ies tutorial 2011

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Building Energy Simulation

1 Introduction

1.1 A Brief History of Building Energy Simulation

The changing importance of building physics in design, along with improved technologicalcapabilities, has led to an evolution in the attempts to model the complex dynamics of the energy

flows in buildings. Ultimately, the need for accurate modelling and simulation techniques is to aid

design decisions.

Early modelling attempts would generally be “steady-state” models, whereby a building could be

broken down into an array of points or “nodes”, with energy flows between different nodes, as

shown in Figure 1. Such a system of nodes can be thought of as an electrical network: each node is

at a different temperature (analogous to voltage), and there are heat flows between nodes

(analogous to current), with the rate of transfer dependent on the thermal resistance (analogous to

electrical resistance).

Figure 1 – Energy flows in buildings1

1 Clarke J.A. (2001), “Energy Simulation in Building Design, Second Edition”



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The main problem with such a steady-state model is that the environment clearly varies with time;

weather variations, both daily and annually, result in significantly varying external temperatures,

wind speeds, and incident solar radiation. Not only are there weather variations, but the activity

within the building also varies, and thus casual gains are constantly changing. Meanwhile, the effect

of thermal mass in the building allows energy to be stored and released, adding yet another

temporal variation.

As computing power increased, dynamic models of energy flows in buildings began to appear. Thesedynamic models are based on the equations governing energy and mass transfer, and avoid many of

the assumptions and limitations of previous simplified models. For example, dynamic models can

capture the time-dependency of energy flows, such as climactic conditions, thermal mass, and

internal gains. The added complexity of dynamic models comes as a cost though: they are more

time-intensive than steady-state models, both in terms of the time needed to construct the model

and also the time needed to run the simulations, whilst they also require a greater level of details in

terms of inputs to the model.

Ultimately it is up to the individual to decide which type of model is more appropriate on a case-by-

case basis. For some studies, a quick estimate of the monthly energy use will be adequate. In thesecases, steady-state models (often spreadsheet based) would be most appropriate. In other studies,

an accurate profile of the energy use and internal conditions will be required. In these cases a

dynamic model should be used.

1.2 Integrated Environmental Solutions Virtual Environment (IES-VE)

“Virtual Environment” by Integrated Environmental Solutions (IES-VE) is a modern example of

dynamic building energy simulation software. IES-VE consists of a suite of integrated analysis tools,

as shown in Figure 2, which can be used to investigate the performance of a building either

retrospectively or during the design stages of a construction project.

Figure 2 – Modules and analysis tools available in IES Virtual Environment

The VE software does not require the user to have any knowledge of computer programming or ofthe mathematics and equations that govern building physics, as all the interaction between the user



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and the software is done through a graphical user interface (GIU). Such a piece of software is known

as a “black box” in computing parlance. The user, therefore, is only required to give the software

specific inputs, whilst the outputted results are given graphically; however, knowledge of building

physics is fairly essential in being able to interpret the results with any sense.

A model of a building can be constructed within VE using the “ModelIT” module, which can then be

analysed in a variety of ways; for example, the software includes a module called “Radiance” that

looks at the viability of day-lighting and a module called “MacroFlo” that investigates theeffectiveness of natural ventilation.

IES-VE is commercially available software, and is regularly used within the building services industry.

It is a powerful piece of software, which is capable of modelling complicated building environments

– even the Engineering Department (see Figure 3 below). However, like all pieces of software, it has

a learning curve associated with it, and it has its quirks – lots of them! If you are patient though, IES-

VE will reward you with a good understanding of how your modelled building should operate.

Figure 3 – IES-VE model of Cambridge University Engineering Department (CUED)

1.3 Getting Started

IES-VE is available in the Design and Project Office (DPO) in CUED and via Citrix in the Architecture

Department. It can also be downloaded and used on your own computer, provided you pay £50 for

an annual student license (see www.iesve.com for more details).

http://www.iesve.com/






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2 Constructing a Model

2.1 Some Quick Tips

IES-VE includes a navigator that is designed to guide you through the process of constructing a

model and conducting energy or lighting analysis. The navigator, shown in Figure 4, also enables you

to quickly find the appropriate menu, button, or tab for the task you are working on by simply

clicking on the description of the task that you want to carry out. This can be very helpful, since itcan be difficult for beginners to find their way around the software otherwise. The navigator also

includes check boxes and text boxes to allow you to add notes and tick off completed stages in a

project. This can be useful when collaboratively working on a project.

