DE2509965B2 - Process for space heating by means of a heat pump cycle - Google Patents

Description

45

The invention relates to a method for space heating by means of a heat pump circuit, on the cooled side of which there is a heat accumulator, which is used as a heat source if required. Such a method is known (US Pat. No. 2,677,243).

In the known method, heat can be stored on the cold side of the heat pump. It However, no measures are taken that the storage on the use of the practically free Could extend hypothermia of the Carnot cycle.

In connection with heat pumps, the use of solar energy has also been considered (Journal »Sanitäre Technik« 1957, No. 1 page 4). It is In this context, however, it has not been shown how a heat pump with storage on the cold side that uses a different energy source - z. B. Outside air as a heat source - uses when the sun is shining could also enter solar heat into the storage tank.

There are basically different attempts to be made, by means of electrically powered Heat pumps to heat living spaces, being as Heat transfer medium the groundwater, the soil or the Loss of heat in wastewater or the exhaust air - z. B. commercial operations - is included, is used.

According to a variant it is provided that the heat pump at each outside temperature, at the one Space heating is necessary, so even if you see? low outside temperatures, the outside air the required Removes heating heat and feeds it to the object to be heated. This process should be »always direct effective heat pump «. Low outside temperatures are seen over the year comparatively seldom. Such a heat pump must therefore for a rarely used maximum electrical power requirements are designed. The period of use is therefore short. If you think about it now, that the coefficient of performance of a heat pump is a function of the temperature difference to which the Heat must be raised to a higher temperature level, then you can see that one after this Process working heat pump at low outside temperatures of z. B. -18 ° C for hot water heating systems with a low flow temperature of around 55 ° C a performance figure of only

X I / =

333

333-250

χ 0.5 * 2

Tl - Tl

can provide; here mean:

ε = performance figure

7 * 1 = absolute condensation temperature

= 273 + 60 = 333 ° K Γ2 = absolute evaporation temperature

= 273 -23 = 250 ° K η = efficiency

The associated evaporation temperatures are then between minus 23 ° C and minus 28 ° C and the Condensation temperatures at plus 60 ° C. With one kWh of electrical drive, the heated The object is only supplied with two kWh of heat. If the outside temperature rises, it improves Performance figure when the control system of the heat pump adapts to the changed conditions This allows for a group of such operated, e.g. B. controlled with two-point regulators Heat pumps that the power requirement and the daily consumption of electrical work with increasing Reduce the outside temperature disproportionately. So they decrease relatively more than with a direct one effective resistance heating. The resulting low annual usage time enforces one high electricity price, which endangers the economic viability of the process

A second well-known variant of the heat pump, which extracts the required heat from the outside air, is described in the "Yearbook of Heat Recovery", 2nd edition, page 21, published by Vulkan-Verlag Essen. According to this variant, the heat pump only provides the required heat at outside temperatures that are not below freezing point. At low outside temperatures, a second, additional heating system takes over the heat supply. This heating system works with storable energies. The process is referred to as a bivalent heat pump. As shown in FIG. 1 shows, in Central Europe around 85% of the annual heat is generated at outside temperatures of # _a > 0 ° C. In this area, the heat pump can be equipped with a

better coefficient of performance than work at outside temperatures # _a <0 ° C.

Assuming the same heat distribution system as in the first case, ie a maximum flow temperature of the hot water heating of 55 ° C, then with an outside temperature of 0 "C a flow temperature of approx. 45 ⁰ C, ie a condensation temperature of 50 ⁰ C, and an evaporation temperature with an ^{outside temperature of 0} ° C. of -5 ° C. is sufficient, which would increase the coefficient of performance to: ι ο

323

323-268

■ 0.5 = 2.94

The mean annual output figure for all heating days would be 0 ^o C <# «<15 ^o C assuming an average outside temperature of +7.5" C in this area

15th

323

20th

323-275.5

0.5 = 3.4.

A method is also known in which small heat pumps are set up in a building and draw their heat from a pipe system whose heat transfer medium is about 25 ° C ("Yearbook of Heat Recovery", 2nd edition, page 15, Vulkan-Verlag Essen). Before the pipe system, a hot water storage tank is connected, which is heated to temperatures of fuels or electricity at 8O ⁰ C, to provide the heat for the entire object. The disadvantage of this process is that, as a result of high storage temperatures, quantities of heat can only be stored in the event of large losses, that is to say practically not over a long period of months. It is also not possible to use solar or environmental heat to heat the contents of the storage tank in warm weather, for example to obtain heating heat from the outside air.

