CLTD Method Again 3

[SDTH]

thread403-426357

Dear All,
I use HAP software for cooling load calculation. This is good for detailed design submissions.
I was thinking to develop a simpler excel based cooling load calculation using CLTD method so that i can use it for Concept design stage.
Has anyone scratched their brain on this topic ? Especially on the formulas to develop the CLTD tables and CLFs.

I also hope to have my basics sharpened through this exersice.

Regards

SDTH

SDTH

 

[KYROUS]

Check this out . I use that sheet for quick calculation. Downloaded from

http://www.mepwork.com.

Hope you find this useful.

 

[cdxx139]

Great resource KYROUS

From memory CLTD you have to select a few different times of the year to confirm the largest load, and you hope one of the few was close to your worst case. The beauty of software is it calculates the full 8000+ hours of the year.

That seems like a lot of work for Schematic design. When at the concept stage, rules of thumbs usually suffice.

Last thought, the amount of data entry required for an excel CLTD sheet is probably going to be more than the data entry into the HAPS software. (FYI - HAPS had a BLOCK LOAD option of HAPS which is exactly what you are looking for)

knowledge is power

 

[SDTH]

Thanks Kyrous, cdxx139

I have no idea why I'm obsessed behind CLTD - probably bcz I cant 'SEE' all those calculations behind HAP.
I understand that CLTD table differ with type of wall and orientation and its tedious to develop all those tables.

Let me share a thought. Feel free to correct me please.

Qx=0,θ =UA(Tsol−air,m − Ti ) + UAλ(Tsol−air,θ−φ − Tsol−air,m )

In the above expression, Tsol-air,m is the time averaged sol-air temperature,
Tsol-air,θ-φ is the sol-air temperature φ hours before θ, U and A are the overall heat
transfer coefficient and area of the wall, λ is the decrement factor and φ is the time
lag.
If we develop Sol Air Temperature and assume values for λ (decrement factor) and time lag φ on the conservative side, then we wouldn't need to develop all the CLTD tables right ?





SDTH

 

[EnergyProfessional]

Since you already own HAP, and know how to use it, why would Excel be faster?
The most work is entering the building geometry, windows etc. You have to do that either way, except in Excel you create a huge mess.

And HAP is already validated, who is validating your Excel spreadsheet is correct?

 

[BronYrAur]

Kyrous,

i can't download your attachment. Anyone else having trouble? Can you re-attach please?

SDTH,
If you are looking for a very rough load calc, you could make a spreadsheet where you just input basic wall dims, window dims, and roof dims. You would have to create a "typical" building in HAP and then use those BTU/SQFT numbers in your spreadsheet for the various wall and window exposure directions. Then add number of people, lighting loads, equipment loads, etc. It would be a very limited program for a given region of the country and given building materials. Otherwise, I think it would be too complicated to properly model in Excel.

The most important thing of course would be to use this for budgeting and ball-parking only. Concept designs as you mentioned.

 

[EnergyProfessional]

For heating one could do that, but for cooling you need to deal with all the sun angles and at what time you have the peak. for example, you have a room with SE and SW facing windows, and next to it a room with E-facing window. it isn't that easy to determine when you have the actual peak.

Considering OP owns a software already, Excel is a bad solution in search of a problem. Doing a sloppy job in Excel may even take more time than doing a good job in a software the OP is already fluent in. and that HAP file can be used again for later design stages. If you start a project in Excel, you start all over again later in design.

 

[KYROUS]

EnergyProfessional (Mechanical)

I agree with you 100%. I always use HAP 4.9 in my projects. But in case , I'm a gatherer of useful files dealing with HVAC. SDTH says he needs CLDT content excel file so I just share it 'cause I believe that excel sheet is usable.If anything is wrong , that would be my fault. I apologizes to you all.

BronyrAur

I re-attached the link but not sure it works or not. But you cal also download it in

http://www.mepwork.com.This

site can be trust and have a lot of Building science material.Hope you have a productive day in work.

 

[SDTH]

Thank you all..
HAP is indeed good..i use the latest version too..
But how many of us know the calculations that go behind it...TRANSFER FUNCTIONS to be precise...
Ofcourse why would we know?..it simply works perfect with the software..
Im just curious about the calculations.
I found CLTD more open and clear..thats why set out to make an excel for it myself.
Yes, its difficult and less accurate than HAP. But if we define the wall types that we normally encounter and generate the CLTDs then it should be fine..
Will see how to go about it..
Thanks for all your suggestions..
If i make one, i will upload it here for sure..

Have a great day all of you..

Thanks again..


SDTH