off, our new automobile has a throttle and can drive at varying speeds that meet conditions. This is sometime referred to as load matching, or replacing only the heat the house is losing to the environment. This allows modern equipment to get the equivalent of 60-mpg city and 80 mpg highway. With multi-stage and modulating equipment, highway use can be achieved most of the time, without setback trickery. In fact, setback trickery REDUCES efficiency by asking this new equipment to switch from cruise control to full throttle.

Technology Changes, Strategy Needs To Change With It

Modern equipment design works more efficiently when running on LOWER settings. In Germany, for years now code design has required 150 degree radiant design instead of 180 degree design. They found there are tremendous energy savings and comfort improvements from delivering cooler temperatures. This in part led to the development of modern modulating or “Mod-Con (iv)” equipment. It is widely understood that lower return temperatures dramatically improve equipment efficiency. Colder supply means colder return which means more heat pulled from combustion, which means higher efficiency. More heat can be removed from combustion due to a larger heat exchanger to delivered BTU ratio, and lower return temperatures.

It is now generally recognized that perfect sizing and load matching is the most efficient approach. Providing no more than the heat lost, and running continuously, is the goal the industry is moving closer to. Increased heat exchanger size (condensing) and smart controls modulate output, which reduces and sometimes completely avoids inefficient shut down periods.

Your Friends With Radiators Knew Setback Didn’t Work

Even 40 years ago setback was not as effective for cast iron radiator heat. Hi Mass hot water situations are less affected by leaky shell and mechanical ventilation magnifying leakage is not a factor. Also dramatic adjustments in temperature lead to control issues.

BTU loss through a tight, well insulated shell at differentials of a few degrees is and has always been fairly insignificant. Households today are dramatically tighter, so Delta-t (v) stack loss (vi) savings due to setback are also insignificant.

Remember, savings from setback was not from reduced losses; it was from tricking the equipment into longer more efficient run times and thus more efficient delivery. With the development of High Efficiency Modulating Equipment combined with Hi Mass delivery setback does the opposite of what it did before. Instead of allowing the equipment to operate at optimum efficiency, it has the effect of putting the pedal to the floor. Recovering from setback no longer cheats short cycling and shutdown losses; technology has fixed those problems.

Mass And Control

In High Mass situations use of setback can seriously impact control. Typically the thermostat calls until air temperature is satisfied. If returning from a large setback the boiler puts a tremendous amount of heat into the radiators before the air warms up enough to tell it to stop (again, high throttle city driving). This heat doesn’t stop just because the boiler shuts off.

Once the thermostat is finally satisfied these BTU’s continue to transfer into the living space quicker than they are lost. This flywheel effect causes wasteful overshooting. Also, this approach somewhat nullifies the benefit of a modulating boiler by having it fire on high, then shut down. Outdoor reset attempts to temper this, but at the expense of slowing recovery from setback.

Comfort, The True Driver Of Energy Cost

This is the whole point of heating. We are throwing money at spaces to make them comfortable to occupy. Is there a large chair or couch people occupy? Allowing a space to drop to uncomfortable temperatures means furniture gets cold.  While it may not take long to warm air from setback, large objects (walls, furniture, etc.) are still cold for a long time. These objects will pull heat from occupants making them uncomfortable. This discomfort creates the need for higher temperatures to compensate negating any savings that might have occurred.

There are a tremendous number of variables affecting heat loss in any space, so the strategy to maximize comfort and efficiency for any given space will take time and thought to achieve. That said, the technology of heat generation has made huge gains. Understanding how a heat generating plant and a heat distribution system work best together can have dramatic impact on comfort, control, and consumption.

Setback strategy forces modern equipment to drive in the city for 2 major heat generation requirement periods a day. Now recovering from setback causes throttle up, which reduces efficiency by increasing return temperatures and reducing the heat exchanger surface area to BTU ratio. Setback is very hard to control, which often means putting more heat to a space than is necessary. Set back cools everything off, which forces the equipment to start from zero and means more recovery to provide comfort. Setback means the equipment has to ramp up to recover. The greater the setback strategy, the more the equipment needs to run full out.

Always beware of conclusions based upon partial information, avoid rules of thumb or at least understand to which circumstances they apply.

