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Civil-Comp Proceedings
ISSN 1759-3433
CCP: 81
Edited by: B.H.V. Topping
Paper 163

Modelling of Heat and Moisture Transport in Buildings with Control Applications

X. Lü, T. Lu and M. Viljanen

Laboratory of Structural Engineering and Building Physics, Department of Civil and Environmental Engineering, Helsinki University of Technology, Espoo, Finland

Full Bibliographic Reference for this paper
, "Modelling of Heat and Moisture Transport in Buildings with Control Applications", in B.H.V. Topping, (Editor), "Proceedings of the Tenth International Conference on Civil, Structural and Environmental Engineering Computing", Civil-Comp Press, Stirlingshire, UK, Paper 163, 2005. doi:10.4203/ccp.81.163
Keywords: heat transfer, moisture transfer, buildings, mathematical modelling, indoor thermal and moisture control, energy consumption, energy cost.

The moisture problem is one of the most serious factors in the building and housing industry. Over the last decade, moisture failures in building systems have reached billions of Euros in damage in Europe. Additionally, excess moisture in envelopes can lead to the presence of moulds which results in poor indoor air [1].

The very fundamental mechanism on moisture transport in buildings is related to thermal and moisture transfer in building systems subject to the outside climatic changes. Therefore, a precise heat and moisture transfer model for buildings is required. The model can be firstly used as an important tool in predicting heat and moisture transfer in buildings, and then serves as a useful means in estimating the thermal and moisture loads for further performing thermal and moisture control strategies for buildings. This paper deals with these two main themes. Computer software has also been accomplished for these two simulation purposes.

Through an elaborated literature survey on heat and moisture transfer in buildings [2,3,4,5,6,7,8,9], the heat and moisture transfer equations have been given in this paper based on the fundamental thermodynamic relations. The final numerical solution provides transient temperature and moisture content distributions in building envelopes as well as temperature and moisture content for the building's indoor air subject to outdoor weather conditions such as temperature, relative humidity and solar radiation [10,11].

Validation of the model can be found in [10]. In control applications, simulation has been made to study the possibilities of controlling indoor thermal and moisture content by heating indoor air and ventilating outdoor air. To include the factor of energy conservation or cost, the simulated house is categorised as (1) residential house; (2) commercial house; (3) unheated house; (4) other types of house. Different control regulations are applied. For example, regarding the residential house, the desired indoor condition has to be fulfilled the whole year around. Situation is differential for the commercial house in that for certain hours of a day, normally off-working hours, occupants are not present, hence the requirements for the indoor condition can be relieved. Simulation results are demonstrated in this paper for our test house with different types of condition. The indoor condition is well controlled, and significant amounts of energy consumption and cost are saved. For example, compared with the case that the house was treated as a residence house, energy consumption has been reduced by 12% for the test house as a commercial house for the first three days.

The main contribution of this paper is that it combined the detailed heat and moisture transfer model for buildings with simple heating and ventilation control applications, where such research in the literature is normally accomplished with simple dynamic models for buildings. The detailed model can also serve as a completely independent simulation model in predicting heat and moisture transport in building systems. The final program has been named HMTB which will be presented in our companion paper.

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