5.7.5.2 - DX Cooling Efficiency

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What NACM Section(s) are relevant to this issue?
5.7.5.2 - DX Cooling Efficiency

Explanation of issue:
The adjustment to EER have not been revised to follow AHRI fan energy 
assumptions.

Proposed resolution:
Revise to use same Q_fan, rated assumptions in the Gross Total Cooling Capacity 
equations.

Please provide any additional information below.

Original issue reported on code.google.com by da...@360-analytics.com on 1 May 2013 at 8:33

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Fixing this in release 1.9 (Friday May 3)

New equation reads:

EERadj = (Q_t,rated + Q_fan,rated) / (Q_t,rated/EER - Q_fan,rated/3.413)

Original comment by JohnJArent on 2 May 2013 at 5:24

• Changed state: Resolved

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Recommend revising the equation and terms in this section to add the term "net" 
correct the units of Q_t,rated. This will make the equation consistent with the 
equations in the capacity section

Revised eqn:
EERadj = (Q_t,net,rated + Q_fan,rated) / (Q_t,net,rated/EER - Q_fan,rated/3.413)

also revise 

where...

Q_t,net,rated     The AHRI rated total net cooling capacity of the packaged 
unit (Btu/h)

Original comment by da...@360-analytics.com on 18 May 2013 at 7:11

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Also, for the fan heat equation in Gross Total Cooling Capacity, I calculate 
the multiplier to be 0.0415:

400cfm/ton * 12000Btu/hr/ton * 3.413 Btu/hr/W * 0.365 W/cfm

Am I missing something?

Original comment by da...@360-analytics.com on 18 May 2013 at 7:59

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John, any input on the last two comments?  Is this something that you agree 
should be added to the ACM?

Original comment by da...@360-analytics.com on 24 Sep 2013 at 7:05

• Changed state: Discussion

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I believe that adding the "net" to the terms should be fine.

For the constant in the equation, I believe it is "0.040", not "0.0415". I will 
have to locate where I did the algebra for this, or redo to confirm. 

Original comment by JohnJArent on 15 Nov 2013 at 1:13

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Closing issue - it appears that the recommended set of curves for different 
SEER/EER combinations have been added to the Appendix.

Original comment by JohnJArent on 19 Dec 2013 at 6:58

• Changed state: Fixed

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John, this issue is still outstanding. See comment #2 and #3.

Original comment by da...@360-analytics.com on 15 Feb 2014 at 7:40

• Changed state: Discussion
• Added labels: Priority-High
• Removed labels: Priority-Critical

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David, I am making the change for comment #3.  At some point I had come up with 
0.040, but I'm not sure how.

For comment #2: I don't think your change is correct - I think it should be the 
gross cooling capacity that is entered for the adjustment, not net, for 
calculating the adjusted EER.

Original comment by JohnJArent on 21 Mar 2014 at 5:18

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John, re: comment #2.  If you have access to the 90.1-2007 User's Manual, 
please review equations G-A thru C and example G-G for their guidance.  If you 
don't have a copy of this, I can send you excerpts. I think you'll find that 
what I describe matches ASHRAE's guidance.

Original comment by da...@360-analytics.com on 21 Mar 2014 at 5:29

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Original comment by cnambiar@archenergy.com on 20 May 2014 at 9:24

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An important issue related to this existing issue came up in testing the user's 
model in issue 601.  

In that model, the user defined both the gross and net rated capacity for the 
DX cooling coil.  The problem is the difference between the two values was 
about 3x the standard assumption of 0.365 W/cfm @ 400 cfm/ton. The ACM and 
current rules are written such that if the user specifies gross and net 
capacities, the difference is assumed to be the rated fan power, with no limit 
and no checking for consistency with design fan power. 

Increasing the rated fan power dramatically skews the proposed simulated EIR, 
and therefore results in unwarranted cooling energy savings. I suggest we 
revise the ACM and CBECC to not allow entry of gross capacity for DX and HP 
coils. Instead, only allow input of Net capacity and let the tool calculate the 
gross based on the ACM assumptions.  Rated net capacity is readily avaialble in 
the AHRI directory and in manufacturer's literature, gross is hard to come by, 
especially for small units...

Original comment by da...@360-analytics.com on 27 Jun 2014 at 6:52

• Added labels: Priority-Critical
• Removed labels: Priority-High

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I agree with David's comment #11 - we should allow entry of gross rated 
capacity or net rated capacity, but not both. I will look back at ACM RM to see 
what changes would be required.

Original comment by JohnJArent on 17 Jul 2014 at 8:55

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To simplify things, I propose that the use only be allowed to enter the net 
capacity.  For DX coils, that is what the AHRI ratings indicate.  For water 
coils, the assumption will be that Gross = Net.  Does this work?
David

Original comment by da...@360-analytics.com on 17 Jul 2014 at 8:58

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*** Yes, I think this is the preferred approach. ***

This will require some slight modifications to the ACM. I will do that today.

Original comment by JohnJArent on 31 Jul 2014 at 5:37

• Changed state: Resolved

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Changing status to FIXED.  This should be ready to close as "Done Verified" 
with no further action, since the change makes the ACM RM consistent with CBECC.

Original comment by JohnJArent on 12 Aug 2014 at 9:32

• Changed state: Fixed

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Original comment by JohnJArent on 12 Aug 2014 at 10:58

• Changed state: DoneVerified