[Bldg-sim] EPlus Dehumidification Subcooling Temperature Too Low?
Ivan Korolija
ivankorolija at yahoo.com
Wed Mar 18 16:57:49 PDT 2015
Hi Jacob,
I'm glad you like an EMS solution.
Regarding the single setpoint thermostat, I haven't seen your file so it's very difficult for me to make any comment. The system behaviour is affected by thermostats setpoint type. If you only applied single cooling thermostat than you would have an issue with zone temperature during heating period. If you created a separate single heating thermostat and assigned it for winter months while the rest of the year was controlled by a single cooling thermostat than you would not cover cooling/dehumid requirements which even appeared during some days in January.
Since EMS is just workaround, could you upload the chart similar to https://drive.google.com/file/d/0B6aA8ZsOIiibbFFNQUU4N0xNYzA/view
but with your original file with no dehumid instead of EMS_no dehumid. The EMS_W/dehumid should remain.
Cheers,Ivan
On Wednesday, March 18, 2015 11:03 PM, Jacob Dunn <jdunn at eskewdumezripple.com> wrote:
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EMS SYSTEM Thank you so much for making the EMS system to get around the single setpoint thermostat scheduling issue. I ran a pre and post case and everything looks good! There’s a 15% increase in total energy, the RH is being controlled almost perfectly (<1% over 62.5%RH), the zone setpoints look good, and the supply air temperature only drops slightly below 15 deg C during the summer. Here’s an image of all those variables: https://drive.google.com/file/d/0B6aA8ZsOIiibbFFNQUU4N0xNYzA/view?usp=sharing The only thing I’m still having trouble with is that it seems like this is an “ideal” control. I always thought that systems won’t subcool much below 55 deg F, but this might be a question for the MEs that we work with. Now at least we’ve got the Eplus system working reasonably. Thanks again! FAN ISSUES Thanks for the info, after running your model with the fan changes it looks like we got the same results. However, given the huge jump in fan energy from a constantly running fan, it is not a feasible workaround. I thought you were seeing something that I wasn’t. Thanks for sending that over! SINGLE SETPOINT THERMOSTAT I’m intrigued by the single setpoint workaround. If you read my response to Michael’s post, you’ll see that I ran it with the single setpoint thermostats and the energy does look much more reasonable. Here’s an image to some temperature graphs that show the difference between the single and dual setpoint thermostat. Everything looks good except for the inability to schedule dual setpoints. But now that the EMS system works, this issue is obsolete. https://drive.google.com/file/d/0B6aA8ZsOIiibWVpqYXpUT3Z0NnM/view?usp=sharing Cheers and thanks! Jacob Dunn LEED AP BD+C
ESKEW+DUMEZ+RIPPLE, APC 2014 AIA National Architecture Firm Award 365 Canal Street Suite 3150 New Orleans LA 70130 504.561.8686 eskewdumezripple.com From: Bldg-sim [mailto:bldg-sim-bounces at lists.onebuilding.org]On Behalf Of Ivan Korolija
Sent: Wednesday, March 18, 2015 5:02 PM
To: Michael J Witte; bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] EPlus Dehumidification Subcooling Temperature Too Low? Hi Jacob, Replacing an OnOff fan with a constant volume is relatively easy. Just search for Fan:OnOff and replace with Fan:ConstantVolume. In addition to this you'll need to replace outside_air_schedule_compact, !- Fan Operating Mode Schedule Name with schedule with positive values (Mike's comment mention this). I used one of your already existing schedules 'Always On Discrete'. Anyhow, you can download the adjusted file from: https://drive.google.com/open?id=0B3HgHZG0Dps8MnlXWmItV29SZ2M&authuser=0 Regarding your comment ("The single setpoint t-stats are a nice idea, but forcing the building to have a single setpoint thermostat designated for a seasonal period is not ideal") I fully agree. I was just briefly testing to spot where the issue is with sub-cooling the zone to heating setback temperature. My idea was to try to replace dual setpoint thermostat with one single cooling thermostat and one single heating thermostat which can be assigned by implementing EMS program. You would not loose Fan cycling energy savings opportunity by this. There was one answer on your question earlier today on E+ yahoo group which mentioned that EMS might be suitable to adjust operational schedules. I did a brief exercise and got (I think) acceptable results. The procedure for updating your file is following: 1. Delete existing ThermostatSetpoint:DualSetpoint and ZoneControl:Thermostat objects 2. Create ThermostatSetpoint:SingleHeating and ThermostatSetpoint:SingleCooling objects ThermostatSetpoint:SingleHeating, H, waterlab_htg_setpoint_compact; ThermostatSetpoint:SingleCooling, C, waterlab_clg_setpoint_compact; 3. Create new ZoneControl:Thermostat object ZoneControl:Thermostat, thermal zone 1 Thermostat, thermal zone 1, ThermostatControlSCH, ThermostatSetpoint:SingleHeating, H, ThermostatSetpoint:SingleCooling, C; 4. Create new ThermostatControlSCH which will be modulated by EMS to switch between single heating thermostat and single cooling thermostat Schedule:Constant,ThermostatControlSCH,ControlType,1; ! Schedule type limits associated with a new ThermostatControlSCH ScheduleTypeLimits, ControlType, 0, 4, Discrete; 5. Create an EMS schedule control program which modulates ThermostatControlSCH according to the following control logic: If the Zone Temperature is above the Heating Setpoint set Thermostat Setpoint to Single Cooling, otherwise set Thermostat Setpoint to Single Heating EnergyManagementSystem:Sensor, !- Zone temperature ZonepTemp, Thermal Zone 1, Zone Mean Air Temperature; EnergyManagementSystem:Sensor, HeatSP, waterlab_htg_setpoint_compact, Schedule Value; EnergyManagementSystem:Actuator, ThermostatControlSCH_Overwrite, ThermostatControlSCH, Schedule:Constant, Schedule Value; EnergyManagementSystem:ProgramCallingManager, Overwrite ThermostatControlSCH, BeginTimestepBeforePredictor, OverwriteProg; EnergyManagementSystem:Program, OverwriteProg, IF (ZonepTemp > HeatSP), Set ThermostatControlSCH_Overwrite = 2, ELSE, Set ThermostatControlSCH_Overwrite = 1, ENDIF; The file with the EMS program can be downloaded from: https://drive.google.com/open?id=0B3HgHZG0Dps8blktVzhnSnFZWTA&authuser=0 I hope this might help you getting more acceptable outputs. Cheers, Ivan _____ Dr Ivan Korolija IESD, De Montfort University, Leicester, UK On Wednesday, March 18, 2015 8:56 PM, Michael J Witte <mjwitte at gard.com> wrote: The overall logic is:
Determine the supply air temp to meet the cooling setpoint in the control zone
Check to see if the humidity setpoint is met, if not go colder until the humidity setpoint is met
if this results in cooling the zone below the heating setpoint, reheat to the heating setpoint
It's the humidity setpoint that is driving what the cooling coil is asked to do. This is a unitary heatcool system, so it does not operate on setpoints per se. It's responding to the load request in the control zone. It will run the DX coil as much as it needs to meet the humidity control requirement. So, if you raise the heating setpoint, you'll use the same amount of cooling plus more reheat. But on the other hand, the absolute humidity ratio can be higher for the same RH if the zone is warmer, so it will shift from cooling energy to heating energy - hard to know which will use more.
Regarding the fan. The furnace object fan control is currently set to cycle for part of the day and run continuously for the rest of the day:
outside_air_schedule_compact, !- Fan Operating Mode Schedule Name
That's why it needs Fan:OnOff.
Mike
On 3/18/2015 3:48 PM, Jacob Dunn wrote: Ivan –
Thanks for the info! I did get your previous message, my apologies for not responding sooner. Your answers were very helpful, but as you mentioned they are workarounds. The single setpoint t-stats are a nice idea, but forcing the building to have a single setpoint thermostat designated for a seasonal period is not ideal. Additionally, I’ve swapped out the Fan:onoff to Fan:constantvolume as you mentioned, but am getting some strange results. Can you send me the .idf that you modified? I essentially changed the fan object’s name and modified the “Supply fan object type” in the “Airloophvac:unitary:furnace:heatcool” object. However, when I ran the simulation I got a severe error. I had to modify the “Fan Operating Mode Schedule Name” to a schedule that had “1s” constantly. I also changed the fan’s availability schedule to the same thing. Thus, the fan runs all the time. The EUI jumped up considerably (to 111 kBtu/sf-yr) because of the fan and cooling energy, but both the zone RH looks good and the supply air temperature never goes below 15 deg C. Here’s an image -https://drive.google.com/file/d/0B6aA8ZsOIiibc0ZhSTdDVmtQSVE/view?usp=sharing Am I missing something?
