One of the sources of secondary energy resources in the building is the thermal energy of the air removed into the atmosphere. The consumption of heat energy for heating the incoming air is 40 ... 80% of the heat consumption, most of it can be saved in the case of using the so-called waste heat exchangers.
There are various types of waste heat exchangers.
Recuperative plate heat exchangers are made in the form of a package of plates installed in such a way that they form two adjacent channels, through one of which the removed air flows, and through the other - the supplied outside air. In the manufacture of plate heat exchangers of such a design with a high air capacity, significant technological difficulties arise, therefore, designs of shell-and-tube heat exchangers-utilizers TKT have been developed, which are a bundle of pipes arranged in a staggered manner and enclosed in a casing. The removed air moves in the annular space, while the outside air moves inside the tubes. The movement of streams is cross.
Rice. Heat exchangers:
a - plate heat exchanger;
b - TKT utilizer;
в - rotating;
g - recuperative;
1 - case; 2 - supply air; 3 - rotor; 4 - purged sector; 5 - exhaust air; 6 - drive.
In order to prevent icing, the heat exchangers are equipped with an additional line along the outside air, through which, at a tube bundle wall temperature below the critical one (-20 ° C), a part of the cold outside air is passed.
Heat recovery units in exhaust air with an intermediate heat carrier can be used in mechanical supply and exhaust ventilation systems, as well as in air conditioning systems. The unit consists of an air heater located in the supply and exhaust ducts, connected by a closed circulation loop filled with an intermediate carrier. The circulation of the coolant is carried out by means of pumps. The extracted air, being cooled in the air heater of the exhaust duct, transfers heat to the intermediate heat carrier that heats the supply air. When the exhaust air is cooled below the dew point temperature, water vapor condenses on a part of the heat exchange surface of the exhaust duct air heaters, which leads to the possibility of ice formation at negative initial temperatures of the supply air.
Heat recovery units with an intermediate heat carrier can operate either in a mode that allows ice formation on the heat exchange surface of the exhaust air heater during the day with subsequent shutdown and defrosting, or, if shutdown of the unit is unacceptable, when using one of the following measures to protect the exhaust duct air heater from ice formation :
- preheating the supply air to a positive temperature;
- creation of a bypass for the coolant or supply air;
- increasing the flow rate of the coolant in the circulation loop;
- heating the intermediate heat carrier.
The choice of the type of regenerative heat exchanger is made depending on the design parameters of the removed and supplied air and moisture release inside the room. Regenerative heat exchangers can be installed in buildings for various purposes in the systems of mechanical supply and exhaust ventilation, air heating and air conditioning. The installation of a regenerative heat exchanger must ensure countercurrent air flow.
The ventilation and air conditioning system with a regenerative heat exchanger must be equipped with control and automatic regulation devices, which must ensure operating modes with periodic defrosting or prevention of frost formation, as well as maintain the required parameters of the supply air. To prevent frost formation in the supply air:
- arrange a bypass channel;
- preheat the supply air;
- change the frequency of rotation of the regenerator nozzle.
In systems with positive initial supply air temperatures during heat recovery, there is no danger of condensate freezing on the surface of the heat exchanger in the exhaust duct. In systems with negative initial temperatures of the supply air, it is necessary to use utilization schemes that provide protection against freezing of the surface of the air heaters in the exhaust duct.
2006-02-08The need for energy saving in the design, construction and operation of buildings of any purpose is beyond doubt and is primarily associated with the depletion of fossil fuel reserves and, as a consequence, its continuous rise in price. In this case, special attention should be paid to reducing heat costs specifically for ventilation and air conditioning systems, since the share of these costs in the total energy balance can be even higher than transmission heat losses, primarily in public and industrial buildings and after increasing the thermal protection of external fences.
One of the most promising, low-cost and quick-payback energy-saving measures in mechanical ventilation and air conditioning systems is the utilization of the exhaust air heat for partial heating of the inflow during the cold season. Apparatuses of various designs are used for heat recovery, incl. plate cross-flow recuperative heat exchangers and regenerators with a rotating rotor, as well as devices with so-called heat pipes (thermosyphons).
