Dimensions of a room to be electrically heated

[jase03]

A room 7m x 6m x 3m high is to be electically heated to maintain the inside temperature at 20 C, when it is 0 C outside. The room has 2 windows each 1.2m x 1.8m and a sliding glass door 2.4m x 2.1m. The transmission coefficients u in Wm^2/C are given below.

Floor: concrete slab (100mm thick) : 11.5 W/m^2/C

Walls: Cavity Brick (280mm thick) : 2.0 W/m^2/C

Windows and door (Single glazed) : 5.8 W/m^2/C

Ceiling: (do not consider a roof) : 1.0 W/m^2/C

Ignore the effects of furnishings, presence of humans, orientation to sun or any wind exposure

Assume:

There is no requirement to heat the air in the room

Calculate the power rating of the electric heater required to maintain the required temperature.
You are required to tabulate your calculations providing one row for each part of the buildings structure and column headings of area, u and heat loss. The total heat loss should be provided at the bottom of the table. Provide a table number and a suitable caption for your table.


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I've pretty much worked out the table.

However except for the area of the walls. The answer is coming to 68.64 m^2

I just don't know how they got that answer. Any light.

Cheers

 

[collinsmark]

A room 7m x 6m x 3m high is to be electically heated to maintain the inside temperature at 20 C, when it is 0 C outside. The room has 2 windows each 1.2m x 1.8m and a sliding glass door 2.4m x 2.1m. The transmission coefficients u in Wm^2/C are given below.

Floor: concrete slab (100mm thick) : 11.5 W/m^2/C

Walls: Cavity Brick (280mm thick) : 2.0 W/m^2/C

Windows and door (Single glazed) : 5.8 W/m^2/C

Ceiling: (do not consider a roof) : 1.0 W/m^2/C

Ignore the effects of furnishings, presence of humans, orientation to sun or any wind exposure

Assume:

There is no requirement to heat the air in the room

Calculate the power rating of the electric heater required to maintain the required temperature.
You are required to tabulate your calculations providing one row for each part of the buildings structure and column headings of area, u and heat loss. The total heat loss should be provided at the bottom of the table. Provide a table number and a suitable caption for your table.


-------------------------------

I've pretty much worked out the table.

However except for the area of the walls. The answer is coming to 68.64 m^2

I just don't know how they got that answer. Any light.

What's your method of calculating the area of the walls? Did you forget to subtract out the areas of the windows and door?