| WO/1984/003353 | HEAT EXCHANGER FOR TWO GASEOUS MEDIA |
| WO/2006/040070 | FRAME, IN PARTICULAR FOR WINDOW, DOOR OR FAÇADE ELEMENTS |
| WO/1988/006702 | A VENTILATION AND HEAT RECOVERING SYSTEM FOR PLURAL ROOM BUILDINGS |
CARLSSON, Björn (Hagbynäsvägen 5, Kalmar, S-392 43, SE)
| Claims 1. A method for removing compounds for freezing point de- pression in a heat recovery system in a building, which heat recovery system comprises a first circuit (1) with process water and a first heat exchanger (2) in order to remove heat from warm air that is leaving the building and using the heat to heat the process water, and a second heat exchanger (3) in order to remove heat from the water that has been heated in the first heat exchanger (2) and use the heat to heat colder outdoor air, which first circuit (1) comprises a pump (4) for pumping the process water around the circuit, where a compound for freezing point depression is added as necessary to the process water, where a fraction of the process water from the first circuit (1) is withdrawn to a second circuit (5) that is connected in parallel with the said first circuit and that comprises a pump (6) and an ejector (7) in order to achieve negative pressure, c h a r a c t e r i s e d in that the process water that is removed is led away in a line (19; 20) through a valve (20; 22) to an evaporation tank (8) that is connected to the low-pressure side of the said ejector (7), in that water is separated in the evaporation tank (8) from the compound for freezing point depression, in that the water from the evaporation tank (8) is caused to be led to the low-pressure side of the ejector (7), and in that the compound for freezing point depression that has been separated in the evaporation tank is led to a storage tank (10; 13) for the compound for freezing point depression and in that, when higher levels of the compound for freezing point depression are necessary in the first circuit, the compound for freezing point depression in the storage tank (10; 13) is caused to be led to the ejector (7) through a stop valve (11; 15) . 2. A method according to claim 1, in the case in which the compound for freezing point depression has a higher boiling point than that of water, c h a r a c t e r i s e d in that water that has been vaporised in the evaporation tank (8) is led through the line (9), which constitutes the said connection between the evaporation tank (8) and the low-pressure side of the ejector (7), and in that the compound for freezing point depression that remains in the evaporation tank (8) is led through a valve (25) to a storage tank (10) for the compound for freezing point depression, and in that, when necessary, the compound for freezing point depression in the storage tank (10) is caused to be led to the ejector (7) through a stop valve (11) . 3. A method according to claim 1, in the case in which the compound for freezing point depression has a lower boiling point than that of water, c h a r a c t e r i s e d in that the compound for freezing point depression in the evaporation tank (8) is led through a line (9), which constitutes the said connection between the evaporation tank (8) and the low- pressure side of the ejector (7), in that the compound for freezing point depression is caused to condense in a condenser (12), in that the condensate is led to a storage tank (13) through a valve (26), and in that separated water in the evaporation tank (8) is led to the low-pressure side of the ejector (7) , and in that, when necessary, the compound for freezing point depression in the storage tank (13) is caused to be led to the ejector through a stop valve (15) . 4. A method according to claim 1, 2 or 3, c h a r a c t e ri s e d in that the pressure before the ejector (7) is between 3 and 6 bar and that the pressure on the low-pressure side of the ejector is between 0.05 and 0.4 bar. 5. A method according to claim 1, 2, 3 or 4, c h a r a c t e r i s e d in that the process water in the evaporation tank (8) is caused to be heated to at least 50 °C. |
RECOVERY SYSTEMS IN BUILDINGS
The present invention relates to a method for removing corn- pounds for freezing point depression in energy systems, such as heat recovery systems in buildings.
Heat recovery systems for buildings are available, in which air leaves the building through a heat exchanger in which the heat of the air is withdrawn and used to heat water, which heated water is led to a heat exchanger in which its heat is withdrawn and used to heat external air, which is introduced into the building. The water is pumped around in a circuit that contains the two heat exchangers. When the weather is cold and the external temperature below zero degrees Celsius, it would be possible for the water in the heat exchanger into which external air is fed to freeze. A compound for freezing point depression is for this reason added to the water. One compound for freezing point depression is ethylene glycol. In Stockholm, Sweden, for example, ethylene glycol is added to the water in such an amount that a depression of the freezing point to -18 degrees Celsius is obtained. Another compound for freezing point depression is alcohol. A major disadvantage of ethylene glycol is that the heat transfer in the heat exchangers falls when glycol has been mixed into the water. It is therefore desirable that the added glycol be removed when the outdoor temperature rises. The present invention offers a very simple method of removing glycol from the water. Glycol can, according to the invention, be continuously removed during operation of the heat recovery system. In this way, it is possible to remove only a certain amount of the glycol, such that the depression of the freezing point is adapted to the actual outdoor temperature.
