@EnergyArchmage @lgentile it has been 14 days since this pull request was last updated.

This comment provides discussion of integration test warning and failures for this pull request. These are expected and usually widespread for this PR.

AUD Diffs in 389 files because of increases in value of numColumnTag= because of added columns to some tabular summary reports.

Integration test "Failures" of the following are widespread.

AUD diffs
EIO Diffs:
ESO big diffs
MTR Big Diffs
Table Big diffs

1. Widespread EIO and Table changes.

Additional EIO and summary table content is added for all test files with any AirLoopHVAC. The following Component Sizing Information is added for each air loop

         Sum of Air Terminal Maximum Heating Flow Rates [m3/s]
         Sum of Air Terminal Minimum Heating Flow Rates [m3/s]
         Sum of Air Terminal Maximum Flow Rates [m3/s]
         Adjusted Heating Design Air Flow Rate [m3/s]
         Adjusted Cooling Design Air Flow Rate [m3/s]
         Adjusted Main Design Air Flow Rate [m3/s]
         Calculated Heating Air Flow Ratio []
         User Heating Air Flow Ratio []

The Standard 62.1 summary tables have been changed to increase the precision of reported values and extra columns are added to two tables.

The Object count summary table shows diffs because number of autosizable fields increases for all files that have Sizing:System objects.

2. Central Cooling Coil Sizing Changes
   Files with big ESO and MTR diffs are often caused by central cooling coils getting sized to be larger because a larger design airflow rate is being used. This leads to larger chilled water flow rates, changes to controller size, larger chilled water plants etc and signficant diffferences in ESO and MTR results (and slight reductions in hours not met). HVAC energy increases from larger chilled water pumps. It appears that, in the cases spot checked, the coils were previously being sized with too low of a flow rate and with the changes here are now being sized using the proper flow rate. The design main flow rates did not change but the values used for cooling coil sizing did change. These are all Noncoincident sizing method. Did not find a good explanation for why the previous sizing calculations were not using the full flow rate. Here are some examples of air flow rates from a handful of integration tests:

3. In RefBldgLargeHotelNew2004_Chicago there are some additional causes for differences in sizing. The two DOAS air handlers have mixed hard sizes for the air loop design flow rate and autosized coils. The code uses the hard size for air flow as the design size for the coil sizing which is a correction. The main VAV WITH REHEAT air handler does have autosize air flow rate the air handler FLR_3_DOAS_COOLC is sized slightly larger because the adjusted sizes are set upward to match the minimum outdoor air requirement of 2.3788 m3/s.

4. VRP corrections in test file 5ZoneAirCooled_VRPSizing show large differences in the minimum outside air flow, Vot. The new code is producing lower values for Evz (by zone) because it is producing higher values for Zpz (=Zdz for single path). The Xs values do not change. The new code is using a different value for the minimum value for Vpz (or Vdz) when calculating zone outdoor air fraction Zpz = Voz/Vpz_min ( = Zdz = Voz/Vdz_min). The new method of mining the data from the air terminal component models obtains the value directly from the size of the minimum flow at lowest (30%) damper operation. The old/current method for Vpz_min is to use the value in FinalZoneSizing.DesCoolVolFlowMin, which in this file and the zones triggering min Evz it is being filled from FinalZoneSizing.DesCoolMinAirFlow2 which itself is based on a default value for flow per area of ZoneSizingInput.DesCoolMinAirFlowPerArea = 0.000762 m3/s-m2 (0.15 cfm/ft). Tthis is for the input field called Cooling Minimum Air Flow per Zone Floor Area in the Sizing:Zone object and is used here because the cooling flow sizing uses DesignDayWithLimit. So the old method for Vpz_min was based on a rule of thumb for a cooling flow rate to use as a lower limit for sizing the maximum box flow rate, to ensure that the box is large enough. However during operation the box can turn down the flow and the VRP cooling calculations should use the minimum box flow for the final size of the VAV box and how the VAV box will actually operate. The standard says "Vpz is the lowest zone primary airflow value expected" and the examples in "Single-Path Multiple-Zone System Design" (D. Stanke, ASHRAE Journal 2005) clearly uses the minimum damper flow for calculating Zp in Figure 4. The following tables highlight differences between current "master" and "dev" which has the changes in this PR.

5ZoneAirCooled_VRPSizing comparison of zone VRP related terms.

System level VRP terms for 5ZoneAirCooled_VRPSizing.

