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[EnergyPlus_Support] Simulation Speed

Hi all,

 

I?m simulating a large/complex  hospital facility.

The geometric model is not very complex but it  has a large number of
thermal zones.

 To calculate the energy consumption of primary and secondary system I?ve
defined a model with the following characteristics:

 

Inside and Outside Detailed Convection algorithm.

Solution Algorithm: CTF

 

For the plant loops:

 

·         Cooling and heating  equipment are simulated with
Purchased:ChilledWater and Purchased:HotWater respectively

 

For Air  loops:

 

·         I?ve created constant volume air handling units (AHU) with cooling
and heating coils. Some AHU provide  treated air to a single zone( AHU
type1)  and other ( AHU type2),   provide treated air  to several zones. 

 

For zone equipment:

 

·         For AHU type 1 zone equipment is a reheat coil. Some zones have
only temperature control and others have temperature and humidity control.  

·         For AHU type 2 zone equipment is Direct Air to provide the
necessary outside air. In controlled zones I ?ve also defined fan coils to
provide the remaining necessary heating or cooling energy.

 

For Zone Sizing:

 

·         For zones controlled by AHU type 1 I?ve defined the Outside Air
volume flow rate, the cooling and heating design air flow rates  and the air
flow method as ?flow/zone?. 

·         For the remaining zones outside air is supplied by Direct Air
through system AHU type 2. For this reason, and because some zones have also
fan coil systems, I set the zone outside air volume flow rate as zero and
defined the the flow rate in the Direct Air object to avoid outside air
being supplied by fan coil systems.

 

For system sizing:

 

·         For AHU type2  I?ve defined the total Outside Air volume flow rate
(as the sum of the corresponding Direct Air flow rates).

·         For AHU type1 I?ve defined the total Outside Air volume flow rate
with the ?autosize? option.

 

For all components (coils, fans?) except for Direct Air, I let the autosize
option in the autosizable fields to let the program calculate the necessary
values. 

 

The convergence parameters defined were:

 

Building:

·         Loads Convergence Tolerance value       0.04

·         Temperature Convergence Tolerance value        0.4

 

Time step in Hour:

·         Time step in Hour            2

 

System Convergence limits:

 

·         Minimum System time step        1

·         Maximum HVAC iterations          50 

·         (I?ve raised up this value from 20 to 50  because I got a warning 

?** Warning ** SimHVAC: Maximum iterations (20) exceeded for all HVAC loops?
)

 

Fan Coil Unit: 4Pipe  and Single Duct: Const Volume: Reheat

 

·         Convergence Tolerance                0.001

 

 

 

With this model I performed two different simulations:

 

1)      The described building  with high internal gains (electric
equipment, people  and lights) which corresponds to the sizing HVAC
equipment conditions, to estimate annual building HVAC energy consumption 

 

2)      The same model as 1 but with lower internal gains (~50% of total
internal gains of simulation 1) to estimate total energy consumption to
check portugueese building energy code

 

The hourly simulation for an entire year took 9 hour for case 1.  For case 2
it took almost one week and a half!!

 

Is it normal to have such a difference in total simulation time?

 

Could this simulation time difference be due to the lower internal gains?
With lower internal gains conduction effects could be more important and
this could slow down simulations?

 

The convergence parameters are reasonable?

 

To define Direct air flow rates instead of autosizing is a correct
procedure?

 

Thanks in advance for your help,

 

Best Regards

 

 

Filipe Madureira

Tel: +351 919 293 876 | E-mail: filipe.madureira@xxxxxxxxxxxxx

__________________________________________________________________

FluidInova, Engenharia de Fluidos, SA

TECMAIA - Parque de Ciência e Tecnologia da Maia

Rua Engº Frederico Ulrich, nº 2650  |  4470-605 Moreira da Maia | Portugal


Tel: (351) 229 408 265  |  Fax: (351) 229 408 266

E-mail:  <mailto:geral@xxxxxxxxxxxxx> geral@xxxxxxxxxxxxx  | Web:
<http://www.fluidinova.pt/> http://www.fluidinova.pt/

 



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