Julien,
Thank you. This is very helpful, since my knowledge of
EnergyPlus has been basically dormant since 2005, when I was last
part of the development team. I only know of EMS from its mention
by others, but haven't a clue how to use it. Now that you've
given me a mock-up, I'll have to look at the documentation to
make sense of it. I don't know about others' experience, but for
me working examples are always much more helpful than reading the
documentation :-)
Joe
Joe,
You'll find in attachment a file that shows the gist. I took the E+ Example file WindACAuto.idf and added a simple EMS program to compute the @TrendSum over 384 timesteps = 4 days (at 4 timesteps/hours).
The interesting bit is right at the end.
Hope that helps,Julien
Le dim. 9 juin 2019 à 23:42, Julien Marrec <julien.marrec@xxxxxxxxx> a écrit :
Hi Joe,
I am unaware of something built-in but it's certainly possible via EMS.
You'd use a trend variable on an ems sensor like "cooling power W" or On/Off status (whichever variable on your specific cooling object that will serve as a proxy for cooling operation).
In your EMS program you can do a @Sum (or @max...) on your trend variable for the past N timesteps and check if > 0, meaning the AC would have been on during that time.
Hope that helps,
Juliem
--
Sent from a mobile device, please excuse the brevity.
Julien Marrec, EBCP, BPI MFBA
Owner
Direct: +33 6 95 14 42 13
Website: www.effibem.com
On Jun 9, 2019, at 12:08, "Joe Huang YJHuang@xxxxxxxxxxxxxxxxxxxxxxxx [EnergyPlus_Support]" <energyplus_support@xxxxxxxxxxxxxxx> wrote:My apologies if my question in the subject line seems unclear. I've been having
difficulties getting good correspondence in residential runs done with DOE-2.1E to doing
them with EnergyPlus, with EnergyPlus showing more than twice the Heating Energy as shown
by DOE-2.1E. By process of elimination, I've narrowed down the discrepancy to how natural
ventilation through windows is being modeled. These runs are in California climates where
overcooling by natural ventilation during the day can substantially increase heating
energy at night during the swing season, leading to the 2X increase over the entire year.
The natural ventilation model in DOE-2 has a feature that checks whether the AC had been
on for the previous X number of days. If so, the program then knows that it's the cooling
season, and will then permit window ventilation based on either temperature or enthalpy
difference between the indoor and the outdoor. If the check finds there was no cooling
the previous X number of days, it then knows it's not in the cooling season and window
ventilation is not permitted. For those who are curious, the actual BDL inputs are as follows:
VTSCH SCHEDULE $Vent schedule based on previous 4 days load
THRU MAY 14 (ALL) (1,24) (-4)
THRU SEP 30 (ALL) (1,24) (-4)
THRU DEC 31 (ALL) (1,24) (-4) ..
VOPSCH SCHEDULE $Vent operation schedule
THRU DEC 31 (ALL) (1,24) (VTYPE) .. (where VTYPE =1 for
temperature difference, -1 for enthalpy difference, 0 for no ventilation)
WINDOPER SCHEDULE $No window operation between 11 p.m. and 6 a.m.
THRU DEC 31 (ALL) (1,6) (0.0)
(7,23) (1.0)
(24) (0.0) ..
I've looked into my EnergyPlus idf and found this:
Controller:OutdoorAir,
SYS OA Controller, !- Name
SYS Relief Air Outlet, !- Relief Air Outlet Node Name
SYS Air Loop Inlet, !- Return Air Node Name
SYS Mixed Air Outlet, !- Mixed Air Node Name
SYS Outside Air Inlet, !- Actuator Node Name
autosize, !- Minimum Outdoor Air Flow Rate {m3/s}
autosize, !- Maximum Outdoor Air Flow Rate {m3/s}
DifferentialDryBulb, !- Economizer Control Type
ModulateFlow, !- Economizer Control Action Type
, !- Economizer Maximum Limit Dry-Bulb Temperature {C}
, !- Economizer Maximum Limit Enthalpy {J/kg}
, !- Economizer Maximum Limit Dewpoint Temperature {C}
, !- Electronic Enthalpy Limit Curve Name
, !- Economizer Minimum Limit Dry-Bulb Temperature {C}
LockoutWithCompressor, !- Lockout Type
FixedMinimum; !- Minimum Limit Type
which seems not to have such a load-based toggle. Is there another Residential or Window
Ventilation Object that I should use? Or is this something that can be programmed using
EMS? I've sorry if I'm asking a well-known question, but I have simply not followed the
development of EnergyPlus for the past 15 years.
Any advice or suggestions would be appreciated.
Joe
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