Keep the heating in a house all day on? - Page 1
Forum section: electronics / general

author: Picuino
author_rank: Super Contributor
timestamp: October 26, 2021, 03:48:51 pm
content: There are several oppinions about how to manage the house heater.1. Some think it is cheaper to keep the heater all day on.2. Others think it is better to switch off the heater and heat the cold house every time you arrive.In my opinion is always better the option 2. You can waste a lot of energy heating the cold house, but it's less than maintaining all the time the house hot.What are your arguments about the question?

author: Kleinstein
author_rank: Super Contributor
timestamp: October 26, 2021, 03:55:07 pm
content: It depends:If the house is very well insulated, there is not much difference, as even if one would turn of the heat, it would not cool down very much.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.I may need less energy to get it warm only ehen you really need it, but it is also more complicated to regulate an one may overshoot to more than actually needed.It also depends on the type of heating system. Some (like a wood oven) work better when at a relatively high power and than off for longer. Other work better at partial power. This can especially be the case for a heat pump / air conditioner in heating mode. Here the outside temperature also make a difference.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: October 26, 2021, 04:20:40 pm
content: I have temperature logging on my house, and examining the slopes of the heating and cooling curves the results show that if the heat is off for roughly twice the normal thermal cycle of the heater, energy is saved. My house is well insulated and have a modest output fuel burning heater which results in a roughly two hour thermal cycle (temperature varies by about 1.5 deg C). I find these results are in line with Kleinstein's observations and confirm the choice of option 2 if you are gone from the house for a normal workday. In my situation it makes no sense to turn the heater off for short times away from the house. Your situation may be different.You also have to understand your needs. In my case the house is a few degrees below comfort temperature for a sizeable part of an hour upon return from a long off cycle (also in the morning after leaving off at night). You can usually conquer this by appropriate use of a timer, but not everyone will find this approach adequate.

author: Alti
author_rank: Frequent Contributor
timestamp: October 26, 2021, 05:04:59 pm
content: Quote from: Picuino on October 26, 2021, 03:48:51 pmI think your question is poorly posed.You compare two different situations with vastly different comfort levels.With first scenario you do not need to bother about planning or changing settings, every time you want to enter the room/house, in every imaginable scenario, it is already cosy, no compromises. With second scenario it is all about planning and additionally it comes with the penalty when you sit and wait in cold house till it gets to temperature. You trade comfort for kWh in your question, IMHO.Or did you intend to ask in #2: "(..)heat house upbeforeyou arrive."?

author: Siwastaja
author_rank: Super Contributor
timestamp: October 26, 2021, 05:26:58 pm
content: Insulate your house. Then you can utilize the thermal capacity of the structures to your benefit. I live in a 1952 house with some insulation added in 1982 and I can cut all heating for half a day with little effect in room temperature.When this is the case, i.e., the RC time constant is long enough, you can't save anything by cutting power for half a day; the "RC circuit" smoothes the "voltage" and same amount of power is delivered into the system in either case. I.e., you need more power to catch up with the small temperature drop.But for reducing temperature during long enough, so that the duration of reduction last for longer than a few RC time constants, then sure it helps. For a well insulated house with some thermal capacity, that could be the "holiday temperature reduction". For a poorly insulated house (high "conductance" or low thermal resistance of materials), or one with very lightweight materials (low "capacitance" I mean thermal capacity), it could make sense to drop the temperature for just a few hours.Given linear heating cost (like with gas, oil, resistive electicity), basically the average temperature directly determines the heating cost. In a well insulated house, you can't change the average fast. In poorly insulated, you can and should.This is also why such trickery is not used in really cold climates; we have to insulate our houses and then the trick doesn't work. Except for those longer "holiday reductions".

