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  1.  
    Is there a ball park figure for the %age increase in energy use for a typical residential property for every degree the internal temperature is increased above 20deg. C..
    I realize there is a whole bunch of variables that will alter the answer but I am looking for a rough guide number.
    • CommentAuthorowlman
    • CommentTimeFeb 18th 2021
     
    As you say Peter there are so many variables, so as to make any calculation a bit of a nightmare.
    However, the nearest rough guide/ rule of thumb I got to on an internet calculator, was; in order to achieve approx 21-22 degrees C. 1kW is required for every 14 cu metres with an outside temp of 0 degrees C. on a property with average insulation, ( whatever that is ).
    • CommentAuthortony
    • CommentTimeFeb 18th 2021
     
    I use a rule of thumb for heating energy use, one degree higher =5% extra 2 degrees 7 and three is close on 15% additional heating bill - on average when it is very cold outside costs can be higher

    Note, heating energy as opposed to total energy use (I include most lighting energy in heating energy use)
  2.  
    Think you can do that with Heating Degree Days for your location

    Let's imagine a location with 3000HDD @ 15C baseline. You can search figures for wherever you are.

    Often this is with a baseline of 15degrees, so the house is assumed to need no heating when the outside temperature is above 15degC, you can tweak this if your house performs better. This accounts for solar gains, lighting, etc.

    If the internal temperature is now made 1deg greater, the total heating demand increases, by (1deg * 365) = 365HDD extra

    So the increase in paid-for heat is 365/3000 = 13%

    If you lived in a place that only needs borderline heating, say 1000HDD, the effect of each extra degree heating is more pronounced as you would expect. 365/1000 = 37%

    You can do this better by recalculating the HDD with a higher baseline, and by questioning whether the extra 1degC is 24/7/365 or just on winter evenings, but sounds like you wanted a round number.

    Aberdeen:2500HDD
    Budapest:2100HDD
    Penzance:1700HDD

    (Edit to add: I live somewhere that needs heating all year round, whether by incidental heat or by fuel. However if you live somewhere that needs cooling, then choosing a higher indoor temperature would reduce your energy use, not increase it, for that part of the year)
    • CommentAuthorEd Davies
    • CommentTimeFeb 18th 2021
     
    My attempt to come up with the inverse of this - how the boiler run time varies with outdoor temperature and wind - for the rental house I'm now in:

    https://edavies.me.uk/2021/02/heatreq2/
    •  
      CommentAuthordjh
    • CommentTimeFeb 18th 2021
     
    I've never really understood HDD. For some reason they make my brain hurt.

    Posted By: WillInAberdeenIf the internal temperature is now made 1deg greater, the total heating demand increases, by (1deg * 365) = 365HDD extra

    Is that right? You don't need to increase the temperature by 1°C on days when it was already warmer than that.

    If you lived in a place that only needs borderline heating, say 1000HDD, the effect of each extra degree heating is more pronounced as you would expect. 365/1000 = 37%

    Which would be true on more days in the second case so the numerator would be less than for the first case?
  3.  
    As I mentioned earlier, if you live near me then you need heating every day, whether incidental or deliberate, the proportion depending what base temperature you specified.

    If I can insulate enough, I can reduce my non-incidental heating demand maybe even to 1000HDD, so then each degree of heating becomes more significant, as I mentioned.

    If you live somewhere else, then you can adjust your base temperature and recalculate, as I mentioned, which will account for however many days you have when the average temperature is above 21degC. There are several other adjustments you can make for improving accuracy, like Ed has done, but I understand that isn't what PiH is looking for.
  4.  
    For example:
    Budapest
    2089HDD with a baseline temperature of 15.5deg
    2318HDD with a baseline temperature of 16.5deg

    Additional heating required = 229HDD so that's seven or eight months of the year

    Additional heating required = 229/2088 = 12%

    This still includes a bunch of approximations such as that the incidental gains are not dependent on internal temperature. You can carry on tweaking as much as required. SAP does this for you, and I expect PHPP does too.
  5.  
    Thanks for the answers so far.

