If all aspects of your simulation are correct (zone geometry, material properties, constructions, infiltration levels, etc.), I would say that you have calibrated the model to more closely represent the building.
Keep in mind there are many ways to modify a specific simulation. In this example, the decay curve when the system was off (HVAC not responsible for zone temperature change) tells me that either the inputs are incorrect (thermal characteristics of building materials) or the simulation does not accurately represent the actual building. By changing the zone capacitance, you may just be compensating for inputs that are incorrect. Such as thermal capacitance of building materials or internal furnishings.
You must ensure that the inputs are entered correctly first, and then use the capacitance term to calibrate the model. Also, the capacitance terms can be used to model the impacts of indoor furnishings without having to enter them explicitly (this may very well be what you have done if your building is correct). This calibration procedure can be done with or without an HVAC system, however, measured data is typically necessary to perform an accurate calibration.
For example, if you turn off the AC system in your home and measure the outdoor/indoor T/RH for a period of time, can you calibrate the model of your house to yield the same T/RH profile. You have to get the building construction and all uncontrolled air flows (infiltration) correct before you start tweaking the model with other available inputs (e.g. air capacitance). The same could be said for when the AC is operating.
On 11/17/2010 11:43 AM, Lee Cleef wrote:
Thank you Richard!
I have set the ZoneCapacitanceMultiplier to 10 and the graph is much more realistic now. However, I still do not fully understand what this multiplier does. Have I just hacked my model to force it to work as I would expect or was something wrong with the capacitance of the air in the volume of my zone?
Thanks again
From: Richard Raustad <RRaustad@xxxxxxxxxxxx>
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Sent: Wed, 17 November, 2010 13:20:40
You might try changing the air capacitance. See this object (I believe new to V6):
ZoneCapacitanceMultiplier:ResearchSpecial,
10, !- Temperature Capacity Multiplier
10, !- Humidity Capacity Multiplier
1; !- Carbon Dioxide Capacity Multiplier
Or, if using a previous version, a different air heat balance solution method (see documentation):
The default if this object is not present in the input file is ThirdOrderBackwardDifference which may be susceptible to very small simulation time steps (due to rapidly changing zone temp). You could try a method which is less susceptible to variations in simulation time step.
ZoneAirHeatBalanceAlgorithm, AnalyticalSolution;
or
ZoneAirHeatBalanceAlgorithm,EulerMethod;
On 11/17/2010 8:08 AM, cleef_lee wrote:Hi,
I am using E+ with BCVTB to test heating control in domestic houses.
In order to validate the heating behaviour of a simple house with regular materials, I have built a simple 5m x 3m x 3m box house with an electric radiator (700W capacity) and no windows or doors or any kind of internal loads. The construction materials have values based on a BRE measured u-values report and more or less are average materials used in UK domestic houses.
I run the simulation in E+ for 5 days with outdoor temperature between
-4 and 9 degrees Celsius and the temperature graph was somehow weird. When the heating goes to ON the temperature initially increases rapidly (more than 1 degree per 3 minutes) and then increases with a slightly more expected way (1 degree per 20min). In a similar way when the heating gets to OFF the temperature initially decreases too quickly (1 degree in 3 minutes) and then the decrease rate gets a little bit smoother.
Do you have any idea why the temperature curve follows this positive or negative "logarithmic" form ?
Thank you very much!
-- Richard A. Raustad Senior Research Engineer Florida Solar Energy Center University of Central Florida 1679 Clearlake Road Cocoa, FL 32922-5703 Phone: (321) 638-1454 Fax: (321) 638-1439 or 1010 Visit our web site at: http://www.fsec.ucf.edu UCF - From Promise to Prominence: Celebrating 40 Years
-- Richard A. Raustad Senior Research Engineer Florida Solar Energy Center University of Central Florida 1679 Clearlake Road Cocoa, FL 32922-5703 Phone: (321) 638-1454 Fax: (321) 638-1439 or 1010 Visit our web site at: http://www.fsec.ucf.edu UCF - From Promise to Prominence: Celebrating 40 Years
__._,_.___
Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx
The primary EnergyPlus web site is found at:
http://www.energyplus.gov
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
Attachments are currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
Change settings via the Web (Yahoo! ID required)
Change settings via email: Switch delivery to Daily Digest | Switch to Fully Featured
Visit Your Group | Yahoo! Groups Terms of Use | Unsubscribe
__,_._,___