There have been posts as to how a VAV with reheat work during cooling mode. This will explain the supply air temp being at the heating setpoint temperature during cooling operation. This was quite a headache in the past and often an EMS or schedule were required to set the heating coil off during cooling to allow nice cold supply (SP-11 C for ASHRAE 90.1 App. G) otherwise the amount of air required would be huge at such a small dT. You will have to check the developement items to know if the newer e+ code still behaves like this of if there are additional points to consider and or new controls. Also, check that there is no availibility managers like nightventilation, during your trouble shooting as they often tend to muddle things. Classic example is the nightventilation override being available to override during occupied hours. It should always have an availibility schedule reciprocal to the occupancy schedule.
Mit freundlichen Grü�en
On 18.03.2015, at 03:10, "Ivan Korolija ivankorolija@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
Hi Jacob,I think I identified a problem but not the full solution for it. If you check the zone temperature during summer period you'll see that during unoccupied period the zone is cooled down to 15C which is actually your heating setback temperature. To achieve such a low temperature the supply air has to be sub-cooled to 5C which, as you mentioned, is unrealistic. I cannot source the root of this issue.The partial solution is to control the zone conditions by single heating and single cooling thermostats. As soon as I changed to single cooling thermostat during summer period, the system behaves as it should (supply air temperature around 15C, zone air temperature according to cooling occupied/unoccupied setpoints).Another possible way of overriding the issue is to replace Fan:OnOff with Fan:ConstantVolume and keep DualSetpoint control. This doesn't completely remove periods when the supply air temperature is around 5C, although it significantly reduces it.I hope you'll find this answer useful.Best regards,Ivan_____Dr Ivan KorolijaIESD, De Montfort University, Leicester, UKOn Tuesday, March 10, 2015 7:56 PM, "Jacob Dunn arch.dunn@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx> wrote:
Hello all!I'm attempting to model dehumidifcation in EnergyPlus and I'm getting some strange results. When using a constant 62.5% Relative Humidity setpoint versus no dehumidification in New Orleans LA, the EUI jumps from 70 kBtu/sf-yr to 91 kBtu/sf-yr. Cooling energy increased by about 30%, and heating increases by a factor of 5.6!The project is a 400 square foot classroom "shoebox" that I'm running some infiltration sensitivity analysis on. Thus, I want to make sure I'm capturing the energy impact of dehumidification accurately. I'm using the HVACTemplate:System:Unitary template (everything is autosized), and I've input "CoolReheat" in the "! - Dehumidification Control Type" field. I've added a "ZoneControl:Humidistat" object that uses a compact schedule with a "percent" schedule type limits that uses 62.5 all year. After inspecting the expanded file, the AirLoopHVAC:Unitary:Furnace:HeatCool object has a "CoolReheat" designation in the "! - Dehumidification Control Type" and an additional reheat coil appeared. Everything looks good.So, why is the reheat and cooling energy increase so high? The scheme seems to be working, only 6% of all hours are above 62.5% relative humidity. I think the main problem is that with dehumidification, the cooling coil drops the temperature to 5 deg C (42 deg F) in some cases (see below graph). This seems unreasonable, and may be why there is so much reheat and coling energy, as actual systems would never really drop it below 55 deg F. I don't know how to control this, and I can't find a setpont manager that controls the subcooling routine for the dehumidification.here appears to be a "!-minimum supply air temperature" field in the "SetpointMnager:SingleZone:Reheat" object set at 13, but it doesn't seem to have an effect.Is there a way to control this? Am I missing anything?Here is a link to the .idf in case it helps - https://drive.google.com/file/d/0B6aA8ZsOIiibLWpqR1JCbVhyOWs/viewThanks ahead of time for your help!--
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