The role of the design engineer is crucial in the creation and implementation of every stage of the construction-investment process – plumbing, electrical, HVAC installations, etc., which directly affect the energy consumption of building systems, the energy efficiency of the building, and its maintenance costs. The requirements for practicing design engineers are based on the Law on the Chambers of Architects and Engineers in Investment Design (ZKAИIP) in the relevant professional field, as well as the statutes of the Chamber of Engineers in Investment Design (CIID).
To obtain design authorization, engineers are required to have a diploma for a completed master’s or bachelor’s degree in engineering, a certain amount of professional experience in a design office or a company operating in the relevant field, as well as detailed knowledge of the stages of investment design. The work of an HVAC design engineer is defined by the qualification characteristics of the "Heating, Ventilation, Air Conditioning and Refrigeration, and Thermal and Gas Supply" section of the CIID. Practicing designers in this field are primarily graduates of Thermal Engineering at TU – Sofia, TU – Varna, or the University of Food Technologies (UFT) in Plovdiv.
“The actual design work consists of creating modern, energy-efficient HVAC installations, as well as implementing RES (Renewable Energy Systems)” , says Eng. Banov.
According to the Chamber’s regulations, engineers with a master’s degree who have two years of experience in a design office or relevant experience in the field acquire full design authorization (FDA), unlike bachelor’s degree holders, who may have limited authorization.
Peculiarities in the work of an HVAC designer.
"Every design engineer must understand the work of their colleagues and, in addition, be familiar with the entire investment process", asserts Eng. Banov. “They need to be informed about the operation of the system they are designing and the conditions in which it will be applied”, he adds. "The investment process, which includes design and subsequent construction supervision of the installation itself, is continuously coordinated", the specialist says. “Often, structural or other changes are required that could fundamentally alter the initial calculations”.
"The investor’s wishes are another significant factor in design changes", clarifies Eng. Banov. "The brief provided by the investor or an authorized consulting firm is a mandatory element of investment design. Often, the investor may make subsequent changes driven by the desire to reduce investment in certain installations and equipment."
"Creative disputes also arise between architects and HVAC designers during the design process", acknowledges Eng. Banov. "They are triggered by the architects’ desire to create buildings with beautiful architecture, large glazed or curtain façades, which often leads to higher energy consumption. Therefore, mutual compromises are necessary in the interest of better energy efficiency", adds Eng. Banov.
Energy Efficiency and HVAC Installations.
"It is well known that the façade is an extremely important element for the energy efficiency of a building", explains Eng. Banov. “Choosing a thicker layer of thermal insulation is suitable only for the winter period because adding external insulation to the façade blocks the flow of solar radiation. This reduces the walls’ thermal storage capacity, lowers the instantaneous energy load, and extends the heating period. As a result, the heating system has to operate for a longer time. That is why energy audits are carried out on buildings, examining the annual energy consumption for heating, ventilation, and air conditioning”, he adds.
“A significant factor for the air conditioning of a building is the choice of windows, because in most residential buildings they hermetically seal the space,” reflects Assoc. Prof. Ivaylo Banov. "The lack of air exchange and the accumulated moisture in the rooms cause condensation on the exterior walls and windows, as well as on columns and thermal bridges of the building structure."
“Therefore, when we talk about an air-conditioning system, a mandatory element is the supply of fresh air, which is treated depending on the season—cooled or humidified”, summarizes Eng. Banov.
“To achieve optimal energy efficiency in buildings, the choice of HVAC systems, their zoning, and placement is of crucial importance. This complicates the work of the HVAC engineer-designer,” emphasizes the specialist. “In practice, the selection of an air conditioner, for example, is usually based mainly on the room’s square footage, without taking into account the geographic location of the site or the building’s orientation to the sun,” explains Eng. Banov. “The role of the engineer-designer is to make the correct decision for the air conditioning of the rooms in a given building.”
Modern solutions for air conditioning.
Air conditioning systems are divided into two types – industrial and comfort.
For industrial systems, the leading factor is the technological process, which determines the microclimate parameters of the spaces. Engineer Banov gives the example of a textile factory, where it is necessary to maintain a high relative humidity of 60–80%, even though the normal moisture level for humans is around 50%. “In such cases, humidification or ventilation systems are most often developed,” he explains.
For comfort-type air conditioning, applied in residential, business, and administrative buildings, hotels, restaurants, etc., the microclimate parameters are also crucial. A determining factor here is the provision of fresh air.
In our country, there are sanitary-hygienic standards as well as standards for designing HVAC systems. Depending on the category of the room and whether smoking is allowed, there are specific norms for the amount of fresh air that must be supplied per person in the space.
"According to Regulation 15, which sets the technical rules and standards for designing HVAC systems, for rooms occupied by non-smokers, the required fresh air flow per person is 36 m³/h. If the room is occupied solely by smokers, 108 m³/h of fresh air per person is required. This means three times the air flow, larger and more extensive HVAC equipment, and consequently higher energy consumption. It is no coincidence that smoking is prohibited indoors—not only for health reasons but also to improve energy efficiency. It is worth reflecting on this aspect as well ", advises the specialist.
Comfort HVAC Systems
“For comfortable air conditioning, air or water–air systems are used. Air systems are the most energy-efficient way to save energy,” says Assoc. Prof. Banov. In these systems, both fresh and recirculated air (processed air from the rooms) are treated. During the summer, the air is cooled and dried to absorb the heat load and moisture from the rooms. In the winter, the processed air is heated and again kept at lower humidity. According to the air conditioning instructor, each person releases 100 g of moisture per hour, which, in a building with 5,000 occupants, results in a significant amount of moisture that must be handled by the corresponding system.