author: Picuino
author_rank: Super Contributor
timestamp: October 26, 2021, 05:29:26 pm
content: Quote from: Alti on October 26, 2021, 05:04:59 pmOk, you can change "(...) heat house upbeforeyou arrive"For my it doesn't matter.When you switch off the heater and the house lowers the temperature, you save energy always from the first minute. it doesn't matter if the house has to be reheated later.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 26, 2021, 05:35:41 pm
content: Yes, you are right. The saving starts immediately.You seemingly "lose" part of the savings if you need higher power to heat up back later. But you did save more than that.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.With heat pumps, cost of heating is not linear so such trickery can be used in our advantage, i.e., heating when COP is better and not heating when it's worse. But there is usually not much to be gained.

author: Neper
author_rank: Frequent Contributor
timestamp: October 26, 2021, 06:13:45 pm
content: For those who want to save without returning into a cold house:We've fitted our radiators with radio-controlled thermostats and when we leave for a whole day we lower the temperature and then crank it up again via a mobile internet access an hour before coming home.

author: Alti
author_rank: Frequent Contributor
timestamp: October 26, 2021, 07:25:08 pm
content: Quote from: Siwastaja on October 26, 2021, 05:26:58 pmShorter 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.#I assume we are talking about working mammals in this topic, those who sleep 1/3 of the time and spend significant part of the remaining time outside. If someone lives ones life running around the house 24/7 then whole setback saving won't work, irrespective of RC.

author: elekorsi
author_rank: Regular Contributor
timestamp: October 27, 2021, 07:50:33 am
content: We have it ON all the time, with the temperature setpoint reduction during the night. Water temperature to the radiators is regulated by outside temperature and fine correction is done via current room temperature... Nice and comfortable all the time, higher setpoint kicks in about an hour before we wake up, so it is already warm.We have a wood gasification boiler from Herz and a 2000 Liter buffer, at current weather (0°C - 10°C) we load it and fire it up every 2 days, in the winter once a day. It burns for around 6-7h, everything that is not consumed by the house goes to the buffer, which is then the source of the energy until next boiler loading...I attached the screenshot of the current operation (just fired it up about an hour ago), if anyone is interested. It's from my little supervisory systemI can access it from anywhere via web browser.

author: richard.cs
author_rank: Super Contributor
timestamp: October 27, 2021, 09:05:41 am
content: Quote from: Siwastaja on October 26, 2021, 05:35:41 pmIn 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 particularcomfort levelrather than a particulartemperature.Quote from: Kleinstein on October 26, 2021, 03:55:07 pm

author: armandine2
author_rank: Frequent Contributor
timestamp: October 27, 2021, 10:34:43 am
content: .... 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!

author: EEVblog
author_rank: Unknown
timestamp: October 27, 2021, 10:50:40 am
content: 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.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 27, 2021, 12:58:12 pm
content: Quote from: Alti on October 26, 2021, 07:25:08 pmShort 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 allowsdifferentsaving tricks:* No need to switch between heating and cooling (or suffering overheating) when theaverage(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.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 27, 2021, 01:05:05 pm
content: Quote from: richard.cs on October 27, 2021, 09:05:41 amYes 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.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 27, 2021, 01:12:26 pm
content: Quote from: EEVblog on October 27, 2021, 10:50:40 amThis is what I'm doing, I have a 3kWp system so during a sunny day run the air-to-water heatpump to store the energy into the 1200 l buffer tank, which then cools down during night back to the starting point. The larger the tank, the lower dT is required to store the same energy. The problem with my 1200l tank is, I need to bring it to some 15degC higher, which already significantly reduces the COP of the heatpump. But it's still way better than selling the power to grid, then buy it back for 2.4x the price. A larger tank would help, but I'm also letting the thermal capacity of the house participate, i.e., the heating water temperature could start dropping already at say 4 a.m., reducing the output power into radiators, but the inside temperature won't fluctuate much if heating is restarted around 10 a.m.

author: Zero999
author_rank: Super Contributor
timestamp: October 27, 2021, 01:28:05 pm
content: It depends on what temperature you heat the house to, compared to the outside.I like my house to be on the cool side. I'd rather wear an extra layer, if needs be, so I set the thermostat to 15°C. The timer turns the heating on, just before I get up in the morning and again, when I get home from work. I very much doubt it would be more efficient for it to run 24/7.I can't remember how much gas and how often my heating kicks in. It hasn't been on since April. It will probably turn on next week, as a cold snap is forecast, which could bring the first frost of the season.

