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Comparison of Design Alternatives for BREEAM Certification Project

A project in Prague using DesignBuilder to identify the best design alternatives to maximise BREEAM

At a glance:

 Office building with multiple design alternatives.

 Analysis provided recommendations for further operational costs savings.

 BREEAM 2011 credits - Ene 01 (Reduction of emissions), Hea 07 (Potential for Natural ventilation), Hea10 (Thermal comfort).

Project details

Project description: Office new-build, 24,000 m2
Performance criteria: BREEAM certification
Location: Prague, CZE Project status: Planned Introduction
The design team had multiple design alternatives and wanted to include the energy performance in
the decision-making process. The aim was to find the most cost and energy effective design in line with architectural concept. The energy performance analysis tools typically used in the Czech market
are limited to monthly calculation steps and are not suitable for such a complex building. Therefore a fully integrated dynamic simulation in DesignBuilder was introduced.

Approach and Analysis

We were invited into the design team at the point where the form and the volume of the building had been set. Three major questions to be answered were:

 Is an atrium cost beneficial?

 Could a 0.9 m high window sill bring some extra savings on operational costs?

 Which glazing system and thermal

insulation thickness would be most cost- effective for the building?
Using DesignBuilder’s user-friendly interface to EnergyPlus we found suitable possibilities that satisfied requirements of all members in the design team (architects, investors, HVAC engineers).
For each combination a full annual thermal simulation was run. The results are stated in the table below.
On completion of the initial analysis the client asked us to undertake additional studies with the prepared model, including:

 The influence of the amount of fresh air supplied to the building.

 The difference between sensible-only and

sensible with latent heat recovery device.

 Comparison of different lighting sources and lighting control.

 Thermal comfort study focusing on the

use of convectors under the windows.

 Cooling and heating design loads calculation.

These additional studies were very quick and easy to complete, with minimum time needed to adjust the DesignBuilder model to the new conditions.

3-D Modeller


Façade and external shading

Design Alternative

A) Atrium, full height windows, double-glazing

Change in Annual Heating Energy [%]

Change in Annual Cooling Energy [%]

Change in Annual Heating and Cooling Energy [%]

B) Atrium, full height windows, triple-glazing

C) Atrium, sill, double-glazing

D) Atrium, sill, triple-glazing

E) No atrium, full height windows, double- glazing

F) No atrium, full height windows, triple- glazing
Baseline Baseline Baseline

 4%  2% - 0%

 1%  4%  3%

 5%  2%  3%

 3%  5%  4%

 1%  7% 4%

G) No atrium, sill, double-glazing

H) No atrium, sill, triple-glazing


The final choice was the option D) Atrium, sill windows, and triple-glazing.

 1% - 0% - 0%

 3%  2% - 0%

Triple-glazing has quite similar energy performance compared to the double glazing, however, it provided better thermal comfort during the cold season. Reducing heat losses via triple glazing meant that convectors were not required beneath windows, and the higher price of the glazing was offset by these savings on the heating system. Omitting the convectors also enables a wider range
of possible fit-out solutions.
The window to wall ratio remains high despite adding the sill, so the offices remain well daylit.

Thermal comfort study using

DesignBuilder’s fully-integrated CFD tool

Established as a technical department of DEKTRADE in 1997, and since 2007 Dekprojekt exists separately as a limited company. Our major activities are: technical assessments and designs of building envelopes with specialization on waterproofing, thermal insulation, and water vapour regime. Further building energetics, building physics, micro environmental engineering, building services engineering and sustainable building consultancy.

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  • "I have watched the steady progression of DesignBuilder for the last 10 years or so, and having seen recent improvements in DesignBuilder’s HVAC and LEED modeling I decided to attend their training. I was both surprised and pleased to find how easy to use DesignBuilder is compared to the other similar tools I’ve tried, especially given the power and flexibility offered by the underlying EnergyPlus, Radiance and CFD engines. I’m really pleased that after a week’s training I feel ready to produce accurate results and outputs for loads and sizing calculations and energy analysis. The ability to also undertake fully-integrated daylighting and CFD analysis from the same model you use for loads and thermal simulations is also a very big plus point."
    David Ellis PE, Virginia 22102, USA
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    Dr Shahaboddin Resalati - Senior Lecturer in Sustainable Architecture and Building Physics Architectural Engineering Group, School of Architecture, Oxford Brookes University, UK
  • " The graphical user interface of DesignBuilder is comprehensive and intuitive, allowing us to model complex buildings simply and quickly. The data management structure (data hierarchy and inheritance) allows us to assign model data quickly and accurately, improving our efficiency. The power and flexibility of EnergyPlus, the underlying simulation engine, enables us to model a building in fine detail where required so that we can accurately analyse its performance. This is particularly helpful when calibrating the model with actual energy consumption to obtain a reliable close match when assessing potential improvements and energy conservation measures."
    Alessandro Righi, architect and researcher at IUAV - Laboratory technical physics
  • " We utilised DesignBuilder software to carry out detailed natural ventilation assessments on buildings at our UK gas plants in order to demonstrate compliance with hazardous area regulations. First of all I would like to praise the initial support received from DesignBuilder staff, who were extremely knowledgeable and provided a welcoming point of contact for support and advice. Having used the majority of the alternative building simulation software packages on the market, I found without a doubt DesignBuilder the most user friendly and enjoyable to use. The modelling program itself is fantastically simple allowing even complex buildings to be developed quickly and easily. The user interface of the calculation part of the software is well thought out and the results outputs are graphical and concise. Within a few hours I had got to grips with the software and obtained the results I desired. It has allowed Shell to present compliance to regulating authorities, who were also impressed with the visualisation displays and graphical outputs. I fully endorse DesignBuilder, and in particular how easy it was to learn and use compared to similar building simulation software on the market. "
    Iain Begg, Senior HVAC Engineer, Shell Projects and Technology Group, Aberdeen, Scotland
  • " DesignBuilder’s clear, well-structured layout and intuitive help system makes it a much simpler tool to learn and use, and compared to other simulation packages the creation of professional-looking geometry is much easier. The ease of use extends to other areas of the program such as thermal bridging analysis and setting up HVAC systems, and the capability to easily model adjacent ground conditions is very useful. A very important aspect of our work is optimisation, and DesignBuilder seems to be the only software that currently provides this functionality. We are encouraged that the development team have taken some of our functionality and user efficiency suggestions on board for the next release. We are already using DesignBuilder for research, and for the above reasons we think it is a tool that our students will find easier to use so we will be using it for teaching next academic year. "
    Professor Ljubomir Jankovic, Birmingham School of Architecture, Birmingham City University
  • " We decided to go out and measure some natural light levels in buildings that we have access to.... One building was our own office, and the other was a green building we worked on which will be tenanted in 2 weeks so we had a chance to take readings in the same environment for which we simulated. I am happy to say that the DesignBuilder results are very close to what we measured... What impresses me is that if we measure a value of 250 lux at 3m from the facade, DB returns similar values. This means that if we say that 40% of a building's usable area will have lux levels of 250 or above, then the measured results correlate with that. ... It certainly makes us confident in the results we give to clients."
    Warren Gray, Mechanical Engineer, Solid Green Consulting
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    Dr Manfred J. Zapka, University of Hawaii
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    Mark O’Neill, DM Hall LLP, Glasgow, Scotland

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