dual duct system
The saving in terms of side surface varies between 27 and 21% with reference to the traditional approach for method 1 and between 14 and 17% for method 2. We are a community of more than 103,000 authors and editors from 3,291 institutions spanning 160 countries, including Nobel Prize winners and some of the world’s most-cited researchers. A mixing box, thermostatically controlled, draws air from the hot and cold ducts and supplies each zone with the required flow rate, at the appropriate supply air conditions. The dual duct system ensures excellent IAQ and good control of the thermo-hygrometric conditions and allows temperature adjustment in each zone, up to individual environments (rooms). This chapter is distributed under the terms of the Creative Commons Attribution 3.0 License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Our readership spans scientists, professors, researchers, librarians, and students, as well as business professionals. These new methods of sizing a dual duct network allow for a lighter network, with obvious economic advantages, and are easier to place. Data for each network, namely, the lengths, airflow rates and maximum speeds in the trunks, are given in Tables 3 and 4 for building A and building B, respectively. The factor tends instead to 2 when the both hot and cold ducts can both carry the entire flow rate of the trunk. The first method requires the “cold” channel to transport air at a temperature value slightly lower (1 ÷ 2°C) than the minimum inlet temperature (variable with time) required by the zones. *Address all correspondence to: email@example.com, Edited by Mohsen Sheikholeslami Kandelousi. For each zone, sensible thermal loads can be calculated as a function of time, and the same can be done for the supply air temperature values in the environments of the zone: The minimum value of the supply air temperature tin,minτreduced by δ, hour by hour, represents the temperature of the cold channel tc∗τ. Air Conditioning Systems with Dual Ducts: Innovative Approaches for the Design of the Transport Network of the Air, HVAC System, Mohsen Sheikholeslami Kandelousi, IntechOpen, DOI: 10.5772/intechopen.80093. For the building B, the maximum is obtained for the network BC when method 2 is used; the minimum occurs for the network BA with method 2 again. The proposed method is applied here to calculate the dual duct networks of two reference buildings. The AHU processes a total flow rate of air that obviously is the sum of the greatest of the three previous values, extended to all the zones. The method proceeds as follows: The total airflow rates at each level of the network, that related to system (departing from the AHU) and those related to the various trunks, are determined from the supply airflow rates required by individual environments and served by the trunk, as it has been previously described. The diameters of the hot and cold channels are representative of the size of the whole network; the peripheral surface of the ducts stands as indicative parameter for the weight of the network and therefore of its cost. This reduction is largely shared by the whole network. In this system, the air from the supply fan is split into two parallel ducts, downstream of the fan. For method 2: tc,sum=13°C,tc,win=7°C. From the total flow rate Gkof the trunk, one can obtain the airflow rate of the cold channel Gc,kof the trunk from the ratio of column B. Therefore, it has been possible to define the thermal zones and to evaluate the airflow rates required for each environment, to cope with the maximum sensible load in summer, the maximum sensible load in winter, and the ventilation needs. In order to make a comparison between the results obtained with the traditional sizing method, the savings are briefly presented in Tables 5 and 6, respectively, for building A and building B, as they are obtained for the five networks, in terms of the peripheral surface of the channels and of the evaluated values of the network factor Fnet. The first (building A) is a day center for dialysis located in the city of Lecce (Southern Italy); the second is a private hospital located in the city of Rome (Central Italy). The Fkfactor takes values between 1 and 2; it approaches 1 when only one of the two ducts actually carries the entire flow rate of the trunk, while the other duct carries only a small correction. Once that the air velocity values in all different trunks are fixed, referring to Table 1, for example, and from the maximum values of the cold and hot airflow rates in the trunks, the diameters of the hot and cold ducts of each trunk can be evaluated. Similarly, the airflow rates of hot and cold channels in the first trunk departing from the AHU are evaluated, once that the temperatures tc,sum, tc,win, th,sum, and th,winhave been set. Publishing on IntechOpen allows authors to earn citations and find new collaborators, meaning more people see your work not only from your own field of study, but from other related fields too. Announcing our NEW encyclopedia for Kids! In the 1960s the so-called dual-duct system appeared; both warm and cold air were centrally supplied to every part of the building and combined in mixing boxes to provide the appropriate atmosphere. Indeed, in order to avoid huge overall dimensions of ducts that may become excessive with respect to the spaces normally available for their installation, high values, depending on the flow rate, are set for velocities through the ducts. In this chapter, an innovative approach is presented for the channel dimensioning, based on the choice of not constant values for the temperatures of hot and cold duct. Then, both the cold and the hot ducts should each be able to carry more than 80–90% of the flow rate of the zone. The room temperature in summer is equal to 26°C for both the buildings; the room temperature in winter is equal to 22 and 20°C, respectively, for building A and building B. which represents the flow rate that the trunk, already dimensioned, could carry if the air flowed at the maximum set speed. In these cases (particularly in operating rooms, intensive care units, or departments for immunosuppressed patients), the air conditioning systems generally used are all-air systems with (outdoor) constant flow (CAV), since the high number of air changes per hour (ACH) must be guaranteed (sometimes values up to 50 are achieved). In this chapter, an innovative approach is presented for the dimensioning of the channels, based on the choice of not constant values for the temperatures of hot and cold duct. With reference to the traditional method, the savings range between 14 and 27% for the building A (located in Lecce), when methods 2 and 1 are used, respectively, and between 17 and 21% for the building B. These relationships, in conditions of maximum sensible load in summer Φs,sumand in winter Φs,win(subscripts “sum” and “win” refer to these conditions, respectively) become. As PhD students, we found it difficult to access the research we needed, so we decided to create a new Open Access publisher that levels the playing field for scientists across the world. The trunk, which consists of the pair of hot and cold ducts, is coherently dimensioned to carry 1.7–1.8 times the supply airflow rate of the zone, once that one sets the values of the airspeed, and this occurs at all the levels of the network, with consequently considerable overall dimensions and high costs. The leading value of the flow rate is that related to ventilation, rather than to summer or winter loads, and all-air systems with variable airflow (VAV) have to be excluded. Our team is growing all the time, so we’re always on the lookout for smart people who want to help us reshape the world of scientific publishing. For the second one, the hot duct transports air at a temperature value slightly higher than the maximum inlet temperature (variable with time) required by the zones, while the cold duct delivers air at a constant temperature, lower than the absolute minimum value of the zone supply temperature. How? The new approach implies reduced overall dimensions (reduced space requirements) and lower installation costs of the networks and therefore represents an improvement with regard to the two critical aspects of the dual duct systems currently designed. We can write similar equations for any trunk. Once the layout of the network is given, the sizing of the channels can be derived if the air speeds in the various trunks k are properly set; a usual criterion to choose the air speeds, starting from the range of values of the airflow rates Qhk,Qckcarried by the trunks, is reported as example in Table 1 [20, 21].
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