Heat Loss Calculations - Which program are YOU using?

canmar

I have gone back and forth between programs for years and heard many different opinions.  I am at the point where I no longer do the installation work, unless absolutely necessary, however I run across many sets of prints I need to do a take off on.  I am wondering all those out there, which program do you use?  I want something that is obviously Manual J and ASHRAE compliant, but I don't need it to be extremely in depth.  Most of the calculations I do are for average to slightly larger size homes or light commercial.  I have used Wrightsoft and Elite, and though these are great programs, they can be very time consuming and as we all know time is money, especially when not all jobs are guaranteed.  Any thoughts or information that can be shared would be extremely valuable.  

Brad White

I use Elite CHVAC

for my commercial work and for residential. The principles of A x u x Delta-T are common to each, the only difference is in cooling if you are using the RTS method which takes building mass into account.



I also use HAP (a Carrier product) in the office. Both do the same thing differently, but I find that Elite matches my hand calculations a lot better.



Once you get things set up, a library of common constructions, your speed will increase.

canmar

thanks

I am finding that there really aren't many options out there.  I have aan old version of hvac calc, but I think that the makers of the program are out of business.  Its a nice quick calc, but doesn't state Manual J 8th on it which is a problem.  I use all current calculation and numbers with it, but its not acceptable by most.  Thanks for the info.

Brad White

Seriously,

and not to minimize the work it takes, there may still be Manual J tear-off pads available. Not sure if ACCA still publishes them, but they at least state Manual J on the top.



Building and energy codes are funny. In some jurisdictions they say "Manual J", others say ASHRAE but without declaring the method (CLTD or RTS for cooling as one example). 



Typically, when I point out to an AHJ that ASHRAE 90.1 is the genesis of most state building codes and that I use an ASHRAE algorithm (either by hand or by software), they accept that.  The ones that do not and can be educated, see this eventually. The ones that refuse to see this, frankly, are not motivated by forces most of us understand. Fortunately, they are few.



EDIT: Personally, I think ALL of the programs work well and get within a few percentage points of one-another. The underlying issue as I see it, is that certain state (and now local!) energy codes specify a certain method be used, not understanding that the results are very similar. It is that branding, that "standard of assurance" they seek. Slant-Fin and other programs are easy to use and accurate for what we are all doing, no question.  What would be great is for these codes to reference a wider range of acceptable standards. As stated, MOST use the ASHRAE or Manual J methods (similar) and if a program can state that this is part of their DNA, I would hope most authorities would accept them.

icesailor

A question:

I've used IBR for over 30 years. I only do hydronic heat. After I started using IBR, I never had a problem. The heat calculations and radiations I got from sales persons were off the charts. Figured like there was no insulation in the building. I never had a problem heating a building. In 1992, when I got my first computer, I started looking for computer programs. I never found an IBR based one that was affordable. The ones I bought were based on Manual J which was for HVAC. More AC. Hydronic heat seemed an afterthought. The room losses were all over the charts. My biggest problem was that they always wanted room orientation and compass direction. To account for solar gain during the day. That doesn't cut it at night when the sun isn't out. And a South facing room may get solar gain in the winter but the opposite room on the North will have greater heat loss making the room cold.

Slant Fin came out with their free program which I found is based on IBR. I carry it in my laptop. I can walk into a house with a heating problem and do an immediate calculation. I can compare installed radiation in rooms and compare them to each other. It is the handiest program I have ever found for hydronic heat. Is there some reason that this program is never mentioned? Or is not popular because it was free and easy and uncomplicated to use? I gave a copy to someone and my old laptop died, loosing my program. I tried to get one from Slant Fin but they never responded. I found another copy and installed it.

It drives me nuts because I do a heat loss for a kitchen where they want to use radiant in-floor and they don't have enough free floor space for the radiation without additional radiation. Then someone comes along and puts it in without.

