Implementation of an algorithm for determining the effectiveness of ventilation and energy efficiency in industrial ventilation systems

The requirements for good indoor air quality and energy efficiency have often been considered to conflict with each other, however, buildings with low energy consumption in Europe seem to have also a lower rate of building related health symptoms. The paper aims to develop a succession of necessary operations, an algorithm, for the determination of ventilation efficiency and energy efficiency in industrial ventilation systems, starting from a general model that will be developed according to the particularities of the industrial ventilation system. These systems are important as they are related both to energy cost and indoor climate management as well as to the health of the occupants. The stages of algorithm development will include: source control and efficient removal of contaminants, proper location of fresh air intakes, cleaning of intake air, efficient air distribution in rooms with improved ventilation efficiency, heat recovery from exhaust air, night time ventilation cooling, ventilation rates control by air quality, correct balancing of air flows and controlling the indoor climate locally.


Introduction
Ventilation plays an important role in maintaining good indoor air quality. Ventilation air transfers the internal pollutants efficiently from a building. When ventilation rates are reduced, energy is saved, but at the same time indoor air quality deteriorates, therefore it is important to use heat recovery systems to increase energy efficiency.
Industrial ventilation is imposed by law so that besides ensuring the necessary conditions for the technological processes, the conditions of the safety and the labor protection technique are ensured and fulfilled. According to the Environmental Law, exhaust air from industrial ventilation facilities must be cleaned before being discharged into the atmosphere to limit environmental pollution.
All these industrial ventilation systems have to be chosen depending on the location of the sources of pollution and the type of pollutants, so as to achieve a high ventilation effectiveness.
In order to design a proper ventilation system in terms of ventilation efficiency and energy efficiency we need to develop an algorithm that will meet the particular requirements of each application.

The structure of the algorithm
The algorithm is shown in figure 1 and will include 4 phases: -the particularities of the environmental factors in the industrial field; -experimental measurements in the case of an existing building or analytical calculations and simulation of values for newly designed buildings, both for indoor air and for exhaust air; -determination of the flow rate, selection of the ventilation system (local, general, overpressure, depression, equal pressure, mixed ventilation or displacement) and determination of ventilation effectiveness; -choosing heat recovery and determining the energy efficiency.

Fig. 1
The logic scheme of the algorithm for choosing the optimal industrial ventilation system

Particularities of environmental factors in the industrial field
The microclimate of a room involves maintaining at certain values the factors of thermal comfort (air temperature, relative humidity, air velocity, average temperature of radiation) and indoor air quality, by reducing the pollutants [1]. The thermal limits admitted to the workplaces, respectively the correlation between the minimum temperature and the maximum speed of indoor air according to the working category, are presented below: The relative humidity of the indoor air correlates with the indoor air temperature and the work category during the hot season of the year and is limited to 65% during the cold season of the year.
Indoor air quality -technological processes in the electrotechnical, mechanical, pharmaceutical, and other industries impose restrictions on dust concentration and particle diameter. In addition to outdoor air filtration operations, a special system for the retention and neutralization of various pollutants is provided on the fresh air circuit.

Experimental measurements / analytical calculations
In the case of existing buildings, experimental measurements will be made to determine the current situation and how the ventilation system can be improved if necessary. Measurements will be made according to a certain plan, and the sensors will be mounted respecting the distances by EN ISO 7726 (EN 12599), namely 3 different planes (0,1m, 1,1m, 1,7m for standing persons, respectively, 0.1m, 0.6m, 1.1m for seated persons). For new buildings, the values of the indoor air and evaporative air parameters will be calculated and simulated and compared to the maximum permissible values.

Effectiveness of ventilation
Depending on the measurements or the simulations, the value of the calculation flow rate will be determined as the maximum value between the relations (1) and (2).
The ventilation rate needed for the emission rate and the allowed concentration level in the room give the dilution of a known emission, as follows [2]: where: qv,SUP -volume flow rate of supply air in m 3 /s; qm,E -mass flow rate of emission in the room in mg/s; cIDAallowed concentration in the room in mg/m 3 ; cSUP -the concentration in the supply air in mg/m 3 . In case of different pollutants, it is necessary to check all relevant pollutants in order to determine the most critical one [2]. To determine the air flow that takes into account the thermal balance and the moisture balance, the relation (2) is applied: The actual temperature values are calculated for each point. A satisfactory thermal comfort is considered to be: The ADPI performance index is established as a ratio of the number of points Ncf in which tef satisfies the comfort condition and the total number of points Nt in which the measurements were made. It is considered that the ADPI index proves a satisfactory choice of ventilation system and the type and location of the air devices if the ADPI value approaches 100%. The ventilation effectiveness will be determined in the algorithm subroutine for each of the 12 possible systems (figure.2).

Fig. 2 Ventilation system subroutine
The efficiency of ventilation depends on certain factors such as: avoiding and limiting recirculation areas and avoiding the by-pass areas [4]. Recirculation areas can be avoided or limited by increasing the jet trajectory by using the wall effect (ceiling jet bonding) by providing the exhaust air devices on the same side with the supply air devices (subject to comfort conditions) by changing the temperature of the jet air jet , in accordance with the thermal load and the air flow rate. Recirculation areas may also occur due to temperature differences between supply air temperature and indoor air temperature, ∆t0. It is defined criteria Ar (Arhimede): It is believed that the air jet will provide ventilation over the entire length of the room if Ar = 1300 -1500. If Ar = 2800-3000 the jet blows the room 2/3 of its length and if Ar> 3400 the jet reaches only 1/3 of the length room. It is therefore advisable to avoid strong non-isothermal jets. By-passing the supply air can occur during the summer when the supply air devices are placed on the same wall as the exhaust air devices [5]. In the winter situation, the by-pass between the supply air and the exhaust air occurs if the supply and exhaust devices are placed at the top of the room on the same or opposite sides of the room.

Fig. 4 By -passing zone in ventilated room
To avoid that cold air jets fall on the floor and the hot one remains at the ceiling, it is recommended that the value of the Archimedes criterion, calculated with the characteristic size of the supply air device:

Energy efficiency
Depending on the level of pollution in the rooms, the quality of the air extracted from the rooms is classified into four categories (ETA1 -ETA4

Conclusions
After developing this algorithm using a programming language, it will result in an industrial ventilation system optimization software for which ventilation efficiency will be obtained by taking and evacuating the hazards on the shortest way by avoiding the recirculation and short circuit areas. Also, a high energy efficiency of the entire ventilation system will be achieved by choosing the optimum heat recovery system. This software will determine a supply air flow, qv,SUP, with a minimum value, or which the value of εv and IPDA to be as close to 1 and the value of ƞRC to be maximum.