Clarification needed - Report: Sensible Heat Gain Summary

asked 2017-10-31 08:58:03 -0600

Amir Rezaei
841 ●1 ●7 https://www.linkedin.c...

updated 2018-05-31 17:32:12 -0600

Can someone once and for all help me understand the Sensible Heat Gain Summary table and how it relates to the end use table? Here are my questions:

What efficiencies are factored in from sensible gains HVAC heating/cooling numbers to get to end use table?
What is the difference between the first 2 columns and column 3-4 on sensible gain summary table? One says zone equipment and the other terminal units, I am not sure if that is trying to separate the AHU level from zone somehow?
On cooling columns, why is one number positive and one negative under "zone & other" and "terminal unit" columns?

The tables below are from a building with DOAS + FCUs, so it kinda makes sense to me if I read it as some cooling happens at AHU level (HVAC Zone Eq and Other sensible air) and some at terminal (HVAC terminal unit sensible air cooling). Not sure why I don't see terminal level heating with this example but that might be due to something wrong at terminal FCUs.

Gains Summary:

$C:\fakepath\Heat Gains.png$

End uses:

$C:\fakepath\End uses.png$

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Hi, I am wondeirng if this problem has been saved as I encounters similar issue as in ur gains summary uploaded. I do not understand why 'HVAC Zone Eq & Other Sensible Air Cooling [kWh]' and 'HVAC Terminal Unit Sensible Air Cooling [kWh]' are posstive and negative value respectively if they both stand for cooling action. Does it mean some unintended reheating happened at terminal end?

Allison

Allison Pan 611 ( 2018-05-31 21:09:47 -0600 )edit

Amir Rezaei it would be helpful to have this idf file to test the fix. Please post a link here or send to energyplus-support@gard.com

MJWitte ( 2018-06-21 18:53:44 -0600 )edit

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answered 2018-06-21 18:52:44 -0600

MJWitte

9740 ●6 ●10 http://www.gard.com/

The HVAC systems are simulated in their full glory to calculate the end-use utility numbers. Consult the HVAC equipment inputs to determine nominal efficiencies which are typically then adjusted using curves for off-design operation.
Columns 1 and 2 are for zone HVAC equipment (fancoil, PTAC,PTHP, etc.). Columns 3 and 4 are for air terminal units supplied from an air loop (AirLoopHVAC). The underlying output variables which feed this report are documented in detail in the Input Output Reference, search for "Sensible Heat Gain Summary." However these particular columns (1-4) are not quite clear, because the original report only had two columns for "HVAC Input Sensible Air Heating" and Cooling. When these were split between zone equipment and air loop equipment, apparently the documentation was not updated to match.
As mentioned in the I/O Reference overview for this report "positive values are shown as additions and negative values are shown as removal for most variables." Running some example files shows that the two cooling columns generally show negative values, except an annual run of HVACTemplate-5ZoneFanCoil-DOAS.idf does have a positive value for "HVAC Zone Eq & Other Sensible Air Cooling" for Space5-1. So it appears there is a problem with the method for splitting the total HVAC impact between zone equipment and air loop. I can't say for sure, but my guess is that the sum of the first four columns is correct as shown and the positive values belong in the heating column.

Found the problem in the source code. The zone equipment contribution is not being separated every time step, but the split is being done at the end of the simulation: ZoneEqCooling = NetHVACCooling - AirTerminalCooling. Likewise for heating. So, over the course of the year, the DOAS air terminals are overcooling the zones and the zone equipment is providing heating to offset the overcooling.

Issue #6794 posted to correct the documentation and fix the positive "cooling" values.