3 ms·

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 essent

by lucb1e 4y ago

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.

ZeroGravitas 4y ago
These guys cover it, and despite the cheesy Youtube thumbnail, cover it with reasonable nuance: https://www.heatgeek.com/should-your-heating-be-left-on-all-the-time-or-not/ https://www.heatgeek.com/should-your-heating-be-left-on-all-... > heat loss is not the same as fuel consumption. > 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?
- lucb1e 4y ago
  (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!
  - ZeroGravitas 4y ago
    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.

by lucb1e 4y ago

ZeroGravitas 4y ago

These guys cover it, and despite the cheesy Youtube thumbnail, cover it with reasonable nuance: https://www.heatgeek.com/should-your-heating-be-left-on-all-the-time-or-not/ https://www.heatgeek.com/should-your-heating-be-left-on-all-... > heat loss is not the same as fuel consumption. > 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?

lucb1e 4y ago
(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!
- ZeroGravitas 4y ago
  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.