As is well known, conventional heating plants for heating rooms or buildings and production of tappable hot water, which plants are operated by means of a boiler heate with a fossil fuel such as oil, gas or the like, have con- siderable drawbacks due to the fact that a substantial por¬ tion of the supplied energy is wasted by heat losses with the flue gases escaping through the chimney. In order to improve the economy of the heating one has begun to use heat pumps which raise heat of low temperature to a higher temperature level. The most usual source of heat in this connection has turned out to be air, both outdoor air and indoor air. When using outdoor air, the drawback is in¬ curred that the efficiency of the heat pump falls drasti¬ cally at low temperatures, such as lower than -5°C, for example, at which temperature there also arise problems associated with frost deposition on the aggregate. There¬ fore, in connection with heat pumps operating with outdoor air, another source of heat must be provided, such as an oil-fired boiler or an electric boiler, which is operative during the coldest season.

Return air is profitable assource of heat in such adaptions only, where a great portion of the air usually is vented out, but, when a heat pump is used, is recycled via the heat pump. When using outdoor air as source of heat, attempts have been made to meet the heat demand by means of solely a heat pump, but the measures which must be adopted in this connection for ensuring the operation of the heat pump at low outdoor temperatures, result in that the construction. of the heat pump becomes complicated, so that the heat pump becomes expensive both in installation and maintenance. There exist, for example, heat pumps running multi-stepwise

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to raise the temperature of the air with each step.

The present invention has for its object to provide a method for operation of a heating plant as well as a heating plant for realization of the method, where the above-mentioned drawbacks inherent to the solutions known hitherto are eliminated and a heating plant is accomplished which affords extraordinary operational economy, while at the same time the function and high efficiency of the plant are ensured at all outdoor temperatures. This object is attained by the method and the heating plant having.been given the characterizing features stated in the subsequent claims.

The invention will be described nearer with reference to the attached drawing. Figure 1 shows in a diagrammatic manner a cross-sec¬ tion through a heating plant according to the invention. Figure 2 shows a principal diagram of the heat pump forming part of the heating plant shown in Figure 1. In the heating plant shown in Figure 1 reference numeral 1 denotes a burner for oil or gas and disposed in a water-carried boiler 2, to which a tank or space 13 for production of hot water is connected. The boiler 2 and the tank 13 are positioned on a support 11. Disposed with an interspace above the boiler 2 and the tank 13, which in- terspace constitutes an air channel 3, are a heat exchanger 4 of the cross-flow type and a heat pump 5 for air circu¬ lation. Disposed above the heat exchanger 4 is an exhaust chamber 7 equipped with a suction fan 7 connected to an exhaust tube 9 for consumed air or flue gases, respective- ly, as will be described more below. Reference numeral 8 denotes a space containing control equipment for the heat¬ ing boiler. The entire heating plant is located in a closed boiler room 10.

Connected to the heat exchanger 4 are an intake chan- nel 12 coming from outside for fresh air and an inlet open¬ ing 14 for return air from the boiler room 10, which return air circulates in the plant through the heat exchanger 4

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and the heat pump 5, as will be described nearer herein¬ after. The heat pump 5 has an exhaust opening 15 for the mixture of fresh air and return air circulating after the passage through the heat pump. Reference numeral 16 denotes 5 an intake opening for supply of air from the boiler room 10 to the air channel 3. Opening into the air channel 3 is also an exhaust channel 17 for flue gases from the heating boiler 2.

For control of the function of the heating plant a 10 plurality of feelers is arranged which in a manner not pre¬ sented in detail are connected to the control equipment located in the space 8. Thus, the heating boiler 2 is pro¬ vided with a temperature feeler TC 1, the fresh air inlet 12 with a temperature feeler TC 2, and the boiler room 10 15 with a temperature feeler TC 3. A pressure responsive fee¬ ler PD 1 and a temperature responsive feeler TC X are dis¬ posed in the exhaust chamber 6. The burner 1 or the heating boiler 2 is started and stopped via a control relay denoted AY. 20 The heating plant shown in the Figure 1 works in the following manner. The heating plant has an air flow circu¬ lating through the heat pump 5 and resulting from fresh air entering through the fresh air inlet 12 and a return air flow which through the inlet opening 14 together with the 25 fresh air is supplied to the heat exchanger 4 and therefrom to the evaporator of the heat pump 5 as heat emitting me¬ dium. In the shown embodiment, wherein the heat pump is of a type which heats the water in a water-carried heating system, the circulating air is blown out from the heat ex- 30 changer 5 through the exhaust opening 15 into the closed space 10 which in the present case is constituted by a

_*> boiler room within which the heating plant is located. It should, however, be clearly understood that the space 10 may be. a larger premise, wherein the heating plant is lo- 35 cated, the air exhausted at 15 then constituting the heat¬ ing medium for the premise. It is also conceivable that the exhaust opening 15 from the heat pump 5 is connected

4 to a heating system which works with blast injection of hot air into the spaces to be heated, the exhaust opening 15 in this case cupplying air to said system. This implies, of course, that the return air from the ventilation system is returned to the space 10 in which the heating plant is located.

