Exhaust air heat recovery devices as a promising energy-saving measure. How to calculate ventilation: formulas and an example of calculating a supply and exhaust system Production of ventilation units with rotary heat exchangers

LECTURE

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

(for the curriculum 200__g)

Lesson No. 26. Heat exchangers - heat exchangers. Designs, principle of operation

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

Discussed at a department meeting

protocol No. _____

from "_____" ___________2008

Kazan - 2008

Lesson No. 26. Heat exchangers are heat exchangers. Designs, principle of operation

Learning objectives:

1. Study the designs and principles of various waste heat exchangers

Type of lesson: lecture

Time spending: 2 hours

Location: room ________

Literature:

1. Electronic resources of the Internet.

Educational and material support:

Posters illustrating educational material.

Lecture structure and timing:

One of the sources of secondary energy resources in a building is the thermal energy of air removed into the atmosphere. Thermal energy consumption for heating the incoming air is 40...80% of heat consumption, most of it can be saved by using so-called waste heat exchangers.

There are different types of heat recovery 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 exhaust air moves, and through the other, the supply outside air. In the manufacture of plate heat exchangers of this design with high air capacity, significant technological difficulties arise, therefore, designs of shell-and-tube heat exchangers TKT have been developed, which are a bundle of pipes arranged in a checkerboard pattern and enclosed in a casing. The removed air moves in the inter-tube space, the outside air moves inside the tubes. The movement of flows is cross.

Rice. 1 Heat exchangers:
A- plate recycler; b- TKT recycler; V- 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 flow of outside air, through which part of the cold outside air is bypassed when the temperature of the walls of the tube bundle is below critical (-20°C).

Exhaust air heat recovery units with an intermediate coolant can be used in mechanical supply and exhaust ventilation systems, as well as in air conditioning systems. The installation consists of an air heater located in the supply and exhaust ducts, connected by a closed circulation loop filled with an intermediate medium. The coolant circulates through pumps. The exhaust air, cooling in the exhaust duct air heater, transfers heat to the intermediate coolant, which heats the supply air. When the exhaust air is cooled below the temperature dew point On part of the heat exchange surface of the exhaust duct air heaters, condensation of water vapor occurs, which leads to the possibility of ice formation at negative initial temperatures of the supply air.

Heat recovery installations with an intermediate coolant can operate either in a mode that allows the formation of ice on the heat exchange surface of the exhaust air heater during the day with subsequent shutdown and thawing, or, if shutting down the installation 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;
creating a bypass for coolant or supply air;
increasing coolant flow in the circulation circuit;
heating 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 releases inside the room. Regenerative heat exchangers can be installed in buildings for various purposes in mechanical supply and exhaust ventilation, air heating and air conditioning systems. The installation of a regenerative heat exchanger must ensure countercurrent movement of air flows.

A 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 defrosting of frost 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 rotation speed of the regenerator nozzle.

In systems with positive initial temperatures of the supply air 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 recovery schemes that provide protection against freezing of the surface of the air heaters in the exhaust duct.

2. OPERATION OF HEAT EXCHANGER – RECOVERY IN VENTILATION AND AIR CONDITIONING SYSTEMS

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

The flows of supply and exhaust air are supplied 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 corresponding outlet pipes.

As it passes through the heat exchanger, the temperature of the supply air decreases. At low outside air temperatures, it can reach the dew point temperature, which leads to the precipitation of droplets of moisture (condensation) on the surfaces limiting the heat exchanger channels. At negative temperatures of these surfaces, 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 operation of this heat exchanger, measure the temperature in the coldest corner of the heat exchanger or (optionally) the pressure difference in the exhaust air duct before and after the heat exchanger unit. When the limiting, predetermined value of the measured parameter is reached, the heat exchange block rotates 180" around its central axis. This ensures a reduction in aerodynamic drag, time spent on preventing the formation of frost or removing it, and using the entire heat exchange surface.

The goal is to reduce the aerodynamic resistance to the flow of supply air, use the entire surface of the heat exchanger for the heat exchange process when carrying out 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 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.

Preventing the formation of frost by heating the surface supplied to the channels from their outlet side by turning the heat exchanger at an angle of 180 o with the exhaust air flow (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 the entire time of his work.

