Utilization of thermal energy of exhaust ventilation. Fundamentals of design and installation of heating systems. Lecture structure and timing

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 thermal energy for heating the incoming air is 40 ... 80% of heat consumption, most of it can be saved in the case of the use of 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, one of which moves the removed air, and the other - the supply air. In the manufacture of plate heat exchangers of this design with a large air capacity, significant technological difficulties arise, therefore, the designs of shell-and-tube waste heat exchangers TKT, which are a bundle of pipes arranged in a checkerboard pattern and enclosed in a casing, have been developed. The removed air moves in the annular space, the outer one - inside the tubes. Cross flow.

Rice. Heat exchangers:
a - plate heat exchanger;
b - TKT utilizer;
in - rotating;
g - recuperative;
1 - body; 2 - supply air; 3 - rotor; 4 - blowing sector; 5 - exhaust air; 6 - drive.

In order to protect against icing, the heat exchangers are equipped with an additional line along the outside air flow, through which, at a temperature of the tube bundle walls below the critical temperature (-20°C), part of the cold outside air is bypassed.

Extract air heat recovery units 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 circuit filled with an intermediate carrier. The circulation of the coolant is carried out by means of pumps. The exhaust air, being cooled in the air heater of the exhaust duct, transfers heat to an 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 frost 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 the formation of frost on the heat exchange surface of the exhaust air heater during the day with subsequent shutdown and defrosting, or, if the shutdown of the unit is unacceptable, when applying one of the following measures to protect the exhaust duct air heater from frost formation :

preheating of supply air to a positive temperature;
creating a bypass for the coolant or supply air;
increase in coolant flow in the circulation circuit;
heating of the intermediate coolant.

The choice of the type of regenerative heat exchanger is made depending on the calculated parameters of the exhaust and supply air and moisture release inside the room. Regenerative heat exchangers can be installed in buildings for various purposes in systems of mechanical supply and exhaust ventilation, air heating and air conditioning. The installation of a regenerative heat exchanger must provide countercurrent air flow.

The ventilation and air conditioning system with a regenerative heat exchanger must be equipped with control and automatic control means, which must provide operating modes with periodic frost thawing or frost formation prevention, as well as maintain the required supply air parameters. 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 supply air temperatures, it is necessary to apply recycling schemes that provide protection against freezing of the surface of the air heaters in the exhaust duct.

In an air conditioning system, the heat of the exhaust air from the premises can be utilized in two ways:

· Applying schemes with air recirculation;

· Installing heat exchangers.

The latter method, as a rule, is used in direct-flow circuits of air conditioning systems. However, the use of heat recovery units is not excluded in schemes 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 indoors. A lot of energy is required to maintain all this equipment. Heat exchangers are an effective solution for saving energy in ventilation systems. The basic principle of their operation is the heating of the air flow supplied to the room, using the heat of the flow removed from the room. When using a heat exchanger, less power is required for heating the supply air, thereby reducing the amount of energy required for its operation.

Heat recovery in air-conditioned buildings can be done by recovering the heat from ventilation emissions. Waste heat recovery for fresh air heating (or cooling of incoming fresh air with waste air from an air conditioning system in summer) is the simplest form of recovery. In this case, four types of disposal systems can be noted, which have already been mentioned: rotating regenerators; heat exchangers with an intermediate coolant; simple air heat exchangers; tubular heat exchangers. A rotary heat exchanger in an air conditioning system can increase the supply air temperature by 15°C in winter and can reduce the supply air temperature by 4-8°C in summer (6.3). As with other recovery systems, with the exception of the intermediate heat exchanger, the rotary heat exchanger 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 rotary heat exchanger. In the system shown, 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 rotary regenerator have moving parts (the pump and the electric motor are driven and this distinguishes them from air and tube heat exchangers. One of the disadvantages of the regenerator is that fouling can occur in the channels. Dirt can be deposited on the wheel, which then transfers it to the suction channel.Most wheels are now equipped with scavenging, which reduces the transfer of contaminants to a minimum.

A simple air heat exchanger is a stationary device for heat exchange between the exhaust and incoming air flows, passing through it in countercurrent. This heat exchanger resembles a rectangular steel box with open ends, divided into many narrow channels like chambers. Exhaust and fresh air flow 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. The heat pipe heat exchanger can be seen as a logical development of the heat exchanger design described above, 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 considered as additional thermal resistance, the efficiency of heat transfer within the pipe itself, in which the evaporation-condensation cycle takes place, is so high that up to 70% of waste heat can be recovered in these heat exchangers. One of the main advantages of these heat exchangers compared to the intermediate heat exchanger and rotary regenerator is their reliability. The failure of several pipes will only slightly reduce the efficiency of the heat exchanger, but will not completely stop the disposal system.