Testing also reveals that there is problem with the VAV air terminal sizing in zone SPACE5-1. The minimum VAV flow of 0.066333 m3/s is less than the required outdoor air of 0.102859 m3/s. This causes Zpz to be large but gets limited to 1.0 so that Evz = Xs which is extreme.

The test file should be fixed to serve as a better example. The input file does not use the input field called Minimum Zone Ventilation Efficiency in the DesignSpecification:ZoneAirDistribution object, so the the Evz value is not limited and goes very low (would probably be improved example if it did use this minimum at say 0.65).

The larger value of Vot increases the size of the outdoor air handler and affects the OA cooling and heating coils by a lot.

5ZoneAirCooled_VRPSizing main coil sizing. Main cooling coil size went way down but OA cooling coil (above) went up.

Before:

Component Sizing Information, Coil:Cooling:Water, MAIN COOLING COIL 1, Design Size Design Coil Load [W], 5278.83016
Component Sizing Information, Coil:Cooling:Water, MAIN COOLING COIL 1, Design Size Design Water Flow Rate [m3/s], 3.14398E-004
Component Sizing Information, Coil:Cooling:Water, MAIN COOLING COIL 1, Design Size Design Air Flow Rate [m3/s], 0.91260
Component Sizing Information, Coil:Cooling:Water, MAIN COOLING COIL 1, Design Size Design Inlet Air Temperature [C], 15.50224
Component Sizing Information, Coil:Cooling:Water, MAIN COOLING COIL 1, Design Size Design Inlet Water Temperature [C], 7.00000
Component Sizing Information, Coil:Cooling:Water, MAIN COOLING COIL 1, Design Size Design Outlet Air Temperature [C], 12.80000
Component Sizing Information, Coil:Cooling:Water, MAIN COOLING COIL 1, Design Size Design Inlet Air Humidity Ratio, 8.56498E-003
Component Sizing Information, Coil:Cooling:Water, MAIN COOLING COIL 1, Design Size Design Outlet Air Humidity Ratio, 8.46737E-003
Water Cooling Coil Capacity Information,Coil:Cooling:Water,MAIN COOLING COIL 1,9162.19,7334.61,1827.58,0.80,632.95,6.42
Component Sizing Information, Coil:Heating:Water, MAIN HEATING COIL 1, Design Size Rated Capacity [W], 4539.58860
Component Sizing Information, Coil:Heating:Water, MAIN HEATING COIL 1, Design Size Maximum Water Flow Rate [m3/s], 9.86217E-005
Component Sizing Information, Coil:Heating:Water, MAIN HEATING COIL 1, Design Size U-Factor Times Area Value [W/K], 72.10500

After:

Component Sizing Information, Coil:Cooling:Water, MAIN COOLING COIL 1, Design Size Design Coil Load [W], 898.56612
Component Sizing Information, Coil:Cooling:Water, MAIN COOLING COIL 1, Design Size Design Water Flow Rate [m3/s], 5.35170E-005
Component Sizing Information, Coil:Cooling:Water, MAIN COOLING COIL 1, Design Size Design Air Flow Rate [m3/s], 1.04833
Component Sizing Information, Coil:Cooling:Water, MAIN COOLING COIL 1, Design Size Design Inlet Air Temperature [C], 11.00000
Component Sizing Information, Coil:Cooling:Water, MAIN COOLING COIL 1, Design Size Design Inlet Water Temperature [C], 7.00000
Component Sizing Information, Coil:Cooling:Water, MAIN COOLING COIL 1, Design Size Design Outlet Air Temperature [C], 12.80000
Component Sizing Information, Coil:Cooling:Water, MAIN COOLING COIL 1, Design Size Design Inlet Air Humidity Ratio, 8.00000E-003
Component Sizing Information, Coil:Cooling:Water, MAIN COOLING COIL 1, Design Size Design Outlet Air Humidity Ratio, 8.00000E-003
Water Cooling Coil Capacity Information,Coil:Cooling:Water,MAIN COOLING COIL 1,0.00,0.00,0.00,0.00,3487.24,35.37
Component Sizing Information, Coil:Heating:Water, MAIN HEATING COIL 1, Design Size Rated Capacity [W], 4539.58860
Component Sizing Information, Coil:Heating:Water, MAIN HEATING COIL 1, Design Size Maximum Water Flow Rate [m3/s], 9.86217E-005
Component Sizing Information, Coil:Heating:Water, MAIN HEATING COIL 1, Design Size U-Factor Times Area Value [W/K], 72.10500

@EnergyArchmage why is the design size inlet air temperature now 11C while before it was 15.5C? Shouldn't it have been 11C before also?

