Incorporating a modular system simulation program into a large energy analysis program : the linking of IBLAST and HVACSIM+

Most currently available hourly energy analysis programs utilize separate and sequential simulations of the building, air handling systems, and primary energy plants. This results in a lack of feedback from the system to the building and from the pIant to the system and building. This is especially a problem when an undersized system or plant is simulated. If an undersized system were actually installed in a building the zone cooling and or heating loads could not be met all the time causing the temperatures to float out of the desired range. An integrated building simulation can represent this condition well but the BLAST simulation, because of its sequential nature cannot. The BLAST program has recently been revised to eliminate the separate simulations. The resulting integrated program is called IBLAST and it contains a large library of system and plant types which can be selected and sized by the user. This work further improves user flexibility in defining system and plant arrangements by incorporating MODSIM, a program. element of the HVACSIM+ package, into IBLAST. The combined program is substantially enhanced and retains all of the functionality of both components. In addition, MODSIM can obtain all required system parameters from the IBLAST input file or they may be specified in a MODSIM data file. 
The adaptive time step feature of MODSIM is utilized to allow the fast responding elements of a system to be simulated at a time step on the order of seconds. The slow response of massive building elements is simulated at larger time steps, typically fifteen minutes or longer, which are user specified. The MODSIM time step is always smaller, and adapts to provide an integral number of steps between IBLAST time steps. 
This paper presents results obtained using MODSIM systems with IBLAST. Specifically, a single zone draw through and a multizone fan system are illustrated along with a description of the steps required to produce the MODSIM connection diagrams for each system. Methods used to símulate non-traditional systems are also discussed.