With all the variety of design solutions for heat recovery devices of secondary energy resources, each of them has the following elements:

· The environment is a source of thermal energy;

· The environment is a consumer of thermal energy;

· Heat receiver - a heat exchanger that receives heat from a source;

· Heat transfer device - a heat exchanger that transfers thermal energy to the consumer;

· A working substance that transports thermal energy from a source to a consumer.

In regenerative and air-air (air-liquid) recuperative heat exchangers, the heat exchange media themselves are the working substance.

Application examples.

1. Air heating in air heating systems.
Air heaters are designed for rapid heating of air with the help of a water coolant and its uniform distribution with the help of a fan and guide blinds. This is a good solution for construction and production shops, where fast heating and maintaining a comfortable temperature is required only during working hours (the ovens are usually working at the same time).

2. Water heating in the hot water supply system.
The use of heat recovery units allows you to smooth out peaks in energy consumption, since the maximum water consumption occurs at the beginning and end of the shift.

3. Water heating in the heating system.
closed system
The coolant circulates in a closed circuit. Thus, there is no risk of contamination.
Open system. The coolant is heated by hot gas, and then gives off heat to the consumer.

4. Heating of blast air for combustion. Allows you to reduce fuel consumption by 10%-15%.

It has been calculated that the main reserve for saving fuel during the operation of burners for boilers, furnaces and dryers is the utilization of the heat of exhaust gases by heating the combusted fuel with air. The heat recovery of exhaust flue gases is of great importance in technological processes, since the heat returned to the furnace or boiler in the form of preheated blast air makes it possible to reduce the consumption of fuel natural gas by up to 30%.
5. Heating of the fuel going to combustion using "liquid-liquid" heat exchangers. (Example - heating fuel oil to 100˚–120˚ С.)

6. Process fluid heating using "liquid-liquid" heat exchangers. (Example - heating a galvanic solution.)

Thus, the heat exchanger is:

Solving the problem of energy efficiency of production;

Normalization of the ecological situation;

Availability of comfortable conditions in your production - heat, hot water in administrative and amenity premises;

Reducing energy costs.

Picture 1.

Structure of energy consumption and energy saving potential in residential buildings: 1 – transmission heat losses; 2 - heat consumption for ventilation; 3 - heat consumption for hot water supply; 4- energy saving

List of used literature.

1. Karadzhi VG, Moskovko Yu.G. Some features of the effective use of ventilation and heating equipment. Guide - 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 DIA M., 2008

LECTURE

by academic discipline "Heat and mass transfer equipment of enterprises"

(to the curriculum 200__)

Lesson number 26. Heat exchangers - utilizers. Designs, principle of operation

Developed by: Ph.D., Associate Professor Kostyleva E.E.

Discussed at the meeting of the department

Protocol No. _____

dated "_____" ___________2008

Kazan - 2008

Lesson number 26. Heat exchangers - utilizers. Designs, principle of operation

Learning goals:

1. To study the design and principle of various waste heat exchangers

Class type: lecture

Time spending: 2 hours

Location: aud. ________

Literature:

1. Electronic resources of the Internet.

Educational and material support:

Posters illustrating educational material.

Lecture structure and timing:

There are various types of waste heat exchangers.

Rice. 1 Heat exchangers-utilizers:
a- lamellar utilizer; b- TKT utilizer; v- rotating; G- recuperative;
1 - body; 2 - supply air; 3 - rotor; 4 - blowing sector; 5 - exhaust air; 6 - drive.

Extract air heat recovery units 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 circuit filled with an intermediate carrier. The circulation of the coolant is carried out by means of pumps. The exhaust air, being cooled in the air heater of the exhaust duct, transfers heat to an intermediate heat carrier that heats the supply air. When the exhaust air is cooled below the temperature dew points water vapor condenses on a part of the heat exchange surface of the air heaters of the exhaust duct, which leads to the possibility of ice formation at negative initial temperatures of the supply air.

preheating of supply air to a positive temperature;
creating a bypass for the coolant or supply air;
increase in coolant flow in the circulation circuit;
heating of the intermediate coolant.

arrange a bypass channel;
preheat the supply air;
change the frequency of rotation of the regenerator nozzle.