author: Marco
author_rank: Super Contributor
timestamp: October 27, 2021, 01:36:21 pm
content: Homes built with below slab insulation and minimal above slab insulation will have too much thermal mass to get to a comfortable temperature from cold in a reasonable time frame.Don't build homes like that.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 27, 2021, 01:41:22 pm
content: Quote from: Zero999 on October 27, 2021, 01:28:05 pmSounds very British!What I mean is not an offence, but a cultural observation that the colder climate you get into, the higher the indoor temperatures. I'm like you and like my house to be on the cool side, also to save energy, to the point many would say I'm almost an extremist...... but it's not 15degC - it's 20.5degC!I'd hazard a guess the average here would be 23degC and it's not uncommon at all to set thermostats to 25degC. And if the indoor temperature fluctuates even by +/- 1degC, we instantly complain*. If it ever gets below 20 degC in a rented apartment, we ask for the authorities to perform official measurements and file complaints, or seek criminal charges against the owner; it's considered ahealth safety issue. At very least, your kids would be taken into custody if somebody heard you live at +15 degC.*) necessitating a carefully tuned feedforward+P control system as described above by elekorsiWe also are almost hysteric when it comes to mold, and even the idea of dynamic temperature adjustments, or going below 20degC triggers irrational fears that it somehow automatically turns the house into mold nest in no time. This has a grain of truth in it, obviously; some temperature difference between indoors and outdoors is needed to prevent condensation.

author: Zero999
author_rank: Super Contributor
timestamp: October 27, 2021, 01:59:27 pm
content: Quote from: Siwastaja on October 27, 2021, 01:41:22 pmI don't see how anyone could consider 15°C to be cold, unless they live in the tropics. Admittedly it's a little cool to be scantly dressed but perfectly fine with a jumper on. Heck it's 17°C outside today. I walked to the shop this morning wearing a jumper and by the time I got home, I was too warm and had to take it off.I find it difficult to sleep in 25°C. When it's that hot, I just wear a pair of boxer shorts in bed: no sheets, blankets, or duvet. If I rented a place which didn't allow me to control the thermostat and it was that hot, I'd open all the windows and not pay the rent, until the landlord sorted it out.I don't get much mold in my house. Perhaps a little bit around my bedroom window and bathtub, but it's easy to clean off. It's caused by humidity, not cold. I imagine increasing the temperature in my house would make it worse, since warm air holds more moisture, which would condense more on the colder walls and windows.

author: tszaboo
author_rank: Super Contributor
timestamp: October 27, 2021, 02:15:15 pm
content: Depends on the weather more than you think. I have Nest thermostat at home, which has away assist, so it turns down the heating when I'm not at home. I checked the usage for last week, and during the day it was off, whether I was at home or not, because the sunshine, it was only going during the night.But otherwise during the winter it does make a difference, which I can clearly see on the usage. And I can start the heating away from home early, so I arrive into a warm home.So if you wonder, invest into a smart thermostat. I wouldn't actually recommend the Nest, as it measures the temperature wrong (wifi chip heats up the measurement, and I'm not even kidding here), had to RMA one, and it's not possible to extend it to multiroom, because they don't sell the same hardware in europe. So get some other type. It pays for itself, if you forget it on during one 1 week long winter vacation. But I would argue that it will pay for itself just with regular usage within a year or two.

author: themadhippy
author_rank: Super Contributor
timestamp: October 27, 2021, 02:15:43 pm
content: QuoteTalk about nanny state,if that was the case when i was a kid half the population would be in care,waking up to frost on the inside of the windows was accepted,you just got dressed and downstairs as quick as possible, hoping your mum had got the fire going.Maybe that's why i can sit here comfortable in a t shirt and shorts with the thermometer reading 18.4c