    The story behind the question is that I have a tenant who has made the life style choice that in the winter he likes to sit in the lounge (and move around the house) in shorts and a tee shirt and for this he wants a temp. of 26 - 27 deg. My resources can't keep up with this ! I just don't have enough forest to sustain this rate of energy usage (all heating is done with wood), quite apart from what I would consider the ethical issues of squandering resources with the attendant pollution.

    I can quantify the central heating which they want on evenings and over night (1800 to 0600) which last month amounted to 1450kWh but in addition to this there is a wood burning stove which is lit about 1400hrs when they come home from work and is run flat out until they go to bed about 2300hrs. The wood stove is close to impossible to quantify as wood is so variable, I just see the rapidly diminishing pile. The energy is charged for by a kWh meter for the CH and the WBS by volume of wood.

    I would consider about 20degC to be a reasonable domestic temp. (our tourist regs. stipulate that property should be capable of heating to 20degC)The answer from Will implies a 12% increase in energy from 15 to 16 and the reply from Tony implies that a 3deg increase = +15% so putting those together running 6 - 7deg higher is probably going to use something around 30% to 40% more energy

    Next question is - what to do about it !
    •  
      CommentAuthordjh
    • CommentTimeFeb 18th 2021
     
    Posted By: WillInAberdeenAdditional heating required = 229HDD so that's seven or eight months of the year

    Additional heating required = 229/2088 = 12%

    This is the kind of thing I was thinking about, that your original post didn't seem to take into account, just using 365 all the time. Thanks.

    PS Where you live is irrelevant, since we're talking about where Peter lives. no?

    PHPP uses a fixed internal temperature of 20°C and generally uses the European standard climate data for the region unless you override it, I think.
    •  
      CommentAuthordjh
    • CommentTimeFeb 18th 2021
     
    Posted By: Peter_in_HungaryThe story behind the question is that I have a tenant who has made the life style choice that in the winter he likes to sit in the lounge (and move around the house) in shorts and a tee shirt and for this he wants a temp. of 26 - 27 deg. My resources can't keep up with this ! I just don't have enough forest to sustain this rate of energy usage (all heating is done with wood), quite apart from what I would consider the ethical issues of squandering resources with the attendant pollution.

    I can quantify the central heating which they want on evenings and over night (1800 to 0600) which last month amounted to 1450kWh but in addition to this there is a wood burning stove which is lit about 1400hrs when they come home from work and is run flat out until they go to bed about 2300hrs. The wood stove is close to impossible to quantify as wood is so variable, I just see the rapidly diminishing pile. The energy is charged for by a kWh meter for the CH and the WBS by volume of wood.

    I would consider about 20degC to be a reasonable domestic temp. (our tourist regs. stipulate that property should be capable of heating to 20degC)

    What does your contract say? i.e. the lease? Does it make any promises about fuel supply, who and how much? Is the CH a wood-burning boiler or somesuch?

    Assuming no legal problems, just tell him the maximum quantity of wood you are willing/able to supply. Perhaps advise him where he might be able to buy more.
    • CommentAuthorJeff B
    • CommentTimeFeb 18th 2021 edited
     
    <blockquote><cite>Posted By: Ed Davies</cite>My attempt to come up with the inverse of this - how the boiler run time varies with outdoor temperature and wind - for the rental house I'm now in:

    <a href="https://edavies.me.uk/2021/02/heatreq2/" rel="nofollow">https://edavies.me.uk/2021/02/heatreq2/</a></blockquote>

    Very interesting report!

    I know anecdotally that the outside temperature and wind speed have a big effect on our wood pellet usage, in particular the combination of very low temperature and high wind. Where we live in west Wales the prevailing wind is normally westerly but during the recent cold spell was N to NE and was quite strong from about the 10th to the 13th Feb.