The invention is based on the object of a method for space heating by means of a heat pump circuit to develop the storage using the supercooling heat of the Carnot cycle enables

The object described is achieved in that on the cooled side of the condenser Accumulated heat is introduced into the heat accumulator as supercooling heat, its temperature is lower than the temperature of the heat transfer medium occurring in liquid form behind the condenser and that the heat transfer to the heat store in the liquid area of the heat transfer medium of the heat pump circuit takes place.

This makes it possible to heat undercooling in a storage tank at a low temperature level to bring in the heat pump as a heat source on days when the outside temperature is lower serves. This achieves a breakthrough in the use of outside air as a heat source for Heat pumps for space heating. This reduces the performance of the compressor and its efficiency better, and the electrical annual service life of the system increases significantly.

The use of the supercooling heat is in principle b5 known (magazine "sbz" 1974, issue 23 page 1626). the known use of the supercooling heat does not serve to increase the efficiency of the Arrangement. Rather, it is intended to overheat the refrigerant vapors sucked in to such an extent that that there is a high probability that no refrigerant drops will get into the cylinder of a compressor, where they could trigger the dreaded fluid hammer. As is known, these could damage the Call up the compressor. These measures are also required in the known method, since there The heat pump described works with a flooded evaporator, in which the probability is high is that liquid particles are entrained in the vapor stream. The use of the hypothermic heat in the The sense of the method according to the invention for overheating the sucked in vapors would be with the known The process does not make sense, as the steam volume increases considerably and with it a compressor correspondingly larger stroke volume and thus higher price made necessary. The resulting larger frictional losses would in turn destroy part of the heat recovery.

According to a further development of the method according to the invention, one can in a multi-storey residential building assign each apartment its own heat pump, which both its excess heat and its Subcooling heat in a common for several apartments for the group of heat pumps Storage brings in In times of above-average heat demand, heat is only or in addition to the extraction of heat from the environment and via a distribution system Evaporators supplied to the heat pumps

The group of heat pumps, which extract heat from the environment, can advantageously be used by a second group of heat pumps, which, as soon as the heating system is no longer sufficient Heat flows in and goes into operation and heat from the long-term heat storage tank into the heating system transported

In general, the heat storage tank can be operated with water.

The invention is intended to be based on exemplary embodiments shown schematically in the drawing are explained in more detail:

F i g. 1 uses a time-temperature diagram to illustrate that to be generated by a heat pump Power.

An energy flow diagram is shown in FIG. The amount of heat Qu is withdrawn from the environment by the heat pump 1 by means of the electrical drive energy E and used as heating Qh to cover the heat demand of a house, for example. The excess or undercooling heat Qu is fed to a memory 6. The storage unit can be designed as a latent heat storage unit and use the heat of conversion during the transition from water to ice.

In Fig. 3 is shown in the representation according to FIG. 2 illustrates how some or all of the heat extracted from the environment is fetched from the heat accumulator 6 in order to cover the heat demand for the heating, Qh. This is necessary when the outside temperature falls below a predetermined lower threshold value, for example 0 ^{° C.}

In FIG. 4, the mode of operation in the case of excess heat, instead of heat demand, is illustrated in the representation according to FIG. In this way, released heat Qiaim can be supplied to the heat accumulator 6 in the summer when the house is air-conditioned. With Ou is here

absorbed by any outside air heat exchanger Solar heat may be taken into account without the interposition of a heat pump.

In Fig. 5 is the method according to the invention using an arrangement with a heat store 6 and a buffer store 27 shown.

In Fig. 6 shows a system for carrying out the method.

In Fig. 7 illustrates another arrangement for performing the method according to the invention light.

In Figure 8 is an arrangement for the configuration of the Procedure shown.

In the method for space heating, the heat pump is designed so that it is in the range of the greatest frequency of outside temperatures, z. B. up to temperatures ^ aSiO ⁰ C, the required heating work Q /, withdraws directly from the outside air and feeds it into the heat distribution system. If the heat requirement of the building is less than the amount of heat provided by the heat pump, then the refrigerant cannot completely condense in the condenser of the heat pump, the vapors are fed into a second condenser, through which the excess heat Qa is transferred to a heat storage, for example a latent heat storage, is fed in, which can store heat over long periods of time with little loss at low temperatures, as shown in FIG. 2 shows. An arrangement in which the subcooling heat of the system is used is particularly suitable, since this indirectly improves the performance factor ε of the heat pump. By supercooling the refrigerant liquid to + 25 ° C to + 3O ⁰ C, in a downstream condenser or heat exchanger, the cooling capacity Qo and thus the heating capacity Q of the heat pump with a constant power consumption of the compressor increases. The subcooling heat that is extracted from the refrigerant in the downstream heat exchanger cannot be used directly for heating because the temperature level is too low; however, it can be introduced into the latent heat accumulator and stored there. If the outside temperature falls below the value 0 ⁰ C, then the heat pump takes partially or completely the required amount of heat from the latent heat store, as shown in the drawing F i g. 3 represents