If you have a Mod Con, match your boiler’s water temperatures to your house’s heat loss and leave the temps set. Let it run on low. If you use setback, use it delicately. I use mine to control when the radiant peaks occur to enhance comfort, particularly for my bathroom floors. If you want to use aggressive setback your Mod Con will have to provide higher temperatures to the radiators than would be necessary without setbacks. It is unlikely setback will accomplish anything other than making the achievement of comfort complicated.

If you have a ground or air source heat pump, using setback will often mean that recovery uses very expensive backup resistance electric heat. People with heat pumps usually have a clear understanding that setback does not save them money.

The best way to understand how operator behavior (and error) might apply to your situation is to have a home energy audit

 

Read the Energy Vanguard response:

If You Think Thermostat Setbacks Don't Save Energy, You're Wrong!

 

 

 

Thanks to Bob Siegel, Margie Campaigne, and Liz Cameron for their help editing this paper.

 

END NOTES/TERMINOLOGY

(i) High Mass - This refers to heating systems that have a lot of mass. Typically hot water with cast iron radiators, systems that heat concrete floors.

(ii) Building Shell or Envelope – This refers to the thermal and pressure boundary of a building. Outside walls, ceilings, floors, generally where indoors and outdoors meet. 

(iii) Short Cycling – This occurs when equipment turns on and runs for a very short period, then shuts off. This can lead to very high energy bills and frequent repair costs. 

(iv) Mod Con is short for Modulating Condensing Boiler. These boilers not only pull a tremendous amount of heat out of exhaust gases due to their ability to lower those gas temperatures to the point where they condense (state change), they also have the ability to throttle up and down instead of simply running at full throttle.

(v) Delta-T – This refers to difference in temperature. Heat goes to cold (envision a magnet pulling steel), the bigger the difference or delta, the faster that movement or pull. Delta T refers to temperature difference. As the temperature difference from outside to inside increases the upward pressure, thus air leakage or change, increases.

(vi) Stack Loss – As the temperature difference from outside to inside (delta t) increases, the upward pressure on the air increases. Think Hot Air Balloon. As this pressure increases, air leakage out of any holes increases as well.

 

 

Photo of window by Wetsun from flickr.com, used under a Creative Commons license.

Comments

First, I would like to see the evidence that furnaces are grossly inefficient for the first 5-10 minutes of run time. For my natural gas furnace, it seems intuitively unlikely. More info or education is needed, at least on my part. 
 
Second, it is indisputable that the envelope has less heat loss when in the (8-degree) setback state. That is one source of savings, and my Manual J calculation for my house tells me the savings is substantial. So a substantial inefficiency needs to be present to offset this savings. 
 
In my Texas region I would like to see the analysis applied to cooling as well as heating. While the physics is similar, the equipment is entirely different and may have different efficiency vs. runtime curves. According to one utility study I have seen, AC manufacturers over the years have evolved to shorten the time required to reach high efficiency from a cold start -- addressing one of the downsides of oversizing.
Posted @ Wednesday, January 18, 2012 6:45 AM by M. Johnson
Ted, 
Tanks for you guest post. Lots of BS on savings calcs everywhere you look. 
 
I would only add wrt oversizing, 
 
New Condensing Furnaces show almost no statistical correlation between oversizing to energy use, unlike my old coal converted cast iron boiler with the Timpkin rotary cup burner. On the AC side FSEC studies show systems 20% over can have up to a 3.7% penalty. Over sizeing my geo HP actually saves me money due to less backup electric heat equipment. Most Furnaces are "sized" to deliver CFM not BTUs.  
 
So, 
 
Perpetuating the load calc myth is nothing more than an engraved invitation for the Government to enter our business and a welfare program for those perpetrating it. Obviously if we need this silly calculation, we need inspectors, certifiers, trainers, software companies, and lots of bureaucracy, all so we can deliver a bogus piece of paper we make say whatever we want, describing a condition that may occur .01% of the time, to an inspector, who generally has no clue what it means, all in the name of energy savings that in fact don’t add up to a hill of beans(maybe 3.7% on cooling for me is $1.50/month) not to mention the masses in the biz who will spend more energy figuring out how to beat the rules and pull less permits.Gotta love it  
 
Keep em coming, 
 
Pj
Posted @ Wednesday, January 18, 2012 7:38 AM by pj
You make some nice points Ted & it will be interesting seeing what Allison disagrees with.  
 