2. OPERATION OF THE HEAT EXCHANGER - HEAT EXCHANGER IN VENTILATION AND AIR CONDITIONING SYSTEMS

Waste heat exchangers can be used in ventilation and air conditioning systems to recover the heat of exhaust air removed from the room.

The supply and exhaust air flows are fed through the corresponding inlet pipes into the cross-flow channels of the heat exchange unit, made, for example, in the form of a package of aluminum plates. When flows move through the channels, heat is transferred through the walls from the warmer exhaust air to the colder supply air. These streams are then removed from the heat exchanger through appropriate outlets.

As it passes through the heat exchanger, the temperature of the supply air decreases. At low outdoor air temperatures, it can reach the dew point temperature, which leads to the loss of droplet moisture (condensate) on the surfaces that limit the heat exchanger channels. At a negative temperature of these surfaces, the condensate turns into frost or ice, which naturally disrupts the operation of the heat exchanger. To prevent the formation of frost or ice or their removal during the operation of this heat exchanger, the temperature in the coldest corner of the heat exchanger or (as an option) the pressure difference in the exhaust air duct before and after the heat exchanger is measured. When the limit, predetermined value by the measured parameter is reached, the heat exchange unit rotates 180" around its central axis. This ensures a reduction in aerodynamic resistance, time spent on preventing the formation of frost or removing it, and using the entire heat exchange surface.

The task is to reduce the aerodynamic resistance to the supply air flow, use the entire surface of the heat exchanger for the heat exchange process during the process of preventing the formation of frost or removing it, as well as reducing the time spent on carrying out this process.

The achievement of this technical result is facilitated by the fact that the parameter by which the possibility of formation or the presence of frost on the surface of the cold zone of the heat exchanger is judged is either the temperature of its surface in the coldest corner, or the pressure difference in the exhaust air channel before and after the heat exchange unit.

Prevention of frost formation by heating the surface with the exhaust air supplied to the channels from their outlet side by turning the heat exchanger at an angle of 180 ° (when the measured parameter reaches the limit value) ensures constant aerodynamic resistance to the supply air flow, as well as the use of the entire surface of the heat exchanger for heat exchange during throughout his work.

The use of a waste heat exchanger provides significant savings in space heating costs and reduces heat losses that inevitably occur during ventilation and air conditioning. And due to a fundamentally new approach to preventing the formation of condensate with the subsequent appearance of frost or ice, their complete removal, the efficiency of this heat exchanger is significantly increased, which distinguishes it favorably from other means of utilizing exhaust air heat.

3. HEAT EXCHANGERS FROM FINISHED TUBES

Today, energy conservation is a priority in the development of the world economy. The depletion of natural energy reserves, the increase in the cost of thermal and electrical energy inevitably leads us to the need to develop a whole system of measures aimed at improving the efficiency of energy-consuming installations. In this context, the reduction of losses and the reuse of the consumed thermal energy becomes an effective tool in solving the problem.

In the context of an active search for reserves to save fuel and energy resources, the problem of further improvement of air conditioning systems as large consumers of thermal and electrical energy is attracting more and more attention. An important role in solving this problem is to be played by measures to improve the efficiency of heat and mass exchangers, which form the basis of the polytropic air treatment subsystem, the operating costs of which reach 50% of all costs for the operation of SCR.

Utilization of thermal energy from ventilation emissions is one of the key methods for saving energy resources in air conditioning and ventilation systems for buildings and structures for various purposes. On fig. 1 shows the main exhaust air heat recovery schemes implemented on the market of modern ventilation equipment.

An analysis of the state of production and use of heat recovery equipment abroad indicates a trend towards the predominant use of recirculation and four types of exhaust air heat utilizers: rotating regenerative, plate recuperative, based on heat pipes and with an intermediate heat carrier. The use of these devices depends on the operating conditions of ventilation and air conditioning systems, economic considerations, the relative position of the supply and exhaust centers, operational capabilities.

In table. 1 shows a comparative analysis of various exhaust air heat recovery schemes. Among the main requirements on the part of the investor for heat recovery plants, it should be noted: price, operating costs and work efficiency. The cheapest solutions are characterized by simplicity of design and the absence of moving parts, which makes it possible to single out an installation with a cross-flow heat exchanger (Fig. 2) among the presented schemes as the most appropriate for the climatic conditions of the European part of Russia and Poland.