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

3. HEAT EXCHANGERS FROM FINNED TUBES

There are different types of heat recovery heat exchangers.

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

Exhaust air heat recovery units with an intermediate coolant can be used in mechanical supply and exhaust ventilation systems, as well as in air conditioning systems. The installation consists of an air heater located in the supply and exhaust ducts, connected by a closed circulation loop filled with an intermediate medium. The coolant circulates through pumps. The exhaust air, cooling in the exhaust duct air heater, transfers heat to the intermediate coolant, which heats the supply air. When the exhaust air is cooled below the dew point temperature, condensation of water vapor occurs on 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.

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

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

Description:

Currently, the thermal protection indicators of multi-storey residential buildings have reached quite high
values, therefore the search for reserves for saving thermal energy is in the area of increasing the energy efficiency of engineering systems. One of the key energy-saving measures with a fairly high potential for saving thermal energy is the use of exhaust air heat utilizers 1 in ventilation systems.

Currently, the thermal protection indicators of multi-storey residential buildings have reached quite high values, so the search for reserves for saving thermal energy is in the area of increasing the energy efficiency of engineering systems. One of the key energy-saving measures with a fairly high potential for saving thermal energy is the use of exhaust air heat utilizers 1 in ventilation systems.

Supply and exhaust ventilation units with exhaust air heat recovery have a number of advantages compared to traditional supply ventilation systems, which include significant savings in thermal energy spent on heating ventilation air (from 50 to 90% depending on the type of heat exchanger used). It should also be noted the 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.

Types of recyclers

The most widely used:

1. Regenerative heat utilizers s. In regenerators, the heat of the exhaust air is transferred to the supply air through a nozzle, which is alternately heated and cooled. Despite their high energy efficiency, regenerative heat recovery devices have a significant drawback - the likelihood of mixing a certain part of the exhaust air with the supply air in the device body. This, in turn, can lead to the transfer of unpleasant odors and pathogenic bacteria. Therefore, they are usually used within one apartment, cottage or one room in public buildings.

2. Recuperative heat recovery units. These heat exchangers, as a rule, include two fans (supply and exhaust), filters and a plate heat exchanger of counterflow, cross and semi-cross types.

When installing recuperative heat recovery units door-to-door, it becomes possible to:

flexibly regulate the air-thermal regime depending on the type of operation of the apartment, including using recirculated air;
protection from city and external noise (when using sealed translucent fences);
purification of supply air using highly efficient filters.

3.Heat utilizers with intermediate coolant. Due to their design features, these heat exchangers are of little use for individual (apartment) ventilation, and therefore in practice they are used for central systems.

4. Heat utilizers with a heat exchanger on heat pipes. The use of heat pipes makes it possible to create compact, energy-efficient heat exchange devices. However, due to the complexity of the design and high cost, they have not found application in ventilation systems for residential buildings.

In basic indicators, the distribution of thermal energy costs in a typical multi-storey building is almost equally divided between transmission heat losses (50–55%) and ventilation (45–50%).

Approximate distribution of annual heat balance for heating and ventilation:

transmission heat loss – 63–65 kW h/m 2 year;
heating of ventilation air – 58–60 kW h/m 2 year;
internal heat release and insolation – 25–30 kWh/m2 year.

The introduction of mass construction into the practice of increasing the energy efficiency of apartment buildings allows:

modern heating systems using room thermostats, balancing valves and weather-dependent automation of heating points;
mechanical ventilation systems with exhaust air heat recovery.

With similar weight and size indicators, the best results in residential buildings are shown by regenerative heat recovery devices (80–95%), followed by recuperative ones (up to 65%), and in last place are heat recovery devices with an intermediate coolant (45–55%).

Mention should be made of heat reclaimers, which, in addition to transferring thermal energy, transfer moisture from the exhaust air to the supply air. Depending on the design of the heat transfer surface, they are divided into enthalpy and sorption types and make it possible to utilize 15–45% of the moisture removed with the exhaust air.

One of the first implementation projects

In 2000, one of the first apartment-by-apartment mechanical supply and exhaust ventilation systems was designed for a residential building at 6 Krasnostudentsky Prospekt with heat recovery from exhaust air to heat the supply air in a cross-flow air-to-air plate heat exchanger.

