×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

methods for determining heat/cooling(?) loads

methods for determining heat/cooling(?) loads

methods for determining heat/cooling(?) loads

(OP)
all,

this question is directed to skilled engrs whom practice hvac.  i've studied hvac (college) and extensively worked in the hvac industry, but have not done any hvac design work.  so i am inquisitive!

this question is realted to arch5599 post on 05-01-03.

i heard of engineers determining heat loads (or cooling loads?) based on a Btu/hr-sq.ft and by ASHRAE standards (fundamentals handbook) - determining overall room/bldg U based on design of bldg.  i understand that there is a difference in construction (residential and commercial), and considering what tools are available,...

Please clarify which method is actually practiced most often and for what reasons (client specified?)

for what reasons is the Btu/hr-sq.ft method used?

the Btu/hr-sq.ft method seems too simple and can provide results which lead to over/undersized equipment (example of air conditioners running 100% of time during summer months in houston, tx and not keeping apt. rooms adequately cooled).

which method provides results that are realistic - i understand that in the hcav world, results can vary >10%, depending upon method used.

it seems to me that determining heating and cooling loads as stated in the ahsrae fundamental handbook )or by other recognized industry stds) is the more appropriate and professional method.

thanks!
-pmover

RE: methods for determining heat/cooling(?) loads

There are those that might use "rule-of -thumb" methods to estimate cooling/heating loads for buildings, but in my opinion they are asking for trouble. Rule-of-thumb guidelines work well for initial estimates, but a cooling (or heating) load calculation using ASHRAE or DOE methedologies should be performed for every building before selecting final equipment is selected.

When we get estimates from building owners prior to our design, they are almost always suprised to find that their estimates are low. They are usually based on a contractor's rule-of-thumb estimate. These estimates almost never account for the impact of ventilation on the cooling load.

ASHRAE's published methods essentially require you to employ a computer program. If you want to run a cooling/heating load for a building, and don't want to shell-out the big money, I recommend getting Carrier's "System Design Manual Part 1: Load Estimating". It guides you through a hand calculation procedure and would be good for simple jobs. I still use it and have never had a problem with over/under-sizing equipment. In the same vein, ASHRAE's method for Residential load analysis (Fundamentals Ch. 27) works well too.

RE: methods for determining heat/cooling(?) loads

I vote DouginMB.Rule of thumb is only for initial estimation
i.e to determine the project cost. But it should never be used for selecting the equipment for actual installation.
There are many Heatload software available in the market the best is carrier's E-20 II, which gives you energy analysis also.

RE: methods for determining heat/cooling(?) loads

(OP)
thank you gentlemen!

your responses confirms what i suspected.
-pmover

RE: methods for determining heat/cooling(?) loads

(OP)
any suggestions as to where i can obtain Carrier's "System Design Manual Part 1: Load Estimating and Psychrometrics"?
i investigated carriers web site and was not able to find it.  is the manual discontinued?
-pmover

RE: methods for determining heat/cooling(?) loads

Contact your local Carrier commercial sales rep.

RE: methods for determining heat/cooling(?) loads

The de-facto standard is the Manual J inspection which is in it's eighth printing and is the one that you should get. It cna be purchased at ASHRAE, RSES,there is an online shortform that will perform some of the simpler calcs at Mr.Hvac.com, you can also purchase the full software which complies with Manual J standard. Also a good residential and commercial version is available at www.webworks.com.
To comply in New York State for any rebates you must use manual J speciifications. This was instituted to reduce the tendency for installers to oversize units for a "safety" factor. Oversizing tends to utilize too much power, and due to shortcycling, is not able to properly dehumidify the space.

RE: methods for determining heat/cooling(?) loads

Dear Pmover,

could u get the carrier systems design manual.

I too need a copy can u help
reg
grnblr

RE: methods for determining heat/cooling(?) loads

Use rule of thumb for bidding purposes.

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources