What percentage of total heat loss is through air leakage?
user-912539
| Posted in Energy Efficiency and Durability on
I’m looking for modeling or test data that defines the ratio of convective losses to conductive losses. My real goal is to find the tipping point when a leaky building losses more energy via air changes then via the insulated envelope. I’ve had many answers where the losses from air leakage have been as low as 10% or as high as 50%. However, any number has to coincide with a stated leakage in terms of ach@50 or similar. Anyone have access to a study or paper that charts this ratio? Thanks, AL Cobb
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"What percentage of total heat loss is through air leakage" in what structure?
Your question is similar to "Whats the difference between an apple?"
The answer could range from near zero to near 100%, and is entirely dependent on whole house R-value and whole house air exchange rate during normal operation (not under blower door testing).
If you're asking about "average" existing housing, there is some data on that. If you're asking about a particular new construction project, you have to do the heat loss analysis for that specific building including design or actual air exchange losses.
Al, if you enjoy multi-variable algebra you can play with the heat loss load formulas developed by ASHRAE. Infiltration is one formula of several used to determine the total heat loss of an entire building in order to size HVAC equipment. Here is an excerpt from ASHRAE 2005 publication Chapter 29:
"Infiltration is generally a significant component of both cooling and heating loads. Refer to Chapter 27 for a detailed discussion of residential air leakage. The simplified residential models found in that chapter can be used to calculate infiltration rates for load calculations. Infiltration should be evaluated for the entire building, not individual rooms or zones.
Natural infiltration leakage rates are modified by mechanical pressurization caused by unbalanced ventilation or duct leakage. These effects are discussed in the section on Combined Ventilation and Infiltration Airflow.
The infiltration airflow rate depends on two factors:
• The building effective leakage area (envelope leaks plus other air leakage paths, notably flues) and its distribution among ceilings, walls, floors, and flues.
• The driving pressure caused by buoyancy (stack effect) and wind.
Using the simplifying assumptions presented in Chapter 27, these factors can be evaluated separately and combined using Equation (8)."
Al Cobb,
Are you still there? Would you like to refine your question?
According to a study performed by the Lawrence Berkeley National Laboratory in 2002, average air tightness of all houses, new and existing, in the United States was 1.18 ACHnat. All new homes (post 1993) that were tested within a year of construction had a mean ACHnat of 0.55. Homes that were constructed under some local or national energy-efficient homes program had a mean ACHnat of 0.31 (excluding Alaska which averaged 0.23 ACHnat).
Energy Star has established a natural infiltration target threshold of 0.35 air changes per hour.
Here's my problem. I struggle with modeling software that asks for input that defines R & U values to within a tenth or more. However, these same "high powered" programs ask for input under the heading of "air-tightness" or "Quality of construction" as good, better, & best.
When selling energy efficient construction to the buying public, they have been brain washed to consider R-value as the sole factor. This should come as no surprise since the code largely ignores air-tightness when defining energy efficiency (I'm not talking about ventilation requirements)
Therefore, I'm looking for a study or analysis of homes (real or not) that have been modeled to the extent that heat loss from conductive and air infiltration losses are clearly defined. It only makes sense that as leakage rates increase, the decision to ignore air-sealing can be shown as a critical mistake.
What modeling have any of you done that may help to show the importance of building air tight.
Al,
Maybe the simplest approach would be to model a house and then adjust those variables to see how it changes the performance/heating load of the model. You probably won't find an across-the-board answer to your question since there are too many variables involved in house design and site conditions. Better to look at it on a project by project basis, but after doing this for a while you will get a feel for it.
Brainwashed? Whose fault is that? If you can't articulate to a client the importance of over all energy and resource efficiency, then you're not doing your job as a building professional (I'm assuming that's what you are).
Energy Star and DOE have widely publicized the HERS rating system as a comprehensive measure of actual total operating energy requirements for a new house.
The 2009 IECC section 402.4.2 has a comprehensive set of standards for air-sealing.
Then make your own. It's quite easy using spreadsheets. I've been doing all my energy modelling on my own spreadsheets for more than 20 years.
R value. My biggest pet peave, especially when discussed here on this supposedly leading source of green building advice site!!!!!
You all love to quote rules and "the codes" yet two homes can be built with the same approved R value insulation and have 100% different energy needs.
The codes should spec insulation in more regard as to how continuous it is, in how it actually performs at all temperatures when it is needed most and other aspects of the entire assembly.
I.E. We all know that fiberglass batts in an attic that is at 0*F is not giving the same true R value as say the R of other installs but where is the beloved code address this fact??????? If it does then great and I stand corrected and will embrace it whole heartedly.