 
 
MJohnson - until a furnace reaches steady state it is not running efficiently which can easily be seen via a combustion analyzer. You will have a huge initial spike on many units that slopes downward until it hits steady state & the readings stabilize. With that said, 5 to 10 minutes is completely dependent on the system, design, and maintenance of the unit.
Posted @ Wednesday, January 18, 2012 7:53 AM by Sean @ AlaGBS / SLS Construction
Mr. Johnson, Here is a self demonstration of the inefficient operation when a fuel fired furnace starts up. Obtain 2 stick type thermometers, place one into the supply plenum, the other in the return plenum. Depending on the quality and age of your ducts, you may not have to drill holes.  
 
Trip the furnace to run for at least 10 minutes. Depending on the trip used, (I use the thermostat), a delay may occur, then the draft inducing motor will start. Somewhere between 20 and 120 seconds, the burners will fire. Star a timer for 5 minutes. Now read the return temperature thermometer. When the blower starts moving heat into the duct work, record the supply temperature. Typically 10 - 20 degrees above the return temperature. At this point, 100% of the fuel $$ have not put a BTU into the home, they have all gone into the heat exchanger. 
 
Read the manufacturers specifications on heat rise, attached to the furnace data plate. Now at the end of 5 minutes read both the supply and return temperatures, subtract to get the difference and compare to the data plate spec. If it is not within the limits of the manufacturer, call a service tech now. 
 
Go up and untrip the furnace and allow it to finish the cycle. When the fan shuts off, record the supply temperature. This is the amount of heat the furnace has left in the heat exchanger. Again a measure of inefficient operation. 
 
Typically, i find a blower kicks on 10 - 15 degrees above the return temperature and the blower stops about 25 - 30 degrees above return temperature. Since this is controlled by a black box, meaning the tech cannot change it, the inefficiency is built in. 
 
I once tested a furnace with a data plate showing 100 - 150 F heat rise and the date of manufacture was 1955. The homeowner had not cared about efficiency. He owned a natural gas well that was hooked to his home. 
 
Most 20 year old furnaces have a heat rise more like 40 - 75 degrees. I am seeing furnaces in the last 10 years with 30 - 50 degrees.  
 
Then you can start measuring any inefficiencies in heating the ducts, the duct leakage, and finally getting to the whole reason for the furnace coming on, heating the home. 
 
Posted @ Wednesday, January 18, 2012 8:03 AM by John Nicholas
This article is dangerously uninformed. 
 
When a boiler/furnace is first switched on it indeed delivers minimal heat as metalwork is heated - this is not inefficiency because...  
 
If the boiler is internal to the building this heat is "fully recovered" when the boiler is switched off (conservation of energy - Law of Physics) as during cooling it gives up exactly as much heat as it took in.  
 
If alternately the boiler is exposed - then during this phase the rate of heat loss is far lower than when up to operating temperature - so losses are lower on a cold or cooling boiler (again a Law of Physics - heat flow is proportional to temperature difference). 
 
Additionally from a loss perspective; the heat produced either serves the building or passes up the flue. The colder the boiler the less heat goes up the flue (stack temperatures are lower) so a lower proportion is power used is lost to the atmosphere. 
 
The absolute humidity content of cold flue gases is also lower so enthalpy (energy content due to latent heat of evaporation can also be recovered) - but beware of condensate damage - though this is not a problem with an economizer of modern condensing boiler. 
 
If a building is ventilated this should also be switched off when unoccupied and any dampers closed. 
 
Finally loss rate from the building spaces is directly proportional to inside / outside temperature differential - so again a cooler room requires less power to maintain state. 
 
Conclusion 
 
If comfort allows to switch heating off it should always be done. 
 
More informed opinion is available on this and associated topics at  
<a ref="http://kWIQly.blogspot.coml">kWIQly - Building Energy Intelligence 
 
Posted @ Wednesday, January 18, 2012 8:09 AM by James Ferguson @kWIQly
Ted and Allison, 
 
What a great guest post! I love it. 
 
Ted makes a great point that cannot be over emphasized.  
 
People want comfort! 
 
I would agree that hugh setbacks 8 degrees over 8 hours are probably not efficient any longer. I am curious to find out what level of set back is effective. 
 
My beginning experience with the Nest Thermostat may show some insight - or it may not. You can follow along on my blog here: bit.ly/yNhq3x 
 
Again, Thanks for the info and the challenge.
Posted @ Wednesday, January 18, 2012 8:11 AM by John Nicholas
Indoor mean radiant temperature, the average of the radiant temperatures of the walls and furniture of the home - as opposed to - just the air temperature.  
 
