Heat Loss/ Gain Calculation
Heat Loss/ Gain Calculation
(OP)
It might be a funny question but here goes..I'm just curious, how do they do the heat loss calc back when theres no computer or software. How do they do it manually. I ask someone, and says 'you can only get the value on the computer, it calculates it for you'..and i say, is there a way to do it without the software?.answered no. hmmm. makes me wander..





RE: Heat Loss/ Gain Calculation
You solve them the same way a computer solves them. A computer is no smarter than a human, only faster.
TTFN
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RE: Heat Loss/ Gain Calculation
still works for heating, but the U value changes with cooling (because of the sun - north face vs south; time delay of sune heat etc), so you have to look it up in charts. And then you did a couple iterations to see what month and time of day was the worst case. More experience equalled less iterations.
Our computers now do an iteration for all 8700 hours of the year, and tell you the worst case.
I believe ASHRAE called this the CLTD method and was the last hand calculation method accepted. Now it is all heat transfer and time related.
knowledge is power
RE: Heat Loss/ Gain Calculation
I still do small jobs by hand...
Good on ya,
Goober Dave
RE: Heat Loss/ Gain Calculation
RE: Heat Loss/ Gain Calculation
"For a manual cooling load calculation method, refer to the CLTD/CLF method in Chapter 28 of the 1997 ASHRAE Handbook—Fundamentals"
knowledge is power
RE: Heat Loss/ Gain Calculation
similar to the computer programs we manually filled out sheets(room size, height, orientation, u values,etc.) and manualy crunched the numbers on a calculator. the hardest part was the the sun load. even then we had a standard sheet for the local areas and orientation.
alot of the information needed at the firm i worked for was already on paper(mimeograph!) and i still have some of it in my old files.
it was alot of work but was pretty automatic after the first couple of dozen rooms.
I learned from the manual calculations where the values came from.
RE: Heat Loss/ Gain Calculation
RE: Heat Loss/ Gain Calculation
Don't blankedly trust the computer results. You need to know how to do this manually to get a feel for the program and know when and how to tweek the input to get the correct results. To do otherwise is blind engineering.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Heat Loss/ Gain Calculation
Since no program will ever be fully tested, you can be certain that there are errors. Some will result in the program stopping (these are the "good" kind). Some will run to completion and simply give you wrong answers (these are the bad kind). If you don't have an order-of magnitude feel for your calculations then you will never know when the program is lying to you. The only way to get that feel is to be able to do the calcs on a calculator (or spreadsheet, or slide rule). I'm not advocating redoing every calculation on an Engineering Pad, but when you are expecting the answer to be "100" and it comes back "7000", you need to be able to satisfy yourself whether your expectations were wrong or the program hit one of those non-documented bugs.
The guy that said there was no way to do the calculations without the software was a VERY dangerous idiot. He needs to understand that every program was written by a person referencing calculations that were developed by (usually) another person.
David
RE: Heat Loss/ Gain Calculation
Regards
Pat
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RE: Heat Loss/ Gain Calculation
I do not advocate this approach but the building services industry is considered to be at the bottom of the pile when it comes to engineering fundamentals. Lifts and air conditioning plant is always undersized as the contractors try and save money. Sustainability is all worth less mouthings. Lip service is paid to this when the embedded energy of systems is not taken into account. Mechanical services equipment last 10 years if you are not on the coast or just get lucky. No provision is made for expansion.
RE: Heat Loss/ Gain Calculation
AUTOKAD: It's rather exceptional that you desire to know the fundamentals upon which your loads program is based. Don't lose that desire! It's what has kept engineering interesting for me for 30+ years...
Good on ya,
Goober Dave
RE: Heat Loss/ Gain Calculation
I belong to the "older gard" who did almost everything by hand at least on few small projects, and now I see young engineers who seem to be completely relying on pressing software buttons, which goes really close to driving car by looking at the map without taking a look through windshield.
The main problem is that there is less and less effort to provide basic eduction on that through regular courses that are inclined to provide very generic and oversimplified explanations.
That is why Autokad's desire to learn about process is really smart.
ASHRAE Fundamentals book gives exact overview of the process, and I would recommend that you do it manually for several typical rooms, but to avoid too many repetitions as once you get a grasp of process, you can spend your time better by reviewing software results and comparing them.
Personally, I have more trouble currently with infiltration issues for residential projects than with anything else.
After you finish several projects for your frequent location, you will have many data about losses/gains per area and orientation both for outer walls/roofs and glasses with some typical SHGF, interior loads as well, but infiltration is real burden and you actually need to assess it.
RE: Heat Loss/ Gain Calculation
Since then, I have always checked computer output by hand calculation. It takes more time but weeds out many unintended buggers that you may gloss over in front of a computer. It's the difference between an Engineer and a computer jock.
ASHRAE fundamentals is the source for heat gain/loss.
RE: Heat Loss/ Gain Calculation
Nver stop learning!