AJ,
You are half right. There are some places where the code acknowledges that fiberglass isn't as good as rigid foam. For example, in Zone 6, a basement wall has to be insulated to R-19 if you use fiberglass batts (don't try this option), but only to R-15 if you use XPS.
Martin,
Where do you find this in code? The IECC R-value table for zone 6 walls stipulates R-19 (R-20 in 2009 code) cavity insulation or R-13 cavity + R-5 sheathing.
Perhaps you're confusing the basement wall requirement, which is R-15 for continuous exterior or interior insulation or R-19 for interior cavity insulation (regardless of the type of insulation).
Robert,
Not confusing it, just stating it.
For all intents and purposes, "cavity insulation" means fiberglass or cellulose, although it could mean spray foam. The point is, the code indirectly acknowledges the superiority of continuous insulation -- in this context, almost always rigid foam -- in its basement wall insulation requirements.
No they can't - not if they meet all the requirements of the IECC.
The IECC does specifiy thermal continuity, continuity and contiguity of air barrier, fenestration U-values and air leakage limits, limits on can light and duct leakage, duct insulation requirements, fireplace sealing standards, different R-value requirements for cavity vs continuous insulation vs a mix of the two...
The code has become quite comprehensive in regard to ALL elements of operating energy efficiency, so that there cannot be a significant variation between two similarly-sized homes that meet code.
Martin,
You're reading between the lines what is neither stated nor intended by code.
The distinction is only between ANY insulation material that is discontinuous (i.e. has thermal bridges) and ANY insulation that is continuous without bridging.
Continuous insulation could be semi-rigid fiberglass or mineral wool or foam board or spray foam - and cavity insulation can be any of those as well. The only differentiation in the code is between continuous and discontinuous. In fact, continuous interior basement insulation can be those plastic-wrapped fiberglass batts that are draped over the walls from the sills.
Thank you AJ.
I'm in complete agreement with you. The average consumer, building official, and architect are consumed with the perception of the importance of R-Value. That mis-perception is the basis of my question that started this thread. If modelling identifies the cost of ignoring good air-sealing, it can be used as a tool that educates all people about building better buildings by using products and systems that perform properly.
The suggestion that the code has comprehensive standards is laughable . If you (Robert) build a truly high performing home, your building far exceeds the MEC. I'm looking for data to help us build better homes and help the consumer make better choices. What I'm not looking for is criticism of my professional capabilities.
Al,
Energy Star has already been suggested.
Have you tried to work with an Energy Rater?
Robert, I gave a good example of a problem I have with R discussion. Attic glass batts. Another example would be the differences in non continuous insulation differences. My last frame had half as much wood as some use but that isn't in the code that I know of. And you did not address the fact that insulations differ in their actual performance. Nor does the code address such.
The code and discussions here would make much more sense if R value was actual whole assembly rated at worst design temp of stated climate.
Otherwise the info is garbage.
Same to be said about energy. We should be talking E/sqftlivablespace/hr or season or year at what T set points in what climate zone at what altitude.
No one mentions altitude. Go to Equator with just your bathing suit and post here upon your return your pics freezing your butt off.
Should say Equador (which the "equator" runs thru)!!! Damn this autospellchanger!
Al, You ask a very valid question and I agree with earlier posts you should use your energy modeling software to provide some answers. With increasingly higher R-values a static NAC will be a larger % of the heat loss.
So, Al, apparently its OK for you to blame everyone else in the building industry for your frustration, but you can't take any professional criticism yourself. How about taking some responsibility for your own confusion and misperceptions?
But the misperception seems to me entirely your own. You apparently don't understand proper energy modelling that includes infiltration (as any decent program does), and your question was premised on the false assumption that there was a way determine the ratio between conductive and infiltrative losses that is universally applicable to any structure. There is not.
If you would read the 2009 IECC, you would see that it has an extensive section on air-sealing requirements.
There is no "The Code". There are international model codes which are becoming more comprehensive by the year and which each jurisdiction can choose to adopt or modify. And all building codes are minimum standards. You're free to exceed them as much as you'd like.
As I already mentioned, the increasing popular HERS modelling does show the effect of air sealing on the operating energy consumption of a house. The tools are out there. Don't blame others for your failure to use them.
AJ Low Horse,
If you really believe that all the data out there is garbage, then feel free to make up your own.
The FTC R-value rule (which is the law of the land) is very specific about the five ASTM tests which can be used for various insulation materials and precisely how that R-value information must be displayed to the end user. The current testing procedure requires that all insulations be tested at a delta-T of 50°.
