Abridged Version of Manual J 8th Addition Excel Program & MANY other questions
I am working on trying to do some sort of reliable energy modeling/comparison for a house that I am designing (and for future projects). I was trying to find out a few things: the difference in energy use between a standard 2×6 wall & a double stud wall, good windows & code, Code 2×6 construction/insulation levels & a better insulated shell with good windows (U-value between .20-.24, Floors R-38 to R-42, Whole Wall R-24+- & thermal break, Ceiling R-60). I downloaded a number of programs and they all seemed very tedious, had a tendency to crash, and seemed very difficult to use. I found the Excel program mentioned in the subject line from the ACCA website and spent a little time discovering how to use it. I believe I have been successful at modeling the project, but I am not sure if I should be impressed with my results or not.
The house is 2,312 sq. ft.
I used Olympia, Wa as the modeled city (it’s 20 miles away and was the closest in the database. It has very similar HDD). HDD is 5655
We are a Marine 4 Climate
One story House over Crawlspace
Vented Attic
9′ Ceilings
72 degree indoor temps (I know that is high, see the “energy hogs” part way farther below)
Just to give you an idea.
So here are the results that I have come up with:
Standard Construction: R-30 Floors, R-21 (Whole wall equivalent) Walls, R-38 Ceilings, U .20-.24 Windows, & “Average” Tightness=25,043 BTU’s/Hr.
Well Insulated Shell Construction: R-40+- Floors, R-24+- Double Stud Whole Wall, R-60 Ceilings, U .20-.24 Windows, & “Average” Tightness=21,332 BTU’s/Hr.
Better Insulated Shell But 2×6 Wall: Same as Well Insulated above but with 2×6 @ 24″ O.C. R-21 (whole wall equiv.) Walls=22,391 BTU’s/Hr.
Now for questions:
Is the Heat loss for this house at least in the neighborhood of legitimate? It isn’t calculating for duct losses, HRV, or anything, but is this reasonable?
If it is reasonable/normal it seems from other discussions on here that it would need a smaller than standard heating system. From many other discussions on here and other research I have done wouldn’t it be normal for a house this size to require a furnace/heat pump system larger than 40,000 btu/h? I realize this design is supposed to be the MINIMUM needed as it projects the houses needs for 97.5% of heating and is regularly upsized by HVAC contractors. I have looked at a few online guides for standard construction and they seem to be all over the place (48,000 BTU’s to 104,000 BTU’s). What is a good standard for BTU/Sq. Ft. and more importantly BTU/Sq. Ft./Yr. for different amounts of insul. and different climates? I have found one discussion that said that it should range from 1BTU/Sq.Ft.xHDD. for super insulated (I think near PH) to 5BTU/sq xHDD for new well designed construction. Is that reasonable? This is also only to 65 degrees which may be my norm, but definitely is not for most people.
The Manual J Abridged Addition notes state that it shouldn’t be used for houses that have more than 15% glazing (which this house surpases with 22%) nor should it be used if an HRV system will be used. Will that make any difference in the programs ability to tell me how many BTU’s or allow me to compare side by side building assemblies as I have done? The BTU’s/Hr #’s I am using are coming from the “Sub Totals” Line 14 not lower lines that take into account HVAC related items. It seems like it should be able to accurately allow me to compare assemblies especially since I am only looking at heating load and not cooling.
Are the decreases I am showing in BTU’s/Hr from standard construction valuable/good or is it just peanuts? Meaning will this result in a ROI that is reasonable? What I am really asking for is what is a good range of energy use for the standard version of this house/year? How much can I expect to lessen the energy bills for the house with the other two building scenarios (more insulation) using the BTU’s/Hr that the program gave me? What is a good way for me to calculate annual usage with the numbers I currently have? I have been converting any BTU numbers into KW for price comparisons since I know what electricity costs and it is pretty cheap ($.069/KW).
