Heating Coil and Air Terminal translation updates

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In testing the sensitivity of VAV supply air design and setpoint limits, a few 
reverse translator issues were identified.

To clarify, a mapping of SDD to E+ has been developed for the TrmlUnit:Type = 
VAVReheatBox and its child CoilHtg object. That mapping is shown here:
https://docs.google.com/a/360-analytics.com/spreadsheet/ccc?key=0Aq3Ndkzvj2l6dDB
kelVaeDVGNHhCTW8xUnpuZndOd2c&usp=drive_web#gid=10

Items in yellow are currently not translated, so are highest priority, but I 
would like to get an overall review of the translation in this area for 
completeness.

Note, the SDD AirSys:Type = SZVAVAC/HP system also uses the 
AirTerminal:SingleDuct:VAV:Reheat object (with a furnace coil), but the 
translation rules for that system are independent of these translator rules.  
However, the translation rules for the Coil:Heating:Water object apply to any 
reheat coil, whether used in a VAV or PIU box.

Any chance you can pencil in time to review this before the Friday AM call?

Please provide any additional information below.

Original issue reported on code.google.com by da...@360-analytics.com on 8 May 2014 at 1:46

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Kyle, 
I just wrapped up some revisions to the Google doc, these are good to go for 
your review/work.  These changes should mitigate the simulation failure we were 
seeing with lower setpoint/design supply temperatures.  

However, in reviewing the documentation and sizing output further, the meaning 
of the heating coil sizing output assumptions are really not that clear. 
Therefore, we've decided to just try to revert to defaults, which should be OK 
for the near term.

Original comment by da...@360-analytics.com on 8 May 2014 at 7:20

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OK just to clarify.  You want me to leave the VAV terminal properties the way 
they are if SZVAVAC/HP?

Original comment by kbe...@gmail.com on 8 May 2014 at 8:14

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Yes, the updated AirTerminal translation assumptions only apply to 
VAVReheatBoxes.

The updated Coil:Heating:Water translation assumptions apply to all HotWater 
coils. 

Original comment by da...@360-analytics.com on 8 May 2014 at 8:18

• Changed state: Discussion

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On review the hot water coils are already initially defaulted to the values you 
prescribe.  However there is a bit of code to match the coil properties to the 
plant sizing parameters.

        coil.setRatedInletWaterTemperature(sizingPlant.designLoopExitTemperature());

        coil.setRatedOutletWaterTemperature(sizingPlant.designLoopExitTemperature() -sizingPlant.loopDesignTemperatureDifference());

I will remove this code.

Original comment by kbe...@gmail.com on 9 May 2014 at 2:00

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Still need TrmlUnit:ZnServedRef:HtgDsgnSupTemp -> Field: Maximum Reheat Air 
Temperature {C}

Original comment by kbe...@gmail.com on 9 May 2014 at 4:34

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For reference, here is a relevant definition from the E+ 8.0 'Output Details 
and Examples' reference:

Field: Nominal Total Capacity {W}
This field contains the nominal heating capacity of the coil in Watts. The 
capacity is calculated using the rated inlet conditions: inlet air dry bulb 
temperature = 16.6C,  inlet relative humidity = 50%, inlet hot water 
temperature = 82.2C.

In E+ v8.1, a relevant IDF field was revised:
Coil:Heating:Water
v8.0 -> Field: Rated Capacity
v8.1 -> Field: Gross Rated Heating Capacity

The output variable name was not changed, but the E+ 8.1 'Output Details and 
Examples' reference was revised slightly:

Field: Nominal Total Capacity {W}
This field contains the nominal heating capacity of the coil in Watts. The 
nominal capacity is the gross capacity, i.e., the supply air fan heat NOT 
accounted for. Note: For water heating coils the nominal (gross) capacity is 
calculated using the rated inlet conditions: inlet air dry bulb temperature = 
16.6C, inlet relative humidity = 50%, inlet hot water temperature = 82.2C. For 
DX heating coils the nominal (gross) heating capacity is calculated using the 
rated conditions: the heating coil inlet air dry bulb temperature of 21.11C, 
heating coil inlet air wet-bulb temperature of  5.55C, outside air dry-bulb 
temperature of 8.33C and outside air wet-bulb temperature of 6.11C.

Original comment by da...@360-analytics.com on 9 May 2014 at 4:55

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I understand there may have been some translation or related issues on the VAV 
reheat coils, but I would like to clarify the issue as I saw it (without having 
determined the root cause), and provide some supporting information.

With the Medium Retail prototype building, which has a PVAV system, if I change 
the maximum SAT allowed for the SAT reset to 60F, and run the simulation, it 
results in a fan energy that is approximately 1/4 of the fan energy of the 
default SAT reset setting, which has the maximum allowed reset up to 70F. The 
reset strategy is to reset by Warmest Zone (ResetWarmestAirflowFirst).  I 
believe this is either an EnergyPlus problem, or a problem/inconsistency with 
how the model input file is specified, since the fan energy shouldn't vary that 
wildly with a higher maximum reset setpoint if the controls are operating 
properly.

If required, absent any other fixes, I recommend limiting the SAT reset to 5F 
above the setpoint (60F), to prevent these issues from occurring.