In a further advantageous arrangement according to FIG. 5, the heat pumps 1 emit their heat of condensation to a buffer memory 27 for heating and to a hot water memory 30 for domestic water preparation. The excess or undercooling heat Qo flows to the latent storage device 6. If necessary, the amount of heat Qt $ can be taken from the store 27 in order to defrost the outside air heat exchanger 2 in the event of icing.

The latent heat storage 6 of this method must be able to store a lot of heat at a temperature level adapted to the environment with the smallest possible volume, so that no significant heat losses occur. A suitable medium for this is water, which is converted ^{into the solid state of aggregation when heat is removed at 0} ° C. and gives off 80 kcal / kg of heat.

In summer or in the transition period, the ice can z. B. melted by solar heat and the melt water can be partially heated. In the transition period of autumn, when the heat pump is not fully utilized, the melt water heats up to around 50 ^° C thanks to the excess or undercooling heat. Per kg of water, there is then a heat quantity of 80 + 50 = 130 kcal = 0.15 kWh stored, which is available to cover the peak heat demand on very cold days with outside temperatures below 0 ^° C. When using a latent memory of the evaporator of the heat pump will never is connected to a heat carrier, the cold as, for example, 0 ⁰ C, charged. This means that the minimum and mean performance ratio of the heat pump with latent storage is significantly higher than that of the always direct-acting heat pump.

Assuming a future average apartment size in Germany of 80 m ^{2 of} living space, and assuming a heat requirement of 100 watts per square meter of living space on the coldest winter day in climate zone II (# 1 = -15 ° C) with thermally insulated construction, then this is required caloric heating power on the coldest winter day P = 8 kW. If one also assumes that the room temperature is lowered during the eight hours of the night, the result on the coldest winter day is a required caloric heating work of W _d = & (kW) ■ 20 (h / d) = 160kWh / d.

From the climatic statistics it is known that the days with mean outside temperatures of ■ & _M7 <0 ° C on average in extremely cold winters are mean

Outside temperature comprise ft of _the 5 ° C. (Not

all days with # _a <0 ⁰ C have a daily mean temperature # _a = -15 ° C). The average daily work at very cold outside temperatures is at # «= 22 ° C room temperature

= 160 ·,? - <-. ⁵ > -117JEWH

According to long-term climate statistics, there are only a few days with low outside temperatures in western Germany in uninterrupted sequence; in climate zone II a maximum of 12 days; are facing a new wave of cold always a number of warmer days during which the heat pump has excess or subcooling heat can feed into the latent storage. During the continuous 12 very cold days The following caloric heat quantity per apartment unit (WoE) is required for room heating:

65

<?, ₂ </ = Π7 - 12 = 140OkWhAVoE

22 - (- 15) electrical work plus 2 kWh of the environment or the The work withdrawn from heat storage would result in useful heat of 3 kWh) the amount to be stored is calculated Amount of heat too

W _sp = 1400

= 930kWh / WoE

The water mass m required for storage is thus

m = WoE '

kg

= 6200kg / WoE

With a coefficient of performance of ε = 3 (ie IkWh and the storage volume V = 6.2 m ³ .

A cube-shaped, thermally insulated water storage z. B. made of concrete should have an edge length s

s = V6.2 = 1.8 m.

The conditions in apartment buildings are particularly favorable if each apartment has one its own heat pump is assigned and controlled depending on the heat demand of the apartment. The ι ο Electricity consumption of the heat pump in question can then be billed via the apartment meter, see above that the individual householder has an opportunity to save heat. Every apartment heat pump would feed their excess or undercooling heat into the shared latent storage and Obtain additional heat from the latent storage system on very cold days. Experience has shown that in a Residential house with heating power consumption measured and billed per apartment, even on very cold ones Days, on average, only approx. 60% of the theoretically required amount of heat is used, because it is not Every room in every apartment is always fully heated. Under these conditions z. B. at the frequently encountered eight-family dwelling house has a storage volume of