I know there are a lot of factors that play in here. One I want to discuss is the tightness of the house. I left them all at “Average” as noted, but the double wall I have detailed for the house includes a very good air barrier and good air barriers for the ceiling. However, the builder will probably maintain at a meeting we are going to have with the home owner that he can make a “pretty tight house” using the run-around-like-a-chicken-with-your-head-cut-off method (traditional) of air sealing a house. Therefore, I was hoping to prove that the reduction in BTU’s by insulation alone would be worth the investment. However, this doesn’t seem to necessarily be true. Another “however”, If I adjust the Double 2x wall to “Tight” the BTU’s/Hr drops to 17,365. As noted earlier though in a meeting with all parties this will certainly look like cheating (much like politicians reworking numbers in their favor) since I can not say for certain that my wall would SUBSTANTIALLY be more tight than the builders method (he has previously done a house that was blowerdoored after extensive traditional air sealing that proved to be “really tight”. What the data actually was I don’t know. The technician was really impressed, but then again he works for the Power company and they normally only look at older houses and not new construction).
A few estimations on ROI:
Assuming that the house with normal construction would use $2,000 worth of electrical or electrical equivalent energy a year it appears that I could assume a few things from the data I have:
21,332 BTU’s/Hr. / 25,043 BTU’s/Hr=.8518 or 14.8% decrease in energy consumption throughout the year?
Which would equal $296.37 per year or $2,963.70 after 10 years assuming nothing changes. I doubt this is going to pay for the increased labor/materials + extra insulation in 10 years. Am I on track here? Increased homeowner comfort levels and lowered maintenance costs of mechanical and heating/cooling equipment (due to using HRV/Mini Splits instead of central furnace/heat pump, no bath fans, etc.) may make it worth it (it would to me).
17,365 BTU’s/Hr. / 25,043= 30.66% decrease in energy consumption with a tighter shell. This would result in a potential decrease of $612.19/yr or $6,131.85/10yrs. Much more justifiable.
I want to add to this, at the risk of making this so long and involved that no one will bother reading it (which I think I surpassed a LONG time ago), is that I believe the home owners are heating and cooling energy hogs. I get this from time I have spent around them. I lived (refrigerated) in there daylight basement for a summer and my parents and my clients have been comparing energy bills for quite some time. It is entirely possible that they have lived in energy inefficient housing, but I am proposing that for people like this paying extra for extra insulation is extra justifiable. This is because the energy conscious/misers are more likely to turn their heat down to save money/energy but an energy hog will not. Additionally warming air is not a linear curve…it takes exponentially more btu’s per degree of temperature rise correct? Therefore, energy hogs will have a better chance of shortening their ROI than an energy conscious person.
I can attach house plans or the excel files for viewing if anyone wants to dig into what I am doing.
Anyways thanks. I am looking forward to some answers.
Spencer
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Spencer interesting post, be nice to see the plans and excel files
Spencer,
That's a long post, with way too many questions.
Here are just a few quick answers:
1. Yes, most heating systems are oversized, and it's often hard to find a furnace small enough to match your heating load. (Although with newer multi-stage furnaces with variable fan speeds, this fact doesn't matter so much.)
2. The design heating load you are discussing is the maximum heat output required for the coldest day of the year. Most of the time, your heating requirements will be lower.
3. Airtightness matters, so you don't want to build a house with "average" air leakage. You want to build a tight house. This requirement should be in the specs and should be verified by a blower door.
4. Energy prices are now so cheap that it's hard to justify many energy-efficiency measures on payback alone.
Spencer, it's going to be hard to quantify heat losses for really good house shell designs if you rely on drop-down menu items like "Tight" in canned software. A term like that is too vague. You need to know what that translates to in order to assess design alternatives. Sometime within the last six months, I think, Martin posted a request for information on heat loss software for use in an upcoming article. There were some good comments posted on that thread, well worth your reading.
Spencer,
Here is a link to the Q&A thread that Dick is talking about:
https://www.greenbuildingadvisor.com/community/forum/energy-efficiency-and-durability/21865/upcoming-article-energy-modeling-software
Thank you for the replies, but I think most of you are missing the point about what I am asking. I know it is a long post and that doesn't help.
