L2 Compliance: Project Darwin
SBEM vs Apache Sim
© Integrated Environmental Solutions Ltd. 2007
Design, simulate & innovate with the IES <Virtual Environment>
Introduction
Neil,
This document is just to give you a feel for the major differences which exist between the SBEM & Apache Sim L2 Compliance
Frameworks.
SBEM is by definition “simplified”. It is a form of steady state calculation which runs a series of iterations to obtain the annual
overall energy results. Apache Sim however uses Dynamic Thermal Simulation (DTM).
DTM breaks the analysis down into 6 minute time steps - or less if required. By monitoring the building at this very detailed level
over the full year and using real site historical weather data recorded at hourly intervals a very detailed energy analysis can be
simulated.
SBEM uses simple calculations whereas Apache Sim models the complex building physics which are at work. By modelling
these building physics at 6 minute intervals a multitude of variables can be monitored which are simply not possible using the
SBEM framework – these include solar shading, interzonal bulk airflow, thermal storage of concrete slabs etc
What this really means is that an SBEM calculation can not really be compared with an Apache Simulation. The main purpose of
SBEM is to provide a free tool endorsed by the UK government which can be used to assess all new buildings for compliance
under the newly implemented National Calculation Methodology (NCM).
The NCM is the UK’s official framework which has been created in order to allow the energy performance and CO2 emissions of
all new buildings to be assessed and compared against target benchmarks in order that the UK can achieve the targets
specified by the European Performance of Building Directive (EPBD).
Although SBEM is the UK’s official tool for assessing the performance of a building under the NCM it is not exclusive. Other
tools are available and can be used to assess whether or not a building complies - providing the tool is approved by the UK
Department of Communities & Local Government (DCLG).
The IES Apache Sim method has been approved by the DCLG as an official tool which can be used to test a building under the
NCM – but this does not mean that the results obtained from an Apache Simulation will be the same as results obtained for an
identical building modelled using the SBEM interface.
There a number of major differences which exist between both methods – these are summarised on the following pages.
© Integrated Environmental Solutions Ltd. 2007
Design, simulate & innovate with the IES <Virtual Environment>
HVAC System Specification – in SBEM
final tab allows
for any
additional
control
corrections
to
be
defined,
HVAC
system
specification
is limited
default
system
options
type
must
for
heating
any
be
additional
system
specified
options
system
from
pre-defined
are
adjustments,
restricted,
list
cooling
system
options
are also
choices
made
here
again
effect
the
calculation
of
SCoP,
SSEER
&
auxiliary
energy
choices made here effect
heating
the SSEER
calculation
SCoP is calculated
of SCoP, using
SSEERa &
auxiliary
energy
cooling
default
algorithm
.........................................................................
auxiliary energy is non-editable & is a function of system type selection
which is calculated using a default algorithm within SBEM
© Integrated Environmental Solutions Ltd. 2007
Design, simulate & innovate with the IES <Virtual Environment>
HVAC System Specification – in Apache Sim
SCoP linked to generator efficiency via
entered manually
generator seasonalSCoP
efficiency
fuel
type selected
“heating
delivery
efficiency”
entered
manually
i.e. not
calculated
via SBEM algorithm
from
drop down
note: this approach differs from SBEM
“Auxiliary Energy” is
fully editable – any W/m²
value can be entered in
order to make an
allowance
the HVAC
coolingfor
mechanism
systems
combined
chosen manually
annual energy usage.