Set backs are not so good at the first objective of comfort, because the mean radiant temperature is not maintained. 
 
Which, this thermal mass, by the way is the one thing that is not calculated in the sizing of equipment for residential dwellings. But this plays a huge part, and probably allows us to install equipment 20% under the most aggressive Man J and S calculations. This is an empirical observation based on high performance install after install. These homeowners are rave about the comfort and energy savings - they had no idea how comfortable a home really could be, until they experienced it.
Posted @ Wednesday, January 18, 2012 8:22 AM by Christopher Cadwell
I've started thinking about setbacks in relation to time-of-use electricity rates that we have here now in Ontario. Not all of us have EC motors in our furnaces. I'd be interested to hear if anyone has done research on this.
Posted @ Wednesday, January 18, 2012 8:48 AM by Franklin Menendez
some comments on the comments and the story: 
 
1. inefficiencies of oversized heating equipment is well documented. When you do setback you force the equipment to run less often for longer times... another way to say this is you make the "apparent load" much higher and thus the heat source operates more efficiently. this is all well documented stuff from brookhaven and others. See discussions of buffer tanks and modulating burners and why they increase efficiency. to all those disputing the "less cycle" efficiency gain theory... you're missing the boat. 
 
2. the author is also missing the boat quite a lot. "leaky shell" is just code for "high heat loss". It's not that it's "leaky" it is simply that heat loss is high enough to drop the temperature in the building significantly to achieve significant savings. I think one thing often missing in this debate is a basic understanding of bin data and degree day distributions... I dont' throw too many stones, I just got up to speed on all that myself, but really, pop over to degreedays.net sometime and pull up the degree day count for a given area at "base 65" and, say, "base 55" sometime. it's a dramatic difference. So if you spend half your time at base 55 and half at base 65... well, that's a pretty significant reduction in energy loss. 
 
Mass just makes your ability to drop temperature lower, so you don't get down to as low of a 'base'. Low heat loads can do teh same thing. You actually have to drop your temperature to get lower degree day counts. 
 
3. to the guy advocating for not doing load calcs, I can only sigh. Modulating combustion equipment (not fans) still have minimum modulation rates. those rates are often the maximum heat load in many buildings, and cycling inefficiencies still exist with modulating equipment as well as the paired reduction of life expectation from increased wear and tear on the equipment. Oversizing your modulating combustion equipment raises your minimum modulation rates, and will reduce your efficiency as well as the lifespan of your equipment.
Posted @ Wednesday, January 18, 2012 9:18 AM by Rob Brown
Personally, I'm not largely convinced that residential building shells in more recent production housing perform remarkably better than the 60's era, marginally insulated, single pane windowed ranch models I grew up in. 
 
 
 
Oh, they have more insulation, yes. And many times double pane windows. But they are also larger. Sometimes much larger for the same purpose the 60's ranch tract house was bought for...a family of four to six. The much larger proportions invite more surface area to footprint heat transfer through the shell, along with more opportunities for that same shell's air pressure boundaries to be perforated for countless reasons, perhaps most vainly for an over abundance of "can" light fixtures poking up into a ventilated attic. And that ceiling where they reside being sixteen to twenty feet, unobstructed, above the ground floor. Talk about an architectural chimney. 
 
 
 
But we're discussing setbacks, yes? Such a discussion can't be well-rounded without looking at the building envelope. Residential and much light commercial HVAC strategy for years has been brute force overcomes building envelope deficiencies. Design for the worst expected condition, setting the system up to operate most of the time like Ted says above: pedal to the metal or parked in the garage, engine off and going cold. 
 
 
 
Long term outlook has me envisioning a closer cooperation between HVAC equipment and building envelopes to where setback strategies become laughable without dispute. That is where HVAC equipment modulates to meet the real-time load, and the building shell is slow to gain or lose heat, reducing the role of the HVAC to ventilation and climate maintenance vs. a hot rod drag strip tug of war between the envelope and the HVAC gear. 
 