1: I know I don't want to build a leaky envelope. That isn't what I was saying. I could have put them all on tight, semi tight, or leaky. I was trying to compare the shells on insulating value alone, not on infiltration AND insulating value. I did however, point out that if standard construction is "leaky" and my plans call for "tight" then yes if my assumption/estimations of the cost of energy usage for the house were correct then they may end up with substantial savings.
2: I was curious why they didn't define "tight" or "leaky" it says in the literature that there are definitions, but I couldn't find them.
3: the excel program came right from the ACCA.org website (Air Conditioning Contractors of America). The link to the Excel program is https://www.acca.org/industry/system-design/speedsheets They call them "Speed Sheets". Is anyone else familiar with this? I thought it was a pretty nice gadget once you learn what all the abbreviations mean and you know what U-values you are dealing with. I will attach my excel files here as well so you can see what the program can do without having to jump through all the hoops yourself.
4: I am planning on using Mini Splits for this house with an HRV/ERV system to help distribute the heat (and an open main living area). With the kind of BTU requirement I am showing it would seem that this would be easily achievable with most mini split systems. This came as a surprise to me since most furnaces produce a lot more BTU's than the house requires and this house is really pretty standard in size, occupants, bedrooms, etc.
5: I know the heating load will be much lower most of the time. I am wondering because this calc didn't show a huge disparity (That was another question I had up there: am I actually showing a decent decrease in BTU's/Hr? I think I may be, but I don't know enough to know...I was hoping to find an HVAC person who would be able to answer that) between good insulation and not so good insulation? Can I tell the owners they should have a decent decrease in their energy bills? If so what is a good general % decrease? From the numbers I ran up there I think I could reasonably tell them %15 less to %30 less than what the house would be under standard construction practices. The would also have all the added benefits of more insulation/better systems...comfort, noise reduction, less system maintenance, less costly system replacement (min splits compared to furnaces), etc.
Thanks,
Spencer
I am attaching the plans in PDF. It will be in two or three posts because of file size. Martin I tried your techs advice and lowered the DPI on the PDF. It does muddle the image if you get to 72DPI. Fortunately I was able to set it to 144DPI and that doesn't muddle it enough to make it hard to read...it's just not as clear as I would like (but I'm a draftsman so that makes me nerd about print quality). Very good to know though and I appreciate you looking into it for me.
Thank you for your comments and interest AJ. This house is intended to be in the Pretty Good House vein.
If you need any clarification on the U-values I used in the program let me know.
Thanks again,
Spencer
Great thread, long posts w good info are most worthy. Will take me some time now to look into your attachments. There is info to do with percentage of savings in the blogs. 50% savings is good. PH shoots for 90%. I think you should shoot for at least 50%.
I really like PGH combined with going net zero as per Martin's Proper Ecoeconomics (add solar goodies).
Will need the help for sure. Ajbuilderny g mail dotcom.
This sheet is the real meat of the design and has all of the details on it. I can't get the file size down low enough without muddling the drawing a lot. This one is on letter sized paper. If anyone wants I would gladly email them the full size PDF version of it so you could actually look at the details.
Thanks,
Spencer
AJ I just sent you some additional info via email. If you don't get it let me know.
Thanks,
Spencer
Spencer,
I'm not able to download two of your attachments -- I assume because the file sizes are too large, or perhaps for another reason.
But I notice that you located the HRV in the garage. Bad idea; that's where the car exhaust is. Put the HRV somewhere else.
Spencer, the pre construction energy/design planning including comparisons and ROIs has you in a leadership position in our field. That in itself is the value you are most generating for you and your present and future clients. You are ahead of most and rapidly moving in the right and "green" direction.
What to do next is build and then follow up with checking the actuals of all verses your predicted numbers. And take all to improve as you go.
It's the green path you travel, the destination is always ahead of us.
Hello Martin,
Which were you not able to download? Was it the excel programs or the PDF's? I can send either of them directly to your email if you would like.
