5.7.5.1 - Describing Coil Latent Performance

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What NACM Section(s) are relevant to this issue?
5.7.5.1 - Coil Bypass Factor

Explanation of issue:
NACM describes the sensible/latent performance of cooling coils using bypass 
factor and related curves, which is indicative of the DOE-2 coil model. The IDF 
cooling coil model uses the rated coil capacity and rated SHR to calculate the 
rated BF.  It then uses the NTU heat exchanger model to determine the coil BF 
at non-rated air flow rates. Given that coil modeling methods of the NACM and 
E+ differ, it is not clear how the current NACM properties are going to be 
translated.  

Proposed resolution:
Suggest revising NACM/SDD to describe properties for both methods, or have E+ 
development team provide an outline for how DOE-2 coil model properties will be 
translated to the E+ coil model, and add to NACM as a reference document.

Please provide any additional information below.
THIS ISSUE ORIGINALLY SUMMARIZED IN "SDD_XML_to_OSM_Review-20120604.docx"

Original issue reported on code.google.com by da...@360-analytics.com on 21 Jun 2012 at 5:28

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Original comment by da...@360-analytics.com on 21 Jun 2012 at 5:34

• Changed title: 5.7.5.1 - Describing Coil Latent Performance

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I will have to review the E+ model to see if we are lacking any important 
inputs that would be entered by the user. I currently have an input for total 
cooling capacity and another for sensible heat capacity, which can be used by 
the software to calculate SHR.

The coil bypass factor (if we keep it) will not be used by E+. Perhaps it would 
be cleaner to add an additional building descriptor for "Coil Latent Modeling 
Method" which would have 1 of 2 values, and then that would trigger the use of 
a list of inputs depending upon the choice (which would normally be fixed for a 
given program).

As much as I would like to remove the BF from the ACM, it seems to have a 
significant effect on the cooling kWh, so we may need to keep it.

Original comment by JohnJArent on 22 Jun 2012 at 10:27

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Original comment by JohnJArent on 27 Jun 2012 at 9:40

• Changed state: Started

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Current plan is to:
1. Keep Coil Bypass Factor specified as fixed default by equipment type
2. Keep Coil Bypass Factor performance curves with fixed defaults
3. EnergyPlus can determine Sensible Heat Ratio from Total Cooling Capacity and 
Sensible Heat Capacity

Any other inputs required for EnergyPlus?

Original comment by JohnJArent on 6 Jul 2012 at 11:57

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The curve "Total Cooling Capacity Function of Flow Fraction" appears to be 
important for determining the DX coil capacity at reduced flow rates, which in 
turn, will impact the latent coil capacity. Since the System 5 is a PVAV w/ DX 
coil, I think this curve is important to define in the ACM.

Other than this, I would have to dig into the the equations deeper and run some 
simulations to provide any more input.  Perhaps Kyle or some of the other E+ 
experts at NREL would have some better insight.

Original comment by da...@360-analytics.com on 7 Jul 2012 at 6:28

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The solution is to add a Coil Latent Modeling Method building descriptor that 
indicates which model is to be used:

bypass factor  (DOE-2)
NTU effectiveness (EnergyPlus)

Coil Bypass and Coil Bypass Factor Adjustment Curve are only applicable to the 
"bypass factor" method.

Add a Total Cooling Capacity function of flow" curve to ACM and Appendix 5.7. 
Curve shall be fixed in proposed and standard design.

updating ACM in v1.6, need to add new performance curve in Appendix 5.7.

Original comment by JohnJArent on 27 Mar 2013 at 6:19

• Changed state: Fixed

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Reviewed and confirmed in v1.6.  Adding relevant terms to SDD master update list

Original comment by da...@360-analytics.com on 3 Apr 2013 at 12:48

• Changed state: DoneVerified