author: Siwastaja
author_rank: Super Contributor
timestamp: October 27, 2021, 03:21:51 pm
content: Quote from: Zero999 on October 27, 2021, 01:59:27 pmIncreasing temperature means aircanhold more moisture, it doesn't mean extra moisture is generated, so increasing temperature by heating (by a heat source which doesn't put water into the air, so a boiling tea kettle does not work) reduces RH, absolute humidity being what it is (as defined by how much moisture you breath out, wash dishes, bath, and so on). Now the surface mold you wipe off is caused by said surfaces being cold, below the dew point (which is an alternative way to describe absolute humidity). Absolute humidity is almost always higher indoors than outdoors which is why you will get condensate on the coldest surfaces if the heating or insulation is lacking. But increasing temperature of all surfaces removes this condensation because dew point is not reached, in other words, 100% RH is never reached.This is also why we almost never ever see surface mold here anymore and if we do, many get totally hysterical seeing it (not understanding surface mold is not a big deal, you can indeed just wipe it off). Instead, the big issue is having leaks in vapor barrier so that hot and humid air goes inside structures where it cools down, hits the dew point, and condensates inside the insulation. If the insulation is otherwise OK, surfaces are nice and warm and always stay dry, but the problem is under the surface.But totally cut the heating and buildings will slowly develop mold due to temperature and humidity variations causing conditions where RH hits 100% on a regular basis. Just a tiny bit of heating is enough to prevent this if there are no sources ofaddedhumidity (i.e.,absolutehumidity). The more there is added humidity such as bathing and breathing, the higher the temperature of surfaces must be to keep them below RH100%.And to be clear about what I said earlier, I would enjoy living in 15degC if I had to, this like frozen windows was a normal living standard in 1950's, and I wouldn't want to control others about this choice but the boomers decided no one is allowed to experience what they did when they were kids.So just describing the attitudes as they are here. Combining our standards of insulation (new buildings are required with equivalent of 250mm of top-class mineral wool in the walls, and 400-500mm(!) in the attic), heatpumps, and the British standard of acceptable room temperatures, we could cut CO2 down much more than we currently can due to people wanting to live at +25degC for reasons I really don't understand. Putting clothes on works for me.

author: emece67
author_rank: Frequent Contributor
timestamp: October 27, 2021, 04:01:04 pm
content: .

author: tunk
author_rank: Super Contributor
timestamp: October 27, 2021, 04:26:07 pm
content: Around here much of the heating is done with electricity.And the price varies during the day - I think it's lowestduring the night, and highest around breakfast and dinnertime. So you can save a bit if you switch off heating duringthe high price periods.More info here:https://www.nordpoolgroup.com/Market-data1/Dayahead/Area-Prices/NO/Hourly/?view=chart

author: Vovk_Z
author_rank: Super Contributor
timestamp: October 27, 2021, 04:52:38 pm
content: Quote from: Zero999 on October 27, 2021, 01:59:27 pmThe Earth needs more people like you. As for me, any inside temperature lower than 22 C is cold (in autumn/winter).(because of cold external wall, small but cold droughts).

author: Alti
author_rank: Frequent Contributor
timestamp: October 27, 2021, 07:14:21 pm
content: Quote from: Siwastaja on October 27, 2021, 12:58:12 pmIncreasing R reduces the consumption, at a cost of raised investment, quite obviously. Had you been offered an R for free - go for it. However, keeping same R for two houses with vastly different RC constants and using them for N-th part of the time (lets say RC1>>RC2, N=1 / N=2 examples), the second house would require half of the energy of the first one. So instead of investing into raising R, you can invest into lowering RC, reaching sametotalcosts. In this sense, I disagree with the quote.I'd rephrase: Heating well insulated house 24/7 costs same as heating a not so well insulated low RC house occupied 1/N-th of the time. Whether this tie is for N=1.1 or N=13 for specific design is a different story.