Recent studies in the field of creating new and improving existing heat recovery units for air conditioning systems indicate a clear trend in the development of new design solutions for plate heat exchangers (Fig. 3), the decisive moment in choosing which is the possibility of ensuring trouble-free operation of the unit in conditions of moisture condensation at low temperatures outside air.

The outdoor air temperature, starting from which frost formation is observed in the exhaust air ducts, depends on the following factors: the temperature and humidity of the exhaust air, the ratio of the supply and exhaust air flow rates, and design characteristics. Let us note the peculiarity of heat exchangers operation at negative outdoor air temperatures: the higher the heat exchange efficiency, the greater the risk of frost formation on the surface of the exhaust air channels.

In this regard, the low efficiency of heat exchange in a cross-flow heat exchanger can be an advantage in terms of reducing the risk of icing on the surfaces of the exhaust air channels. Ensuring safe modes is usually associated with the implementation of the following traditional measures to prevent freezing of the nozzle: periodic shutdown of the outdoor air supply, its bypass or preheating, the implementation of which certainly reduces the efficiency of exhaust air heat recovery.

One of the ways to solve this problem is the creation of heat exchangers in which the freezing of the plates is either absent or occurs at lower air temperatures. A feature of the operation of air-to-air heat exchangers is the possibility of implementing heat and mass transfer processes in “dry” heat transfer modes, simultaneous cooling and drying of the removed air with condensation in the form of dew and frost on the entire or part of the heat exchange surface (Fig. 4).

The rational use of the heat of condensation, the value of which reaches 30% under certain operating modes of the heat exchangers, makes it possible to significantly increase the range of changes in the parameters of the outside air, in which icing of the heat exchange surfaces of the plates does not occur. However, the solution of the problem of determining the optimal operating modes of the heat exchangers under consideration, corresponding to certain operating and climatic conditions, and the area of its expedient application, requires detailed studies of heat and mass transfer in the packing channels, taking into account the processes of condensation and frost formation.

Numerical analysis was chosen as the main research method. It also has the least laboriousness, and allows you to determine the characteristics and identify the patterns of the process based on the processing of information about the influence of the initial parameters. Therefore, experimental studies of heat and mass transfer processes in the considered devices were carried out in a much smaller volume and, mainly, to verify and correct the dependencies obtained as a result of mathematical modeling.

In the physico-mathematical description of heat and mass transfer in the recuperator under study, preference was given to the one-dimensional transfer model (ε-NTU model). In this case, the air flow in the packing channels is considered as a liquid flow with constant velocity, temperature and mass transfer potential over its cross section, equal to the average mass values . In order to increase the efficiency of heat recovery in modern heat exchangers, finning of the packing surface is used.

The type and location of the ribs significantly affects the nature of the heat and mass transfer processes. The change in temperature along the height of the rib leads to the implementation of various options for heat and mass transfer processes (Fig. 5) in the channels of the exhaust air, which significantly complicates mathematical modeling and the algorithm for solving the system of differential equations.

The equations of the mathematical model of heat and mass transfer processes in a cross-flow heat exchanger are implemented in an orthogonal coordinate system with the OX and OY axes directed parallel to the cold and warm air flows, respectively, and the Z1 and Z2 axes, perpendicular to the surface of the packing plates in the supply and exhaust air channels (Fig. 6 ), respectively.

In accordance with the assumptions of this ε-NTU model, heat and mass transfer in the heat exchanger under study is described by differential equations of heat and material balances, compiled for interacting air flows and nozzles, taking into account the heat of the phase transition and the thermal resistance of the resulting frost layer. To obtain an unambiguous solution, the system of differential equations is supplemented with boundary conditions that establish the values of the parameters of the exchanged media at the inputs to the corresponding channels of the recuperator.

The formulated nonlinear problem cannot be solved analytically, so the integration of the system of differential equations was carried out by numerical methods. A fairly large amount of numerical experiments carried out on the ε-NTU model made it possible to obtain a data array that was used to analyze the characteristics of the process and identify its general patterns.

In accordance with the objectives of the study of the operation of the heat exchanger, the choice of the studied modes and the ranges of variation of the parameters of the exchange flows was carried out so that the real processes of heat and mass transfer in the packing at negative values of the outdoor air temperature, as well as the conditions for the flow of the most dangerous operating modes of the heat recovery equipment from the point of view of operation, were most fully modeled. .

Presented in fig. 7-9, the results of calculating the operating modes of the apparatus under study, which are typical for climatic conditions with a low calculated outdoor air temperature in the winter period of the year, make it possible to judge the qualitatively expected possibility of the formation of three zones of active heat and mass transfer in the channels of the exhaust air (Fig. 6), which differ in character the processes taking place in them.