A compact, low-noise apartment air handling 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, the intake of outside air 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 taking air from the loggias, the air intake grilles are located directly on the facade.

The outside air is cleaned, if necessary, preheated to prevent freezing of the heat exchanger, then heated or cooled in the heat exchanger due to the removed air, then, if necessary, it is finally heated to the required temperature by an electric heater, after which it is distributed throughout the premises of the apartment. The first heater with a nominal power of 0.6 kW is designed to protect the exhaust duct from condensate freezing. The condensate is discharged into the sewer system through a special drainage tube through a water seal. The second heater with a power of 1.5 kW is designed to heat the supply air to a predetermined comfortable value. For ease of installation, it is also electrical.

It should be noted that, according to the designers’ calculations, the need for additional heating of the air after the heat exchanger could arise only at very low outside air temperatures. However, taking into account that twice as much supply air passes through the heat exchanger of the supply and exhaust unit as exhaust air, an electric heater was installed on the supply air. Operational practice has confirmed these assumptions: additional reheating 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 to residents.

The heat exchanger is equipped with an automation system with a controller and control panel. The automation system provides for the first heater to be turned on when the temperature of the heat exchanger wall reaches below 1 °C, the second heater can be turned on and off, ensuring a constant set temperature of the supply air.

There are three fixed rotation speeds of the supply fan. At the first speed, the volume of supply air is 120 m 3 /h, this value meets the requirements for one- and two-room apartments, as well as three-room apartments with a small number of inhabitants. At the second speed, the volume of supply air is 180 m 3 /h, at the third – 240 m 3 /h. Residents use the second and third speed very rarely.

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 to the residents.

Exhaust air is taken from the bathrooms, then, after filtration, it is passed through a heat exchanger and discharged through a central collection exhaust duct. Prefabricated exhaust air ducts are metal, made of galvanized steel and laid in fenced-off fireproof shafts. On the upper technical floor, prefabricated air ducts of one section are combined and removed outside the building.

At the time the project was implemented, regulations prohibited combining bathroom and kitchen hoods for disposal, so kitchen hoods were separated. The heat of approximately half the volume of air removed from the apartment is utilized. This ban has now been lifted, allowing for further improvements in the energy efficiency of the system.

During the heating season of 2008–2009, an energy survey of heat consumption systems was carried out in the building, which showed heat savings for heating and ventilation of 43% compared to similar houses of the same year of construction.

Project in Northern Izmailovo

Another similar project was implemented in 2011 in Northern Izmailovo. In the 153-apartment building, apartment-by-apartment ventilation is provided with mechanical stimulation and heat recovery from exhaust air to heat the supply air. Supply and exhaust units are installed autonomously in apartment corridors and are equipped with filters, a plate heat exchanger and fans. The installation package includes automation equipment and a control panel that allows you to regulate the air capacity of the installation.

Passing through a ventilation unit with a plate heat exchanger, the exhaust air heats the supply air 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 devices.

Outside air is taken from the loggia of the apartment, and exhaust air from baths, toilets and kitchens (within one apartment) after the heat exchanger is discharged into the exhaust duct through a satellite and removed within the technical floor. If necessary, condensate drainage from the heat recovery unit is provided in a sewer riser equipped with a drip funnel with an odor-locking device. The riser is located in the bathrooms.

Regulation of the supply and exhaust air flow is carried out using one control panel. The unit can be switched from normal operating mode with heat recovery to summer mode without recovery. Ventilation of the technical floor occurs through deflectors.

The volume of supply air is taken to compensate for the exhaust from the bathroom, bathtub, 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 throughout the living rooms. Provision is made for covering the ventilation unit in the apartment corridors with a building structure with hatches for maintenance and an exhaust air duct from the ventilation unit to the exhaust shaft. There are four reserve fans in the maintenance warehouse.

Tests of a heat recovery unit have shown that its efficiency can reach 67%.

The use of mechanical ventilation systems with exhaust air heat recovery is widespread in world practice. The energy efficiency of heat recovery devices is up to 65% for plate heat exchangers and up to 85% for rotary heat exchangers. When using these systems in Moscow conditions, the reduction in annual heat consumption to the base level can be 38–50 kWh/m2 per year. This makes it possible to reduce the overall specific heat consumption to 50–60 kWh/m2 per year without changing the basic level of thermal protection of fences and to ensure a 40 percent reduction in the energy intensity of heating and ventilation systems, envisaged from 2020.