HRV: I am not exactly sure where that will go. I actually just put it where I had originally designated the furnace to go before we changed directions. I was hoping to put it in an attic bonus room utility space, but that got vetoed. I am planning on suggesting it go inside in maybe the Utility room mounted on the ceiling.
Is it really a problem for it to be in the garage? Are you concerned about Car exhaust leaking into the system? It will be vented outside through duct work. This is also where my parents HRV is located in their house. I think you would agree though that it should go somewhere in the conditioned floor space.
AJ: thanks again for the comments. I have been trying to peddle energy efficiency based on the monetary and comfort advantages since I started designing on my own in 2005, but living in a rural area has made change all the more difficult (I know it isn't easy for anyone really to change builders minds in any part of the country). In the last two years or so though I have been able to try to design some real increases in efficiency thanks to the recession making people think twice. I have seen some positive changes in builder and owner awareness. This will be the 4th actual try to get one of these built so I can monitor the result. The first two were gutted of EE details, the second is on hold, and this one is in limbo at the moment. It's been a long road, but not all bad.
I have two examples to point to...both built by my father (I "helped" on the first...but I was like 6 so I just picked up nails and stole doughnuts...and was very involved in the second)....one in southeast Alaska and the other in town here in Western Washington. Both utilized a poly (which I am not using) & strapped wall system (also not using) with an HRV and both perform very well relative to other houses in the area. The irony is that the one built down here was built with the help of the builder who may be advising my clients that the system I am proposing will be expensive (I say "may" since I have not confirmed that this is where the home owners waffling has come from). I don't think people really believe it when I tell them what my parents houses costs to operate, that they too can have a lot lower energy bills, and it probably won't cost them as much as their super delux kitchen they want is going to.
Thanks,
Spencer
Spencer,
On my computer, I can't open two of your pdf attachments.
Q. "Is it really a problem for the HRV to be in the garage?"
A. Yes. Neither a furnace nor an HRV should ever be located in a garage, because duct seams can leak.
Q. "Are you concerned about car exhaust leaking into the system?"
A. Yes, car exhaust, paint fumes, gasoline fumes, pesticide fumes -- all that good stuff generally stored in a garage.
Q. "This is also where my parents' HRV is located."
A. Not good.
Q. "I think you would agree though that it should go somewhere in the conditioned floor space."
A. Yes.
As per email, Moony wall I think would be the sellable solution and then as you get some solds go deeper green.
Spencer,
There are lots of details on your plans that invite comment; I'll post a few here.
You have a crawl space with two details I'm not fond of: instead of insulating the crawl space walls, you have chosen to insulate the crawl space ceiling; and you have a crawl space floor that is below grade. (In my opinion, if you want a crawl space foundation, it's best to make sure that the grade of the crawl space floor is higher than the exterior grade.)
Finally, assuming that your plan is drawn to scale, it looks like a very low crawl space -- maybe only 18 inches or 24 inches high. That's not enough.
Spencer,
You are specifying Tyvek as an air barrier. I suggest that you choose a more durable material; builders who have experimented with using Tyvek as an air barrier usually aren't satisfied with their results. Better air barrier materials include plywood, OSB, gypsum drywall, or (if you insist on a flexible membrane) one of the air barrier membranes manufactured in Europe.
Thank you for your interest.
Before I go any further I want to point out that this thread was about whether or not I could use the BTU/hr numbers I had generated, not how well the insulation details were done. With that being said I appreciate the feedback.
I also want to note that you have to get people to follow you before you can lead them. What I am trying to do with my houses is to SLOWLY encourage builders to do better, not to change all of their building practices at once. If it was my own house I would do all sorts of radical things (which I did/am doing with my 1945 bungalow) but because this involves other people who are not always so open to change I have found that I need to do it slowly. Ideally by building a house like this I am hoping to change some peoples minds about the benefits of good windows, extra insulation, air sealing, HRV's, thermal bridging, etc. Most of this is alien (actually just about all of it) to most people so it's an uphill battle (as you all know). Then when I get examples and real world numbers I can keep going and getting people to do better while keeping cost in mind (baby steps).