But R-value is prescribed only for insulation materials. Because wall systems are more complex, the IECC takes into account insulation continuity, thermal bridging, and dynamic mass effects in its prescriptive standards. It requires air-sealing, which is the great equalizer, making all insulations with the same R-value perform approximately the same. It also allows performance-based compliance if you want to do your own energy modelling for whole-wall R-values.
A little trouble with those pesky HTML codes? They are a PITA!
Well, there are some elements of the PassivHaus concept that I can't account for, either ;-)
And HERS isn't designed for extreme aberrations, but for the majority of efficient homes.
Ironically, the ones who scream most loudly about the uselessness of R-values are the spray foam hucksters who try to convince everyone that half the code R-value is OK as long as the house is hermetically sealed.
R-value, or at least as-built whole assembly R-values, are still the single most important tool for designing energy-efficient homes. The other is ACH50 or, more pertinently, ACHnat combined with ACHmechanical.
To find the optimum balance between the two is an exercise in elementary math, and It constantly amazes me that so few designers or builders know how, or are willing to take the time, to do this. A 2-page spreadsheet is all it takes: one for heat losses and one for internal and solar gains (OK, maybe a third for summer heat gains for those of you unfortunate enough to have to AC your homes).
Wrong
So, if R-value (conductive heat transfer) is the be all -end all of the energy conversation, then what does the R-value have to say about Convection, radiant heat transfer and thermal mass?? I think that's the point that AJ is trying to get at?
JC,
You wrote, "So, if R-value (conductive heat transfer) is the be all -end all of the energy conversation..."
I'm not sure who you are challenging, JC. But I don't remember anyone posting that belief. I think we all agree that air leakage matters.
In fact, we all agree that convection, radiant transfer and thermal mass matter, in addition to R-value. AJ's point was that R-value is worthless, which it's clearly not. ASTM testing and building codes consider all modes of heat transfer in their standards.
And, by the way, R-value is a laboratory measure of heat transfer from one side of a piece of insulation to the other under stipulated conditions, regardless of how the heat is transfered, so it includes internal convection and radiation as well as conduction.
Wow -you guys can be so rude to each other. I will be the 'girl' in the room for a moment and just say 'can we all just chill out and accept that we are all on the same team?' I don't think anyone on this thing said anything wrong or not valid. I think Al and AJ and Martin made some very great points there is no need to beat anyone up.
Maybe I am wrong but I think that Al was asking a more general question (Eek! I know! I have spend my whole life in geek-ville. I know it is a sin- trying to get a general grasp of something! )
But really I have been designing, living in and building very energy efficient houses since 1992. I go to all of the seminars. I have heard all of the data for years and still I notice that there is a tide turn JUST RECENTLY of finally accepting and prioritizing what people like Marc Rosenbaum have been saying for years- Air sealing is the bomb! (yes yes yes we have all been doing it for years but thetide change IS happening- suddenly builders I know who don't know much are talking about air sealing!!)
This is so much so that I went to a demonstration recently of Owens Cornings new product called Energy Complete a spray on 1/4" thick permanently flexible, clean green air sealing wonder. ( I like it we will use it on a house soon as a trial.) The OC rep at the install said basically 'Heh heh ~ if you air seal with this stuff your house will be so tight you barely need insulation. heh heh heh.' (Then he told me to also buy some pink batt. I haven't put fiberglass batt in a house in 20 years! I know if it is done perfectly it would be ok - maybe - but when he said that thing about not needing insulation I almost bought it! AND I almost thought well then you could put glass batt in there)
SO on my drive home I though a lot about how the talk lately is all focused on the air sealing and how it has become more important lately (last 2-3 years?) I don't think any of us can deny that- the code reflects it ... But is the talk - the general talk - making us think it is more important than it is or not.
I think what Al was trying to ask is 'what sort of importance factor is air sealing in ratio to insulation?' I would love to have a grasp of this myself. I know each case is different. I design different wall assemblies all day long, get them built and get them rated. I get that, they are each unique. We all get that.
I am wondering if there is an ability to have a general conversation on the relative importance of air sealing. I think the answer may simply be- its really really important! but duh you need to insulate well too and make sure you have managed vapor and water etc. Bobs your uncle.
Like everything in this energy efficient building world I think we are just experiencing the pendulum swing of air sealing. Yes of course it is majorly important! the pendulum is swinging so right now perhaps it is the silver bullet! Next year it will probably settle into just being majorly important.
