FI113203B - A method of pumping heat in a cooling system, particularly a district cooling network, to recover the waste heat from the water circulating therein, and a device for that purpose - Google Patents

Description

113203

A method of pumping heat in a cooling system, in particular to recover wasted heat from water circulating in a district cooling network, and a device for this purpose. a way of pumping heat from the water circulating in the cooling system, preferably the district cooling network, and utilizing the waste heat thus generated.

The present invention further relates to an apparatus for cooling water circulating in a district cooling network and utilizing the waste heat thus generated, and in particular an apparatus comprising a compressor-driven refrigeration apparatus having a cooling medium in a sequential circuit: a compressor, a condenser, a the water supply line and the evaporative cooling water return line.

In Finland, the demand for district cooling and, in general, the need for refrigeration of apartments 20 has only become topical since the early 1990s, when the rapid development of information technology increased the heating load and air conditioning demand of office premises. Due to demand 1, production of district cooling has begun in a few cities in Finland. In general, attention has been paid to the quality of room air in every way. Studies have shown that workplace comfort and efficiency at work ** · * '25 are significantly improved under well-ventilated conditions. Old office, hotel or business premises generally do not have the space to build appropriate air-conditioning and cooling systems. In addition, condenser units installed in confined spaces may cause a noise problem such that the desired improvement in comfort does not occur; be reached. This problem occurs especially in house or apartment-specific cooling systems.

* »2 113203

It is known that, under certain conditions, centralized cold production, so-called district cooling, can provide significant advantages over property-specific cooling, despite the fact that a separate pipeline network for the distribution of district cooling is required. The existing district heating pipeline network cannot be used for cold distribution, as heat is also needed in summer, for example. therefore, the supply of domestic hot water cannot be interrupted. However, the high set-up costs of the pipeline network have meant that, so far, at least in Finland, no comprehensive district cooling systems for large agglomerations are sought, but smaller, typically a few MW, local district cooling centers are being built where there are more the other can be centralized.

The refrigeration plant of such a district cooling center always produces a waste heat stream 15 which is greater than the refrigeration capacity of the plant. Until now, this waste heat stream has generally been eliminated by introducing it into the open air or waterways through efficient heat exchangers. It is an object of the present invention to provide a way and apparatus for advantageously utilizing this waste heat stream to produce district heat.

: 20 'In the past, it has been known that condensate heat is supplied to the return line of the district heating network ... ... or raised by an additional heat source and then • · supplied to the district heating network supply line. In the first case, heat production has little or no technical benefit in all parts of the district heating network. As heat is transferred to the return line, the return temperature of the return line increases, and the heat loss of the return network increases accordingly. In addition, the measure caused: 'Ensures higher pumping costs as a result of increased water circulation. Transferring waste heat to the return water outside the power plant is of no significant benefit or is technically not feasible in all parts of the district heating network. As the heat is transferred to the return line, the return temperature of the return line increases 1 * 113203 3 and the heat loss increases accordingly. In addition, the operation will result in higher pumping costs as a result of increased water circulation.

Finnish patent publication FI 98858 C discloses the introduction of 5 waste heat generated in the district cooling network into the return line of the district heating network.

It is therefore an object of the present invention to provide a way of pumping heat in a cooling system, preferably in a district cooling network, to utilize the waste heat thus generated from the water circulating.

10

It is a further object of the present invention to provide an apparatus for executing the above method for cooling water circulating in a district cooling network, comprising a compressor-driven refrigeration system having a cooling medium in a sequential circuit: a compressor, condenser, a a hot water supply line and a water line returning to the evaporator cooled district cooling network.

The main features of the invention are set forth in claims 1 and 8 of the appended claims, which separately define the scope of the present invention. Other claims only define the invention. ··, popular embodiments by way of example.

• <: ***: The present invention is therefore based on the utilization of waste heat pumped from water circulating in a cooling system, and especially in a district cooling network: · in district heat production, i.e. the so-called combined cold and heat production.

