Patent Application
20110072573
1. Field of the Invention
This invention relates to spa control systems and, more particularity, to methods of monitoring water flow through the heater of a spa.
2. Discussion of Related Art
For several years spa manufactures have been using two or more solid-state sensors to monitor water temperature in the spa as well as temperature somewhere near the heater. One sensor is needed to monitor temperatures at the heater according to the requirements in UL 1563, a standard for electric spas. Another sensor is usually located in the water of the spa to measure the temperature of the spa water.
In conjunction with solid-state sensors, a flow-monitoring device has commonly been used. The spa industry has long used pressure switches in the plumbing as an indication that the circulation pump is running and water is present. This usage of pressure switches has the drawback that certain types of blockage can stop the flow of water but still indicate pressure in the plumbing from the pump.
A better plan has been the usage of flow switches. Many spas being built today employ a flow switch to determine if it is appropriate to activate the heater. Flow switches are somewhat expensive, however, and often unreliable.
U.S. Pat. No. 5,361,215, Tompkins, et al, teaches the use of two temperature sensors to determine water flow thought the heater. One sensor is upstream from the heater while the second sensor is downstream from the heater. A significant difference in temperature between the two sensors is an indication of a flow problem. In all cases, one of the sensors is in the spa water. The other sensor is near the heater. U.S. Pat. No. 6,282,370, Cline, et al, teaches the use of two sensors at separated locations on or within the heater to determine water flow through the heater and also to measure the temperature of the water in the spa. Again, the difference in temperature between the two sensors is used to evaluate the flow of water through the heater.
The Cline approach has several disadvantages. The first problem is that the difference in temperature between the two sensors is very small, even with significant blockage in the plumbing. The Cline approach can be accurate only when the flow is at some minimum level. Another problem is that the spa water temperature is not known when the pump is off. The only solution is to turn on the pump for a short period several times a day in order to measure the water temperature as it passes through the heater and to see if the heater function is needed. Clearly, this approach is not energy friendly.
The present invention teaches the use of a single temperature sensor in the body of the heater to monitor water flow conditions through the heater and to also measure water temperature in the spa.
In a preferred embodiment, a thermistor is placed into a stainless steel closed-end tube and coupled to a microprocessor with wire connections. The tube may be filled with heat conductive epoxy to secure the thermistor in the tube.
The tube is connected to the body of the heater with a compression fitting in a manner that will allow the end of the tube to be close to the heating element inside the heater.
Prior to a flow measurement, the circulation pump is activated for perhaps a minute to bring the temperature inside the heater to approximately the same temperature as the spa water.
As soon as the temperature becomes stable, the pump is turned off and the heater is immediately turned on. After just a brief period of time, the heater is turned back off. Now with both the heater and the pump turned off, the sensor is monitored for heat rise. When a few degrees of heat rise occurs within a short period, say about 30 seconds, it is proven that the sensor is in place and working.
Now, with a working sensor, the circulation pump is turned back on and the sensor is now watched for the effect of the cooling water. If, in a brief period, the sensor returns to a temperature near what it was before the heater was briefly energized, it is proven that flow exists. The heater can now be safely turned on for as long as necessary to bring the spa water up to the desired temperature.
On the other hand, if the flow is inadequate, or there is no water in the heater, the temperature at the sensor will continue to increase for several more degrees.
This proves that there is no flow and the heater, therefore, cannot be turned on for a longer period of time. A flow problem may then be indicated to the user to explain why the heater is not energized. With the pump and heater now running normally, the next task is to watch for a loss of flow of water in the heater. This is accomplished by monitoring the sensor for a high rate of change in temperature whenever the heater is on. An increase of 3-4 degrees Fahrenheit in a period of 30 seconds would be a clear indication that flow, or water, has been lost. If this occurs, the heater will be deactivated immediately and a suitable indication will be provided to the user.
The temperature of the water in the spa will be known by the temperature of the water passing through the heater and over the sensor, as long as the pump is activated. In some cases the pump will not be constantly activated, so the temperature of the spa water is unknown. The Cline patent addresses this problem by turning the pump on several times a day, just to check the water temperature and the possible need for heat.
The present invention solves these problems with artificial intelligence. Each time the pump and heater are activated due to an apparent need for heat, based on the water temperature inside the heater, the pump will run long enough to compare the real water temperature with the previous heater temperature. Any difference will be recorded and applied as an offset to the next activation. New offset errors will recorded with future activations, adapting the process to changes in ambient conditions.