But I think people like the OC rep are getting the wrong idea...
ok Robert and everyone - you can rip me to shreds now. Just really try to be nice to each other its the holiday season : ) and you can say very productive things without being mean if you try harder.
Elizabeth,
I really appreciate your appeal that we all be nice to each other. An excellent message.
But believe it or not, this thread has been pretty good -- everyone has been much nicer than on some other recent threads.
In any case, good post! And thanks.
Al - back to your original question. BPI does give some very basic formulas for heat loss thorugh both conduction and air leakage. Although these are not as accurate as an energy modeling program would be, they are a good tool in determining ROR/simple payback period and weighing options such as air sealing vs. adding insulation. There is a 25% safety factor built into these equations intended to avoid overstating potential savings to homeowners so again not 100% accurate but a good place to start and easy to run a few scenarios to see if you can come up with some sort of ratio, but it really is going to depend on each individual house, the geometry and how tight it is.
Annual Conductive Heat Loss
Q = U x A x HDD x 24 x .75
Q - will give you BTUs lost from conductive heat loss.
HDD - Annual Heating Degree Days
You will need to do seperate calculations for each wall, floor, ceiling, windows, etc.
Annual Heat Loss through Building Leakage
Q = CFMn x 1.08 x 24 x HDD x .75
Hope these help some.
Danny,
UxAx24xHDD = total annual heat loss. What's with the 0.75 factor? There's no reason to reduce the calculated heat loss. If you want to convert to amount of purchased energy, then you would divide by the percent conversion efficiency factor, which would increase the total. Why would you want to underestimate the heat loss by 25%?
And the air conversion factor should be 1.092 (0.0182 is the specific heat of 1 CF of air x 60 min/hr = 1.092).
Amazing how different we all read the same post. I am quoted as not liking R values. What I have said and will say again is I love WHOLE ASSEMBLY R VALUE and desire that in writing about R value and in stating wall and roof and any other assemblies R value that we should at the least state always what the stated R value is pertaining to. Such as "fiberglass batts in standard 2x4 16"oc framing. And better yet state the predicted WHOLE ASSEMBLY R VALUE as the whole assembly R value is a magnitude of order more informative than saying, "the walls were built to R 38. NO ONE can infer a damn thing from this. The walls could be studded with steel studs 12"oc and be dropping all down to WHOLE ASSEMBLY R 6 or whatever. My point is, bragging about your walls R is providing absolutely no useful info to anyone. It's just window dressing. Post your assembly specs and your WHOLE ASSEMBLY R VALUE. Then we can work on raising the bar even higher. Sustainability is standing still with the posting of fluffernutter articles. Anyone that doesn't understand my point by now can go fly a kite and I love kite flying. Elizabeth, nice post.
(two spelling edits)
AJ,
You're the one flying the same old kite with the little key into the lightning storm. I'l wager than not 5% of the participants here and a much smaller percent of builders and designers even know how to calculate an accurate whole wall R-value.
That's why the codes are based on installed R-value and include a built-in adjustment factor for whether it's continuous insulation or cavity insulation.
Given that 99% of all homes today have approximately the same framing factor, this is a very simple conversion to make at the code or rating level and, contrary to your assertions, completely unnecessary (let alone impossible) for most people to do on their own.
For those using advanced framing or other efficiency techniques, there is always the performance compliance option instead of the prescriptive option. You're making a mountain of a mole hill.
Elizabeth,
You're right that too many people, particularly insulation hucksters, are taking advantage of the current emphasis on air sealing to make the kind of outrageous claims that the O.C. guy made (and are make by most in the spray foam industry).
But, as for the original question of where the tipping point is - there is no generalizable answer to that. But I'll get back soon with more specifics (have to run, now).
Thanks to all for joining in on this thread.
In light of the absence of the type of comparison data I was looking for, I've decided to gather this info myself. I've sourced a number of modelers who use different packages. At this point, I have a building coming out of the ground 2030 sqft with a SIP envelope and Heizmann window package. The infiltration rate I'll be shooting for is around .3@50. In addition, I have a monitoring system that gathers energy consumption data on every electric circuit in the building. It also collects and stores weather data, HVAC system data, etc. The programs included in this review include: Energy plus, Rem Rate, PHPP (passive House), Wright Soft, and the good old Manual J long hand version.
With a little luck, I hope to see which programs best model extreme energy efficiency and how they realistically attribute energy consumption as a function of air-infiltration. My current work on a Passive House in Maryland has fueled my desire to better model these extremely tight buildings.
Al Cobb, great posts, keep the faith... share your knowledge, let's keep greening this neat planet we share.
