Heating of production halls in starch/potatoes/ grain mill production
- 1 GENERAL INFORMATION
- 2 DESCRIPTION OF TECHNIQUES, METHODS AND EQUIPMENT
- 2.1 Changes in the process
- 2.2 Energy saving potentials
- 2.3 Changes in the energy distribution system
- 3 REFERENCES
Within an industry, being from the food and drink sector o from other sectors, exist different final energy uses for the heat production. The main consumption is the productive process itself. However, one should not neglect the energy consumption used in the workspaces heating.
The energy demand required for the workspaces heating depends on the same factors that also affects building energy demand:
- Architectural design and constructive materials
- Comfort and healthy criteria
- Internal gains as persons, equipment and lighting.
In the case of industries, not that the health and comfort requirements, and internal gains due to the process are the main factors affecting energy demand (heating or cooling). Productive process with a large amount of heat emission reduces the heating demand for the building acclimatization.In the other hand, spaces with large air renovation requirements due to pollutants, presents high heating energy demands. In the food and drink industry, it is also important that the quality of the produced food is not affected in the process for heating, cooling or ventilation.
DESCRIPTION OF TECHNIQUES, METHODS AND EQUIPMENT
Not all the industries requires heating energy in the productive process. Nor all industries requires additional heat generation for heating spaces, as workspaces or offices. In industries were both are required, two situations in the halls heating may arise:
- Heat energy supply from the same heating generators that feeds the process.
- Heat energy supply from specific heat generators independents of the process.
In an industrial process, heat can be classified according to the fluid temperature:
- Low temperature up to 60ºC
- Medium temperature from 60 to 80ºC
- High temperature above 80ºC
Changes in the process
HEATING OF PRODUCTION HALLS FROM THE INDUSTRIAL PROCESS HEAT
The energy levels required in the heating of production halls uses to be lowers than required in productive process, making it possible to use part of the produced heat in the process for the air conditioning. Although full recovery is expected or desired in a process to process application, recovery heat for a process-to-comfort application must be modulated to prevent over heating the make up air.
The use of part of the heat generated for the process can be done in two ways:
- Taking part of the heated fluid that outcomes from the process heat generator.
- Using the wasted heat after the fluid has passed through the industrial process.
Heating at process temperature
This heating method uses the boiler or other heating generators for producing hot water at a process temperature that will feed both the process and the space conditioning. The hot water at process temperature passes through a heat exchanger that heat up the water in the distribution system.
- A single heat production unit
- Less space requirements
- Less variations in the energy supply (if applicable)
- Easy distribution system
- Lower initial investment (in certain cases)
- Inefficiency in the heat production for air conditioning.
- Higher heat production costs
- Higher energy distribution losses due to the higher temperature and the heat exchanger efficiency.
HEATING WITH WASTE HEAT
Depending on the process temperature, it is possible to use the waste heat from the fluids that already has been involved in the process and transfer this waste heat to the distribution system for air conditioning. The unique characteristics of the different industrial sector and its production process will draw the lines of the heat recovery, if it is possible, or if it is enough to cover the heating demand, or if it is also required an auxiliary system to cover the whole heat demand. The recovery heat techniques are widely diverse, depending on the fluids, but usually implies the use of a heat exchanger. The use of waste heat in the air conditioning of the production halls means large energy savings.
- Energy savings
- Money savings and best payback periods for heat production machinery
- Sometimes is difficult to implement energy recovery techniques and equipment in an already built industry. Furthermore if the industry is already in operation.
- The heated liquid may not be a clean liquid so it makes more difficult the heat exchange and needs more auxiliary power in order to pump it through the system.
- Greater complexity in the distribution system for the air conditioning.
Some typical applications for air to air energy recovery are:
- Flue stacks
- Paint exhaust
- Welding exhausts
HEATING APART FROM HEATING PROCESS
When the heat produced for the process cannot be used for the air conditioning of the production halls (because any reason) and there is heating needs, it is necessary to install specific air conditioning equipment. The variety of air conditioning systems is very rich and is only limited by terms of comfort, design and characteristics of the production process.
Classification by range
Central heating A single unit or a connected and modular package that supplies hot water to a main distribution system does the heat production. From this primary distribution circuit, many secondary loops can be supplied.
Distributed heating The heat production is splat up in different units that supplies different distribution circuit or directly supplies the thermal zone.
Classification by fluid
Coolant In those heat-cool cycles that uses condenser and evaporator units, the common fluid is a coolant, with different thermal characteristics than water. This system configuration implies that the primary fresh air renovation have to be carried out by another system. In comparison with aire and even water, coolant distribution systems are of less diameter and needs less space. In the other hand, leaks are very troublesome.
All air When the system is air distributed, it is common to combine the heated air for the air conditioning and the fresh outdoor air for ventilation requirements. These two flows are mixed and treated in Air Handling Units, that regulates the proportion of air depending on the specific requirements.
Water/air Distribution is done by water. Hot water is distributed to the terminal units. In the terminal units heat passes from the water to the air with a heat exchange usually using coils.
All water Distribution and emission is done with water without any heat exchange with air. Thermal diffusion is done with radiative terminal units. With this kind of systems, an auxiliary ventilation system is needed.
Energy saving potentials
Changes in the energy distribution system
- HVAC System and Equipment. 2012 ASHRAE Handbook.