An analysis of the heat and mass transfer processes occurring in these zones makes it possible to evaluate possible ways to effectively capture the heat of the removed ventilation air and reduce the risk of frost formation in the channels of the heat exchanger packing based on the rational use of the phase transition heat. Based on the analysis performed, the boundary temperatures of the outside air were established (Table 2), below which frost formation is observed in the exhaust air ducts.

conclusions

An analysis of various schemes for the utilization of heat from ventilation emissions is presented. The advantages and disadvantages of the considered (existing) schemes for utilizing the exhaust air heat in ventilation and air conditioning installations are noted. Based on the analysis carried out, a scheme with a plate cross-flow heat exchanger is proposed:

on the basis of a mathematical model, an algorithm and a computer calculation program for the main parameters of heat and mass transfer processes in the heat exchanger under study were developed;
the possibility of formation of various moisture condensation zones in the channels of the heat exchanger nozzle, within which the nature of heat and mass transfer processes changes significantly, has been established;
the analysis of the regularities obtained makes it possible to establish the rational modes of operation of the studied devices and the areas of their rational use for various climatic conditions of the Russian territory.

SYMBOLS AND INDICES

Legend: h reb — rib height, m; l rib - length of the rib, m; t is temperature, °C; d is the moisture content of the air, kg/kg; ϕ—relative air humidity, %; δ rib is the thickness of the rib, m; δ in is the thickness of the frost layer, m.

Indices: 1 - outside air; 2 - removed air; e - at the entrance to the nozzle channels; rb - rib; in - frost, o - at the outlet of the nozzle channels; dew - dew point; sat is the state of saturation; w is the channel wall.

In Northern Europe and Scandinavia, ventilation systems of multi-storey residential buildings with supply air heating due to the heat removed with the help of heat recovery units have become widespread. Heat exchangers in ventilation systems were developed in the 1970s during the energy crisis.

To date, heat recovery units have been widely used: - recuperative type based on plate air-to-air heat exchangers (Fig. 41); - regenerative with a rotating heat exchange nozzle (Fig. 42); - with an intermediate heat carrier with "liquid-air" heat exchangers (Fig. 43).

According to their execution in multi-storey residential buildings, heat exchangers can be central to all buildings or a group of apartments and individual, apartment-by-apartment.

Rice. 42. Heat exchanger with a rotating heat exchange nozzle

Rice. 41. Heat exchanger of recuperative type (ventilation air heat recovery unit)

With similar weight and size indicators, regenerative heat exchangers (80-95%) have the highest energy efficiency, followed by recuperative ones (up to 65%), and heat exchangers with an intermediate coolant (45-55%) are in last place.

According to their design features, heat exchangers with an intermediate heat carrier are not very suitable for individual apartment ventilation, and therefore, in practice, they are used for central systems.

Rice. 43. Ventilation air heat recovery unit with an intermediate heat carrier: 1 - supply ventilation unit; 2 - exhaust ventilation unit; 3 - heat exchanger; 4 - circulation pump; 5 - filter; 6 – body of the utilizer

Regenerative heat exchangers have a significant drawback - the possibility of mixing a certain part of the exhaust air with the supply air in the unit body, which, in turn, can lead to the transfer of unpleasant odors and pathogenic bacteria. The volume of overflowing air in modern devices is reduced to fractions of a percent, but, nevertheless, most experts recommend limiting their scope to one apartment, cottage or one room in public buildings.

Recuperative heat exchangers, as a rule, include two fans (supply and exhaust), a plate heat exchanger, filters (Fig. 41). In modern designs, two water or electric heaters are built into the heat exchanger. One serves to protect the exhaust tract of the heat exchanger from freezing, the second - to reheat the supply air temperature to a predetermined value.

These systems, in comparison with traditional ones, have a number of advantages, which include significant savings in thermal energy spent on heating ventilation air - from 50 to 90%, depending on the type of heat exchanger used; as well as 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.

When installing recuperative heat exchangers for apartments, the following appear: - the ability to flexibly regulate the air-thermal regime depending on the mode of operation of the apartment, including using recirculated air; - the possibility of protection from urban, external noise (when using sealed translucent fences); – the possibility of cleaning the supply air with the help of highly efficient filters.