Once again - and this should be obvious to anyone who does energy modeling - there is and can be no generalizable ratio of convective to infiltrative heat losses. The ratio can be determined, or varied, only for a particular house with a particular thermal envelope, with a certain amount and type and orientation of glazing, in a particular climate (HDD and solar availability).
And will you be comparing conductive losses to the heat losses from assumed natural air exchange alone, or mechanical air exchange, or a combination of the two, with or without heat recovery? Does it depend on occupant behavior?
As an example, a superinsulated, passive solar 2000 SF house in my north central VT climate (8500 HDD), with high end triple-glazed windows would have to have 0.7 ACH with no heat recovery for the infiltrative losses to equal all the envelope conductive losses. With a healthy mechanical 0.225 ACH (60 CFM constant, 15 CFM/person) and no heat recovery, the same house would have about 25% of its total heat loss by air exchange. And the only reason it's that much is because of the extremely low envelope losses. As with any fixed thermal bypass, it becomes more significant with higher insulation levels.
But this infiltrative loss is still less than the heat loss through 350 SF of R-5 windows. We don't want to scrimp on windows, however, because they also provide views, daylighting, a sense of connection to the outdoors, and significant solar gain (72% of total load in a not-so-sunny climate). And neither should we scrimp on fresh air, since it offers priceless value to the occupants.
Since the air exchange can't go much below that level to maintain a healthy indoor environment and protect against moisture damage, the issue becomes the type and percentage of heat recovery in the ventilation system.
Ironically, a house with a "balanced" ventilation system will still suffer from the same natural exfiltration rate - with or without active ventilation - because the ventilation system does not change the internal pressure balance. A house with an exhaust-only ventilation system (with or without some form of passive air tempering) can reduce it's natural exfiltration theoretically to zero by maintaining the entire conditioned space at enough negative pressure to overcome the stack effect of the building height (about 5 Pa for a 2-storey house).
But my concern about what I consider to be the extremely excessive air tightness of a so-called Passive House is that they cannot, in fact, ventilate passively. I prefer a house that is very tight (perhaps 2 ACH50) with an exhaust-only ventilation system and passive make-up air inlets for two reasons. One, the exhaust-only system (at least when it's running) will prevent exfiltration - which is the only air movement that can cause condensation in the winter. Two, the building can exchange a limited amount of air passively if the electricity is down, making it a much more "passive" house than a Passive House.
Is there an energy price to pay for a healthy indoor environment? You bet! But a highly-insulated envelope can more than compensate for that necessary cost. And, if the envelope improvements are made using materials with the least impact on the environment (i.e. no plastic foams or fiberglass), and the house is made from as many natural (i.e. healthy) materials as possible, then the balance is an appropriate one between energy efficiency, ecological footprint, occupant health and building durability.
My actual use of Icynene spray foam is making my customers very very happy. It is one of many methods of insulating. It is not being sold by hucksters in my area, it is sold by friends I regard highly. Robert is a cellulose promotor. So am I for it's "greener" aspects. The truth is my Icynene installations are way outperforming what we have installed in the past, which due to customer choices was fiberglass batts. And this is with less thickness at the roofline 5" of Icynene unvented verses 12" of fiberglass with a vented roof. That said, of course I am all for increasing Whole Assembly thicknesses of insulation closer and closer to Passive House numbers (R-40-60 or even more).
8,000 heating degree climate area
Robert, we could agree on much, you just don't want to. Who knows... maybe someday... no... not gonna happen is it oh High Horse one? LOL
Low Horse
Since our + is not visible.. let me say very informative post Robert. We can get along, but it takes two. I'll keep trying with you.LOL
A + for you
AJ low horse,
I don't "promote" cellulose. I promote intelligent and ecological (i.e. truly green) building, and there are few better insulation options to meet that standard than cellulose (straw bale is another, but not nearly as much of that dreaded R-value). It is neither intelligent nor ecological (i.e. not green) to insulate with toxic petrochemical foams where other options are available.
And I never disagree with YOU (it's really you who put yourself on a high horse, thinking you're important enough to warrant a personal competition). I disagree with wrong-headed, inappropriate, unecological building methods and materials and the unfounded justifications (or rather, rationalizations) that are used to support them.
It just happens that a great deal of that BS comes from you.
