Electronic control of a dual-stage water heater in a hot-beverage vending machine

Abstract

Control of temperature of water delivered by a dual-stage water heater having an external boiler with a first heater as first stage and an internal duct (water booster) with a second heater as secondstage. A control loop based on a measured water temperature in the boiler and controls the first heater. A second loop calculate a reference booster water temperature based on the temperature error atthe outlet (difference between a measured outlet water temperature and a reference outlet water temperature) and controls second heater based on error between reference booster water temperature andmeasured booster water temperature. The reference outlet water temperature depends on type of beverage (eg espresso, cappuccino) and includes a temperature profile with different temperature for different sub- beverages (eg coffee, milk). Takes into account physical response times, inertia of heater and anticipate sudden changes of reference water temperature at hot water outlet.

Description

technical field [0001] The present invention relates generally to hot beverage vending machines, and more particularly to the application of hot beverage vending machines for beverages such as coffee-based beverages (e.g., espresso (ES), instant coffee (INST), and / or fresh brew coffee (FB)). Electronic control of the two-stage water heater. Background technique [0002] Hot drinks vending machines are known to be equipped with a single-stage water heater, i.e. with a single water tank and a single water heater placed inside the tank, usually of the resistive type, or with a dual-stage water heater, i.e. with two Water tanks in series (one arranged inside the other) and two water heaters associated with both tanks. [0003] An example of a two-stage water heater is described in DE 3218442 or US 2004 / 0079749. In these examples, the water heater comprises a main tank provided with a first heater operable to heat and maintain water at a first predetermined standby temperature,...

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Problems solved by technology

[0008] ii) low thermal efficiency, which is a result of the high heat loss to the outside due to the relatively high standby temperature and the metallic materials used to construct the tank;

[0009] iii) Little flexibility of use, since even by adjusting the resistance it is impossible to change the temperature of all the water contained in the tank in a relatively short period of time; therefore, vending machines capable of dispensing different hot beverages at different temperatures must usually be equipped with Multiple water heaters, preferably as many as the type of beverage being dispensed

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