China
Africa
Explore chapters and articles related to this topic
Air Conditioning
Published in Fred Hall, Roger Greeno, Building Services Handbook, 2017
Hydrochlorofluorocarbon (HCFC) — refrigerant is a subclassification of CFC that has the addition of hydrogen. HCFCs have less impact on ozone depletion and global warming than CFCs due to a lower chlorine content. However, there is some environmental effect, so HCFCs are only regarded as transitional CFC replacements before being completely phased out in 2015. the HCFC Chlorodifluoromethane (R22) has been widely used in domestic fridges and freezers as well as commercial heat pump, air-conditioning and refrigeration equipment.
Reactions between lithiated 1,3-dithiane oxides and trialkylboranes
Published in Journal of Sulfur Chemistry, 2021
Basil A. Saleh, Keith Smith, Mark C. Elliott, Gamal A. El-Hiti
Reactions of trialkylboranes with various trisubstituted methanes such as chloroform (CHCl3), dichlorofluoromethane (CHCl2F), chlorodifluoromethane (CHClF2) and 1,1-dichloromethyl methyl ether (DCME) in the presence of a strong base result in the transfer of all three alkyl groups from boron-to-carbon in a single process [9,10]. Even trialkylboranes having a tertiary alkyl group, such as a tert-butyl or thexyl moiety, on reaction with DCME and lithium triethylcarboxide at 25°C, transfer all three groups successfully [9,10]. A reagent with three different leaving groups attached to a central carbon atom could, in principle, be used as an alternative to DCME, opening up possibilities for asymmetric induction to generate enantiomerically enriched chiral tertiary alcohols. Compounds having two sulfur-containing leaving groups have been used successfully to perform up to two 1,2-boron to carbon migrations [11–15], and in principle, a third leaving group could be incorporated to allow a third migration. A potential advantage of using sulfur-based leaving groups might be that stereoselectivity could be controlled, as it can, for example, in reactions of various electrophiles with metalated 1,3-dithiane oxides [16–21]. Such reagents might be able to offer possibilities for the generation of appropriately substituted chiral reagents for reactions with trialkylboranes. However, some basic studies are needed in order to underpin such possibilities.
Assessment of indoor levels of volatile organic compounds and carbon dioxide in schools in Kuwait
Published in Journal of the Air & Waste Management Association, 2018
Between both the roofs in the two schools (Figure 9a), the highest monthly average TVOC concentration was 397 ppb in ABZ school in February 2011. The halogenated functional group represented 49% of the TVOCs (Figure 9b); the primary constituent was chlorodifluoromethane (R22), which had dispersed from the seeped refrigerant of nearby mounted condensers of HVAC systems. The condensers were fixed either outside in the yard or on the roof in harsh corrosive environment, causing refrigerant to leak from the AC assembly. The daily maximum concentration of R22 was 109 ppb on 9 February 2011. The overall monthly average TVOC concentrations ranged between 71 and 397 ppb on the roofs in both schools. The detailed VOC sources have been listed in Arcus-Arth et al. (2009), assuring alcoholic compounds in painting room as in this research. Al-Mudhaf et al. (2013) and Al-Dabbous et al. (2013) have reported indoor prevalent pollutant ethanol similar to indoor VOC pollutant ethanol.
Energo- and exergo-technical assessment of ground-source heat pump systems for geothermal energy production from underground mines
Published in Environmental Technology, 2019
Leyla Amiri, Edris Madadian, Ferri P. Hassani
The integrated system comprises a closed-loop geothermal system along with a heat pump. In the former case, the purpose is to employ the trapped heat in underground in order to raise the temperature of the working fluid in the loop. In the latter case, a heat recovery unit is following the main heating system which is useful for large-scale sectors. The quality of heat pump is characterized by an index called COP which defines the ratio between thermal power of heat pump ( in Watt) and drive power of heat pump ( in Watt). COP is an index which indicates the relationship between the gained energy from geothermal source and the required work for fulfilling the heat transfer process. A heat pump’s COP is defined as follow:Considering efficiency of a heat engine (denoted by ε) defined as the power required to drive the engine over the thermal heat power, i.e. , COP which is an inverse of the efficiency function is regarded as a significant factor in the calculations. Therefore, the efficiency of heat pumps must be less than unity, and inversely, the pump’s COP index is expected to be greater than unity. In other words, the amount of heat energy transfer in a heat pump is greater than its required power (). In fact, transcendent levels of heat pump’s COP can occur due to the small difference between the inlet and outlet temperature. A detailed illustration of the heat pump system is shown in Figure 1. An efficient geothermal cooling/heating system necessitates employment of a working fluid with a fairly high critical temperature, in order to transfer higher amounts of heat from the closed-loop system to the desired end-users. In the present analysis, Chlorodifluoromethane (R22) is used as the refrigerant in the water-to-water geothermal heating/cooling system. The water-to-water geothermal heat pump receives the geothermal energy from the water (or antifreeze fluid) circulated in the geothermal loop and delivers it to the working fluid of the heating system. The efficiency of the water-to-water geothermal systems has been exceedingly improved within the past few decades. Hence, we chose such system in the light of recent growth in popularity of hydronic heating/cooling systems, in particular in residential, commercial and large-scale industrial sectors.