 
 
This outlook would also entail a more rational approach to architecture. Why the voluminous interior ceiling heights that make you feel like you're living at the bottom of a well? My idea of a house is perhaps old-fahsioned...it should feel cozy and convey a sense of shelter. Being a speck at the bottom of a mine shaft does not fit my imagery...and it doesn't do a lot for reducing energy demand, either. That said, aesthetics so often win out over energy and comfort choices when building owners decide how to spend money on their structures. I'm merely of the belief that aesthetics can still be had, but with a more rational base. Super high ceilings may be the modern way of "keeping up with the Jones", but I'm not interested in mimicking what the Jones' energy bill. It's high time our design approach to housing involves a nuanced balance between aesthetics, HVAC, and building shell thermal and air pressure boundaries. Then all this talk about "setback" will seem so...well...1960's.
Posted @ Wednesday, January 18, 2012 9:22 AM by Cameron Taylor
Rob Crown is quite right. Readers might also be interested to bookmark  
kWIQLY - Building Energy Intelligence who are releasing a new set of free degree-day tools later this week. 
Positioning a site on a Google map will automatically identify the local sources of free weather data. And by storing Balance Point temperature requirements - accessing the data regularly becomes less of a chore. 
In the medium term a full set of free on-line degree-day analysis tools will be made available.
Posted @ Wednesday, January 18, 2012 9:37 AM by james ferguson
OK, 
 
I am currently(right now) in a meeting with Carrier's top product managers and Dealers. No one agrees with the premise that a moderately oversized condensing gas furnace has any significantly measurable efficiency degradation. For those selling this proposition, please provide your test data and/or studies that support this old wives tale. 
 
Different story on ancient furnaces. 
 
It is agreed their is a very small but significantly measurable (3.7%) impact on cooling.  
 
So as we discussed selling the idea that your goofy load calc is saving energy or money is total Hogwash. leaving aside the fact that you don't know any of the inputs on old houses anyway and work it backwards to get the numbers you like. 
 
It is a great scam and some guys have turned it into truly entertaining Performance Art an their sales calls.So there is some value from an artistic perspective. 
 
just saying, 
 
Pj
Posted @ Wednesday, January 18, 2012 9:49 AM by pj
My backround is hydronic, so there may be some variance in your results, but at first blush I don't see why it would be all that different... I'm open to why it might be, but I don't think air equipment is magic so you still have minimum modulation rates to deal with (still a 5 to 1 turndown in air, right?), and even absent an efficiency hit, you are reducing the life of your equipment. 
 
Further, you can't design a comfort system without knowing the targets you are trying to hit and as the article notes the whole freaking reason to have heat is to improve comfort. But hey, whatever you say, I'll just keep fixing systems that tried to "guess their way to success" practically every day. certainly the advent of modulating equipment has not magically made everyone fall in love with their systems. 
 
http://www.harscopk.com/uploads/files/short%20cycling%20prevention.pdf is part 1 of a well researched opinion on this hydronically. 
 
Posted @ Wednesday, January 18, 2012 10:03 AM by Robert Brown
TOU rates is probably the strongest argument for setback thermostats at the present time. In Oklahoma City I did the TOU rates last summer with peak time being 2-7pm weekdays. Saved about 25% on my bill vs. standard rates.  
 
This year OG&E is rolling out the "smarthours" plan where TOU peak price varies designed on the load of the utility. An optional thermostat capable of radio control by OG&E will automatically adjust the thermostat based on the price of electricity. The thermostat screen will let the user see what the power rate is. The thermostat and installation is free if you choose to have one installed. if the user doesn't like it OG&E will come out and reinstall the old thermostat at no charge. I've signed up, and am going with the free thermostat. 
 
Let it be known that although high tech multistage/modulating equipment exists it is almost never installed in new construction unless the buyer pushes for it. 90% of new homes get the lowest cost builder grade equipment with mediocre at best ductwork. Oversizing is the norm because larger equipment isn't that much more expensive on the wholesale level. Oversizing covers up poor ductwork and insulating/air sealing practices.  
 
Correctly sized and installed equipment will almost always result in lower power bills than setback stats on oversized equipment. However, few people will replace otherwise functioning equipment just for energy savings, it's just not worth it in most cases. When the equipment dies it tends to be when it's freezing or 100 degrees outside, and customers just want heat or cool NOW, no time to do research on what to buy. The contractor is busy and doesn't want to mess with a Manual J so just sells the same size the customer previously had installed. 
 
Getting building science pros to convince HVAC contracts there is a better way is going to be a long battle. HVAC trade is typically passed from generation to generation w/o much "new school" though processes added.
Posted @ Wednesday, January 18, 2012 10:09 AM by Bob
Hey Bob, 
 
Getting Building Science Pros to stop acting like know it alls while taking handouts, subsidies, and living off unfunded mandates and rate payer money,all while working on one or two science project houses per year is an even bigger challenge.  
 