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 27, 2021, 08:12:51 pm
content: Depends, of course, as said above, on various factors.One thing in favor of heating at all times is managing humidity. RH can be pretty high indoors during fall and winter in the absence of heating, depending on where you live, the kind of house, etc. This can be nasty.Of course, if you go for constant heating, you can set it for lower temperatures when you're away. Just enough to manage humidity levels and make it reach a comfortable temperature in just a few minutes when you get home.

author: langwadt
author_rank: Super Contributor
timestamp: October 27, 2021, 08:22:23 pm
content: Quote from: Marco on October 27, 2021, 01:36:21 pmwell, it should also mean that it stays at a comfortable temperature longer

author: Siwastaja
author_rank: Super Contributor
timestamp: October 28, 2021, 08:32:32 am
content: Quote from: Alti on October 27, 2021, 07:14:21 pmYes you are right, and as a consequence, houses that are not constantly occupied do not require as much insulation, it would be money wasted. This holds even in very cold climates. It's an easy thing to do if duty cycle is a few % and the period is a month (for example, spending weekends somewhere once a month).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.Because given cold enough climate - Canada or Northern Europe for example - amount of insulation absolutely needed to make the houses liveable without exploding heating costs pretty much forces the RC time constant in the range of a few days or more, which then prevents optimizing on a 24hrs cycle period, but still allows doing that with longer cycle (holiday reduction, etc.).But really, the equivalent circuit is parallel RC with a current source (heating supply) feeding power into it, voltage being room temperature. Small R (poor insulation) seemingly increases controllability giving the false impression that you can save energy by "dropping" the temperature, but in reality that drop is caused by wasting the energy so you are not saving anything compared to having higher R.Except, as you mention, high R has an investment cost, you do save by not having to invest into insulation materials and thicker walls and more expensive windows and so on. This is a classical optimization problem which can be performed in Excel quite well.In my opinion, designing buildings that last for a long time is the best idea. When building, insulating properly is not that big of an extra expense and it pays back within the first decade or so, and generates savings for the next 50-100 years. I don't like the idea of buildings lasting for only 30-40 years.Retrofitting insulation is a significantly higher expense, usually.

author: Alti
author_rank: Frequent Contributor
timestamp: October 28, 2021, 10:27:53 am
content: Quote from: Siwastaja on October 28, 2021, 08:32:32 amI 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 toestimatethe 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 wallswhen 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 theoccupancyof 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 insavingnot wasting huge amounts of energy. Alternatively, keeping wasting same amounts of energy but at lower investment cost.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 28, 2021, 10:55:10 am
content: 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'salsoa sign that you are saving every minute by turning off that heat.

author: Alti
author_rank: Frequent Contributor
timestamp: October 28, 2021, 11:28:24 am
content: Quote from: Siwastaja on October 28, 2021, 10:55:10 amBy 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.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 28, 2021, 11:41:07 am
content: Low RC has advantages.The problem is, with real building materials including furniture etc., C can't be arbitrarily low, soin 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 hasdifferentset of advantages.I'm sure you have noticedenergy storageis 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 canreversethe 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.

author: Marco
author_rank: Super Contributor
timestamp: October 28, 2021, 12:02:45 pm
content: Quote from: langwadt on October 27, 2021, 08:22:23 pmWhen 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.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 28, 2021, 12:03:34 pm
content: ... and when building from scratch, cost optimization for amount of insulation is quite simple. I did rebuild the upstairs here, completely insulating the attic, and did "napkin" calculation in Excel. I ended up with average 180mm of PIR (polyisocyanourate) sheet because calculated that way, payback time for increasing further 50% from there would be well over 20 years. But going from say 80mm to that 180mm pays for itself in just 10 years.And the cost of energy source of course affects that payback time. Choices of poor insulation have been always made when energy has been cheap.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 28, 2021, 12:06:17 pm
content: Quote from: Marco on October 28, 2021, 12:02:45 pmThis is demonstrably just a false claim. Thermal mass is very useful energy storage as proved by myself and many others. Of course the amount of energy that can be stored is limited by low dT range available, but it's still not meaningless. It's in the range of some 5-50 kWh depending on the house and living standards (how much temperature variation is acceptable), and can carry over high-cost hours with practically no further investments at all.Similar li-ion storage system would cost like some $3000-5000.Those who have a thick concrete slab with in-floor heating pipes and a heatpump, notice the advantages immediately by making the heatpump run by daytime.Sure, on paper, given same R, it's best to use as small C as possible, then use external C (like that water tank) for more controllability. But this also costs more to build.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 28, 2021, 12:11:49 pm
content: Quote from: Marco on October 28, 2021, 12:02:45 pm... and if youreallywant to simulate the leak-the-heat-out behavior of poorly insulated house, nothing prevents you from actively cooling a room with a heat pump, and putting that heat into a storage tank. Obviously such high-tech solution never pays back for itself, but this is just the demonstration of the fact that poorly insulated house leaking out the heat is not an advantage even if it seemingly gives you control "by only having to heat when heat is needed".