I'm curious.

canmar

slant fin

I actually have and continue to use the same slant fin program to this day.  Most of the calculations I do are for hydronic systems and this is more than adequate.  If I were desinging geothermal on the side of a mountain on teh highest peak in the us I would be more inclined to get in to a real in depth load calc to give to one of my contractors, but considering the btu load of the domestic hot water almost always trumps the need for heat in the house and I quote out modulating boilers its alomst a moot point.  In a way I am glad to see that I am not really missing anything.  I am looking at a new calc program an industry freind created through an excel spreadsheet foprmat on Monday that has quick and easy clacs for all hydronics including full radiant layout and will comment again after I try that.

CMadatMe

Wirsbo ADS

I have been using this program since it came out 20 or so years ago. It is ASHRAE based. It's simple. Can do cooling loads. It is also free..

icesailor

Programs:

Like I said, I only do hydronic. Heat loss is heat loss. As long as the factors for heat loss are the same, the emitter don't change and is part of a different equation. If a room looses 10,000 BTU's per hour, you only need to add 10,000 BTU's per hour to keep it warm. It's how many available in the water and how you get them there that counts. I've used Wirsbo, Heatway, EasyCalc and others I can't remember. I always get back to IBR for room loss. How I get there is another issue.

NRT_Rob

actually

I'm dissastisfied with all major load calculators including my own internal method. Most do not use any even vaguely pseudo scientific method of accounting for infiltration.



Working with a green building professional on a project recently, he turned me on to a method where he calculations infiltration based on envelope square footage.



Still not ideal, but a lot nicer than ACH method. Still need to guess at "leakiness" but at least rooms with more or less external exposure reflect that in the ACH calc that way. Very nice.



I find with equivalent inputs, Manual J calculates the same heat load as any other program. Equivalent means you don't put in a duct load, etc. they don't account for solar gain for heating, they want exposure to count for solar gain for *cooling* only.

icesailor

Infiltration factors:

I find that the IBR method works pretty well and is something I can use to "fudge" odd rooms. I always felt that the other programs I tried fell down in infiltration. Where I work, infiltration is the biggest factor. And that's where the high wind loads come from.

What do you find?

Mark Eatherton

I roll my own....

Excel spread sheet. A/R*delta T, + infiltration estimates.



Or U*A* DT, which ever tickles your pink, or pickles your tink :-)



ME

NRT_Rob

I'm not sure

exactly what the IBR method is. If it's just the slant fin calculator, it seems pretty straightforward, but it's been awhile since I used it... doesn't it still just use ACH?



My internal calculator allows me to fudge individual rooms for ACH but still, that's just guessing. I am finding on the tight end of the spectrum, my ACH rates are less than most and I am suspicious that my estimates are still at least 50% high in those cases...

icesailor

Programs: IBR

IBR was the first to set up schools to train people in designing and installing hydronic heating systems. They did these two day courses all over the country. IBR was a trade organization. ALL the boilers and radiation have a symbol on them that is supposed to signify that their ratings meet the IBR standards. There's a number of ratings on hydronic boilers. Gross, DOE and IBR. The IBR will be the lowest rated output. It allows for 15% allowance for piping and pick-up. If you have a "normal" system, and you don't install more than the rated IBR amount, piping and pick up are allowed for the boiler will do the job. Way back when, lots of guys took the courses. I never took the course but I bought all the books which were the courses. They followed the courses with work examples. I have never met anyone who took the courses. When everyone knew all the stuff, hard times fell upon "The Hydronics Institute" in Russo NJ. They were taken over by GAMA and started selling the books again. They do courses again. They eliminated one book which I considered it my piping and radiation bible. I loaned it out to someone and never got it back. I've tried to get a new/used one but to no avail.

As far as infiltration is concerned, They use air changes per hour and how many exposed walls there were in a room. You use the factor and go to a table. That did room volume. When I got the Slant Fin HL Explorer, I saw the factors and such and recognized it as the IBR method.

Slimpickins

Heat Load Pro

Is anyone using Heat Load Pro?

Brad White

I have

and have at most toyed with it. The strong points are in basement/sub-grade applications. The version I have is the first I believe and I do not know if there have been updates.



What I found limiting (and maybe this is because I did not RT*M), is in printing out reports. I found myself copying the heat loss numbers off the screen and into a spreadsheet.



