BEOpt and Manual J
mhenson
| Posted in Energy Efficiency and Durability on
Hi,
I am building a new house and everyone has been very helpful, but said I really needed a Manual J. BEOpt was recommended, and after entering data for hours I hit run. There is a lot of data there, but I don’t know how to interpret the data or get the magical BTU’s per hour number.
Any help is much appreciated.
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BEopt is a useful tool but unfortunately it does not provide the same output as Manual J calculations.
Go to the Output screen. In the graph window click on the down arrow and select "Graph Type" and set it to "HVAC Capacities." This shows your heating and cooling size. It's not as detailed as Manual J but it gives the number you need.
I'm sorry my description of how to do this is kind of vague, BEopt doesn't label its components very well.
The only problem with that approach is that it depends to some degree on which heating system you selected. You also need to go to the output graph labeled "Loads Not Met (hrs/yr) to make sure that you don't have an excessive value there. It should be under 88 hours (and ideally only a few hours at most).
Well so far no joy. HVAC Capacity says 153.4, cooling says 236.2.
But loads not met says 303! I forget who told me to use this program, but it just a couple days ago here on the forum.
Can this work or should I be using a different program? Have entered the exact same data on several web sites including coolcalc and got wildly different results from each site.
You had several suggestions for other programs here: https://www.greenbuildingadvisor.com/question/manual-j-calculations. I don't see anyone recommending BEopt for Manual J calcs. Someone there said Dana, a long-time, trusted GBA member, recommended this one: https://hvac.betterbuiltnw.com/Common/Sites.aspx.
I use BEopt on most of my projects and it usually works for equipment sizing but sometimes it doesn't and I don't understand why not. In my opinion it's best used for comparing different assemblies and seeing the relative impact of things like different window specs or different air leakage rates. But I'm also self-taught and I know there are elements of the program I am not taking advantage of.
On the slim chance it will help, what are you selecting for equipment?
Thank you Michael, which of the recommended programs to you think will work best? BEOpt may help in being more efficient with my insulation etc. To answer your question the place is off-grid with a 17Kw ground mount array with over 30Kwh of battery storage, so there are no electrical costs day-to-day. The primary boiler to heat the water in the slab is propane fired. It is a condensing 96% efficient unit. I did enter data for the refrigerator, freezer, dishwasher, etc,. Because I wanted them calculated into the amount of heat produced in the conditioned space. We don't think we will need a cooling system at 10,500ft in Colorado, opening a few windows at night should do it, but we are running a few extra ducts so if we are wrong we can install a heat pump to cool in the summer and as backup for heat in winter.
I don't have experience with any of them; I've only used BEopt and the PHPP (Passive House modeling program). It's on my to-do list to learn and start doing my own Manual Js. Dana is highly respected around here so I trust his recommendation and have downloaded it myself to try out.
I'm not sure if BEopt is sensitive enough to account for appliance waste heat. It might be but I doubt it. The PHPP gets into that level of detail but if you think BEopt was onerous, you really won't like the PHPP.
I just test-ran a BEopt case with a 96% propane unit and it worked fine, so I'm not sure why yours is not.
Your values are quite large; literally ten times what my test shows for an 1800 sf house with a reasonable amount of glazing and 7500 HDD. Is your house very large and/or do you have a lot of windows facing south or west? Or low R-values in your enclosure?
10,500 ft - maybe Leadville, CO, with approximately 10,000 HDD/yr. This is from the DRI WRCC climate site; the data are a few decades old so a bit warmer now but still really cold.
Oops - when I totaled the rows, I also added in the annual total in the last column - should have been ~10,000.
I just ran the last three years for Leadville and the average is 10,854 HDD. Colder than Maine for sure, but not enough to justify a 10X difference in heating load.
(I use this site to generate HDDs: https://www.degreedays.net/#generate)
I am a big proponent of BEopt but I do not think it is a substitute for a manual J calculation.
What it is best at is to help you make economic choices. Like should I upgrade the attic insulation from R38 at X$ per SQF to R60 at Y$ per SQF then it draws you a graph showing the best return on investment closest to the bottom.
Yes, thank you I am playing with it. I did get a Manual J using "HVAC Sizing Tool" and it came out at 31,609btu/hr (heating) which isn't bad for a house this big at this altitude. I am now using BEopt to play with the cost benefit. I wish there more comprehensive tools that would tell me real-world numbers for some things. Like, if I only rely on sealing tape on the exterior wall, for air tightness vs tape sealing plus 2" of closed cell spray foam on the inside of the siding to double seal the walls inside and out, and then less total fiberglass in the double stud wall. It is expensive, but it might improve infiltration enough to be worth it.
In my opinion if anyone says spray foam and new construction together, they have made a mistake. Ok around the floor joists and sill plate is the exception.
I spent my infiltration budget on Zip sheeting and tape and very happy with the results. Seems to me if you make it clear to every worker that airtightness is important to you suddenly it becomes a nonissue as people don’t do stupid when they know you care and are watching.
Walta