author: Siwastaja
author_rank: Super Contributor
timestamp: October 28, 2021, 12:43:29 pm
content: Simplified,Heating(t) = k*(t_in - t_out) - sun_through_windows - human_generated_heat - non_heating_electric_power, when t_in > t_outCooling(t) = k*(t_out - t_in) + sun_through_windows + human_generated_heat + non_heating_electric_power, when t_out > t_inWithout heat capacity,energy consumption = integral over time of (COP_h*heating + COP_c*cooling)Every integration time step will have either heating or cooling.With heat capacity, heating and cooling needs can be averaged together, and so the integral will be smaller. Ignoring complex math, you get into the ballpark by taking the average during the RC time constant. For example, with 24 hrs:Heating(t) = k*(t_in_avg_24h - t_out_avg_24h) - sun_through_windows - human_generated_heat - non_heating_electric_powerCooling(t) = k*(t_out_avg_24h - t_in_avg_24h) + sun_through_windows + human_generated_heat + non_heating_electric_powerenergy consumption = integral over time of (COP_h*heating + COP_c*cooling)With conditions changing between heating and cooling, the latter integral will be significantly smaller.This is well evidenced in old massive brick houses of pre-WW1 where significant part of the year goes without any heating power yet they are quite comfortable in summer even without cooling, and reportedly measured energy consumption is significantly lower than calculated based on the U-values of the structures.At the same time, many "passive homes" or "low-energy homes" of 2000's have failed to get even close to the calculated near-zero energy consumption because they have low C, they overheat already early in spring and require constant switching between heating/cooling to be comfortable. But their consumption has been calculated by taking the sun into account as a positive only, but when the calculated heating power goes into negative, it has been just clipped to zero, causing temporary overheating, which wont't be automatically stored due to low C. But people won't accept that so they let the aircon to switch into cooling mode, following what would have been the correct calculation (negative heating power in the integral -> cooling power).The high-C old brick houses overheat much less due to sunshine, and that little amount of overheating carries long into the night and morning.The trick here is that the old high-C brick houses also have surprisingly high R for their age. C is not any good if the insulation leaks the power out.Value of R is most critical, different ranges of C can be worked around and have different advantages but claims that high C is definitely bad are wrong. In my opinion, high C have more advantages than low C, but only if R is properly chosen for the climate. This is an opinion and I might change it seeing different evidence.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 28, 2021, 03:21:14 pm
content: Attached is a simulation (yes, I'm working on this problem) that fairly well matches my house, simulating May-June 2012*, model includes temperature, wind, solar radiation from different data sources (PV generation simulation is also included for cost analysis, but let's skip that for now), also waste power from electricity used indoors.*) Why 2012? Because it happened to be a very "average" year here, also containing a balanced mix of extremes, so good for design of systems. Last few years have been warmer.The top graph shows, in blue, the calculated heating power demand, in Watts, to keep +21degC indoor temperature. Negative values mean cooling is required. Orange line specifically shows the solar irradiance input power.Mid graph shows outdoor temperature.The last one is interesting as it is the simulation of the room temperature, just for this discussion I chose to set heating/cooling power to constant zero. Now the blue graph is resulting room temperature if thermal capacity of the house is 1kWh/degC, orange graph when it's 10 kWh/degC. The heating/cooling cost is the same by definition (zero in this simulation). Which one you would prefer to live in?

