GB1570844A

GB1570844A - Heating system for space heating and water heating

Info

Publication number: GB1570844A
Application number: GB12307/78A
Authority: GB
Original assignee: Stal Refrigeration AB
Current assignee: Stal Refrigeration AB
Priority date: 1977-04-20
Filing date: 1978-03-29
Publication date: 1980-07-09
Also published as: DE2815523A1; SE405409B; SE7704492L

Description

(54) A HEATING SYSTEM FOR SPACE HEATING AND WATER HEATING (71) We, STAL REFRIGERATION AB, a Swedish Corporate Body, of 601 87 Norrkoping, Sweden, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a heating system in which so-called heat pumps, either alone or in combination with an additional heat source, supply heat required for heating a building and also for heating completely or partly the hot-water to be consumed.

Buildings for living purposes require much energy for water heating. Usually at least 30% of the total energy need of the building is expended in this way. It is therefore advantageous, in respect of operation economy, to use a heat pump used for space heating for water heating to the greatest possible extent. Since the operation economy of a heat pump is highly dependent on the operating conditions, the use of heat pumps for water heating should not result in deterioration of the operation conditions as determined by the main space heating duty.

The heat requirement of a building is roughly proportional to the difference between the interior temperature of the building and the exterior temperature. If the building is heated by means of heat exchanging devices such as radiators through which heated water is circulated, the larger amount of heat to be supplied from the radiators, the higher the water temperature which is needed.

As an example it is supposed, that a building heat system is dimensioned to maintain a room temperature of +20"C at an exterior temperature of -20 C. The power of the heating system is then utilized to 100%. The radiators are dimensioned to transfer this maximum power at a temperature of +60"C for the water being supplied to the radiators and at +400C for the water leaving the radiators. At an exterior temperature of 0 C, about 50% of the heating system maximum power is needed. To transfer this power, a feed water temperature of 40"C and a return water temperature of 30"C are needed.At an exterior temperature of +10"C, about 25% of the heating system maximum power and the corresponding water temperatures of 30 and 25"C are needed. The values mentioned above are theoretical and do not include consideration taken to for example sun radiation, different degree of ventilation etc. They clearly demonstrate, however, the possible strong reduction of the feed temperature at exterior temperatures higher than the minimum temperature allowed for.

Now consider systems, in which heat pumps completely or partly cover the heat requirement of the building. A characteristic of a heat pump is that its heat emission is always larger than the drive energy needed.

The ratio heat emission/drive energy, the so called heat factor, is a measure of the efficiency of the heat pump. The higher the heat factor is, the higher the energy saving possible. The heat factor is strongly dependent on the temperature at which the heat is emitted, i.e. the water temperature in the example above. The lower this water temperature is, the higher the heat factor. For the economical operation of the heat pump it is necessary to utilize the possibility of reducing the feed temperature when exterior temperatures are higher than the minimum allowed for. According to known solutions, this is achieved by controlling the heat pump power so as to heat the circulating water to a temperature which varies with the exterior temperature analogous to the theoretical example stated above.

The example also shows that the temperatures, specially at high exterior tempera tures, which are sufficient for heating, will not be sufficient for heating the consumption water. Therefore, for the preparation of the hot water for consumption, use is generally made of the fact that the gas after compression in the heat pump compressor has a temperature which is considerably higher than the condensation temperature in the heat pump condenser. Heat pumps being employed for space heating as well as heating hot water are for this reason provided with an additional heat exchanger, a so called gas cooler, for heating the hot water, the gas cooler being located between the compressor and the condenser of the heat pump.

The amount of heat which can be taken out from the gas cooler, however, is directly dependent on the power level at which the heat pump operates. At periods with low heating need, the heat available from the cooling of the compressed gas is insufficient for hot water preparation. The problem has earlier been solved by increasing the power and condensation temperature of the heat pump above the level required for the space heating, causing the refrigerant to be condensed in the gas cooler and increasing the heat supply to the hot water.

According to the present invention there is provided a heating system for space heating and providing hot water for consumption, comprising a heat pump including a compressor, a gas cooler and a condenser, the gas cooler being arranged to transfer heat from gas discharged from the compressor to the consumption water for heating the consumption water to a temperature above the condensation temperature in the condenser, and a space heating circuit including the condenser, heating units connected to the condenser for the supply of hot water to the heating units for space heating, and a heat exchanger connected to the heating units and arranged to preheat the consumption water with return water from the heating units.