HRV:
1. I understand your concern for furnaces/hrv's in the garage. However, that is the standard. Hopefully it will not go there. My personal HRV will be in a heated utility space, but my parents have been just fine with it in the garage. I'm not really looking to debate it. You are right it doesn't need to be there.
Crawlspace
1: yes it is a short crawl but it should meet code. Therefore, it is a short crawl, but not too short. Hopefully no one will go down there much, or because the home owner does his own dirt work maybe he will opt for a deeper crawl.
2: The standard in this part of the country is a ventilated crawl.
3: I agree an insulated crawl is not a bad idea. One of the issues (not a deal breaker by any means) I had with doing it on another project was trying to cover the board insulation over the foundation since most materials are not rated for ground contact...it sounds like that is a common issue from the research I did. It also sounds like that is beginning to be solved by some fibrous drain boards correct?
4: I would like to do better with the stemwall to floor joint, but again I can't win all the battles.
Air Barrier:
1: I was very curious what you would think about my choice of air barrier. For what reasons have builders been unsatisfied with tyvek as an air barrier? If it survives the construction process it should not break down over time so I am betting that isn't the problem. I would wager that getting it through the construction process is the problem? In the middle of the wall it should be pretty well protected from the home owners in the future. It is also repairable during construction if someone takes the time to inspect it (which is more or less in the specs).
2: Board air barrier systems are a good idea. However, I doubt anyone involved in this project will be really enthusiastic about them. Cost would be the primary driver in this. I was going to add to the list, but I will leave it at that.
3: I am not super familiar with any european membrane systems except Tenoarm which is a poly vapor and air barrier. My parents used it in their houses both here and in Alaska, it is very common up there, and both houses had excellent air leakage results.
To Bill:
Thank you very much for doing that for me. It appears that you have confirmed exactly what my primary question was. Now I just need to know how those numbers should effect the yearly energy use.
Thank you for noting the ACH numbers. I just realized after reading your post that they did give numbers for infiltration and I probably could have used that to interpret the meanings of "tight", "average", etc. I am assuming that is what you are referring to and did. I want to go check that out now.
I was a little confused about their floor designation as well. It is a naturally ventilated crawl space (vents through the concrete stem wall). I believe it is true that the air on the ambient side of the floor is assumed to be 22 degrees. From what you are saying it appears that you should be able to reduce the delta t normally in crawlspaces due to the influence of the ground temp? Good stuff.
Thanks a lot,
Spencer
Spencer,
First a disclaimer: I've been poking around in your spreadsheet, but I don't claim to understand it. Please disregard any silly comments on my part.
I share your quandary in that, as an amateur, can I calculate heat losses accurately? (I build my own spreadsheets, because then I know where the bodies are buried!). Your question "Is the Heat loss for this house at least in the neighborhood of legitimate?" resonates with me.
A question. I downloaded the first spreadsheet and couldn't find a ground temperature entry. Am I missing something? Since your floor is above a crawlspace (which I assume is sealed), I expected to see the heat flow calculation for that to require a ground temperature entry. I also noticed that you used the "Exposed Floor" designation. I can't help but wonder if the spreadsheet therefore assumes your floor as exposed to the 23F design temperature.
To answer the question above, I'd say that the numbers are legitimate. If I (crudely) toss your areas, R-values and such into my spreadsheet I get 24.2 kBtu/hr instead of your 25.0 kBtu/hr (using the full outside/inside temp difference for the floor). If I use a ground temperature equal to Olympia's average temperature (50F) to calculate the floor heat loss, then I get 22.1 kBtu/hr.
Note: to do this I had to set the ACH50 of your house to 5 to match your spreadsheet's 6.0kBtu/hr air infiltratration heat loss... ( used ACH(nat) = ACH50/16).
For what it's worth!
Bill Dietze