However, it can be shown that in the conditions of the prevailing level of prices for ventilation equipment in the Russian Federation and, mainly, due to the practical absence of own production of the listed types of devices, from a technical and economic point of view, it is advisable to consider heat utilization only on the basis of devices with an intermediate coolant. This design is known to have a number of advantages.
First, for its implementation, serial equipment is used, since here the supply unit is supplemented only with a heat recovery heater, and the exhaust unit - with a heat recovery unit, which are structurally similar to conventional heaters and coolers. This is especially important, since there are a number of enterprises in the Russian Federation that conduct their own production of the products under consideration, incl. such large ones as Veza LLC.
In addition, this type of heat recovery equipment is very compact, and the connection of the supply and exhaust units only through a circulation circuit with an intermediate heat carrier allows you to choose a place for their placement almost independently of each other. Low-freezing liquids such as antifreeze are usually used as a coolant, and the small volume of the circulation circuit makes it possible to neglect the costs of antifreeze, and the tightness of the circuit and the non-volatility of the antifreeze make the issue of its toxicity secondary.
Finally, the absence of direct contact between the flows of the supplied and removed air does not impose restrictions on the cleanliness of the hood, which practically infinitely expands the group of buildings and premises where heat recovery can be used. As a disadvantage, they usually indicate not too high temperature efficiency, not exceeding 50-55%.
But this is just the case when the question of the expediency of using heat recovery should be decided by a technical and economic calculation, which we will talk about later in our article. It can be shown that the payback period for additional capital costs for a heat recovery device with an intermediate heat carrier does not exceed three to four years.
This is especially important in the context of an unstable market economy with a noticeably changing level of prices for equipment and tariffs for energy resources, which does not allow the use of capital-intensive engineering solutions. However, the question remains about the most economically feasible temperature efficiency of such heat recovery equipment k eff, i.e. the share of heat spent on heating the inflow due to the heat of the exhaust air in relation to the total heat load. Typically used values for this parameter are in the range from 0.4 to 0.5. Now we will show on what basis the indicated values are accepted.
This problem will be considered on the example of an air handling unit with a capacity of 10,000 m 3 / h using the equipment of Veza LLC. This task is an optimization one, since it comes down to identifying the value of k eff, which provides a minimum of the total discounted costs of the SDZ for the device and operation of ventilation equipment.
The calculation should be carried out subject to the use of borrowed funds for the construction of ventilation units and bringing the SDZ to the end of the considered time interval T according to the following formula:
where K is the total capital costs, rubles; E - total annual operating costs, rubles / year; p - discount rate,%. When calculating it, it can be taken equal to the refinancing rate of the Central Bank of the Russian Federation. Since January 15, 2004, this value has been equal to 14% per annum. In this case, it is possible to investigate the problem in a fairly complete volume by comparatively elementary means, since all cost components are easily taken into account and quite simply calculated.
For the first time, the solution to this problem was published by the author in a paper for the level of prices and tariffs in force at that time. However, as it will be easy to see, when recalculated for later data, the main conclusions remain valid. At the same time, we will show how the feasibility study itself should be carried out when it is necessary to select the optimal engineering solution, since all other tasks will differ only in determining the value of K.
But this is easily done according to the catalogs and price lists of manufacturers of the corresponding equipment. In our example, capital costs were determined according to the data of the Veza company, proceeding from the productivity and the adopted set of sections of the supply and exhaust units: a front panel with one vertical valve, a cell filter of class G3, a fan unit; in addition, in the supply unit there is also an additional air heater for the heat recovery system and a reheating heater with heat supply from the heating network, and in the exhaust unit - an air cooler for the heat recovery system, as well as a circulation pump. The diagram of such an installation is shown in Fig. 1. Expenses for installation and adjustment of ventilation units were taken at the rate of 50% of the main capital investments.
The costs of heat recovery equipment and a heating coil were calculated based on the results of calculations on a computer using the programs of the company "Veza", depending on the efficiency of the heat recovery unit. At the same time, with an increase in efficiency, the value of K increases, since the number of rows of tubes of heat exchangers of the utilization system increases faster (for k eff = 0.52 - up to 12 in each installation), than the number of rows of the preheating heater decreases (from 3 to 1 under the same conditions) ...
