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| Keep the heating in a house all day on? |
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| Alti:
--- Quote from: Siwastaja on October 28, 2021, 08:32:32 am --- (..) Yes you are right, and as a consequence, houses that are not constantly occupied do not require as much insulation (..). Now the question is what to do when duty cycle is say 50% but period is as short as 24hrs - people live in the house but go to work and so on. --- End quote --- I am glad you asked. Forget about Finland and EU, lets move to the Dreamland for a moment. If we relax this problem of multitude of constraints, it can be quite easy to estimate the potential of OP's concept/question. Imagine a house with super low RC, but with standard R. In terms of engineering design, imagine a model, a free standing single room house, insulated from INSIDE, with floors and walls layout and furniture made out of low Cp*mass materials and machinery for injecting/extracting heat. Not a concrete slab, in other words. Imagine RC=5s. My conclusion is that in Dreamland a room only needs the amount of energy that goes through the walls when there is someone in it, and only this part of the energy is used really. All the remaining energy for heating demand is not used but wasted. Under this definition, when you are not inside, there is no need for the temperature inside to be different than outside temperature, when no energy escapes through the insulation, losses=0. Now, I do not know how about the rest of you but since usually people can typically be present only in one place at a time, this gives an estimation of what this setback concept is worth, the bordering case. Had buildings been built with low RC, these would have required only the fraction of the energy that comes from the occupancy of rooms. So if P people live in Q room apartment, sleep 1/3 of the time, leave for shopping, work, etc, there is no way they could all be in more than P places at the same time. Of course once you return back to Finland, add more constraints, insulated internal walls, RH, high powers required to heat up room to temperature in seconds, things get messy. But the lesson from it is that, depending on occupancy, there is a potential in saving not wasting huge amounts of energy. Alternatively, keeping wasting same amounts of energy but at lower investment cost. |
| Siwastaja:
Yes, your model is correctly build but it's impractical, it doesn't match with reality. But it's really useful demonstration to aid understanding. Add thermal insulation to internal walls, build with low-C materials (so that significant part of heat capacity is in the air), and install a ducting system with shut-off valves and huge fan units so that you can, at any time, swap air between any two arbitrary rooms using laminar flow to prevent air mixing. Now you can keep one room heated, and when you are entering another room, the warm air is quickly swapped to that room, bringing it up to heat in seconds, while cooling down the room where you were earlier. You can also install water pipes in all inner walls, floor and ceiling, even inside heavy furniture, and use powerful (think about megawatts) heatpumps with ultracapacitor supply to swap the heat between rooms in seconds. Doing this, average loss through the outer envelope of the house is only that of one room, yet you always have a heated room wherever you are! It's left to the reader to decide if this could ever work in practice. I have a better idea for anyone who has much larger number of rooms than occupants and are really concerned about their energy usage: move to a smaller house, with fewer rooms ;). Or, just insulate, and failing that, do the dynamic temperature control tricks as discussed, they do work and have quite some real saving potentials in poorly insulated houses, there is no question about it. If your temperature drops quickly after turning off the heat, that's a sign that you are losing quite a lot of energy due to limited insulation, but that's also a sign that you are saving every minute by turning off that heat. |
| Alti:
--- Quote from: Siwastaja on October 28, 2021, 10:55:10 am ---Yes, your model is correctly build but it's impractical, it doesn't match with reality. --- End quote --- By definition. The purpose of model is not to convince someone to install water pipes in furniture. It is to show that total cost of heating the building (investment + energy) is a continuous function of RC step response of powers installed. For ridiculously short step response and high powers this total cost is astronomical. For ridiculously long RC this total cost is also higher than necessary because of the energy and insulation needed to justify heating 24/7 when in reality you are not everywhere at the same time. So this total cost has to have minimum, with minimum location that heavily depends on the occupancy. For occupancy=1 the 24/7 house is the solution. But for all other occupancies it is not. And assuming we are talking here about mammals who sleep 1/3 of the time, the 24/7 house should have never happened. IMHO. |
| Siwastaja:
Low RC has advantages. The problem is, with real building materials including furniture etc., C can't be arbitrarily low, so in reality, low RC is "achieved" by low R. This changes the "low RC advantages" into "low R workarounds". Sure, they still help, given that R is fixed and can't be changed (and this is quite fair, retrofitting insulation is many times more expensive than just do it right the first time). However, you did miss my earlier points that high RC has different set of advantages. I'm sure you have noticed energy storage is now a really hot topic, and for a good reason. We already have hourly energy pricing as an option, and I'm sure it will be forced down our throats want it or not. Uncertain and uneven production of renewables, and uneven consumption are the root causes, and it's not getting any better. Another point is, heatpump efficiency is not a constant. You can fight this by having Tesla install massive grid-connected li-ion packs and that's fine too, but that's not the only way. Large RC households offer distributed energy storage capability with little effort and cost (often it already exists, and only lacks monitoring and control). If you have that concrete slab and decent insulation, you can just cut heating for the most costly hours no problem. This can reverse the whole thing; I'm running a heat pump during daytime, when my PV installation is generating, and outdoor temperature is at highest, so that heatpump efficiency is at highest as well. But I have fairly stable indoor temperature because the house itself has quite decent R, mediocre but not too low C, with another C (1200 liter water tank) in parallel. Mixing valve to that tank increases controllability but for now it just stays fully open. |
| Marco:
--- Quote from: langwadt on October 27, 2021, 08:22:23 pm ---well, it should also mean that it stays at a comfortable temperature longer --- End quote --- When it's not needed. At equilibrium to keep at a constant temperature takes the same power regardless of how much thermal mass is inside the insulation. Ignoring power failure all thermal mass does is force you to start heating earlier when you need it and carry heat to times when you don't need it. Thermal mass in your home is not terribly useful storage, you generally want to keep storage separate from your living room, so you can heat it to say 60 degrees Celsius and not die. |
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