Figure 4 – IES-VE navigator

IES have also created a simplified version of IES-VE called “VE Gaia” that is aimed at architects and

those less used to energy modelling. It contains most of the same functionality as IES-VE, but with

fewer numerical inputs and more emphasis on presentation of models, results, and analysis.

Annual academic licenses of VE Gaia can be downloaded for free from www.iesve.com. There arealso demonstration videos of the software on YouTube.

2.2

Creating a Geometrical Model

When using IES-VE, the first step in creating a full energy model of a building is to define the

geometry of the building by creating a geometrical model. This specifies the dimensions of the

building, including the floor area and height of every room, as well as the positions and sizes of any

glazing or doors.

Geometrical models can be created in the ModelIT module of VE, and are constructed in a similar

manner to other 3D building modelling programs such as Google SketchUp. In fact, for those whoare comfortable using Sketchup, an IES-VE plug-in is available for Sketchup, which allows the user to







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specify building parameters inside Sketchup and then export the model to IES-VE for the full dynamic

energy calculations. This isn’t necessarily advisable, however, as importing models from Sketchup

often introduces a number of compatibility errors. In most cases, it’s easier just to build your model

in ModelIT. Existing models can also be imported using gbXML.

Figure 5 – ModelIT in IES-VE

Figure 5 shows some of the toolbars that are available in the ModelIT module. The modules box

contains a list of all the various modules that are available. For now we will stay in the ModelIT

module, but we’ll use other ones later. Also displayed is a room list , which shows all the spaces thathave been created. So far we haven’t created any spaces, so it’s empty, but soon it will start to fill

up.

Various toolbars are also available. Placing the mouse over any icon should display a short

description of the icon’s function. For more details on each icon, or i f you ever encounter any

trouble and are unsure of how to proceed, press F1 to get the (very useful) help menu.

To create a new space, you can use any one of the draw icons, shown in

Figure 6. The draw prism icon can be used to construct simple cuboids,

by clicking and dragging to achieve the required area. You can specify

the height of the room, and also give the room a reference to help you

navigate your model later on.

Figure 6 – Draw icons in ModelIT



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Figure 7 –

Shape settings box and simple cuboid room

2.2.1

Specifying room dimensions

Figure 7, above, shows some of the features for drawing a room, along with a simple cuboid room

that is 5m x 5m x 3m. If you tick the box marked “create inner volume”, the room is not modelled as

a thin-walled structure. You can also specify the plane at which you wish to have the room created.

For example, if we wanted to add a second room on top of this first one, we can create another

room at plane 3.0m. You can also use the different viewing options in the view toolbar to create

rooms from different perspectives.

You can also check (and admire) your model as you go along using the model viewer , as shown inFigure 8. And don’t forget to save your work regularly as you go along!

Figure 8 – Model viewer



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If you make a mistake when you’re trying to create a space, either select the room, delete it, and try

again, or use the various icons in the edit toolbar to change the dimensions of the room. The edit

toolbar can also be used for other operations, such as copying rooms, moving rooms, or rotating

them, as shown in Figure 9 below.

Figure 9 – The edit toolbar

2.2.2

Specifying windows, doors, and holes

So far we have a two-storey building with no windows. This won’t be much fun to live in. Luckily, we

can use ModelIT to add windows, doors, and holes to our building. This can be done in one of two

ways (see Figure 10 also):

1. Select the room where you wish to place the window/door. Move down one level using the

arrows (move down one level ) on the view toolbar and then select the surface on which you

wish to add a window/door. Moving down one more level gives you a view of the surface

from the inside looking out . Select the add window or add door icon, and then draw your

window in. Window or door objects can be drawn rectangular or polygonal, or specified to

take up 100% of the surface.

2. Select the add window or add door icon when at the top-level of viewing (i.e. as shown in

Figure 7). The place opening box will open up, allowing you to specify the base height of the

window/door, along with the dimension of the object itself. This can be a convenient way of

placing multiple identical objects on your building.