The application of this type of air system is found in large office buildings, cinemas, sports halls, atriums (open spaces) in shopping malls, and so on. They are often complemented with fan coil units or air curtains, which help block cold air streams coming from exterior walls, display windows, or openings.
Water–air systems handle the required volume of outdoor air through a separate air-handling unit (system) and then supply it to the room. The energy load within the space is managed by fan coil units (installed in suspended ceilings, high walls, wall-mounted, floor-standing, or embedded in the floor structure, etc.). Fan coil units consist of a heat exchanger, a fan, a filter, and control and shut-off valves.
In water–air systems, the heat exchangers receive hot water in the winter and chilled water in the summer. In this setup, two-pipe systems are built, where all fan coil units operate in the same mode—either heating or cooling. There are also fan coil units with two heat exchangers—one for hot water and one for chilled water. These are used in four-pipe systems, which allow different temperatures to be maintained in different rooms. Such systems are typically installed in more luxurious office or business buildings, hotels, etc., allowing individual temperature control for each separate room.
Modern air conditioning systems use a refrigerant instead of water, which allows multiple indoor units to be connected to a single or a group of outdoor units. These are direct-expansion and condensation systems, commonly known by commercial names such as VRV/VRF, KX-2, etc. In the indoor unit, the refrigerant evaporates, while in the outdoor unit, it condenses. When operating in heat pump mode (heating), the indoor unit acts as a condenser, and the outdoor unit functions as an evaporator.
"In an air-conditioning system serving multiple rooms, one of them acts as the representative, and all others are controlled based on it," explained Eng. Banov. In this case, only the airflow rate can be controlled, whereas in water-air and refrigerant-based air systems, the microclimate parameters of each room can be individually controlled.
Stages of design.
The design of any HVAC system depends on the microclimate parameters of a specific room or building, as specified in the aforementioned Regulation 15. It begins with general information about the location where the project will be implemented, since each geographic latitude has its own external climate data. The second element of the HVAC project is defining the indoor parameters – temperature, humidity, air velocity, and others – which determine the sanitary and hygiene standards for each enclosed space.
Next, the summer and winter heat loads for the space are calculated, after which the type of installation is specified – single-zone air system, multi-zone system with fans and convectors, industrial humidification or dehumidification system, and so on. These are standard schemes familiar to every HVAC engineer, based on which the various types of climate control devices are calculated – heaters, air coolers, spray chambers, etc.
“There is no difference in the methodology for these calculations between comfort and industrial air conditioning, except that a particular type of heat exchanger operates under different conditions,” explained Eng. Banov. After selecting the air handling unit and all associated equipment, the next step is the aerodynamic sizing, i.e., designing the air ducts. This includes calculating: the cross-sections of the ducts, the paths they must follow, and the aerodynamic resistances, based on which the fans are selected. For supplying the heat exchangers with a heating or cooling medium, the hydraulic resistances of the piping network are calculated, which serve as the basis for selecting the circulation pump.
The selection of air ducts is identical for an industrial facility or an administrative building, with the difference being the layout of the air handling unit and any specific requirements for temperature and humidity treatment of the air”, clarified Assoc. Prof. Banov.
“After calculating the loads and establishing the air handling processes, the selection of the air handling unit is made. At this stage, the type of fan, heat exchanger, etc., is also specified. This is precisely where competition among manufacturers of heat exchangers, fans, and other equipment comes into play. The choice of manufacturer is guided primarily by the designer’s experience and proven, field-tested equipment,” he commented.
The methods for calculating heat loads are described in the aforementioned Regulation 15, whose latest amendment dates back to 2005, and it is considered the primary and mandatory handbook for every HVAC design engineer. It aligns the methods for calculating heat losses with European standards, particularly regarding the determination of thermal bridges, heat losses through the building envelope, and so on. Other regulations used in design include Regulation 7 – concerning energy efficiency, heat retention, and energy savings in buildings; Regulation 4 – covering the scope and content of investment projects; as well as additional methodological guidelines.
Experience and Knowledge.
According to Eng. Banov, an active lecturer in “Air Conditioning” at TU – Sofia, HVAC design is a lifelong learning process. “New products constantly emerge, requiring new calculation methods and design techniques. If we rely solely on old knowledge and standard calculations, it means we are not keeping up with the present. In the field of ‘Thermal Engineering,’ students study the fundamentals of designing HVAC systems, thermal engineering systems in industry, and technologies related to energy consumption,” he explains. Bachelor’s degree graduates are familiar with the construction and application of thermal engineering installations, while those with a master’s degree gain deeper knowledge and practical experience in the construction and design of HVAC systems.
According to Assoc. Prof. Banov, the thesis is the first proof of an engineer’s ability to design. Each year, at least 12–15 of his students from this specialty complete theses, and their HVAC projects are worthy of implementation, he proudly notes. A key factor in the students’ strong preparation is the laboratory “Systems for Maintaining Microclimate Parameters in Buildings,” established on Assoc. Prof. Banov’s initiative. It is equipped with various climate control installations, provided with the support of leading HVAC system manufacturers and suppliers in Bulgaria, such as Tangra, Oventrop, Grundfos, Techem, LG Electronics, and others.
“Thermal engineering is one of the most sought-after specialties for aspiring engineers,” states Eng. Ivaylo Banov. “And most of them come from families of thermal engineers.” According to him, this specialty has a significant history within the engineering sciences. It was established in 1946 with the founding of the first higher education institution— the Polytechnic— from which the technical universities in Bulgaria were later developed.
"Source – TD Installations magazine", www.tech-dom.com
