Refrigeration – Material cooling means including gas-liquid contactor – Gas recirculated relative to enclosure
Patent
1996-04-19
1999-08-03
Ford, John K.
Refrigeration
Material cooling means including gas-liquid contactor
Gas recirculated relative to enclosure
62171, 62DIG22, 62314, 165 54, 165 60, 165 66, 261153, 261157, F25B 2900, F25D 1704, F24F 300, F24F 3147
Patent
active
059310170
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to an arrangement for cooling supply air in an air-conditioning installation, comprising air by means of heat transfer surfaces; and exhaust air side.
Efforts made to reduce the use of freons have compelled the air-conditioning industry to look for alternative cooling systems in place of compressor cooling utilizing freons. The best-known of such systems is the so-called indirect evaporative cooling described e.g. in Finnish Patent Specification 67 259. In this method, exhaust air is humidified by an evaporative humidifier positioned in an exhaust duct, whereby water binds heat as it evaporates so that the temperature of exhaust air drops close to the saturation point. "Coldness" in the cooled exhaust air is recovered into supply air by a heat exchanger presently used widely in the recovery of heat in winter; in other words, supply air is cooled.
A drawback of the system is its limited cooling power. Especially when exhaust air and/or outdoor air is warm and moist, the cooling power is not sufficient. This is due to the fact that moist air is not able to receive any greater amounts of water steam, and so its saturation temperature is high. In addition, evaporative humidifiers are not usually able to humidify air up to the dew point. The humidification ratio has been defined as the mass ratio between the amount of water that in theory can be evaporated into air and the amount of water that actually is evaporated. The humidification ratio of the best evaporative humidifiers ranges between 80 and 90%. In addition to this, the cooling power is reduced by the efficiency of the heat exchanger, which is usually defined as the ratio of the temperature drop of supply air to the difference between the initial temperatures of supply air and exhaust air. This ratio, called temperature efficiency, is between 70 and 80% for the best air/air heat exchangers. As a whole, the ratio between the actually achievable cooling power and the theoretical cooling power usually remains below 70%. Not even the theoretical power would be sufficient in all cases.
Various attempts have been made to compensate for the limited cooling power. The simplest way is to provide the missing power by the use of compressor cooling, which, however, involves considerable investment and operating costs. Even though the use of freons is reduced, it cannot be totally avoided.
Another approach is described in Finnish Patent Specification 88431. Additional cooling is accomplished by the use of cold tap water before the water is passed into the network of water pipes in the building. A drawback of this method is that in many cases the tap water consumption of buildings is so low and varies to such an extent that it is able to meet the need of additional cooling only in a limited number of buildings. Overflowing cooling water into the drain easily raises the operating costs unreasonably. Moreover, an additional piping has to be provided in the building for cold drinking water, which increases the investment costs. For this reason, tap water can be used to cut down load peaks only in some buildings.
Still another approach is described in Finnish Patent Specification 57 478. Instead of using a separate humidifier, air is humidified by allowing humidifying water to run onto the heat transfer surfaces on the delivery side of a plate heat exchanger. In this patent specification, in an attempt to increase power, 2-step cooling is used, where so-called auxiliary air, which may consist of exhaust air or supply air, is first cooled in an auxiliary heat exchanger and then humidified and used for cooling supply air.
Due to its high investment and operating costs, the 2-step cooling has not been used widely. In order that real benefit could be derived, an extra heat exchanger is needed as well as a blower or the like for drawing the auxiliary air flow through the heat exchanger. Air cooling as such will not give the desired result, as the mass ratios vary. It may be used successfully when the amount of exhaust air is
REFERENCES:
patent: 3808832 (1974-05-01), Zusmanovich
patent: 4938035 (1990-07-01), Dinh
patent: 5078208 (1992-01-01), Urch
patent: 5187946 (1993-02-01), Rotenberg et al.
Evaporative Air-Cooling Equipment, Chapter 4, Ashrae Equipment (no date).
"Evaporative Air-Cooling Equipment", 1983 Equipmnt Handbook, Chapter 4, pp. 4.1-4.10.
Kanninen Seppo Kalevi
Leskinen Seppo Juhani
Rolin Ingmar Erik
ABB Installaatiot oy
Ford John K.
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