Literature

1. Serov S. F., Milovanov A. Yu. Apartment ventilation system with heat recovery units. Residential building pilot project// ABOK. 2013. No. 2.
2. Naumov A.L., Serov S.F., Budza A.O. Apartment exhaust air heat recovery units// ABOK. 2012. No. 1.

1 Initially, this technology became widespread in Northern Europe and Scandinavia. Today, Russian designers also have significant experience in using these systems in multi-storey residential buildings.

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

To date, heat exchangers have found widespread use: – recuperative type based on plate air-to-air heat exchangers (Fig. 41); – regenerative with a rotating heat exchange nozzle (Fig. 42); – with an intermediate coolant with liquid-air heat exchangers (Fig. 43).

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

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

Rice. 41. Recuperative heat exchanger (heat recovery unit for ventilation air)

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

Due to their design features, heat exchangers with an intermediate coolant 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 intermediate coolant: 1 – supply ventilation unit; 2 – exhaust ventilation unit; 3 – heat exchanger; 4 – circulation pump; 5 – filter; 6 – heat recovery body

Regenerative heat exchangers have a significant drawback - the likelihood of mixing a certain part of the exhaust air with the supply air in the device body, which, in turn, can lead to the transfer of unpleasant odors and pathogenic bacteria. The volume of flowing air in modern devices has been reduced to a fraction of a percent, but, nevertheless, most experts recommend limiting their scope of application 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, and filters (Fig. 41). In modern designs, two water or electric heaters are built into the heat exchanger. One is used to protect the heat exchanger exhaust tract from freezing, the second is to heat 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 apartment by apartment, the following appears: – the ability to flexibly regulate the air-thermal regime depending on the operating mode of the apartment, including using recirculated air; – the possibility of protection from city and external noise (when using sealed translucent fences); – the ability to purify the supply air using 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 placing heat exchangers and additional air ducts; – protection against freezing of heat exchangers should be provided at low outdoor temperatures (-10 °C and below); – waste disposal units must be low-noise and, if necessary, equipped with additional noise suppressors; – it is necessary to provide qualified technical maintenance of heat exchangers (replacing or cleaning filters, washing the heat exchanger).

A total of more than 20 companies produce various modifications of exhaust air heat utilizers. In addition, the production of energy-saving equipment begins at domestic enterprises.

The sound power level is given without the air duct network, without silencers for an openly located heat exchanger.

The widespread use of mechanical ventilation systems in residential multi-storey buildings with heat recovery from exhaust air is hampered by a number of factors: – there is practically no material incentive for energy saving among consumers - apartment owners; – investor-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 determining the market value of housing; – “discourages” the need for maintenance of mechanical ventilation; – the population is not sufficiently informed about the criteria for air-thermal comfort of a home, 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 are becoming interested 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 construction.

Three options for organizing ventilation in residential 17-story buildings of the P-44 series are proposed for Moscow conditions:
A. Ventilation according to a standard design (natural duct exhaust from the kitchen, bath and toilet areas and inflow due to infiltration and from
closing window transoms).
B. Mechanical exhaust, central ventilation system with installation of supply and exhaust valves of constant air flow in apartments.
B. Mechanical supply and exhaust ventilation system with heat recovery from exhaust air in recuperative heat exchangers.

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

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

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

Heating system with traditional convectors with coolant parameters of 95/70 °C.

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 hood 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 of the apartments by a network of air ducts. Consistency of air exchange is ensured by the use of constant flow supply 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 to recover the heat of the exhaust air to heat the supply air in a plate heat exchanger. When comparing, the condition of constant air exchange is also accepted.

According to the air quality criterion, option A is significantly inferior to options B and C. Ventilation is carried out periodically for a time arbitrarily chosen by residents, i.e., it is subjective and therefore not always effective. In winter, ventilation is associated with the need for residents to leave the ventilated room. Attempts to adjust the opening of transoms for constant ventilation most often lead to instability of ventilation, drafts, and temperature discomfort. With periodic ventilation, the air quality deteriorates after closing the windows, and residents spend most of their time in a polluted air environment (Fig. 45).

