nv-calc is a program for the design of natural, mechanical and hybrid ventilation in industry
nv-calc is intended for designers to calculate natural, mechanical and hybrid ventilation i.e. natural and mechanical ventilation in the same hall or / and in one ventilation unit. The program is mainly suitable for industrial halls where large heat gains are generated as a result of the technological process.
Use of nv-calc
For industrial ventilation designers, an important feature of the innovative nv-calc program is the ability to include mechanical ventilation (supply and exhaust) operating in the same hall in the calculations.
The innovative nv-calc program is used to create a digital model of natural and mixed ventilation of existing facilities to be retrofitted.
The nv-calc program calculates the temperature under the roof and at arbitrary heights in an imperceptibly short time from a click, and gives the airflows and the pressure difference from the atmospheric pressure outside for each group of devices at a given height.
The undoubted advantage of nv-calc is the extremly fast calculation time.
Thanks to the high speed of nv-calc, design is done iteratively in successive "try and improve” steps.
The design process is also easy to learn for designers who are just building their professional experience
Design of natural and hybrid ventilation in new construction facilities.
Note: The nv-calc program (NaturVents-calc) is not suitable for designing gravity ventilation systems in residential houses and office buildings.
The nv-calc program (NaturVents-calc) – what is it used for?
The nv-calc web program has been specifically created for the design of natural and hybrid ventilation in industrial applications. More specifically, it is used for ventilation in glass and metal works, power blocks, waste incineration plants, etc. All these types of facilities share the common characteristic of releasing a significant amount of heat into the building.
To date, no one has figured out how to sensibly engineer and economically recover this heat. Therefore, the nv-calc program is an innovative tool for designing natural ventilation in such a way as to remove only as much of this heat as necessary and thus save energy (gas, electricity, etc.) consumed in industrial processes.
For natural ventilation designers in industry, the nv-calc program is a very effective design tool. With some skill, it is possible to perform basic design calculations for the ventilation of a steel mill or similar facility in one working day, or even less.
The design of industrial ventilation in such facilities generally involves determining the aerodynamically active area of supply wall intakes and exhaust roof vents to ensure that the temperature in work zones is satisfactory and that the maximum temperature under the roof is not exceeded. These conditions must be met in all seasons, i.e. over the full range of possible outdoor temperatures.
In order to start calculations with nv-calc, the dimensions of the newly constructed building being designed and the heat gains released in the interior are needed. The natural ventilation designer enters into the program the assumed geometric areas of the supply wall louvers and industrial exhaust vents (along with the cV0 flow coefficients provided by manufacturers) and the heights at which these devices are to be built in. The program calculates the temperature under the roof and at any selected heights instantly, and gives the air flow rates and the pressure difference with respect to the atmospheric pressure outside for each group of devices at a given height. By making corrections using the method of successive approximations, the location and open areas of supply louvers and industrial roof vents are iteratively improved in successive steps until arrivinguntiling at the required configuration of equipment. This process of designing natural ventilation should be repeated for subsequent outdoor temperatures.
For designers of industrial ventilation, an important feature of the innovative nv-calc program is the ability to include in the calculations mechanical ventilation (supply and exhaust) operating in the same building. It is also possible to make calculations for facilities with heaters in supply louvers.
Although nv-calc is primarily used for the design of natural and hybrid ventilation (natural and mechanical), it is also applicable to facilities ventilated only mechanically. With its help, it is possible to obtain temperature and pressure distributions for selected levels in the building. However, the amount of heat released inside the building and a sufficiently large height of the building to allow the formation of a thermal draft are prerequisite information.
Analysis of natural ventilation in existing facilities.
Note: The nv-calc program (NaturVents-calc) is not suitable for analysing of gravity ventilation systems in residential houses and office buildings.
The nv-calc program (NaturVents-calc) – What does it apply to?
The innovative nv-calc program is used to create a digital model of natural and hybrid ventilation of existing facilities slated for retrofit. The retrofit plan is usually driven by the need to save energy or bring the facility into compliance with production requirements and current administrative regulations.