    Being a bit of a geek I keep a daily log of pellet usage (have done for many years!) and so for interest I have done a plot of the daily pellet consumption for the months of January and February (to date) this year. The room stat is set at a constant 21C.

    Unfortunately I did not record the outside temperature or the wind speed (athough I have no means of measuring the latter anyway – I would have to use the Met Office’s local data). I was surprised to see the size of the effect, in particular the very cold windy days from the 10th to the 13th Feb, when it hovered around 0 to 2C outside. January was not very cold here this year and this is reflected in the figures.

    Although I have, IMO anyway, insulated and draught-proofed the house pretty well, it appears that it could be a lot better sadly!
    • CommentAuthorJeff B
    • CommentTimeFeb 19th 2021
     
    <blockquote><cite>Posted By: Ed Davies</cite>My attempt to come up with the inverse of this - how the boiler run time varies with outdoor temperature and wind - for the rental house I'm now in:

    <a href="https://edavies.me.uk/2021/02/heatreq2/" rel="nofollow">https://edavies.me.uk/2021/02/heatreq2/</a></blockquote>

    I realise from your article that you are not happy with your 2019 heatreq equation, but just for interest I put a few figures together in an Excel spreadsheet and came up with a plot of heatreq vs wind speed for three typical winter scenarios where t = -5C, 0C and +5C and wind speeds from 0 to 25 m/s (plotted as mph equivalent). Intuitively the plots "feel" correct (no pun intended!) as there is an exponential effect with increasing wind speed. I'm not sure how to interpret the results as it surely cannot mean for example that at 0C and a wind speed of 55 mph the heat requirement to maintain an indoor temperature of approx 20C would be nearly 5 times as much as that required when there is no wind at all at the same exterior temperature?

    As you can see from my last post our wood pellet consumption increases significantly when the external temperature gets down to around 0C, combined with a strong N/NE wind, so anecdotally at least there is a definite correlation.
    • CommentAuthorEd Davies
    • CommentTimeFeb 19th 2021
     
    Posted By: Jeff B: “I'm not sure how to interpret the results as it surely cannot mean for example that at 0C and a wind speed of 55 mph the heat requirement to maintain an indoor temperature of approx 20C would be nearly 5 times as much as that required when there is no wind at all at the same exterior temperature?”

    55 mph (24.59 m/s) is pretty extreme. There have been gusts here this winter just over that (maximum 25.7 m/s on Nov 18th) but the highest sustained wind was 18.5 m/s (41.38 mph) for the same half hour.

    Agreed, though, that the equation probably breaks down at the higher wind speeds though that's not obvious from the scatter plots in my earlier posts on the subject such as https://edavies.me.uk/2019/01/continuous/ . Of course, a house with reasonable airtightness would be expected to have smaller numbers for those parameters.
  6.  
    Posted By: djh
    Posted By: Peter_in_HungaryThe story behind the question is that I have a tenant who has made the life style choice that in the winter he likes to sit in the lounge (and move around the house) in shorts and a tee shirt and for this he wants a temp. of 26 - 27 deg. My resources can't keep up with this ! I just don't have enough forest to sustain this rate of energy usage (all heating is done with wood), quite apart from what I would consider the ethical issues of squandering resources with the attendant pollution.

    I can quantify the central heating which they want on evenings and over night (1800 to 0600) which last month amounted to 1450kWh but in addition to this there is a wood burning stove which is lit about 1400hrs when they come home from work and is run flat out until they go to bed about 2300hrs. The wood stove is close to impossible to quantify as wood is so variable, I just see the rapidly diminishing pile. The energy is charged for by a kWh meter for the CH and the WBS by volume of wood.

    I would consider about 20degC to be a reasonable domestic temp. (our tourist regs. stipulate that property should be capable of heating to 20degC)

    What does your contract say? i.e. the lease? Does it make any promises about fuel supply, who and how much? Is the CH a wood-burning boiler or somesuch?