* · '· · · * By combining district cooling production with a district heating distribution system, in the summer conditions in Finland all that can be produced in cold production can be utilized; ; 30 waste heat, or condensate energy, especially when the heating network covers the whole of the heat and the condensate energy generated in cold production and the required district heating energy are in balance. In general, this is not possible in a building-specific system, even if partial accumulation or similar phasing is used. In addition, the interests of the heat network operator 5 and the desire to absorb the energy generated must be taken into account. As a property-specific, this type of waste heat recovery is not economically viable either for technical reasons alone or for heat quality liability.

When heat is pumped to utilize the waste heat thus generated from the water circulating in the district cooling network, it is preferable that the district cooling generating center is located close to the district heating network with a sufficient amount of heat behind the waste heat output. By introducing waste heat from district heating production into a side stream separated from the return line of the district heating network before returning it to the supply line of the district heating network, there are not only 15 additional savings in district heating production costs.

In the production of district cooling it has proved to be e.g. The following problem areas for which the present invention provides a solution, a) Installation of large air condensers in the urban area, which is very difficult, is eliminated because condensate heat can be transferred to the district heating network.

'(B) Similar condensation-based condensation water vapor is a problem. those that are expensive to maintain and winter maintenance due to freezing or drainage in Finnish conditions. In the present invention, the condenser circuit is continuously connected to the district heating network, whereby there is no risk of freezing and the condenser circuit does not require the use of glycol.

> · · • · 'c) The installation of heavy condenser units in the old building stock is indicated;' For reasons of strength and space technology, it has become difficult or even impossible.

'' In addition, the premises in question should be located above the roof of the building or in the yard, so that they are not landscaped or façade; 30 desirable.

5 113207 d) Old buildings would have plenty of usable space, such as old boilers, carbon storage or oil storage facilities, when the property has moved to district heating. These facilities are located separately from the living quarters and generally underground and centrally located in the same location as the district heating connection. The present invention enables the utilization of these spaces. Property or area-specific cold production equipment can be located in these spaces, and in some cases, house piping can be used to transfer heat generated in cold production to the district heating network. Compressors installed in rooms can be sound-proofed so that they do not cause noise problems to the environment, for example in the form of chime noise.

e) The advantage of small-scale centralized refrigeration can also be that the summer load level of the power grid in the center of the city allows the start-up of reasonably sized compressor units. In contrast to Central Europe, electricity consumption is at its peak in mid-winter during peak heating demand, whereas in Central Europe it is in summer during peak cooling. Thus, there is a large amount of so-called surplus electricity available in Finland during the summer, either non-fossil electricity from nuclear or hydropower. The present invention enables the conversion of non-fossil electricity to non-fossil heat at the present state of the art and in the best environmental conditions. , 20 in the most eco-friendly way.

;! > (f) A unique district heating network infrastructure is available in Finland, enabling the implementation of the present invention. Similar networking: * * iot is just developing in the rest of Europe with the rise of central heating ::.

G) In addition, the interconnection of the district heating network and the cold network, as disclosed in the present invention, allows additional cooling of the condenser circuit of the refrigeration equipment to be carried out away from the immediate vicinity of the refrigeration unit. This is possible by cooling the return water of the district heating network with a separate heat exchanger (auxiliary condenser), either to the water or; 30 air. This system may need to be used in a situation where the remote 11320? 6 the return water from the heating network is not sufficient for condensation of this cold production unit for one reason or another.

h) Due to the present invention, district heat production in connection with district cooling production reduces the cost of pumping district heat and heat losses, since in the case of long distance distances, so-called circulations have to be used in the long-distance district heating network. The current recommendation allows the supply water temperature to be lowered up to 60 ° C, whereby the hot 10 hot water will be sufficiently hot in the condominium network.

i) By producing cold according to the invention, a small overall cost is achieved in network investments and equipment investments. In addition, the plant's operating, maintenance and space costs are low. Short transmission distances in the district cooling network reduce pumping costs and heat losses.

