Browse Forums Heating, Cooling & Insulation 1 Oct 24, 2020 3:10 pm I've been doing some comparisons of potential insulation upgrades that we're thinking of adding to our tender and thought I would share them as I wasn't able to find much in the way of similar comparisons and thought it may help others. It's hard to find much info like "What's more cost effective to upgrade, my ceiling, wall or window insulation?" But understandable as there's a lot of variables involved! Maybe someone might point out my calculations are wrong or something I'm missing!
This mostly started as a comparison of whether we would be better off adding low-e glazing to windows or upgrading wall insulation from R2.5 to R2.7 in case we can't afford both, but added a few other things to the comparison as well. Some background: Our build will be in Melbourne, double storey approx 40SQ and currently has R5.0 to ceilings, R2.5 to external walls, R2.5 between floors and double glazed windows. We will also add anticon 60 to the roof and R2.5 to most of the internal walls. Some dimensions: - Roof/ceiling approx 205sqm (approx 25sqm of flat-deck roof on ground floor that won't have the benefit of the anticon) - Between floors/ceiling approx 150sqm (approx 18sqm over "outside" areas alfresco and porch) - Walls approx 228sqm ground floor hebel walls - Walls approx 202sqm first floor mostly exsulite 75mm cladding some 50mm exsulite and some fibro cladding - Windows approx 70sqm My results: (Note I've updated these from the original posting as I had calculated incorrectly, hopefully they are correct now) Upgrading roof/ceilings from R5.0 to R6.0 - 0.03 U-value improvement - 354 KWH saved per year - $1200 approx cost - $21 saved per year - 1.7% ROI - Note this isn't taking into account any effect from the anticon Upgrading external wall batts from R2.5 to R2.7 - 0.02 U-value GF 0.01 U-value FF improvement (see note regarding total wall R value) - 336 KWH saved per year (223 GF 113 FF) - $3000-5000 approx cost - $20 saved per year - 0.6%-0.4% ROI - Note the difference in exteriors. I've calculated based on GF hebel the total R would be going from approx R3 to R3.2 whereas FF exsulite is more like R4 to R4.2. Upgrading between floors from R2.5 to R3.5 - 0.11 U-value improvement - 226KWH saved per year (107KWH over outside areas) - $500 approx cost - $13 saved per year ($6 over outside areas) - 2.6% ROI (1.2% over outside areas) - Note there is a lot of approximation here as it is mostly internal floors so a bit more difficult to approximate the temperature difference. I suspect I've overestimated the benefits of this one a bit. I calculated just the outside areas (alfresco/porch) separately which should be more accurate for that small area. - I calculated the total at approx. 25% of the temp differential as to the other external insulation to account for it being mostly internal. Upgrading all windows to Low-e glazing. - 0.5-0.6 U-value improvement - 2180 KWH saved per year - $4000-$7000 approx cost - $127 saved per year - 3.2%-1.8% ROI Upgrading the windows is the most effective, both ROI and total energy saved, especially if the cost is toward the lower end. Aside from the energy saving it provides other benefits in reducing cold spots near the window and reducing the need to close blinds on cold days to keep the heat in. Upgrading external walls isn't hugely effective considering the large area. It saves less than the ceiling upgrade and cost 3-4 times as much. If the R value of the external walls was lower the 2.7batts would add more value. I may have overestimated the benefit here as well as I used R1.5 for the external walls on FF however it's probably about 90% R1.9 (exsulite 75mm) 5% R1.2 (exsulite 50mm) and 5% R0.1 (fibro) so closer to R1.8. Upgrading ceilings to R6 also provides only a small improvement. Since it would be possible to add more insulation to 90% of the ceiling (not the flat deck) later on, it's hard to justify spending budget on it upfront. Also the calcs don't take into account any benefit from the anticon, but also don't take into account the difference in temperature on the ceiling vs at the walls eg. heat rises so temp differential at the ceiling could be 2degrees warmer than at the walls that are lower down, so relatively the ceiling insulation would provide a better benefit compared to walls than the numbers suggest (which were all calculated with same temp). Upgrading between floors to R3.5 is also only a tiny improvement. Main concern being cold spots over the alfresco and porch, however for the rest of the internal floors the effect is probably minimal, but builder doesn't like having differing values of insulation within a section. As mentioned by alexp79 the other layers of carpet, ceiling, underlay, OSB might add another R0.5 which reduces the impact of the extra R1 of batts even more. The areas of concern are also not really high traffic areas so even if they do feel a little cooler it won't be noticeable that often. ROIs could change