As mentioned above, you can also add internal holes to your building (you can’t have holes on

external surfaces). These can be used, for example, to allow natural ventilation between adjacent

rooms, or to represent a stairwell. Holes can be added in the same way as windows or doors, as

described above (but only to internal surfaces). Surfaces can also be selected from the room list on

the left-hand side of the screen.

That covers the basics of how to create a geometrical model. However, before we can run any

analysis, we need to define properties for the model that specify the materials and constructions

that are used, the sources of internal heat gains, and the methods by which rooms are heated,

cooled, and ventilated. This is done using the Apache thermal module of IES-VE.



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Figure 10 – Alternative methods for adding windows/doors

2.3 Applying Properties

The easiest way to apply properties to your building is to create templates using the building

template manager (shown as (A) in Figure 11), which can be accessed from the Tools tab. The

building template manager is the gateway to accessing other databases, such as the constructions

database, the openings database, and the profiles databases. Once a template has been created, it

can be applied to rooms or surfaces, in order to specify properties for that space. Multiple templatescan be created and assigned to different rooms, to represent the different activities of each room.

2.3.1

Creating constructions

We can begin by going into the constructions database, in which we can create new constructions

that define the materials of the building. This allows for insulation and glazing to be specified, which

will have an important affect on the energy efficiency of a building. After opening the constructions

database, the project constructions box should open up (as shown in (B) in Figure 11), listing all the

different constructions that are available. New constructions can be created by clicking on the add

default construction icon, which can then be edited by double-clicking on the construction

description. This should open up a new box where the construction is defined, as shown in (C) in

Figure 11.

The construction definition box shows the various layers that make up a construction (from outside

to inside), including the material, the thickness, the conductivity, and the density. Based on what

layers are defined, IES-VE will automatically calculate the U-value (measure of insulation ability) for

the layer. To add layers, use the buttons marked copy, paste, add, insert, etc. Thicknesses can be

altered by typing in the required thickness of each layer (in metres). To change the material of a

layer, use the systems materials database, shown as (D) Figure 11, which contains a list of hundreds

of different materials, organised into 14 categories. To change the material of a layer, right-click on a



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material inside the systems materials database, click copy material , and then return to the

construction description (C) to paste the material onto the appropriate layer.

Figure 11 – Defining constructions: (A) Building template manager; (B) Constructions database;

(C) Construction definition; (D) Materials database

A similar process can be used to define glazed constructions, such as windows or rooflights. When

creating glazed constructions, shading devices can be specified, such as shutters, curtains, or blinds,

and activity profiles (see §2.3.2) can be used to indicate under what time periods or conditions

shading devices will be used.

Once all the necessary constructions have been created, they can be assigned to the building by

selecting the appropriate surfaces and using the assign constructions option in the Apache module

of IES-VE, as shown in Figure 12. To assign a construction to a surface, select the surface you wish to

alter, click on assign constructions, select the surface type and the existing construction, and then

select the replacement construction and hit Replace.



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Figure 12 – Assigning constructions in Apache

2.3.2

Creating activity profiles

A building’s energy demand is not only dependent upon the physical properties and dimensions of

the building, but also upon its internal activity and use. For this reason, it is necessary to specify

activity profiles, which describe the duration and magnitude of any occupant activity, such as

window openings, appliance use, and heating time-periods. This is done from the Apache profiles

database in the thermal conditions tab in the building template manager .

Profiles can be created to specify activity that varies by day, week, or year. A list of available activity

profiles is shown in (A) in Figure 13. The most common is a daily profile. In the daily profile,

modulating values (between 0 and 1) are set at different time points to specify the length and

amplitude of any activity. For example, if the profile represent the occupancy of a four-person room,

then a value of 1.0 is used to represent a full room (with four people), 0.5 is used to represent a half-

full (or half-empty) room (with two people), and 0.0 is used to represent an empty room. The daily

profile shown in Figure 13 indicates an activity that is done between 9am and 5pm.

Weekly profiles can also be made (see (C) in Figure 13), using a combination of daily profiles.

Similarly, annual profiles can be created from a combination of weekly profiles. For example, a

profile could be created for a school to model the fact that the building would only be in use for the

term time.

