DE3039476C2 - Process for the recovery of waste heat in the air conditioning of buildings - Google Patents

Description

The invention is based on a method for recovering waste heat from air conditioning of buildings by means of warm air, with the outside air at The lower end of the building is heated and the exhaust air exiting at the upper end is used to heat a Evaporator is used, in which a liquid heat carrier is evaporated, which is then compressed and then in a condenser at a temperature that is higher than that of the evaporator condensed, then recirculated to the evaporator and the condensation heat released in the condenser is used according to the principle of the heat pump to preheat the supply air.

With the aim of saving energy, the use of heat pumps is currently being discussed in many places. This is especially true for large buildings, which today in most cases receive a ventilation system. Various methods are known in the field of heat recovery in ventilation systems. When using a heat pump, the following basic principle applies:

The outside air is drawn into the outside air shaft by a fan at floor level of the building. At the A condenser with tubes with ribs on the air side is located at the entrance to the outside air shaft. Through the The substance flowing in the heat pump circuit is liquefied at this point Warming the outside air. After flowing through the individual rooms, the exhaust air leaves the building through the exhaust duct, the outlet of which is at roof height. Near the exit is im Exhaust air shaft an evaporator arranged with tubes ribbed on the air side. By cooling the exhaust air is transfer a heat flow for evaporation of the heat carrier of the heat pump circuit. The one so recovered The amount of heat can only be used to heat the outside air if the Heat transfer medium to the temperature or energy level required for heat transfer at the condenser is raised. For this purpose there is a circuit between the evaporator and the condenser Installed a compressor that compresses the evaporated heat carrier to a condensation pressure that corresponds to a condensation temperature above the temperature of the heated outside air After heat has been transferred to the condenser, the liquid heat transfer medium is due to the between Condenser and evaporator conveyed back to the evaporator if the pressure gradient is present. That closes

is the thermal cycle. This method : st z. B. in the magazine "Heating, Ventilation, Haustechnik 8/1974", pages 243-252 described. The installation a compressor is associated with a relatively high technical effort. If the Compressor, e.g. B. in maintenance or service, the entire cycle fails.

The invention is based on the object of providing a heat pump cycle without the use of a compressor to develop. This cycle is intended to recover waste heat from air conditioning of buildings using hot air.

According to the invention, this object is achieved on the basis of the method described at the outset solved that the evaporated heat transfer medium can flow through a vertical drop section and the Compression takes place solely due to the static pressure of the gas column in the fall section

In this process, most of the heat energy required for heating is used taken from the warm air, the z. B. by an air heater located within the ventilation system provided. The cycle according to the invention is now a considerable proportion of the Recovered heat output. Especially in large buildings with high hourly demand for electricity and thus If the heat output is high, a significant reduction in the energy requirement of the ventilation system can be expected. Due to the lack of an increase in the energy level during the condensation, the inventive Cycle process can be viewed as a recuperative waste heat recovery system, with the heat transfer medium a phase change in each of the two heat exchangers (evaporator and condenser) passes through. A pump is used to recirculate the heat transfer medium from the condenser to the evaporator a relatively low electrical power consumption, so that practically no additional energy costs develop.

In tall buildings, the arrangement of the evaporator at roof level and the condenser at A long pipe section (downhill section) through which the gaseous heat transfer medium flows. at Appropriate dimensioning of the pipe cross-section, the flow pressure loss is so low that the static pressure of the gas column depending on the density of the gaseous heat carrier and the for The available height difference results in a sufficient increase in the pressure at the condenser Has. The associated increase in the temperature or energy level compared to the state on Depending on the density of the fluid and the building height, the evaporator can reach up to 4 ° C (at a building height of approx. 400 m) be.

A much greater increase in the temperature level on the condenser and thus a considerable one The efficiency can be improved if a liquid flows into the upper end of the drop section the gaseous heat transfer medium is injected. Appropriately, one proceeds so that a part of the liquid Heat transfer medium is branched off in front of the evaporator and is injected into the fall section at the upper end. Alternatively, however, a foreign liquid can also be injected, which after the condenser of the liquid heat transfer medium is separated again.

