Patent Application
20250237419
The present disclosure relates to a system and method to prevent frost accumulation on components in an HVAC or refrigeration system.
When a standard HVAC or refrigeration system is absorbing heat from a low temperature environment—either an artificially cool space, such as a refrigerated container, or when ambient external temperatures are relatively cool—the surface temperature of a heat exchanger with the HVAC system, such as an evaporator coil, may drop below the ambient dew point of the ambient external air. The dew point is the temperature for a body of air at which the air becomes saturated with water vapors. At temperatures below the dew point of air, moisture from the air will condense as liquid water. This can be problematic in the context of a heat exchanger as the moisture from the air accumulates on the surface of the heat exchanger. When the refrigerant flowing through the heat exchanger is less than 0° C. (32° F.), the heat exchanger itself may drop below the freezing point of water and the condensed moisture may freeze or frost on the surface of the heat exchanger, which in turn lowers the efficiency and effectiveness of the heat exchanger.
Some current models of HVAC and refrigeration systems address this issue by shutting off the heat exchanger (and stopping the flow of refrigerant through the system). However, this method effectively turns off the HVAC and refrigeration system and prevents a user from heating or cooling an enclosed space to a desired temperature.
Therefore, there is a long felt need for a system and method to limit or prevent frost accumulation on the surface of a heat exchanger in an HVAC or refrigeration system without needing to reverse the flow of refrigerant or temporarily shut off the HVAC or refrigeration system.
The present disclosure relates to a system and method to prevent frost accumulation on a heat exchanger in an HVAC or refrigeration system. Generally, the method comprises the steps of (1) identifying a saturated suction temperature; (2) measuring the dew point of air entering the HVAC system; (3) determining whether the saturated suction temperature is below 0° C. (32° F.); (4) determining whether the dew point of the air entering the HVAC system is greater than the saturated suction temperature; (5) recalibrating the saturated suction temperature to equal the entering dew point value or 0° C. (32° F.); and (6) continuing to monitor and the dew point of the air entering the system. These steps are repeated as necessary. In this way, the HVAC or refrigeration system can be constantly monitored to determine an ideal operating temperature of the heat exchange system. The temperature can be controlled to counteract a low dew point by changing the speed of the compressor to raise the temperature of the refrigerant in the system to be above the ambient dew point.
In an embodiment of the present disclosure, the method to prevent accumulation of frost on a heat exchanger in a refrigeration cycle system includes an initial step of measuring a saturated suction temperature of a refrigerant entering the heat exchanger. The next step requires measuring a dew point of an ambient air flowing through the heat exchanger. The next step includes comparing the saturated suction temperature to the dew point of the ambient air. When the saturated suction temperature is less than the dew point of the ambient air and a freezing temperature of water at standard pressure (i.e., at approximately 0° C. or 32° F.), the next step is to recalibrate a mass flow rate of refrigerant in the refrigeration cycle system. The step of recalibrating the mass flow rate of refrigerant includes: instructing a compressor within the refrigeration cycle system to decrease the mass flow rate of refrigerant in order to increase the saturated suction temperature of the refrigerant in the heat exchanger; measuring a change in the saturated suction temperature of the refrigerant; and repeating the instructing and measuring steps until the saturated suction temperature is greater than or equal to at least one of the dew point of the ambient air and the freezing temperature of water.
In an embodiment, the initial step of measuring the saturated suction temperature further comprises the steps of: orienting a pressure sensor upstream of an entrance of the compressor; measuring a saturated suction pressure of the refrigerant flowing into the compressor; and calculating the saturated suction temperature of the refrigerant from the saturated suction pressure of refrigerant.
In an embodiment, prior to measuring the dew point of an ambient air, the method comprises the step of orienting a dew point sensor downstream of the compressor.
In an embodiment, the method further comprises the step of continuously recycling refrigerant fluid throughout the refrigeration cycle system. The refrigeration cycle system comprises an evaporator in fluid connection with the compressor. The evaporator is oriented downstream of the compressor. A pressure sensor is disposed upstream of the compressor to measure the pressure of refrigerant entering the compressor. A dew point sensor is downstream of the compressor to measure the dew point of air flowing through the evaporator.
In an embodiment, the method further comprises the steps of increasing the mass flow rate of refrigerant in the refrigeration cycle system when the saturated suction temperature is greater than one of the dew point of the ambient air and the freezing temperature of water.
In an embodiment, the method further comprises the steps of maintaining the mass flow rate of refrigerant in the refrigeration cycle system when the saturated suction temperature is greater than one of the dew point of the ambient air and the freezing temperature of water.
