EmbErna wrote in news:XvtXb.34827$yE5.117742@attbi_s54:
The bucket is a good analogy, since the water will run out the hole at a higher rate when the water level is higher. This is how heat loss works -- more differential between the inside and the outside will result in a higher heat flow/loss.
Actually, you should think of it more like placing your bucket under your tap and turning the tap either fully on or fully off. You will need to cycle the tap on less frequently when the bucket's water level is lower.
This isn't an efficiency loss, since the burner resides inside the house. Only heat that is lost out the chimney is wasted -- heating the burner itself is merely part of heating the thermal mass of the house itself.
To sum it up accurately, "Any set back, for any length of time, will save you money - -providing there is no triggering of expensive emergency heat by a heat pump," Now, what you pay for that savings is lack of comfort for the time you are waiting for the system to bring back the desired temperature. So it boils down to a tradeoff between savings and comfort.
There was one very beautiful chart published by FORTUNE Magazine about the rise and fall of the PC makers over the years. The vertical axis showed their relative rankings. The new and very informative innovation was to thicken each company's chart line to refelct the volume of its sales as the company rose and shrunk. The same plots showed clearly their relative market sizes over the same period. One look and each PC company's history was immediately evident and agreed with the impressions all of us had formed from reading the news over the years.
My visualization of a useful chart would be to plot room temperature against time (24 hours over several weeks), with the thickness of the plot line to represent the BTU required to maintain whatever the thermostat setting is. Then have different thermostat setbacks.
I haven't figured out how to relate these plots to the outside temperature conditions. But then this is what we have experts for - to make studies and present them kin an easily readable form.
I am numerically challenged so please make allowance for my description. The flat part of the chart plot was the heat loss (as a reciprocal percentage?) curve against the R value. So the heat loss curve would rise steeply and linearly before it flattens off at just over 80%.
The interpretation is that below R30 every bit of extra insulation will significantly improve heat retention for the house, to equal big energy savings. Thereafter adding thicker insulation (higher R value) will not improve this ~80% efficiency significantly and doubling the R value may perhaps help you achieve 85% efficiency. It would of course never reach 100%. It convinced me to stay with 2 x 6 studs for my outside walls and R30 batts when I built my house. I was also convinced that triple glazed insulated windows was not worth the money.
I went through a course that enabled people to be their own general contractor. I really learned a lot. It helped me to plan my HVAC so that it is centrally located and had the shortest straight runs thereby avoiding trunking losses and enabling easy heat balance throughout the house.
That said the course instructor's caution was to insulate the house well but not over seal it. This was during the 70/80s energy crisis when retro-insulating old houses was the rage. (Mine was a new build.) We need the house to be slightly leaky to get fresh air in. There were many reported examples then of people who overdid this sealing in their old homes and died of suffocation.
I set my thermostat at 68 degF. I tried the electronic programmable thermostat and hated that thingy because its so hard to alter the setting when I want to lower or raise the temperature on demand.
You should have a second look at thermostats -- many of the new ones are extremely easy to use. Mine (a Honeywell) has two buttons to increase/decrease the temperature -- as soon as you do so, it overrides the temperature setting for that time period.
Nothing is cut and dry when it comes to engines. It all depends on how well the engine is designed and the quality of the materials to build it.
For starters, not all V8 cars are ocean liners. Corvette's, Camaro's, Mustangs, Vipers ect. are all very small cars that make use of V8 engines. My favorite car that I ever owned was my '78 Chevy Monza notchback with the very rare factory optional 5.0 liter V8. The car was a Chevette sized sub-compact designed around a 4 cylinder and the only added weight with the V8 model came from the engine itself. The V8 version averaged 12 mpg less than the wimpy 4 cylinder even on the highway. It also never ran cooler than the 4 cylinder models...in fact cooling the large V8 was much more difficult and critical in that car. The V8 engines in those cars DID NOT have a longer life span than the
151 Iron Duke 4 bangers (only use "banger" when referring to 4 cylinders) or the 3.2 or 3.8 V6s. The V8 served one purpose only and that was to ROAST any car on the road. One of these days I'll find another one so I'll be able to stop kicking myself for selling mine 10 years ago. fwiw, the longest lived engine out of all of those was probably the 3.8 V6...just a very well designed engine.
Now look at a 4 cylinder engine like Toyota's 22RE. Great power even in the small pick up trucks, great gas mileage and it's rare that one doesn't make it to 250,000 miles.
And to prove that bigger isn't always better...I have a factory stock
650cc 2 cylinder motorcycle that produces well over 100 HP and gets 52 mpg. The engine's are known to go over 130,000 miles before needing a rebuild. Find me a Harley with over 2X the displacement that can come close to any of that.
And I'm not following you on the tire life/wheel base theory...can you explain how a cars wheel base effects tire life? Or did you by chance mean the diameter of the tire? A taller tire will have less rotations per mile but in reality I don't think they last much longer. Look at manufacturers warranties, a certain model tire will have the same mileage warranty no matter what the diameter.
The problem is that the amount of savings depends on dozens of different factors - a graph simple enough for everyone to understand would represent only a tiny fraction of "real systems". Degree days, heating system type, energy costs, etc. etc. etc.