Sizing:System,
  VAV Sys 1,               !- AirLoop Name
  sensible,                !- Type of Load to Size On
  autosize,                !- Design Outdoor Air Flow Rate {m3/s}
  0.3,                     !- Central Heating Maximum System Air Flow Ratio
  4.5,                     !- Preheat Design Temperature {C}
  0.008,                   !- Preheat Design Humidity Ratio {kgWater/kgDryAir}
  11.0,                    !- Precool Design Temperature {C}
  0.008,                   !- Precool Design Humidity Ratio {kgWater/kgDryAir}
  12.8,                    !- Central Cooling Design Supply Air Temperature {C}
  16.7,                    !- Central Heating Design Supply Air Temperature {C}
  noncoincident,           !- Type of Zone Sum to Use

This also looks like it was fixed.

@rraustad This one I think is because previously, the system wasn't at 100% OA, so only some of the air was at 11C and it mixed with return air. I still don't understand why this one sizes out to 100% OA. It also has coil sizing warnings now. Oh wait, the main cooling coil is sizing to zero now. Should that be so?

@EnergyArchmage why is cooling flow rate being adjusted upwards? Can't the cooling coil be sized on the cooling load flow rate?

 } else if ( FinalSysSizing( AirLoopNum ).sysSizeHeatingDominant ) { // use maximum heating flow sum from air terminals 
    FinalSysSizing( AirLoopNum ).DesHeatVolFlow = max ( airLoopHeatingMaximumFlowRateSum, FinalSysSizing( AirLoopNum ).DesHeatVolFlow );
    FinalSysSizing( AirLoopNum ).DesMainVolFlow = max( airLoopHeatingMaximumFlowRateSum, FinalSysSizing( AirLoopNum ).DesMainVolFlow );
    //make sure cooling is at least at minimum.
    FinalSysSizing( AirLoopNum ).DesCoolVolFlow =  max( airLoopHeatingMinimumFlowRateSum, FinalSysSizing( AirLoopNum ).DesCoolVolFlow );

Design size inlet air temp = 11C, design outlet = 12.8C. So in this case it looks like it should size to 0.

I imagine the reason that min OA increased is in these numbers. Zone Ventilation efficiency went down for cooling. 0.2731 / 0.2519 = 1.08 m3/s so it's capped at 1.0483?.

The biggest question here is how do we know the 62.1 calculations are correct? There is a lot going on here. One way would be let users have a crack at proving this wrong. I don't know enough about VRP calculations to validate these equations or results.

I think the only way we could know if this is correct now is to identify the limiting zone, the one that sets down zone ventilation efficiency, and manually calculate the OA amount, then see if that amount of OA makes it to the zone before and after this fix. I will attempt this but not sure when I can get this done.

Trying to figure out just how much OA is required for the 5ZoneAirCooled_VRPSizing simulation. I reported occupancy and then calculated OA based on occupancy and floor area. Each zone used 0.00236 m3/s per person and 0.000305 m3/s per m2 of floor area. I also calculated max OA based on max occupancy and floor area.

Before these changes, it appears that the required amount of OA was met (as long as VRP uses my calculation method). With these changes there is more OA.

1st figure - compare OA mixing box OA with max OA needed by zones
2nd figure - compare OA mixing box OA with sum of OA provided to zones (match, sum of difference is 2.4 m3/s over entire year)
3rd figure - compare max zone OA with sum of actual OA (never need more than max sum, obviously)

So what would be the reason for increasing min OA amount?
Should outdoor air system be limiting OA based on zone requirement for VRP method?
Is there some other way of looking at this to know what amount of OA should be brought in at mixing box?

@EnergyArchmage comments?

OutdoorAir:Mixer,
  OA Mixing Box 1 Inlet Node,  !- Outdoor Air Stream Node Name

Difference of sum of actual zone OA reported by TU minus mixing box OA, basically a match for this discussion.

There does appear to be an issue with Zone 5 where insufficient OA enters the zone. Will look at Std 62.1 results next. Negative number indicates insufficient OA (last figure is calculation of zone OA reported by TU - zone OA need)

This branch does not correct what appears to be low OA in zone 5.

Not sure what else to look for.

ah lets see, I also spent several hours investigating the file 5ZoneAirCooled_VRPSizing. I did side calcs in this file to check.
misc calcs1.xlsx

I had a long comment on this file above, did you see that in number 4. Basically the file should be fixed up by changing inputs, but I did convince myself that the results are correct for the poor input.