So no, I do not use it regularly.



One application I do use is in conjunction with LoopCAD 2010, there is a heat loss program integrated with the pro version built around a BIM engine within the program. It makes a 3D model of the space including circuits and has ample pull-down menus for the various constructions.  The Uponor software is similar I was told.



But start to finish, Elite CHVAC is my stand-by.

Tim_75

Trane TRACE 700

I have been using this program for load calculations, including accurate infiltration determination, and for all types of energy modelling. This program is awesome for suppoting LEED projects and comparing various choices of system types and control as well as thermal storage and load shifting.

rlaggren

Curious about door tests

If the building has a blower door test is there a place to plug the results into the heat loss programs?



Rufus

Brad White

That could be an entirely separate

thread!



This is what I do, for what it is worth. (And for background, I do have a blower door, FLIR camera, etc. and do energy audits aside from the day job, so have access to this data.)



1. Each and every room will at some point need 100% of the heat determined for it. This is the number used to size and assign radiation to each.



2. Infiltration is more dynamic and fluid. 

Take a typical and hypothetical 4-sided structure. Air enters on the windward two sides (plus more on lower floors, less on upper floors due to stack effects). Little or no air enters on the "leaving sides", the leeward sides at those times.  The air leaking out of those spaces has been pre-heated by the spaces where the air entered. Infiltration is neutral to these spaces in other words.



A wind shift will change this, but at any one time, half the house sees "INfiltration, the other half -more or less- sees EXfiltration.



The point being to all of this is that if you take your sum of room heat losses (and sum of all infiltration by default), you will overstate your infiltration to the building as a whole, simply because air cannot leak in to every space at the same time.



Unless you are in a tornado in which case heat loss theory is pretty far down the list of your immediate concerns.



3. Once the heat losses are established for each room, I "back out" (subtract) the infiltration numbers from the mix and deal with that as a separate "system number". Essentially, separate "transmission (conductance)", from infiltration.



In answer to your question, in my program of choice, (Elite CHVAC), this is a manual procedure penciled on the hard copy I keep for records. I do not know if this method is possible to enter specifically to any input field of any commercially available program.



To be frank, this "back out the infiltration method", very rarely affects the size of a boiler or system. It may give a deciding tip if I am on the edge, do I go to the next size or stay where I am?



As for infiltration itself, or specifically, "how does one translate blower door test data to "actual infiltration rates in real life?"- I will be happy to share what I know, not that it is anything remotely resembling the entire picture. But let me know if you need that.



Best,



Brad

gerry gill

i use HVAC CALC.

and they do have an update cd disc version..the company is still in business.. their web site is http://www.hvaccomputer.com/ and i used to use their older version..tried siggys program, tried slant fins, and came back to hvac calc..maybe its because i know how to use it real well, but for some reason i can fly through the input with it.

neilc

simple as that ?

Hey Mark,

is it as simple as that?

area / r value times delta tee?

what calc are you using for infiltration or orientation?

or the u value calc,

surely you must plug in other variables, yes ?

any chance you would post your home grown ?



I feel like I am on the cusp of a career change, to weatherization, insulation, and right sizing,,,, not that I intend to scam your worksheet, except perhaps at my own home,,,

currently employeed and dismayed in the most drafted, non eveloped, poorly assembled (did I say drafty ?) institution of private primary education,

and therebyl director of facilities to its grossly over sized, and still underutilized heating and cooling equipment.



boy am i on the horse today,,,

rlaggren

Infiltration = 1/2 blower door figure

Brad, thanks for your analysis.



If I understand it right, the above is a nutshell of what you said and it sounds like a good cut to me. It'd have to depend on how the wind speed translates to Pascals across the pressure and the suction sides of the house, but the difference between "inflating" a house, where you measure all the leaks at once in once direction, and wind blowing into and then out of a house, where 1/2 the leaks are used to vent the incoming air from the other 1/2 of the leaks, sounds like a core concept here. I think I can get my head around that.