In the shown embodiment where the heat pump 5 serves for heating of the circulating water, as is mentioned above, the air is thus blown out from the exhaust opening 15 into the space 10. From the space 10 a partial air flow ad¬ vances through the intake opening 16 and the gas channel 3 to the heat exchanger 4 which is of the cross-flow type, i.e. with two entirely closed systems of channels which separated from each other extend in directions vertically opposed to each other. After having passed through the heat exchanger 4 this partial air flow, which through the opening 16 has entered from the space 10, is discharged in¬ to the atmosphere through the exhaust pipe 9 located at the top. During ist passage through the heat exchanger 4 said partial air flow preheats the mixture of fresh air entering into the channel 12 and return air from the boiler room 10 and entering through the intake opening 14 into the heat exchanger 4. The air flow circulating through the heat pump shall surpass the quantity of air discharged through the exhaust tube 9 so as to cause a higher pressure to prevail in the boiler room 10 or the space corresponding thereto than in the exhaust chamber 6 in the heating plant. The described operation conditions of operation of the heating plant prevails if the circulation heat pump primarily sole- ly provides for the energy supply to the heating system.

When it becomes necessary to increase the content of energy in the circulating air flow through the heat exchanger 4 to the heat pump 5, as for example during the warm and moist period of the year when the heat pump solely stands for the energy supply to the heating plant, the suction fan 7 is started which increases the passage flow through the heat exchanger 4 of both exhausted air and entering air

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which has a higher value of entalphy. During the colder period of the year or when the outdoor temperature is low, which is percepted by the temperature feelers to be de¬ scribed more below, the burner 1 for the heating boiler 2 is started additionally and the flue gases from the heating boiler 2 are delivered through the exhaust tube 17 to the channel 3 to be mixed with the exhaust air from the opening 16, whereby the content of energy in the air flow from the heat exchanger 4 to the heat pump 5 is in- creased further.

It will be evident from the description made herein¬ before, that the combination of the heating boiler 2, the heat exchanger 4 and the heat pump 5 results in a plant in which the heat pump 5 always is operated under favourable conditions. When the temperature at TC 1 has fallen below a predetermined set value, the heat pump starts, and when the outdoor temperature at TC 2 surpasses the set prede¬ termined value, the suction fan starts in order to increase the content of energy in the air flow to the heat pump. When the temperatures at TC 1, TC 2 and TC 3 at the same time lie below the set values for all of them, the suction fan starts, and when the partial vacuum at PD 1 in the ex¬ haust chamber 6 has fallen below the set predetermined value, the burner 1 of the heating boiler 2 is made opera- tive over the control relay AY. When the temperature in the boiler room 10 at TC 3 has surpassed the set value, the burner 1 stops up, and the suction fan 7 and the heat pump 5 consume the heat accumulated in the boiler room and start again when the temperature has fallen below the set value. When the temperature in the water flow at TC 1 has surpassed the set value, the burner and the suction fan are stopped, but the heat pump continues to work until a slightly higher temperature at TC 1 has been reached, and when the temperature falls, the burner and the suction fan become operative again. The temperature feeler disposed at TC X in the exhaust chamber prevents the burner becoming operative as long as the temperature is higher than the

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set value. The circulation pump of the heat pump 5 works continuously.

Due to the feature that the heat pump 5 for the cir¬ culating air, the suction fan 7 and the heating boiler 2 each are started in sequence the one after the other when the energy demand grows, the most favourable conditions of operation of the plant are achieved. In connection with a water-carried heating boiler 2 and a heat pump 5 with heating by means of water, it is suitable that the water systems of the boiler 2 and the pump 5 are interconnected in sequence in order to obtain a higher outgoing water temperature from the heating plant. The combustion air to the burner 1 of the heating boiler 2, which consists of room air, is also condensing dried by the circulation air heat pump 5, for which reason no condensation occurs on cold channel surfaces. All condensation of the moisture existent in the fresh air introduced through the intake 12 is effected in the evaporation section of the heat pump 5, where the pure condensation water can be collected and re- moved.

The heat pump forming part of the plant may be of conventional type, as is shown in Figure 2, for example. From the evaporator 30 the working agent flows via a heat exchanger 31 to the compressor 22 provided with a pressure setter 21 via a counter-valve 32 to a coaxial condenser

24 for heat exchange with water in a water-carried system having inlet and discharge conduits 27. From the condenser 24 the working agent flows over a receiver 25 and a filter 26 back to the heat exchanger 31 and via a theremostat valve 28 to the evaporator 30. Reference numeral 29 denotes a rotary blower located in the evaporator unit. A branch conduit 33 leading to the evaporator 30 is controlled by a solenoid valve 23. In a heating system working with warmed air, the condenser unit 24 will, of course, be given a shape corresponding hereto.

The moist generated, in the combustion process is con¬ densed in the heat exchanger and gives away its condensing

energy to the circulation air stream. The acid condensate with pH about 2,5 is drained off through a neutralization system and led to waist, whereby it is given an acidity of about 6 pH. It is obvious that the description given hereinbe¬ fore does not present more than an advantageous embodi¬ ment of the invention and that changes and modifications thereof can be made within the scope of the subsequent claims.

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