    Assuming no legal problems, just tell him the maximum quantity of wood you are willing/able to supply. Perhaps advise him where he might be able to buy more.


    The contract gives the price / kWh for the CH which is a wood burning boiler with a TS where the kWh is measured by an inline kWh meter and the wood for the stove is priced / m3. There are no amounts of fuel specified.

    Reading through the WBS manual it would appear that the amount of wood being used puts the stove outside of the operating specifications. I suspect they are running the stove with the door wedged open to get a hotter burn (I caught them at this once on a casual visit and mentioned it but without barging in it is now difficult to prove) However the amount of wood used , putting the stove out of spec. would mean that they are failing in their duty of care of the property which would be a breach.

    I will be telling them that the amount of wood they are using is beyond my forest management plan and they will have to source their own supply.

    The attitude of heating the house to shorts and tee shirt temps. in the winter goes against my ethics. But at least they don't smoke in the house, (also in the contract) but they put on a dressing gown to stand outside to have a fag.
    •  
      CommentAuthordjh
    • CommentTimeFeb 19th 2021
     
    Posted By: Peter_in_HungaryThe attitude of heating the house to shorts and tee shirt temps. in the winter goes against my ethics. But at least they don't smoke in the house, (also in the contract) but they put on a dressing gown to stand outside to have a fag.

    Mine too, so I sympathise, but letting properties and other legal contract-driven endeavours tend to test our morals and ethics at times. Personally I wrap up in the house and more so outside but I guess Putin doesn't and even the youth we buy our eggs from regularly wears shorts in the snow.

    You'll likely find out how much they care from what happens when you tell them they will need to find and buy their own wood. :bigsmile:
    • CommentAuthorJeff B
    • CommentTimeFeb 20th 2021
     
    <blockquote><cite>Posted By: Ed Davies</cite>Posted By: Jeff B: “I'm not sure how to interpret the results as it surely cannot mean for example that at 0C and a wind speed of 55 mph the heat requirement to maintain an indoor temperature of approx 20C would be nearly 5 times as much as that required when there is no wind at all at the same exterior temperature?”

    55 mph (24.59 m/s) is pretty extreme. There have been gusts here this winter just over that (maximum 25.7 m/s on Nov 18th) but the highest sustained wind was 18.5 m/s (41.38 mph) for the same half hour.

    Agreed, though, that the equation probably breaks down at the higher wind speeds though that's not obvious from the scatter plots in my earlier posts on the subject such as<a href="https://edavies.me.uk/2019/01/continuous/" rel="nofollow">https://edavies.me.uk/2019/01/continuous/</a>. Of course, a house with reasonable airtightness would be expected to have smaller numbers for those parameters.</blockquote>

    I can see now that this is a fiendishly complicated business! There are cold days with or without wind or cold days with intermittent wind. A further complication in my case is that we have solar thermal so the difference between a cold sunny day and cold cloudy day can have a big impact on the DHW heating requirement which in turn affects the amount of pellets burned! (Note: our wood pellet boiler serves both C/H and DHW).

    Attached is a plot of pellets consumed vs degree days for February (1st to the 18th). The r squared value (correlation coefficient) is pretty poor but there is a visual trend at least. I realise the degree day figure does not take the wind chill factor into account but I was just interested to see if this would work. Also degree day data are readily available for my postcode.

    There are two major outliers (circled) and when I looked into these apparent anomalies I found that the lower one at 12.9kg/8.08 degree days was on the sunniest day of the month (9 kW PV against the average of 3.5 for the month), hence reduced heating demand for DHW. The higher one at 22.9kg/7.00 degree days was on the 14th Feb, the day after the coldest day of the month (13th Feb, with 25.5kg pellets used) and the house was still "cool" from the night before and therefore required more heat.

    I haven't done the calculation but I suspect that leaving these two outliers out would improve the r squared value quite a bit!
  7.  
    They both look the same distance from your trendline so shouldn't affect the R². But if you discard one and not the other, the trendline will change, that's the problem with picking data to make a trendline 'fit better'! If you have data going back further, just adding a lot more datapoints to dilute the 'outliers' is more robust.

