WO1995020133A1

WO1995020133A1 - A method concerning a thermal energy distribution system, and a thermal energy distribution system

Info

Publication number: WO1995020133A1
Application number: PCT/FI1995/000026
Authority: WO
Inventors: Seppo Leskinen
Original assignee: ABB Installaatiot Oy
Current assignee: ABB Installaatiot Oy
Priority date: 1994-01-24
Filing date: 1995-01-20
Publication date: 1995-07-27
Anticipated expiration: 1996-07-24
Also published as: FI940344A7; JPH09507705A; AU1419295A; NO963070D0; CA2181574A1; SK95896A3; ES2128707T3; DK0740760T3; FI98858C; NO963070L; FI98858B; ATE175264T1; EP0740760B1; PL315524A1; DE69507013D1; FI940344A0; CN1139478A; KR970700849A; EP0740760A1; CZ216396A3

Abstract

The invention relates to a method concerning a thermal energy distribution system, and a thermal energy distribution system. In the invention, heating energy absorbed into a heat carrier and concentratedly generated for heating of buildings (4) is distributed by means of one pipe or one group of pipes (1) to heating devices (6) arranged in the buildings and, correspondingly, cooling energy concentratedly generated by a cooling aggregate (16-19) is distributed by a second pipe or group of pipes (3) to cooling devices (5) in the buildings. To lower the costs, the cooling aggregate (16-19) is arranged to be condensated by return liquid obtained from a return pipe (2) of a heating energy/cooling energy transferring system, and at least part of the liquid used for the condensation is arranged to be supplied directly back to the return pipe (2).

Description

A method concerning a thermal energy distribution system, and a thermal energy distribution system

The invention relates to a method concerning a thermal energy distribution system, in which method heating energy absorbed into a heat carrier and concen¬ tratedly generated for heating of buildings is distrib¬ uted by means of one pipe or one group of pipes to heat¬ ing devices arranged in the buildings and, correspon - ingly, cooling energy concentratedly generated by an absorption-type cooling aggregate is distributed by a second pipe or group of pipes to cooling devices in the buildings. The invention also relates to a thermal energy distribution system. Today the most common way of cooling buildings is using cooling aggregates that are based on a com¬ pressor aggregate and are dispersed to places of use. In them, cooling power is generated by means of electri¬ city. The proportion of the cooling of buildings to the consumption of electricity is already significant; e.g. in the South of Europe the electricity consumption peaks in the summer. Further, the timing of the consumption is disadvantageous in view of the production. Apart from the production of hot tap water, there are hardly any other uses for the heat inevitably generated as electri¬ city is produced, and so it has to be condensated in the waterways e.g. by sea-water condensers or in the air by means of cooling towers.

Cooling power could also be produced by waste heat obtained from the production of electricity in so- called absorption aggregates, the best known of such aggregates being lithiumbromide/water and ammonia/water aggregates. Consumption of electricity and thus e.g. C0₂ emissions could be reduced thereby, and waste heat, which at present is totally wasted, could be put into use.

The most inexpensive way of generating cold would be a so-called district cooling system, in which cooling power would be concentratedly produced in power plants and distributed to users via a piping network in the same way as district heat. This would have a posit¬ ive effect e.g. on servicing costs - which in the pres¬ ent, dispersed systems are high - and on reliability of use, levelling down of the effect of occasional load peaks, etc.

However, district cooling systems have not become general due to heavy investment costs. Although the kWh price of the chill generated in this way is low as compared with the price of electricity, the number of hours when chill is needed is too small to cover the investment costs in those climatic zones where district heating systems are worth building. For example in Fin¬ land, such systems have thus not been built. The major- ity of them exist in Japan, Korea and the U.S.A.

Simultaneously filed Finnish Patent Application 940,342 discloses a thermal energy distribution system in which the costs of the distribution network can be essentially reduced by arranging a common return pipe for the cooling and heating water. The application also discloses embodiments by which the costs of a district cooling network can be lowered further. The condition is that the heating, plumbing and air conditioning sys¬ tems of the building are designed in accordance with the principles set forth in Finnish Patent Applications 941,034 and 915,511.

