EP1490636A1

EP1490636A1 - Heat pump system

Info

Publication number: EP1490636A1
Application number: EP03706656A
Authority: EP
Inventors: Risto Antero Ojala; Juha Matti NYKÄNEN
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-03-04
Filing date: 2003-03-04
Publication date: 2004-12-29
Also published as: FI20020407A; AU2003208369A1; WO2003074953A1; FI117024B; FI20020407A0

Abstract

A heat pump system, wherein the flowing speed of the heating circuit liquid is adjusted in the condenser to regulate the temperature of the heating circuit liquid. The system also includes a sub-cooling heat exchanger for sub-cooling the refrigerant after the condenser to the ground heat collection circuit liquid. Domestic hot water is produced in two phases: in the first phase water is pre-heated with the heat absorbed from the refrigerant in the condenser. A super-heat exchanger is provided for heating the domestic hot water to its final high temperature in the second phase. The super-heat exchanger includes a flowing tube which is used to control the position of the condensing point of the refrigerant vapor and to remove the excessive super-heat to a heat accumulator when domestic hot water is not used.

Description

HEAT PUMP SYSTEM

The present invention relates to a heat pump system as defined in the preamble of claim 1.

Known heat pump systems, particularly ground source heat pump systems commonly employ following basic components: a compressor, a condenser, an expansion valve, an evaporator, a circulating pump of the ground heat collection circle, a circulating pump of the heating system circuit, thermostatic switches and pressure switches of the refrigerant circuit and other auxiliaries for the same such as a refrigerant accumulator, a filter, an inspection glass, a magnetic valve, and a controller of the compressor.

In known technical solutions concerning ground source heat pumps compro- mises in aspects of the heating capacity, of the domestic hot water production capacity, and of the system Coefficient Of the Performance (COP) have had to be accepted. Following solutions for heating energy production are known:

A common solution is to underdimension the heat pump and to produce additional heating power with an electric resistance element when required. In case of an ideal dimensioning of this type of a heat pump the unit will work with its best COP the outdoor temperature being within the range of -10°C ... 0°C, i.e. approx. half of its annual working hours in Scandinavian varying weather conditions. Need for additional electric heating increases with the outdoor temperature falling below -10°C and the total COP of the heating system will then drastically drop. The outdoor temperature being warmer than 0°C heating is still required but the heat pump is then overdimensioned for such warmer weather conditions and will again work with less good COP, which will further drop with rising outdoor temperature.

It is also known to dimension the capacity of the heat pump to cover the maximum need of heating power in order to avoid need for additional electric heating. In this case the heat pump is overdimensioned for the most part of the year working then with a low COP. With this solution, however, the total economy of the system is no more additionally affected as the system do not employ additional electric heating element.

It is known to produce domestic hot water in two phases: Water is preheated with the heat absorbed from the condenser in the first phase and an electric heating element is used to heat the water to its final temperature in the second phase. Use of the electric heating element in this solution affects lowering the system economy and the COP.

It is also known to use heat pump with so high a pressure rating that the temperature will rise to a level allowing production of the domestic hot water. Increased pressure rating i.e. higher compressor load will lead to a lower COP and the unfavourable situation does not change during the production of the heating energy as an adjustable pressure rating is not known technology on ground source heat pumps.

It is also known to produce domestic hot water in two phases while preheating it with the heat absorbed from the condenser and rising the temperature to its final height in a super-heat exchanger while absorbing the super-heat of the vaporised refrigerant to the water. The efficiency of this solution is the best of the above listed. It does not, however, allow the control of the position of the condensing point of the refrigerant vapor. If domestic hot water is not used, its temperature in the super-heat exchanger will rise finally nearing the temperature of the refrigerant vapor. In such a case heat exchange from the refrigerant vapor to the water become slower and finally stops. As the super-heat of the refrigerant vapor is no more absorbed to the water, the condensing point of the refrigerant will move into the main heat exchanger i.e. super-heated refrigerant vapor gets into the condenser, which has a harmful effect to the function of the condenser while heat is fed to the heating circuit. An object of the present invention is to provide a heat pump system from which such disadvantages as mentioned above are removed and that is capable of producing both the domestic hot water and the heating energy with good efficiency in all weather conditions.

In the present invention a ground source heat pump is provided, in which the temperature of the heating circuit liquid is adjusted by changing its flowing speed in the condenser, which method improves efficiency of the condenser and enhances COP of the system.

Further, in the present invention a ground source heat pump is provided, in which a sub-cooling heat exchanger is installed after the condenser to sub- cool the refrigerant to the incoming ground source liquid, which improves the efficiency of the function of the evaporator and enhances COP of the system.

And further, in the present invention a ground source heat pump is provided, in which the domestic hot water is produced in two phases: In the first phase water is preheated with the heat absorbed from the condenser. A super-heat exchanger is provided to heat the domestic hot water to its final high tempera- ture in the second phase. The super-heat exchanger is connected with a heat accumulator via a tube called flowing tube. This flowing tube is used for controlling the position of the condensing point of the refrigerant vapor and to remove excessive super-heat to the heat accumulator. This method improves functioning of the condenser and the COP of the system while domes- tic hot water is produced.