    In Excel you can do two dimensional regression, so fit your data to both temperature and windspeed? (Or more, fit it also to hours of sunshine, wind direction, electricity used, etc?)

    The smart bit is to use your data to inform choices you make and monitor the results! Eg if you add insulation, did it reduce energy consumption, or did the wind still blow it away?

    Edit: when you downloaded the degree days, you specified a baseline temperature, maybe 15deg? You can tweak this to make the line fit better. Start by regressing the pellets used against outside temperature, to find the temperature at which zero heating is needed. (above this is the DHW usage, knock this off to find the CH)

    Also beware the source of the data - our last house was 15miles from an airport which was the source of all met readings, but we were uphill and away from the sea, so had visibly more frosty/snowy and less foggy weather than them.
    • CommentAuthorJeff B
    • CommentTimeFeb 20th 2021
     
    Leaving out the two outliers, r squared = 0.64. (was 0.42).
    • CommentAuthorJeff B
    • CommentTimeFeb 20th 2021
     
    <blockquote><cite>Posted By: WillInAberdeen</cite>They both look the same distance from your trendline so shouldn't affect the R². But if you discard one and not the other, the trendline will change, that's the problem with picking data to make a trendline 'fit better'! If you have data going back further, just adding a lot more datapoints to dilute the 'outliers' is more robust.

    In Excel you can do two dimensional regression, so fit your data to both temperature and windspeed? (Or more, fit it also to hours of sunshine, wind direction, electricity used, etc?)

    The smart bit is to use your data to inform choices you make and monitor the results! Eg if you add insulation, did it reduce energy consumption, or did the wind still blow it away?</blockquote>

    Agree but that is the tricky bit with all the variables. I can indeed go back as I have many year's worth of pellet usage data and solar PV data but nothing on external temperature or wind speeds. There is a lot of Met Office data on the Internet from the local weather station (Aberporth) but do I have the time? My wife thinks decorating is far more important for some reason! :wink:
  8.  
    Posted By: meThey both look the same distance from your trendline so shouldn't affect the R².

    Sorry my typo - should have said they shouldn't affect the trendline, not the R².
    I tinker with this kind of stuff to look busy and avoid decorating....
    • CommentAuthorEd Davies
    • CommentTimeFeb 20th 2021
     
    Posted By: Jeff B…14th Feb, the day after the coldest day of the month (13th Feb, with 25.5kg pellets used) and the house was still "cool" from the night before and therefore required more heat.
    Yes, you have to choose your timescales carefully. An ideal model would take into account the temperatures in the building fabric but then you'd finish up with a lot of parameters to fit. It's the reason I went for weeks rather than days to do the comparison as anything much shorter is too noisy.
    • CommentAuthorJeff B
    • CommentTimeFeb 20th 2021 edited
     
    Posted By: owlmanAs you say Peter there are so many variables, so as to make any calculation a bit of a nightmare.
    However, the nearest rough guide/ rule of thumb I got to on an internet calculator, was; in order to achieve approx 21-22 degrees C. 1kW is required for every 14 cu metres with an outside temp of 0 degrees C. on a property with average insulation, ( whatever that is ).


    Our place is 180 sq.metres, so multiply by 2.4 (average room height) = 432 cu.metres. Divide by 14 = 31. So 31 kW required to keep house at 21C when outside temperature = 0C. We burn approx 22 kg of pellets on such days, equivalent to 100 kW, so either the formula is very dodgy or our house is appallingly insulated!
    •  
      CommentAuthordjh
    • CommentTimeFeb 20th 2021
     
    Posted By: Jeff BWe burn approx 22 kg of pellets on such days, equivalent to 100 kW

    So many kg of pellets would be equivalent to so many kWh, a measure of energy. kW is a measure of power, so so many kg of pellets per day is indeed a power, but I'm not sure that's what you meant. 100 kW would make your place very toasty indeed, no matter how poorly insulated, I think.
    •  
      CommentAuthordjh
    • CommentTimeFeb 20th 2021
     
    Posted By: owlman1kW is required for every 14 cu metres with an outside temp of 0 degrees C. on a property with average insulation, ( whatever that is ).