My view is that there are terminal sizing problems that are separate from the focus here. The terminals get sized on zone loads and don't always size based on minimum OA per std. 62.1

Some of that may correct itself with #6327 so we'll revisit these after this goes in which should be soon.

regarding question above: why is cooling flow rate being adjusted upwards? Can't the cooling coil be sized on the cooling load flow rate?

FinalSysSizing( AirLoopNum ).DesCoolVolFlow = max( airLoopHeatingMinimumFlowRateSum, FinalSysSizing( AirLoopNum ).DesCoolVolFlow );

The idea is that the cooling air flow rate should be at least as high as the minimum operating flow rate. If the design cooling air flow rate comes out lower than that it needs to be adjusted (increased) because the air handler will never run below that lower limit. We now know more about the air handler operating limits and can use that information to make adjustments. This is in the heating dominant code block so heating design flow rates are dominating the air handler design. This ensures that the cooling coil is able to make setpoint during operation at the minimum damper positions.

In 5zoneAirCooled_VRPSizing, the air handler becomes 100% OA because the inputs for zone 5 are bad, discussed above.

Single stepping this shows 0 OA mass flow rate during the TU calculations (i.e., Sys( SysNum ).NoOAFlowInputFromUser = true;). Further investigation shows that the TU's in 5ZoneAirCooled_VRPSizing do not include the name of the DesignSpecification:OutdoorAir so the TU thinks there is no OA requirement. This is probably why I saw low OA amounts last night. I wonder if/how the html tables would change if this name were included in each TU.

A11; \field Design Specification Outdoor Air Object Name
   \type object-list
   \object-list DesignSpecificationOutdoorAirNames
   \note When the name of a DesignSpecification:OutdoorAir object is entered, the terminal
   \note unit will increase flow as needed to meet this outdoor air requirement.
   \note If Outdoor Air Flow per Person is non-zero, then the outdoor air requirement will
   \note be computed based on the current number of occupants in the zone.
   \note At no time will the supply air flow rate exceed the value for Maximum Air Flow Rate.
   \note If this field is blank, then the terminal unit will not be controlled for outdoor air flow.


AirTerminal:SingleDuct:VAV:Reheat,
  SPACE1-1 VAV Reheat,     !- Name
  ReheatCoilAvailSched,    !- Availability Schedule Name
  SPACE1-1 Zone Coil Air In Node,  !- Damper Air Outlet Node Name
  SPACE1-1 ATU In Node,    !- Air Inlet Node Name
  autosize,                !- Maximum Air Flow Rate {m3/s}
  Constant,                !- Zone Minimum Air Flow Input Method
  0.3,                     !- Constant Minimum Air Flow Fraction
  ,                        !- Fixed Minimum Air Flow Rate {m3/s}
  ,                        !- Minimum Air Flow Fraction Schedule Name
  Coil:Heating:Water,      !- Reheat Coil Object Type
  SPACE1-1 Zone Coil,      !- Reheat Coil Name
  autosize,                !- Maximum Hot Water or Steam Flow Rate {m3/s}
  0.0,                     !- Minimum Hot Water or Steam Flow Rate {m3/s}
  SPACE1-1 In Node,        !- Air Outlet Node Name
  0.001,                   !- Convergence Tolerance
  NORMAL,                  !- Damper Heating Action
  AUTOCALCULATE,           !- Maximum Flow per Zone Floor Area During Reheat {m3/s-m2}
  AUTOCALCULATE;           !- Maximum Flow Fraction During Reheat
  ,
  ;         < --- DesignSpecification:OutdoorAir name goes right here

DesignSpecification:OutdoorAir,
  SZ DSOA SPACE1-1,        !- Name
  sum,                     !- Outdoor Air Method
  0.00236,                 !- Outdoor Air Flow per Person {m3/s-person}
  0.000305,                !- Outdoor Air Flow per Zone Floor Area {m3/s-m2}
  0.0;                     !- Outdoor Air Flow per Zone {m3/s}

Yes, I found the same thing. I think there should be a follow up issue/PR to fix up the VRP test files.

@EnergyArchmage @rraustad Some of the TU vs OA stuff may get fixed in #6338. I've posted some followup needs in #6481. You can add the VRP idf to that list or make a separate issue. The Std62 sizing changes also slowed down the performance tests by about 10%. Any idea where the extra time would be coming from here?

I would guess the performance hit is from the population diversity side calculation.