J) Cold production carried out in the manner of the invention does not cause any special measures during the winter, since the equipment is completely indoors and, if there is no need for district cold in winter, the district cooling network can be kept mild with a small side water flow.

I. In a preferred embodiment of the invention, the waste heat produced in the district cooling network is conducted to a side stream separated from the return line of the district heating network before returning it to the district heating network supply line. Returnable '- ·: side current temperature can be even lower than district heating supply line: temperature, whereby the addition of waste heat reduces the district heating water temperature and the 25 energy increase is only visible as an increased mass flow. During the summer months, it is common for district heating water temperatures to be "unnecessarily" high in the supply line, since lowering it to a minimum supply contract would not compensate for the mass flow, would no longer be of real benefit to the district heat supplier.

Instead, there would be savings in reducing power output, so it is worthwhile to compensate the waste heat producer 30 despite the fact that the increase in waste heat 113203 7 pays off despite the fact that the increase in waste heat reduces the water temperature in the district heating pipeline.

In an alternative embodiment of the invention, heat is pumped in several 5 successive stages, whereby several compressor-driven refrigeration units are in series, and the district heating network and the side stream separated from the district heating network are adapted to flow either downstream or upstream.

Compared to the corresponding single-compressor cooling system, the advantage of this embodiment is that only the first circuit has a temperature difference equal to that of a single-circuit solution. In the following circuits, the temperature difference between condensation and evaporation is substantially smaller. This, in turn, means a better coefficient of refrigeration, that is, lower electricity consumption in relation to the cold power of 15. This embodiment is particularly advantageous when, for example, the extraordinary stringent reliability requirement requires that there should be more compressors.

On the other hand, it is also known that the efficiency of compressors, as with many other devices, generally improves as the size of the device increases, and that the purchase price increases less than directly in relation to capacity. This aspect, in turn, would favor a single compressor process. Ideally, if the multi-compressor process is ':'; modularity could also be achieved with a single compressor.

According to a particularly preferred embodiment of the invention, this is possible · * .List, albeit at the expense of a more sophisticated control system and accessories, mainly tanks. In this embodiment, instead of the multi-compressor process, periodic heating of a side stream separated from the return line of the district heating network is used in one and the same compressor circuit using intermediate storage and directing water from each intermediate storage via said compressor circuit to the next intermediate storage. 8 finally to the district heating supply line. Intermediate storage is preferably carried out vertically in an elongated container which maintains a bottom-up temperature gradient. The container is preferably provided with overlapping midsoles or the like, which are preferably vertically adjustable.

5

According to a further embodiment of the invention, the heated water can be similarly drawn from the district cooling network and fed back to the district cooling network via several serially connected intermediate storages, after the heat is first pumped from each intermediate store in successive and 10 Also in this embodiment, intermediate storage is preferably carried out in a vertically elongated container which maintains a top-down temperature gradient. Similarly, the container is preferably provided with overlapping midsoles or the like, which are preferably vertically adjustable.

15

The advantages of periodic cold processes have hardly received any attention in the literature, with the exception of the Granryd process (U.S. Patent 4,014,182). However, therein, the cyclicity and the benefits thereof are provided by additional coolant tanks and repeatedly changing flow paths of coolant medium! . 20. In a preferred embodiment of the present invention, the cooling medium: *, instead, is circulated just as in a continuous process, while the cyclic process; '': The addition is caused by the environment, that is, the inlet temperatures of both the heat-releasing and the heat-receiving water flows vary periodically. In the present invention, the amount of refrigerant medium is not higher than normal and the load changes of the compressor 25 are smooth.

In a further embodiment of the invention, the compressor-driven refrigeration system is provided with a countercurrent heat exchanger between the condenser and the pressure relief valve for sub-cooling the cooling medium in the district heating network! 30 at a fractional flow of cooled water to increase the coefficient of cooling and volumetric cooling power. Said countercurrent heat exchanger and pressure relief valve 11320? 9 missions. Preferably, there may be another countercurrent heat exchanger between said countercurrent heat exchanger and the pressure relief valve, which may then be connected to an additional intermediate storage, which may from time to time be connected to the heat supply water

The terms district heating and district cooling are used broadly in this context as opposed to property-specific heat and cooling. The first 10 signs are called district heating.