Rice. 45. Changes 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 area. When cooking food, an over-stove hood equipped with a high-performance multi-speed fan is switched on. The air productivity of modern over-slab umbrellas reaches 600-1000 m3/h, which is many times higher than the calculated air exchange rate in the apartment. To remove air from over-slab hoods, as a rule, separate air ducts are provided that are not connected to the general exhaust ventilation system from the kitchen. Compensating supply air flow is provided by a supply valve in the wall, which is opened during the operation of the umbrella. The general conclusion regarding the compared options can be drawn as follows: the greatest efficiency in terms of air-thermal comfort and thermal energy savings is option B with exhaust air heat recovery; To normalize the acoustic conditions, 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. Although it is recommended to place supply valves above or behind heating appliances, experts in Western Europe limit the effective scope of such ventilation systems to areas with an outside air temperature of at least -10 ° C. Of greatest interest is ventilation option B, i.e. mechanical supply and exhaust ventilation with heat recovery from the exhaust air in recuperative heat exchangers. It was according to this system that the experimental system was designed and built.

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 upper two floors are reserved for a sports and fitness center. Residential apartments are located from the 2nd to the 16th floor. In open-plan apartments from 60 to 200 m2 of total area, in addition to living spaces, there is a kitchen, a bathroom with a toilet, a laundry room, a guest toilet, storage rooms, and glazed loggias. The building was built according to an individual project (architect P. P. Pakhomov). The structural solutions of the building are a monolith with effective insulation and brick cladding. The concept of energy-saving solutions for the building was developed under the leadership of the President of the Association of Heating, Ventilation, Air Conditioning, Heat Supply and Building Thermal Physics Engineers, Professor Yu. A. Tabunshchikov, the architectural studio “Architects-XXI Century”, OJSC TsNIIPROMZDANIY, LLC NPO TERMEK "

The project provides a comprehensive solution in which energy-saving architectural and planning solutions, efficient building envelopes and new generation engineering systems are functionally linked.

The 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 are 0.61 m2*°C/W, top coverings are 4.78 m2 °C/W, loggias are glazed with sun-protective tinted glass.

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

The building is designed with a horizontal 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 “subfloor”. For the entire building with a total area of about 44 thousand m2, the heating system of the residential part has 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.

An apartment-by-apartment adjustable supply and exhaust ventilation system with heat recovery from the exhaust air was designed and implemented in the building.

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

The supply air is taken in 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 exhaust from the toilets and bathroom is not heat-recovered, because at the time of approval of the project, the standards prohibited combining kitchen, bathroom and toilet exhaust hoods within an apartment into one ventilation network. Currently, according to the “Technical recommendations for organizing air exchange in apartments of a multi-storey residential building,” this restriction has been lifted.

In conditions of open-plan apartments, combining three or four zones with a common horizontal exhaust air duct requires special architectural and planning solutions and the installation of a horizontal network of air ducts in the apartment, which is difficult to implement for design reasons.

During the heating period of 2003-2004, preliminary tests of the apartment ventilation system with heat recovery from the exhaust air were carried out in a 3-room apartment on the 12th floor. The total area of the apartment is 125 m2. The tests were carried out in an apartment without finishing, without interior partitions and doors. Selected test results are given in table. 22. Outdoor air temperature 4 ranged from +4.1 to -4.5 °C with mostly cloudy weather. The room temperature 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. During the tests, the relative air humidity f was changed from 25 to 45% using air humidifiers.

A recuperative heat exchanger was installed in the apartment, with a maximum supply air capacity of Lnp = 430 m3/h. The volume of removed air, b'igutl, was approximately 60-70% of the supply air, which was due to the device being configured to utilize only 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 nominal power of 0.6 kW is designed to protect the exhaust tract from freezing of condensate, which is discharged into the sewer system through a special drain tube through a water seal. The second heater with a power of 1.5 kW is designed to heat the supply air tw to a predetermined comfortable value.

Rice. 46. Apartment plan with a ventilation system: 1 – supply and exhaust unit with a heat exchanger; 2 – air intake from the loggia; 3 – kitchen hood; 4 – extractor from the guest toilet; 5 – hood from the dressing room; 6 - extractor from the bathroom; 7 - ceiling perforated air distributor

For ease of installation, it is also electrical.

