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from Anne Caminade (Lemon Consult), with contributions from Eline (UGent) and Wim (Boydens)

Dear Practitioner,

Part 1 - Intro

The hybridGEOTABS project was born after a simple realisation that (hybrid)GEOTABS, although based on proven technology and one of the most energy efficient building solutions available on the market, was unfortunately seldom implemented in practice - and more specifically did not go very far in the race against other more traditional fossil fuel based technologies during early design.

We believe that the main reason behind this is due to the high level of system integration required, which can be a significant challenge for HVAC designers and architects during the early design phases. After reviewing the existing methodologies available, it became clear that one major hurdle is the lack of available design sizing guidance and user-friendly tools that all HVAC designers usually rely on to get started with a design. For example, if you combine GEOTABS with a secondary heating and cooling system, what is then an optimal sizing for both systems? In answer to this, the hybridGEOTABS project team is developing a reliable and user-friendly tool for the feasibility study and pre-design of hybridGEOTABS buildings.


Part 2 - On what is our hybridGEOTABS design method based? Research and development towards a new hybridGEOTABS design method.


The new sizing methodology is based on splitting the heating and cooling demand of a building into a baseload that is covered by GEOTABS, and a remainder load, covered by the secondary systems. The load splitting algorithm is capable of working out the best size for the primary system components for you. On the other hand, dynamic building energy simulations of a variety of buildings in the EU building stock are performed, allowing the identification of heating and cooling demand curves for a wide range of buildings and building properties. The resulting building stock database eliminates the need for time consuming dynamic simulations by the building designer that are usually required for hybridGEOTABS design.

The sizing methodology is also validated by comparison with a more complex control-integrated sizing approach, that allows to quantify the effect of different control strategies on the key component sizing. Because, in the hybridGEOTABS project, a semi-automated new and innovative control technique for hybridGEOTABS buildings is further devleoped, using a white box model predictive controller (MPC) which will help to further optimise the building operation and reach its optimal performance, with an additional 15-30 % savings in practice compared to a rule based controlled (RBC) similar building.


Having such a controller implemented on a building will also enable the drastic cutting down of control design engineering costs as well as installation costs that are normally associated with this high level of system integration. The MPC controller will be installed and commiissioned in  less time than required in a conventional control design, therefore reducing further the commissioning time (and cost). Its outlook towards predictive maintenance and automated fault detection is within reach.

During the last year of the project, the main focus of the project will be clearly on wrapping up the results and rolling out a user friendly design tool as well as a guidebook to translate and apply these results into practice.


Part 3 - How will this design tool benefit you?


During this last upcoming year of the project, the main focus will be on wrapping up the results and rolling out a user-friendly design tool as well as a guidebook to translate and apply these results into practice.

The design tool will be equipped with a user-friendly interface for simple data input: only few basic building geometry, building physical and boundary condition parameters will be required.

The ultimate objective of the tool is to show the feasibility of hybridGEOTABS by answering questions such as:  Is comfort guaranteed in the building?  What is the payback time? What is the energy and environmental performance? and calculate key component sizing (primary energy & CO2 savings).


It will display 3 main outputs (or results):


  • The early design size estimation of each system (primary vs. secondary components) and therefore the degree of hybridity of the building concept, based on the monthly heat balance of the building over one year. This will be complemented by an annual bore field heat balance to decide if or to what extent is regeneration of the ground heat storage necessary.

  • A set of graphs showing the building load patterns for 3 representative weeks (winter, summer, and a transition seasons) helping the HVAC designer to gain further insight regarding the daily amplitude of the building peaks, based on the load duration curve generated for the building. This will define the level of hybridity required on the emission side (e.g. between 30-100 % TABS) and also what type of secondary emission systems is required (e.g. no need for a secondary emission system, or 2, 3, or 4-pipe fan coil units building ventilation only, etc.)

  • A decision making table displaying the different design variations with a simple comparison of payback times, CO2 savings and comfort levels summary (and all other relevant information required during feasibility and pre-design stages that can be easily derived from the results).


With this streamlined sizing method and interface tool putting our research results into practice, we believe to have eliminated some major design hurdles like the need for costly and time consuming simulations. Any HVAC specialist should then be able to size and draft a hybridGEOTABS concept in the same way as he would perform any other conventional design calculation, thus creating a fair level playing field for the possible concept approaches.

All these concurrent measures developed in our research project should ensure that hybridGEOTABS solution is no longer overwhelming for building practitioners and also become a standard option to investigate right from the start of a building project, clearly displaying its potential in terms of energy-efficiency, costs and sustainability.

Anne Caminade is a Project Manager at Lemon Consult AG. She has a Thermal Power Engineering Degree from the National Institute of Applied Sciences (INSA) in Rouen, France combined with a MSc degree in Energy Systems & Thermal Processes Engineering from Cranfield University, UK. Anne has over 11 years’ experience in consulting engineering firms in the UK and Switzerland developing customer orientated sustainable solutions for the built environment.