The above system provides the advantageous possibility of preparing hot water during a longer part of the heating season without increasing the condensation temperature of the heat pump above the level required for the space heating. Furthermore, the gas cooler can be dimensioned and designed just for the cooling of the refrigerant, rendering a simpler and more economic design.

The preheating of the hot-water by means of the return water from the heating circuit is also advantageous in that the return water is cooled before entering the condenser, providing a lower condensation temperature and a higher heat factor. A further advantage is provided in that it is possible in a simple way to divide the heat delivered from the heat pump between building heating and hot water preparation according to the prevailing needs. Finally, since the gas cooler as well as the condenser can be used for hot water preparation, a further advantage is obtained in that a certain part of the total heat delivery can always occur at a temperature above the condensation temperature, when the heating need in the heating circuit is low or when the temperature of the return water due to the use of an additional heat source is higher than the permitted condensation temperature.

Two embodiments of the invention will now be described in detail, by way of example, with reference to the accompanying drawings, in which: Figure 1 shows schematically the main parts of a heat pump system; Figure 2 shows a smaller heating system embodying the invention; and Figure 3 shows a larger heating system embodying the invention.

The heat pump system shown in Figure 1 includes a gas cooler 1, a condenser 2, an expansion device 3, an evaporator 4 and a compressor 5. A refrigerant is circulated in the system and takes up heat in the evaporator at a low temperature level. The heat is given up by the refrigerant partly in the gas cooler 1 in which the refrigerant gas, compressed by the compressor 5, is cooled from a high temperature, often above 100"C, and partly in the condenser 2 in which the refrigerant is condensed. Figure 1 has been included simply to illustrate the relative positions of the gas cooler and condenser in a heat pump. It is understood that the heat pumps of systems can vary, according to the invention, in design and the exact form of the heat pump is not important.

Therefore, in Figures 2 and 3 only the gas coolers 1 and the condensers 2 of the heat pumps are shown.

Figure 2 shows a small heating system suitable, for example, for use in private houses. The system includes a hot water heater 7, 8 of so-called storage type having an interior vessel 7 for water to be consumed arranged to be heated by the water contained in an exterior vessel 8. The use of a so-called by-pass heater, in which the hot water passes through a tube coil surrounded by a warm water storage, does not alter the fundamental operation of the system.

A gas cooler 1 is designed as a coiled tube located in the exterior vessel 8 of the hot water heater.

The consumption water is fed to the interior vessel 7 of the heater through a tube 9 opening at the bottom of the vessel. Preheated water from the level of the gas cooler is discharged through a tube 10 and is mixed in a valve 12 with hot water taken from the top of the heater through a tube 11.

From the bottom of the exterior vessel 8 water is passed by means of a pump 13 through the condenser 2 and an additional, electric heating battery 14 to heating units 15, such as radiators. The water flow rate through the radiators and hence the heat delivery rate can be controlled by means of radiator valves 16. A by-pass 17 permits recirculation of the water to the hot water heater if the radiator valves 16 are throttled or closed.

Additional heat is taken from the electric heating battery 14 when the heat supplied from the heat pump is insufficient. The electric power input is controlled to maintain a desired feed temperature to the radiators 15, but other methods of controlling the supply of additional heat and forms of energy other than electric energy can be used. The heating battery 14 can also be used for heating hot water. A pipe 18 connects the battery 14 with the exterior vessel 8 of the hot water heater. If a valve 19 in the pipe is opened, part of the water pumped by the pump 13 is returned directly to the hot water heater after having been heated in the battery 14.

The power of the heat pump is controlled so that the water being fed to the radiators has a certain temperature, the so called feed temperature, which is adjusted in accordance with the exterior temperature. Normally, attempts are made to control the feed temperature so that the desired room temperature, whatever the exterior temperature happens to be, is obtained with the radiator valves fully opened. Then the flow through the by-pass valve is equal to zero and all the circulated water passes through the radiators.

Systems for controlling the feed temperature according to the exterior temperature are known and therefore are now shown in Figure 2.

