A HEATING MODULE AND SYSTEM CONTROLLER THAT INCREASES THE EFFICIENCY OF HEAT PUMPS FOR DOMESTIC HOT WATER AND HEATING

BACKGROUND OF THE INVENTION

This invention relates to a heating module and system controller designed to increase the efficiency of heat pumps for domestic hot water and heating.

Until recently, R22 has been the refrigerant used in heat pumps to heat water but maximum temperatures have been limited and an extra heat source has been required to achieve a satisfactory water temperature. Also, R22 has a relatively high evaporating temperature, which means that R22 air to water heat pumps are unable to operate efficiently during UK winter months.

R410A heat pumps give relatively high COP's even at low ambient conditions and evaporating temperatures down to -20 degrees C are possible. This much lower evaporating temperature has meant that air to air heat pump systems can run efficiently all year round.

Tests already conducted by myself have proved that an R410A heat pump can supply adequate air to air heating throughout the winter. Further tests that I have conducted have proved that substantial water temperatures can be obtained from an R410A air to water system.

However, to obtain these high temperatures, pressures in the system rose above 36 bar g. Long term operation at these high pressures would substantially reduce the life of the system.

Similar tests that I have conducted using an inverter drive compressor have failed to produce a water temperature that would be high enough for domestic hot water. This is because the inverter drive system controls limit head pressure by controlling compressor speed.

STATEMENT OF THE INVENTION

To overcome the above problem of refrigerant pressure increase as water temperature increases the present invention proposes the control of the condensing refrigerant to a sustainable pressure whilst also providing an increase in water temperature.

Condensing pressure is stabilised by passing the refrigerant through a primary refrigerant to water heat exchanger where superheat is extracted. The refrigerant then passes in to the secondary heat exchanger where condensation and sub cooling of the refrigerant takes place.

These heat exchangers can be plate or coaxial type, where heated water can be circulated through a primary and secondary water tank, or direct refrigerant to water heat exchangers can be around or inside the tanks.

Also, to overcome the problem of high condensing pressure, a system controller modulates the flow of both water and refrigerant as the water temperature increases.

The system controller monitors ice build up on the outside coil and allows for defrost on demand, thus limiting defrost time.

A third heat exchanger can be built into the system to allow waste domestic hot water to pre heat the stored domestic water, thus reducing reheat time.

ADVANTAGES OF THE INVENTION

The proposed invention can control the flow of the primary and secondary heat carrying fluid i.e. the refrigerant and the water, so that the operating pressure of the refrigerant can be reduced with a subsequent gain in performance. This allows an R410A air to water heating system to provide hot water at an increased temperature while ensuring long term reliability.

The proposed invention overcomes this problem of high discharge pressure whilst also providing increased water temperature and an increase in compressor efficiency in an air to water heating system.

As well as a direct refrigerant to water system that would be installed by a refrigeration engineer a system with plate or coaxial heat exchangers allows the refrigerant to be

contained in a packaged system where the only connections required to be made by the installer are water connections.

A 16 amp electrical supply is required.

No adjustments are required to be performed by the installer.

Reheat times for 150 litre cylinders can vary between 15 minutes and one hour, depending on the size of outdoor unit.

The same system can be used to supply hot water for a heating as well as domestic hot water.

EXAMPLE OF THE INVENTION

An example of the invention will now be described by referring to the accompanying drawings on pages 1/4, 2/4, 3/4 and 4/4.

Figure 1 shows an existing heat pump outdoor evaporator unit (3), which contains an evaporator, expansion valve, fan and compressor. Added to this are the heating module (1 ) and system controller (2) a primary heat exchanger (5), a secondary heat exchanger (4), a water modulating valve (6) and a water pump (7). In Figure 1 these are all enclosed in the module (1 ). Also shown are domestic water supply and return (8) and (9) and the signal wires from the controller, (10), (11 ) and (12).

Figure 2 shows the components of Figure 1 with primary and secondary heat exchangers (5) and (4) fitted inside the water tanks (15 and 16) in a design which can be used for an air to refrigerant or a geothermal heat pump with a water to refrigerant evaporator.

Figure 3 shows an existing heat pump (3) linked to a combined primary and secondary direct refrigerant to water heat exchangers (4 and 5) in a primary water tank (15) and second primary heat exchanger (5) in a secondary water tank (16).

In Figure 1 , the controller (2) monitors water tank and domestic hot water temperature, set temperature and refrigerant discharge pressure/temperature. Using this

information the controller sends a signal to the existing outdoor unit (3) and modulates the compressor cycles and the electronic expansion valve thus altering the amount of refrigerant passing through the system but also, most importantly, controlling the refrigerant pressure. The controller uses a transducer to measure discharge pressure and sends a signal to inverter to control the compressor operating pressure.

In systems using hot water coils in the water tanks as in Figure 2, the controller also sends a signal to the heating module (1) which changes the settings on the modulating valves (6) and on the water pump (7) thus ensuring maximum heat exchange by adjusting the flow rate of both refrigerant and water whilst maintaining the minimum and maximum temperature difference between the two.