During the test, measurements were taken of the temperature and humidity of the external, internal and exhaust air, the flow of supply and exhaust air, the heat consumption of the apartment heating system Qm according to the heat meter, and the electricity consumption.

The heat exchanger is equipped with an automation system with a controller and 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 during testing was in the range from 15 to 18.3 °C. The fan control system allows you to select three fixed air flow modes, corresponding to an 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 heat recovery from the exhaust air.

It is worth noting a number of features in conducting research that cannot be ignored when assessing the air-thermal conditions 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 reaches an equilibrium state reaches 1.5-2 years. Thus, as a result of tests, approximately six months after filling the monolith and laying the screed, the moisture content of the internal air in the presence of ventilation was 4-4.5 g/kg of dry air, while the moisture content of the external air did not exceed 1-1.5 g/kg of dry 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 constitutes a significant part of the heat balance of the apartment during the cold period of the year. It is reckless not to take this factor into account when implementing heating and ventilation, especially in monolithic housing construction.

2. During the tests, 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 resident.

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 thermal power of heating and ventilation systems of buildings may be underestimated by 10-30%.

However, it is more advisable during construction, in particular of buildings with monolithic structures that release a lot of moisture into the premises, before handing over the buildings and especially before moving into them, to dry them using powerful electric heaters at the disposal of the builders. Unfortunately, such drying was not carried out before testing.

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

The calculation results showed that after the apartments are finished and the building is occupied, the specific estimated annual heat consumption for heating and ventilation is reduced by almost half 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 make it possible to verify the assumptions made in the preliminary calculations.

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

Electrical heating of air in the experimental system is not economically justified compared to using heat from the district heating system to which the building is connected for this purpose. This decision was made for the convenience of the experiment, in particular, for measurements regarding heat consumption. However, according to the authors, over time, humanity will begin to switch to full electric 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.

The main purpose of exhaust ventilation is to remove exhaust air from the serviced premises. Exhaust ventilation, as a rule, works in conjunction with supply ventilation, which, in turn, is responsible for supplying clean air.

In order to have a favorable and healthy microclimate in the room, you need to draw up a competent design of the air exchange system, perform the appropriate calculations and install the necessary units according to all the rules. When planning, you need to remember that the condition of the entire building and the health of the people who are in it depend on it.

The slightest mistakes lead to the fact that ventilation ceases to cope with its function as it should, fungus appears in the rooms, finishing and building materials are destroyed, and people begin to get sick. Therefore, the importance of correct calculation of ventilation should not be underestimated in any case.

Main parameters of exhaust ventilation

Depending on what functions the ventilation system performs, existing installations are usually divided into:

Exhaust. Necessary for intake of exhaust air and its removal from the room.
Inlet. Provides fresh, clean air from the street.
Supply and exhaust. At the same time, old musty air is removed and new air is introduced into the room.

Exhaust units are mainly used in production, offices, warehouses and other similar premises. The disadvantage of exhaust ventilation is that without a simultaneous installation of a supply system, it will work very poorly.

If more air is drawn out of a room than is supplied, drafts will form. Therefore, the supply and exhaust system is the most effective. It provides the most comfortable conditions both in residential premises and in industrial and working premises.

Modern systems are equipped with various additional devices that purify the air, heat or cool it, humidify it and distribute it evenly throughout the premises. The old air is removed through the hood without any difficulty.

Before you begin arranging a ventilation system, you need to approach the process of calculating it with all seriousness. The ventilation calculation itself is aimed at determining the main parameters of the main components of the system. Only by determining the most suitable characteristics can you make ventilation that will fully fulfill all its tasks.

During the calculation of ventilation, the following parameters are determined:

Consumption.
Operating pressure.
Heater power.
Cross-sectional area of air ducts.

If desired, you can additionally calculate the energy consumption for operating and maintaining the system.

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Step-by-step instructions for determining system performance

The calculation of ventilation begins with determining its main parameter - productivity. The dimensional unit of ventilation performance is m³/h. In order for the air flow calculation to be performed correctly, you need to know the following information:

The height of the premises and their area.
The main purpose of each room.
The average number of people who will be in the room at the same time.

To make the calculation, you will need the following equipment:

Tape measure for measurements.
Paper and pencil for notes.
Calculator for calculations.