V = 6.2 - ^ - ■ 8 WoE · 0.6 = 30 m *

The internal dimensions of a cubic storage tank with a maximum water height of 2.2 m are:

30th

2.2

- 3.7 m by 3.7 m

The drawing Fig.6 shows an objectively designed example for the case that the supercooling heat is being used:

Heat pump 1 extracts heat from the outside air via evaporator 2 and transfers it via condenser 3 to heating system 8, e.g. B. controlled by the return admixture 7, from. Condenser 4 feeds the subcooling heat of the system into latent storage unit 6. If the outside temperature falls below the system's design value, e.g. B. 0 ⁰ C, then switch the three-way valves 9 and 10, which can also be replaced by solenoid valves, the evaporation of the refrigerant to evaporator 5, which extracts the required heat from the memory 6. This method also allows the heat during the next frost taken from the memory and brought back through capacitor 4 at the higher day outside temperatures.

Another variant is shown in FIG. 7 of the drawing. The heat exchanger 11 extracts the outside air Heat and transfers it to a frost-resistant liquid circulated by pump 17, which is in the evaporator 2 the heat is extracted by the heat pump 1. A control device 12 monitors the system once to the effect that the heat pump according to the temperature sensor 13 (heating water temperature) and 18 (outside temperature) determined heat demand of the building is controlled, on the other hand that Three-way valve 9 always when the frost-resistant liquid at the point 15, d. H. after exiting the Evaporator, is even warmer than the contents of the storage tank (sensor 14) the frost-resistant liquid in the as Evaporator 5 acting heat exchanger of the memory 6 is reversed, so that the excess heat flows into the memory. This applies in particular to the downtime of the WS pump 1 in summer and possibly even when the weather is more tired, when the control device 12 temporarily turns off the heat pump has switched off because the heating system 8 has sufficient heat. Circulation pump 16 ensures that in the Storage tank 6 no temperature stratification occurs. Valve 19 prevents the refrigerant at high storage temperatures flows through capacitor 4. If the outside temperature is below the design value of z. B. 0 ° C dropped, then the control device 12 controls the valves 9 and 20 so that the required heat to the Memory 6 is withdrawn via the evaporator 5.

The execution of a heat pump system in a multi-storey house is shown in Fig. 8 of the drawing. The heat pump la is on the ground floor, 16 on the first floor and Ic on the second floor, etc. Since the heat pump's power requirement for an apartment is 3 kW, each floor can be assigned a hermetically sealed unit that is installed directly in the apartment . The heating systems 8a, % b and 8c etc. emit the required heat to the apartments. The heat pumps extract the necessary heat from the heating flow and return lines 24 and feed the undercooling heat into the latent storage device 6 via the heat exchangers 22 by means of the pipe system 25. The heat pumps la to Ic are controlled by the controllers 26a to 26c and only heat the apartments to the temperatures that the apartment owner desires and only if he so desires. The circulation pumps 17 and 21 ensure the transport of the heat transfer medium, the valves 9 and 20 in a manner similar to that in FIG. 7 described, can be controlled. The great advantage of this solution lies in the described better individual controllability per apartment and the associated considerable energy savings in the low flow temperature of the flow and return line 24, the associated low distribution losses and the possibility of feeding the undercooling heat into the latent storage via the line system 25 , justified

In addition 6 sheets of drawings

Claims (4)

Patent claims: 1. Procedure for space heating by means of a heat pump circuit, on the cooled side of which is a heat accumulator is located, which can be used as a Heat source is used, characterized in that on the cooled side The heat generated by the condenser is introduced into the heat accumulator as supercooling heat whose temperature is lower than the temperature of the liquid downstream of the condenser accumulating heat transfer medium, and that the heat transfer to the heat storage in the liquid area of the heat transfer medium of the heat pump circuit takes place Z method according to claim 1, characterized in that the heat accumulator with water is operated. 3. The method according to claim 1, characterized in that in a multi-storey house or comparable buildings each apartment is assigned its own heat pump, which both their excess heat as well as their supercooling heat in one for several apartments for the Groups of heat pumps brings in common storage, from which heat is exclusively used in times of above-average heat demand or in addition to the extraction of heat from the environment, via a distribution system fed to the evaporators of the heat pumps, raised to the required temperature level by heat pumps and made usable. 4. The method according to claim 3, characterized in that the group of heat pumps, the removes heat from the environment, is supplemented by a second group of heat pumps that, as soon as the heating system no longer receives enough heat, it goes into operation and heat is removed from the long-term heat storage tank transported into the heating system.