    Hmm, so if our property was averagely insulated, we'd need about 30 kW. As it is we need 1 kW (about 3.5 kW for 7 hours). So clearly, estimating how average your insulation is, is quite important.
    • CommentAuthorEd Davies
    • CommentTimeFeb 20th 2021 edited
     
    https://en.wikipedia.org/wiki/Pellet_fuel#Energy_output_and_efficiencyThe energy content of wood pellets is approximately 4.7 – 5.2 MWh/tonne[41][42] (~7450 BTU/lb), 14.4-20.3 MJ/kg.
    That's 4.7 to 5.2 kWh/kg, so

    Posted By: Jeff BWe burn approx 22 kg of pellets on such days, equivalent to 100 kW, …
    should obviously be 100 kWh/day which is 4.167 kW.

    I hate kWh, the persistent confusion is just tedious.
    • CommentAuthorJeff B
    • CommentTimeFeb 20th 2021 edited
     
    Posted By: djh
    Posted By: Jeff BWe burn approx 22 kg of pellets on such days, equivalent to 100 kW

    So many kg of pellets would be equivalent to so many kWh, a measure of energy. kW is a measure of power, so so many kg of pellets per day is indeed a power, but I'm not sure that's what you meant. 100 kW would make your place very toasty indeed, no matter how poorly insulated, I think.


    The 100kWh output is spread over about 11 hours, which is the total time the boiler runs every day. Yes, if I set fire to the whole 22kg of pellets in my fireplace the place would indeed be pretty toasty (for a short time anyway!).
    • CommentAuthorJeff B
    • CommentTimeFeb 20th 2021
     
    Posted By: Ed Davies
    https://en.wikipedia.org/wiki/Pellet_fuel#Energy_output_and_efficiencyThe energy content of wood pellets is approximately 4.7 – 5.2 MWh/tonne[41][42] (~7450 BTU/lb), 14.4-20.3 MJ/kg.
    That's 4.7 to 5.2 kWh/kg, so

    Posted By: Jeff BWe burn approx 22 kg of pellets on such days, equivalent to 100 kW, …
    should obviously be 100 kWh/day which is 4.167 kW.

    I hate kWh, the persistent confusion is just tedious.


    Sorry, yes, my mistake with the units. As I wrote above, the boiler runs for about 11 hours a day, so an average of 9 kW per hour*. That is an oversimplification though as the boiler modulates in response to the demand, starting off at 27 kW (after an initial warming up period) and then gradually modulating down to a minimum of 4.7 kW. It rarely goes off completely though and typically will tick-over at 4.7.

    *Note - that is when the outside temperature is close to zero; the average winter daily usage would be around 18kg.
    • CommentAuthorJeff B
    • CommentTimeFeb 20th 2021
     
    Posted By: owlmanAs you say Peter there are so many variables, so as to make any calculation a bit of a nightmare.
    However, the nearest rough guide/ rule of thumb I got to on an internet calculator, was; in order to achieve approx 21-22 degrees C. 1kW is required for every 14 cu metres with an outside temp of 0 degrees C. on a property with average insulation, ( whatever that is ).


    Does that mean 1 kW per hour for every 14 cu.metres? If so, then for my 432 cu.metre house I would need 432/14 = 31kW every hour? If so, then my average of 9kW per hour doesn't seem too bad!
    •  
      CommentAuthordjh
    • CommentTimeFeb 21st 2021 edited
     
    Posted By: Jeff BkW per hour

    Sorry, but kW per hour doesn't make much sense as a unit. It makes my brain hurt even thinking about it. :bigsmile::devil:
   
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