When the system starts up the refrigerant in the existing outdoor unit (3) passes through the existing expansion device which controls the pressure and temperature of evaporation. The refrigerant gains heat from the outside air as it boils off in the outdoor evaporator. The refrigerant changes into a vapour and is superheated. The compressor then raises the temperature and pressure of the refrigerant vapour.

In Figure 1 , the refrigerant vapour then enters the heating module (1 ) and passes through the primary high pressure heat exchanger (5) where the sensible heat of the refrigerant vapour is absorbed. The refrigerant vapour now enters the second component of the heating module, the secondary high pressure heat exchanger (4) where it condenses and gives off the heat energy gained from the outside air, to the water flowing through this heat exchanger. In a direct refrigerant to water heat exchanger these heat exchangers are around or within the water tanks.

Still in the heating module (1 ), the water enter the secondary heat exchanger (4) where it absorbs the heat energy from the refrigerant as it condenses.

This heated water, at a temperature just below the condensing temperature of the refrigerant, then passes through the primary heat exchanger (5) where it is heated further by absorbing sensible heat from the superheated refrigerant vapour.

Thus, the first heat exchanger adds the sensible heat that would normally be lost to the air, to the water which has passed through the second heat exchanger which is the condenser.

Tests of the invention have shown that the use of this first heat exchanger overcomes the problem of high condensing pressure in a R410A heat pump and that water temperatures of up to 20deg.k higher than the corresponding condensing pressure would normally allow, can be achieved.

In Figure 2 and 3, where the heating modules are in or around the water tanks, the two heat exchangers can be utilised together to provide a fast reheat time until the water temperature is just below the normal operating condensing temperature and then, by means of the modulating value (6), work separately, in separate water tanks (15 and 16), to increase the water temperature by absorbing the higher sensible heat from the refrigerant discharge vapour.

In this example, the two heat exchangers are in the form of spiral coil copper pipes each placed in a separate water cylinder. The coils can be operated in series or a solenoid valve can isolate the smaller coil. In this embodiment, each cylinder has a different water capacity and the capacities are in the ratio of approximately 2:1.

The smaller capacity cylinder having the smaller coil allows the discharge superheat of the refrigerant to be dissipated into the water and will heat the water up to 70 to 80deg C. The larger capacity cylinder holds the condenser coil and will bring the water temperature up to about 50 deg C.

When the system starts from cold, the solenoid valve closes and the refrigerant passes through the larger cylinder where the condenser coil is housed. In this way the sensible superheat and the latent heat of change of state is transferred to the water through the condenser coil.

When the water temperature in this cylinder reaches approximately 45 deg C, the solenoid valve opens and the discharge gas enters the smaller coil in the smaller cylinder where the superheat is given off to the water in this cylinder. The refrigerant, still in vapour form but with reduced superheat and just about to change state into liquid, enters the condenser coil in the larger tank and gives of the latent heat into the water in this cylinder. By separating the processes of desuperheating and condensing in this way water temperatures of 83 deg C have been achieved by the inventor.

In this way, the greatest heat input into the water is provided by the refrigerant changing state as it condenses in the secondary heat exchanger (4) while a sufficient amount of sensible heat is absorbed by the water as it passes through the primary heat exchanger (5) thus raising the water leaving temperature without increasing refrigerant discharge pressure.

The controller (2), as well as controlling compressor speed, refrigerant flow and pressure in the existing outdoor unit, also modulates the water flow through the heat exchangers in the heating module (1). In this way, the correct temperature difference between refrigerant and water is maintained.

As the temperature of the water in the tank rises the controller (2) modulates the refrigerant flow and the water flow through the heat exchangers (4) and (5), again to maximise heat exchange with minimum discharge pressure.

In the systems where the heat exchangers or the heating module are on or in the water tanks, when a preset temperature is obtained in the primary tank the controller will switch the primary heat exchanger to operate the secondary tank. In this way, water in the secondary tank will heat to a higher temperature then the primary tank.

The controller will normally be fitted to a system using an inverter drive compressor but a non inverter drive compressor can also be utilised. On a standard, non inverter drive compressor the controller modulates the refrigerant, water pump (7) and the water modulator valve (6), which allows evaporating temperature to increase while maintaining a low discharge pressure.

Temperatures between 65 and 75 degrees C have been obtained in tests.

If required, the controller (2) can be set to activate an additional water heater in the water tank to eliminate Legionella bacteria when very low temperature ambient conditions cause a drop in the system COP. This will have little impact on system running costs due to the high efficiency of the system at all other times.

The controller (2) can also include an auto defrost start/stop sensor which measures ice build up on the outdoor heat exchange coil. This can be activated by pressure or

infrared sensor and further improves system efficiency by providing the minimum defrost time.

By diverting waste hot water through the heating module (1 ) the heat exchanger can be utilised to preheat water.

Figure 4 shows how the controller adjusts discharge pressure as water temperature increases.