The implementation of these advantages is associated with the solution of a number of problems: - it is necessary to provide appropriate space-planning solutions for the apartment and allocate space for the placement of heat recovery units and additional air ducts; – it is necessary to provide protection against freezing of heat exchangers at low outdoor temperatures (-10 °С and below); – heat exchangers must be of low noise design and, if necessary, equipped with additional silencers; – it is necessary to ensure qualified maintenance of heat recovery units (replacement or cleaning of filters, flushing of the heat exchanger).

Various modifications of exhaust air heat exchangers are produced by a total of more than 20 companies. In addition, the production of energy-saving equipment begins at domestic enterprises.

The sound power level is given without duct network, without silencers for an open heat exchanger.

The widespread use of mechanical ventilation systems in residential multi-storey buildings with exhaust air heat recovery is constrained by a number of factors: - there is practically no financial incentive for energy saving among consumers - owners of apartments; - Investors-developers are not interested in additional costs for engineering equipment in economy and business class houses, believing that the quality of ventilation is a secondary indicator in the formation of the market value of housing; – “scars away” the need for maintenance of mechanical ventilation; - the population is not sufficiently informed about the criteria for air-thermal comfort of the dwelling, its impact on health and performance.

At the same time, there has been a positive trend towards overcoming the noted problems, and both investors and apartment buyers have a practical interest in modern technical solutions for ventilation systems.

Let's compare the effectiveness of traditional ventilation and new technical solutions in relation to residential multi-storey buildings of mass development.

There are three options for organizing ventilation in residential 17-storey buildings of the P-44 series for Moscow conditions:
A. Ventilation according to a typical design (natural ducted exhaust from the kitchen, bathroom and toilet rooms and inflow due to infiltration and from
window transom covers).
B. Mechanical exhaust, central ventilation system with the installation in the apartments of supply and exhaust valves with a constant air flow.
B. Mechanical supply and exhaust ventilation system with heat recovery of the removed air in recuperative heat exchangers.

The comparison was carried out according to three criteria: – air quality; - consumption of thermal energy in ventilation systems; – acoustic mode.

For the conditions of Moscow, according to meteorological observations, the following climatic conditions were accepted.

The following values of heat transfer resistance were taken into account in the calculations: - walls - 3.2 m2 °C/W; – windows – 0.62 m2 °С/W; - coatings - 4.04 m2 °C / W.

Heating system with traditional convectors for coolant parameters 95/70 °С.

In each entrance on the floor there are two 2-room, one 1-room and one 3-room apartments. Each apartment has a kitchen with an electric stove, a bathroom and a toilet.

The extract is produced in accordance with the standards: - from the kitchen - 60 m3 / h; – from the bathroom - 25 m3/h; - from the toilet - 25 m3 / h.

For the analysis, it is assumed that in option A, due to ventilation by opening the transoms of the windows, the average daily volume of inflow corresponds to the volume of exhaust from the apartment.

Rice. 44. Recuperator with installation of air heaters in the apartments of the experimental building: 1 - exhaust air fan; 2 – supply air fan; 3 - plate heat exchanger; 4 – electric heater; 5 – heat exchanger heater; 6 - filter for outside air (class EU5); 7 - filter for exhaust air (class EU5); 8 - sensor against freezing of the heat exchanger; 9, 10 - automatic reset of thermal protection; 11, 12 - manual reset of thermal protection; 13 - supply air temperature sensor

In option B, constant air exchange is ensured by the operation of a central exhaust fan connected to each apartment by a network of air ducts. Consistency of air exchange is ensured by the use of constant flow inlet valves installed in the window sashes and self-regulating exhaust valves in the kitchen, bathroom and toilet.

In option B, a mechanical supply and exhaust ventilation system is used with heat recovery from the exhaust air to heat the supply air in a plate heat exchanger. When comparing, the condition of constancy of air exchange was also accepted.

According to the air quality criterion, option A is significantly inferior to options B and C. Ventilation is carried out periodically during a time arbitrarily chosen by residents, that is, it is subjective and therefore far from always effective. In winter, ventilation is associated with the need for residents to leave the ventilated premises. Attempts to adjust the opening of the transoms for constant ventilation most often lead to ventilation instability, drafts, and thermal discomfort. With periodic ventilation, the air quality deteriorates after the vents are closed, and residents spend most of their time in a polluted air environment (Fig. 45).

