Refrigeration – Processes – Defrosting or frost inhibiting
Reexamination Certificate
2001-12-04
2003-04-01
Esquivel, Denise L. (Department: 3744)
Refrigeration
Processes
Defrosting or frost inhibiting
C062S325000
Reexamination Certificate
active
06539728
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a hybrid heat pump system and, more particularly, to a heat pump system that utilizes a combination of a conventional heat pump and a membrane permeator flow device for conditioning gas, preferably air, within an either enclosed or open space before the gas is treated by the heat pump.
2. Description of the Prior Art
Humidity has an effect upon a building. As humidity increases, so does the presence of bacteria, mold and mildew. Therefore, having an ability to control humidity and lower its level will contribute to an elimination of microorganism propagating environments. For example, refrigeration air conditioner systems in humid environments are often inadequate with respect to acceptable humidity control, with or without refrigeration incorporated therein. In wet or damp environments refrigeration air conditioner systems utilizing refrigerant cooled air coils are often overtaxed and their efficiency adversely affected. Humidity control becomes an important factor, not only as related to human comfort, health and structural deterioration, etc., but also as to adequacy of dehumidification and its efficient application.
A heat pump is a system that utilizes a thermodynamic process for taking thermal energy from a low temperature heat source and releasing it at higher temperature utilizing an input of energy from another source. A significant problem with heat pumps is that under certain circumstances an outdoor coil will, during a heating mode of operation, have frost accumulate thereon. Efficient operation of the system requires that sufficient heat be transferred from air flowing through an outdoor heat exchanger to maintain adequate capacity to meet a heating demand in a comfort zone. If the outdoor ambient air temperature is less than approximately 32° F., frost and ice may accumulate on the heat exchanger, blocking air flow therethrough to such an extent that its capacity for heat transfer is reduced below that required to meet the heating demand in the comfort zone. As the frost thickness increases, the overall efficiency of the system decreases dramatically, and energy is wasted. Accordingly, many schemes have heretofore been proposed for detecting the frost and for taking corrective action for removing the frost from the outdoor coil. Examples of prior art systems include U.S. Pat. Nos. 3,170,304, 3,170,305, 3,400,553, 4,373,349, 4,102,389, 4,209,994, 4,406,133 and 5,507,154.
Two significant factors that determine a rate of accumulation of frost on an outdoor coil during the system-heating mode are relative humidity and temperature of the outdoor air. Some prior art systems have attempted to solve the defrost problem by programming a fixed length of time of running a compressor before initiation of a defrost mode of operation based on an assumed value of outdoor air temperature. It has been a common practice to activate a reversing valve and remove heat from the system, “dumping” the heat into the outdoor coil to melt the ice. The equipment has usually been left in this defrost mode until the coil temperature reached 75° F. This causes a serious waste of energy. Also, the defrost action is frequently accomplished by reversing the main system to a “cooling” mode. This causes relatively hot refrigerant to be directed to the outdoor coil to melt the accumulated frost. However, this also causes cooling of the controlled building which is in turn typically offset by a use of high cost, lower-efficiency, electric resistance heating. Again, energy is wasted.
The accumulation of frost on evaporator coils of either a home or commercial refrigerator has been recognized as a problem for many years. To overcome the problem, defrost systems have been developed, some of which have been commercially successful. Examples of prior art systems include U.S. Pat. Nos. 3,084,520, 3,126,716, 3,499,295, 4,122,687, 5,406,805 and 5,867,994. Solutions suggested in these patents include additional heating, a dual evaporator or changes in air circulation.
The addition of heat to the system thus utilizes energy to melt ice on the coils and energy to cool the refrigerator to the extent of heat added by the heating coils. Thus, there is a substantial increase in energy requirements in the defrost step and in the subsequent cooling step, as a result of using heating for defrosting the evaporator coils.
Systems with two evaporator coils alternately cool the air passing therethrough. Such systems require complex valving for the refrigeration fluid and add some heat from the refrigeration fluid to the defrost coils.
In a system that change air circulation, a refrigeration unit has a defrost system that defrosts the evaporator coil by passing warmer air across the evaporator coil to heat the defrosting air. Although such a system offers an improvement, it still consumes additional energy.
Desiccation is a process of removing vapor of one or more liquids out of a gas containing the vapor, resulting in vapor depleted or dry gas. Usually this is done by adsorption material such as zeolites or silica gel. However it can be done by absorption, for example, absorption of water vapor by sulfuric acid.
To overcome the moisture problem in refrigeration, several inventors have suggested hybridization of a heat pump with a desiccation system. U.S. Pat. No. 4,941,324 describes a hybrid air conditioning system that simultaneously dehumidifies and cools air using standard vapor-compression equipment and aqueous solutions of liquid desiccant. U.S. Pat. Nos. 4,700,550, 5,517,828, 5,551,245 and 5,816,065 describe hybrid air pump systems that combine solid desiccation systems mostly in the form of a rotatable moisture transfer wheel with desiccant material, and a rotatable heat exchange wheel with heat pumps that include an evaporator, compressor, condenser and metering device operatively coupled by a refrigerant circulating line for evaporation of refrigerant and transfer of heat to the refrigerant.
Using desiccant systems for removing moister from the processed gas or air is subject to several limitations. The process of dehumidification with desiccant adds heat to a column of air being treated, it being desirable to remove this heat before it reaches the refrigeration cooling coil. The process of dehumidifying with desiccant requires the regeneration or strengthening of a weakened moisture laden desiccant. This process requires an application of heat to the desiccant material and requires either alternating desiccation regeneration cycles or use of a mechanically cumbersome desiccant wheel.
A membrane is a semi permeable barrier capable of selectively permeating certain constituents our of fluid mixture. A membrane permeator is a self contained assembly of membrane packaging, including all required housings and piping components, capable of rendering perm selective separation of a fluid mixture.
A membrane separation method for removing water vapor in gases is a method in which a gas containing water vapor is contacted to one side of a vapor permselective membrane assembly, and a dry gas is contacted to the other side of the membrane. The water vapor is selectively permeated and separated through the membrane. In principle, it has merits over other methods such that running cost is low, the structure of the apparatus is simple, and dry air can continuously be obtained without polluting the air.
As a vapor permselective membrane for permeability of water vapor, an ion exchange membrane as well as a dehumidifying method using such membrane have been proposed by U.S. Pat. Nos. 3,735,558 and 4,909,810. Hollow fiber membrane-based dehydration is also known. See, for example, U.S. Pat. Nos. 4,783,201, 4,725,359, 4,718,921, 4,497,640, 4,583,996 and 3,511,031. U.S. Pat. No. 4,900,626 discloses a hollow composite fiber for dehydration having a polydimethylsiloxane coating on a dense layer of the fiber support.
Although membranes have been used in various separation applications, their use for heat pump systems has been limited. U.S. Pat. Nos
Esquivel Denise L.
Jones Melvin
Ohlandt Greeley Ruggiero & Perle LLP
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