In an embodiment, the method further comprises the steps of orienting a condenser and expansion valve downstream of the compressor and upstream of an evaporator within the refrigeration cycle system.
Accordingly, it is an object of the disclosure not to encompass within the disclosure any previously known product, process of making the product, method of using the product, or method of treatment such that Applicants reserve the right and hereby disclose a disclaimer of any previously known product, process, or method. It is further noted that the disclosure does not intend to encompass within the scope of the disclosure any product, process, or making of the product or method of using the product, which does not meet the written description and enablement requirements of the USPTO (35 U.S.C. § 112, first paragraph) or the EPO (Article 83 of the EPC), such that Applicants reserve the right and hereby disclose a disclaimer of any previously described product, process of making the product, or method of using the product disclosed herein.
It is noted that in the present disclosure and particularly in the claims and/or paragraphs, terms such as “comprises,” “comprised,” “comprising” and the like can have the meaning attributed to them in U.S. patent law; e.g., they can mean “includes,” “included,” “including,” and the like; and that terms such as “consisting essentially of” and “consists essentially of” have the meaning ascribed to them in U.S. patent law, e.g., they allow for elements not explicitly recited, but exclude elements that are found in the prior art or that affect a basic or novel characteristic of the invention.
These and other embodiments are disclosed or are obvious from and encompassed by the following Brief Description of the Drawings and Detailed Description.
The following detailed description, given by way of example, but not intended to limit the invention solely to the specific embodiments described, may best be understood in conjunction with the accompanying drawings.
When an HVAC or refrigeration system absorbs heat from a relatively low temperature atmospheric source, there is a tendency for the surface temperature of the heat exchanger within the refrigeration system to fall below the dew point of the ambient air drawn into the system. This may cause frost to form on and within the heat exchanger when the heat exchanger surface is less than 0° C. (32° F.) which dramatically decreases the performance of the heat exchanger. Dew point is the temperature at which air can hold no more water. Reducing the temperature below the dew point condenses excess water out of the air.
Therefore, when the surface temperature of the heat exchanger temperature drops below dew point of the ambient air circulating through the heat exchanger, excess water in the air condenses out of the air and accumulates on the surface of the heat exchanger. Because portions of a heat exchanger will be relatively cold, and frequently below the freezing point of water, any condensed moisture along the surface of the heat exchanger may quickly freeze and form frost. Frost accumulation can limit the ability of a heat exchanger to exchange heat between the HVAC/refrigeration system and the ambient environment, thereby requiring more energy to operate the system and an overall reduction in efficiency as well as inefficient defrost cycles when the system is using energy without providing any benefit.
One method to prevent frost accumulation is to raise the temperature of the refrigerant in the system to be above 0° C. (32° F.). This will increase the temperature within the heat exchanger and will limit the production of moisture and frost along the surface of the heat exchanger. One method to increase the temperature of the refrigerant is to regulate the flow rate of the refrigerant throughout the system. The flow rate of refrigerant is modulated via a compressor. When the compressor decreases the flow rate of refrigerant, the pressure of the refrigerant in the evaporator increases, raising the heat exchanger's overall temperature and also making it less likely that the temperature of the surface of the heat exchanger will drop below the ambient dew point. Conversely, when the compressor increases the flow rate of the refrigerant, the pressure of the refrigerant will decrease in the evaporator, decreasing the overall temperature and making it more likely that the surface temperature of the heat exchanger will fall below the ambient dew point.
The method 100 includes the steps of (a) initializing a saturated suction temperature lower limit 102, (b) measuring the dew point of the air entering the system 104, (c) analyzing whether the saturated suction temperature is greater than or less than 0° C. (32° F.) 106, (d) analyzing whether the saturated suction temperature is greater than or less than the dew point of the air entering the system 108, (e) recalibrating the lower limit of the saturated suction temperature to be equivalent to or greater than the dew point of the air entering the system 110 or 0° C. (32° F.), and (f) delaying the system until the mechanical devices catch up 112.
The initializing step 102 allows the controller 212 to determine the baseline temperature of the saturated suction temperature. This data serves as a baseline for recalibrations in response to an increase or decrease in the dew point for the air entering the HVAC system 200. The controller 212 may be used to instruct recalibration of the HVAC system 200 if the saturated suction temperature drops below the dew point of the entering air. The saturated suction temperature, being a proxy for the surface temperature of the heat exchanger within the evaporator 208, and the lower limit, can be modulated as the system 200 operates to be approximately equivalent to the dew point of the air entering the system 200.
The relationship between the pressure and temperature is known to those having skill in the art based on the properties of the refrigerant fluid used in the refrigeration system, such as the BWR equation.
