Water heater with buffer battery

Abstract

Water heater with buffer battery, characterized by the partial or complete substitution of the heat storage by an electrochemical battery (7) for heating domestic hot water by means of an electric instantaneous water heater (8) and the integration of all modules for control, regulation, monitoring and remote control of the battery, and power supply via grid or PV solar modules and optionally heat recovery from the ambient air by a heat pump in a central control unit (9), wherein, through spatial proximity and thermal conductivity, the waste heat from the battery and power electronics is transferred to the fresh water to be heated. In combination with a heat pump, two storage tanks (1) and (2) are provided, which are alternately charged and discharged, thereby minimizing efficiency losses due to mixing and ensuring stable thermal stratification.A wireless sensor (12) for measuring the water temperature directly at one or each tap (21) improves the precision and comfort of temperature control and minimizes distribution losses.

Description

[0001] The invention relates to a water heater with buffer battery.

[0002] A household is supplied with hot water as needed using electric instantaneous water heaters, gas boilers or by heating and storage in boilers that are decoupled from consumption and heated directly with electricity or via a heat pump or fired directly or via a heat exchanger with a fuel or thermal solar energy.

[0003] Electric instantaneous water heaters are inexpensive and space-saving, but they place a strain on the distribution grid due to their high connected load. Boilers, regardless of the energy source, require a lot of space and incur supply losses due to heat dissipation through insulation and connecting pipes.

[0004] Further exergy losses arise from mixing processes during discharge and especially during heating. These mixing losses reduce the effective storage capacity and, in conjunction with a heat pump, their efficiency by reducing the coefficient of performance.

[0005] Heating with fossil fuels, which is less sensitive in this regard, is only partially sustainable due to CO2 emissions and is becoming increasingly uneconomical with CO2 pricing.

[0006] The object of the invention is therefore to create a water heater that enables a climate-friendly supply of hot water with little space requirement and low network load.

[0007] Due to high demand, electrochemical storage systems are continuously being improved in terms of energy content, performance, and cost-effectiveness and are now competitive with water as a storage medium. They have virtually no downtime losses and are therefore also suitable for bridging long cycles. Unlike hot water, stored electricity can be used universally in households and fed back into the power grid with minimal loss. Electricity can be generated in many households using PV modules without placing a strain on the distribution grid and stored in a battery. Electricity can be drawn from the grid during off-peak periods in a grid-friendly and economical manner and fed back into the grid unused.

[0008] The solar systems, which are popular for this purpose as so-called balcony power plants, are therefore combined with boilers and also with batteries as part of the PV system.

[0009] The goal is to combine the discrete devices into a single unit. Water is heated in an electric instantaneous water heater, which is powered primarily by the battery and only receives a small amount of additional power from one phase of the power grid.

[0010] This saves installation space and cabling. The close proximity of the water heater and battery provides the opportunity to cool the battery and utilize the waste heat. The waste heat from the power electronics can also be transferred to the water, enabling an efficiency of nearly 100%. If all integration options are utilized, the compact storage center combines PV integration, grid-connected inverters, battery chargers and battery management, grid-friendly load shifting, uninterrupted or standalone power supply, and an instantaneous water heater with temperature control and pressure-triggered convenience functions in a single space-saving unit.

[0011] All parameters of this combination are sustainable. Batteries will become even more economical and efficient in the short term, and grid-friendly behavior will become increasingly important with the increase in volatile sources such as solar and wind, and a reward for this is foreseeable.

[0012] Living space, or rather, space, is becoming increasingly valuable. The trend toward tiny houses is an extreme expression of this development.

[0013] PV systems are becoming cheaper and can be used particularly intensively with battery storage.

[0014] One option for using a buffer battery for hot water production is the integration of a heat pump. However, this requires the storage of hot water.

[0015] According to the invention, two separate storage tanks are used, which are alternately charged and discharged. If no charging occurs during discharge, the thermal stratification is maintained as optimally as possible. This allows one storage volume to be withdrawn almost entirely unmixed, while the heat pump regenerates the other, almost completely cooled storage tank with high efficiency. The heat pump heats the selected storage tank via an external heat exchanger with a circulation pump at a low temperature gradient and to a uniform and relatively low temperature of 35°C. The operating temperature of 40 to 50°C is achieved by reheating with an instantaneous water heater during withdrawal. The energy for this is provided by the battery.

[0016] The small temperature variation requires only minimal power. The battery can be supported by the power supply. Operation with battery voltage minimizes the effort required for PWM power control. The low storage temperature minimizes supply losses and provides capacity for cooling the battery and power electronics.

[0017] Switching is performed by a 4-way valve (3). The domestic water from tank (1) can be drawn off via the instantaneous water heater, while tank (2) is connected to the heat pump's refrigerant circuit via a circulation pump (23) and a plate heat exchanger (22).