significantly if - cost of electricity were to rise or - heating system was more/less efficient or - when we eventually get solar installed. Although a large portion of heating would be when the solar is ineffective. From a purely financial/ROI point of view, only the window upgrade is worth considering, and only if the costs come out at the lower end. For the rest we'd be better off just putting the money in offset/borrowing less. Puting the money toward solar panels or insulating blinds would probably have significantly better ROI than the above. Of course there are other reasons other than financial to do the insulation, such as environment and comfort. Environmentally, putting the $ toward solar would save more energy as it will offset more energy than just heating/cooling, especially if a battery is added. Comfort, I'm fairly confident that the existing wall/ceiling/between insulation with the central a/c will provide a high enough comfort level, however I have some concerns with the windows still. If we could afford it we'd definitely go further with the windows i think, better frames etc. I think putting the $ saved from insulation toward insulating blinds will have a better impact per $, at least at night. Unfortunately we can't easily upgrade the wall, floor or some of the ceiling insulation later on, but with the energy savings Calculations: I used the following formula to calculate the above values: U value improvement/difference = 1/old R - 1/new R (in the case of windows: old U - new U) KWH savings = U value difference * area sqm * (heating degree days + cooling degree days) * 24 / 1000 $ saved per year = KWH savings * cost of electricity / COP ROI = $ saved per year / cost * 100 I used www.degreedays.com as mentioned on the above calculator to calculate the heating degree days. Values for area and r values are mentioned above. Values I used are as follows: - 1963 heating degree days - 200 cooling degree days - $0.18 / KWH cost of electricity - 3.1 heating COP, 3.1 cooling COP (our COP is actually a bit better but I'm sure there will be some losses in the system via heat loss in the ceiling ducts etc. (Note: I previously used http://chuck-wright.com/calculators/insulpb.html to calculate the values but this required converting multiple inputs to american from standard/metric units so was a bit complicated and error prone. It ended up easier to just calculate it with the formula). Based on the calculations and already stretching the budget I think we will upgrade the windows to low-e, (hopefully the cost comes in at the lower end) and leave the other 3 options. Do these numbers and conclusions look about right? Hope it helps others too! Re: Comparison of insulation upgrades 2Oct 24, 2020 5:28 pm I don't see much sense in insulating between floors. What is the main purpose for that and how you calculate the savings? Timber or carpet flooring + OSB provides fairly decent level of insulation and the temperature difference should be already fairly insignificant inside (due to external insulation). Plus it is only beneficial to warm your bedrooms a bit when you warm up your ground level. Thermal mass provides additional benefits here, too, e.g. in case of Hebel Panels or concrete slab between floors. Windows/Doors will be acting as major thermal bridge for your walls (and will be accounting for over 30% of your overall heat loss alone), so if you increase your walls by R 1.0 but your glazing area is 50% of the wall, you will be only adding as much as R 0.5 to your walls, but in real life it will be only about R 0.3 improvement due to multiple other factors, such as timber framing acting as a thermal bridge as well as quality of your insulation installation, number of penetrations as well as windows/doors sealing. The main advantage of Hebel Panels is not only R value they provide but also that it offers a layer of continuous insulation (when well sealed between panels), so I wouldn't rely purely just R values here as I wouldn't rely on R values only for thermal mass enhanced walls. For ceiling insulation, I don't think that difference from 5.0 to 6.0 is really that significant as only about 25% of total heat is lost through the roof, it rather makes sense to increase R value for West and Northern sides of the roof though, where the main heat will be coming from. Hope it helps. Re: Comparison of insulation upgrades 3Oct 24, 2020 8:56 pm Thanks! Upstairs floors are carpeted. I guess the point of insulating between floors is to reduce the heat escaping from heating zones t reduce heating requirements when you only need to heat those specific zones. But you're right it's difficult to calculate. I just used a complete guess of a temperature differential that's a quarter of outside. We do have the 18sqm that is over outside porch/alfresco so is easy to calculate, but the small size of the area means it doesn't have a huge impact overall. We'd love to do more to insulate the windows but upgrading frames might be beyond our