Operating costs consist of annual costs for heat and electricity, and depreciation charges, respectively. When calculating them, the duration of the operation of the installation during the day in the calculations was taken equal to 12 hours, the air temperature behind the preheating heater + 18 ° C, and after the heat exchanger - depending on keff through the average outside temperature for the heating period and the temperature of the exhaust air.
The latter is equal to + 24.7 ° С by default (program of selection of heat recovery units of LLC "Veza"). The heat energy tariff was adopted according to the data of Mosenergo OJSC as of mid-2004 at the rate of RUB 325 / Gcal (for budget consumers). Obviously, with an increase in k eff, the amount of costs for heat energy decreases, which, generally speaking, is the purpose of heat recovery.
Electricity costs are calculated through the electrical power required to drive the heat recovery system circulation pump and the fans of the supply and exhaust units. This power is determined based on the pressure loss in the circulation circuit, the density and flow rate of the intermediate heat carrier, as well as the aerodynamic resistance of ventilation units and networks. All the listed values, except for the density of the coolant, taken equal to 1200 kg / m 3, are calculated according to the programs for the selection of heat recovery and ventilation equipment of Veza LLC. In addition, the efficiency expressions of the pumps and fans used are also involved in the power expressions.
Average values were used in the calculations: 0.35 for GRUNDFOS pumps with a wet rotor and 0.7 for RDH fans. The electricity tariff was taken into account according to the data of Mosenergo OJSC as of mid-2004 at the rate of RUB 1.17 / (kWh). With an increase in k eff, the level of electricity costs increases, since with an increase in the number of rows of utilization heat exchangers, their resistance to air flow increases, as well as pressure losses in the circulation circuit of the intermediate heat carrier.
However, in general, this component of costs is significantly less than the cost of heat energy. Depreciation deductions also increase with increasing k eff, insofar as capital costs increase. The calculation of these deductions is carried out on the basis of ensuring the costs of full restoration, overhaul and current repairs of equipment, taking into account the estimated service life of TAM equipment, taken in the calculations equal to 15 years.
In general, however, the total operating costs decrease with increasing utilization efficiency. Therefore, the existence of a minimum of SDZ is possible at one or another level of keff and a fixed value of T. The results of the corresponding calculations are shown in Fig. 2. It is easy to see on the graphs that the minimum on the SDZ curve appears practically at any calculation horizon, which, in the sense of the problem, is equal to the required payback period.
This means that with the existing prices for equipment and tariffs for energy resources, any, even the smallest, investments in heat recovery will pay off, and rather quickly. Therefore, the utilization of heat with an intermediate heat carrier is almost always justified. With an increase in the estimated payback period, the minimum on the SDZ curve quickly shifts to the area of higher efficiency, reaching 0.47 at T = T AM = 15 years.
It is clear that the optimal value of k eff for the accepted payback period will be the one at which the minimum SRS is observed. The graph of the dependence of such an optimal value of k eff on T is shown in Fig. 3. Since a longer payback period, exceeding the estimated service life of the equipment, is hardly justified, one should, apparently, stop at the level of k eff = 0.4-0.5, especially since with a further increase in T, the increase in optimal efficiency slows down sharply.
In addition, it should be taken into account that the considered method of heat recovery for any heat exchange surface and coolant flow rate in general, in principle, cannot provide a value of keff higher than 0.52-0.55, which is confirmed by the calculation according to the program of the company "Veza". If we accept the tariff for heat energy as for commercial consumers in the amount of 547 rubles / Gcal, the decrease in annual costs due to heat recovery will be higher, therefore the graph in Fig. 3 shows the upper limit of the possible payback period.
Thus, the specified range of values of k eff from 0.4 to 0.5 finds a complete feasibility study. Therefore, the main practical recommendation based on the results of the above study is the widest possible use of the utilization of the heat of exhaust air with an intermediate heat carrier in any buildings where mechanical supply and exhaust ventilation and air conditioning are provided, with the choice of a temperature efficiency coefficient close to the maximum possible for this type of installation. Another recommendation is the mandatory for a market economy accounting for the discounting of capital and operating costs in the technical and economic comparison of options for engineering solutions according to formula (1).
Moreover, if only two options are compared, as is most often the case, it is convenient to compare only additional costs and assume that in the first case K = 0, and in the second, on the contrary, E = 0, and K is equal to additional investments in activities. the expediency of which is substantiated. Then, instead of E in the first option, you need to use the difference in annual costs for the options. After that, graphs of the dependence of SDZ on T are built, and the estimated payback period is determined at the point of their intersection.