Whenever you're looking into something like this, add "CMHC" into the google search.
The search "cmhc setback thermostat savings" finds _lots_ of solid data.
"CMHC" is a Canadian government agency "Canadian Mortgage and Housing Commission" and is one of the very best (and unbiased) sources of information regarding this sort of thing.
Their "Keeping the heat in" booklet is about the very best homeowner material regarding energy conservation there is.
They still do that. It sounds counter intuitive, but the vehicle under power is constantly accelerating (constantly decelerating without power). All manufactures of cars say drive at a steady speed for maximum mpg, but then car engines aren't wrapped in insulation to hold heat in either.
Theoretically, one can calculate the energy consumption of a heating system, (if it's not too complex) but there are always errors due to unknowns, inaccurate extimates, etc.,. The truth (proof) of the matter is often better determined by empirical (experimental) methods. For example, One can monitor the temperatures both inside and outside the building/structure along with the energy consumption for each of the two heating system operating procedures, and compare the results statistically. This is what the energy providers do. I would trust empirical results better than purely hypothetical ones in almost any case. However, think of the classical problem of designing and exploding the first atomic bomb - necessarily based mainly on theoretical predictions. Nobody really knew what to expect for sure. Apparently, it was a big relief to those few in charge to find that the world was still intact after the explosion. The rest of humanity knew nothing about what was going on - the world might have ended that day.
Hmm... the heat loss rate tends to be related to the temperature differential between indoors, and outdoors...
For your statement: "when a room remains warm at a constant temp, a furnace will have no need whatsoever to kick on and thus consume more energy than one that's simply idling with nothing more than the pilot light burning during the same period of time" My question is, what is keeping the room warm during this timeframe? This is not an adiabatic process... there will be heat loss due to convective, conductive and radiational transfer. Once you warm a room up, the furnace will HAVE to run periodically to maintain that temperature. If if didn't, you could shut it off (and leave it off)! So back to the original assertion: whatever method maintains the lowest average temperature differential between indoors and outdoors, will consume the least amount of fuel.... the lower limit being that of maintaining the indoor temperature the same as that ouside... no fuel comsumption at all.
I think I touched on that earlier, and I realize the furnace/boiler will kick on *eventually*. It's a matter of how often it needs to kick on and consume fuel. What's keeping the room warm (or not warm) in the first place is the heat already blown or radiated by the heating unit AND proper insulation to hold on to that heat you already have. Leaky or ancient single-pane windows, doors that don't fit properly or lack weatherstripping, inadequate wall insulation, etc. etc. do wonders to slow the natural disssipation of room heat -- which is why insulation is one of the more popular topics in this newsgroup.
This is, at least according to my thinking, where I would imagine shutting down or turning the thermostat way down IN A WELL-INSULATED HOME for 8 hours a day as opposed to not would be pretty close to a wash as far as the heating bill goes.
I do know that installing a programmable thermostat three years ago cut my gas usage by approx 15-20% . It was previously set at 66, but with the programmable I set it for 60 overnight, 62 in the morning and afternoon, and 66 in the evenings.
I can only make rough guesses as the weather is never identical. This is for a forced-air gas system, and my average gas bill in the cold months is around $120 this year.
A couple of days ago, with daytime highs in the upper 30's and overnight lows in the low single digits, I turned it completely off, and it took 48 hours to drop from 66 to 46. I then turned it on again and the furnace had to run near continuously for a few hours to get back to 66, but there was about a 20% drop in gas usage from the previous (normal) 48 hour period according to the meter. I am however in an odd situation regarding the weather; the average difference here between daytime high and overnight low is over 30 degrees (year round).
These results are about what I'd expect given my limited knowledge of thermodynamics, and are about what I believed prior to my conversations with the gas company.
This of course begs the question; why on earth is the gas company giving out bad advice? I'd assumed they were right and I was wrong when I spoke to them, but my test results, and most of what I see in this thread, contradict that.
Well, I gave it my best try, and listed my results in a post I just made. Long story short, a 48 hour shutdown under very similar weather to the previous 48 hours saved me around 20%, and the temp was still falling (around 46 degrees) when I switched back on.
That was due to Edward Teller's concern that the bomb might ignite a hydrogen fusion chain reaction in the atmosphere, essentially turning the atmosphere of the planet into one big hydrogen bomb. He gave it an exceedingly small chance (under 1% as I recall) but with the state of theory at that time there was no certainty.
And, it may be Urban Legend, but there is a story that one of the scientists, referring to this theoretical risk, quipped "If Teller is right, and we blow up the Earth, Teller is going to be insufferable..."
That's the way I used to argue it; I just couldn't comprehend how it could be otherwise due to heat loss over time being a function of temperature differential.
And I was one for listening to them. I just assumed they knew a lot more about the thermodynamics at work in this situation than I did. So, I accepted that I was wrong, but it's been nagging at me for quite a while because I just could not comprehend how leaving the heat up was more efficient. That's why I finally decided to post my question.
Ahhh... That makes sense; the person I spoke to was unaware of the real position of the Utility, and had just "heard" what he passed on to me and claimed it was real? That makes more sense than an energy company not understanding thermodynamics.
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