budget but currently looking into it. In future we plan to install honeycomb/cellular blinds on the windows which will help at night. Re: Comparison of insulation upgrades 5Oct 25, 2020 8:18 am No, we actually have a void above the dining area which is also adjacent the stair well, so I don't expect the between floors to do anything for the hallway and activity room upstairs. However it should provide some benefit where the bedrooms are, which can be closed off, both reducing heat flow into bedrooms during the day and reducing heat flow out of bedrooms as night. Also our lounge, study and guest bedroom at the front of the house does have a hallway door between them and the stairwell/void so there should be some benefit there, particularly on work from home days where we would mainly heat the study/lounge zone. Bedrooms also have R2.5 acoustic in the internal walls, between floors is just thermal though. Are you suggesting soundchek for the downstairs ceiling? Re: Comparison of insulation upgrades 7Oct 25, 2020 2:41 pm From bedrooms the hot air will be escaping mainly through the roof, not through the floor. Bringing in some heat to be bedrooms is actually beneficial, how many people would like to go to bed in "cold" bedrooms? But as you are still having void space, most of the heat will be escaping through it, anyway. Re: Comparison of insulation upgrades 8Oct 25, 2020 10:55 pm I had another look at this tonight and my calculations were very wrong. I was using the calculator I linked incorrectly and using the total new R value for the "Added R Value" field instead of just the additional increase of R value. Also when using the correct values in the calculator, if I do the calculations myself I get a different answer so not sure if the calculator or my calculations are incorrect. With the correct inputs/calculations the savings are less impressive, I'll update the main post shortly but by my manual calculations: R5->R6 ceiling saves 354KWH/year R2.5->R2.7 wall insulation saves 336KWH/year (223 GF and 113 FF) R2.5->R3.5 between floors saves 226KWH/year, 107KWH/year for just the outside areas over alfresco/porch Low-e windows saves 2180KWH/year Calculation is: U diff * sqm * (heating degree days + cooling degree days) * 24 / 1000 where: (heating degree days + cooling degree days) * 24 = (1963 + 200) * 24 = 51912 Windows are still worth doing for both comfort and energy saving, but the other 3 would hardly seem worth it. Financially savings would be tiny (payback > 50 years) and I feel the difference in energy transfer may not be noticeable from a comfort perspective, but that's just a guess. Re: Comparison of insulation upgrades 11Oct 26, 2020 3:06 pm aussieta i think there is something wrong with those numbers saving 1kw/h per day by increasing ceiling from r5 to r6 saving 1kw/h per day by increasing wall from r2.5 to r2.7 If you have a look at the U values and the area covered by the insulation it makes sense. Increasing ceiling from R5-R6 decreases U value by approx 0.033 (1/5 - 1/6) and covers 205sqm. Increasing wall batts from R2.5 to R2.7 is actually R3-R3.2 on GF and R4-R4.2 on FF once the external wall material is taken into account which decreases U value by approx 0.021 GF (1/3 - 1/3.2) and 0.012 FF (1/4 - 1/4.2) and covers 430sqm. So increasing the wall insulation is about half the improvement in U value but covers about twice the area compared to ceiling insulation so they work out about the same. Assuming my calculations are correct! Re: Comparison of insulation upgrades 12Oct 26, 2020 3:27 pm that calculator doesnt breakdown floor /wall values what i meant by the savings is 1kw/h walls plus 1kw/h ceiling i have as good a zero insulation, old draughty house costs me 20kw/h per day to heat on a very cold day with rc split systems Re: Comparison of insulation upgrades 13Oct 26, 2020 8:42 pm Are you saying that an average 1kwh saving per day is too big a saving for the increase in insulation? I guess there's some other factors to consider: these calculations are based on keeping the entire house at 20C 24/7, in practice only bedrooms would be heated 6-8hrs a day to a lower temp, and wouldn't be heated during the day etc. So the savings are definitely an overestimate. Also the kwh saving is the reduction in heat lost through the ceiling/wall not the amount of energy required to replace the lost heat, this is taken into account in the $ saved though: lost kwh * cost of electricity * COP of heating unit. The calculations aren't perfect, they're just the most basic calculation of heat transfer I guess, there's lots of other variables that affect the effectiveness of the insulation (additional layers, bridging, air layers etc) and how much additional heating is required to heat the home (solar heat gain, body heat, appliances etc). Certainly if I was to use the formula to calculate the heat loss of a poorly insulated ceiling on a cold day the numbers do look really high. 200sqm single storey house: Using uninsulated ceiling R