[nat vent, mech vent
note: auxiliary energy is
orSBEM
air-con]
non-editable in
and
is dependent on the
Note: this is not an option
system type selection.
in SBEM, instead
a default algorithm is then
cooling mechanism is
used to calculate the final
automatically determined
auxiliary energy value
from system type
selection
generator seasonal
Energy Efficiency Ratio (EER)
entered
manually
System
Seasonal
Energy Efficiency Ratio
(SSEER)
entered manually
i.e. not calculated via SBEM
algorithm
SSEER linked to EER
via “cooling delivery
efficiency”
and “heat rejection
pump & fan power”
note: this approach differs
from SBEM & is required
due to the differences
between steady state &
dynamic simulations
© Integrated Environmental Solutions Ltd. 2007
Design, simulate & innovate with the IES <Virtual Environment>
DHW System Data
DHW specification in
Apache Sim mode is
handled differently. A
dedicated system must be
created within the main
HVAC view
empty
DHW specification in SBEM
mode allows the system
type to be selected from a
pre-defined list
© Integrated Environmental Solutions Ltd. 2007
Design, simulate & innovate with the IES <Virtual Environment>
Lighting Data
LIGHTING POWER DENSITY
LIGHTING CONTROLS
LIGHTING POWER DENSITY
SENSOR SETTINGS FOR DETAILED DYAMIC SIMULATION
OF DAYLIGHT CONTROLS USING APACHE SIM MODE
LIGHTING CONTROLS & OCCUPANCY
SENSING CONTROLLED VIA DYNAMIC
“DIMMING PROFILES”
OCCUPANCY SENSING
in SBEM a dedicated lighting dialogue allows for a range
of lighting control options to be specified at a basic level.
Apache Sim requires that lighting is handled differently due to
the nature of dynamic thermal simulation. Sensors can be
placed in zones and lighting controlled via “dimming profiles”
which allow complex controls to be modelled at each time step
of the simulation using the real site solar intensity weather data.
© Integrated Environmental Solutions Ltd. 2007
Design, simulate & innovate with the IES <Virtual Environment>
Additional Extract & Destratification Fan Energy
LOCAL MECHANICAL EXHAUST
& DESTRATIFICATION FAN POWER SETTINGS
SBEM provides check-boxes for specifying “mechanical extract”
& “destratification fans” at local zone level.
AUXILIARY ENERGY ENTERED MANUALLY
IN APACHE SIM MODE
Apache Sim mode allows an exact value of auxiliary energy to
be entered manually – so in this way the energy requirement for
extract & destratification fans can be allowed for at system level.
These options exist because auxiliary energy cannot be edited
directly in SBEM, so by specifying these options at zone level
correction factors are then made to the final auxiliary energy
algorithms used in the overall energy calculation.
© Integrated Environmental Solutions Ltd. 2007
Design, simulate & innovate with the IES <Virtual Environment>
CHP & Link to Absorption Chiller
Apache Sim allows a CHP link to be modelled and
monitored at every time step of the dynamic
CHP SETTINGS
WHICH
ARE AVAILABLE
SBEM
does not
support
CHP and it is therefore
simulation.
WHEN USING APACHE SIM MODE
not
possible to model Project Darwin directly.
Project
Some form of assumption would need to be
made Darwin utilises CHP which serves both
space
& water heating requirements in addition to
to allow for an approximate figure on CO
2
cooling requirements via an absorption chiller.
reduction due to CHP and tri-generation.
Fuel Type, Heat Output and Thermal & Power
Efficiencies at both full & part load can all be
allowed for using Apache Sim mode.
© Integrated Environmental Solutions Ltd. 2007
Design, simulate & innovate with the IES <Virtual Environment>
Solar Shading Calculations
Apache Sim uses a geometric model to represent
the building. This then allows the Suncast link to
be used to simulate solar shading in detail which
monitors the exact percentage of surfaces which
are in/out of shade for each time step of the
simulation.
SBEM does not support solar shading calculations.
This means that the benefits of self shading on the building
cannot be modelled which could potentially lead to large
differences in results when compared against Apache Sim mode.
When linked into the Apache Simulation engine
these geomteric shading calculations translate
directly into reductions in solar gain based on
the real site weather data.
© Integrated Environmental Solutions Ltd. 2007
Design, simulate & innovate with the IES <Virtual Environment>