Glass factories are a good example of the use of nv-calc to retrofit natural ventilation. The industrial plant production hall in these facilities are often in use for decades at a time, but the useful life of a glass furnace is at most a dozen years. The construction of a new glass furnace is an opportunity to increase production efficiency, for which it is necessary to provide efficient natural ventilation. An innovative tool such as the nv-calc program allows you to create a digital model of the facility, speeding the design process.
Some of the data entered into the model is accurate – for example, the measured temperatures of outdoor air, exhaust air from the building and at selected heights from the floor, as well as the pressure differences between the interior of the production hall at the selected height and the atmosphericpressure outside. We can also accurately determine the geometric area of the exhaust.
In many cases, the remaining parameters should be estimated according to the available data and your own experience in this area. This applies primarily to the supply area (this is not only the wall intakes, but also the inflow through connected rooms and many other uncontrolled openings, referred to as infiltration). In the case of production halls that are several decades old, it is unlikely that we will find documentation of the natural ventilation equipment used with the aerodynamic flow coefficients cV0 .
The heat gain emitted into the volume can be measured at the roof vents (or at the exhaust louvers), but this is only the heat exhausted by natural ventilation. The heat emitted from the production hall by penetration through the walls and roof will not be calculated analytically, because air temperatures will be different at different heights of the hall, neither will they be identical at different locations under the roof.
In general, the methodology adopted is not about creating a super-accurate representation of the plant, because the amount of inventory work and accurate heat balance will certainly be too difficult to model. However, the quantities and parameters missing to build the model can be selected by the method of successive approximations, since the undoubted advantage of nv-calc is the extremely short calculation time. Having at our disposal the measurements described above, which can usually be done in a day’s work, a few hours of work at the computer is enough to build a model of the natural ventilation of a glass factory or a power unit for example.
The resulting model of the natural ventilation of a glass factory metal smelter or rolling mill is used for calculations for the full range of possible outdoor temperatures. Performing calculations, for example, every 5°C in the range of -20°C to +35°C, we select the open supply area (the number of open wall air intakes) and the open exhaust area (the number of open roof industrial vents) to achieve the expected temperature in the work zone and at the same time not to exceed the maximum allowed temperature under the roof.
The nv-calc program will verify the design regarding the number of air vents on the roof – too few means exceeding the maximum temperature under the roof. It will also show whether the number and location of wall air intakes above the floor are correct – if, for example, the intakes are in the pressure equalization zone inside the production hall, they will not be adequately efficient.
Calculation of natural ventilation
Program nv-calc (NaturVents-calc) – how does it work?
nv-calc is an innovative web-based program (a.k.a. web application) for designing natural and hybrid ventilation in industry. For each set of outdoor temperatures, the program calculates two balances:
- the amount of heat supplied to the volume of the facility (heat from plant, insolation and supply air) must be equal to the amount of heat removed from the facility (through exhaust air and penetration through the walls and roof), and
- the mass of supply air to the facility must be equal to the mass of exhaust air
Both of these balances are performed using an iterative method, and the program algorithmically reduces the number of iterations so that the result of the calculation is ready at the click of a button, almost instantaneously.
The high speed of calculation is a great advantage of nv-calc , because it allows the design of natural and mixed ventilation (natural and mechanical operating in the same volume) by the “try and correct” method.
The required data to be entered into nv-calc are:
- the amount of heat emitted by the technological process to the interior of the facility (corrected by the estimated heat by penetration),
- geometric dimensions of the production hall (length, width, height),
- the number and geometric dimensions of supply wall louvers and industrial roof exhaust vents, along with the manufacturers’ reported aerodynamic flow coefficients cV0
- possibly the amount and temperature of mechanically supplied air and/or the amount of mechanically exhausted air.
As a result of the calculations, the designer gets:
- temperatures under the roof and in the work zone,
- the height of the pressure equalization zone above the floor,
- the magnitudes of the airflows passing through the groups of equipment at the various heights above the floor,
- the pressure differences inside at these heights relative to the atmospheric pressure outside.
Thanks to the high speed of nv-calc, design is done iteratively in successive “try and improve” steps. In this way, the design process is also easy to master for designers, who are just building their professional experience in the field of natural ventilation of large industrial facilities.