COOLING CHARGE DETERMINATION FOR A LOCAL THERMAL MANAGEMENT SYSTEM

Abstract

A system and method for estimating the state of charge, i.e., the amount of cooling remaining, in a latent heat thermal storage module of a local environmental control system. The local environmental control system stores cooling energy at night by freezing a latent heat phase change material (PCM), and then releasing the stored cooling energy by removing heat from room air flowing through the PCM during the day. Differential temperature sensors are used measure the air temperature drop across the latent thermals storage unit and the fan voltage, which is directly related to fan air flow rate, is sampled. A controller is programmed to determine the charging state from these measurements.

Claims

1. A system for determining remaining cooling charge, comprising: a latent thermal storage unit having a predetermined total cooling charge; a fan positioned to direct a flow of air over the latent thermal storage unit and having a power circuit for driving the fan to produce the flow of air; a first temperature sensor positioned upstream of the latent thermal storage unit relative to the flow of air for providing a first temperature of the flow of air; a second temperature sensor positioned downstream of the latent thermal storage unit relative to the flow of air for providing a second temperature of the flow of air; and a programmable device coupled to the power circuit of the fan, the first temperature sensor, and the second temperature sensor, wherein the programmable device is programmed to determine an amount of cooling charge remaining in the latent thermal storage unit.

2. The system of claim 1, wherein the programmable device is programmed to determine the amount of remaining cooling charge based on an amount of input voltage to the fan and room temperature.

3. The system of claim 2, wherein the programmable device is programmed to determine the amount of cooling charge based a fan flow rate that is calculated from the amount of input voltage to the fan and room temperature.

4. The system of claim 3, wherein the programmable device is programmed to determine the amount of cooling charge remaining based on the fan flow rate and room temperature over time.

5. The system of claim 4, wherein the programmable device is programmed to determine the amount of cooling charge remaining based on the predetermined total cooling charge less an amount of cooling charge used.

6. The system of claim 5, wherein the amount of cooling charge used is calculated from the fan flow rate over time and a temperature differential across the latent thermal storage unit as determined from the first temperature sensor and the second temperature sensor.

7. The system of claim 6, wherein the fan flow rate is recorded over time according to a predetermined schedule.

8. The system of claim 7, wherein the predetermined schedule is every thirty minutes from when the fan is first powered by the power circuit.

9. The system of claim 8, further comprising a display interconnected to the programmable device, wherein the programmable device is programmed to display the amount of cooling charge remaining on the display.

10. A method of monitoring a local environmental control system, comprising the steps of: providing a cooling device having a latent thermal storage unit with a predetermined total cooling charge, a fan that is powered by a power circuit to direct a flow of air over the latent thermal storage unit, first and second temperature sensors providing first and second temperatures upstream and downstream of the latent thermal storage unit, respectively, and a programmable device coupled to the power circuit and the first and second temperature sensors; and using the programmable device to calculate to determine an amount of cooling charge remaining in the latent thermal storage unit.

11. The method of claim 10, wherein the programmable device determines the amount of cooling charge remaining based on an amount of input voltage to the fan and room temperature.

12. The method of claim 11, wherein the programmable device determines the amount of cooling charge based a fan flow rate that is calculated from the amount of input voltage to the fan and room temperature.

13. The method of claim 12, wherein the programmable device determines the amount of cooling charge remaining based on the fan flow rate and room temperature over time.

14. The method of claim 13, wherein the programmable device determines the amount of cooling charge remaining based on the predetermined total cooling charge less an amount of cooling charge used.

15. The method of claim 14, wherein the programmable device calculates the amount of cooling charge used from the fan flow rate over time and a temperature differential across the latent thermal storage unit as determined from the first temperature sensor and the second temperature sensor.

16. The method of claim 15, wherein the programmable device records the fan flow rate over time according to a predetermined schedule.

17. The method of claim 16, wherein the predetermined schedule is every thirty minutes from when the fan is first powered by the power circuit.

18. The method of claim 10, wherein the cooling device includes a display interconnected to the programmable device and the programmable device displays the amount of cooling charge remaining.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)

[0009] The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which:

[0010] FIG. 1 is a schematic of a local environmental control system having a cooling charge determination system according to the present invention;

[0011] FIG. 2 is a graph of air flow rate versus state pressure difference for a local environmental control system according to the present invention; and

[0012] FIG. 3 is graph of fan input voltage versus air flow rate for a local environmental control system according to the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0013] Referring now to the drawings, wherein like reference numerals refer to like parts throughout, there is seen in FIG. 1 a local environmental control system 10 that control the temperature in the near range personal microenvironment that is equipped with a system and method for determining the state of charge of the latent thermal storage unit 12 of a local environmental control system. The present invention measures the temperature differential between the air entering and leaving the thermal storage (using differential thermocouples or thermistors) as well as the speed of the air moving fan, which can be inferred from the fan driving voltage. From this data, the cooling state of the latent thermal storage unit may be determined and displayed for a user.