If it turns out to be higher than T AM, or the graphs do not intersect at all, the measures are economically unjustified. The obtained results are of a very general nature, since the dependence of the change in capital costs on the degree of heat utilization under the current market situation is little related to a specific manufacturer of ventilation equipment, and the main influence on operating costs is generally exerted only by the costs of heat and electric energy.
Therefore, the proposed recommendations can be used when making economically sound decisions on energy saving in any mechanical ventilation and air conditioning systems. In addition, these results have a simple and engineering form and can be easily refined when current prices and tariffs change.
It should also be noted that the payback period obtained in the above calculations, depending on the accepted k eff, reaches 15 years, i.e. up to TAM, is in some respect the marginal arising when all capital costs are taken into account. If we take into account only additional capital investments directly in heat recovery, the payback period is really reduced to 3-4 years, as indicated above.
Consequently, the utilization of the heat of the exhaust air with an intermediate heat carrier is indeed a low-cost and quick-pay-off measure and deserves the widest application in a market economy.
- O.D. Samarin. On the regulation of thermal protection of buildings. Magazine "S.O.K.", No. 6/2004.
- O. Ya. Kokorin. Modern air conditioning systems. - M .: "Fizmatlit", 2003.
- V.G. Gagarin. On the insufficient substantiation of the increased requirements for thermal protection of the outer walls of buildings. (Amendments No. 3 SNiP II-3-79). Sat. report 3rd conf. RNTOS April 23-25, 1998
- O.D. Samarin. Economically feasible efficiency of heat recovery units with an intermediate heat carrier. Installation and special works in construction, No. 1/2003.
- SNiP 23-01–99 * "Construction climatology" .- M: GUP TsPP, 2004.
Description:
At present, the indicators of thermal protection of multi-storey residential buildings have reached sufficiently high
values, therefore, the search for reserves for saving thermal energy is in the field of improving the energy efficiency of engineering systems. One of the key energy-saving measures with a rather high potential for saving thermal energy is the use of heat recovery units 1 of the exhaust air heat in ventilation systems.
At present, the indicators of thermal protection of multi-storey residential buildings have reached rather high values, therefore, the search for reserves for saving thermal energy is in the field of improving the energy efficiency of engineering systems. One of the key energy-saving measures with a rather high potential for saving thermal energy is the use of heat recovery units 1 of the exhaust air heat in ventilation systems.
Air handling units with exhaust air heat recovery have a number of advantages in comparison with traditional supply ventilation systems, which include significant savings in heat energy spent on heating the ventilation air (from 50 to 90%, depending on the type of heat exchanger used). It should also be noted a high level of air-thermal comfort, due to the aerodynamic stability of the ventilation system and the balance of supply and exhaust air flow rates.
Recyclers types
The most widely used:
1... Regenerative heat exchangers NS. In the regenerators, the extract air heat is transferred to the supply air through a nozzle, which is heated and cooled alternately. Despite their high energy efficiency, regenerative heat exchangers have a significant drawback - the possibility of mixing a certain part of the removed air with the supply air in the apparatus body. This, in turn, can lead to the transfer of unpleasant odors and disease-causing bacteria. Therefore, they are usually used within one apartment, cottage or one room in public buildings.
2. Recuperative heat exchangers. These heat exchangers, as a rule, include two fans (supply and exhaust), filters and a plate heat exchanger of counterflow, crossover and semi-cross types.
With the door-to-door installation of recuperative heat exchangers, it becomes possible to:
- flexibly regulate the air-thermal regime depending on the type of apartment operation, including the use of recirculated air;
- protection from urban, external noise (when using sealed translucent barriers);
- cleaning the supply air with high-efficiency filters.
3.Heat recovery units with intermediate heat carrier. By their design features, these utilizers are of little use for individual (apartment) ventilation, and therefore, in practice, they are used for central systems.
4. Heat recovery units with heat exchanger on heat pipes. The use of heat pipes allows you to create compact energy efficient heat exchangers. However, due to the complexity of the design and high cost, they have not found application in ventilation systems for residential buildings.