Further, simultaneously filed Finnish Patent Application 940,343 discloses a heat transfer system by which separate heat-exchangers between the cooling net- work of the building and the district cooling system become unnecessary. This eliminates one of the big cost items of the district cooling system.

The biggest cost item of the system, however, consists of absorption aggregates and their condensers. For example in 'Concentrated cooling', a research con¬ ducted by order of the Finnish Ministry of Trade and Industry and the Thermal Power Plant Association, their proportion to the overall investments was observed to be about 50%. The object of the invention is to provide a method and a system by which the drawbacks of the prior art can be eliminated. This is achieved with the method and system according to the invention. The method of the invention is characterized by using return liquid of a heating energy/cooling energy transferring system as condensation water in the cooling aggregate, and supply¬ ing at least part of the condensation water leaving the cooling aggregate directly back to the return liquid of the heating energy/cooling energy transferring system. The system of the invention, in turn, in characterized in that a cooling aggregate is arranged to be con- densated by return liquid obtained from a return pipe of a heating energy/cooling energy transferring system, and that at least part of the liquid used for the con- densation is arranged to be supplied directly back to the return pipe.

The major advantage of the invention is that the overall costs of the absorption aggregate can be essentially lowered as compared with the prior art, which greatly improves profitability of the district cooling system. The heating power conducted to the absorption aggregate can be re-used in its entirety for pre-heating the supply water of the district heating system. Further, the invention solves many technical problems that concern corrosion, treatment of raw water, hygiene, and health hazards. When construction of a district cooling system becomes possible in practice, the above advantages of district chill are also achieved. In the following, the invention will be described in greater detail with reference to the embodiments illustrated in the attached drawing, wherein Fig. 1 shows a general view of a 2-chamber absorption aggregate, Fig. 2 shows, schematically, how the aggregate of Fig. 1 is connected to a district cooling and an energy production system,

Fig. 3 shows a general view of a first embodi¬ ment of the system according to the invention, and Fig. 4 shows a general view of a second embodi¬ ment of the system according to the invention.

Fig. 1 shows a conventional 2-chamber lithiumbromide/water absorption aggregate. Fig. 2, in turn, illustrates how the aggregate of Fig. 1 is connected to a district cooling and an energy production system. Fig. 1 also shows the temperatures prevailing at different parts of the absorption aggregate. For the sake of clarity, Fig. 2 does not include a circuit for a refrigerant. The aggregate operates on the following principle. In a boiler element 17 of the aggregate, where the pressure is higher, water and lithiumbromide are present as a solution. The lithiumbromide is boiled from the solution by means of hot water or steam, which is obtained from a condensation pipe 20 of a turbine 9 by means of a pump 22, and returned to the condensation pipe at a lower temperature through a control valve 21.

The evaporated lithiumbromide is condensated to liquid form in a condensation element 18, where it is cooled by condensation water withdrawn from a water cooler through a condensation pipe 25 and through a control valve 24 by a cooling water pump 23.

The lithiumbromide condensed to liquid form flows to an evaporator element 16, where it is evapor- ated by low pressure. During evaporation, heat is absorbed, and so the temperature marked in Fig. 1 is achieved. The water obtained from a return pipe 2 of the district cooling network via a control valve 14 by a pump 15 is cooled in the evaporator element 16 and pumped into a supply pipe 3 of the district cooling system.

In the absorption aggregate, the lithiumbromide flows from the evaporator element 16 to an absorption element 19, where it absorbs water, re-producing a solu- tion, and is pumped back into the boiler portion 17 by pump 23. The liquefaction in the absorption element is effected by cooling with the condensation water obtained through pump 23, valve 24 and pipe 25.

The figures do not show a device for cooling the condensation water. In an absorption aggregate, heated water is usually cooled in sea water heat- exchangers, cooling towers or the like.

The temperatures at the different parts of the absorption aggregate marked in Fig. 1 show that the temperature of the condensation water is almost the same as the temperature of the return water in a district cooling/district heating system.

The above observation has led to the realiza¬ tion on which the present invention is based: instead of water produced in separate cooling apparatus, return water obtained from the district heating/district cool¬ ing system is used as condensation water in the absorp¬ tion aggregate, and when it has absorbed the excess heat of the absorption aggregate, the return water is returned, pre-heated, to the return pipe for use in the production of hot tap water.

