HVAC systems modeling

If the hypothesis or model does not seem to be a good predictor of what is happening in the building, you probably need to collect more information about the occupants, HVAC system, pollutant pathways, or contaminant sources. Under some circumstances, detailed or sophisticated measurements of pollutant concentrations or ventilation quantities may be required. Outside assistance may be needed if repeated efforts fail to produce a successful hypothesis or if the information required calls for instruments and procedures that are not available in-house. Analysis of the information collected during the LAQ investigation could produce any of the following results ... 

Many HVAC system engineering problems focus on the operation and the control of the system. In many cases, the optimization of the system s control and operation is the objective of the simulation. Therefore, the appropriate modeling of the controllers and the selected control strategies are of crucial importance in the simulation. Once the system is correctly set up, the use of simulation tools is very helpful when dealing with such problems. Dynamic system operation is often approximated by series of quasi-steady-state operating conditions, provided that the time step of the simulation is large compared to the dynamic response time of the HVAC equipment. However, for dynamic systems and plant simulation and, most important, for the realistic simulation... 

Building modelization is the process by which the program s user represents a building as a number of thermal zones, separated by walls. HVAC systems are connected to these zones. Abstraction is necessary for the definition of the zones and the buildup of walls, and those components available in the code which match the reality best must be selected. 

Another system program has been developed by SEI Associates, Boulder, CO, incorporating a desiccant dehumidification system model into the Trane Company s energy and economic simulation program TRACE (Trane Air Conditioning Economics). This program has not been used widely by the researchers and other HVAC users. 

To measure the particles concentrations in the workplace air, the Dust-Trak TM Aerosol Monitor (model 8520) was used, which is the reference equipment for sampling and measuring indoor air quality under buildings HVAC systems regulation. This equipment measures the fine and coarse particles concentration by weight (PM, <1,0 im, PM2 5 < 2,5 p,m and PM, < 10,0 jim). In this study, the i (xm nozzle was used with the aim to detect particles with lower dimension than those of the applied sand. The established maximum concentration limit in Portugal is 0.15 mg m for particles smaller than 10 (im. (M.O.P.T.C., 2006). 

In accordance with the requirement of Slovak Nuclear Regulatory Body in BNS 1.4.2 and general international requirements (SSG-3 and SSG-4), the PSA model shall be a comprehensive description of the NPP. In order to have useful information from PSA, a realistic model of the plant is necessary. To account for all relevant dependencies, all necessary support systems are included in the model such as HVAC, electrical supply and heat sink are included in the PSA model. The success criteria for front-end safety systems are derived based on detailed thermal hydraulic analysis specific for the plant and the fuel under analysis, both for core damage and for radiological releases. 

Toxic gas detectors should be provided in air intakes of ventilation systems for pressurized enclosures where dispersion modeling indicates that toxic gas could generate hazardous concentrations at the HVAC inlet prior to a flammable hazard being generated. 

---