value of 0.4 = U value 2.5: 2.5 * 200sqm * 15 degree average temp diff * 24 / 1000 = 180kwh lost Adding 2.5 batts for total R3 = U value 0.33: 0.33 * 200 * 15 * 24 / 1000 = 24kwh lost Total of R5 = U value 0.2: 0.2 * 200 * 15 * 24 / 1000 = 14kwh lost Total of R6 = U value 0.167: 0.167 * 200 * 15 * 24 / 1000 = 12kwh lost For your uninsulated house using 20kwh on a very cold day to heat: - what is very cold temp - what temp are you keeping your house at - what's the surface area of walls/ceilings/floor - are you keeping your house at that temp for all 24 hours (you might turn it down at night when you sleep?) - are you heating the entire house for all 24 hours or do you have zones - what is the COP of your R/C heaters - solar heat gain Re: Comparison of insulation upgrades 14Oct 26, 2020 10:18 pm Thanks to everyone for your comments, it's helped pick up a few errors in my original calculations (now fixed hopefully) and made our decision much clearer. We'll just upgrade the windows to low-e. The ROI isn't great at over 30 years, but it does save a fairly significant amount of energy and I believe it will have comfort benefits in a few locations where people may be seated near a window. The $ saved from not doing the other insulation upgrades will mean we can get the solar panels a little sooner. It will pay for about half of a 7kw solar which should generate an average 25kwh per day which is significantly more than the 2kwh or so saved by the insulation upgrades (the solar does have a shorter lifetime than the insulation though). Re: Comparison of insulation upgrades 15Oct 27, 2020 3:17 pm 24 sq house with flat metal roof with anticon insulation, maybe 25mm, mostly windows and some double brick, concrete slab heat to 22 if under 10 outside, heat from about lunch time to 10pm Re: Comparison of insulation upgrades 16Oct 27, 2020 5:00 pm just found this calculator https://www.builditsolar.com/References ... atLoss.htm Re: Comparison of insulation upgrades 17Oct 29, 2020 6:54 am They all look like very minimal upgrades. As you can see from the ROI, financially none of them are worth it. You haven't really said much about your double glazing. What type of frames are specified? If they are aluminium frames, then I'd be spending money upgrading these to uPVC (might be a similar price), timber or thermally broken frames. As aluminium has very high thermal conductivity, these frames become very cold in winter - leading to condensation, & possibly mould - & hot in summer. I'd be looking at low-e glass for any unshaded eastern & western windows are least. In saying that, with good design you should have very few western windows. But I'd be looking to do something that will save you a lot of money, & greatly reduce your hearing & cooling loads. Reducing the size of your home. 40SQ is more than 150% the size of the average Australian new build, already the largest homes in the world. Not only will reducing the size of the home save on building costs, heating & cooling costs, maintenance costs & shorten the time to clean the home. It will also be much better for the environment, greatly reducing the embodied energy in the home. Embodied energy is the energy (& emissions) that have gone into the build. All the energy used creating all the building products. The energy used to mine the raw materials in Australia. The energy used transporting these materials to China. The energy used converting these materials into the manufactured products. The energy transporting these materials to Australia, & to your building site. As you'd expect, the embodied energy in a home is very LARGE. On average, the embodied energy in a newly built home roughly equals about 15 years worth of operational energy! A large, energy efficient home, far more. So the GHG emissions created building your 40SQ home may equal all the energy you'll use in the home for 30 years! Not great for the environment. On top of this, large houses need large blocks. Leading to more urban sprawl. Creating longer commutes to work. Far, far worse, urban sprawl leads to elevated levels of land clearing. Australia has the highest levels of land clearing in the developed world. Even before the bushfires last year, the koala was a threatened species. Why, land clearing! It's be building smaller, & smarter. You'll save money, & be able to spend some of your funds on better design. Ditch any thought of gas in the build. Go all-electric. Install a good sized solar PV system on your roof. I am saying that double brick has similar thermal performance due to thermal mass effect. It will be still very interesting to see the state of your framing after 10-15… 10 29740 Hey guys building a new place through a volume builder and just wondering if i should complain to the site supervisor as we just had plasterboard installed. Looks like… 0 11254 1000000% definitely add insulation. I have in my home and it makes a big difference minimising sound transfer. Insulation is pretty cheap and definitely worth it 2 6173 |