Cooling charge determination for a local thermal management system
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.
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;
wherein the programmable device is programmed to determine the amount of cooling charge remaining based on a predetermined total cooling charge less an amount of cooling charge used;
wherein the amount of cooling charge used is calculated from a 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; and
wherein the fan flow rate is calculated from an amount of input voltage to the fan.
2. The system of claim 1 , wherein the fan flow rate is recorded over time according to a predetermined schedule.
3. The system of claim 2 , wherein the predetermined schedule is every thirty minutes from when the fan is first powered by the power circuit.
4. The system of claim 3 , 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.
5. 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;
wherein the programmable device is programmed to determine the amount of cooling charge remaining based on a predetermined total cooling charge less an amount of cooling charge used;
wherein the amount of cooling charge used is calculated from a 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; and
wherein the fan flow rate is calculated from an amount of input voltage to the fan.
6. The method of claim 5 , wherein the programmable device records the fan flow rate over time according to a predetermined schedule.
7. The method of claim 6 , wherein the predetermined schedule is every thirty minutes from when the fan is first powered by the power circuit.
8. The method of claim 5 , wherein the cooling device includes a display interconnected to the programmable device and the programmable device displays the amount of cooling charge remaining.