Building Science Guys come off as arrogant and yet live under bridges with out handouts. Thier business model does not work in the real world. 
 
Maybe BS guys should take a different less holier than thou approach since the HVAC guys have the customer base. 
 
Best, 
 
Pj
Posted @ Wednesday, January 18, 2012 12:36 PM by pj
Interesting points and conjecture, but I'd love to see some more data to back up the claims. Yes, the efficiency of the system as it warms up matters, but does it matter more than heat loss? Is the temperature of my furniture really driving behavior change?  
 
The answer, as with everything, is "it depends." That's why I think it's just as bad to say "Don't use setbacks" as it is to say "Install a programmable thermostat." This is not a one-size-fits-all question. 
 
For the next post, I'd love to see some treatment of heat pumps and A/C equipment. Since outside temperature impacts the efficiency of these machines, a sensible setback in the winter (where afternoon temperatures may help with heating) or pre-cooling (to utilize cooler night time temps in the summer) may have a bigger impact than the factors discussed above.
Posted @ Wednesday, January 18, 2012 1:20 PM by Daniel
I like PJ's argument. Most homes in this country are builder specials... built as cheap as possible and sold as expensively as possible. that's the "real world". If all we can do is the "real world" we're all screwed.  
 
the real world needs to be changed. Efficiency and operating costs needs to be factored into mortgage calculations, or NOTHING will ever change. 
 
and guess what? that will take math. TEH HORRORZ.
Posted @ Wednesday, January 18, 2012 1:38 PM by Robert Brown
No doubt setback will save more in an inefficient home with oversized equipment. And we all know that thermostat manufacturers (and many industry practitioners) overstate the potential savings from setback. Also true that most folks have no idea how much they might or might not be saving from setback. As if any of this is unique to setback? But to suggest that setback cannot save significant energy, even in most new homes, is simply wrong. The fact is, there have been plenty of studies that demonstrate just the opposite, even if you don't like the results. Blasnik listed some of the data and sources in your exchange of comments last fall at Home Energy Pros blog here
 
I particularly disagree that the primary mode of savings from setback is from longer runtimes @ recovery. Throughout the article, you intentionally overstate the significance of cycling losses to prop up your position regarding setback. And finally, your assertion that envelope savings from setback are "miniscule" (sic) or "insignificant" is laughable. Most folks don't live in a high mass or PassiveHouse. The vast majority of the housing stock still has leaky, poorly insulated shells with oversized equipment. More importantly, the majority of new builds are not what I would consider 'tight, well insulated', and very, very few have load matching equipment. You must live in a dream world. 
 
One of the arguments against setback you often cite is that it requires equipment to be oversized. However, except for the hottest and coldest days, a properly sized air conditioner or furnace already has plenty of capacity to recover from setback in a reasonable time. And on design days, even a slightly oversized system, say 15%, can recover quickly enough. But when sizing a system that closely, it's important to manage homeowner expectations. Most folks figure that out pretty quickly that setback is a bad idea on extreme hot or cold days. The key is for the homeowner to understand that's a 'badge of honor', not a defect. In any case, I've yet to see a furnace that it couldn't handle rapid recovery from even the most aggressive setback. It's well known that Manual J significantly overstates design heat loads. 
 
Using a setback with a heat pump is another matter entirely, worthy of a separate discussion. Ditto with high mass homes and radiant floors, due to the mass issue you correctly noted. If you had pitched your position against setback solely on the basis of these situations, we'd be having a different conversation. But instead, you rant on about how setback is outdated. Yeah, for maybe a fraction of 1% of the housing stock. 
 
I have no problem calling a spade a spade when it comes to irresponsible marketing claims, but you seem to be on a mission to discredit the use of setback thermostats in general, and the only reason I can imagine you've taken such an extreme position is because you don't want to deal with callbacks from irate (uninformed) homeowners. You've said as much in your comments in other blogs. The approach I've found works best is to listen to the client, and to *encourage* those who use setback as a savings strategy. It only takes a few words for most folks to understand how to use setback effectively, and what they should expect from their system. 
 