The above basic idea significantly reduces the investment costs of the absorption aggregate. According to the research mentioned above, the cooling of the condensation water makes up about 30% of the overall costs of the absorption aggregate, i.e. about 15% of the investments in the whole district cooling system. This cost item is here totally eliminated, or at least essen- tially reduced.

In addition to the above, it should also be noted that the condensation circuit can be implemented as a closed-loop circuit, whereby the corrosion, dirty¬ ing and clogging problems of the cooling systems and the associated maintenance costs can be either fully elimin¬ ated or essentially reduced. When the invention is used, no investment or operational costs concerning the treat¬ ment of water are needed, nor fees for the consumption of water. A special problem with cooling towers is a health hazard brought about by the fact that legionella and other similar bacteria grow in these cooling towers. This drawback is also eliminated or at least essentially reduced by the present invention.

The above is intended to clarify the background and basis of the invention.

Fig. 3 shows a first embodiment of the system according to the invention. In Fig. 3, water is with¬ drawn from the return pipe 2 of the district heating/cooling system through a pipe 34 and control valve 24 by pump 23, and pumped into the absorption element 19 of the absorption aggregate and further to the condensation element 18. Most of the water is con¬ ducted through return pipe 26 back to the return pipe 2 of the district heating/district cooling system. If full cooling power is not needed, part of the water is returned through the circulating pipe 25 to pump 23.

The water pumped through return pipe 26 into the return pipe 2 of the district heating system and pre-heated to a temperature of about 40°C mixes with that part of the return water which has not been separ¬ ated by valve 14 and pump 15 to be cooled in the evaporator element 16 of the absorption aggregate and to be conducted as district cooling water to the supply pipe 3 of the district cooling system. The mixed water is pumped through a control valve 28 into a heat- exchanger 11 by means of a pump 27; in the heat- exchanger, it is heated to a temperature of about 65° to 75°C in the summer and conducted to a supply pipe 1 of the district heating system. A valve 7 closes the pipe between the district heating pipe 1 and the district cooling pipe 3 in the summer; in the winter the pipe is opened if the district cooling pipe 3 is to be used for storing heat or for transferring district heat. Part of the condensate obtained from the turbine 9 is pumped by pump 22 into the boiler element of the absorption aggregate, where it evaporates the lithiumbromide from the water, and further through control valve 21 back to the condensation pipe. The mixed condensate flows through the heat-exchanger 11 to a condenser 12, which is cooled e.g. by raw water obtained through a control valve 30 by a pump 29. From there the water is pumped by a supply water pump 13 into a steam boiler 8, and the steam generated therein is conducted by a pipe 10 to the turbine 9, where the steam condenses and subsequently returns to the condensation pipe 20.

District heating water is conducted by pipe 1 to heat-consuming devices 6 in buildings 4, in the summer usually to the tap water heat-exchangers. Corre- spondingly, district cooling water is conducted by pipe 3 to devices 5 that require cooling power, usually to the heat-exchangers serving air-conditioning apparatus. From both the above devices, the water returns to common return pipe 2.

The problem with the application of the inven¬ tion is that the consumption of tap water in the build¬ ings varies greatly, and that the estimated daily con¬ sumption in buildings where cooling is necessary is not sufficient to cover the water current needed for the cooling of the absorption aggregate, if the water tem¬ perature before the aggregate is +25°C and after the aggregate +40°C, and if the supply water temperature is +65°C. Usually in communities in the temperate zone, most buildings do not have a cooling system; e.g. in dwelling houses a cooling system is very rare. Further, for most buildings, evaporative cooling is sufficient. For example in Finland, less than 10% of all new build- ings have a mechanical cooling system. Even in these buildings, however, tap water is needed. The overall consumption of tap water in a community is usually sufficient to cover the cooling water demand of an absorption aggregate serving buildings that need cool- ing. To illustrate this, the district heating pipe 1 and the return pipe extend in Fig. 3 past the buildings 4 that need to be cooled. Fig. 3 also illustrates the fact that it is usually not economic to build a district cooling network but in the very centre of the community.

