> you will just burn the "saved" energy trying to cool down the house
Did you read the article you linked? It says:
> What we found was that even when the A/C temporarily spikes to recover from the higher indoor temperatures, the overall energy consumption in the setback cases is still less than when maintaining a constant temperature throughout the day.
Even if you ignore the whole thing (as I should have, I was validating their method because the conclusion you cited sounded wrong... but then it turns out the conclusion isn't what you claim) and just read the concluding two sentences of the post, you'd have read: "An eight-hour setback on weekdays provides savings regardless of the system type"
It's a convenient myth that not turning off the heating when you're not home saves energy because the heater would otherwise have to work extra hard when you come home / wake up and consume more energy. I've heard it told by people that usually have sensible opinions. I guess it's the inverse myth in the hot places of this world. It is indeed very nice to walk into a climate-controlled place, so I can see why people love to believe it.
It makes no sense. Think about it: in the scenario where you let the AC run all day long (or leave the heater on overnight), the temperature differential between inside and outside is larger. More heat enters/leaves the house when the differential is greater, so it makes sense to let this grow smaller when you're not there anyway and only increase the differential when you're (almost) coming home or coming out from under the blankets.
Why would a heat pump run more efficiently when maintaining a temperature differential? From my rudimentary physics knowledge, a heat pump works best when the temperature difference between hot and cool side is lowest. So the first Joule pumped out of a warm house is the cheapest.
I'm having a hard time finding good information on this, or at least I was a few months ago when I was looking into whether I'm being stupid for thinking essentially what I said in the last paragraph. Do you have a link where I could read more about why it makes sense for heat pumps? I don't understand why the same logic shouldn't apply there.
> That is to say, if a property lost 40kW/h of heat through its walls throughout a 24 hour period, that typically doesn't mean you have used 40kW/h of gas from your boiler or 40kW/h of electricity from your heat pump.
> If the boiler has consistently run at 85% efficiency you will use 47kW/h of gas. If you can get 93% efficiency from that same appliance you will only use 43kWh gas.
> And therein lies the problem. Many arguments for turning the heating off are talking about saving heat loss, not saving primary fuel usage. The difference between the two relies heavily on the first variable we need to ask ourselves, what is our heat source?
(That "kW/h" is a red flag for me. I'm not super knowledgeable about electricity myself, so if a blog can't even tell kWh from kWh/h from kW/h, I usually try to avoid it. Anyway, this is not a random source that I found but something being vouched for, so I'll trust it.)
This seems to be the core argument:
> most people have condensing boilers. These can run at lower temperatures which cause some of the fumes to condense into liquid water (hence the name). And this action extracts extra efficiency from the appliance.
> If you have a heat pump, the gains from running at lower temperatures are even higher here. Running at high temperatures of 50 to 55°C all the time year-round to maximise the responsiveness of the unit, and switching the heat pump on and off regularly will result in [~half the] efficiency.
I like this comparison:
> It's a bit like saying, I'm going to drive 100mph to the shops as I'll only be driving for 30 seconds. Actually, if you drive at 5 mph you will take 3 mins, it may ‘take longer’ but it will be much more efficient with fuel.
Because it also highlights the fallacy: this is wrong. At 5 mi/h, my car uses something like 30l/100km (rough estimate, maybe +/-10). At 40mi/h, it's around 3.3l/100km if I remember correctly (+/-0.3). But, yeah, at 100 mi/h you're obviously battling a lot of air resistance and slower would be more efficient... just not excessively slow.
The article would benefit from some actual numbers. It explains the general concept, but how many hours would you have to leave it off for, for it to be more efficient again? Is there a formula or curve to use with time on the X axis and... house volume or outside temperature on the Y or something, or are there too many variables to dumb it down to a line that works as general advice per heater type in typical climates? Surely for those that don't work from home, using reverse AC to blow some hot air, for 15 minutes in the bathroom and 30 minutes in the kitchen while you get ready in the morning, is more efficient than having base heating turned on during the 8 hours that you sleep + 2×45 minutes that you commute + 8 hours that you work?
But I understand the concept at least, thanks for the link!
The link at the bottom about why zonal heating doesn't make sense gets deep into the numbers and calculations.
I hadnt read the Ars Technica link before, but it makes the same argument, with graphs, a low efficiency device in a poorly insulated home left off for a 4 hour period makes sense, but in that situation you probably want to insulate and/or use a more efficient heat pump rather than do that.
Did you read the sentence after the one you quoted? It then says
>On an annual scale with a conventional central A/C, this could result in energy savings of up to 11 percent.
That's basically what the poster above was claiming (though they seemed to be under-estimating the effect a little). Obviously turning the AC off will reduce the amount of heat leaving the house, but the point is the gains are not super large, even with an inefficient AC and a poorly insulated house. If you have an efficient AC and a well insulated house then the difference could be even smaller (it's even possible that the trend could reverse at some point, if the efficiency of the AC goes down when it is pumping more heat to cool down faster as opposed to consistent low-power heating: you can actually see this in the charts if you look at the mini-split system: it actually uses less energy to turn run the system all the time than to have it off for 4 hours a day, though 8 hours off time is still more efficient). Add in the effects discussed elsewhere in this thread where not all energy consumption is equal from the point of view of the grid and it may even make sense to do the opposite: run the A/C hard during the day while you're not home but green electricity is cheap so you can have it off when you get home and elecriticy demand spikes and solar power is falling off, flattening out the dreaded 'duck curve'.
Yes I read and you can see clearly on charts switching of AC for 1/3 of time (8 hours) saves only ~10% energy. So yes, you will save negligible amount of energy by having switched off AC for non-negligible amount of time.
> It's a convenient myth that not turning off the heating when you're not home saves energy
Stop twisting my words, I didn't say anything like that, I just said thosae savings are negligible and irelevant.
Not just you who's saying that, but it's a thing that keeps being repeated. You didn't say it helped at all, while in reality it does. That's the thing people are going to remember.
Ask anyone if they want a 10% discount on their energy bill (while helping the environment / energy transition to boot) and see what they say. I don't think it's going to be "nah, not worth it".
I said "it doesn't save even 10% of energy", maybe work on your reading skills if that means for your it doesn't help at all.
Yeah and ask those people if they wanna come for this saving to hot home. This negligible at best 10% discount ain't for free, it cost you convenience which I value at more than some negligible saving.
Did you read the article you linked? It says:
> What we found was that even when the A/C temporarily spikes to recover from the higher indoor temperatures, the overall energy consumption in the setback cases is still less than when maintaining a constant temperature throughout the day.
Even if you ignore the whole thing (as I should have, I was validating their method because the conclusion you cited sounded wrong... but then it turns out the conclusion isn't what you claim) and just read the concluding two sentences of the post, you'd have read: "An eight-hour setback on weekdays provides savings regardless of the system type"
It's a convenient myth that not turning off the heating when you're not home saves energy because the heater would otherwise have to work extra hard when you come home / wake up and consume more energy. I've heard it told by people that usually have sensible opinions. I guess it's the inverse myth in the hot places of this world. It is indeed very nice to walk into a climate-controlled place, so I can see why people love to believe it.
It makes no sense. Think about it: in the scenario where you let the AC run all day long (or leave the heater on overnight), the temperature differential between inside and outside is larger. More heat enters/leaves the house when the differential is greater, so it makes sense to let this grow smaller when you're not there anyway and only increase the differential when you're (almost) coming home or coming out from under the blankets.