[0014] System 10 generally includes a fan 14 for directing air over the latent thermal storage unit 12 during cooling operations. A pair of temperature sensors 16 and 18 are positioned upstream and downstream of latent thermal storage unit 12 to measure the temperature of air driven by fan 14 prior to and after the air has been exposed to latent thermal storage unit 12 and, if a charge is remaining, cooled by latent thermal storage unit 12. A programmable device 22, such as microprocessor or microcontroller, is coupled to the circuitry of fan 14 and is programmed to receive the outputs from pair of temperature sensors 16 and 18, and calculate the amount of cooling charge remaining, as described in detail below. Programmable device 22 may additionally comprise a smart phone or computer interconnected to pair of temperature sensors 16 and 18, such as by a wireless connection (e.g., 802.11 network or Bluetooth protocol) that is programmed with an application to perform the cooling charge calculation.

[0015] Measurement of the air temperature drop (T) across latent thermal storage unit 12 and the fan input voltage (V) every half-hour (or any predefined time period) during melting may be used by device 22 to calculate the amount of cooling energy remaining. For example, starting with a fully charged PCM module, T and V.sub.F may be recorded after 30 minutes of start and every hour after that. As the fan flow rate for the type of brushless DC (BLDC) fan motor used in system 10 changes linearly with the input voltage, the input voltage to fan 14 may be sampled by device 22 and used to calculate the air flow rate. Device is further programmed to calculate the amount of energy transferred from latent thermal storage unit 12 based on the air flow rate of fan 14 to latent thermal storage unit 12 and temperature differential across latent thermal storage unit 12 as measured by temperature sensors 16 and 18. As a result, the amount of stored cooling that has been consumed can be estimated and subtracted from the total cooling power of latent thermal storage unit 12 to determine the amount of cooling charge remaining.

[0016] The calculations required to estimate the amount of the stored cooling that have been used, and thus the state of the remaining charge are presented by the set of equations below. This approach assumes that the PCM will be frozen to full capacity prior art to use.

[00001]$Q^{*}\left(t_k\right)=Q_o-Q\left(t_k\right)..Math.Q\left(t_k\right)=\underset{i=1}{\overset{k}{.Math.}}.Math..Math.\stackrel{.}{Q}\left(t_i\right).Math..Math..Math.t;\mathrm{where}.Math..Math..Math..Math.t=1.Math..Math.h..Math.\stackrel{.}{Q}\left(t_i\right)={\left(c_p.Math.\right)}_{\mathrm{air}}.Math.\stackrel{.}{V}\left(t_i\right).Math..Math..Math.T\left(t_i\right)..Math..Math..Math.T\left(t_i\right)=.Math..Math.V_T\left(t_i\right),$

[0017] where .sub.VT is the TC's measured differential voltage.

{dot over (V)}(t.sub.i)=V.sub.F(t.sub.i), [0018] where V.sub.F is the fan's measured input voltage.

[0019] Q* in the above equations represents the state of charge (how much is remaining), c.sub.p is the known specific heat of air, is the known density of air, {dot over (V)} is the air volume flow rate, V is the fan driving voltage, T is the air temperature drop and t is time. It should be recognized that device 22 may be programmed to sample the appropriate sensors and perform these calculations as needed or on a predetermined schedule. As is known in the field, device 22 may be interconnected to a display 24 or screen to provide such information to a user. In addition, device 22 may communicate the determined charging state to a remote host, such as a connected smart device or a central system in a building that is tasked with monitoring multiple local environmental control systems 10. Alternatively, programmable device 22 may comprise a smart device in communication with fan 14 and temperature sensors 16 and 18 and include an application configured to perform the cooling charge calculations.

[0020] As described above, the present invention may be a system, a method, and/or a computer program associated therewith and is described herein with reference to flowcharts and block diagrams of methods and systems. The flowchart and block diagrams illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer programs of the present invention. It should be understood that each element of the controller can be implemented by computer readable program instructions in software, firmware, or dedicated analog or digital circuits. These computer readable program instructions may be implemented on the processor of a general purpose computer, a special purpose computer, or other programmable data processing apparatus to produce a machine that implements a part or all of any of the blocks in the flowcharts and block diagrams. Each block in the flowchart or block diagrams may represent a module, segment, or portion of instructions, which comprises one or more executable instructions for implementing the specified logical functions. It should also be noted that each block of the block diagrams and flowchart illustrations, or combinations of blocks in the block diagrams and flowcharts, can be implemented by special purpose hardware-based systems that perform the specified functions or acts or carry out combinations of special purpose hardware and computer instructions.