[0018] The heat pump's evaporator (26) serves to cool the ambient air and is therefore part of an active ventilation system with heat recovery. The air duct contains a replaceable insertable air filter (30) for removing dust and pollen and a UV-C light source (28) for hygienic disinfection.

[0019] The air is guided by a radial fan through filters and heat exchangers and is optionally sucked in from the outside via a switchable 4-way distributor (31), dehumidified, filtered and cooled and fed into the interior, or extracted from the inside, deheated and discharged to the outside.

[0020] The connection to the outside is made through a wall opening, the distribution in the building can be made centrally via open doors or through ducts.

[0021] The distribution in the rooms depends on the decentralized supply or exhaust air flow.

[0022] All functions of the storage and ventilation system are coordinated by a (9) system. PV integration, grid feed-in, grid-friendly load shifting, battery management, boiler management, instantaneous water heater with safety monitoring and comfort functions, as well as, if necessary, control of the heat pump and ventilation functions.

[0023] The installation space of the system is smaller than that of a conventional domestic hot water heat pump.

[0024] Due to the low mixing losses, the swappable storage units have a smaller total volume than a single tank, and can be further reduced in size thanks to reheating from the battery storage. This saves 50% of the storage volume, which is only partially required for the additional components.

[0025] The optimal operation of the heat pump with a low temperature in the condenser and a high temperature in the evaporator through heat recovery ensures maximum efficiency of the overall system. Since the battery only has to provide a small temperature increase, its capacity can be relatively small, but can be expanded if necessary to achieve a high solar contribution to household electricity.

[0026] The compact energy and ventilation center is particularly suited to the needs of small living spaces such as apartments, residential containers and tiny houses.

[0027] For 70% of a typical hot water requirement of 1000 kWh for two people, covered by the heat pump with a coefficient of performance of 3, a compressor power output of just 60W is required over 4000 operating hours, comparable to that of a refrigerator. This guarantees full utilization of the waste heat. However, for a cooling load exceeding heat recovery, an additional air conditioning system in recirculation mode may be required. Even if heat from losses in the electric drives is retained in the system, high efficiency of the pumps and fans is essential. BLDC motors, which are powered by battery voltage, are particularly well suited to this. The electrical power for the compressor, circulation pump, and fan can therefore be less than 100W. This corresponds to an electricity requirement of 400 kWh / a for heat recovery. In addition, there is a turnover of 300 kWh / a in the battery for reheating.

[0028] The solar coverage of the total of 700 kWh with a PV output of 600Wp will be approximately 50%.

[0029] Electricity costs for 350kWh of grid power benefit predominantly from the off-peak tariff and will currently amount to approximately €100 / year, which will be further reduced by the PV coverage of general electricity consumption of a similar magnitude.

[0030] For comparison: it would cost around €400 if heated directly using mains electricity.

[0031] Fig. 1 shows an instantaneous water heater with buffer battery according to the invention.

[0032] Cold water enters an outer pipe (1.1) at the bottom (c), flows upwards within it, and is diverted at the end into a concentric inner pipe (1.2). It flows around an electric heating element (8) and passes a pressure and temperature sensor (5) upon exiting (h) at the bottom from the connection fitting 6). The outer pipe (1.1) is encased in a heat-conducting extruded profile (10), into which batteries (7) with good thermal conductivity are embedded around the circumference. The heat lost from the batteries during high current loads is thus reliably and efficiently dissipated to the water preheated in the countercurrent. The batteries therefore always operate under optimal thermal conditions.

[0033] A safety temperature monitor (4) is positioned in the center of the instantaneous water heater and, together with the heating element (8), is directly connected to the control board (9).

[0034] All control modules are combined on the control board.

[0035] The need for thermal insulation is minimal because the warm side is inside and the cold incoming water in the countercurrent preheats to approximately room temperature.

[0036] Even an outlet temperature of 45°C would not be a problem for the battery in the event of a fault and is measured and regulated using the signal from sensor (5). The pressure sensor (5) provides additional safety by monitoring water shortages using the system pressure. In addition, the pressure sensor (5) enables instantaneous heating start-up and other convenience functions such as remote temperature selection based on the flow rate indirectly measured via the pressure drop. A further convenience function is offered by an optional radio sensor (12) (or several radio sensors) that transmit the outlet temperature at one or more tap points (21) to the control unit and enable haptic remote control or setting via an app on a smartphone using NFC, such as the personalized or localized selection of a setpoint for each tap point, as well as regulation to an exact tap temperature and thus a minimum of distribution losses.

[0037] The temporal control behavior, which is specific to each tap point due to the pipe length, can be recorded based on the tap temperature and automatically trained and optimized. Ideally, a model of the pipe system is created in the control system that reflects the current state known from all sensors.

[0038] Fig. Figure 2 shows the system schematically. The control unit (9) is connected bidirectionally to the power grid (20) via a grid inverter (17) and to the solar modules (19) of the PV system via an MPP tracker. The battery is protected by a battery management system (BMS) (13) and connected to the charger, inverter, MPPT, and the power controller (14) for the heating element.