author: Marco
author_rank: Super Contributor
timestamp: October 28, 2021, 05:27:57 pm
content: Now get it to 21 degrees 50% of the time, starting early enough to get it there 50% of the time, and let it coast for the rest of the time. Which power bill would you rather pay?

author: Siwastaja
author_rank: Super Contributor
timestamp: October 28, 2021, 05:50:27 pm
content: OK, I'll run the sim. But hold on a bit, I want to make sure it goes right. I'm happy to be shown wrong so if necessary I can fix my understanding, because long term I can't afford putting a biased opinion ahead of facts, because this simulation and understanding the subtleties of the control is the basis of the business and I need the model to correctly represent and control many different types of houses, including very low and very high thermal capacity.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 28, 2021, 06:56:56 pm
content: OK, here are some results.Now in the model, heating is arranged with simple electronic thermostat, which senses current indoor temperature and provides a variable heating power using a steep P controller (Google "heat anticipator" for explanation of the classic mechanical PWM device), capping max power to 10kW.Again, at the top/blue is the calculated "required" heating/cooling power if steady 21degC would be desired. This info is not used in calculation, just for reference. Top/orange is the solar irradiance power. Again, second graph is outdoor temp. Third graph is simulated room temp. Fourth graph is cumulative output energy.Blue is low thermal capacity house (3kWh/K), orange is high thermal capacity house (15kWh/K). Insulation (i.e., average heat flow through envelope) is the same.First, bear with me, without hourly cutting of powersee thermo1.pngAs you can see, the cumulative energy drifts apart whenever there is overheating due to solar irradiance. Higher thermal capacity house shows reduced consumption right after such sunny days as it stores the energy. This is even with a "dumb" thermostat which does not understand the thermal capacity. Two month consumption, 1015.8kWh vs. 976.53kWh in favor of higher thermal capacity house.Now let's cut the power to both houses. Let's cut it for 12 hours per day, say between 6am to 6pm when going to work and, in very non-Finnish way, eat out after work.see thermo2.pngTwo month consumption is now to 948.45 and 948.56 kWh, basically the same result. As you can see, the average temperature of the low-C house dropped, which also dropped its consumption, but not very much. With high-C house, consumption also dropped, but not as much; but it's still as good.You asked to "start early enough to get it there". Now this expectation comes from the mindset of low thermal capacity. I didn't implement such logic in the model, but as you can see the high thermal house keeps decent nice indoor temperature without such trickery. Here's a zoom-in on transient response:see thermo3.pngSo while you can see that high-C house heats up slower, it starts from higher temperature. You decide which one is better, especially if you miss-schedule and fail to predict your living patterns.This example data was not cherry picked. I'm sure I could find examples of both high-C building showing significantly better result (now the difference was marginal), but also could find data to prove your point where low-C building shows better result.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 28, 2021, 07:06:07 pm
content: ... I made one more simulation where I swapped the on/off time, turning heat off overnight, from 6pm to 6am. With such case, lower C house wins, probably because the reduction now coincides with the time of highest demand so there is potential to drop the average temperature so much it obviously finally does what was discussed in this thread.Consumption:ans = 818.80ans = 924.00But who wants to wake up in such cold rooms. If heating is started already at 4 a.m., the difference reduces:ans = 885.60ans = 942.45

author: Marco
author_rank: Super Contributor
timestamp: October 28, 2021, 10:50:03 pm
content: I thought high performance windows we're pretty much energy neutral in cold weather on a sunny day? (ie. no solar heating in winter.)