The return water from the radiators is fed to the bottom of the exterior vessel 8 of the hot water heater for preheating cold consumption water being supplied to the interior vessel 7 through the pipe 9. As a result the return water is cooled down before entering the condenser, making it possible to transfer heat to the water at a lower condensation temperature resulting in a higher heat factor. Simultaneously the upper part of the hot water heater is heated by the heat given up at high temperature in the gas cooler 1.

During a great part of the cold season, controlling the heat pump power according to the building heating need, is satisfactory.

The power is normally sufficient for the hot water to be heated only by the heat supplied from gas cooler. The preheating of the hot water with return water from the radiators improves the operation economy in two ways. Firstly, the heat exchange in the condenser occurs at a lower condensation temperature giving an increased heat factor, and secondly, during those operation periods when the heat delivery occurs at low temperature, the period of time is increased during which sufficient hot water can be heated with the heat pump power controlled only in accordance with the building heating needs.

If the amount of hot water heated in this way is insufficient, the heat pump power is increased above the level required to obtain the feed temperature which corresponds to the exterior temperature. This tends to increase the room temperature, and the radiator valves 16 throttle the flow through the radiators. The by-pass valve 17 is then opened and passes a part of the water being heated in the condenser directly to the hotwater heater. A varying fraction of the heat being delivered in the heat pump condenser is thus used directly for heating consumption water. An extreme situation is when the building heating need is zero, when all the circulated water is returned to the hot water heater after having been heated in the condenser. The whole heat pump power is then used for heating consumption water.As the gas cooler always delivers heat at a temperature above the condensation temperature, it is possible to heat the water to a temperature above the condensation temperature. A signal for increasing the heat pump power above the level required for heating the building heating can, for example, be provided by temperature transducer located in the hot water heater when the hot water temperature falls below a predetermined value.

A larger heating system suitable, for example, for apartment buildings is shown in Figure 3. Some components of the system are the same as those of the system in Figure 2 and are designated by the same reference numerals in the two Figures. In Figure 3, 17' and 19' designate three-way-valves. The gas cooler 1 is located outside the hot water heater 7, 8. Additional heat is obtained from an oil-fired boiler 14'. The system of Figure 3 includes the following parts which have no counterpart in Figure 2: a pump 21, located in the heating circuit, a pump 22, which circulates the water through the gas cooler 1, a three-way-valve 23, by means of which warm water can be shunted from the furnace 14' into the heating circuit as required, and a valve 24 in the return line from the radiators and a non-return valve 20.

The system according to Figure 3 functions in an essentially analogous manner to the system according to Figure 2, and will therefore be only briefly described. A pump 13 circulates return water from the main circuit through the bottom of the hot water heater through the condenser 2 and back to the main circuit. A pump 21 circulates the water further through the radiators 15. A pump 22 circulates the water from the hot water heater through the gas cooler 1 back to the hot water heater.

The heat pump power is controlled to obtain a suitable feed temperature with regard to the temperature outside the building in which the system is used. The hot water for consumption is partly heated by means of the return water from the radiators and partly by the heat delivered from the heat pump in the gas cooler 1. Should the temperature to which the hot water is heated in this way is insufficient, which for example can be indicated by a temperature transducer in the hot water heater, the heat pump power is increased and hence so is the temperature downstream of the condenser 2. The feed temperature then reaches a higher level than required with regard to the prevailing exterior temperature. This is compensated by returning to the hot water heater through the valve 17' a part of the water being circulated by the pump 13.A varying part of the heat being delivered in the condenser can therefore be directly used for heating water for consumption. An extreme situation is when the building heating need is zero, when all the water circulated by the pump 13 is returned to the hot water heater directly from the condenser.

Additional heat possibly being required for building heating is obtained by shunting warm water from the boiler 14' into the main circuit through the three-way-valve 23.

Additional heat from the boiler 14' can also at need be used for the preparation of hot water by supplying warm water through the three-way-valve 19'.

Besides the advantages stated in the above description of the system according to Figure 2, the system according to Figure 3 also has the advantage that the valves 17' and 24 can be gauged for preheating of the hot water in the hot water heater with essentially only warm water from the condenser.

This possibility is of value in the case when the return water from the radiators due to additional heat has a temperature above the permitted maximum condensation temperature in the condenser. The heat pump can then still be in operation for preparation of hot water.