In basic terms, the distribution of heat energy consumption in a typical multi-storey building is carried out almost equally between transmission heat losses (50–55%) and ventilation (45–50%). Approximate distribution of the annual heat balance for heating and ventilation:
The energy efficiency of apartment buildings can be increased by introducing into the practice of mass construction:
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With similar weight and dimensions, the best result in residential buildings is shown by regenerative heat exchangers (80–95%), followed by recuperative heat exchangers (up to 65%), and heat exchangers with an intermediate heat carrier (45–55%) are in last place.
We should mention heat recovery units, which, in addition to transferring heat energy, transfer moisture from the extract air to the supply air. Depending on the design of the heat transfer surface, they are subdivided into enthalpy and sorption types and make it possible to utilize 15–45% of the moisture removed with the extract air.
One of the first implementation projects
In 2000, for a residential building on Krasnostudensky prospect, 6, one of the first systems of apartment mechanical supply and exhaust ventilation with heat recovery from exhaust air for heating the supply air in a cross-flow air-to-air plate heat exchanger was designed.
A compact, low-noise apartment supply and exhaust unit is located in each apartment in the space of the false ceiling of the guest bathroom located next to the kitchen. The maximum supply air capacity is 430 m 3 / h. To reduce energy consumption, outside air intake in most apartments is carried out not from the street, but from the space of the glazed loggia. In other apartments, where there is no technical possibility of air intake from loggias, air intake grilles are located directly on the facade.
Outside air is cleaned, if necessary, it is preheated to prevent freezing of the heat exchanger, then it is heated or cooled in the heat exchanger due to the extracted air, then, if necessary, it is finally warmed up to the required temperature by an electric heater, after which it is distributed throughout the apartment. The first heater with a rated power of 0.6 kW is designed to protect the exhaust duct from condensate freezing. Condensate is discharged into the sewer through a special drainage tube through a water seal. The second heater with a power of 1.5 kW is designed to heat up the supply air to a predetermined comfortable value. It is also electrical for ease of installation.
It should be noted that, according to the calculations of the designers, the need to reheat the air after the heat exchanger could arise only at very low outside temperatures. Nevertheless, taking into account that twice as much supply air passes through the heat exchanger of the air handling unit as the extract air, an electric air heater was installed on the supply air. Operational practice has confirmed these assumptions: additional heating is almost never used, the heat of the exhaust air is quite enough to heat the supply air to a temperature that does not cause discomfort among residents.
The heat exchanger is equipped with an automation system with a controller and a control panel. The automation system provides for turning on the first heater when the temperature of the heat exchanger wall reaches below 1 ° C, the second heater can be turned on and off, ensuring the constancy of the set temperature of the supply air.
There are three fixed speeds for the supply fan. At the first speed, the supply air volume is 120 m 3 / h, this value meets the requirements for a one- and two-room apartment, as well as a three-room apartment with a small number of residents. At the second speed, the supply air volume is 180 m 3 / h, at the third - 240 m 3 / h. Residents rarely use the second and third speeds.
Acoustic measurements were carried out at all fan speeds, which showed that at the first speed the noise level does not exceed 30–35 dB (A), and this value is valid for an unfurnished apartment. In an apartment with furniture and interior items, the noise level will be even lower. At the second and third speeds, the noise level is higher, but when the door of the guest bathroom is closed, it does not cause discomfort among residents.
Exhaust air is taken from the bathrooms, then, after filtration, it is passed through a heat exchanger and discharged through a central collecting exhaust duct. Prefabricated exhaust air ducts - metal, made of galvanized steel and laid in fenced-in fire shafts. On the upper technical floor, prefabricated ducts of one section are combined and led outside the building.
At the time of the implementation of the project, it was forbidden by the regulations to combine the hoods of bathrooms and kitchens for disposal, therefore, the hoods of the kitchens are isolated. The heat of about half of the air volume removed from the apartment is recovered. This ban has now been lifted, further improving the energy efficiency of the system.
In the 2008-2009 heating season, an energy survey of heat consumption systems was carried out in the building, which showed a 43% heat savings for heating and ventilation compared to similar buildings in the same year.