A number of pre-made daily, weekly, and annual profiles exist, which can be found from the icons at

the top of the profiles database window. Again, don’t forget to save as you go along!



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Figure 13 – Apache profiles database: (A) Profiles database; (B) Daily profile creator; (C) Weekly profile

creator

2.3.3

Specifying thermal conditions

Back in the building template manager , templates can be created to specify heating systems,

internal heat sources, and air exchanges of a room. This can be done in the thermal conditions tab,

as shown in Figure 14. The building regulations tab is only used if you plan on conducting a “Part L”

assessment. The other four tabs are likely to be more useful.

In the room conditions tab, the desired internal conditions of the room can be specified, such as the

duration and magnitude of the heating and cooling. Time profiles, such as those created in §2.3.2

can be used to specify the length of the heating/cooling period, whilst the simulation set-point can

be used to specify the temperatures at which heating/cooling will be turned on/off. For example, ifthe profile shown in Figure 13 (B) was used, along with a heating set-point of 19°C, then the heating

would be turned on at any point between 9am-5pm when the internal temperature drops below

19°C, and heating will be permanently off between 5pm-9am.



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Figure 14 –

Specifying thermal conditions: room conditions; HVAC system; internal gains; and air

exchanges

The heating, cooling and ventilation system can be specified in the system tab. Different system

profiles can be specified in the Apache Systems database, shown in (B) in Figure 15. For example,

some rooms in your building may be mechanically heated and ventilated, whilst others might have

radiators and natural ventilation. To specify a particular system configuration, open up the UK NCM

system wizard , and select a system type and other options from those given, as shown in (C) in

Figure 15. Pressing “Yes, save and apply” (as shown in (D) in Figure 15) will apply the system

parameters for the selected system configuration.

Detailed HVAC systems can be specified and modelled in the standalone module ApacheHVAC,

which can be linked to any analysis done in the main Apache module. ApacheHVAC allows for more

complex systems to be analysed, included mixtures of energy supply sources, detailed control

schemes, renewable energy sources, heat-exchangers, ventilation, humidification, and cooling.

After selecting and applying a system configuration, specific parameters of the system can be

changed in Apache Systems, such as the fuel type or the heating system efficiency. Properties of the

domestic hot water (DHW) system can also be specified in Apache systems, as shown in Figure 15.

Internal gains for each room, such as lighting, occupants, and computers, can be specified in the

internal gains tab, as shown in Figure 16. Multiple sources of internal gains can be added, with

parameters set for each source, such as the heat output per square metre. The activity profiles



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created in §2.3.2 can be selected under variation profile, in order to specify the magnitude and

duration of each internal gain.

Figure 15 – Specifying system properties: (A) System tab; (B) Apache Systems; (C) System data wizard;

(D) Apply system parameters



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Figure 16 – Specifying internal gains

Finally in the thermal conditions section of the building template manager there is the air

exchanges tab, which can be used to specify the volumetric flow rate of infiltration, natural

ventilation, and mechanical ventilation. These are added in a similar manner to the internal gains,

with the magnitude of the air flow defined and the duration specified using activity profiles. If you

are confident that you know the magnitude and duration of the air flows into a space, then it is

reasonable to specify them in the air exchanges tab. However, there is a more accurate way of

defining natural ventilation, via the MacroFlo module or tab, as described below.

Once a thermal conditions template has been created – which includes room conditions, system

details, and information about internal gains and air exchanges – it can be applied to a room in the

Apache module, by selecting the space in question, and then using the assign room thermal

template to selection set button.

2.3.4

Modelling natural ventilation

IES-VE provides separate modules for modelling natural ventilation. If a detailed analysis of the flow

through a single space is required, then the MicroFlo module can be used, which is a CFDprogramme (computational fluid dynamics). If only an estimate of the volumetric flow rate (i.e. l/s or

m³/s) is needed to integrate with the dynamic energy model, then MacroFlo can be used.

MacroFlo will calculate the volumetric air flow rate through different openings (such as windows,

doors, etc.), based on weather conditions, size and orientation of the opening, etc., and can also be

used to model interactions between an occupant and an opening. For example, a window can be

specified to open and provide natural ventilation if the internal temperature of a space exceeds a

certain point. Activity profiles, as described in §2.3.2, can also be used to specify the time periods

that a window/door might be opened. All of this can be done in the MacroFlo Opening Types tab in

the building template manager (see Figure 17).



