If you use a concrete floor as your thermal mass how much is

If you use a concrete floor as your thermal mass, how much is needed?

If all the necessary thermal mass is built into a concrete floor, what is the minimum volume of concrete needed (in ft3) (assuming the concrete heats and cools uniformly)? (Round to the nearest integer.)

You\'ve been asked to help design a modular computer lab for a school in Sacramento, where average high temperatures are 92°F during the day in July and August. Electricity prices are going up, so you\'d like to avoid having to turn on the air conditioner all summer long. Your plan is to use a building material with good thermal mass, blow outside air over it at night to cool it down, and then let it absorb solar gains during the day. You propose a modular building similar to the one shown. The structure has four 10\'x8\' south-facing windows. Each window receives an average solar radiation intensity of 275 Btu/ft2 over the course of the day. As the structure has been sited on the school\'s property, there are large shrubs shading the west- facing windows, making the solar gain on that side of the building negligible. You assume that nighttime ventilation will be sufficient to cool the mass to the average daily low temperature of 54°F. To maintain comfortable conditions, your goal is to provide enough mass so that the indoor temperature does not rise above 78°F during the day. THERMAL PROPERTIES 1 Watt = 3.414 Btu/h or 1 kW = 3414 Btu/h 1 Watt-h-3.414 Btu, or 1 kWh = 3414 Btu 1 kJ = 0.948 Btu 1 kg = 2.2 lb !gallon water = 8 lb = 0.1 3 ft3 Specific Heat mitm |Density abit3) |Volumetric Heat Capacity (Bu Air Concrete 0.2 Water 1 0.24 0.075 120 a 0.018 24 ?

Solution

As per the information, which in itself doesnot seem complete.

Per window area = 10*8 =80 sq ft

Radiation =80*275*4 =320*275

Temperature (dT) =92-78=14

V*S*dT = 320*275 <S = 24BTU/ft3 F>

V = 262 ft3