[0039] The control unit for the heating element also monitors the safety temperature monitor, regulates the output temperature, and operates other comfort functions and the interface for a display and control unit (15). The usual interfaces, such as Wi-Fi and Modbus, are available here for grid and load management, smart metering, and remote monitoring.

[0040] Fig. Figure 3 shows an alternative design of a battery-buffered hot water system with heat recovery from the room air using a heat pump, schematically and with a practical spatial arrangement of the essential components. The two storage tanks (1) and (2) are in good thermal contact with the buffer battery (7), which is electrically connected to the central control unit (9). Preferably, the batteries are placed under the bases of the storage tanks, and the control elements are located at eye level.

[0041] Cold water enters the water heater via the inlet (c) and is distributed between the two storage tanks. Flow is generated in one of the storage tanks by circulation to the plate heat exchanger (22) using a circulation pump (23), and in the other when drawn off at the outlet (h) via the electric instantaneous water heater (8). The storage tanks are selected and assigned using a 4 / 2-way changeover valve (3), e.g. in the form of an electrically operated ball valve. Circulation is activated in conjunction with the heat pump, which supplies the plate heat exchanger (22) with the transformed energy from the evaporator (25) via the compressor (24), which is extracted from the exhaust or supply air from the air conditioning system, to the heat exchanger. For this purpose, air flows through the evaporator, which is exchanged between the interior (33) and the environment (32) via a replaceable air filter (30) by a radial fan (27) and a switchable 4 / 2-way distributor (31).

[0042] The summer operating mode is shown, in which the supply air is cooled and dehumidified. Dripping condensate is blown away with the air flow and drained from a drip tray (29) into a collecting container or a drain.

[0043] Turning the distributor (31) by 90° changes the air flow for the recovery of room heat in winter.

[0044] The air filter (30) located upstream of the heat exchanger protects the heat exchanger from clogging and, in summer mode, traps dust and pollen from the outside air. UV-C light (30) disinfects the filter between filter changes.

[0045] The control unit (9) contains the Fig. 2 control modules shown and described and additional inputs for sensors and switching outputs for changeover valves and drives of circulation pump, refrigerant compressor and fan and their monitoring.

[0046] The storage tanks are switched over depending on the water temperature, which is measured at the top of the storage tank using sensors (34).

[0047] The tanks are surrounded by thermal insulation (35), which can be designed to save space due to the low storage temperature. List of reference symbols Fig. 1 1.1 outer tube 1.2 inner tube 1.3 Annular space 4 safety temperature limiters 5 Sensor for pressure and temperature 6 connection fitting 7 electrochemical battery 8 heating elements 9 Board with control modules 10 heat conducting bodies c Water ingress h Water leak Fig. 2 11 tap 12 radio sensor 13 Battery management system 14 Power electronics for instantaneous water heaters 15 Control module for display and interfaces 16 Charger for battery from the mains 17 inverters for grid feed-in and grid protection 18 MPP trackers for PV modules 19 PV modules 20 Mains connection 21 tap Fig. 3 1 Tank 1 2 Tanks 2 3 4-way switching valve 22 Heat exchanger as condenser 23 Circulation pump 24 compressors 25 Expansion valve 26 air heat exchangers as evaporators 27 blowers 28 Condensate collection tray 29 air filters 30 UV-C lamp 31 air distributors 32 Interior connection 33 Outdoor space connection 34 Temperature sensor 35 Thermal insulation

Claims

[1] An electrochemical battery (7) for the complete or partial energy supply of one or more electric heating elements (8) for heating drinking water in flow to the tap (h) [2] The placement of the buffer battery (7) in a heat conducting body (10) with thermal contact to the medium flowing through and to be heated. [3] An annular space between the outer tube (1.1) with contact to the heat conducting body (10) and the inner tube (1.2) with a heating element (8) mounted from above to guide the water from the inlet (c) to the outlet (h) in countercurrent. [4] The combination of modules for the control, regulation and monitoring of buffer battery, heating systems, power grid, PV solar modules, interfaces for data and remote control in a central control unit (9). [5] A mobile radio module (12) for temperature measurement and remote control at one or each tap (21) with radio connection to the central control unit. [6] Two water storage tanks (1) and (2) which can be alternately switched by a 4-way valve (3), which are alternately charged via a heat pump and discharged via an electric instantaneous water heater (8) for reheating. [7] A heat exchanger (22) as a condenser of the heat pump, which charges one of the storage tanks via a circulation pump (23), switched by the 4-way switching valve (3). [8] A temperature sensor (34) on each of the water tanks to control the tank change depending on the tank temperature [9] The combination of the two storage units with heat recovery from the ambient air. [10] A switchable air distributor (31) for the optional heat extraction from supply air or exhaust air.

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