As external air entering the system 200 interacts with the heat exchanger and HVAC system 200, the saturated suction temperature will change. If the saturated suction temperature falls below the freezing point of water 0° C. (32° F.) at standard pressure, the heat exchanger is at risk of frost accumulation, as any water released from the ambient air is likely accumulate along the surface of the heat exchanger (i.e., the evaporator 208) and freeze.
The relationship between flow rate and temperature of a fluid (such as the refrigerant), is known to those of skill.
Increasing the refrigerant 210 flow rate has the opposite effect and decreases the temperature of the refrigerant 210, the saturated suction temperature.
To prevent frost accumulation, The recalibration step 110 is required when the saturated suction temperature drops below the dew point of the ambient air and is below 0° C. (32° F.). During the fifth step 110, the controller 212 instructs the compressor 202 to modulate the mass flow rate of refrigerant 210 within the heat exchanger, reads temperature changes in saturated suction temperature of the refrigerant 210 based on data acquired by the pressure sensor 214, and elevates the lower limit of the saturated suction temperature to a temperature that is greater than or equal to the lesser of the dew point of the ambient air and 0° C. (32° F.).
If the saturated suction temperature is below the freezing point of water and the saturated suction temperature is also below the dew point of the air entering the system 200, the heat exchanger is at risk of frost accumulation. Specifically, under these conditions, the moisture within the ambient air will condense out of the air passing through the heat exchanger and accumulate on the heat exchanger. This accumulated moisture will begin to freeze and form a layer of frost on the heat exchanger. To remedy this risk, the system 200 requires recalibration of the compressor 202.
Recalibration of the mass flow rate of refrigerant 210 can increase the acceptable minimum value of the saturated suction temperature to be at least equal to the dew point of the ambient air entering the system 200. This recalibration can occur at any rate to allow the system to adjust to changing dew points through the period of operation. Preferably, recalibration of mass flow rate of refrigerant 210 to raise the modulate limit temperature occurs continuously to ensure than any change in dew point is reflected in an ideal lower limit temperature.
The mass flow rate of refrigerant is directed by a compressor 202 component of the HVAC/refrigerant system 200. Decreasing the mass flow rate will have the effect of increasing the pressure of refrigerant in the HVAC system's evaporator 208, which will result in a higher overall temperature, including a higher saturated suction temperature. In the preferred embodiment, the mass flow rate is decreased until the lower limit of the saturated suction temperature is greater or equal to at least one of the dew point temperature and freezing temperature of water, 0° C. (32° F.).
In alternative embodiments, where the saturated suction temperature is above either or both of the dew point temperature and freezing temperature of water, and there is no risk of frost accumulation along the surface of the heat exchanger, the controller 212 can be programmed to increase the mass flow rate of refrigerant 210, which reduces the saturated suction temperature.
Generally, the controller 212 will take readings of acquired sensor 214, 218 data several times per second and will be able to immediately send instructions to the system components 200. The delay period is necessary as the system 200 will take time to carry out the instructions provided by the controller 212. For instance, the controller 212 may instruct a compressor 202 to modulate its flow rate, however, it will take anywhere between a few seconds to a few minutes before the controller 212 obtains feedback from the sensor(s) 214, 218 that the instruction was effectively carried out.
The delay may persist for any amount of time as may be required and is preferably as short as possible. This delay can be set manually by the agency commissioning the equipment or determined through various control algorithms. A delay that is too short can cause the system to become unstable, operate outside of its intended limits, and create user discomfort, cause the energy cost to be increased due to inefficient operation, and reduce the equipment's lifetime.
The above identified steps are regularly repeated to ensure the dew point temperature of the incoming air does not fall below the lower limit of the saturated suction temperature or 0° C. (32° F.).
The controller 212 will continue to take readings of the sensor data and continue to issue instructions to the system 200 based on the sensor data. As depicted in
In Region A of
In Region B of
In Region C of
In Region D of
Any of the operating conditions identified in Region A, B, or C are suitable for operation of the heat exchanger according to the method 100. At any of these operating conditions, the controller 212 may be used to increase or decrease the flow rate of refrigerant 210 as desired, so long as the saturated suction temperature is equivalent or greater than at least one of the dew point of the ambient air and the freezing temperature of water.
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made herein without departing from the spirit and scope of the invention as defined in the appended claims. Having thus described in detail preferred embodiments of the present invention, it is to be understood that the invention defined by the above paragraphs is not to be limited to particular details set forth in the above description as many apparent variations thereof are possible without departing from the spirit or scope of the present invention.
This application claims the benefit of and priority to U.S. Provisional Patent Application No. 63/623,293 filed Jan. 21, 2024, the content of which is hereby incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 63623293 | Jan 2024 | US |