The embodiment of the invention can be implemented by a plurality of device connections, some of which are illustrated in detail by way of the accompanying drawings, in which: Figure 1 schematically illustrates connecting a district cooling and district heating network according to the invention to effectively utilize wasted heat generated in the district cooling network; 2. Fig. 2 shows a cooling apparatus having three compressor circuits, '! Fig. 3 is a vertical view of a single compressor circuit arrangement with intermediate storage; and Fig. 4 is a vertical view of an alternative embodiment. equipped with cooling medium subcoolers.

'; * In Figure 1, the district heating network is generally represented by reference numerals 1-4 and consists of '..: 25 district heating plants 1 where water is heated and supplied to the consumer 2 via the supply line 3 and back to the return line 4. The return line 4 is connected to the ... 'a diverging side line 5 leading to a portion of the water flowing through the return line 4 to the remote cooling: compressor cooling unit of the cooling plant, generally denoted by * 7, and where the water 30 heated by waste heat from the cooling unit is recirculated to the district heating? Although the temperature of the hot water in the condenser cooling system 7 of the returning district cooling plant 7 is lower than that of the flow water 3 of the district heating plant 1, it nevertheless increases this mass flow, whereby the district heating plant 1 can accordingly reduce the output.

The water cooled by the compressor-driven cooling apparatus 7 is supplied via a supply line 9 to the consumers 8, and from there the heated water is recycled via a return line 10.

10

In the embodiment shown in Fig. 2, the cooling apparatus 7 consists of three series and in this case downstream connected compressor circuits, each comprising a cooling medium in the downstream direction: a compressor 11, a condenser 12, a pressure relief valve 13 and a through the condenser 12 to the heat receiving side and thus heated with waste heat back to the district heating network in the flow line 3 along the return line 6.

. 20, district cooling water heated in the network, whereas the return conduit 10 is conducted successively for each compressor circuit through the evaporator 14 of the heat emitting side of a later: upstream of the cooling entered with respect to the page on the flow and, finally, back to the flow line temp • ohtoon 9j kaukoj a äähdytyksen to the consumer through 8.

Fig. 2 shows only one example of a series connection of a plurality of compressor circuits, and it is clear that there may be fewer or more compressor circuits than three and vice versa; Current coupling is thermodynamically at least as advantageous as downstream coupling. Serial connection of multiple compressor circuits is particularly advantageous when exceptionally harsh operating reliability requires the use of compressors of up to 30 amps.

113203 n

On the other hand, it is generally known that the efficiency of compressors, as with many other devices, generally improves as the size of the device increases, and that the purchase price increases more modestly than in direct relation to capacity. This aspect again would favor a single compressor circuit solution. Ideally, the thermodynamic advantage of a multi-compressor solution could also be achieved with a single compressor.

According to the invention, this is possible, albeit at the expense of a more complicated control system 10 and some accessories, mainly tanks. This is made possible internally by a periodic process. The district heating and district cooling water inlet flows 5,10 to the cooling apparatus 7 and out to 6,9 are thus still constant and temperatures constant, as in the embodiment of Figure 2, but one efficient compressor circuit in a way takes over the functions of the three compressor circuits of Figure 2. Such a principle can be implemented in many different ways, but one thing in common is the need for intermediate storage of heat and cold 15 ', 16' at different temperatures. The simplest but not necessarily the only solution is that the intermediate storage facilities consist of water tanks through which district heating and district cooling water are filed. In fact, an arrangement where there are several temperature zones within the same container that do not mix too much: • is enough. In narrow vertical tanks 15,16, where the temperature of the zones increases as they go up, the difference in density may already prevent excessive mixing: but the freestanding midsoles do the same. The volumes of the zones vary over the period, but their sum remains constant. However, district heating water and district cooled water have their own tanks 15,16, or alternatively they could be separated by a solid and sealed septum in a common vessel.

i I.