By introducing finely divided droplets with the smallest possible droplet size into the fall section a two-phase heat transfer medium is obtained, which increases the mean density in the fall section causes. Here, the effect achieved, i.e. the increase in the pressure on the condenser, is all the more more intense, the more liquid can be injected into the gas flow. Depending on the density of the gas and the density of the liquid as well as with increasing volume fraction of the liquid in the gas flow the mean density increases in the fall section and with it the static pressure at its lower end. For a given height difference thus results in a certain final pressure and thus also the desired one Raising the temperature or energy level on the condenser.

In the following an embodiment of the invention is explained in more detail with reference to a drawing.

The drawing shows schematically the heat circuit according to the invention for recovering heat from the exhaust air of a building heated with warm air. In the vicinity of the ground, air 1 is sucked in from the outside, preheated in the condenser 2 (heat exchanger) described below and heated to the desired temperature in the air heater 3. The warm air 4 then flows through the heating system of the building. The exhaust air 5 is extracted from the roof of the building. In the exhaust duct 6 there is a second heat exchanger 6, which is designed as an evaporator for a liquid 7 that is circulated. The delivered by the circulating pump 11 liquid 7 is evaporated in the evaporator 6 at a Temperatumiveaü Tv The required heat of evaporation is derived from the exhaust air 5. The steam flows in a beginning on the roof of the building and ending at the bottom Fallstrekke 8 with the height H. Before Evaporator 6, part of the circulating liquid is branched off and injected into finely divided form at the upper end of the drop section. (Nozzles 9). The atomized liquid flows together with the steam as a two-phase mixture 10 through the fall section 8. The two-phase mixture has a significantly higher density than the steam alone. This results in a significantly higher static pressure at the end of the fall section, ie on the ground. Downstream of the fall section 8 is the condenser 2 mentioned at the beginning. Like the evaporator 6, this is a heat exchanger provided with ribs on the air side. In the condenser 2, under the static pressure of the gas / liquid column with the height H, the vaporous portion of the two-phase mixture is condensed out again at a higher temperature level Τ _κ δ Rv corresponding to this pressure. There '. ^{For the} vapor fraction, the amount of heat recovered at the evaporator 6 by condensation is transferred to the warming supply air 1. The heat transfer medium 7, which is again present as a liquid from here on, is recirculated to the evaporator 6 or to the injection point 9 by means of the circulating pump 12.

Instead of the liquid heat transfer medium 7, a foreign liquid can also enter the drop section via the line 12 be injected.

After passing through the fall section and after condensation has taken place, the foreign liquid is then with a Separator separated from the heat carrier 7 again.

The method described can be used with success in particular in the air conditioning of tall buildings (high-rise buildings). The height of the falling distance then allows the temperature level T _{K to be} increased by 3 to 6 ^° C. This is sufficient to make a considerable part of the residual heat in the exhaust air flow usable again. Otherwise this energy would be lost.

1 sheet of drawings

Claims (3)

Patent claims: 1. Process for the recovery of waste heat in the air conditioning of buildings by means of Warm air, in which outside air is heated at the lower end of the building (supply air) and that at the upper end Exiting exhaust air at the end is used to heat an evaporator in which a liquid Heat carrier is evaporated, which is then compressed and then in a condenser condenses at a temperature higher than that of the evaporator, then to the evaporator is recirculated and the condensation heat released in the condenser according to the principle the heat pump is used to preheat the Zuiuft, characterized in that the evaporated heat carrier through a vertical fall distance can flow and the compression solely due to the static pressure of the Gas column takes place in the drop section. 2. The method according to claim 1, characterized in that that part of the liquid heat carrier is branched off in front of the evaporator and injected into the fall section at the upper end. 3. The method according to claim 1, characterized in that at the upper end of the drop section a Foreign liquid is injected into the gaseous heat transfer medium after the condensation of the Heat carrier is separated again.