ARCH 348 BUILDING AND ENVIRONMENTAL SYSTEMS

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1 ARCH 348 BUILDING AND ENVIRONMENTAL SYSTEMS Instructor: Prof. Dr. Uğur Atikol Web site for instructor: Web site for the course:

2 Grading Policy Percentages Used For Grading Midterm 1 25% Term Project 30% Participation 5% Final Exam 40% NG Policy: If a student misses any two of the above assessment activities and/or does not submit any stages of the term project and/or attends less than 70% of the lectures will obtain NG grade.

3 THERMAL COMFORT Heat and Temperature: Heat is the energy of vibrating molecules in a substance. Heat always flows from warmer to cooler substances. Three modes of heat transfer are: conduction, radiation and convection. Temperature is the concentration of heat within a substance

4 Modes of Heat Transfer

5 Modes of Heat Transfer

6 Conduction Conduction is the transfer of vibrating energy between adjacent molecules of a substance HEAT Molecules Heat transfer by conduction

7 Thermal Radiation When molecules on the surface of a substance vibrate, they give off (emit) radiant energy in the form of electromagnetic radiation. Hot emitting source Cooler absorbing surface Vibration of molecules sets up waves Wavelength

8 Convection Convection is the transfer of heat by a moving fluid medium (e.g. air or water). The energy is transferred by the physical relocation of the molecules (i.e., the molecules are not fixed as in the case of conduction.) Warm air molecules Cool air molecules

9 Heat loss through walls Heat loss by conduction and convection through a wall Convection Conduction Heat flow T HIGH Wall T LOW

10 Heat Loss Calculation Heat loss through the walls: Q U A where, ( T In TOut U = Overall heat transfer coefficient (U-value) A = Area of the wall T= Temperature ) T in A T out U-value of wall depends on the materials used Q

11 Heat Loss Calculation Example: The U-value of a wall of area 15m 2 is 2.45 W/m 2 K. If the indoor temperature is 20 o C and the outdoor temperature is 5 o C, what is the heat loss through the wall? Q = = W

12 Thermal Insulation U-value of walls are reduced by using insulation materials. The following is an example of using polystyrene foam on the walls for thermal insulation purposes. Source: 1) Cushion, 2) Beam rafter, 3) Polystyrene foam thermal resistance board 4) Water proofing membrane 5) Tilling battens 6) Counter battens 7) Face wood 8) Roof cover (roof tiles, schingle)

13 Greenhouse Effect Radiation of heat can be visible, in the form of light, or invisible in the form of heat waves. Although light and heat are related, they occupy two ends of spectrum. Light is a high temperature visible type of energy Heat is a low temperature invisible type of energy Electromagnetic spectrum (Source:

14 Greenhouse Effect Materials transparent to visible radiation are not necessarily transparent to thermal radiation. Solar radiation passig through glass strikes objects inside and warms them. These objects, in turn, radiate heat energy in the thermal range, which can no longer pass through glass and is captured within. This method of trapping heat is called the greenhouse effect. (Source: )

15 Thermal Storage Massive materials (such as concrete, brick) store significant amounts of heat and are slow to warm up and cool down. The thermal storage of the building elements can significantly affect the thermal performance of building. Specific heat capacity (C) is a measure of a material to store heat, and is defined as the energy required to raise the temperature of a material by one degree, such that energy stored: Q m C ( T Final Tinitial Here m is the mass of the material and T stands for temperature. )

16 Thermal Storage Wall (Trombe Wall) Overhang Heat loss Winter sun Glazing Room Qin Qdump Dumped heat Heat loss Absorber storage wall Qaux Auxilliary heating Sectional view of a room

17 Bodily Heat Transfer

18 Evaporation As temperature increases the body can not maintain the thermal balance solely by conduction and radiation. As skin temperature increases, perspiration increases, and the skin is cooled by evaporation. The rate of evaporation is dependent on both the relative humidity and the velocity of surrounding air. At 100% relative humidity no evaporation occurs and cooling by evaporation stops.

19 Human Body

20 Psychrometric Chart

21 Comfort Zone

22 Comfort Zone from ASHRAE T = 1.8T + 32