• »,:. Figure 3 shows one such embodiment. Temperature zones or interim storage. the to 15 'is four on the warm side and three 16' on the cold side. It is also possible to leave the cold side of the tank 16 completely off, but then have to be 30-höyrystymisläm patient's time should be less than kaukojäähdyty p throughout the network supply pipe 9 113 203 12 returned to the water outlet temperature, wherein the thermodynamic preference of course suffer. In the embodiment of Figure 3, the mass flow rate of the water pumped through the condenser 12 is three times that of the continuous throughflow of the tank 15, and the mass flow rate through the evaporator 14 is twice the flow rate of the cold tank 16.

In the embodiment of FIG. is fed back to the district heating network supply line in the return line 6.

Similarly, in the district cooling network, the heated water is led from the return line 10 15 vertically to the upper part of the elongated tank 16, which has overlapping intermediate storage tanks where the temperature goes down and the cooled water from the lower intermediate storage 16 '

The intermediate storage tanks 15 ', 16' of the tanks 15 and 16 are periodically coupled to the cooling apparatus 7 such that two overlapping intermediate storage tanks are connected in turn, the intermediate storage tanks 15 'outlets 22 to the heat receiving side of the cooling system 7 countercurrent condenser 12 on the heat transfer side of the countercurrent evaporator 14.

The cold coefficient and the volumetric cooling power can be further improved by fitting one or preferably two subcoolers 17,17 'to the compressor circuit 11-14 prior to the pressure relief valve 13, as shown in Figure 4. The subcoolers 17,17 'are heat exchangers connected to a compressor circuit between the condenser 12 and the pressure relief valve 13 upstream of the cooling medium.

: 30 113203 13 Viewed in the flow direction of the coolant medium, the coolant medium stream from the condenser 12 in the first subcooler 17 is cooled by a stream drawn from the lower intermediate store 15 'of the tank 15 to a temperature close to the The heated water stream in the subcooler 17 is then connected to the return stream from the condenser 12 to the tank 15. The thermal power transferred in this way is utilized and the mass flow of district heating water flowing through the subcooler 17 is much smaller than that of the condenser 12.

However, cooling of the cooling medium may be continued even further in the second sub-cooler 17 'by using remote cooling water 20 from the secondary cooler 17 to the upper part of the tank 16 from the return line 10 of the district cooling network and heated by the district cooling The water returning in the conduit 23 cannot be mixed with the district heating but is collected in a separate intermediate storage 19, from which it is once recycled for one period, ie cooled back to its original temperature by circulating it through the evaporator 14 (not shown).

It is clear that the present invention can be varied within a very wide range; within the scope of the appended claims 1 and 8 utilizing cold and in particular; utilization of the waste heat from district cooling production in the heating of the by - pass from the return line of the district heating network before returning it to the supply line of the "!" district heating network.

; 25

Claims (14)

