Refrigeration – Automatic control – Humidity sensor
Reexamination Certificate
2000-01-10
2001-08-07
Tanner, Harry B. (Department: 3744)
Refrigeration
Automatic control
Humidity sensor
C062S176300, C062S201000, C062S185000, C062S229000, C062S228400, C062S228300, C236S04400R
Reexamination Certificate
active
06269650
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to air conditioning improvements.
An object of this invention is to assist in reducing energy required to effect air conditioning while obtaining high performance standards over the full operating range. Environment control by air conditioning means involves more than simply increase or decrease of the total capacity, but rather, dependent on the relative values of latent heat which are to be simultaneously offset in a manner that the lag in the process of mass transfer behind heat transfer does not contribute an energy penalty.
The problem to which this invention is directed is the problem of how to reduce energy required to effect acceptable refrigerant air conditioning for comfort purposes. The system presented here resolves the chaos arising from the contradictory effects of numerous variables in infinite combinations which are involved in refrigerated air conditioning design. Two of these unrelated variables, sensible and latent heat appear in both the room treated air and the outside air introduced for ventilation. Sensible cooling and dehumidification pass through unrelated processes. Heat transfer can occur with only a dry bulb temperature difference between the air and the cooling coil whereas mass transfer will not proceed at all without contact with a cooling surface which is below that of the dew point temperature of the moist air. To put it in terms of the partial pressure of the water vapour in the treated air, dehumidification from the treated air will not proceed until there is a partial pressure difference with the wetted interface of the cooling surface.
PRIOR ART
Closest prior art known to the Applicant are publications of Australian Patents entitled “Method of Air Conditioning” AU-B-49875/79 (597757),
“Air Conditioner and Method of Dehumidifier Control” AU-B-81946/87 (662336), and “Air Conditioning for Humid Climates” AU-B-18873/92.
BRIEF SUMMARY OF THE INVENTION
In one form the invention can be said to reside in an air conditioning system including refrigeration means to effect a highest evaporator temperature for its refrigeration cycle when it treats either directly or indirectly cooling and dehumidifying of air to be conditioned, dry bulb temperature measuring means to measure the temperature of air within a space to be conditioned, humidity measuring means to measure humidity of air within the space to be conditioned, and control means adapted to offset both sensible and latent heat loads of the air at each of the climatic and interior building load conditions over the operating range of the air conditioned system, and control means to establish humidity performance in the treated space at a high end of an acceptable range, and, if a chiller is employed, at the high end of the acceptable coolant coil velocity performance range, where the higher of these two properties reach its set point value, in combination with the sensible heat and latent heat loads being offset by the refrigeration cycle, will be generating the value of an evaporator temperature set point varying to be as high as design condition permits to minimise input energy to the refrigeration compressor and maintain high standard performance conditions compatible with the particular operating condition in the range and on a change of load, will automatically vary the evaporator temperature set point so that it is again compatible with each of all the sensible and latent heat loads occurring over the operating range of the system, the control means employed would at each operating condition in the range determine the specific volume at the saturated suction temperature of the refrigerant leaving the evaporator to establish the higher of the said two constant space humidity or coil coolant velocity set points and then calculate the evaporator set point which in the case of this embodiment drives the variable speed control of the compressor motor.
In an alternative description there is proposed method of capacity control of an air conditioning system including a compressor and evaporator in a refrigeration cycle, heat exchanger means, coolant flow conduits, control equipment including compressor, flow control means, proportional plus integral control output equipment and final control means said method including generating an evaporator pressure/temperature set point for the evaporator to vary so as to be as high as sound engineering principles permit in order to address each of the different operating conditions occurring over a total air conditioning range and not to depart from the high standards of performance governed by the principles of combined heat and mass transfer, fluid flow, energy minimisation and human health and comfort.
In a further alternative description there is proposed a refrigerant air conditioning arrangement of a type including refrigeration means to provide a cooling evaporator either directly for air to be conditioned or indirectly for the air to be conditioned through a chiller, dry bulb temperature measuring means to measure the temperature of air within a space being air conditioned, control means connected to the dry bulb temperature measuring means effecting control of the refrigerant flow and/or coolant flow through the area of cooling surface available to the air being cooled, further characterised in that there are included humidity measuring means to measure humidity of air within the space being air conditioned, and further control means to effect a change in the evaporator temperature in response to the treated space humidity measuring means or the coolant velocity through the coolant coils interfacing with the treated air means to maintain a refrigerant evaporator temperature which is as high as sound engineering principles permit in order to address each of the operating internal and external heat and moisture load conditions occurring over a total air conditioning range.
This invention is applicable to both constant air volume and variable air volume refrigerant air conditioning systems, and enables higher efficiencies in such air conditioning systems over that which is currently the case.
This is achieved, by setting control means to vary the value of a high evaporator temperature to be compatible with each operating condition in the range within the bounds of good performance standards including fluid flow, heat and mass transfer principles and energy minimisation as a priority.
In preference the method includes utilising a control system to effect humidity control and coolant velocity control to use set points representing a design space humidity or design coolant velocity through the tubes of the coils, whichever is the greater, with reference to their respective set points. Thereby this control system will establish a highest acceptable evaporator temperature set point for that particular operating condition in the air conditioning range.
In the absence of chillers, when the evaporator interfaces directly with the treated airstream there is only a humidity set point required. However when a humidity of air in the space to be conditioned does not reach its set point, as may be the case during low humid outside air conditions, in lieu of a secondary coolant velocity set point, a minimum speed setting of the compressor determined by the compressor manufacturer can be supplied within a variable speed control device as is employed in the embodiment of this invention or equivalent means to increase the saturated suction temperature/pressure of the evaporator.
In explaining this invention I observe that there is complex incompatibility in relationships between heat and mass transfer, limitations applied to maintain turbulent coolant flow performance at the heat exchangers and the problems arising when a ratio of internal sensible heat loads to internal total heat loads present a design problem. Reducing total heat loads are not necessarily associated with reducing volume flow rate at the suction of the compressor and increasing total heat loads are not necessarily associated with increasing the volume fl
Akerman & Senterfitt
Tanner Harry B.
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