Stratification storage water heater

Abstract

Disclosed is a storage water heating system with a heating apparatus external to the storage tank. The external apparatus receives a liquid coming from a lower portion of the tank, heats it, and delivers it to a top portion of the tank, where the hot water outlet is located. In this way, the natural thermocline of temperatures in the storage is maintained, the water delivered is at a greater temperature, efficiency is increased by reducing heat standing losses, and there is greater control over the quantity of energy stored. The external apparatus may be activated in response to a heating demand for the storage or for outlet water, or even in response to a power surplus from photovoltaic equipment and in the absence of withdrawal. A control system may modulate the power of the instantaneous water heater to track the surplus power of the photovoltaic system.

1 . A heating system connected to an electricity grid, the heating system comprising: a storage tank for a liquid, a heating apparatus, a control unit, hydraulic connections, and recirculation devices the storage tank being a tank for a liquid, the lower portion of which is configured to be connected to an inlet connection of a liquid distribution network, and an upper portion of which is configured to be connected to an outlet connection to a liquid delivery point,
 the heating apparatus comprising at least:
 a piping connection arranged between a first end called an inlet and a second end called an outlet, 
 a heating element in a heat exchange relationship with the piping connection, the hydraulic connections include: 
 a lower hydraulic connection between a lower portion of the storage tank and the inlet, 
 an upper hydraulic connection between an upper portion of the storage tank, 
   and the outlet,   the recirculation devices are arranged to convey the liquid through the piping connection,   the control unit is configured for:
 receiving an information about a power supplied into the electricity grid, in a quantity unbalanced versus a power demand and/or about a power produced locally from renewable sources in surplus versus local consumption, and in response to that information, 
 varying the electric power consumption P of the heating element and/or varying a thermostating temperature, from a set temperature T target , to a higher “surplus temperature” T sur , in the case of an available electric power surplus, and to a lower temperature in the case of an available electric power short of demand, 
   the storage tank, the piping connection and the hydraulic connections are arranged to form a hydraulic circuit in which the liquid, under the force of a pressure difference, can be drawn from the lower portion of the storage tank, heated in the piping connection, and sent to the upper hydraulic connection, so that the liquid in the storage tank can be heated with a substantially monotonically increasing temperature gradient from the engagement point of the lower hydraulic connection to the engagement point of the upper hydraulic connection,   so that heating system is configured to store the heat generated in the portion of the water that is substantially likely to be withdrawn first.   
     
     
         2 . Heating system as in  claim 1  wherein the engagement point of the lower hydraulic connection is positioned substantially at the base of the storage tank, and the engagement point of the upper hydraulic connection is positioned substantially at the top of the storage tank. 
     
     
         3 . Heating system as in  claim 1 , which when installed in a facility equipped with electrical power from a local system of renewable energy, is capable of receiving a signal indicative of an amount of a surplus electrical power P sur  received from the local system and fed into the electricity grid and of varying the power P dissipated by the heating element to a value equal to or close to and in any case less than or equal to the surplus power P sur . 
     
     
         4 . Heating system as in  claim 1 , further comprising devices for varying the flow rate m of the liquid through the piping connection. 
     
     
         5 . Heating system as in  claim 4 , configured to vary the flow rate m of the liquid through the piping connection in a manner directly proportional to the power P. 
     
     
         6 . Heating system as in  claim 1 , wherein the recirculation devices are a pump adapted to pump a liquid through the piping connection from the inlet to the outlet and devices for controlling the pump. 
     
     
         7 . Heating system as in  claim 4 , configured for varying the flow rate m of the liquid through the piping connection as a function of the difference between a set temperature T target  and a measured temperature of the liquid T 38  at the outlet end according to the formula: 
       
         
           
             
               m 
               = 
               
                 P 
                 
                   
                     ( 
                     
                       
                         T 
                         
                             
                           target 
                         
                       
                       - 
                       
                         T 
                         
                           3 
                           ⁢ 
                           8 
                         
                       
                     
                     ) 
                   
                   * 
                   c 
                 
               
             
           
         
         or for varying the power P of the heating element according to the formula: 
       
       
         
           
             
               P 
               = 
               
                 m 
                 * 
                 
                   ( 
                   
                     
                       T 
                       
                           
                         target 
                       
                     
                     - 
                     
                       T 
                       
                         3 
                         ⁢ 
                         8 
                       
                     
                   
                   ) 
                 
                 * 
                 
                   c 
                   . 
                 
               
             
           
         
       
     
     
         8 . Heating system as in  claim 1  further configured for activating the heating element according to a temperature demand corresponding to at least one of the following conditions:
 a detection from any outlet temperature sensor, configured to measure the water temperature at the outlet of the heating apparatus, the detection performed after activating the pump; 
 a detection from a lower temperature sensor if present; 
 a detection from one or more temperature sensors located, inside the storage tank if present; 
 the start of a liquid withdrawal; 
 a detection made directly from the storage tank which may be equipped with its own sensors and control system. 
 
     
     
         9 . Heating system as in  claim 1 , further comprising devices for detecting whether a water withdrawal is in progress. 
     
     
         10 . Heating system as in  claim 1 , further comprising devices for regulating or interrupting a flow through the upper branch of the upper hydraulic connection located between the outlet of the storage tank and the connection with the outlet connection. 
     
     
         11 . Heating system as in  claim 1 , wherein the outlet of the piping connection is engaged directly on the outlet connection. 
     
     
         12 . Heating system as in  claim 1  configured to deliver a liquid directly onto the outlet connection at a temperature above the maximum temperature in the storage tank. 
     
     
         13 . Heating system as in  claim 9  configured to detect whether a water withdrawal is in progress from the detection of the temperature change, the temperature measurement performed by a lower temperature sensor or an outlet temperature sensor. 
     
     
         14 . A method of retrofitting a storage tank water heater connected in a lower portion thereof, via a lower hydraulic connection, to an inlet connection to the water supply and in an upper portion thereof, via an upper hydraulic connection, to the outlet connection, the method comprising the following steps:
 obtaining a heating apparatus, as in  claim 1     connecting the inlet via a lower hydraulic connection to the lower portion of the storage tank,   connecting the outlet via an upper hydraulic connection to the upper portion of the storage tank.   
     
     
         15 . Retrofit method in accordance with  claim 14  further comprising the steps:
 connecting the inlet via the lower hydraulic connection to the inlet connection to the water supply of the storage water heater, 
 connecting the outlet via the upper hydraulic connection to the outlet connection of the storage tank water heater.