And I bet there are average wind speed records for a particular location and time of year. And a table somewhere which would give the average pressure differential across a particular sized structure at a particular wind speed - which would then be used to at least approximate what percentage of the blower test leakage number we could figure for infiltration into the house. And we could get different numbers for various wind speeds to tell us how much different it would be on still days opposed to windy ones.



That's fairly good hard info and it seems like there _should_ be a way to enter that info in heat load calcs. Actual measured data seems a lot better way to build a calculation than generalized estimates based on how the construction of a building looks to you. And I'm not sure about your statement that it makes only small difference in heating. A couple of reasons: Icesailor (I think) has mentioned several times that in his experience wind makes a significant difference in the heating load; and I know from personal daily experience that leaky windows cause a room that is quite comfortable one day to be quite chilly the next. Also, it's been mentioned several times that insulating a house changes the heating calcs significantly and everything I've read about insulation says that the most significant part of insulating consists of plugging all the leaks; ie. not plugging all the leaks can easily degrade the insulation by 50%. That sounds to me like leaks aka infiltration must or at least should be a significant factor in heat calcs.  I be most interest in your further thoughts.



If I get what you saying right, that there really isn't any good way to apply good hard infiltration numbers to existing heat calc programs, then it sounds to me like we have an example here of a part of the info highway that hasn't been built yet. A bottle neck like those towns in Nevada where I80 used to die down to 35mph!



Rufus

Brad White

Infiltration vs. Blower Door Data

Well, Rufus, there are legions of articles out there to help translate blower door data into useful actual infiltration data.



I would definitely not take half of the blower door data, those exaggerated numbers have to be adjusted and processed first. Remember, 50 Pascals is the same as a 20 MPH wind hitting all sides at once. It is also very close to one pound per SF all over the house. Exaggerated in order to measure, really.



The most common rule of thumb is "ACH50 divided by 20" and this was borne out by some research at Princeton. However (and there always is a "however"), this "20 divisor" can be lower, especially in a taller home or one that is less sheltered. The 20 divisor I have found mostly applies to single-story ranch houses, not taller ones.



There are two distinct approaches (divisors) out there that I know of and which I use.

One is the "LBL number", named for Livermore Berkeley Laboratories, who developed it. The other is the ZPT number, (Zip Test Pro, a program and application set by Rick Karg out of Maine).  To derive each number, the height of the building, climate zone, relative shielding, etc. are entered. What come out are numbers that can vary in my experience, between 10 and 20. MOST homes average 13-15 in my experience.



Because these numbers are divisors, it means that if you use  "ACH50 divided by these smaller numbers", you would arrive at a larger infiltration number but I take these as more accurate because they are based on factors specific to the home in question.



As an example, from my own database of single family homes in my area, a typical ACH50 would be 13.5 average. If divided by 20 as the base rule of thumb one would have 0.675 ACH, which for homes averaging 97 years (my sample average), is fairly low and optimistic! Instead, if my divisor is 13.5, that is a good solid air change per hour of infiltration. Often it works out to 1.25 actual ACH, sometimes more.



We both agree, wind speed is highly variable and the proverbial average may be exceeded by a factor of three every so often. Does this coincide with the coldest weather? Sometimes but warm building mass helps you to ride it out.



But also, as you mentioned, air sealing is more than half the battle- a good air leak negates many inches of insulation. No point in having thick walls if you leave the front door open.



Anyway, just some thoughts to cap off the weekend...



Brad

rlaggren

Thanks for infiltration overview from your records

Brad,



I'll read up on the ZPT and the LBL methods. But the figures from your area  help put the theory into context; even better the houses I'm dealing with are older (100yrs) 3 floor buildings so they're somewhere in the ball park of your data. I'm glad to hear there is at least a couple of ways to relate the ACH50 data to a heat loss calc.



I asked because I hadn't yet come across any direct mention of how to use the ACH50 test relative to heat loss calcs and to me it's a no-brainer to use that data in the calculations if it's available. Admittedly I've not been doing much HVAC reading of late except to hang out here a bit in the evenings and perhaps I just don't remember it from when I was studying a couple years ago.



IAC, regards,



Rufus