Method for detecting changes in a first media flow of a heat or cooling medium in a refrigeration system

• US 7,685,830 B2
• Filed: 04/12/2003
• Issued: 03/30/2010
• Est. Priority Date: 04/22/2002
• Status: Expired due to Fees

• Current Assignee: Danfoss A/S
• Original Assignee: Danfoss A/S
• Inventors: Izadi-Zamanabad, Roozbeh, Thybo, Claus, Rasmussen, Bjarne Dindler
• Primary Examiner(s): Jiang; Chen-Wen
• Application Number:
  US10/512,210
• Publication Number:
  US 20050172647A1
• Time in Patent Office: 2,544 Days
• Field of Search: 621/51, 621/78, 621/80, 622/72, 165/244, 165/246
• US Class Current: 62/126
• CPC Class Codes: F25B 2500/19 Calculation of parameters
• CPC Class Codes: F25B 2700/1352 at the inlet
• CPC Class Codes: F25B 2700/195 of the condenser
• CPC Class Codes: F25B 2700/197 of the evaporator
• CPC Class Codes: F25B 2700/21163 of the refrigerant at the outlet of the condenser
• CPC Class Codes: F25B 2700/21172 at the inlet
• CPC Class Codes: F25B 2700/21173 at the outlet
• CPC Class Codes: F25B 2700/21175 of the refrigerant at the outlet of the evaporator
• CPC Class Codes: F25D 2500/04 Calculation of parameters
• CPC Class Codes: F25D 29/008 Alarm devices

Abstract

The invention concerns a method for detecting changes in a first flow of a heating or cooling medium in a refrigeration system whereby the first flow is conveyed through a heat exchanger wherein occurs heat transfer from the first flow to a second flow of a heating or cooling medium. The earliest possible detection of the changes is desired. For this it is provided that for the supervision of the first media flow moving through the heat exchanger a change in the enthalpy of the second media stream or a value derived therefrom is determined.

Claims

1. A method for correcting a first media flow of a heat or coldness transport medium in a refrigeration system, the method comprising the steps of:

causing the first media flow to move through a heat exchanger in which a heat transfer between the first media flow and a second media flow of a heating or cooling agent occurs;

determining the second media flow as a linear function proportional to a pressure differential across and the opening degree of an expansion valve;

determining the change in the enthalpy of the second media flow or a value derived therefrom;

determining a change in the first media flow from the change in the enthalpy of the second media flow or from the value derived therefrom; and

correcting the first media flow flowing through the heat exchanger, based on the determined change in the first media flow.

2. The method according to claim 1, wherein for the determination of the change in the enthalpy of the second media flow, a specific enthalpy differential of the second media flow across the heat exchanger is determined.

3. The method according to claim 2, wherein for the determination of the specific enthalpy change of the second media flow, at the input of the expansion valve the temperature and the pressure of the second media flow is determined and the temperature of the second media flow at the output of the heat exchanger and either the pressure at the output of the heat exchanger or the boiling temperature of the second media flow at the input of the heat exchanger are determined.

4. The method according to claim 2, wherein for the determination of the specific enthalpy change of the second media flow, the pressure of the second media flow at the input of the expansion valve is determined and the temperature of the second media flow at the output of the heat exchanger and either the pressure at the output of the heat exchanger or the boiling temperature of the second media flow at the input of the heat exchanger are determined.

5. The method according to claim 4, wherein the first media flow is determined from the second media flow and a ratio of the specific enthalpy change of the second media flow and the specific enthalpy change of the first media flow across the heat exchanger.

6. The method according to claim 4, wherein the first media flow is compared with a desired value.

7. The method according to claim 4, wherein a residual is formed as the difference between a first value, which is formed from a first pregiven mass flow of the first media flow and the specific enthalpy change of the first media flow, and a second value which corresponds to the change in the enthalpy of the second media flow, and determining the change in the first media flow includes monitoring the residual.

8. The method according to claim 7, wherein for the pregiven mass flow of the first media flow one uses an average value over a predetermined time interval.

9. The method according to claim 1, wherein a specific enthalpy change of the first media flow across the heat exchanger is determined.

