Trial / Demo
IESVE has the ability to carry out Steady State peak load calculations, or produce sub-hourly load profiles using Dynamic Thermal Simulation.
Following a recent webinar ‘Using IESVE for Room Loads Analysis’, which showcased the Loads Analysis capabilities within the IESVE software, we received a lot of questions regarding particular areas of software use and therefore I thought the following may assist and give greater functionality when considering the analysis and results.
Heating loads are calculated by the IESVE using a steady state calculation as described in CIBSE Guide A. This will provide a peak load for each zone or room considering the fabric losses/gains and ventilation such as infiltration.
Cooling loads are calculated using the CIBSE admittance method (as described in CIBSE Guide A), which will take into consideration all internal and solar gains applicable to the space. This calculation, considers a number of assumed summer days (the default being 5 sample days May – September). When run in conjunction with SunCast the calculation will take into account any shading applied to the building and solar tacking to ensure the instantaneous solar load is in the correct zone.
For Heating and Cooling loads, each zone or room will include individual peak sensible and latent loads, it is therefore recommended in certain circumstances further thermal zoning is modelled. Areas that include a difference in building design and/or operation need to be considered as a sub-zone of the larger space, so high internal gains from equipment, solar gains adjacent to external glazing, differences in set points, infiltration, or occupants could all be a case for inclusion of a separate zone.
Take a look at our detailed guide to zoning your models with recommendations.
The results of your CIBSE loads calculation can be viewed in several ways.
The VE will create a number of automated reports as well as being able to display specific parameters or combinations of parameters which can be displayed graphically and numerically.
The automated reports that can be created include a room and zones load spreadsheet which details the peak loads for each space in the building for both heating and cooling. It details the room temperature setpoints for review along with other design parameters such as room volume, occupancy, and ventilation. This spreadsheet will list all zones so can be a quick way to summarise peak load values at a room level rather than at the building level. To create the spreadsheet, ensure either your heating or cooling load is selected in VistaPro, select the “Room and Zone Loads” button highlighted below, then ensure the option to create the excel document output is selected.
Once you open the excel file, which can be prompted from the content manager, you will be presented with an excel sheet like the one below.
VistaPro provides default variables to consider different areas of design and results, but IESVE includes the ability to create a custom variable for use. For example, the sensible plant cooling load is given in kW and is dependent on the calendar and time, if either a peak value is required or a result in W/m2 were a more desirable unit type a custom variable can be created to display these units instead.
Formulas such as the below examples can be used consider your peak result as either kW or W/m2:
Take a look at our top tip on custom variables.
Results can be visualised within the model viewer, this will allow quick analysis of multiple rooms. To do this, select the room-level variables to be displayed in the results tab, the result will be dependent on time and therefore I suggest a custom variable is used to visualise the maximum result at any time. Select the rooms where the results are to be displayed, then in the toolbar press the visualisation button: 
This will automatically overlay the data you are looking for onto the building for visual analysis.
Within VistaPro there are a number of data pre-sets that can be selected to show variable groupings. These are accessed using the button and drop-down shown here:
When the Show IES pre-set in the list option is checked a number of blue pre-sets are added to the variables drop down. These will allow quick selection of multiple variables related to a single topic, for example, the Cooling Loads (Detail) pre-set can be used in combination with the room peak timetable VistaPro output option to list each zone cooling peak load as well as the makeup from Conduction, Ventilation, Solar and Internal Gains.
You can also create pre-sets for use within your project, if you have a set of particular variables you like to review together, the use of these pre-sets speeds up workflow and assists in the assessment of the building.
Using Dynamic Thermal Simulation, the IESVE ApacheSim application allows users to perform an annual simulation that considers a more detailed sub-hourly analysis of heating and cooling loads. This calculation type follows a different method of data assignment, an example of this being all dynamic simulations include all assigned data, including room internal gains, also the dynamic simulation considered an annual weather file and can consider both the heating and cooling loads within the same assessment.
Further Resources and Support Watch our free webinar on ‘Using IESVE for Room Loads Analysis’ for a practical example of CIBSE loads in use, with further explanation on the key points mentioned in this top tip. For more information please refer to our CIBSE Loads application webpage.