Rice. 45. Change in air exchange and concentration of harmful substances during periodic ventilation of premises:
1 - air exchange;
2 - concentration of harmful substances;
3 - standard level of concentration of harmful substances

A special ventilation mode is provided for the kitchen. When cooking, an over-stove umbrella equipped with a high-performance multi-speed fan is included in the work. The air capacity of modern over-slab umbrellas reaches 600-1000 m3 / h, which is many times higher than the calculated air exchange in the apartment. To remove air from above-plate umbrellas, as a rule, separate air ducts are provided that are not connected with the general exhaust ventilation system from the kitchen. Compensatory flow of supply air is provided by a supply valve in the wall, which is opened during the operation of the umbrella. The general conclusion on the compared options can be drawn as follows: option B with exhaust air heat recovery has the highest efficiency in terms of air-thermal comfort and thermal energy saving; To normalize the acoustic regime, additional noise protection measures for the fan installation are required.

Constantly operating ventilation of apartments using supply valves (option B) built into window sashes or external walls at low outdoor temperatures can lead to thermal discomfort associated with uneven distribution of temperature and air velocity in the premises. Despite the fact that it is recommended to place supply valves above or behind heating appliances, specialists in Western Europe limit the effective scope of such ventilation systems to areas with an outdoor temperature of at least -10 ° C. Of greatest interest is ventilation option B, i.e. mechanical supply and exhaust ventilation with heat recovery of the exhaust air in recuperative heat exchangers. It is this system that was used to design and build the experimental system.

The experimental building consists of four sections; the total number of apartments is 264. Under the building there is a parking garage for 94 cars. On the 1st floor there are auxiliary non-residential premises, the two upper floors are reserved for a sports and fitness center. Residential apartments are located from the 2nd to the 16th floor. In free-plan apartments from 60 to 200 m2 of total area, in addition to living quarters, a kitchen, a bathroom with a toilet, a laundry room, a guest toilet, storage rooms, glazed loggias are provided. The building was built according to an individual project (architect P.P. Pakhomov). Structural solutions of the building are a monolith with an effective insulation with a brick cladding. The concept of energy-saving solutions for the building was developed under the guidance of the President of the Association of Engineers for Heating, Ventilation, Air Conditioning, Heat Supply and Building Thermophysics, Professor Yu. ".

The project provides for a comprehensive solution that functionally combines energy-saving architectural and planning solutions, effective enclosing structures and new generation engineering systems.

Building structures have a high level of thermal protection. Thus, the heat transfer resistance of walls is 3.33 m2 °C / W, metal-plastic windows with double-glazed windows - 0.61 m2 * °C / W, top coatings - 4.78 m2 °C / W, loggias are glazed with sun-protection tinted glasses.

The internal air parameters for the cold period are taken as follows: - living rooms - 20 °С; – kitchen - 18 °С; – bathroom - 25 °С; - toilet - 18 °C.

The building is designed with a horizontal per-apartment heating system with perimeter piping throughout the apartment. Metal-plastic pipes with thermal insulation in a protective corrugation are embedded in the preparation of the "black" floor. For the entire building with a total area of about 44 thousand m2 in the heating system of the residential part, there are only four pairs of risers (supply and return) according to the number of sections. On each floor in the elevator hall, distribution manifolds to the apartments are connected to the risers. The collectors are equipped with fittings, balancing valves and apartment heat meters.

The building has been designed and implemented per apartment adjustable supply and exhaust ventilation system with heat recovery of the exhaust air.

A compact air handling unit with a plate heat exchanger is located in the false ceiling of the guest toilet next to the kitchen.

The intake of supply air is carried out through a heat-insulated air duct and a hole in the outer wall facing the kitchen loggia. The exhaust air is taken from the kitchen area. The extract from the toilets and the bathroom is not heat-utilized, because at the time of the approval of the project, the standards forbade combining kitchen, bathroom and toilet extracts into one ventilation network within the apartment. Currently, according to the "Technical recommendations for the organization of air exchange in apartments of a multi-storey residential building", this restriction has been removed.

In the conditions of free planning of apartments, the unification of three or four zones by a common horizontal exhaust air duct requires special architectural and planning solutions, the installation of a horizontal air duct network in the apartment, which is difficult to implement for structural reasons.

During the heating period of 2003-2004 in a 3-room apartment on the 12th floor, preliminary tests of the apartment ventilation system were carried out with the heat recovery of the removed air. The total area of the apartment is 125 m2. The tests were carried out in an apartment without finishing, without interior partitions and doors. Selective test results are given in table. 22. The outdoor air temperature 4 ranged from +4.1 to -4.5 ° C with mostly cloudy weather. The air temperature in the room tB was maintained by an apartment heating system with steel radiators equipped with thermostatic valves in the range from 22.8 to 23.7 °C. In the course of tests with the help of air humidifiers, the relative humidity φ was varied from 25 to 45%.