Yes Robert - you are correct, no need to reduce estimated heat loss by 25% but was just passing along the formulas that BPI teach. They are not intended for true energy modeling but merely a quick rule of thumb for an energy auditor use to show a homeowner a potential return on their investment and to guide them in decision making. Since there are so many other factors involved, I assume BPI is merely trying to prevent their building analysts from overestimating savings which seems to be an ok model - under promise, over deliver - no unhappy customers saying they were misled. Maybe trying to prevent getting the reputation of the fly by night contractors with the magic products that will save you 50% energy savings by installing their products (hear these mostly from window, radiant barrier and attic fan salesmen) . As for the specific heat of air - I'm sure you are correct - not sure how these formulas were derived - again, what BPI taught, maybe the specifi heat is different in New York ;-)
By the way, would like to see your spreadsheet you mentioned one of these days.
robert,
to passively ventilate a passivhaus, you merely open the window. tilt turn windows make this a breeze. the QC measures to get from 2.0ACH50 to 0.6 are neither herculean nor excessive.
I don't share my spreadsheets, even to the students in my classes, for several reasons. Primarily it's because I created them for myself with no "instruction manual" and with no intent to make them user-friendly for anyone else. They work for me (I have created hundreds of them) because, as the developer, I understand how they work and so can properly interpret the output.
Also, I'm constantly tweaking them and don't want to take responsibility for any possible errors or for anyone else's use or misuse of them. Plus, I think the great value of spreadsheets is that they are so easy to create and customize for one's personal needs that everyone should make their own. Making them also both requires an understanding of all the principles involved and helps one understand them better.
What I do share in my classes are the formulas I use in my spreadsheets, the required data inputs for the desired outputs, and how to interpret and use the calculations appropriately.
The Heat Loss / Heat Gain Solar Savings Fraction spreadsheet that I use for energy modeling does the following:
Inputs: degree days (base 65), design minimum temperature (dmt), daily average temperature (tavg), average indoor temperature (tin), building envelope area (exterior SF), floor area of heated space, house volume, design air exchange rate, number of occupants, solar availability, solar shading factor - south, solar shading factor - east/west, glazing area - south, glazing percent south, glazing area - east/west, glazing area - north, glazing SHGC, and SF and R-value for each envelope element.
It calculates: heat loss coefficients and percent of total heat loss for each element, total heat loss coefficient (thlc), maximum hourly heat loss (thlc x max delta t), daily heat loss (thlc x 24 x delta tavg), annual heat loss in therms [(thlc x 24 x dd)/100,000], system heat load (btu/dd*sf), internal occupancy heat gain (hint), delta tint (hint/thlc), balance point temperature (tin - delta tint), balance point degree days, adjusted max. hourly heat loss, adj. daily heat loss, adjusted annual heat loss,ajd. system heat load, total annual energy use (kbtu/sf).
It also calculates: insolation – south, insolation - east/west, insolation – total (all in btu/day), supplemental daily heat load, solar contribution (%), solar savings fraction (reduction in net loss compared to identical non-solar house), thermal mass requirement (cu.ft.masonry), required mass area in direct sunlight, supplemental annual heat load, effective system heat load, effective system heat load (btu/dd*sf and kWh/sf).
Additionally, it calculates: wood heat requirement (@ 70% eff.), oil heat requirement (@ 85% eff.), natural gas heat requirement (@ 85% eff.), propane heat requirement (@ 90% eff.), and electric heat requirement (@ 100% eff.). Any of those efficiency factors are easily changed.
The only slightly complicated thing about the spreadsheet is that is has to simultaneously calculate all the same outputs for an identically insulated non-passive solar house in order to compute the solar savings fraction and to use that percentage to calculate the cubic feet of masonry thermal mass requirement. There are some default inputs for the non-solar comparison house.
Of course, in the winter, this completely defeats the integrity of the Passive House and still requires occupant intervention, which - in my mind - makes it NOT a truly passive house. And it creates an uncontrolled air exchange unless the occupant remains at the window all day to adjust it.
That, of course, is a completely subjective judgement, with which 99.9999999% of all builders would disagree. And, based on my 30 years of experience in the pioneering design and building of superinsulated homes, and my years of research and teaching, it's an erroneous judgment.
Thanks Robert - I understand not sharing your spreadsheet - I was actually more interested in your logic and wanting to create my own for the reasons you stated above - was wondering what was fixed/given and what the variables were - the above information is very helpful and enough to get me started. Quick question for you though. Unfortunately BPI pretty much soley concentrates on heating - being in NC we of course have a cooling season as well. Are there a different set of formulas for Cooling Degree Days or are HDD and CDD interchangable in the heat loss formula?
Thanks.
