[Equest-users] High throttling setting and KW/CFM calc

[Carol Gardner]

Jason,

I searched the archives to find this explanation of throttling range written
by Steve Gates. He explains how it works and how eQUEST counts hours outside
of the throttling range. This should help.

Carol

Throttling range is the temperature band between no output and full output,
with the setpoint in the middle of the range.  If the VAV cooling setpoint
is 76F with a throttling range of 2F, then the VAV box is at minimum position
at75F, and at maximum at 77F.

The BEPS and BEPU reports count hours as outside the throttling range if the
zone temperature is more than 1F outside the temperature band.  In the above
example, a zone greater than 78F or less than 74F would be considered out of
control.





On Thu, Mar 10, 2011 at 9:45 AM, Jason Kirchhoff <Jason at ibece.net> wrote:

>
>
> Dear all,
>
>
>
> I’d like to ask for a clarification of the throttling range in eQuest. I
> had been working under the assumption that your zone setpoint is at the
> middle of your throttling range, meaning the conditioned space temp drifts
> by +/- 0.5*TR (modifying the example from Greg’s email…with a 75F set point
> and a throttling range of 8F, the system will begin cooling when the space
> hits 79 and turn off when it hits 71). This seems to be somewhat supported
> by the DOE-2 description which reads:
>
> “The zone temperature heating or cooling set point is assumed to be at the
> midpoint of the throttling range.”
>
> In this case, you get an unmet hour when the space gets above 79F.
>
>
>
>
>
> However, that same DOE-2 description continues with this statement:
>
> “If the zone temperature is more than one THROTTLING-RANGE above the
> cooling set point, the zone for that hour is considered to be undercooled.”
>
>
>
> That would suggest that Greg’s example was correct – for a 75F setpoint,
> you get an unmet hour when the space hits 75+8=83F. I did a google and
> archive search and found statements supporting both interpretations. Can
> anyone clarify this with any sort of authority?
>
>
>
>
>
> *Jason Kirchhoff *
> *Engineer
>
> **IBE Consulting Engineers*
> *14130 Riverside Drive, Suite 201*
> *Sherman** Oaks, CA 91423
> d: (818) 305-3228 o: (818) 377-8220 f: (818) 377-8230
>
> **www.ibece.com
> **Ideas for the built environment*
>
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>   ------------------------------
>
> *From:* Greg Collins [mailto:GCollins at glumac.com]
> *Sent:* Tuesday, March 08, 2011 11:58 AM
> *To:* Travis Miller; equest-users at lists.onebuilding.org
> *Subject:* Re: [Equest-users] High throttling setting and KW/CFM calc
>
>
>
> Travis,
>
>
>
> Bumping your throttling range up will definitely reduce your unmet
> cooling/heating hours, but it's not usually the correct approach to do so.
> You're basically saying that the system is trying to maintain 75°F in
> cooling (hypothetically), but the cooling demand is met as long as it's less
> than 75 + 8°F = 83°F.  Is 83°F a comfortable temperature for your
> occupants?  Probably not.
>
>
>
> I'd check to make sure you have adequate zoning by looking at the SS-R
> report and seeing if the unmet hours are similar between the spaces in your
> zone.  What can happen is your system will maintain temperature in the
> control zone (where the thermostat is) and the other spaces can suffer.  If
> all of the spaces have unmet hours, your system capacity might off.  There
> are lots of things that could be wrong, but the reports are your best friend
> while troubleshooting..
>
>
>
> Regarding your kw/cfm calc - I didn't look at it, but the number looks
> reasonable if you're modeling a 90.1 baseline system.  If you're modeling an
> actual design, you want to use the kW (from bhp) your fan is operating at
> during the design condition.
>
>
>
> *Greg Collins*
> GLUMAC | (949) 833-8190
>
>
>
> *From:* Travis Miller [mailto:tmiller at dcengineering.net]
> *Sent:* Tuesday, March 08, 2011 11:14 AM
> *To:* equest-users at lists.onebuilding.org
> *Subject:* [Equest-users] High throttling setting and KW/CFM calc
>
>
>
> I am looking for a little help in trouble shooting a couple of setpoints on
> the attached model.
>
>
>
> The first concern I have is my throttling setpoint. I have it 8 degrees
> right now. The reason for that was to eliminate unmet cooling hours. Is this
> a feasible approach? Is there something else that I should be looking at?
>
>
>
> Second – Fan design KW/CFM – after reading through the archives I have
> figured out that I just need to restore the defaults in the static in WG box
> to allow the KW/CFM box to become active. Is the next step just to calculate
> the bhp for each unit per table G3.1.2.9, then calculate fan power from
> section G3.1.2.9?
>
>
>
> I did this for my first unit and got a value of .000768318 KW/CFM. This was
> for system S1 with a baseline “design” (from the air side summary report)
> CFM of 1,986 CFM.  Does that seem like a reasonable #? I have attached my
> calc spreadsheet for reference, it is a little crude but I think it is
> correct.
>
>
>
> Thanks again in advance.
>
>
>
> Travis
>
>
>
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>


-- 
Carol Gardner PE
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