General > General Technical Chat
Keep the heating in a house all day on?
richard.cs:
--- Quote from: Siwastaja on October 26, 2021, 05:35:41 pm ---Only the average power matters in the bill, and it depends only on the average temperature difference across the envelope of the house, and by reducing average indoor temperature, you are reducing that average power.
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In a pure physics sense, this totally correct, assuming no cycle-related inefficiencies in the heat source which is probably close enough. However Kleinstein's point about temperature perception and surface temperatures is very valid. If you come into a recently-cold house and all the surface you touch are cold, you will feel cold and likely want a higher air temperature to compensate. Human physiology and psychology comes into this because it is a question of achieving a particular comfort level rather than a particular temperature.
--- Quote from: Kleinstein on October 26, 2021, 03:55:07 pm ---For the temperature felt, the surface temperatures are also part of the temperaure perception. So when the surfaces are still cold one may need a high air temperature to the same subjective feeling.
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armandine2:
.... whatever the physics, :'( I think the psycho-economics will trump this for most of us. I lived next door to a tenant who had a debilitating condition which caused him to stay in all day with the heating on (quite high I thought) doing yoga or reading books. As I returned to my cold flat I often wondered who was worse off!
EEVblog:
Depends on your thermal mass, insulation, and cost of available energy source.
e.g. if you have excess solar during the day then you would absolutely heat during the day and rely on residual heat at night.
Siwastaja:
--- Quote from: Alti on October 26, 2021, 07:25:08 pm ---Shorter RC constant allows deeper setback temperatures and thus lower average temperature#. This can only be improved by either decreasing the Cp*mass of the house, or by increasing available hating and cooling powers. Both require different paradigm in design where the standard is quite opposite: high Cp*mass, lowest heating power (heat pump) and lowest cooling power (good insulation). Does not make much sense to me but somehow this solution is preferred, over a short RC house, at least in colder part of Europe.
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Short RC indeed improves controllability, but for a high cost: small R means high loss of energy. Insulation slows down adjustments but quite obviously reduces the consumption. While it prevents such tricks, it also makes them unnecessary. So if low RC comes with low R, it has no upsides.
Now if we choose large R (good insulation) which is obviously always a good thing, this still lets us to adjust C. Choosing as small C as possible would bring us some of the controllability, not as short RC as in a poorly insulated house, but still something. This allows the trick discussed here (savings by dynamically adjusting the indoor temperature according real needs). However, high value of C allows different saving tricks:
* No need to switch between heating and cooling (or suffering overheating) when the average (24h) outdoor temperature is close (or tad below) to desired indoor temperature. Low-capacity houses suffer from the fact you need to heat the house during night time and then at daytime, when sun is shining (even worse if windows are large), the house overheats (you lose the free energy by opening windows and ventilating) or even worse, you need to start cooling the house.
* You can heat/cool whenever the energy cost is lower; for example, with heatpumps, heat when the temperature difference is smaller, cut down heating power during coldest time. Or, follow the hourly energy SPOT prices. Or, follow your own solar production.
I think these "tricks" are WAY more valuable than the quick controllability of low-C houses.
This is clearly visible here, old-style massive brick houses here, those that survived WW2, are fine without heating or cooling from late spring, through summer, to early fall. They consume less energy in reality than on paper (when simply calculated from thermal resistance of materials, obtaining U value). Modern low-capacity well insulated houses require on/off heating and cooling around the whole year. They consume more in reality than on paper.
But you can have both if you want to: build with low-C materials but add a water storage tank (at least some 2000-3000 liters). Then you have the storage capacity but it's under separate control so you can choose when to charge, when to discharge it by adjusting valve positions.
Siwastaja:
--- Quote from: richard.cs on October 27, 2021, 09:05:41 am ---In a pure physics sense, this totally correct, assuming no cycle-related inefficiencies in the heat source which is probably close enough. However Kleinstein's point about temperature perception and surface temperatures is very valid. If you come into a recently-cold house and all the surface you touch are cold, you will feel cold and likely want a higher air temperature to compensate. Human physiology and psychology comes into this because it is a question of achieving a particular comfort level rather than a particular temperature.
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Yes you are totally right, we can't ignore the temperature perception. Yet it's still the secondary point. It's most important to get the base physics right first, then finetune. For example, as discussed in another thread, in-floor heating and ceiling heating both have the same surface area, resulting in the same theoretical heating water distribution temperature for the same power output, but in-floor heating would allow you to use a bit lower temperature because your feet will feel warm; especially if you are one of those who suffer from cold feet and crank up the temperature to compensate. This could translate into some 5-10% savings. It's important, but still a finetune compared to the base physics behind all this.
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