Room model

For the numerical treatment, the energy exchange processes in a zone, as outlined earlier, are incorporated into a so-called room model. 

The room model consists of nodes, which are interconnected by heat exchange paths (Fig. 11.36). The nodes represent either surface temperatures of the individual walls or the zone air temperature. For each node, an energy balance is formulated. From the resulting set of equations, the temperatures and heat fluxes can be determined. 

Most room models contain only one zone air node, thus assuming perfect mixing of the zone air and a homogenous temperature distribution in the space. Spatial temperature variations, such as vertical temperature gradients, are not considered. For specific applications such as displacement ventilation or atria, models with several zone air nodes in the vertical direction have been developed. ... 

The room models implemented in the codes can be distinguished further by how detailed the models of the energy exchange processes are. Simple models use a combined convective-radiative heat exchange. More complex models use separate paths for these effects. Mixed forms also exist. The different models can also be distinguished by how the problem is solved. The energy balance for the zone is calculated in each time step of the simulation. 

IFIGURE IL36 Th room model characterizes the individua) energy flux paths as thermal resistances. which are connected to the individual surfaces and to the room air node. 

Perfect mixing of the room air is assumed in the individual zone, except in room models with more than one air node (displacement ventilation model, atria model). 

Most room models are nongeometric, with the radiation exchange between surfaces being calculated solely on an area-weighted basis. 

Due to the methods and limitations outlined in Section 11.3..3, in thermal comfort analysis, draft risk evaluations cannot be performed using this type of room model. Analysis of air temperature stratification and thermal comfort for the occupant zone can be achieved only by using multi-air-node room models. 

Gliick B. Room model for heat transfer analysis (in German Wdrmctechnisches Raummodeli]. Heidelberg C. F. Muller V erlag, 1997. 

The relationships between air exchange rate and temperature difference were determined using COMB (Fig. 11.51) and then integrated as the ventilation model in the thermal model. The rhermai behavior is modeled with the TRNSYS multizone type, considering the hall and the room below the thick concrete test floor slab. For the hall, a room model with two air temperature nodes (one for the occupied zone and one for the rest of the hall) and geometrically detailed radiation exchange is used. 

Room model calculations (Porstendorfer et al., 1978 Porstendorfer, 1984) showed the extent of the influence of the different processes... 

Simultaneous measurements of the radon daughter concentrations, the ventilation rate and the size distribution of the inactive aerosol have been performed in two bedrooms, a living room and a cellar. The measured radon daughter concentrations were fitted by the room model to optimize the deposition rate of the unattached daughters. The mean value was 18/h in the rooms and 8/h in the cellar. 

The deposition velocities of the unattached daughters were calculated from the measurements in the radon chamber with the bare filter (Figure 2) and found to equal. 095+.007 cm/s for Po-218,. 085+.012 cm/s for Pb-214 and. 045+.015 cm/s for Bi-214. This decrease in deposition velocity is one of the most important sources of error in the room model. 

Our analysis shows that the unattached fraction in the domestic environment is between. 05 and. 15 without any aerosol sources in the room and can decrease below. 05 in the presence of aerosol sources. These values are much larger than assumed by James (1984) (fp-3%) and by the NEA-report (1983) (fp=2%). However the few experimental results reported in the literature agree with our findings. Bruno (1983) found an unattached fraction of. 07 and Reineking (1985), Shimo (1984) and Duggan (1969) measured about. 10. The last two results are calculated by means of the room model from the reported unattached Po-218 concentrations. 

JACADS Explosive Containment Room Model Test, Southwest Research Institute Project 06-8069, prepared for the U.S. Army Corps of Engineers, Huntsville Division, Huntsville, Alabama, July 1984. 

Zhang, W., Hamer, A., Klassen, M., Carpenter, D., and Roby, R. Turbulence statistics in a fire room model by large eddy simulation. Fire Safety Journal, 2002. 37(8), 721-752. 

Numerical validation for pesticide movement addresses the question of whether the results generated from the model predict actual experimental values. A few models have been validated by correlating the estimated airborne pesticides and/or the amount on room materials with actual measurements in certain specific cases, van Veen et al. (1999) reported an experiment to validate a painting model of CONSEXPO which describes concentrations of a volatile solvent in room air both during and after the application. The concentrations depended on evaporation, initial concentration of solvent in two layers of paint, volume of paint and removal of solvent by ventilation from the room. Model parameters were either measured from the room before the experiment (ventilation rate, room size, physico-chemical parameters, etc.) from the act of painting (surface painted and amount of paint used), or fixed in advanced (relative size of the two layers of paint, transfer rate between the layers, etc.). The model predicted room concentrations that were within 80 % of the actual measured concentrations (Figure 6.1). Important with respect to the evaporation term is that peak concentrations could be predicted very well, so indicating that the source term is appropriate. 

One important aspect of chamber selection is the overall size of the apparatus. Chambers range in size from benchtop models to whole room models. This constraint alone may narrow the field of choice depending on available space for the unit or... 

Rumelhart et al. offer a much narrower view of a schema than the one taken here. Indeed, what they call a schema hardly differs from a concept. For example, they developed a room model to illustrate schemas in a PDP representation. The model learns to recognize five rooms based on forty descriptors such as toaster, bathtub, television, and so on. The model learns to associate particular features with particular rooms, and in fact it develops concepts for the five rooms. Nevertheless, the knowledge structure built by the model lacks many of the critical features of a schema as outlined in chapters 2 and 3. 

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