In the embodiments of the invention described above the hot water heater has been assumed to be one unit. However it is possible to have, for example, two separate hot water heaters, one of which is supplied with heat from the return water and the condenser while the other one is supplied with heat from the gas cooler.

WHAT WE CLAIM IS: 1. A heating system for space heating and providing hot water for consumption, comprising a heat pump including a compressor, a gas cooler and a condenser, the gas cooler being arranged to transfer heat from gas discharged from the compressor to the consumption water for heating the consumption water to a temperature above the condensation temperature in the condenser, and a space heating circuit including the condenser, heating units connected to the condenser for the supply of hot water to the heating units for space heating, and a heat exchanger connected to the heating units and arranged to preheat the consumption water with return water from the heating units.

2. A system according to claim 1, wherein the condenser is also arranged to be directly connectible to the heat exchanger, thereby to enable an increased part of the heat pump power to be used for heating the consumption water when the heating need in the heating units decreases.

3. A system according to claim 1 ro 2, wherein an additional heat source is provided in the space heating circuit, the condenser is connected through a three-wayvalve to the heating units and directly to the heat exchanger, and the heating units are connected to the heat exchanger through a valve, said valves being adjustable for the consumption water to be preheated in the heat exchanger essentially only by warm water from the condenser, whereby the heat pump can be used for heating the consumption water when the return water from the heating units is warmer than the permitted condensation temperature in the condenser.

4. A system according to any of the preceding claims, wherein the heat exchanger comprises a hot water vessel having an inlet for cold feed water opening at the vessel bottom, and outlet means for discharging hot water from one or more higher levels in the vessel, and the heat exchanger is arranged for return water from the heating units to flow through or over a lower part of the vessel, and for heat to be transferred from the gas cooler to the upper part of the vessel.

5. A system according to any of claims 1 to 3, wherein two consumption water heated are provided, one constituting the heat exchanger, and the other being arranged to transfer heat from the gas cooler to the water.

6. A heating system substantially as herein described with reference to Figures 2 or 3 of the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. heater through the condenser 2 and back to the main circuit. A pump 21 circulates the water further through the radiators 15. A pump 22 circulates the water from the hot water heater through the gas cooler 1 back to the hot water heater. The heat pump power is controlled to obtain a suitable feed temperature with regard to the temperature outside the building in which the system is used. The hot water for consumption is partly heated by means of the return water from the radiators and partly by the heat delivered from the heat pump in the gas cooler 1. Should the temperature to which the hot water is heated in this way is insufficient, which for example can be indicated by a temperature transducer in the hot water heater, the heat pump power is increased and hence so is the temperature downstream of the condenser 2. The feed temperature then reaches a higher level than required with regard to the prevailing exterior temperature. This is compensated by returning to the hot water heater through the valve 17' a part of the water being circulated by the pump 13.A varying part of the heat being delivered in the condenser can therefore be directly used for heating water for consumption. An extreme situation is when the building heating need is zero, when all the water circulated by the pump 13 is returned to the hot water heater directly from the condenser. Additional heat possibly being required for building heating is obtained by shunting warm water from the boiler 14' into the main circuit through the three-way-valve 23. Additional heat from the boiler 14' can also at need be used for the preparation of hot water by supplying warm water through the three-way-valve 19'. Besides the advantages stated in the above description of the system according to Figure 2, the system according to Figure 3 also has the advantage that the valves 17' and 24 can be gauged for preheating of the hot water in the hot water heater with essentially only warm water from the condenser. This possibility is of value in the case when the return water from the radiators due to additional heat has a temperature above the permitted maximum condensation temperature in the condenser. The heat pump can then still be in operation for preparation of hot water. In the embodiments of the invention described above the hot water heater has been assumed to be one unit. However it is possible to have, for example, two separate hot water heaters, one of which is supplied with heat from the return water and the condenser while the other one is supplied with heat from the gas cooler. WHAT WE CLAIM IS:

1. A heating system for space heating and providing hot water for consumption, comprising a heat pump including a compressor, a gas cooler and a condenser, the gas cooler being arranged to transfer heat from gas discharged from the compressor to the consumption water for heating the consumption water to a temperature above the condensation temperature in the condenser, and a space heating circuit including the condenser, heating units connected to the condenser for the supply of hot water to the heating units for space heating, and a heat exchanger connected to the heating units and arranged to preheat the consumption water with return water from the heating units.