The heat assistant helps in calculating thermodynamic inputs into the ventilation model. The calculator can quickly establish required cooling, heating or moisture loads, which can then be accepted in the model.
The assistant is also useful for ‘pre-conditioning’ airflow to a required temperature and humidity to more closely simulate observed conditions underground.
Pressing Accept after any calculation will insert the values into the model airway for future simulation. This will overwrite any existing heat values within the airway.
Warning : The assistant calculates estimates only. In some cases, the assistant utilises an iterative technique, with initial values sourced from the airway currently being edited. The initial values can be changed as desired. Because the simulation process utilises a more detailed, multiple pass approach, taking into consideration surrounding airways and rock heat transfer into the airway, the resulting estimates from the assistant may not always equal the values ultimately calculated in the simulator.
The assistant contains five (5) tabs.
Airflow #1 Calculates the required heat loads to condition air from one state to another. The values are returned as sensible and latent heat estimates.
Values returned for sensible heat are generally (+ve) for heating or (-ve) for cooling. Values returned for latent heat are generally (+ve) for humidification or (-ve) for de-humidification or drying of air. The word ‘generally’ has been included as differences in pressure can influence the amount of sensible and latent heat available in the process.
Similar to the Airflow #1 calculator, this calculates the required heat loads to condition air from one state to another, but instead returns values as sensible and an evaporated moisture flow estimate. This may be useful for calculating moisture being evaporated from underground processes such as decline dust suppression sprays, drill machine activity or evaporative cooling chambers.
Diesel engine heat loads can be more accurately calculated by considering the environment and utilisation of the diesel engine within the model. The diesel engine calculator assists with this. The output of the calculator is return as an averaged diesel engine output. The corresponding sensible and latent heats are also provided as a reference, however are not transferred to the model as Ventsim Visual™ automatically calculates these values in the model from the diesel power value.
Diesel Efficiency
The percentage of diesel calorific energy converted into mechanical energy. This diesel efficiency is an estimated value for a typical diesel engine and generally should not be changed unless specifically known for a type of engine or particular type of fuel. The value dictates the amount of heat placed in a model per unit of engine power used.
For example a 200kW rated diesel engine, will consume nearly 600kW in diesel fuel energy, initially rejecting 400kW of waste heat through engine friction and exhaust. In most cases, the remaining 200kW of mechanical power will also be converted to heat through further friction losses, except where the mechanical power may be partially passed to other energy absorbing processes (such as water or transfer of rock uphill). If required, this can be accounted for under the potential energy conversion item.
Utilization
Diesel engines underground rarely operate at full power 100% of the time. It is important to consider the actual weighted percentage of time engines are operated at full power to gain the true heat input into the mine model.
For example, a load haul dump unit (LHD) operates continuously, but uses only full power (100%) while loading buckets and hauling up a ramp for 15 minutes per hour, operates at 50% maximum power tramming horizontally or downhill for 30 minutes per hour, and idles at 10% maximum power for the remaining 15 minutes per hour
=52.5% peak utilisation
Potential Energy Conversion
In some processes, diesel mechanical engine power can be converted into other useful energies. For example a truck hauling rock up a decline will impart a portion of its mechanical energy into the potential energy difference of the change in elevation of the hauled rock. This can be calculated as a percentage of the mechanical output of the diesel engine, and will reduce the amount of heat input into the model. In most cases, this will only be a small fraction of the diesel engine power, and in most cases can be ignored.
The diesel fuel calculator provides an alternative way to calculate engine power within a ventilation model, overcoming the need to estimate engine utilisation. It calculates diesel engine power by using the calorific heat value of fuel, and back calculating engine power using the diesel efficiency setting in Ventsim (by default 35%).
By entering the average fuel usage of a diesel engine, Ventsim Visual™ can calculate the equivalent average engine output for use in the model. If this value is derived from actual engine diesel fuel usage of a particular unit in operation (many modern machines automatically record average fuel flow), this therefore already includes time the machine is not operating at full capacity.
As with the previous tab, a portion of the diesel engine power can be included as potential energy to another process. This reduces the effective diesel heat input into the model.
Similar to the diesel engine calculator, this allows the user to estimate the heat emitting from an electric motor, based on its duty cycle and conversion of work into useful energy.
The water flow calculator estimates the amount of heat entered or removed from a model from water flow source. It can be used for both hot water and chilled water calculations.
The Water tab may be useful for estimating;
- How much cooling power a cooling tower or spray chamber is producing from a refrigeration water source.. Ventsim Visual™ will calculate how much cooling is being generated from the flow and temperature change of the water into the airflow.
- How much heat a geothermal water source may be putting into a model. To calculate the heat input, simply input the average water temperature entering the mine (from a rock fissures for example), and enter the average water temperature and flow exiting the mine (at a pump station discharge for example). Ventsim Visual™ will calculate how much heat is being lost from the water most of which ultimately enters the airflow.