8.9 Heating a room

A simulation of heating a room demonstrates natural convection driven by buoyancy forces. An idealised, ground floor room is presented below, with external glass doors and sloping roof, and internal walls and ceiling.

PICT\relax \special {t4ht=

A heater is located along one side wall, below the point where the roof and ceiling meet. The aim of the simulation was to calculate the room temperature with the heater running at 1kW, when the ambient external temperature eqn.

The thermal boundary conditions were specified as follows: floor temperature eqn; ceiling eqn, representing the first floor temperature; insulated walls, with eqn, see Sec. 4.17 ; glass doors and roof with a heat flux according to Eq. (4.30 ) using eqn and eqn, respectively.

The mesh contained 350,000 hexahedral cells with grading that gave a cell height of approximately eqn along the walls.

Transport properties for air, eqn and eqn, were used. Turbulence was modelled using the eqn SST model described in Sec. 7.11 , with initial levels of eqn and eqn. The near-wall cell centres corresponded to eqn, so the continuous wall function from Sec. 7.6 and thermal wall function from Sec. 7.14 were applied at the boundaries.

The simulation used the transient solution algorithm in Sec. 5.19 , including the buoyancy force eqn in Eq. (2.67 ), with eqn. The condition eqn was applied at all boundaries, combined with the flux calculation in Eq. (5.20 ).

The variations in eqn within eqn were calculated using the ideal gas Eq. (2.55 ) using eqn.

PICT\relax \special {t4ht=

The simulation ran with a time step eqn. The flow is highly unsteady, but at eqn the heat losses through the boundaries oscillate about the mean levels indicated above.

Between the ground and 2m, occupants experience a variation in eqn. In the space adjacent to the roof and ceiling, the higher eqn generates significant heat losses, especially to the outside through the roof.

Notes on CFD: General Principles - 8.9 Heating a room