Cheers and thanks for your help! Jacob Dunn LEED AP BD+C ESKEW+DUMEZ+RIPPLE, APC 2014 AIA National Architecture Firm Award 365 Canal Street Suite 3150 New Orleans LA 70130 504.561.8686 eskewdumezripple.com From: Ivan Korolija [mailto:ivankorolija at yahoo.com]
Sent: Wednesday, March 18, 2015 2:53 PM
To: Jacob Dunn; Jim Dirkes
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] EPlus Dehumidification Subcooling Temperature Too Low? Hi Jacob, It seems my respond to your question hasn't gone through so I'll repeat it again. 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 p.s. I'll post this reply to UnmetHours and Yahoo e+ group as well. _____ Dr Ivan Korolija IESD, De Montfort University, Leicester, UK It seems my respond to your question hasn't gone through so I'll repeat it again. On Wednesday, March 18, 2015 7:38 PM, Jacob Dunn <jdunn at eskewdumezripple.com> wrote: Jim – Thanks for the reply! According to the hourly outputs (currently the simulation is at a “1” timestep) the relative humidity setpoint is indeed being met 94% of the time, so the system seems to be working well, almost too well for a subcool reheat system if you ask me. I do expect an increase, and I’m indeed questioning the magnitude of the jump. I don’t really have much of a frame of reference as research/simulation study material on this is scarce. The ASHRAE 1254-RP from 2006 is the only thing I’ve seen quantifying the energy effect and effectiveness of commercial HVAC systems and dehumidification. They modeled 17 different system configurations in E-plus for a variety of building types/climates, and reported the hours above 65% RH and the increase in annual HVAC cost. For a DX system w/subcool Reheat for Miami and a 9 month school ------ 2222 hours (25%) of hours are above the RH threshold and this creates an 11% increase in HVAC energy. So my 6% of hours above the RH setpoint and 30% energy increase seems too big. However, the main reason why I think it’s unreasonable is that I don’t believe that the supply air temperature should ever drop to 5 deg C (41 deg F) to dehumidify. I think most dx systems won’t go past 55 deg F, but I can’t seem to control this setpoint in Eplus. Cheers and thanks for your help! Jacob Dunn LEED AP BD+C ESKEW+DUMEZ+RIPPLE, APC 2014 AIA National Architecture Firm Award 365 Canal Street Suite 3150 New Orleans LA 70130 504.561.8686 eskewdumezripple.com From: Jim Dirkes [mailto:jim at buildingperformanceteam.com]
Sent: Tuesday, March 17, 2015 4:20 PM
To: Jacob Dunn
Cc: bldg-sim at lists.onebuilding.org
Subject: Re: [Bldg-sim] EPlus Dehumidification Subcooling Temperature Too Low? Jacob, I'm big fan of Output:Variables in E+ and use them liberally to see whether setpoints are met and to get clues about why setpoints are NOT met. I see that you have a number of them in your IDF; have you evaluated those values against the HVAC controls?
- Is the RH setpoint consistently met?
- You expect cooling, heating and overall energy to increase with controlled dehumidification (and they did), so are you concerned only with the magnitude of the jump?
I think some review of the energy for depressing discharge air temp to get lower dewpoint, along with confirmation that the heating energy is appropriate, will help you a lot. You may also benefit from reporting the variables at "timestep" instead of "hourly". (I missed your post on the E+ forum) On Tue, Mar 17, 2015 at 4:56 PM, Jacob Dunn <jdunn at eskewdumezripple.com> wrote:
I posted this question to the EnergyPlus yahoo support group and the Unmet Hours online forum and have received no replies after a week! So I thought I’d pass it along to this group: 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! Image - https://drive.google.com/file/d/0B6aA8ZsOIiibQUJSa2g5Z2pnMkE/view?usp=sharing 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. Image - https://drive.google.com/file/d/0B6aA8ZsOIiibQm9rdDNUZFYwS0E/view?usp=sharing 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/view Thanks ahead of time for your help! Jacob Dunn LEED AP BD+C ESKEW+DUMEZ+RIPPLE, APC 2014 AIA National Architecture Firm Award 365 Canal Street Suite 3150 New Orleans LA 70130 504.561.8686 eskewdumezripple.com
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