113202 A method of pumping heat from water circulating in a cooling system (7), preferably a district cooling network (7-10), and utilizing the waste heat thus generated in the district heating network (1-4), characterized in that the waste heat is at least partially 4) to the isolated side stream (5), which is then returned (6) to the district heating network supply line (3). A method according to claim 1, characterized in that only so much waste heat is supplied to the side stream (5) separated from the district heating return line (4) that the temperature 10 of the side stream (6) to be returned to the district heating supply line (3) is generally lower than the temperature in the district heating supply line. 3). Method according to Claim 1 or 2, characterized in that the heat is pumped in several successive stages (7) to a side stream (5) separated from the water (9-10) circulating in the cooling system from the return pipe (4) of the district heating network. Method according to Claim 1 or 2, characterized in that the side current (5) separated from the return line (4) of the district heating network 15 is supplied to the supply line of the district heating network via three or more interconnected intermediate storage (15 '). (3) and that the waste heat is pumped (7) from each intermediate storage (15 ') in turn; and to the next intermediate storage facility as periodic measures. : 20 Method according to Claim 1 or 2, characterized in that the lateral current (5) separated from the return line (4) of the district heating network is led vertically to the lower part of the conical tank (15) and returned (6) from its upper part to the district heating network. to the supply line (3), whereby the waste heat is pumped (7) from each of the lower levels of the tank (15) to the next higher level by a periodically supplied stream '· *'. ;. * (1 Method for pumping heat from water circulating in a district cooling network according to claim 4 or 5, characterized in that the district cooling network (7-10) extracts heated water (10) which is fed to a plurality of connected intermediate storage tanks (10). 16 ') back to the district cooling network, and that heat is pumped (7) from each of the streams in turn from the intermediate storage (16') to the next intermediate storage by periodic repetitive operations. Method for pumping heat from water circulating in a district cooling network according to claim 4 or 5, characterized in that the district cooling network (7-10) takes in the heated water (10) which is vertically fed to the upper part of the elongated tank (16) and returned (9). ) from its lower part to the district cooling network, whereby heat is pumped (7) from a stream drawn from each level of the tank, which, when cooled, is returned to the next lower level. A device for cooling the water circulating in the district cooling network (7-10) and utilizing the waste heat thus generated in the district heating network (1-4), comprising a compressor-driven cooling system (7) having a compressor (11), a condenser (12) a pressure relief valve (13) and a vaporizer (14) having a heat supply water return line (10) connected to the district cooling network and a water supply line (9) returning to the cooled district cooling network (12) in the evaporator (14), characterized in that a side line (5) detached from the return line (4) of the district cooling network (1-4) and the return line (6) of condensed hot water connected to the main line (3) of the district heating network are connected to the heat receiving side. Device according to Claim 8, characterized in that the compressor-driven refrigeration system (7) has a plurality of compressor circuits (11-14) in series, whereby the heated water (10) in the district cooling network (7-10) is arranged to flow in sequence. the heat transfer sides of the evaporator (14) of each compressor circuit ··. 25 and the side flow (5) separated from the district heating network is arranged to flow in the ma: ··; the heat of the condensers (12) of the cooling equipment of the compressor circuits *. _: downstream or upstream through the receiving sides. 113203 Apparatus according to claim 8, characterized in that the side line (5) detached from the district heating return line (4) is vertically connected to the lower part of the elongated tank (15) and the heated water return line (6) connecting to the district heating supply line (3). ) is preferably divided by partitions 5 (21) or the like into vertically overlapping intermediate storages (15 ') which can be connected in pairs in turn by connecting conduits (22) to the heat-receiving side of the condenser (12) of condenser (7) 15 '). Apparatus according to claim 10, characterized in that in the district cooling network the heated water return line (10) is connected vertically to the upper part of the elongated tank (16) and the cooled water supply line (9) returning to the district cooling network, preferably the tank (16). partitions (21) or the like divided into vertically overlapping intermediate storage tanks (16 ') which can be connected in pairs in turn by connecting lines (18) to the heat transfer side of the evaporator (14) of the compressor-driven refrigeration unit to supply water therethrough Device according to Claim 10 or 11, characterized in that the compressor; The refrigeration apparatus (7) comprises a countercurrent heat exchanger (17) between the condenser (12) and the pressure relief valve (13) for subcooling the cooling medium, part of the cooled water (5), in the district heating network (1-4). Apparatus according to claim 12, characterized in that the compressor-driven cooling apparatus (7) has a second counter-current heat exchanger (17 ') between said countercurrent heat exchanger (17) and the pressure relief valve (13) for further subcooling the cooling medium in the network (7-10). with a portion (20) of hot water (10). i t »· 11320? Apparatus according to claim 13, characterized in that said second countercurrent heat exchanger (17 ') is connected via a pipe (23) to an intermediate storage (19) which is occasionally connected to the heat-releasing side of the evaporator (14) of the compressor-driven cooling system. -5 to at least reach the temperature of the heated water (10) in at least the district cooling network. i t »113203