Briefly and more exactly said, the heat pump system according to the invention is characterized by what is presented in the characterization part of claim 1. Other embodiments of the invention are characterized by what is presented in the other claims. As mentioned above the advantages of the present invention are better efficiency of the condenser and evaporator, and also enhancements concerning the COP of the system . In the following, the present invention will be described in detail by the aid of an example embodiment with reference to the attached drawing, wherein

Fig. 1 presents a schematic diagram of the ground source heat pump utilizing the improvements of the present invention, Fig. 2 is a schematic representation of the super-heat exchanger employed in the improved ground source heat pump,

Fig. 3 presents an alternative design of the super-heat exchanger, in which it is integrated with the heat accumulator and Fig. 4 is a schematic diagram of the improved ground source heat pump with a manifold according to US. PAT. 6, 092, 734 installed.

The basic components of a ground source heat pump are: a compressor 1 , a condenser 6, an expansion valve12, an evaporator 13, a circulating pump 14 of the ground heat collection circle, a circulating pump 5 of the heating system circuit, thermostatic switches 16 and pressure switches 17 of the refrigerant circuit 19 and other auxiliaries for the same such as a refrigerant accumulator 8, a filter 9, an inspection glass 11 , a magnetic valve 10, and a controller of the compressor.

Briefly said, the present invention relates to a ground source heat pump which is characterised in that the flowing speed of the liquid in the heating circuit 18 is regulated while flowing through the condenser 6, the refrigerant flowing in the ground source heat pump is sub-cooled to the incoming ground circuit liquid 7 after the condenser 6, and the position of the condensing point of the refrigerant vapor is adjusted by means of the flowing tube 3, which connects the super-heat exchanger 2 and the heat accumulator 4.

In the present invention a ground source heat pump is provided, in which the temperature of the heating circuit liquid entering the heating circuit 18 from the condenser 6 is adjusted by changing its flowing speed in the condenser. If the flowing speed of the heating circuit liquid is increased in the condenser 6, it will leave the condenser and enter the heating circuit in a lower temperature as the faster flowing liquid will have had shorter time to absorb heat. The quantity of the delivered energy , however, will increase and consequently the temperature of the condenser 6 and the temperature of the refrigerant leaving the condenser will become lower. This improves COP of the system and as the difference of the temperatures of the refrigerant and the incoming ground circuit liquid 7 in the evaporator 13 will now be increased, the heat exchange in the evaporator will be more effective. A practical example of such an arrangement is to control the temperature of the heating circuit liquid in accordance to the outdoor temperature so that the flowing speed is increased in the condenser 6 when the outdoor temperature is rising and correspondingly decreased when the outdoor temperature is getting colder and higher tem- perature of the heating circuit liquid is required. An adjustable-speed circulating pump 5 or by-pass tube of the pump 5 together with a valve and a controller can be used for flowing speed adjustment. This method will essentially improve the COP of the ground source heat pump, if this is connected with a heating system that is build in accordance with the US. PAT. 6, 092, 734, in which heat is fed into the heating circuit by fits and starts and which system allows decreasing of the temperature of the heating circuit liquid by increasing its flowing speed.

In the present invention a ground source heat pump is provided, in which also a sub-cooling heat exchanger 15 is employed for cooling the refrigerant to the ground source liquid 7 after the condenser 6. The refrigerant 7, its temperature immediately after the condenser 6 being approx. +35°C, is sub-cooled to the entering ground source liquid 7, the temperature of this ground source liquid 7 before the sub-cooling heat exchange being approx. +5°C. This arrangement will bring following advantages: the refrigerant will enter and pass the expansion valve 12 in an essentially lower temperature, causing a bigger refrigerant mass to pass the valve, which will increase heat absorption capacity in the evaporator 13. Simultaneously the ground source liquid 7 comes to the evaporator 13 in an increased temperature. The increased difference of the refrigerant and the ground source liquid temperatures will improve the heat exchange in the evaporator 13, in which heat is absorbed from the ground source liquid to the refrigerant. Another advantage is that expansion vapor bubbles, which are harmful for the function of the evaporator, are the less the cooler the refrigerant enters the expansion valve. When the heat pump starts up after a still-stand period, the heat that was left unused in the area between the super-heat exchanger 2 and the expansion valve 12 at the end of the previous running period will now be effectively used by transferring it to the ground source liquid 7. Therefore, as the refrigerant does not need to flow a complete circle to become suitably cool before the expansion valve 12, the reversed Carnot-process will run immediately after the start up of the heat pump with nearly full efficiency.

