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Chapter 1: Problem 121

How do \((a)\) draft and \((b)\) cold floor surfaces cause discomfort for a room's occupants?

Short Answer

Expert verified
Answer: Drafts and cold floor surfaces cause discomfort for a room's occupants by disrupting their thermal balance, making the room feel colder than it actually is, and forcing their body to work harder to maintain a comfortable temperature. Drafts can also carry allergens and cause skin and eye dryness, while cold floor surfaces can lead to fatigue and a sensation of coldness throughout the body.

Step by step solution

01

Understand the cause of drafts

Drafts are caused by air currents or pressure differences within a room. These can result from uneven temperatures, like when warm air rises and cool air sinks. Drafts can also be caused by differences in air pressure due to leaky windows, doors, or walls and may be more noticeable in poorly insulated buildings.
02

Explain the effect of drafts on occupants

Drafts can cause discomfort for a room's occupants in several ways. Firstly, they can make the temperature in the room feel colder than it actually is, due to the cooling effect of air currents on the human body. This is known as the windchill factor. Drafts can also disrupt an individual's thermal balance, causing the body to work harder to maintain a comfortable temperature. In addition, drafts can carry allergens and dry out the skin and eyes, which may lead to further discomfort.
03

Understand the cause of cold floor surfaces

Cold floor surfaces are typically experienced when the floor material (e.g., tile, concrete, or stone) has a high thermal conductivity and/or poor insulation properties. The coldness of the floor may be exacerbated by inadequate heating systems or poor insulation in the building.
04

Explain the effect of cold floor surfaces on occupants

Cold floor surfaces can cause discomfort for a room's occupants in several ways. Since the feet and lower legs are always in contact with the floor, they may become uncomfortably cold, which influences the overall thermal comfort of the individual. Furthermore, cold floors can force the body to constrict blood vessels in the extremities in order to preserve heat and maintain a comfortable core temperature. Over time, this can lead to fatigue and a sensation of coldness throughout the body.
05

Summarize the effects of drafts and cold floor surfaces on occupants' discomfort

In conclusion, drafts and cold floor surfaces can cause discomfort for a room's occupants by disrupting thermal balance, making the room feel colder than it actually is, and forcing the body to work harder to maintain a comfortable temperature. Additionally, drafts can carry allergens and cause dryness of the skin and eyes, while cold floor surfaces can lead to fatigue and a sensation of coldness throughout the body.

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Most popular questions from this chapter

While driving down a highway early in the evening, the air flow over an automobile establishes an overall heat transfer coefficient of \(18 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\). The passenger cabin of this automobile exposes \(9 \mathrm{~m}^{2}\) of surface to the moving ambient air. On a day when the ambient temperature is \(33^{\circ} \mathrm{C}\), how much cooling must the air conditioning system supply to maintain a temperature of \(20^{\circ} \mathrm{C}\) in the passenger cabin? (a) \(670 \mathrm{~W}\) (b) \(1284 \mathrm{~W}\) (c) \(2106 \mathrm{~W}\) (d) \(2565 \mathrm{~W}\) (e) \(3210 \mathrm{~W}\)

A 3-m-internal-diameter spherical tank made of 1 -cm-thick stainless steel is used to store iced water at \(0^{\circ} \mathrm{C}\). The tank is located outdoors at \(25^{\circ} \mathrm{C}\). Assuming the entire steel tank to be at \(0^{\circ} \mathrm{C}\) and thus the thermal resistance of the tank to be negligible, determine \((a)\) the rate of heat transfer to the iced water in the tank and \((b)\) the amount of ice at \(0^{\circ} \mathrm{C}\) that melts during a 24 -hour period. The heat of fusion of water at atmospheric pressure is \(h_{i f}=333.7 \mathrm{~kJ} / \mathrm{kg}\). The emissivity of the outer surface of the tank is \(0.75\), and the convection heat transfer coefficient on the outer surface can be taken to be \(30 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\). Assume the average surrounding surface temperature for radiation exchange to be \(15^{\circ} \mathrm{C}\).

A 5-cm-external-diameter, 10-m-long hot-water pipe at \(80^{\circ} \mathrm{C}\) is losing heat to the surrounding air at \(5^{\circ} \mathrm{C}\) by natural convection with a heat transfer coefficient of \(25 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\). Determine the rate of heat loss from the pipe by natural convection. Answer: \(2945 \mathrm{~W}\)

A 40-cm-long, 0.4-cm-diameter electric resistance wire submerged in water is used to determine the convection heat transfer coefficient in water during boiling at \(1 \mathrm{~atm}\) pressure. The surface temperature of the wire is measured to be \(114^{\circ} \mathrm{C}\) when a wattmeter indicates the electric power consumption to be \(7.6 \mathrm{~kW}\). The heat transfer coefficient is (a) \(108 \mathrm{~kW} / \mathrm{m}^{2} \cdot \mathrm{K}\) (b) \(13.3 \mathrm{~kW} / \mathrm{m}^{2} \cdot \mathrm{K}\) (c) \(68.1 \mathrm{~kW} / \mathrm{m}^{2} \cdot \mathrm{K}\) (d) \(0.76 \mathrm{~kW} / \mathrm{m}^{2} \cdot \mathrm{K}\) (e) \(256 \mathrm{~kW} / \mathrm{m}^{2} \cdot \mathrm{K}\)

A 2.1-m-long, 0.2-cm-diameter electrical wire extends across a room that is maintained at \(20^{\circ} \mathrm{C}\). Heat is generated in the wire as a result of resistance heating, and the surface temperature of the wire is measured to be \(180^{\circ} \mathrm{C}\) in steady operation. Also, the voltage drop and electric current through the wire are measured to be \(110 \mathrm{~V}\) and \(3 \mathrm{~A}\), respectively. Disregarding any heat transfer by radiation, determine the convection heat transfer coefficient for heat transfer between the outer surface of the wire and the air in the room. Answer: \(156 \mathrm{~W} / \mathrm{m}^{2} \cdot \mathrm{K}\)
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