5.2.1
Description of building model
For the modelling of energy savings for different EEMs, TRNSYS (TRansient SYstem Simulation) modelling software is used. TRNSYS is a dynamic simulation software which performs energy balance calculations using transient thermodynamic equations. Its merits are in testing the performance of the different parts of the HVAC system and passive design techniques. Components representing a mathematical description of a sub-system, equipment, or thermal and mass transfer process are compiled and assembled to enable a full building simulation. The flexibility enabled by the modular design of TRNSYS is particularly useful for describing novel systems (Abaza 2008; Al-Homoud 2001; Crawley et al. 2008; TRNSYS 2013; Bradley & Kummert 2005; US Department of Energy 2013). TRNSYS is made up of a suite of programmes; TRNSYS3D is a plug in to GoogleSketchup® which allows the building geometry to be defined, TRNBuild is the interface for the definition of multi-zone building project, and TRNSYS Studio Project is the main visual interface within which projects can be put together. For the rapid comparison of energy efficiency technologies and measures as well as occupancy characteristics, model parameters are specified within a Matlab script developed by the author for this project. The Matlab script edits the TRNSYS input files, calls the TRNSYS simulation to run, and undertakes analysis of the results. The modelling process of simulating the house is shown in Figure 5-1 and the parts of the process are described in Table 5-1. The model process is described in greater detail within Appendix B.1.
Figure 5-1 Building modelling process
Table 5-1 Description of parts that make up the building modelling process
Part Description Program File generated
TRNSYS3D Detail building geometry and
all adjacent walls Google Sketchup TRNSYS3D drawing file (*.idf) TRNSYS
Studio Project
Main simulation interface for
project TRNSYS Simulation
Studio
TRNSYS Project file (*.tpf)
Multizone Building (Type 56)
Visual interface for specifying building inputs
TRNBuild Building description file (*.b17)
TRNSYS Simulation Input file
Contains all details from the project, including inputs and parameters of all 'types' as an input to the model simulation
TRNEdit TRNSYS Input File (.dck)
Model Simulation Run
The model is run through the TRNSYS Executable, which calls the TRNSYS Input file
TRNExe Outputs as described in the project, with results displayed in online plotter, or saved to file as specified
MATLAB Model Simulation Control
Building parameters are selected in order to run varying simulations
MATLAB Results file (*.csv) saved for each simulation listing internal temperatures and heat demand in each zone for each time step. Total heat energy demand for simulation period saved to cumulative results file (Results_writing.csv)
5.2.2
Description of model house and parameters
For the comparison of EEMs for a range of occupancy types, a typical UK house is identified. According to the English Housing survey 2012 (DCLG 2012), the most common dwelling is a semi-detached house (aka twin/duplex in which two entirely separate houses are adjoined on one side), accounting for around a quarter of dwelling types in the UK, with an average floor area of 93 m2. The geometry of the house used in the model is shown in Figure 5-2. The division of rooms in Figure 5-2 is based on realistic house proportions with insight gained by the author from floor plans for similar houses available online from estate agent websites.
Figure 5-2 Plan of modelled house
The process for including each EEM within the building model is presented in section 5.4, including data selection for the input parameters. For other model parameters, data are based on typical values as found in literature or UK government statistics. These are listed in Table 5-2. Bedroom 2: 13.0 m2 Bedroom 3: 5.0 m2 Bathroom: 5.0 m2 Bedroom 3 Bedroom 2 Bedroom 1 Bathroom Hallway Hallway Living room 2 Living room 1 Kitchen Ad join ing house
Ground Floor First Floor
Window Floor Areas
Living room 1: 20.0m2 Living room 2: 7.0 m2 Kitchen: 10.0 m2 Hallway: 18.5 m2 Bedroom 1: 14.0 m2 Ad join ing ho use
Table 5-2 Description of modelling variables with justifications for chosen values Modelling aspect Value Justification
House type Semi-detached (aka
twin/duplex) house Accounts for around a quarter of houses (DCLG 2012) House
construction Solid wall construction Represents around a quarter of UK homes, and those in greatest need of energy efficiency improvements Floor area 92.5 m2 Typical three bedroom semi-detached house
Glazed wall area Approximately 20 % of the internal floor area of each room (10 % for bathroom)
In line with current planning guidance (GLA 2012)
Weather data
(external temperature, humidity and solar radiation)
Meteonorm file for
'London, UK' Representative of a typical meteorological year for the UK Heating season 1st October – 30th April Typical for the UK and suitable for the weather file
used Boundary
temperature (for adjoined house
Identical Represents the adjoining house being at the same temperature therefore there is no heat transfer Ground
temperature
10 °C A simplified ground floor heat loss model is adopted whereby heat transfer through the ground is driven by a ground temperature equal to the average annual air temperature (CIBSE 2006a)
Infiltration rate Constant value of 0.75 air changes per hour (ach)
Representative of typical leaky house
Ventilation rate - Infiltration rate is above the recommended minimum value of 0.5 ach (EST 2006; Jaggs & Scivyer 2009), therefore further sources of ventilation are not included
Internal heat gains - As a simplification, no internal heat gains have been added into the model; these could be included to simulate aspects of occupancy beyond occupancy pattern such as cooking practices and appliance use. Although heat gains will affect heat demand calculations, by treating all model scenarios the same, the effect of this omission is not expected to affect the comparisons of variations in energy consumption and energy savings from EEMs and occupancy patterns.
Maximum heat
input 2 kW in each room Typical radiator power Thermal capacity Twice room volume
(J/m3K)
Approximation based on typical room contents Floor plan As in Figure 5-2 Insight gained from available floor plans of similar