If, however, the consumption of tap water in some special case is not sufficient, the principle of the invention can be applied in accordance with Fig. 4. In Fig. 4 there is a condenser 32 arranged in the circu- lating pipe of the cooling circuit in the absorption aggregate, circulated water being cooled in said condenser e.g. with a pump 31 by means of raw water circulated through a control valve 33. The size of the condenser 32 is, in any case, only a fraction of the size of a condenser in a conventional system. This solu¬ tion still means great savings in investments, but the other technical advantages are partly lost. However, it should be born in mind that the condenser 32 is used only for a short time in a peak load situation, so clog- ging, corrosion and other problems are clearly smaller than in conventional plants, and so are e.g. the raw water costs.

The network has storage capacity by which it is able to level down the short-term, 1- or 2-hour peaks of tap water consumption. Instead, levelling down of long-term peaks is more difficult. In office and busi¬ ness premises and public buildings, the tap water con¬ sumption peak and the maximum cooling power coincide and compensate for each other. Instead, in dwelling houses, which are the buildings whose tap water consumption should be utilized, the situation is different.

In dwelling houses, tap water consumption is fairly even on weekdays from 7 am to 3 pm and then starts to increase. The peak is reached at about 9 pm. Night-time consumption is small.

In office premises, cooling demand already arises at 9 am, reaches the maximum at 11 am and remains constant until 6 pm, coming to an end at 8 pm. The con¬ sumption is even, due to the peak-cutting capacity of evaporative cooling.

The phase shift between the peak consumption of tap water and the maximum cooling efficiency is so great that a district cooling network is not able to compensate for it. The above problem can be eliminated by means of a chill accumulator suitably arranged in the system or in connection therewith.

The invention is described above by means of certain kinds of embodiments. The invention, however, is not limited to the above embodiments, but it can be modified quite freely within the scope of the claims. It is thus to be understood that the system of the invention does not necessarily have to be identical to what is illustrated in the figures but other kinds of solutions are also possible. All pipe connections that are known per se can be utilized in the invention. The absorption aggregate can also be replaced by other known cooling aggregates, if the temperature of the condensa¬ tion water is suitable, etc.

Claims

1. A method concerning a thermal energy dis¬ tribution system, in which method heating energy absorbed into a heat carrier and concentratedly generated for heating of buildings (4) is distributed by means of one pipe or one group of pipes (1) to heat¬ ing devices (6) arranged in the buildings and, corre¬ spondingly, cooling energy concentratedly generated by an absorption-type cooling aggregate (16-19) is distrib¬ uted by a second pipe or group of pipes (3) to cooling devices (5) in the buildings, c h a r a c t e r i z e d by using return liquid (2) of a heating energy/cooling energy transferring system as condensation water in the cooling aggregate (16-19), and supplying at least part of the condensation water leaving the cooling aggregate (16-19) directly back to the return liquid (2) of the heating energy/cooling energy transferring system.

2. The method according to claim 1, c h a r - a c t e r i z e d in that the water circulated in the cooling circuit of the cooling aggregate (16-19) is cooled by means of a condenser (32).

3. The method according to claim 1 or 2, c h a r a c t e r i z e d in that condensation water is used for producing hot supply water for a district heating system.

4. A thermal energy distribution system, in which heating energy absorbed into a heat carrier and concentratedly generated for heating of buildings (4) is arranged to be distributed by means of one pipe or one group of pipes (1) to heating devices (6) arranged in the buildings and, correspondingly, cooling energy concentratedly generated by an absorption-type cooling aggregate (16-19) is arranged to be distributed by a second pipe or group of pipes (3) to cooling devices (5) in the buildings, c h a r a c t e r i z e d in that the cooling aggregate (16-19) is arranged to be condensated by return liquid obtained from a return pipe (2) of a heating energy/ cooling energy transferring system, and that at least part of the liquid used for the condensa¬ tion is arranged to be supplied directly back to the return pipe (2).

5. The system according to claim 4, c h a r ¬ a c t e r i z e d in that a condenser (32) is arranged in a circulating pipe (25) of the cooling circuit in the cooling aggregate (16-19).

6. The system according to claim 4 or 5, c h a r a c t e r i z e d in that the liquid used for the condensation is arranged to be used for producing hot supply water for district heating.