[Bldg-sim] EPlus Dehumidification Subcooling Temperature Too Low?

Ivan Korolija ivankorolija at yahoo.com
Tue Mar 17 19:09:09 PDT 2015

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,Ivanp.s. I'll post this reply to UnmetHours and Yahoo e+ group as well. 
_____Dr Ivan Korolija
IESD, De Montfort University, Leicester, UK


  On Tuesday, March 17, 2015 8:56 PM, Jacob Dunn <jdunn at eskewdumezripple.com> wrote:

  #yiv7764140925 #yiv7764140925 -- filtered {panose-1:2 4 5 3 5 4 6 3 2 4;}#yiv7764140925 filtered {font-family:Calibri;panose-1:2 15 5 2 2 2 4 3 2 4;}#yiv7764140925 p.yiv7764140925MsoNormal, #yiv7764140925 li.yiv7764140925MsoNormal, #yiv7764140925 div.yiv7764140925MsoNormal {margin:0in;margin-bottom:.0001pt;font-size:11.0pt;}#yiv7764140925 a:link, #yiv7764140925 span.yiv7764140925MsoHyperlink {color:#0563C1;text-decoration:underline;}#yiv7764140925 a:visited, #yiv7764140925 span.yiv7764140925MsoHyperlinkFollowed {color:#954F72;text-decoration:underline;}#yiv7764140925 p {margin-right:0in;margin-left:0in;font-size:12.0pt;}#yiv7764140925 span.yiv7764140925EmailStyle17 {color:windowtext;}#yiv7764140925 .yiv7764140925MsoChpDefault {}#yiv7764140925 filtered {margin:1.0in 1.0in 1.0in 1.0in;}#yiv7764140925 div.yiv7764140925WordSection1 {}#yiv7764140925 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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