Danny,
CDD are usually base 70, rather than 65 for heating. And all solar gain and occupancy gains add to, rather than subtract from, the cooling load. You also have to include the latent cooling load of summer humidity. Beyond that, I can't help you much since I've had the good fortune to never have to deal with cooling loads beyond designing good cross-ventilation and summer shading.
The only fixed inputs are for the comparison non-solar house, but that comparison is necessary only for calculating solar savings fraction. The fixed inputs I use for the comparison house are 12% of floor area in glazing, distributed equally on all four sides, and 0.30 SHGC glass.
I also use a standard 0.25 ACH target for a healthy and moisture-controlled indoor environment, but that can be changed to suit your approach and can take into account heat recovery efficiency.
Robert, you act like a 3 year old with me. I am not trying to compete with you. I am setting things straight as you have misquoted me repeatedly including your last quote. You infer that I think differently than you as to what insulations are more green than others. Wrong and you know that. I have always agreed with you on your last points about cellulose and straw bale. You are dead wrong about how well Icynene insulates and I will always say so. And even there my installers and I both totally agree as to what R value is being installed. You just don't like the fact that it achieves a better reduction in heat loss by a large margin over a more insulated fiberglass job. If this is a fillibuster you'd rather not be part of, then stop counterposting me. I am standing up for my valid point not competing.
Hint as to why Icynene insulates well. Because it drastically reduces ACH and it does not lose rated R value due to install gaps, convection, delta T and other basic differences to fiberglass batting. The ACH with Icynene is better than dense pack cellulose too.
And just because I defend Icynene doesn't mean I am for it as my primary insulation for green building, I am not. I am for it and cellulose and possibly Spyder fiberglass and for DIYers straw bale. I also as you know like Bruce Brownell's approach with taped foam sheet outsulation. Foam is a good use for fossil juice as it may be doing it's work for decades to come. And as we both know, out of RPI there is a coming foam product that is completely free of fossil juice.
Your friendly neighbor not your competitor! LOL
robert,
if you've got tilt turns (or even casements) you can trickle vent, and due to balanced ventilation system, won't compromise the passivhaus. also, there are PH buildings w/ windows/vent panels that are computer controlled for increasing ventilation that don't require human intervention.
my statement that pushing for tighter buildings is really no more subjective than yours on the 'excessiveness' of PH airtightness. myself and the builders of over 25,000 passivhaeuser can attest to that. 99% of builders will disagree with passivhaus or other 'energy' improvements anyway, because they don't care they're building leaky, poorly constructed (and in most cases, just plain hideous) buildings.
AJ,
You're more than a little confused. A 3 year old cannot possibly notice the myriad flaws in your arguments and contradictions and absurdities in your statements. I am not misquoting you, but perhaps you are posting things that misrepresent what you think you mean.
I'm "dead wrong" about how well Icynene insulates? I've never said it doesn't insulate as well as any other low-R material. But the constant claims about needing less R because it's more air tight are hucksterism, not fact (Martin has said this repeatedly, as well). And to compare Icynene to fiberglass batts is like saying a Hummer gets good mileage compared to a Mack truck.
Because you've insulated poorly in the past and now your customers seem happy with Icynene is no testimonial for the quality of Icynene. It's just a statement about your modest improvement from poor to mediocre in your thermal envelope design.
And since all tests and studies have proven that most air leakage does not occur in the stud cavities, Icynene (or any spray foam) alone does little to reduce ACHnat.
And, by the way, straw bale is not just for DIYers. Most straw bale homes in New England are being built by high-end custom builders.
So, as usual, you're wrong on every count. Don't blame me for pointing that out. Take responsibility for what you post here.
Mike,
It is nothing but subjective unless you can present a cogent logical argument or objective data that demonstrate the value of extreme air tightness in a home (and, by the way, high-tech computer controlled vents are not passive either). And you have not done that, but merely expressed your opinion.
And when we measure value, let's not limit that to the simple equations of energy use. A green home has to be healthy, inexpensive, accessible and acceptable to the majority of people, durable, made from easily available local materials and as much natural material as possible, easy to build, easy to maintain and repair, buildable with local labor to support the community economy, have an extremely low ecological footprint, high moisture tolerance, and able to breathe both air and moisture (one of the foundations of the Bau Biologie movement, the greener of the two German building philosophies).
robert,
i'm very familiar w/ baubiologie principles - and the DE/AT baubiologie groups push niedrigenergie and passivhaus principles (meaning they are for 'excessive' airtightness w/ mechanical ventilation)
also, green homes are not required to be inexpensive, accessible, acceptable to the majority of people.