Original comment by JohnJArent on 9 May 2014 at 5:03

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John, the change you describe is actually what I would expect, and is also 
inline with that is stated in the E+ I/O ref:

SetpointManager:Warmest
The Warmest Setpoint Manager resets the cooling supply air temperature of a 
central forced air HVAC system according to the cooling demand of the warmest 
zone. For each zone in the system at each system timestep, the manager 
calculates a supply air temperature that will meet the zone cooling load at the 
maximum zone supply air flow rate. The lowest of the possible supply air 
temperatures becomes the new supply air temperature setpoint, subject to 
minimum and maximum supply air temperature constraints. The resulting 
temperature setpoint is the highest supply air temperature that will meet the 
cooling requirements of all the zones. When compared to a fixed cooling supply 
air temperature setpoint, this strategy minimizes zone reheat coil energy (or 
overcooling) and central chiller energy consumption (if the chilled water 
temperature is also reset) at the cost of possible increased fan energy.

I have not reviewed the simulation outputs close enough to know if the 
magnitude of fan energy change is reasonable. I recall that the NACM reset 
strategy (and 70F hi setpoint) was defined by a CASE report. Do you have a copy 
of that, and if so, can you attach to this issue for reference? 

Original comment by da...@360-analytics.com on 9 May 2014 at 8:20

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Yes, I would expect at least a slight increase in fan energy with the "Warmest" 
reset strategy. I'm attaching two documents: the first is an old report that 
documents the intent of the "Warmest" reset strategy for buildings with DDC. 
The second defines a slightly different control strategy, especially for CRAC 
units, which is a "WarmestResetAirflowFirst" strategy. I don't know if this 
strategy or similar is possible in EnergyPlus. With this strategy, the airflow 
decreases first, as load decreases down to a minimum threshold (say, 50% load 
for example). If the load decreases further, the SAT is reset higher, with the 
airflow at the minimum. This is much different than the "Warmest" strategy.

Title 24 requires only a 5F reset, so that should be the standard design 
default.

Original comment by JohnJArent on 9 May 2014 at 9:54

Attachments:

• 7.2006-07-11_DDC_MEASURE5_SATReset.pdf
• 2013_CASE_Data%20Center.pdf

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Just to clarify, the VAV max reset temp was set to 70F in the CBECC ruleset 
because the NACM 'Heating Supply Air Temperature' is defined to be 70F for 
multi-zone systems (see 5.7.2.4).  If we are making the change in CBECC, a 
change should also be made to the NACM.

Original comment by da...@360-analytics.com on 10 May 2014 at 1:18

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I think the 70F Heating Supply Air Temperature should be ok for this type of 
system, but the interior zone will usually need cooler air.  I think it should 
nearly always be in cooling mode.  The issue that I found is that the fan 
energy was very high when the max SAT in cooling setpoint was set to 70F.  Is 
there a distinction between cooling and heating for this type of system?

Original comment by JohnJArent on 12 May 2014 at 4:53

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No, as in DOE-2.2, there is no distinction between cooling/heating for VAV 
systems. For WarmestReset, the fan speed/SAT will adjust within the reset 
limits to meet the warmest zone load.  Therefore, I recommend the ACM be 
consistent on the sizing and reset limits.

I would have expected that even with a high reset limit (70F), the system would 
never reset up that high and that reducing the reset hi limit from 70->65 would 
not have had a significant impact, but Roger's testing clearly shows it does.  
In Q2, I suggest we request NREL to add the other two E+ VAV reset 
SetpointManagers and do some testing with those to see if they have the same 
funny results...

One other point, we should check with NREL, but I don't think we can readily 
represent the CASE studies use of both zone load and OAT to bound SAT. Let's 
leave this topic open for future discussion on that.

Original comment by da...@360-analytics.com on 12 May 2014 at 5:09

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Ok. Yes, I wouldn't expect that increasing the max setpoint would have the 
drastic change that it appears to have.

This building does seem to have a high occupant density --> high ventilation 
loads
--> possibility for need for heating even when SAT setpoint is not that high, 
if MAT is below ~65F. But even so, I wouldn't expect the results I was seeing.

On the other point, I don't think we need to worry about using both load and 
OAT to bound the SAT.

Original comment by JohnJArent on 12 May 2014 at 5:34

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I spoke with Roger. The plan is to update the ACM RM to limit the cooling 
supply air temperature high limit to 60F, and to change the heating supply air 
temperature to 60F.

Original comment by JohnJArent on 12 May 2014 at 6:08

• Changed state: Resolved

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Updating owner and subtype

Original comment by da...@360-analytics.com on 27 Jun 2014 at 3:38

• Added labels: Subtype-CBECC-NRes
• Removed labels: Subtype-OS

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The RstSupHi for PVAV/VAV is now 60F, and I have added @ r2337 on _DR branch 
some COMMONMIN/MAX thresholds for RstHi/Low so that at least the user is warned 
if they put too high or too low values in. 
          COMMONMAX  COMMONMIN  MAX  MIN
RstSupHi  65         55         80   50 
RstSupLow 60         50         75   45

Original comment by da...@360-analytics.com on 6 Aug 2014 at 8:15

• Changed state: DoneVerified