The present invention provides a ground source heat pump, in which the domestic hot water is produced in two phases with the following method:

In the first phase water is preheated upto the temperature of approx. +35°C with the heat absorbed from the condenser 6. In the second phase water is heated to its final high temperature in the super-heat exchanger 2, in which heat is absorbed from the super-heated refrigerant vapor, this being in the temperature of approx. +90°C in this stage. The present invention provides a ground source heat pump being also characterised in that it includes a super- heat exchanger 2 which consists of two copper tubes, these being installed one within the other, and a domestic hot water tank 2.2 through which the said copper tubes are lead. The super-heated refrigerant vapor flows in the inner tube 2.3. The heating circuit liquid flows in the outer tube i.e. in the space between the outer and the inner tube. The outer tube, i.e. the flow of the heating circuit liquid is connected with the heat accumulator 4. This method, compared with conventional methods, will bring following advantages: All energy that is required to produce the domestic hot water is provided by the reversed Carnot-process. Super-heated refrigerant vapor is cooled down to a point of condensing before the condenser 6. Consequently, the refrigerant being entirely in liquid form while entering the condenser, the heat ex- change from the refrigerant to the heating circuit liquid will be as effective as possible. The invention makes possible to control the position of the condensing point of the refrigerant even in such a case when domestic hot water was not used for a longer period and consequently temperature in the super-heat exchanger 2 would rise near its maximum value. In such a case, in order to adjust the position of the condensing point of the refrigerant, overheat is lead from the super-heat exchanger 2 to the heat accumulator 4 with the heating circuit liquid by using the flowing tube 3 and the channel between the outer and inner copper tubes of the super-heat exchanger.

The pressure of approx. 18 bar in the refrigerant circuit 19 or the compressor circuit is provided by a compressor 1. In a case that the inner copper tube 2.3 inside the super-heat exchanger 2 would brake for any reason, the refrigerant flowing through it under the pressure of the refrigerant circuit 19 will override the 1 bar pressure of the heating circuit 18 and consequently the refrigerant will brake out through the safety valve (1 ,5 bar) and can not get mixed with the domestic hot water which is under the pressure of 2...3 bar. The system is therefore safe and the refrigerant can not get mixed with the drinking water.

Alternatively the super-heat exchanger can also be integrated with the heat accumulator to be one larger unit, the super-heat exchanger forming its upper part being separated with a wall from the heat accumulator. The flowing tube 3 can be installed outside of the tank. This kind of an alternative structure has been presented in Fig. 3.

It is obvious to the person skilled in the art that the invention is not limited to the example described above, but that it may be varied within the scope of the claims presented below. Thus, for example the super-heat exchanger can be constructed in many different ways with the only condition that it includes the flowing tube 3 which makes possible to control the position of the condensing point of the refrigerant.

Claims

1. A heat pump system consisting of at least a heating circuit (18) distributing heat to a heating network, and of a refrigerant circuit (19), to which refriger- ant circuit are installed at least a compressor (1), a controller of the compressor, a condenser (6), a magnetic valve (10), an expansion valve (12), an evaporator (13), and a pressure switch (17), and in which system the liquid circulating in the heating circuit (18) is lead to flow via the condenser (6), characterized in that the temperature of the refrigerant of the refrigerant circuit (19) while leaving the condenser (6) and the temperature of the liquid circulating in the heating circuit (18) are changed by changing the circulating speed of the liquid circulating in the heating circuit (18) via the condenser (6).

2. A heat pump system as defined in claim 1 , characterized in that the tem- perature of the refrigerant circulating in the refrigerant circuit (19) while leaving the condenser (6) and the temperature of the liquid circulating in the heating circuit (18) are reduced by increasing the circulating speed of the liquid circulating in the heating circuit (18) by means of the circulating pump (5) of the heating circuit (18).

3. A heat pump system as defined in claim 1 or 2, characterized in that the temperature of the refrigerant circulating in the refrigerant circuit (19) is further reduced to a sub-cooled state after leaving the condenser (6) by means of a heat exchanger (15), which is installed between the condenser (6) and the expansion valve (12) and which heat exchanger takes its cooling energy from the ground heat collection liquid (7) which is circulating in the ground heat piping system.

4. A heat pump system as defined in any of the preceding claims, including a super-heat exchanger (2) for the purpose of producing domestic hot water, characterized in that there are a part of the refrigerant circuit (19) and a part of the heating circuit (18) inside of the super-heat exchanger (2) and the said parts are being arranged in relation to each other so that a part of the refrigerant circuit (19) is inside of the heating circuit (18).

5. A heat pump system as defined in claim 4, characterized in that the part of the refrigerant circuit (19) and the part of the heating circuit (18) being inside of the super-heat exchanger (2) are arranged in relation to each other so that the refrigerant vapor emits heat to the domestic hot water being in the domestic hot water tank (2.2) of the super-heat exchanger (2) via the heating circuit liquid being in the flowing tube (3).

6. A heat pump system as defined in claim 4 or 5 characterized in that the position of the condensing point of the refrigerant vapor is adjusted to a wanted point before the condenser (6) by means of changing the temperatures of the liquid flowing in the flowing tube (3).

7. A heat pump system as defined in claims 4-6, characterized in that the excessive super-heat is removed from the super-heat exchanger (2) by means of the flowing tube (3).