A recuperative heat exchanger was installed in the apartment, with a maximum capacity for supply air Lnp = 430 m3/h. The volume of the removed air Lngutl was approximately 60-70% of the supply air, which is due to the setting of the apparatus for the utilization of only a part of the removed air.
The device is equipped with air filters for the supply and exhaust paths and two electric heaters. The first heater with a rated power of 0.6 kW is designed to protect the exhaust tract from freezing condensate, which 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 reheat the supply air tw to a predetermined comfort value.

Rice. 46. Plan of the apartment with a ventilation system: 1 - air handling unit with a heat exchanger; 2 - air intake from the loggia; 3 - extract from the kitchen; 4 - extract from the guest toilet; 5 - extract from the dressing room; 6 - extract from the bathroom; 7 - ceiling perforated air diffuser

For ease of installation, it is also made electric.

During the test, measurements were made of the temperature and humidity of the outdoor, indoor and exhaust air, the flow rate of the supply and exhaust air, the heat consumption of the apartment heating system Qm according to the readings of the heat meter, and the electricity consumption.

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 supply air temperature, which was in the range from 15 to 18.3 °C during testing. The fan control system allows you to select three fixed air flow modes, corresponding to the air exchange rate from 0.48 to 1.15 1/h.

Control and setting of temperature and air flow is carried out from a remote wired control panel.

Tests have shown the stable operation of the apartment ventilation system and the energy efficiency of utilizing the heat of the removed air.

It should be noted a number of features in the conduct of research, which cannot be ignored when assessing the indicators of the air-thermal regime of an apartment.

1. In new buildings, fresh concrete and mortar release a significant amount of moisture into the premises. The period during which moisture in building structures comes to an equilibrium state reaches 1.5-2 years. So, as a result of tests, approximately six months after filling the monolith and laying the screed, the moisture content of the indoor air in the presence of ventilation was 4-4.5 g/kg of dry air, while the moisture content of the outside air did not exceed 1-1.5 g/kg of dry air. air.

According to our estimates, in a monolithic building, in order to bring structures into an equilibrium moisture state, it is necessary to assimilate up to 200 kg of moisture per square meter. meter of floor area. The amount of heat required to evaporate this moisture in the initial period is 10-15 W/m2, and during the test period - 5-7 W/m2, which is a significant part of the heat balance of the apartment during the cold season. It is reckless not to take this factor into account in the implementation of heating and ventilation, especially in monolithic housing construction.

2. In the process of testing, there were no so-called internal household heat emissions, the size of which in the standards is proposed to be 10 W/m2.
It seems that this indicator should be differentiated depending on the area of the apartment per inhabitant.

In large apartments (more than 100 m2) with an area per person of 30-50 m2, the probable value of this indicator should decrease to 5-8 W/m2. Otherwise, the design heat output of heating and ventilation systems of buildings may be underestimated by 10-30%.

However, during construction, in particular buildings with monolithic structures that release a lot of moisture into the premises, it is more expedient to dry them out with the help of powerful electric heaters at the disposal of the builders before commissioning the buildings and especially before they are occupied. Unfortunately, such drying before testing was not carried out.

As noted, the experimental building under consideration was designed and built as energy-saving. Based on the results of the tests, adjusted for the predicted domestic heat release and the heat of evaporation of moisture in building structures, the specific heat and energy characteristics of a 3-room apartment were calculated per 1 m2 of area while maintaining a temperature of 20 °C in the apartment.

The results of the calculations showed that after finishing the apartments and settling in the building, the specific estimated annual heat consumption for heating and ventilation is almost halved from 132 to 70 kWh/(m2 year), and with the use of heat recovery to 44 kWh/(m2 year).

Further operation of the building will allow checking the assumptions made in the preliminary calculations.

Studies of the experimental system should cover all the factors that characterize its operation, including the psychological attitude of the residents using devices that are new to them.

Electric heating of air in the experimental system, compared with the use of heat from the heating system to which the building is connected, is not economically justified. This decision was made for the convenience of the experiment, in particular, for measurements related to heat consumption. However, according to the authors, over time, humanity will begin to switch to full electrical and heat supply to residential urban buildings. Therefore, an experimental study of a system in which apartment ventilation operates using electric air heaters is of interest for the future.