Project in Northern Izmailovo
Another similar project was implemented in 2011 in Northern Izmailovo. Apartment building 153 provides for apartment ventilation with mechanical induction and utilization of the heat of the exhaust air to heat the supply air. The air handling units are installed autonomously in the corridors of the apartments and are equipped with filters, a plate heat exchanger and fans. The complete set of the unit includes automation equipment and a control panel that allows you to regulate the unit's air capacity.
Passing through a ventilation unit with a plate heat exchanger, the extract air heats the supply air up to 4 ° C (at an outside air temperature of –28 ° C). Compensation for the heat deficit for heating the supply air is carried out by heating heating devices.
Outside air is taken from the loggia of the apartment, and exhaust air from baths, toilets and kitchens (within the same apartment) after the utilizer is discharged into the exhaust channel via a satellite and removed within the technical floor. If necessary, the drainage of condensate from the heat exchanger is provided in the sewer riser equipped with a dropping funnel with a smell-locking device. The riser is located in the bathroom.
Supply and extract air flow rate control is carried out by means of one control panel. The unit can be switched over from normal operation with heat recovery to summer operation without recovery. The technical floor is ventilated through deflectors.
The volume of the supplied air is taken to compensate for the exhaust from the premises of the bathroom, bath, and kitchen. The apartment does not have an exhaust duct for connecting kitchen equipment (the exhaust hood from the stove works for recirculation). The inflow is routed through sound-absorbing air ducts through the living rooms. The ventilation unit in the apartment corridors is covered with a building structure with service hatches and an exhaust duct from the ventilation unit to the exhaust shaft. There are four redundant fans in the maintenance warehouse.
Tests of the installation with a heat recovery showed that its efficiency can reach 67%.
The use of mechanical ventilation systems with heat recovery from exhaust air is widespread in world practice. The energy efficiency of heat exchangers is up to 65% for plate heat exchangers and up to 85% for rotary ones. When these systems are used in Moscow, the annual heat consumption can be reduced to the baseline level by 38-50 kWh / m2 per year. This makes it possible to reduce the overall specific heat consumption indicator to 50-60 kWh / m2 per year without changing the base level of thermal protection of fences and to ensure a 40 percent reduction in the energy consumption of heating and ventilation systems, provided for from 2020.
Literature
1. Serov S.F., Milovanov A. Yu. Apartment ventilation system with heat exchangers. Pilot project of a residential building// ABOK. 2013. No. 2.2. Naumov A. L., Serov S. F., Budza A. O. Exhaust air heat exchangers for apartments// ABOK. 2012. No. 1.
1 Initially, this technology was spread in Northern Europe and Scandinavia. Today, Russian designers have considerable experience in using these systems in multi-storey residential buildings.
In this article, we propose to consider an example of the use of modern heat exchangers (recuperators) in ventilation units, in particular rotary ones.
The main types of rotary heat exchangers (recuperators) used in ventilation units:a) condensation rotor - utilizes mainly sensible heat. Moisture transfer takes place when the extract air is cooled by the rotor to a temperature below the dew point.
b) enthalpy rotor - has a hygroscopic foil coating that promotes moisture transfer. In this way the total heat is recovered.
Consider a ventilation system in which both types of heat exchanger (recuperator) will work.
Let us assume that the object of the calculation is a group of rooms in a certain building, for example, in Sochi or Baku, we will calculate only for the warm period:
Outdoor air parameters:
outdoor air temperature during the warm period, with a security of 0.98 - 32 ° С;
enthalpy of outdoor air in the warm season - 69 kJ / kg;
Internal air parameters:
internal air temperature - 21 ° С;
relative humidity of indoor air - 40-60%.
The required air consumption for assimilation of harmful substances in this group of premises is 35000 m³ / h. The room process beam is 6800 kJ / kg.
Air distribution scheme in rooms - "bottom-up" low-speed air distributors. In this regard (we will not apply the calculation, since it is volume and goes beyond the scope of the article, we have everything we need), the parameters of the supply and exhaust air are as follows:
1. Supply:
temperature - 20 ° С;
relative humidity - 42%.
2. Removable:
temperature - 25 ° С;
relative humidity - 37%
Let's build the process on the I-d diagram (Fig. 1).
First, we designate a point with the parameters of the internal air (B), then draw the process beam through it (note that for this design of the diagrams, the initial point of the beam is the parameters t = 0 ° C, d = 0 g / kg, and the direction is indicated by the calculated value (6800 kJ / kg) indicated on the edge, then the resulting beam is transferred to the parameters of the internal air, keeping the angle of inclination).