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Figure 17 – Modelling natural ventilation in MacroFlo

Once an opening type has been created in the building template manager , it can be applied to the

building in a similar manner to the constructions, as described in §2.3.1 and shown in Figure 12.

After the properties of the building, services, and occupant activities have all been specified, the

model is almost ready to run. First, however, the software needs to know where the building is

located, as this determines climatic conditions, with important factors such as the external

temperature and solar gains.

2.4 Climate and Weather

2.4.1 Setting a location

In the Tools tab on the main menu bar, an option called APlocate is available. By clicking on the

selection wizard option in APlocate, and running through the necessary steps, you can select the

location of your building and thus determine the weather data that IES-VE will use when dynamically

modelling the energy demand. Locations are available for hundreds of locations across the globe.

There are a number of other options available in APlocate, such as changing the terrain type and the

wind exposure, or seeing the path of the sun for the location selected. See Figure 18 below.

2.4.2 Building orientation

The orientation of the building is also an important factor, as it determines how much light enters a

space, which in turn determines the viability of natural lighting and the magnitude of solar gains.

The building’s orientation can be changed in IES-VE in the ModelIT module, by selecting the edit site

rotation button in the view toolbar (see Figure 18). Specifying the site angle rotates the building,

with 0° as North, 90° as South, and 270° as East. When viewing the model in plan view, the default

option is for the view to be orientated to the North.



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Figure 18 – Setting a site location (A) and orientation (B)

2.4.3

Solar gains

The final step is to calculate the solar gains for the building. This is done in the SunCast module, by

selecting the solar shading calculations button. After pressing start, SunCast will calculate the

position of the sun relative to the building for each hour of each day. If the results of SunCast are

saved, then they can be loaded into the dynamic simulation to provide information about solar

gains.

The results of SunCast can also be used to generate images of the sun position in relation to the

building. For example, you can view the movement of the building’s shadow over the course of the

day, or get an idea of the path of the sun during the day by seeing an image from the perspective of

the sun. See Figure 19 below.

Figure 19 – SunCast calculations and images

3 Simulation and Analyses

3.1 Steady State Simulation

A simple steady state calculation can be done by pressing the CIBSE Loads button in the Apache

module. After selecting the appropriate options and calculating, results will be displayed that show

the monthly heating and cooling loads for a typical day in each month, based on “design days”. This

is mainly used in order to size the heating, cooling, and ventilation systems.



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3.2 Dynamic Simulation

The more useful option is the dynamic simulation, which provides hour-by-hour results of the air

temperature, air flow, and heating loads for each space throughout the year. This calculation is done

by selecting the ApacheSim (Dynamic Simulation) option in Apache. The MacroFlo natural

ventilation modelling and the SunCast solar gain calculations can be incorporated, and the

simulation time step can be reduced to improve the accuracy, or decreased to speed up the

calculation.

3.3

Displaying Results

Once the simulation has finished, the results will be displayed in the Vista module of IES-VE. Results

can be displayed for a single space or a combination of rooms, and variables can also be combined. A

variety of options are available in terms of displaying and interpreting the results. Two of the most

useful options are shown in Figure 20.

Figure 20 – Displaying results in Vista: (A) Profile graphs; (B) Monthly tables; (C) Set dates

The graphical display (see (A) in Figure 20) shows the change in different variables over time. The set

dates icon (see (C) in Figure 20) can be used to zoom in on a specific month, week, or day, in order

to examine the profile more carefully. Left-click to select the start date and right-click to select the

end data for the period that you wish to examine.

In Figure 20, the graph (A) shows the variation of the internal air temperature, the space heating

load, and the heat losses due to natural ventilation for the whole building. It can be seen that the

building is operating as expected, with a temperature of 19°C being maintained by the heating

system during the operational hours of 9am-5pm, and with natural ventilation being used to cool the

building when the temperature goes above 25°C.



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The monthly tables (see (B) in Figure 20) can be used to display the monthly (and yearly) totals for

different variables. In Figure 20, the table (B) shows that there is an annual heating load of

approximately 3.3MWh per year for the building, or 112kWh/m² per year – not very good

considering PassivHaus standards recommend less than 15kWh/m² per year.