10. The method according to claim 1, wherein correcting the first media flow includes the introduction of a thawing process.

11. A method for correcting a first media flow of a heat or coldness transport medium in a refrigeration system, the method comprising the steps of:

causing the first media flow to move through a heat exchanger in which a heat transfer between the first media flow and a second media flow of a heating or cooling agent occurs;

determining the second media flow from a pressure differential across and the opening degree of an expansion valve;

determining the change in the enthalpy of the second media flow or a value derived therefrom;

determining a change in the first media flow from the change in the enthalpy of the second media flow or from the value derived therefrom; and

correcting the first media flow flowing through the heat exchanger, based on the determined change in the first media flow,

wherein a residual is formed as the difference between a first value, which is formed from a first pregiven mass flow of the first media flow and the specific enthalpy change of the first media flow, and a second value which corresponds to the change in the enthalpy of the second media flow, and wherein a fault indicator S_i is formed according to the following rule;

$S_i=\{\begin{array}{c}{S}_{i-1}+s_i,\mathrm{if}<br><br><br><br>S_{i-1}+s_i><br><br>0\\ 0,\mathrm{if}<br><br><br><br>S_{i-1}+s_i\le <br><br>0\end{array}<br><br><br><br>\mathrm{with}<br><br><br><br>s_i=k_1<br><br>\left(r_i-\frac{{\mathrm{\mu <br><br>}}_0+{\mathrm{\mu <br><br>}}_1}{2}\right)$

where

r_i;

residual

k_i;

proportionality constant

μ

₀;

first reliability value

μ

₁;

second reliability value,

such that the first media flow is corrected based on the fault indicator exceeding a predetermined value.

12. A computer-implemented method for detecting changes in a flow of air in a refrigeration system, the method comprising the steps of:

causing the flow of air to move through a heat exchanger in which a heat transfer between the air and a flow of refrigerant occurs;

determining the flow of refrigerant as a linear function of a pressure differential across an expansion valve and the degree or period of opening of the expansion valve;

determining a change in the enthalpy of the flow of refrigerant or a value derived therefrom; and

determining a change in the flow of air flowing through the heat exchanger from the change in the enthalpy of the flow of refrigerant or from the value derived therefrom,

wherein for the determination of the change in the enthalpy of the refrigerant, the pressure of the refrigerant at the input of an expansion valve is determined and the temperature of the refrigerant at the output of the heat exchanger and either the pressure at the output of the heat exchanger or the boiling temperature of the refrigerant at the input of the heat exchanger are determined.

13. The method according to claim 12, comprising the additional step of:

initiating a thawing process if a predetermined change is determined in the flow of air.

14. A method for detecting and correcting changes in a flow of air in a refrigeration system, the method comprising the steps of:

causing the flow of air to move through a heat exchanger in which a heat transfer between the flow of air and a flow of refrigerant occurs;

determining a change in the specific enthalpy of the flow of refrigerant;

determining a rate of the flow of refrigerant from an opening degree of an expansion valve and a pressure differential across the expansion valve;

calculating a residual as the difference between a first value, which is calculated from a desired rate of the flow of air and a measured change across the heat exchanger of the specific enthalpy of the flow of air, and a second value which is calculated from the change in the specific enthalpy of the flow of refrigerant and the rate of the flow of refrigerant;

forming a fault indicator Si according to the following rule;

$S_i=\{\begin{array}{c}{S}_{i-1}+s_i,\mathrm{if}<br><br><br><br>S_{i-1}+s_i><br><br>0\\ 0,\mathrm{if}<br><br><br><br>S_{i-1}+s_i\le <br><br>0\end{array}<br><br><br><br>\mathrm{with}<br><br><br><br>s_i=k_1<br><br>\left(r_i-\frac{{\mathrm{\mu <br><br>}}_0+{\mathrm{\mu <br><br>}}_1}{2}\right)$

where

r_i;

residual

k_i;

proportionality constant

μ

₀;

first reliability value

μ

₁;

second reliability value; and

initiating a thawing process when S_i exceeds a predetermined value.