Conversation
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Since I made a claim in the description that I "updated" and made a "more defined" control, based solely on the issue unit test, I figured I would run the SZVAV example file to see what changed. This test file does not seem to change, which is disturbing. The figures in the left column are all data. This system cycles during unoccupied times (SZVAV is not active) and the fan runs continuously during occupancy (SZVAV is active). The right column subsets on occupancy/constant fan (valid data). Why is the supply air temperature below the Maximum Supply Air Temperature at higher loads in Region 3, while the shape of the SZVAV curve looks correct in Region 2? 
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I noticed that the schedule report Schedule Value only reports at the TimeStep frequency. When other Zone frequency reports output at the detailed frequency. All reports are detailed frequency but the schedule is missing in action. 
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| thisSys.simulate(*state, thisSys.Name, FirstHVACIteration, 0, PTUnitNum, HeatActive, CoolActive, 0, 0, true, QUnitOut, latOut); | ||
| EXPECT_NEAR(QUnitOut, 2010.0, 0.01); | ||
| ASSERT_NEAR(thisSys.DesignMaxOutletTemp, state->dataHeatingCoils->HeatingCoil(1).OutletAirTemp, 0.1); | ||
| ASSERT_NEAR(thisSys.DesignMaxOutletTemp, state->dataHeatingCoils->HeatingCoil(1).OutletAirTemp, 1.0); |
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This change was a hard pill for me to swallow. DesignMaxOutletTemp is a target AND is set at design conditions (i.e., meaning that at off design conditions the system may not have the same capacity and cannot provide that same outlet temperature). There is no guarantee that the system will hit that target. The system will certainly attempt to hit the target, and will drive towards the target, but could be several degrees short of the target. Now that the fan is operating correctly (i.e., at a higher air flow rate), the outlet air temp is lower than it was before. So this is why I changed several of these tolerances. The system is not missing the target, it can't actually hit the target but needs to approach the target. Feel free to run several hours of debug and correct me if I'm wrong (I would welcome that).
| HeatCoilLoad, | ||
| SupHeaterLoad, | ||
| CompressorONFlag); | ||
| SZVAVModel.calcUnitarySystemToLoad(state, |
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I'm not sure why this change was required but the debugger showed me these were different (i.e., using thisSys vs SZVAVModel, which are both references to the same unitarySytsem. At line 711 above, where SZVAVModel.FanPartLoadRatio = 0.0, that code DID change FanPartLoadRatio in the SZVAVModel reference but DID NOT change FanPartLoadRatio in the thisSys reference. I know, it's a conundrum. This is the reason for this change, this needs to reference the right system.
| maxAirMassFlow, | ||
| CoolingLoad, | ||
| 1.0); | ||
| iterWaterAirOrNot); |
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This was another subtle but necessary change. This residual function has 2 choices for adjusting air and water flow rates. If the load is in Region 1 or 3 (iterWaterAirOrNot = 0) then the air flow is constant and the compressor speed or water flow rate changes to meet the load. When in region 2 (iterWaterAirOrNot = 1), both change. See the figure in the PR description for clarity or just ask me. Feel free to suggest a different variable name.
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Pull request overview
Description of the purpose of this PR
SZVAV controls were updated to allow a more defined air flow and supply air temperature region as described in the Engineering Reference.
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