3.4

Assessing Improvements

When designing a new building or analysing an existing building, the effect of changes to the

building are likely to be of interest. In particular, the effect of different materials and improved HVAC

(heating, ventilation, and air-conditioning) systems will be of interest. The case study building used

so far has un-insulated cavity walls, double-glazed windows, and a natural gas boiler with an

efficiency of 0.81. Clearly there is plenty of room for improvement here.

Firstly, the insulation of the building can be improved to reduce conductive losses, by adding

insulation into the cavity and upgrading the windows to triple-glazing. This is done by changing the

layers of the constructions that were made earlier in the constructions database in the building

template manager , as shown in Figure 11 and described in §2.3.1. Once the constructions have

been altered in the database, they do not need to be reapplied to the building, as changes in the

databases are propagated through to any constructions that have already been applied.

Secondly, the HVAC system can be improved to increase the efficiency with which heating,

ventilation, etc. are provided. This can be done by altering the HVAC system template in Apache

Systems in the building template manager . For example, the natural gas boiler can be replaced with

an electric heat-pump, which has a higher COP (coefficient of performance). Again, it is not

necessary to reapply the template, as changes will be propagated through.

Other options for the HVAC system that can be modelled in IES-VE include having a CHP (combined

heat and power) boiler or a ventilation heat-recovery system. There is also an option in Apache

Systems to have solar thermal DHW, and there is a Renewables icon in the Apache module of IES-VEthat enables simplified modelling of solar PV, wind turbines, and CHP generators.



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Figure 21 – Assessing improvements in Vista: (A) Weekly profile of heating load and internal air

temperature; (B) Monthly and yearly total heating load; (C) Monthly and yearly total energy delivered

It can be seen in Figure 21 that the improved insulation and heating system reduces the heating load

significantly, and reduces the total energy delivered by 79%. If no room or space is selected, then the

different loads, energy, and CO2 emissions can be displayed and assessed for the building as a whole.

A quick comparison shows that the above improvements have reduced the total annual CO2

emissions by approximately 46%.

The other display options in Vista allow you to assess improvements in different ways. For example,

the synopsis option displays the minimum, maximum, and mean values for a selected variable in a

certain time period. Also, when using the graphical display (see either (A) in Figure 20 or (A) in Figure

21), clicking on the graph itself will bring up the values of the variables displayed at a given point in

the time profile.

The range tests option can be used to show the frequency of a variable having a certain value. For

example, a range test can be conducted to see for how many hours of the year the air temperature

in a room exceeds 25°C. There are also a number of variables that define the thermal comfort in a

room, such as the “predicted mean vote”, which can be used to look at the effect of technologies on

improving the internal conditions of a space.

There are plenty of other ways of improving a building and making it more energy efficient that have

not been described here, such as roof insulation or other HVAC improvements. There are also many

other ways of analysing the data and making an assessment of different technologies. The best thing

is to experiment with the software and look at the effect of changing different properties of the

building and its systems. And don’t forget to save everything as you go along!

4 Conclusion

The notes presented here are only an introduction to IES-VE. As you can see, there is a fairly steep

learning curve to the software, and it definitely has some quirks that make it confusing and annoying

at times. As mentioned above, the best strategy is to play around with the software and to try and

become comfortable with navigating between the various menus, toolbars, and displays. If you ever

get stuck, the manuals in the Help menu (F1) are always a good place to start.

A good place to start would be to try and replicate the example shown here: to build a two room

house with windows on each face, and to investigate the effect of using different insulation

materials, glazing, and heating systems.

Finally, if you get very confident with the software, there are a number of other modules beyond

ModelIT and Apache that can be used to assess the energy efficiency and comfort of your building.

Modules such as SunCast (for solar analysis), MacroFlo and MicroFlo (for natural ventilation

analysis), and Vista (for results analysis) have already been mentioned. In addition, ApacheHVAC can

be used to design and assess more complicated HVAC systems for your building; RadianceIES can be

used to simulate and assess day-lighting in spaces; and CompLib can be used to model and add

components for your building.

Enjoy!

Adam Booth, [email protected]

ies tutorial 2011

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