One final point, regarding comfort... as you improve the shell, the impact of setback on mean radiant temperature becomes smaller as well. If you setback a PassiveHouse, the only energy you're wasting is the calories it took your body to enter the program in the thermostat.
Posted @ Wednesday, January 18, 2012 3:29 PM by David Butler
Daniel uncovered the real point in his statement:  
 
***The answer, as with everything, is "it depends." That's why I think it's just as bad to say "Don't use setbacks" as it is to say "Install a programmable thermostat." This is not a one-size-fits-all question*** 
 
"Cut more holes in your roof to remove the moisture" 
 
"Houses have to breathe" 
 
These things are NOT the same as "wash your hands before you eat".  
 
Proposing a behavior or measure assuming it automatically saves energy when you have no proof in your home or any other that it does, have no intention of tracking results to see if it does, and are using it to personally profit is malpractice.  
 
Furthermore, correlation does not prove causation. Assuming setback saves because less energy is lost rather than more efficient replacement is not proven.  
 
I like to touch base with clients. Their descriptions really help paint a picture for me.  
 
Randy is an engineer who lives in Maryland and works for the NSA. The kind of person who is my perfect client. Not afraid to "push the envelope".  
 
Randy had a 100k furnace and 4 t ac on a 4000 sf home. I wanted him to put in a 60k mod and 2ton heat pump.  
 
He did.  
 
He can't believe how incredibly comfortable and quiet his house is. His neighbors who all have identical homes (minus the leaky sun-room addition Randy's predecessor installed) all have energy bills 50% higher than Randy.  
 
THE PROBLEM: 
 
When Randy goes away and lets his house fall back to 60f, it takes 5-6 hours for it to get back to 68-9. For the average "drop a furnace in and go" person who thinks saving money is "shutting the furnace off", that recovery would mean a very upset, money losing client. 
 
I spent weeks educating Randy. Most HVAC guys have a few minutes.  
 
If we want to start heading down the path of dramatic energy efficiency, understanding of how to OPERATE our homes must change.  
 
AND AS FAR AS BLAMING HVAC GUYS FOR OVERSIZING, I'M WITH MY BUDDY PHIL. We cannot blame nor expect the HVAC guy to aggressively downsize equipment when saving energy is not their goal. They aren't paid for 3 weeks of client education, they are paid to get in and get out.  
 
The client's ignorant behavior, combined with unreasonable expectations of performance are huge impediment. Furthermore, proper sizing when a policy of "setback saves money" is so intrenched, are completely at odds.  
 
Proper sizing under current construct will cause the HVAC guy grief. His primary job is to stay in business and feed his family. We do not want him on unemployment.  
 
Doing THE RIGHT THING is not a reasonable expectation when faced with these hurdles.
Posted @ Wednesday, January 18, 2012 4:43 PM by Ted Kidd
So Daniel, thank you.  
 
No I can't say setback never saves money. I can say aggressive setback is an impediment to good design.  
 
Also, my perspective comes from contacting my clients after work has been performed. I track energy use. My comments are based upon results I've encountered.  
 
Anyone else tracking client energy results?  
 
(If you are, love to see it. If you aren't, how do any claims of what saves and what doesn't have any basis.)
Posted @ Wednesday, January 18, 2012 4:50 PM by Ted Kidd
Hmmm, no comments after my last followup. Allison, this getting any hits?  
 
ROB BROWN - I'll respond to your comment #2 which says I'm missing the boat by not looking at BIN data... 
 
"So if you spend half your time at base 55 and half at base 65... well, that's a pretty significant reduction in energy loss. 
 
At what point in an 8 hour setback will the temperature ever get to 55? Does that occur the minute setback starts? 2 hours in? At what point throughout the season will it ever get to 55?  
 
In fact, will the average base temp using a 10 degree setback even be even 3-4f? DOUBTFUL. If it does you have some envelop issues that can cost effectively be addressed. SO FIX THE HOUSE. 
 
 
I have clients who's homes would take 10 hours to recover 8f if they are anywhere near design temps. So you assumptive calculation of how much time spent at 55 fails out of the gate because recovery has to begin well before they return.  
 
And what horsepower do you need to recover? What size duct work? What amp draw on the ECM at full throttle vs the ECM at low load matching output?  
 
This is not a simple math calc. There are a LOT of subtleties that you need to factor in. When you start digging into the subtleties, setback doesn't save, setback sucks.  
 
Can't find fault with your other comments.
Posted @ Friday, February 10, 2012 3:08 PM by Ted Kidd
Isaac Newton is rolling over in his grave...
Posted @ Tuesday, November 20, 2012 7:02 AM by Christopher Retzler
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