To perform the calculation, you need to find out such a parameter as the rate of air exchange per unit of time. This value is set by SNiP in accordance with the type of room. For residential, industrial and administrative premises the parameter will vary. You also need to take into account such points as the number of heating devices and their power, the average number of people.

For domestic premises, the air exchange rate used in the calculation process is 1. When calculating ventilation for administrative premises, use an air exchange value of 2-3, depending on the specific conditions. The frequency of air exchange directly indicates that, for example, in a domestic room the air will be completely renewed once every 1 hour, which is more than enough in most cases.

Calculation of productivity requires the availability of data such as the amount of air exchange by multiplicity and the number of people. It will be necessary to take the largest value and, starting from it, select the appropriate exhaust ventilation power. The air exchange rate is calculated using a simple formula. It is enough to multiply the area of the room by the ceiling height and the multiplicity value (1 for household, 2 for administrative, etc.).

To calculate air exchange by number of people, multiply the amount of air consumed by 1 person by the number of people in the room. As for the volume of air consumed, on average, with minimal physical activity, 1 person consumes 20 m³/h, with average activity this figure rises to 40 m³/h, and with high activity it is already 60 m³/h.

To make it clearer, we can give an example of a calculation for an ordinary bedroom with an area of 14 m². There are 2 people in the bedroom. The ceiling has a height of 2.5 m. Quite standard conditions for a simple city apartment. In the first case, the calculation will show that the air exchange is 14x2.5x1=35 m³/h. When performing the calculation according to the second scheme, you will see that it is already equal to 2x20 = 40 m³/h. It is necessary, as already noted, to take a larger value. Therefore, specifically in this example, the calculation will be performed based on the number of people.

Using the same formulas, oxygen consumption is calculated for all other rooms. In conclusion, all that remains is to add up all the values, obtain the overall performance and select ventilation equipment based on these data.

Standard performance values for ventilation systems are:

From 100 to 500 m³/h for ordinary residential apartments.
From 1000 to 2000 m³/h for private houses.
From 1000 to 10000 m³/h for industrial premises.

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Determining the power of the air heater

In order for the calculation of the ventilation system to be carried out in accordance with all the rules, it is necessary to take into account the power of the air heater. This is done if supply ventilation is organized in combination with exhaust ventilation. A heater is installed so that the air coming from the street is heated and enters the room already warm. Relevant in cold weather.

The calculation of the power of the air heater is determined taking into account such values as air flow, the required outlet temperature and the minimum temperature of incoming air. The last 2 values are approved in SNiP. In accordance with this regulatory document, the air temperature at the heater outlet must be at least 18°. The minimum outside air temperature should be specified in accordance with the region of residence.

Modern ventilation systems include performance regulators. Such devices are designed specifically to reduce the speed of air circulation. In cold weather, this will reduce the amount of energy consumed by the air heater.

To determine the temperature at which the device can heat the air, a simple formula is used. According to it, you need to take the power value of the unit, divide it by the air flow, and then multiply the resulting value by 2.98.

For example, if the air flow at the facility is 200 m³/h, and the heater has a power of 3 kW, then by substituting these values into the above formula, you will get that the device will heat the air by a maximum of 44°. That is, if in winter it is -20° outside, then the selected air heater will be able to heat the oxygen to 44-20 = 24°.

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Operating pressure and duct cross-section

Calculation of ventilation involves the mandatory determination of parameters such as operating pressure and cross-section of air ducts. An efficient and complete system includes air distributors, air ducts and fittings. When determining working pressure, the following indicators must be taken into account:

The shape of ventilation pipes and their cross-section.
Fan parameters.
Number of transitions.

Calculation of the appropriate diameter can be done using the following relationships:

For a residential building, a pipe with a cross-sectional area of 5.4 cm² will be sufficient for 1 m of space.
For private garages - a pipe with a cross-section of 17.6 cm² per 1 m² of area.

A parameter such as air flow speed is directly related to the cross-section of the pipe: in most cases, the speed is selected within the range of 2.4-4.2 m/s.

Thus, when calculating ventilation, be it an exhaust, supply or supply and exhaust system, you need to take into account a number of important parameters. The effectiveness of the entire system depends on the correctness of this stage, so be careful and patient. If desired, you can additionally determine the energy consumption for the operation of the system being installed.