Referring now to
Pump 9 is coupled to microprocessor 1 through circuit means 11, which may include relays, relay drivers, wires, and connectors. Heater 10 is coupled to microprocessor 1 through redundant circuit means 12 and 13.
In operation, sensor 2 measures temperatures inside heater 10, which may, or may not, contain water. The invention can be accomplished with sensor 2 mounted external to the heater housing, or mounted in a dry well arrangement; however, reaction times for problems are shorter if sensor 2 is in close proximity to the heating element of heater 10. This can be accomplished by providing a threaded hole in the heater housing and securing sensor 2 in the hole with a standard compression fitting.
When the temperature measurement of sensor 2 is less than a set temperature maintained by microprocessor 1, microprocessor 1 will cause pump 9 to be energized in preparation for energizing heater 10 when water flow is found to be adequate. Pump 9 will circulate water from the vessel containing water for one or two minutes, or until the rate of temperature change, as seen by sensor 2, is very small. A stabilized temperature measurement will be recorded by microprocessor 1 as the actual water temperature in the spa prior to the flow test.
The first step in the flow test is to turn off, or de-energize, circulation pump 9. The next step is to turn on heater 10, but only for a few seconds. After heater 10 is turned back off, sensor 2 is monitored for a rise in temperature. With no circulation in heater 10, a rise of several degrees is expected within, say 30 seconds. As soon as the desired rise is seen (perhaps 10 degrees), pump 9 is turned back on so that the cooling water can dissipate the recent heat rise within a few seconds. If the flow is good, the temperature at sensor 2 will be back to near the water temperature recorded prior to the brief heater activation. Finally, now that flow has been verified, heater 10 can be turned or a longer period to heat the water to, or beyond, the set temperature.
If, however, the temperature continued to rise after pump 9 was turned on, a flow problem exists and heater 10 must be left off until the problem is resolved. A signal, such as a flashing LED, or a change of color somewhere on a user interface, can be provided to the user to explain why heating is not taking place.
Flow problems can later occur due to blockage or water loss. Sensor 2 must be carefully monitored for a rapid increase in temperature inside the heater, or for an increase in temperature over a longer period of time that is unreasonable and indicative of a dirty filter, for example. Comparing the rise in temperature with the time required to reach that temperature does this. If the rate of change is greater than a prescribed rate, poor flow may be causing the heater to become hotter than the water in the vessel. Heater 10 must be de-energized immediately and another flow test attempted.
As a further improvement over the prior art, a method for preventing short heating cycles is taught in the present invention. With pump 9 not running and only one sensor in the system, the water temperature in the vessel may be different than the water temperature in heater 10, due to the differences in volume and location. If sensor 2 measures a temperature lower than the set temperature, microprocessor 1 will normally turn on pump 9 and heater 10 to reach the set temperature. If the spa water was not as cold as the heater 10 temperature, which caused pump 9 to be turned on, pump 9 will quickly turn back off as soon as the real water temperature is seen by sensor 2.
This problem can be solved through the use of artificial intelligence. Microprocessor 1 can keep a record of the differences between the apparent water temperature in heater 10 and the real water temperature as will be discovered when pump 9 is turned on and run for a minute or two. This difference can now be applied as an offset to the next heater 10 temperature measurement. For example, if the set temperature is 100 degrees, pump 9 will be turned on at perhaps, 99 degrees. Once pump 9 has circulated the spa water through heater 10 it may be seen that it was unnecessary to turn on pump 9 with only one degree of difference, so one degree of offset will be added to the heater temperature before pump 9 is turned on again at 98 degrees. This process will continue until the heater temperature with the offset added closely matches the actual spa water temperature when the pump is first activated in preparation of a heating cycle.
An additional improvement may be made after observing the rate of change in the heater temperature while the pump is off. In the previous example, the offset may be adjusted to a larger number, perhaps five degrees, if the heater is found to be cooling very quickly. This would provide a closer match between the water in the vessel and the user preferred temperature at the time the pump and heater are turned on.
Housing 1 of sensor 11 may be a closed end stainless steel tube of a size that fits into the heater using a standard compression fitting. Thermistor 2 is attached to connector 6 with wires suitable for the purpose. Thermistor 3 is attached to connector 9 with wires 7 and 8.
After thermistors 2 and 3 are placed in housing 1, housing 1 may be filled with a heat conductive epoxy or similar material, as long as the material is not electrically conductive. Connectors 6 and 9 provide electrical coupling to a microprocessor through circuitry means.
Others skilled in the art of spa control design may make changes to what is taught within this invention without departing from the spirit of the invention.
