[vnorby]

Wasting/saving energy is not as simple a calculation as that. When energy is at peak use (say in the winter, around 5:30/6:00 when everybody returns from work), it becomes more expensive for energy companies to procure the requisite energy needed. During these peak times, they often have to buy energy from other companies at a higher cost or find less efficient means of generating it (e.g. coal) to meet the demand. Getting an accurate picture of estimated energy demand can actually save a lot of money/energy for customers.

I work at Nest and it may be a little unclear at the moment (we're working on it), but The Nest API does not guarantee that if you send an ETA of 15 minutes (docs: https://developer.nest.com/documentation/eta-guide), the home will heat to the appropriate level in 15 minutes. It's actually filtered through our algorithms to determine the best course of action to not waste energy but also provide the appropriate level of comfort.

[ars]

I looked into the nest but I don't think it would save me any energy. And I'm wondering if that's actually true for lots of people.

I have a modulating (i.e. change flame level) condensing boiler (the highest efficiency available). I programmed it to run as close to 24/7 as I could, because that way it uses the lowest flame, which is the most efficient flame.

When I tried a setback thermostat when the boiler attempted to rewarm the house it shifted to a higher and therefor less efficient flame. So I gave up on that and let it run on low all the time. So there would be no peak usage by me.

As people shift to more efficient ways to heating I suspect that this will happen to everyone. Not just modulating boilers, but also multi-stage heating with a heat pump. By trying to rapidly heat the home you can't use the heat pump.

It's also true with an A/C - the faster you are trying to cool the larger temperature gradient you need, and therefor you lose efficiency.

If I'm wrong here I would be happy to be corrected, but the US Government seems to agree with me: https://www.energystar.gov/index.cfm?c=archives.thermostats_...

[mhandley]

It's also true with an A/C - the faster you are trying to cool the larger temperature gradient you need, and therefor you lose efficiency.

I'm not sure that's always correct. The Coefficient of Performance (heat moved/work done, higher COP is better) of an A/C is:

COP = T_hot / (T_hot - T_cold).

T_cold is the inside temp, T_hot is outside of the heat exchanger. The narrow the temperature range, the better the COP. Thus the A/C will actually be more efficient in terms of heat moved per watt while it's cooling a warm house down than when it's already cool.

There's one other factor that applies. The rate of heat transferring into the house is proportional to the temperature difference. Once the house has warmed up, you reach equilibrium. The net heat flow stops, so the total amount of energy you need to remove later stops rising. If you run the A/C all the time, heat is transferring in all the time. So the total amount of heat you need to move back outside in a day increases significantly if you leave the A/C on.

[ars]

I was assuming a home that never warmed up to ambient, but just partly, and a multi-stage A/C. (But forgot to say that in my message.)

Without those assumptions your analysis is correct, and a setback thermostat seems to always be a win for A/C.

[rlpb]

> I programmed it to run as close to 24/7 as I could, because that way it uses the lowest flame, which is the most efficient flame.

The energy loss from your home increases as the differential between inside and outside increases, right? So at night or when you're out, if your house were kept colder, then you'd lose less energy to the outside.

So by keeping your heating running 24/7, you're wasting some energy in the extra energy loss when you're out, right?

How does this compare to the efficiency gain by running your more efficient flame? Have you calculated or measured that you actually save energy overall?

[ars]

> if your house were kept colder, then you'd lose less energy to the outside.

Yes, but I can't let it cool very far, so it's only a small energy saving.

> How does this compare to the efficiency gain by running your more efficient flame?

The boiler can be up to 98.6% efficient at low flame, going down to 86% at full flame.

And after experimenting it always ended up at full flame when trying to rewarm a house.

> Have you calculated or measured that you actually save energy overall?

I tried, but I couldn't, winters are just so variable. I even emailed the EPA asking if they had research data, but they didn't.

[toomuchtodo]

> I work at Nest and it may be a little unclear at the moment (we're working on it), but The Nest API does not guarantee that if you send an ETA of 15 minutes (docs: https://developer.nest.com/documentation/eta-guide), the home will heat to the appropriate level in 15 minutes. It's actually filtered through our algorithms to determine the best course of action to not waste energy but also provide the appropriate level of comfort.

So you're accepting the ETA request not as a demand to obtain a certain temperature, but as a request, and then still taking utility demand information into account. Excellent.

[yitchelle]

I am not talking about wasting money, I am talking about the actual energy itself as money is more renewable than energy. Once it has been used, it is extremely difficult to get back.

Thanks for the insight, btw.

[nardi]

> money is more renewable than energy

This is a nonsensical view of the concepts of value and money.

[marcomonteiro]

Hey Vibhu, Marco on the Apps Team at Nest.