Patent Publication Number: US-6670584-B1

Title: Spa electric heater system using multiple spa heaters

Description:
BACKGROUND OF THE INVENTION 
     The field of the invention is spa controllers and the invention relates more particularly to the control of heaters for spas. Most electrically heated spas are equipped with an electric heating element that is nominally rated at 6 kw, at 240 volts. This same heater is rated at 1.5 kw at 120 volts. A typical spa installation operating at 240 volts requires a 50 amp service to provide enough current to operate the heater and the water and air pumps in the spa. The following table summarizes the current consumption in a typical spa with a heater, a dual speed water pump and an air blower: 
     
       
         
           
               
            
               
                   
               
               
                 Current Draw Amps 
               
            
           
           
               
               
               
            
               
                   
                 Low Range 
                 High Range 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Heater 
                 22 
                 25 
               
               
                   
                 Low pump 
                 2 
                 3 
               
               
                   
                 High pump 
                 6 
                 15 
               
               
                   
                 Air Blower 
                 5 
                 8 
               
               
                   
                   
               
            
           
         
       
     
     Innovations in the spa industry have made it necessary to add a second and even a third water pump. Such additions require more current and, in order to stay within the limitations of the available current, it has become necessary for the spa heater to be turned off when the pumps are operating. With the heater turned off, the spa cools down and a user must turn off one or more pumps in order for the spa to reheat again. 
     In order to stay within the available current limitations, because of the limitations of the driving relays, some spas may be equipped with heaters that have lower wattage ratings. 4 kw and even 3 kw heaters are not uncommon in the spa industry. For larger or commercial institutions, an 11 kw heater is often used. This heater requires at least a 50 amp supply service just for operating the heater alone. 
     Modern spas typically utilize electronic controls. One such control system is shown in U.S. Pat. No. 5,361,215. Such systems, however, typically turn off the single spa heater when there is insufficient supply service. Alternatively, low kilowatt rated heaters are used which slow the initial heating of the spa. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a spa heating system which permits faster initial heating of the spa, as well as faster heat recovery under use, especially in colder weather. 
     It is another object of the present invention to provide a spa control system which permits heating while the spa is being used without the need for higher available current with its concomitant requirement for larger supply wire size and increase of power service to the residence. 
     The present invention is for a process for electrically heating a spa having electrically operated devices connected thereto, such as one or more water and/or air pumps, lights, and at least two heaters in an environment in which there is sufficient current available to operate all spa devices simultaneously. The process includes the steps of providing a control system with data as to which devices are connected to the spa and how much current each device requires, as well as the amount of current available to the spa. Next, the amount of current being used by devices other than the two heaters is calculated and subtracted from the available current to provide the value of residual current. If the spa water is in need of heating, a determination is made as to whether there is enough current available to operate one heater or both heaters, and the control system activates one or both heaters, based upon the results of this calculation. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a flow chart of the spa control system of the present invention. 
     FIG. 2 is a flow chart of the steps used to calculate total consumed current, based on the activated devices in the system. 
     FIG. 3 is a flow chart of the routine to calculate total consumed current. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Residences are typically not wired with the installation of a spa in mind. Most spas are purchased for use in established residences, where the typical service panel is rated at 200 amps. If the spa is plugged into an electrical outlet, the maximum amperage is 20 amps, and only 80% of this is available. Spas which are directly hot wired to the panel are limited by the service panel and if wired at 240 volts, a 50 amp service is used to provide enough current to operate the heater and the water and air pumps. As show above, 50 amps is not sufficient to operate many heaters with the high pump and air blower operating. As the result, most spa controllers turn the heater off when the high pumps and air blowers are operating so that the system limits are not exceeded. Alternatively, low wattage heaters are used which require a long time to reach the initial desired temperature. Also, particularly in cold climates, the spa cools down during use when the heater is not turned on. 
     The present invention eliminates these problems by providing two independently controlled heaters and providing a control system which is capable of operating just one heater when the other devices utilize too much current to operate both heaters. For instance, a 3 kw heater and an independently operated 6 kw heater may be both installed in a spa and operated under the control of a micro-processor which is programmed with data as to which devices are connected to the spa and how much current each device requires. The micro-processor is also programmed with how much current is available to the spa. During operation of the spa, a routine is run to determine which devices are being used, adding the amount of current used by these devices, and calculating a value of residual current. Then, depending upon the value of residual current, either one or both heaters are activated. The micro-processor can receive data from the spa user as to the amount of current used by all of the devices and by the spa assembly. 
     A preferred routine is shown in FIG. 1 of the drawings. When the spa is initially turned on at the start, both heaters are deactivated as shown at reference character  11 . The desired temperature of the spa is entered by the user and the actual temperature of the spa water is determined by a temperature sensor in the spa water. If the desired temperature is above the actual temperature, a determination is made at  12  as to whether or not heat is needed. If heat is needed, a calculation is made as to the amount of current being consumed by box  13 . 
     One system which makes such calculation is shown in FIG.  2 . This program is initiated at  14  where the value for consumed amps is set at 0, count is set at 5, and the device table contains the five devices connected to the spa, each set to a different pointer number. As shown in step  16 , the program determines whether pointer number  5  (for instance, pump number  1 ) is active. If it is, the programmed number of amps utilized by pump number  1  is set to equal the consumed number of amps, as shown at  17 , and the count is reduced from 5 to 4, as shown at  18 . Since the count is not 0, the routine returns to step number  16 , which determines whether device number  4  is active. If so, the preprogrammed amount of current utilized by device number  4  is added to the value previously calculated for consumed amps at  17  and the count is reduced from 4 to 3. At this point, since the count is not 0, the program returns to step  16  where the next device is queried. This loop continues until the count is 0, at which point the consumed current is ascertained. 
     Returning to step  20  in FIG. 1, the residual amps are calculated by subtracting the consumed amps from the preprogrammed system amps. It should be noted that the system amps for a 20 amp system is 16 amps, and thus, system amps does not mean the total amps of the system, but the amps actually available to the system. 
     Next, as shown at  21 , a determination is made whether the residual amps calculated at  20  is greater than the amps required for heater number  1 . If it is not, the program questions whether the residual amps are sufficient to operate heater number  2 , as shown at  22 . If it is not, then heater number  2  is not activated. If any of the devices are turned on or off, the calculation of FIG. 2 is repeated, as is the flow chart of FIG.  1 . If the residual amps are greater than that required by heater number  1 , heater number  1  is activated, as shown at  23 , and a second calculation is made by reducing the residual amps by the amount of amps used by heater number  1 , as shown at  24 , then the decision at box  22  is again made, and if there is sufficient residual amps, heater number  2  is activated, as shown at  23 , or if not, heater number  2  is not activated. 
     It is preferable that heater number  1  and heater number  2  utilize different amperage, although this is not essential. Preferably, heater number  1  would use 6 kw and heater number  2  would use 3 kw. Thus, the larger heater is initially turned on if possible, and if this is not possible, the smaller heater only is turned on. Conversely, if there is sufficient amps, both heaters are turned on. 
     In this way, the initial startup heating time is reduced and the heater is operated while the spa is being used. Because of this, it is often unnecessary to provide higher available current to a spa, since it can be carried out under conditions which heretofore would have caused the heater to be turned off. 
     While two heaters are discussed above, it is, of course, possible that three heaters could be used to provide even more fine tuning of the heating process, although two heaters are preferred. 
     The present embodiments of this invention are thus to be considered in all respects as illustrative and not restrictive; the scope of the invention being indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.