Forum discussion

NC-2009 EAc1:Optimize Energy Performance

PSZ-HP system and preheat coils

In the proposed design an AHU is connected to a lot of zones. In that AHU there is a preheat coil. I have to model the baseline model as system 4 PSZ-HP. In order to meet the setpoint temperatures I think that I cannot create a PSZ-HP that is connected to so many zones, i.e. I have to create more than one PSZ-HP system. According to G3.1.2.3 “If the HVAC system in the proposed design has a preheat coil and a preheat coil can be modeled in the baseline, the baseline system shall be modeled with a preheat coil controlled in the same manner”. If I create many PSZ-HP systems in the baseline model, corresponding to an only AHU system in the proposed building, shall every PSZ-HP system have a preheat coil? With Regards

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Mon, 10/22/2012 - 17:17

No preheat coil is required for a system 4.

Mon, 10/22/2012 - 17:36

Hello, Marcus. Do you mean that for system 4 preheat coil is required even if there is no preheat coil in the proposed building? What is the reason? In EnergyPlus I could satisfy the electric auxiliary heat with an AirLoopHVAC:UnitaryHeatPump:AirToAir in which the electric coil is after the DX heating coil. It is illustrated at p.995 of the manual: http://apps1.eere.energy.gov/buildings/energyplus/pdfs/inputoutputreference.pdf

Wed, 10/24/2012 - 16:16

You do not model a preheat coil for a system 4 in the baseline despite G3.1.2.3. The preheat coil would be electric resistance and the resistance coil cannot operate above 40 degrees so there is a potential conflict in modeling a preheat coil for a system 4.

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