[Bldg-sim] ASHRAE 90.1 Appendix G3.1.2.2

varun kulkarni seldomvarun at gmail.com
Tue Apr 5 11:42:50 PDT 2011


Milda,

If you did notice, HAP uses two different weather files. one for design and
other for simulation. And if you dig into it you'll find out that they both
are different. The simulation weather is the real time (actual) temperature
and other data recorded at the airports for an extended period, which cannot
be overridden, while design weather data is based on extreme or peak
weather as defined by ASHRAE which you can change in the program.

Now if you are looking at LEED unmet load hours they may not be necessarily
due to air sytem size, but may also be due to your plant insufficient
capacity. Download HAP e help 014 from here :
http://www.commercial.carrier.com/commercial/hvac/general/0,,CLI1_DIV12_ETI3906_MID1738,00.html
.
In here you will find a pdf saying understanding the LEED unmet load hours
in HAP.

Simulation results is just for us to know how the building would run in real
time when sized on the design results. In simulation , HAP takes credit of
internal heat gains, which reduces your heating load, which is OK in real
time. While in design , internal heat gain is ignored in heating load
calcualtions. This is just one of the difference in simulation and design in
HAP.

I hope this helps Milda.


On Tue, Apr 5, 2011 at 12:01 PM, milda margarin <empire999 at hotmail.com>wrote:

> hi Varun
>  thanks for your reply! I have another question though based on your
> statement that the system should be based on the 'design results'; I thought
> the whole point of using simulations is to predict the peak capacity
> required and then base your design on this? (possibly by applying safety
> factors according to real life experience).
> And how can you have unmet loads when you design based on the peak load? In
> that case the 'peak load' is not the maximum load?
> Further comments anybody?
>  best regards
> Milda
>
>  ------------------------------
> From: seldomvarun at gmail.com
> Date: Tue, 29 Mar 2011 07:51:29 -0400
> Subject: Re: [Bldg-sim] ASHRAE 90.1 Appendix G3.1.2.2
> To: empire999 at hotmail.com
>
>
> Milda,
> I think if you are performorming energy simulations for the baseline, it
> doesnt matter what is this 25% and 15% upsizing is used for, as it used only
> as much capacity it needs. And your system size should be based on the
> design results and not simulation results (that also proposed model).
> But nevertheless I always interpret this as you said in your first point,
> to cover uncertainity in building simulation.
> I also think it helps baseline to reduce its unmet load hours.
>
> I hope this helps.
>
> On Tue, Mar 29, 2011 at 3:27 AM, milda margarin <empire999 at hotmail.com>wrote:
>
> hi , I already submitted this question but there were no responses so I'd
> like to try again:
>  could somebody share some insight to the ASHRAE 90.1 Appendix G3.1.2.2
> point regarding heating and cooling equipment sizing based on building
> energy simulations. It is stated that the equipment should be oversized by a
> factor of 1.25 for heating and 1.15 for cooling. Are these "safety factors"
> based on the uncertainty associated with building energy simulations or a
> requirement that makes sure that the system can respond quickly enough
> during startup? Why are there different factors applied for heating and
> cooling?
> thanks!
> Milda
>
>
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> --
>
> Thanks and Best Regards,
>
>
>
> Sincerely,
>
> Varun Kulkarni , M.S. , EIT
>
> RMF Engineering
>
> 5520, Research Park Drive, Suite 300
>
> Baltimore, MD - 21228
>
>
>
> Office : 410-576-0505 ext. 5352
>
> Mobile: (+1)405-385-1928
>
>
>
> Note: Please do not print, unless required.
>
>
>


-- 

Thanks and Best Regards,



Sincerely,

Varun Kulkarni , M.S. , EIT

RMF Engineering

5520, Research Park Drive, Suite 300

Baltimore, MD - 21228



Office : 410-576-0505 ext. 5352

Mobile: (+1)405-385-1928



Note: Please do not print, unless required.
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