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Mr. Adalberto Charnichart of York International in cooperation with the Alliance to Save Energy
When hotel managers consider ways to lower operation costs, reducing electrical energy consumption should immediately come to mind, particularly, air conditioning. The amount of electricity used for running air conditioning systems constitutes approximately 30% of total costs, perhaps even more if the system is not operating efficiently. Thus, by ensuring that the cooling system is operating efficiently, hotel managers can lower the costs of operation. In addition to saving money, reducing energy consumption in hotels will also benefit the environment by lowering the amount of carbon dioxide emitted into the atmosphere, the principal cause of global warming. It is first essential to understand that any air conditioning project, whether it involves installing or replacing a system, will require the services of an engineering firm to help evaluate the best options available. Window Units The key motivating factor for installing window units is that the initial costs are lower in comparison to a centralized or water-cooled air conditioning system. A water cooled system requires an initial investment approximately 2.2 times greater than that for window units. Window units, however, consume more electricity than a centralized air conditioning system. More precisely, a centralized air system can be adjusted by the hotel management to operate at greater efficiency levels while window units are individually operated by hotel guests to fit their specific comfort levels. Another important advantage of central air conditioning systems is that they can be automated to reduce the levels of energy use. Centralized Air Conditioning System This system, also known as a water cooled system, comprises one or more central units that cool water down to approximately 7°C. The water is then distributed through a line network to individual rooms and public areas. Each unit contains four basic components: the evaporator, condenser, expansion element or valve, and the compressor. The unit absorbs heat generated within the building (hotel) through the evaporator that acts as a heat exchanger with cold water circulating one way and refrigerant flowing in the opposite direction. The water exits the evaporator at approximately 7°C, and returns at 12°C. This temperature differential is due to the absorption produced by the heat exchanger located in the building. Centralized or Water Cooled Air Conditioning System (Chiller)
There are several centralized or water cooled air conditioning systems available (Chillers). The most appropriate choice depends on such factors as the location of the hotel, clean water costs and access, as well as the local electrical utility rates.
The data in Kw/T.R. is based on conditions set by the ARI (American Refrigeration Institute) The I.P.L.V. is an integrated value of the conduct of partial loads Although the Kw/ T can serve as an initial reference, it should not be taken as an absolute since this value is derived from 100% of the equipment's capacity level and is based on design conditions that are considered the most critical. These conditions occur during only 1% of the total time the equipment is in operation throughout the year. Consequently, it is essential to have data that reflects how the equipment operates with partial loads or in conditions that demand less than 100% of its capacity. To illustrate this, an average of Kw/T with partial loads using water cooled units was formulated. The I.L.P.V. is a more appropriate reference, although not considered the best, because it only captures four points within the operational cycle: 100%, 75%, 50% and 25%. Furthermore, it assigns the same weight to each value, and most equipment usually operates at between 50 % and 75% of its capacity. This is why it is so important to prepare specific analysis for each case that addresses the four points already mentioned, as well as developing a profile of the heat exchanger's operations during the year. The principal equipment manufacturers have developed computerized simulation programs that generate data reflecting real-life conditions, including analysis of various equipment alternatives that contain climate-related data, electrical energy costs, etc. The overall results show that, despite some of the considerations mentioned above, water cooled systems are more efficient than air cooled alternatives because the temperatures produced by refrigerant condensation are lower with water than with air. However, if we consider the overall water condensation option, we need to factor in the cost of treating the clean water used as well as the amount of electricity used by the water condensation pumps and the cooling tower ventilators. Contrary to the aforementioned data that reflects the new units, the efficiency levels of older systems tend to be lower because of system deterioration that can result from insufficient levels of maintenance. During the last 15 years, most of the water cooling systems have been of the reciprocating or centrifugal variety. A reciprocating air cooling unit that has been operating for 15 years consumes approximately 1.7 Kw/T. of electricity while a water-cooled centrifugal unit operated for the same number of years uses 0.9 Kw/T. This clearly illustrates the advantages new technologies provide in helping to reduce electricity bills. A quick calculation clearly shows the energy saving potential obtained by switching from an older cooling system to a modern efficient one.
Calculation 1 (Current Cooling System in use) 0.6 X 300 T.R. X 0.90 Kw/T.R. X 0.35 $/Kwh X 365 Days/Year X 24 h/Day = Calculation 2 (New Cooling System) 0.6 X 300 T.R. X 0.60 Kw/T.R. X 0.35 $/Kwh X 365 Days/Year X 24 h/Day = Difference: 165,564 $/Year As these rough initial calculations show, significant savings can be obtained by using a more energy efficient system. A more specific and detailed analysis would provide statistics that would fully justify a decision to replace or update existing equipment. It has become increasingly crucial to focus our attention on patterns of energy consumption particularly due to the current wasteful use of resources, resulting in higher costs for businesses and higher levels of carbon dioxide emissions into the atmosphere. |
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