R&AC Lecture 35 - Lesson 35 Cooling And Heating...

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Lesson 35 Cooling And Heating Load Calculations - Estimation Of Required Cooling/Heating Capacity Version 1 ME, IIT Kharagpur 1
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The specific objectives of this chapter are to: 1. Introduction to load calculations ( Section 35.1 ) 2. Differences between conventional cooling and heating load calculation methodologies ( Section 35.2 ) 3. Methods of estimating cooling and heating loads on buildings such as rules-of- thumb, semi-empirical methods etc. ( Section 35.3 ) 4. Cooling load calculations using CLTD/CLF method ( Section 35.4 ) 5. Estimation of the cooling capacity of the system ( Section 35.5 ) 6. Heating load calculations ( Section 35.6 ) At the end of the lecture, the student should be able to: 1. Explain the differences between conventional cooling and heating load calculations 2. List commonly used methods for estimating cooling loads 3. Estimate the internal and external cooling loads on a building by separating sensible and latent parts using CLTD/CLF method from building specifications, design indoor and outdoor conditions, occupancy etc. 4. Estimate the required cooling capacity of the coil by taking into account the by- pass factor of the coil, ventilation requirements etc. 5. Explain briefly the procedure for estimating heating loads 35.1. Introduction: As mentioned in an earlier chapter, heating and cooling load calculations are carried out to estimate the required capacity of heating and cooling systems, which can maintain the required conditions in the conditioned space. To estimate the required cooling or heating capacities, one has to have information regarding the design indoor and outdoor conditions, specifications of the building, specifications of the conditioned space (such as the occupancy, activity level, various appliances and equipment used etc.) and any special requirements of the particular application. For comfort applications, the required indoor conditions are fixed by the criterion of thermal comfort, while for industrial or commercial applications the required indoor conditions are fixed by the particular processes being performed or the products being stored. As discussed in an earlier chapter, the design outdoor conditions are chosen based on design dry bulb and coincident wet bulb temperatures for peak summer or winter months for cooling and heating load calculations, respectively. Version 1 ME, IIT Kharagpur 2
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35.2. Heating versus cooling load calculations: As the name implies, heating load calculations are carried out to estimate the heat loss from the building in winter so as to arrive at required heating capacities . Normally during winter months the peak heating load occurs before sunrise and the outdoor conditions do not vary significantly throughout the winter season. In addition, internal heat sources such as occupants or appliances are beneficial as they compensate some of the heat losses. As a result, normally, the heat load calculations are carried out assuming steady state conditions (no solar radiation and steady outdoor conditions) and neglecting internal heat sources. This is a simple but conservative approach that leads to slight overestimation of the heating capacity. For
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R&AC Lecture 35 - Lesson 35 Cooling And Heating...

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