The .75 factor in the equations is likely there to reflect the fact that HDD65 leads to an over-estimate of heating energy use and is largely an anachronism. HDD60 do a lot better for typical homes in heating climates and the ratio of HDD60 to HDD65 is something around 0.75 in moderate heating climates. Even with the correction factor, the simple equations often still lead to large over-estimates of energy use in poorly insulated homes.
Does airtightness below 1.5ACH50 really make that much difference in energy use?
Is not the primary reason for Passivhaus' extreme airtightness...
"To Avoid Structural Damage"
John,
You're right that Passivhaus proponents claim that 0.6 ach50 is necessary to avoid structural damage, but there is absolutely no evidence or justification in physics for the statement.
Plenty of wall systems are robust enough to be fairly immune to structural damage related to air leakage -- for example, ICF walls.
Moreover, there have been examples of extreme structural damage without air leakage -- the most famous being some of the SIP homes in Juneau. Some of these homes had catastrophic roof damage due to convective loops through the SIP seams. These convective loops led to condensation and rot, even when no exfiltration occurred.
Finally, plenty of homes with air leakage rates of 2 ACH50 are doing fine, with no evidence whatsoever of structural damage.
Martin,
I agree with your comment
Concerning extreme airtightness
I think "Where" the Enclosure is leaking is more important than "how much" it leaks.
I can think of a situation where a 0.6 ACH50 house could still have damage caused by air leakage.
If "green" is nothing more than an excuse to build expensive homes for the wealthy or for a niche market, then it's primary purpose is undermined: to improve the earth's environment while creating healthy shelter for human habitation.
That kind of "green" serves egos but not the earth.
John,
I believe you're correct in the presumed justification for extreme air tightness in the Passive House. But the problem of moisture management and durability can be handled better by the use of moisture tolerant hygroscopic materials, which the Bau Biologie movement pioneered as the world's first truly green approach to building.
And, contrary to Mike's assertion, Bau Biologie principles require only modest air exchange rates (≤ 0.25 ACH) to allow the hygroscopic natural building materials time to perform their moisture buffering and redistribution function.
Stay tuned, as I'm about to start a thread on Bau Biologie.
robert,
middle class and wealthy people are going to build homes whether you like it or not. the key is to educate them and make those homes more efficient, healthier to live in, reduce the embodied energy of construction materials, reduce construction waste, etc.
it hardly undermines the purpose of 'green' building, to the contrary - it provides the opportunity to elevate it through education and exposure.
also, you should try learning a little german. most austrian and german baubiologie groups are proponents of passivhaus and niedrigenergiehaus. i met several baubiologisten when i worked in feriburg. if you can't read german, google has this fantastic translation tool that works well at getting the basic point across.
there are a number of articles on the institut fuer baubiologie + oekologie's website regarding moving towards passivhaus and niedrigenergiehaus, spanning the last 6 years or so.
Mike,
I don't need to learn German, since the IBE in Florida has translated all the seminal German texts into English and it's heartening to see that they haven't veered away from the original principles of Bau Biologie.
But it's also true that the German PassivHaus movement tends to use more hygroscopic and vapor open materials than their American counterparts, though still a long way from Bau Biologie standards.
The problem with the "green" building movement on both sides of the pond is that it has gone to extremes to save that last kWhr rather than find the optimum balance of efficiency and healthy environment. And both movements are veering much too far away from natural building principles and a truly passive house that functions without life support.
As for the American middle class - it's a completely unsustainable material lifestyle that has done more to destroy the earth than any other. Saying "well they're going to build houses, so it may as well be me who profits from it" is no different than the engineer at the weapons factory who says "well someone's going to build them so why shouldn't I reap the benefits?".
We each make our choices about what our work supports. We can choose to support a slightly improved version of the status quo or put our effort towards a truly sustainable tomorrow. The latter might - perhaps - leave a future for our grandchildren. The former most assuredly will not.
robert,
baubiologie isn't a static system. the DE/AT baubiologie groups haven't veered from the original principles, they've just adapted to the utilization of uber-airtight construction (passivhaus) with mechanical ventilation to reduce energy and introduce cleaner, filtered air.
and yes, EU passivhaus projects tend to use more hygroscopic assemblies than here in the US, however a number of projects underway this side of the pond have diffusion open assemblies.
i never said i profited from anything, and it's a huge difference between advocating for architects and builders to make significant changes (e.g. from code minimum) and engineering weapons of mass destruction. that's probably the most asinine argument i've seen you post on GBA.
Nice discussion.
I respect those who "stand up" and defend what they believe in.
Very interesting that FEW can resist name calling and personal attacks.
It's not easy.