Simulate temperature inside room with radiator in winter

optimus2007 · February 2, 2019, 14:14

Hi,

I want to simulate in Autodesk CFD following model:

A room with a door (wood) and window (glas)

inside the room there is a radiatior which keeps the room warm.
outside the room it is -10 C.

Inside it must be about 20.

What I have done is to set the air of the room as variable (because depends on temperature)

How to set the other boundary conditions ?

the radiatior as a free convection?

thanx

Simbelmynë · February 2, 2019, 15:19

Hello optimus,

This sounds like a problem you do not need CFD for. Sure, you can get a nice view of the natural convection pattern in the room, but this will only be as good as your boundary conditions. Your boundary conditions are not all that easy to determine. You need to know the wall construction, what insulation and the homogeneity of the wall. Same goes for floor and roof. The heat transfer can also be very dependent on how air-tight the construction is and consequently the heat losses may vary a lot depending on the wind outside.

Modeling air-leakage combined with natural convection and wind outside is no small task, considering the different length and time scales.

You are probably better off using empirical expressions and just adjusting the radiator power to this.

If you still wish to model what happens inside the room, I would set convective boundary conditions on the walls, window and door (different heat transfer coefficients). The radiator can be either a heat source or just a block of constant temperature. Natural convection with Boussinesq approximation is probably ok.

optimus2007 · February 2, 2019, 17:06

thanks

And in the case of open window or door
what I have to do with the boundary conditions.
What about initial conditions?

Simbelmynë · February 2, 2019, 18:48

An open window at -10 oC outside seems unrealistic

Anyways a pressure inlet/outlet seems appropriate in that case, assuming you do not have any wind that day.

For initial conditions I would probably go with 20 oC temperature and zero velocity field. You can perhaps estimate the velocity field due to the natural convection from the radiator and use that as initial condition if you wish to have a faster convergence.

February 2, 2019, 14:14	Simulate temperature inside room with radiator in winter	#1
optimus2007 New Member Jonny Join Date: Jan 2019 Posts: 3 Rep Power: 7	Hi, I want to simulate in Autodesk CFD following model: A room with a door (wood) and window (glas) inside the room there is a radiatior which keeps the room warm. outside the room it is -10 C. Inside it must be about 20. What I have done is to set the air of the room as variable (because depends on temperature) How to set the other boundary conditions ? the radiatior as a free convection? thanx

February 2, 2019, 17:06	Re	#3
optimus2007 New Member Jonny Join Date: Jan 2019 Posts: 3 Rep Power: 7	thanks And in the case of open window or door what I have to do with the boundary conditions. What about initial conditions?

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February 2, 2019, 15:19		#2
Simbelmynë Senior Member Join Date: May 2012 Posts: 551 Rep Power: 16	Hello optimus, This sounds like a problem you do not need CFD for. Sure, you can get a nice view of the natural convection pattern in the room, but this will only be as good as your boundary conditions. Your boundary conditions are not all that easy to determine. You need to know the wall construction, what insulation and the homogeneity of the wall. Same goes for floor and roof. The heat transfer can also be very dependent on how air-tight the construction is and consequently the heat losses may vary a lot depending on the wind outside. Modeling air-leakage combined with natural convection and wind outside is no small task, considering the different length and time scales. You are probably better off using empirical expressions and just adjusting the radiator power to this. If you still wish to model what happens inside the room, I would set convective boundary conditions on the walls, window and door (different heat transfer coefficients). The radiator can be either a heat source or just a block of constant temperature. Natural convection with Boussinesq approximation is probably ok.

February 2, 2019, 18:48		#4
Simbelmynë Senior Member Join Date: May 2012 Posts: 551 Rep Power: 16	An open window at -10 oC outside seems unrealistic Anyways a pressure inlet/outlet seems appropriate in that case, assuming you do not have any wind that day. For initial conditions I would probably go with 20 oC temperature and zero velocity field. You can perhaps estimate the velocity field due to the natural convection from the radiator and use that as initial condition if you wish to have a faster convergence.