Design of Ventilation and Air Conditioning Systems

Design of Ventilation and Air Conditioning Systems

1. Calculation of the heat balance of the room.

Drawing up a heat and humidity balance for an air-conditioned room is carried out by well-known methods adopted in heating and ventilation equipment. Here, all factors affecting the change in the state of the air environment of the room should be taken into account.

To draw up the heat balance of the room, it is necessary to determine all the receipts and heat losses in the room.

In premises for various purposes, there are two main categories of heat loads:

  •  thermal loads occurring outdoors (outdoor);
  • thermal loads occurring inside buildings (internal).External thermal loads are represented by the following components:
  •  heat loss or heat loss as a result of temperature differences outside and inside the building through walls, ceilings, floors, windows and doors. The temperature difference outside the building and inside it in the summer is positive, as a result of which there is an influx of heat from outside to the inside of the room; and vice versa – in winter this difference is negative and the direction of heat flow changes;
  • heat from solar radiation through glazed areas; this load manifests itself in the form of perceived heat; solar radiation always creates a positive load both in summer and in winter. In summer, this load must be compensated, and in winter it is negligible and integrates with the heat generated by the installation of the artificial climate;
  • the outside ventilation air and the air entering the room (due to infiltration) can also have various properties, which, however, almost always contrast with the meteorological requirements of the rooms: in the summer, hot and humid (in some latitudes, vice versa – dry), the outside air significantly affects the operation of the installation cooling and draining air; in winter, cold and dry (or vice versa-humid) outdoor air should be warmed up and humidified. And only in the intermediate period between these two seasons, can outdoor air be used to some extent in the form of free cooling of rooms.

It should be noted that external thermal loads can have different properties, that is, they can be positive and negative depending on the time of year and time of day. Internal heat loads in residential, office or service premises are mainly composed of:

  •  heat generated by people;
  • heat generated by lamps and lighting devices, household appliances: refrigerators, stoves, etc. (in residential premises);
  • heat generated by operating devices and equipment: computers, printers, photocopiers, etc. (in office and other rooms);

In industrial and technological premises for various purposes, additional sources of heat can be:

  • heated production equipment;
  • hot materials, including liquids and various kinds of semi-finished products;
  • products of combustion and chemical reactions.

All of the listed internal thermal loads are always positive, and therefore, in the summer period they must be eliminated, and in winter, the load on the heating installation is reduced due to them.

2. Principles for choosing air conditioning and ventilation systems.

 The task of choosing an air conditioning or ventilation system should be solved on the basis of a technical and economic comparative analysis of several possible options (2, 3 or more).

 For this, it is necessary to comprehensively consider and evaluate the object according to the requirements for it, the main ones of which are:

Sanitary requirements:

  • It is necessary to maintain a certain temperature or temperature and humidity. It should be noted that maintaining humidity significantly increases the cost of the project.
  • Supply fresh air to the premises (naturally or mechanically) or use recirculation systems.
  • To remove air through local exhausts or with a general exchange hood (in the production building), or using a natural exhaust hood (in living quarters).

Architectural and construction requirements:

  • Possibility of installing an outdoor air conditioning unit on the facade of the building, and the indoor air conditioning unit in the room (cabinet air conditioners) or in the false ceiling (split system with fresh air). Possibility to install a central air conditioner on the technical floor or Roof-Top roof air conditioner on the roof of the building
  • Possibility to lay ducts and pipelines communications over a building or premises (especially in reconstructed buildings).

Fire-prevention requirements by categories of premises: normal conditions – premises of category <D> or fire hazardous <B>, or explosion-hazardous <A> and <B> and design solutions corresponding to these categories (installation of check and fire-retardant valves, separate installation of equipment units, various installation schemes communications).

 Operational requirements: is it possible to maintain and control the system from the central control panel or is it necessary to control (adjust the parameters) autonomously (for example, when one part of the rooms is oriented south, the other – north) and it is necessary to provide separate operating modes of equipment for groups of rooms.

System reliability.

Particularly important are the reliability requirements in precision conditioning while accurately maintaining the microclimatic parameters of various processes.

Economic requirements.

It is necessary to optimize the price by comparing equipment of various manufacturers and various classes in the project.

For the object, it is necessary to develop several fundamental options for systems based on various types of equipment and conduct a comparative assessment of them.

3. Stages of design work.

Design of hard currency is carried out mainly in two stages.

Stage 1 – the so-called feasibility study project (feasibility study). At this design stage, according to aggregated indicators, a choice is made and a feasibility study of the type of system is determined, technical areas for the installation of this equipment are determined, as well as a first approximation of its main characteristics is determined: air, cold and heat performance, type and number of central or autonomous air conditioners , their location, type and flow rate of heat and coolants, type and number of refrigeration machines, pumps, installed capacity of electrical equipment, mass of the system. At the same time, the preliminary cost of the system is established. Develop a schematic (preliminary) diagram of the system. Earlier in design practice, a feasibility study was followed by a technical design. With the advent of block equipment, these two stages of design are combined and now in the practice of design organizations this is a feasibility study. In commercial firms, this is a technical project. After approval by the customer, the feasibility studies develop a working draft – this is the most critical design stage.

Stage 2 – a working draft is developed on the basis of building plans, thermal characteristics of building structures and a technological (detailed with specification) task. Calculation of heat dissipation and on its basis the calculation of air exchange for each room, providing the required parameters. Equipment is selected (with the determination of all its characteristics), providing the necessary air exchange and pressure loss in the network. Finally, select the type and circuit diagram of the system and determine its characteristics, the number of air distributors, etc.

Draw plans with the application of equipment and wiring of ducts and pipelines.

Next, axonometric diagrams of duct and pipe networks are drawn. Perform aerodynamic and hydraulic calculations. Determine the noise level. They complete specifications for equipment, materials, fittings, etc., indicating the manufacturer and cost. After the customer has agreed on the project in the SES and the fire inspection, if there are comments on the project, adjustments are made. Based on this documentation, equipment is ordered.

At this stage, the design phase ends.

Working drawings are passed to installers at the facility. After the installation work is completed, installation organizations draw up executive drawings and executive certification.


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