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

[Jason Kirchhoff]

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 <http://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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