Now, knowing the temperatures of the supply and extract air, we determine their points, finding the intersections of the isotherms with the process beam, respectively. We build the process from the opposite, in order to obtain the specified parameters of the supply air, we lower the segment - heating - along the line of constant moisture content to the curve of relative humidity φ = 95% (segment P-P1).
We select a condensing rotor that recovers the heat of the removed air for heating P-P1. We obtain the efficiency (calculated by temperature) of the rotor of the order of 78% and calculate the temperature of the exhaust air U1. Now, let us select an enthalpy rotor that works to cool the outside air (H) by the obtained parameters U1.
We get the efficiency (calculated by enthalpy) of the order of 81%, the parameters of the treated air at the inflow H1, and at the exhaust U2. Knowing the parameters H1 and P1, you can choose an air cooler with a capacity of 332,500 W.
Let's depict the ventilation unit schematically with recuperators (Fig. 2).
Now, for comparison, we will select another system, for the same parameters, but with a different configuration, namely: we will install one condensing rotor.
Now (Fig. 3) heating of P-P1 is carried out by an electric air heater, and the condensation rotor will provide the following: efficiency is about 83%, the temperature of the treated supply air (H1) is 26 ° C. We will select an air cooler for the required power of 478 340 W.
It should be noted that for system 1 less power is required for cooling and, in addition to this, additional energy carrier costs (in this case, alternating current) are not required for the second heating of the air. Let's make a comparison table:
| Compared positions | System 1 (with two heat exchangers) | System 2 (with one heat exchanger) | Difference |
| Rotor motor consumption | 320 + 320 W | 320 Wt | 320 Wt |
| Required cooling capacity | 332,500 watts | 478 340 Watt | 145 840 Wt |
| Power consumption for the second heating | 0 watts | 151 670 W | 151 670 W |
| Power consumption of fan motors | 11 + 11 kW | 11 + 11 kW | 0 |
To summarize
We clearly see the differences in the operation of the condensing and enthalpy rotors, the energy savings associated with this. However, it should be noted that the principle of system 1 can be organized only for southern, hot cities, since with heat recovery during the cold period, the values of the enthalpy rotor do not differ much from the condensation one.
Production of ventilation units with rotary recuperators
Airkat Klimatekhnik has been successfully developing, designing, manufacturing and installing air handling units with rotary recuperators for many years. We offer modern and non-standard technical solutions that work even under the most complex operating algorithms and extreme conditions.
In order to receive an offer for a ventilation or air conditioning system, simply contact any of
In an air conditioning system, the heat of the exhaust air from the premises can be utilized in two ways:
· Using schemes with air recirculation;
· Installing heat exchangers.
The latter method is usually used in direct-flow air conditioning systems. However, the use of heat exchangers is not excluded in circuits with air recirculation.
A wide variety of equipment is used in modern ventilation and air conditioning systems: heaters, humidifiers, various types of filters, adjustable grilles and much more. All this is necessary to achieve the required air parameters, maintain or create comfortable conditions for working in the room. All this equipment requires a lot of energy to maintain. Heat recovery units are becoming an effective solution for saving energy in ventilation systems. Their basic principle of operation is to heat the air flow supplied to the room using the heat of the flow removed from the room. When using a heat exchanger, less power of the heater is required to heat the supply air, thereby reducing the amount of energy required for its operation.
Heat recovery in air-conditioned buildings can be done through heat recovery from ventilation emissions. Recycling waste heat for heating fresh air (or cooling the incoming fresh air with waste air after the air conditioning system in summer) is the simplest form of utilization. At the same time, four types of utilization systems can be noted, which have already been mentioned: rotating regenerators; heat exchangers with an intermediate heat carrier; simple air heat exchangers; tubular heat exchangers. A rotating regenerator in an air conditioning system can increase the supply air temperature in winter by 15 ° C, and in summer it can reduce the supply air temperature by 4-8 ° C (6.3). As in other recovery systems, with the exception of the intermediate heat exchanger, the rotating regenerator can only function if the exhaust and suction ducts are adjacent to each other at some point in the system.
