Numerical Simulations of Gas Burner Experiments in a Residential Structure with HVAC System

Abstract

Controlled fire experiments using a gas burner were previously conducted in a purpose-built, two-story, moderately air-tight residential structure to understand the effect of a heating, ventilating, and air conditioning (HVAC) system and door positions on the fire-induced environment. Temperatures, gas concentrations (oxygen, water vapor, carbon dioxide), and differential pressures were monitored throughout the structure. HVAC status (off vs. on) and stairwell door position of the fire room (open vs. closed) were varied for the experiments analyzed in this paper. In this study, Fire Dynamics Simulator (FDS) v. 6.7.9 was used to simulate these experiments. Experimental data quantifying the air tightness of the building and cold flowrates through HVAC vents were determined to be important to optimize leakages and HVAC loss coefficients for the simulation setup. Pressure development in the structure was predicted correctly to be higher on the first floor and lower in the basement, but the magnitude of steady-state pressure was underpredicted. The measured and predicted steady-state temperature distributions were statistically different for the cases with and without the HVAC on, regardless of the door position. FDS predicted gas transport through the HVAC duct network, and under-predicted temperature rise and water vapor content by about 9% and 10%, respectively, and over-predicted volumetric oxygen and carbon dioxide content by about 21% and 6%, respectively. Temperature rise prediction in the closed room, where the gas transport primarily occurred via the HVAC duct network, improved after including heat loss from the HVAC duct to the ambient.