The present invention thus relates to a method for removing compounds for freezing point depression in an energy system, such as a heat recovery system in a building, which heat recovery system comprises a first circuit with process water and a first heat exchanger in order to remove heat from warm air that is leaving the building and using the heat to heat the process water, and a second heat exchanger in order to remove heat from the water that has been heated in the first heat exchanger and use the heat to heat colder outdoor air, which first circuit comprises a pump for pumping the process water around in the circuit, where a compound for freezing point depression is added when necessary to the process water, where a fraction of the process water from the first circuit is withdrawn to a second circuit that is connected in parallel with the said first circuit and that comprises a pump and an ejector in order to achieve negative pressure, and it is characterised in that the process water that is removed is led away in a line through a valve to an evaporation tank that is connected to the low-pressure side of the said ejector, in that water is separated in the evaporation tank from the compound for freezing point depression, in that the water from the evaporation tank is caused to be led to the low-pressure side of the ejector, and in that the compound for freezing point depression that has been separated in the evaporation tank is led to a storage tank for the compound for freezing point depression and that, when higher levels of the compound for freezing point depression are necessary in the first circuit, the compound for freezing point depression in the storage tank is caused to be led to the ejector through a stop valve. The invention is described in more detail below, partly in association with embodiments of the invention shown in the attached drawings, where
- Figure 1 shows a flow diagram for the removal from a
heat recovery system of a compound for freezing point depression that has a higher boiling point than that of water
- Figure 2 shows a flow diagram for the removal from a
heat recovery system of a compound for freezing point depression that has a lower boiling point than that of water .
Figures 1 and 2 illustrate the present method to remove com- pounds for freezing point depression in a heat recovery system in a building. The heat recovery system comprises a first circuit 1 with process water and a first heat exchanger 2 to remove heat from warm air that is leaving the building and transferring it to process water, and a second heat exchanger 3 to remove heat from the water that has been heated in the first heat exchanger and transfer it to colder outdoor air. The first circuit comprises a pump 4 for pumping process water around the circuit. A compound for freezing point depression is added to the process water when necessary. A fraction of the process water from the first circuit 1 is led to a second circuit 5 that is connected in parallel with the said first circuit 1 and that comprises a pump 6 and an ejector 7 in order to achieve negative pressure. According to the invention, the separated process water is led in a line 19; 20 through a valve 20; 22 to an evaporation tank 8 that is connected to the low-pressure side of the said ejector 7 through a line 9. The water is separated from the compound for freezing point depression in the evaporation tank 8 through the water being vaporised. Water in the form of water vapour from the evaporation tank is caused to be led to the low-pressure side of the ejector 7. Thus the water vapour will condense against the water from the second circuit 5 that flows through the ejector 7. The water vapour may be precondensed in an intermediate condenser 17.
The compound for freezing point depression that has been separated in the evaporation tank 8 is led to a storage tank 10 for the compound for freezing point depression.
When necessary, the compound for freezing point depression in the storage tank 10 is caused to be led to the ejector 7 through a stop valve 11, whereby the compound for freezing point depression is fed out into the said first circuit 1.
In the case in which the compound for freezing point depression has a higher boiling point than that of water, see Fig- ure 1, the invention is characterised in that water that has been vaporised in the evaporation tank 8 is led through the line 9, which constitutes the said connection between the evaporation tank 8 and the low-pressure side of the ejector 7, and in that the compound for freezing point depression that remains in the evaporation tank 8 is led through a line 24 through a valve 25 to the storage tank 10 for the compound for freezing point depression, and in that, when necessary, the compound for freezing point depression in the storage tank 10 is caused to be led to the ejector 7 through the stop valve 11. An example of such a compound is ethylene glycol.
When the compound for freezing point depression is to be added to the said first circuit 1, a valve in the line 9 that runs between the evaporation tank 8 and the low-pressure side of the ejector is closed.
In the case in which the compound for freezing point depres- sion has a lower boiling point than that of water, see Figure 2, the invention is characterised in that the compound for freezing point depression that has been separated in the evaporation tank 8 is led through the line 9, which constitutes the said connection between the evaporation tank 8 and the low-pressure side of the ejector 7, in that the compound for freezing point depression is caused to condense in a condenser 12, in that the condensate is caused to be led to a storage tank 13 through a line 16 and a valve 26, and in that separated water in the evaporation tank 8 is led to the low- pressure side of the ejector 7 through a valve 23 in a line 14, and in that, when necessary, the compound for freezing point depression in the storage tank 13 is caused to be led to the ejector through a stop valve 15. An example of such a compound is alcohol.
When the compound for freezing point depression is to be added to the said first circuit 1, a valve 18 in the line 9 that runs between the evaporation tank 8 and the low-pressure side of the ejector is closed.
According to one preferred embodiment, the pressure before the ejector is between 3 and 6 bar and the pressure on the low-pressure side of the ejector is between 0.05 and 0.4 bar. The pressure in the first circuit 1 may be approximately 2 bar . According to a second preferred embodiment, the process water in the evaporation tank is caused to be heated to at least 50 °C, in order in this way to accelerate the evaporation process in the evaporation tank 8.
As the description given above makes obvious, the present method makes it possible for compounds for freezing point depression to be both easily removed and easily added to the said first circuit. This means that it is possible to add as much of the compound for freezing point depression as is necessary, taking into consideration the actual outdoor temperature. It is, therefore, possible by continuously regulating the level of the compound for freezing point depression to have all the time as good heat transfer as possible in the heat exchangers 2, 3.
Thus, the present invention solves the problem described in the introduction. A number of embodiments have been described above. The invention, however, is not limited to a heat recovery system with the design that is shown. The invention can be used, for example, with a borehole heat exchanger and with other energy systems. The invention, therefore, is not limited to any particular energy system.
Furthermore, the drawings in Figures 1 and 2 show only schematic designs of the arrangements. The invention can, in addition, be applied with compounds for freezing point de- pression and other compounds for freezing point depression than ethylene glycol and alcohol. Thus the present invention can be varied. The present invention is, therefore, not to be considered to be limited to the embodiments specified above but can be varied within the scope specified by the attached patent claims.