An intermediate heat exchanger is less efficient than a rotating regenerator. In the presented system, water circulates through two heat exchange coils, and since a pump is used, the two coils can be located at some distance from each other. Both this heat exchanger and the rotating regenerator have moving parts (the pump and the electric motor are driven and this distinguishes them from air and tubular heat exchangers. One of the disadvantages of the regenerator is that pollution can occur in the channels. Dirt can settle on the wheel, then carries it to the suction port Most wheels nowadays have a purge to keep the transfer of contaminants to a minimum.
A simple air heat exchanger is a stationary device for heat exchange between exhaust and incoming air streams, passing through it in a countercurrent flow. This heat exchanger resembles a rectangular steel box with open ends, divided into many narrow channels such as chambers. Exhaust and fresh air flows through alternating channels, and heat is transferred from one air stream to another simply through the walls of the channels. There is no transfer of contaminants in the heat exchanger, and since a significant surface area is enclosed in a compact space, a relatively high efficiency is achieved. A heat exchanger with a heat pipe can be considered as a logical development of the design of the above-described heat exchanger, in which the two air flows into the chambers remain completely separate, connected by a bundle of finned heat pipes that transfer heat from one channel to another. Although the pipe wall can be viewed as additional thermal resistance, the heat transfer efficiency within the pipe itself, in which the evaporation-condensation cycle occurs, is so great that up to 70% of the waste heat can be recovered in these heat exchangers. One of the main advantages of these heat exchangers over an intermediate heat exchanger and a rotating regenerator is their reliability. Failure of several pipes will only slightly reduce the efficiency of the heat exchanger, but will not completely stop the utilization system.
With all the variety of design solutions for heat utilizers of secondary energy resources, each of them has the following elements:
· Environment - a source of thermal energy;
· Environment - consumer of heat energy;
· Heat receiver - heat exchanger that receives heat from a source;
· Heat exchanger - heat exchanger that transfers heat energy to the consumer;
· Working substance that transports thermal energy from the source to the consumer.
In regenerative and air-to-air (air-liquid) recuperative heat exchangers, the working substance is the heat exchanging media themselves.
Application examples.
1. Heating of air in air heating systems.
Heaters are designed for rapid heating of air using a water heat carrier and its uniform distribution using a fan and guide louvers. This is a good solution for construction and industrial workshops, where fast heating and maintaining a comfortable temperature are required only during working hours (at the same time, ovens are usually in operation).
2. Heating of water in the hot water supply system.
The use of heat exchangers allows to smooth out the peaks in energy consumption, since the maximum water consumption occurs at the beginning and end of the shift.
3. Heating of water in the heating system.
Closed system
The coolant circulates in a closed loop. Thus, there is no risk of contamination.
Open system. The heat carrier is heated by hot gas and then gives off heat to the consumer.
4. Heating of the combustion air. Allows to reduce fuel consumption by 10% –15%.
It is calculated that the main reserve of fuel economy during the operation of burners for boilers, furnaces and dryers is the utilization of the heat of exhaust gases by heating the combustion fuel with air. Heat recovery from exhaust flue gases is of great importance in technological processes, since the heat returned to the furnace or boiler in the form of heated blast air can reduce the consumption of fuel natural gas by up to 30%.
5. Heating of fuel going to combustion using liquid-liquid heat exchangers. (Example - heating fuel oil up to 100˚ – 120˚ С.)
6. Heating of the process fluid using liquid-liquid heat exchangers. (An example is heating a galvanic solution.)
Thus, a heat exchanger is:
Solving the problem of energy efficiency in production;
Normalization of the ecological situation;
Availability of comfortable conditions in your production - heat, hot water in administrative and utility rooms;
Reducing energy costs.
Picture 1.
The structure of energy consumption and energy saving potential in residential buildings: 1 - transmission heat loss; 2 - heat consumption for ventilation; 3 - heat consumption for hot water supply; 4– energy saving
List of used literature.
1. Karadzhi V. G., Moskovko Y. G. Some features of the effective use of ventilation and heating equipment. Leadership - M., 2004
2. Eremkin A.I., Byzeev V.V. Economics of energy supply in heating, ventilation and air conditioning systems. Publishing house of the Association of Construction Universities M., 2008.
3. Skanavi A. V., Makhov. L. M. Heating. Publishing house ASV M., 2008
