[Bldg-sim] ASHRAE 90.1 Appendix G3.1.2.2

[Nick Caton]

Milda,

 

Just as you can use a hammer to both drive nails and extract them, all building energy simulation software is simply a tool that can be used for very different means.  

 

If you wish to use such software to aid in design/selection of HVAC equipment, then fundamentally you are arriving at design capacities by calculating design heating/cooling loads.  These use design heating/cooling weather conditions which are fundamentally different from the hourly averaged (over decades) conditions in a TMY weather file.

 

If you wish to use such software to evaluate system behavior over time, that’s a very different endgame.  A system that is 100% properly sized for capacity at design conditions can easily have “unmet hours” as a result of something beyond capacity.  Many factors independent of capacity come into play for hourly simulations including system setback/warmup functions, economizer operation, load schedules of all sorts, part-load performance curves and sensor/thermostat settings.  These all can determine whether a zone’s conditions are met or not for the hour, in spite of whether a system is properly sized for design conditions.

 

Some software is specific to load calculations and assisting in HVAC sizing.  Some software is specifically targeted at energy modeling to simulate system behavior over time.  Some software is intended/appropriate for both functions, to varying degrees.  It’s up to the end-user to define what she/he is trying to accomplish, and what tool of choice is best for the job at hand.

 

~Nick

 

PS:  It appears you may have missed my response following Varun’s specific to 90.1 and “safety factors” last week – I’ve attached just in case ;).

 

 

 

NICK CATON, E.I.T.

PROJECT ENGINEER

Smith & Boucher Engineers

25501 west valley parkway

olathe ks 66061

direct 913 344.0036

fax 913 345.0617

www.smithboucher.com 

 

From: bldg-sim-bounces at lists.onebuilding.org [mailto:bldg-sim-bounces at lists.onebuilding.org] On Behalf Of Chuck Khuen
Sent: Tuesday, April 05, 2011 2:15 PM
To: varun kulkarni; milda margarin
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] ASHRAE 90.1 Appendix G3.1.2.2

 

If there someone can define/agree upon a solution to the ‘different weather data used for design and simulation’ problem, we are happy to help.  We have the detailed historical data from which we can calculate the design to numbers and we have both raw observations and localized current conditions/forecasts plus an engine to post process this on the fly and deliver it specific to a site.  We are happy to work with anyone who wants to tackle this.

 

Chuck

 

_____________________
Chuck Khuen
Principal
Weather Analytics Inc.
www.weatheranalytics.com
781-856-5383

 

From: varun kulkarni <mailto:seldomvarun at gmail.com>  

Sent: Tuesday, April 05, 2011 2:42 PM

To: milda margarin <mailto:empire999 at hotmail.com>  

Cc: bldg-sim at lists.onebuilding.org 

Subject: Re: [Bldg-sim] ASHRAE 90.1 Appendix G3.1.2.2

 

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 <tel:%28%2B1%29405-385-1928> 

 

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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