author: Siwastaja
author_rank: Super Contributor
timestamp: October 29, 2021, 06:58:50 am
content: Depends on windows and temperatures but for example here the legislation now requires windows to have U < 1.0 W/(m^2 K), and low energy windows down to some U = 0.5 are available, this already equals the insulation level of the walls just a few decades ago!Passive/low energy houses were built here in 2000's with such good materials but fairly low thermal capacity, and with alotof those energy efficient windows (4-glass, with argon filling on the 3-glass element, with spectrally selective coating) facing South. The result was, houses already overheat in early spring. So need to bypass the ventilation (which obviously has thermal recovery) and vent manually. And then when the night comes, heat again. This causes such houses to show significantly, like 20-30% higher energy consumption that was calculated on paper.In any case, my model uses a single 1.5m * 1.1m Window facing South-30deg because that what I have in the 1950's house. If I triple that window area (while keeping my approximately 0.55 U value, i.e., the new windows would be the fancy 4-glass version), the benefit of high-C widens (see attached thermo6.png).OTOH, if we completely remove south-facing windows, then as expected, the low-C solution gets more benefit from the 50% power cutting (see thermo7.png).So I think I'm right about the fact that low-C and high-C solutions have different advantages. And again, IMHO, the advantages of high-C are higher because even if the energy consumption averages to similar values, high-C is less sensitive about prediction errors in human patterns.

author: thinkfat
author_rank: Unknown
timestamp: October 29, 2021, 07:43:05 am
content: One aspect often overlooked is the layout of the house (or apartment) and the possibility to create zones with different temperatures. Bedrooms, hallways and storage spaces with lower, living rooms and offices with higher temperature. Not having to heat the total volume to comfortable temperature saves a lot of energy.

author: Ed.Kloonk
author_rank: Super Contributor
timestamp: October 29, 2021, 09:08:10 am
content: Technology Connections on youtube did a video a few months ago where he figured out that one room in the house could be made to act as a battery for cool air during the off peak power time and in the evening (when he's home) deliver that cool air to the rest of the house.Very clever.

author: cortex_m0
author_rank: Regular Contributor
timestamp: October 29, 2021, 12:42:14 pm
content: It can be complicated. My house has an electric heat pump, and so it has better efficiency when it is 12C than -7C... according to the documentation that's a factor of 2 in efficiency.Given that I work 8-5, and pay the same rate for electricity at all hours of the day, I have the thermostat scheduled to drop 3C at 7:30 and to turn back up at 4:30.So if you imagine a day where the morning low is 0C and the afternoon high is 13C, I effectively eliminate running the heat when it is 1.2 or 1.3 efficient, and run it instead at the warmest part of the day when it is 1.9 or 2.0 efficient (all relative to that -7C figure).If you change the conditions, the answers probably change:With rooftop solar power, you'd want to to use as much of that as possible, meaning running the heat all dayIf the power/fuel has variable pricing through the day, it may be beneficial to run the heat to take advantage of that.If the house was less well insulated and the temperature fell by 6C during the work day, you probably would want to run the heat during the day.I wish there was better tooling to help homeowners optimize their energy use/cost. It seems like some of the "smart thermostats" on the market could provide recommendations, but I'm not aware of any that do so.

author: Siwastaja
author_rank: Super Contributor
timestamp: October 29, 2021, 03:12:47 pm
content: Quote from: cortex_m0 on October 29, 2021, 12:42:14 pmI have noticed exactly the same and think there is a lot to do here with little actual/serious competition. But we'll see.Due to lack of real controls, I simply let my heatpump do the work between 10am to 4am and let it rest when it's coldest. Also having rooftop solar, the operation starting at 10am coincides pretty well with the production.But lack of control also means lack of instrumentation. Even if instrumentation is available (for example, you can install output energy meter in a hydronic system (one that uses accurate flow meter and two accurate thermometers to calculate power), how do you verify if the actions have the effect you expect? Run for a year, then change your habits for another year, while hoping the weather patterns are identical year to year which they are not?Large changes such as replacing COP1 sources with COP3 heatpumps are obviously visible as $$$ saved in bills, but how do you verify what the effect of dynamically changing temperature setpoints is? Theexpectationon the forums seem to be they hold a potential for significant savings, but there is little to prove that except too simplistic napkin calculations. Expect of some low hanging fruit cases, they are micro-optimizations which are easily lost in noise. As you can see from my simulations posted there is no significant difference in energy consumption inanyof the cases.The only solution I can see is simulation with capable enough simulation models. It helps that thermal energy flows are really analogous to electronic design principles and elements like resistors, capacitors, current and voltage sources can be used with Kirchoff laws.