[Bldg-sim] Conservative design cooling load calculations vs baseline sizing

[Robby Oylear]

To be honest, the only potential "overly conservative" sizing I can see
going on here is if the building is served by a central cooling plant and
that plant has been sized based on the sum of the peak loads and not the
peak coincident block load for the building.  If this is in fact how they
sized the system then there is potentially a large cost savings that could
be had by appropriately sizing the central plant.

The "worst case" scenario that you describe is a real scenario that can
happen fairly easily.  All it takes is someone to be at home with their
lights on and appliances running on a peak summer day.  That doesn't seem
like a very unlikely scenario at the zone level.

As for how the Baseline equipment should be sized, it should be no
different in terms of lighting, plug loads, and solar gains.  The only
stipulation on the baseline simulation is that it is oversized by a
prescriptive 25% for heating and 15% for cooling.  ASHRAE 90.1 doesn't
strictly define what a "sizing run" is, but it would be considered standard
practice to utilize the peak lighting and plug loads during your sizing
calculations (i.e. don't assume any diversity on the lights and use the
maximum anticipated coincident plug load value).

-Robby


On Thu, Dec 5, 2013 at 6:43 AM, Patrick Bivona <patrick.bivona at gmail.com>wrote:

> Hi Mike,
>
> I can't say I'm frustrated yet. Just going through the learning curve. I'm
> sure frustration will come in time!
>
> I was musing about the potential imbalance in sizing approach between the
> proposed design and the baseline design. If we assume for a second that
> engineers also use ASHRAE design days when sizing equipment for the
> proposed design, there is still a potentially significant difference
> between schedules used for sizing and normal operation schedules. Is the
> 1.15 sizing factor for baseline cooling enough to cover such imbalance? I
> don't know enough to say so yet.
>
> Patrick
>
>
>
>
> On 5 December 2013 20:19, Michael tillou <michael.tillou at gmail.com> wrote:
>
>> Hi Patrick,
>>
>> I just wanted to clarify for you that Appendix G (G3.1.2.2.1) requires
>> the simulation of sizing runs for equipment selection based on either the
>> peak from the weather file or ASHRAE 99.6% heating and 1% cooling design
>> temperatures.  As far as I know this is not something USGBC or GBCI has
>> written a clarifying rule on for LEED.
>>
>> As far as being frustrated over engineers doing overly conservative load
>> calculations, welcome to life as an energy analyst.  The best you can hope
>> for is to use simulation to show them and the building owner that they are
>> over engineering the system and try to get some concession.  Ultimately at
>> the end of the day it's the engineer who is stamping the work and taking on
>> the liability that has the final say.
>>
>> Mike.
>>
>> Sent from my iPad
>>
>> On Dec 4, 2013, at 11:17 PM, Patrick Bivona <patrick.bivona at gmail.com>
>> wrote:
>>
>> > Hi,
>> >
>> > When sizing cooling equipment for apartments, the design team on my
>> project used a worst case scenario approach of maxing out all internal
>> loads. For instance, lighting would be on during the day, with full
>> occupancy and all plug equipment running, while the sun is hitting the
>> windows. Adjacent rooms would be considered without cooling.
>> > For LEED, the sizing for the baseline is based on schedules
>> representing typical operations for occupancy, lighting, plug, etc. That
>> leads the baseline to size equipment that has smaller capacity than what
>> considered for the proposed design.
>> > There's an extra dimension, in the fact the design team sized equipment
>> for each individual room, reaching their peak load at different times of
>> the day. So the total cooling capacity is the sum of the worst possible
>> scenarios. The model currently uses a single zone per apartment, with a not
>> so worst case scenario.
>> > How do I solve this conundrum? Am I missing something?
>> > Thanks,Patrick
>> > _______________________________________________
>> > Bldg-sim mailing list
>> > http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org
>> > To unsubscribe from this mailing list send  a blank message to
>> BLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG
>>
>
>
> _______________________________________________
> Bldg-sim mailing list
> http://lists.onebuilding.org/listinfo.cgi/bldg-sim-onebuilding.org
> To unsubscribe from this mailing list send  a blank message to
> BLDG-SIM-UNSUBSCRIBE at ONEBUILDING.ORG
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.onebuilding.org/pipermail/bldg-sim-onebuilding.org/attachments/20131205/700daa81/attachment-0002.htm>