Metoder att välja korrektioner vid fuktberäkningar med variabelt utomhusklimat
Research output: Thesis › Doctoral Thesis (monograph)
Determination of the design conditions for moisture resistance requires in a Moisture Design number of different moisture calculations to be made in order to determine the moisture status within, or on the surface of, a structure. The objective of this work has been to ascertain how to allow for variations in climate data in order to be able to determine the most unfavourable moisture status likely to be encountered during the life of a building. The method that has been developed involves the use of real climate data from a reference year in the moisture calculations. A correction that allows for variations in the climate data is then applied to the theoretical value in order to calculate the most unfavourable moisture status. The outdoor climate used in the calculations is real hourly measured data, from ten sites in Sweden, covering the 30-year period from 1961 to 1990. Both steady-state and transient calculations are demonstrated in the application examples. The results from each moisture calculation are a moisture status for each calendar year. The steady-state moisture calculations determine the permissible moisture input and the risk of external surface condensation, while the transient calculations are used to determine the number of freeze/thaw passages on the exterior of a brick wall in relation to the risk of condensation or mildew growth on interior surfaces or in the structure. The theoretical moisture status varies from year to year and from one site to another. A reference year and an extreme year can be identified for each site and for each theoretical value of moisture status. Two different reference years are used: Minimum Deviation year (MDY) and Test Reference Year (TRY). MDY is a year selected such that calculations made using it result in a moisture status that agrees as closely as possible with the mean value of moisture status for a series of years of real climate data. TRY is constructed from climate parameters that are the mean values of the hourly values during a year. The MDY reference year differs from one method of calculation to another, from one set of input values to another and from one type of structure to another, as well as differing depending on the moisture status or risk to be investigated. The TRY reference year gives moisture statuses that differ from those calculated from real climate data, and so such moisture statuses are not regarded as representative of the 30-year period. The correction for variation in the climate data can be either a correction term or a correction factor, and can vary from one type of moisture status to another. The magnitude of the correction depends on the input data used, the type of structure and the moisture status or risk to be investigated: In other words, different correction factors must be used for different moisture statuses. An important conclusion from the calculations is that it is possible to produce corrections for variations in climate data that are in good agreement with theoretical extreme values over the entire 30-year period. The method of starting from real climate data when calculating moisture status has shown itself to provide a considerably better description of the moisture status than that of starting from an assumed climate for which the parameters are treated as independent variables.
|Research areas and keywords||
Subject classification (UKÄ) – MANDATORY
|Award date||1998 Nov 26|
|Publication status||Published - 1998|
Defence details Date: 1998-11-26 Time: 13:15 Place: Sektionen för väg- och vattenbyggnad, John Ericssons väg 1, Hörsal V:C, Tekniska fakulteten vid Lunds universitet External reviewer(s) Name: Nielsen, Anker Title: Prof. Affiliation: Narvik Institute of Technology, Building Science, Norway ---