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90.1 Reference building basic PSZ questions

asked 2017-12-01 22:24:05 -0500

ModellingisLyfe's avatar

updated 2017-12-06 04:39:50 -0500

I have some basic questions, I am in Equest modelling the reference/baseline building to 90.1-2010 standards. 

On the airside HVAC for PSZ systems, what do I enter for the cooling and heating capacity? I am guessing the program sizes it for me? (x1.15 and x1.25 respectively?)

Do I convert EER to EIR and put into unitary power - cooling?

Do I inverse 80% thermal eff and put it into furnace heat input ratio - heating?

How do I calculate fan power without the CFM? Or how do I get the CFM?

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answered 2017-12-08 16:05:25 -0500

yungahhh's avatar

Not a super eQuest user, but...

  1. Yes. Let the program auto-size. Leave the ratio 1.15 for cooling and 1.25 for heating.
  2. I think for packaged equipment, you use this: EIR = (1 / EER - 0.012167) / (1 / 3.413 + 0.012167)
  3. Yes. Convert the efficiency. I think it is Heating EIR = 1/Eff.
  4. Follow instruction from ASHRAE 90.1 Table
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Thanks for your comments! A follow-up to #4. The formula in requires "CFMs".

How do I get CFM of the auto-sized equipment? Do I take the output from the SIM file after I run a simulation? Or do I follow G3. If so, how do I go about doing that?

Appreciate it!

ModellingisLyfe's avatar ModellingisLyfe  ( 2017-12-12 18:26:16 -0500 )edit

I would just look at the SVA report when you do a preliminary run. You can manually calculate it : cooling capacities / (1.08) ( 20 degrees delta T) to get your supply cfm.

yungahhh's avatar yungahhh  ( 2017-12-13 00:56:56 -0500 )edit

Thanks again, really appreciate your clarity. I want to push you a bit further in this. If I make an hourly report of my systems, I can see their auto-sized cooling capacities and CFMs. If I use your formula above (standard heat formula), I get a different CFM from the cooling capacity.

Do I enter this CFM (the one I manually calculated) in the Air-side HVAC tab for my systems?

ModellingisLyfe's avatar ModellingisLyfe  ( 2017-12-13 06:50:29 -0500 )edit

There are several factors affecting the auto-sizing in the model such as the Design Ventilation Rates, minimum flow rate (0.4 cfm/sf), and the sizing factor depend on whether you specified it. I'm using 20 delta degrees based on G3.1.2.8 in the standards. I would use the eQuest autosize. You're just using the supply CFM to calculate the fan power or rate W/cfm, right? Additional references here and here for other opinions.

yungahhh's avatar yungahhh  ( 2017-12-13 13:33:43 -0500 )edit

You are awesome! Yes I'm trying to calculate the W/cfm <-- what cfm do you use? Autosized or manually calculated?

Thanks for the links too

ModellingisLyfe's avatar ModellingisLyfe  ( 2017-12-13 13:47:27 -0500 )edit

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Asked: 2017-12-01 22:24:05 -0500

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Last updated: Dec 08 '17