Module 5. Building construction materials and type of building construction

Lesson 31


31.1 Introduction

The circulation of air in different sections of dairy plant is very important to maintain better quality of air inside the plant. It is also necessary to provide adequate level of illumination in different sections as well as at specific location of the section in order to carry out different operations with safety of workers and inspection of the operations. The control of fly is very essential to maintain sanitary conditions and to meet safety standards for various products.

31.2 Ventilation in Dairy Plant

The term ventilation refers the circulation of air in order to maintain quality of air in the plant. The ventilation system includes supply of fresh air and removal of fumes, heat, dust, toxic gases and undesirable odours. Efficiently designed ventilation provides adequate quantity of fresh air of standard quality. In dairy plants, large quantity of water, cleaning solutions, hot water and steam is used for various purposes. Vaporization of water and flash vapour produced in different sections are causing to increase the relative humidity of the air. Higher level of relative humidity is not desirable as it creates uncomfortable conditions for the persons working in the plant. For human comfort, relative humidity of 60-65% and air temperature of 22-240C are desirable for majority of people. It is reported that each person requires about 0.5-0.75 m3 of fresh air per minute for breathing. The comfort condition is difficult to obtain in a fluid milk plant without providing effective control on the quality of air. Higher humidity is also responsible for corrosion and growth of molds. It may be noted that it may not be possible to achieve desirable condition of air only by ventilation but it may be necessary to use air conditioning system to achieve optimum quality of air in the plant. Ventilation is important in dairies from point of view of sanitation as well as quality of the products. The quality of milk and milk products are adversely affected by odours absorbed in poorly ventilated rooms.

31.2.1 Objectives of ventilation

  • To provide requisite quantity of oxygen by way of fresh air
  • Removal of ventilated air
  • Circulation of fresh air in room
  • Maintenance of necessary level of RH
  • To maintain proper temperature of room
  • To eliminate dust, odor, smoke, etc from the air
  • To remove any pathogenic and other bacteria that might be present.

31.2.2 Methods of ventilation

The conventional methods such as providing windows for cross ventilation, opening of doors, windows and using electric fans are not adequate in dairy plants. These can serve the purpose in small rooms and the sections where generation of water vapour is very less. Therefore, ventilating equipments are required to be installed for replacement of air in large food processing rooms. This can be achieved by providing ceiling ventilators or ventilating sash or ventilating skylights. Ventilation for milk receiving room, can washer area, crate washer section etc. requires special considerations as water vapour generated in these sections is very high. A large quantity air replacement with control is necessary for these sections depending on the size of the section. Thus, the purpose of efficient ventilation is to remove stale air containing excessive water vapour. The number of air changes desired (i.e. number of times the volume of the air of the room is changed by fresh air per hour) types of processes, environmental conditions and number of persons working in these rooms. The methods used for ventilation can be classified as under.

1. Natural ventilation

  • Difference in temperature between the air inside and outside
  • Pressure difference caused by the wind

2. Mechanism ventilation

  • Simple input and/or output fans
  • Plenum ventilation systems

Sensible heating or cooling of air changes the relative humidity of air. The problem of higher humidity is the major consideration in design of efficient ventilation. The knowledge of psychrometry is important in order to measure and monitor the quality of air. The use of different types of air filters followed by suitable air processing/replacement is necessary for optimum result. These aspects are important at design stage of the plant so that location of windows and mechanical system can be accommodated in the plant. The purpose of mechanical ventilation system is to provide large quantities of air changes. It gives 10-15 air changes while normal ventilation gives 4-5 changes. The problems associated with plenum ventilation are the noise and improper distribution of air. It is desirable air should be distributed without producing excessive draft with minimum possible noise level. In large sections many diffusers are installed on the ceiling/wall to distribute the air without producing excessive draft. Rectangular or circular air duct with flow control dampers may be used in specific requirement of the plant.

1 air exchange = total cubic meter of air in the room

Total number of air changes is the number of times the total volume of the room exchanged per hour. For example, if the number of air changes is 10, it means that the total volume of the air of the room is changed 10 times in one hour time.

31.2.3 Maintenance of Ventilating Systems

1. Cleaning, removal of dirt and dust as well as and painting of ventilating sash, ventilating skylights and ceiling ventilating at regular interval.

2. Regular cleaning of fans and blower blades is important for efficient operation. Dust and dirt deposited on the blades of fans and blower may cause unbalancing which may result into vibration and noise. Maintenance should be done carefully so that blades are not damaged.

3. Filters used in the system are to be cleaned on regular basis considering the quality of air and type of filter

4. Wherever corrosion noticed at fan housing or any part of the system, it should be wire brushed and painting is done using antirust paint.

5. The totally enclosed motor should be kept free from lint, dust and paint in order to maintain better heat transfer to cool the motor.

6. Check the electrical connections at regular interval.

31.3 Illumination

Lighting has played very important role in industrialization as it has reduced the difference between day and night conditions to carry out various operations. Dairy plant operates during day and night time to process the milk and to manufacture different products. Proper level of illumination is important for reducing the strain on the eyes of workers and providing safe working conditions in the plant. Selection of most energy efficient lighting system for various sections is very important in dairy and food plants. A well designed, energy efficient lighting system can mean higher lighting levels and lower energy costs. It is possible to reduce energy costs by making small changes to the lighting system. The terms used in connection with illumination are explained below

Illumination usually refers to energy radiated in the visible spectrum from 0.38 to 0.70 u wave length. Illumination is important in the processing plant from the standpoint of visual operation, safety, cleanliness, inspection and colour recognition. Bright light should not be defined as good illumination, because it may cause pain in the eyes. A good illumination is defined as illumination which produces no strain on eyes.

31.3.1 Requirements of good lighting

1. Enough light for all visual tasks

2. Proper distribution and diffusion of light

3. Absence of glare

Wall and ceilings should be painted in light colour, not only to minimize the contrast between work and surroundings but also to give maximum results from illumination. A window area equal to 20 % of the floor area is suggested where dependence is placed upon natural light.

To fulfill the requirement of proper illumination, light should be well diffused without flickering. To achieve optimum result, background ceiling should have a minimum reflectance of 75 % and side walls from 50 to 65 % and the floor a reflectance of about 20%. The reflectance of the floor, walls and ceiling with a given light depends upon the roughness and colour of the surface. A dark colour will absorb more light, giving a lower reflectance, whereas a light colour reflects a large portion of the light. The illumination in a milk plant should be such that the work can be done accurately, with speed and ease without straining the vision of the employees. It is necessary to understand the following terminology to select the most efficient source of light.

• Lumens: It is a measure of light output from a lamp. e.g. 40 watt (W) incandescent bulb produces about 13 lumens per watt (13 lm/W).
• Lux or Foot-Candle: The light level at the working surface is measured in lux or foot-candle (fc). [10 lux =1fc]. e.g. Outside illumination level in summer will be around 80,000 lux or 8,000 fc.
• Average Rated Life: The average time it takes for 50% of light bulbs to fail is called average rated life.
• Colour Rendering Indexes (CRI): The ability of light sources to render colours the same way sunlight does is called CRI.

It is necessary to get maximum lumens per watt to reduce energy costs for illumination. Typical lumen outputs are shown in Table 31.1

Table 31.1 General characteristics of light sources used for lighting


31.3.1 Types of light Incandescent

Incandescent lamps are not energy efficient as shown in Table 31.1. Incandescent lights also attract flies and other insects and are quickly coated with dirt that further reduces the amount of light available. These lamps have relatively short rated life. Fluorescent

Fluorescent light should be the main light source in dairy plants. Fluorescent light is very energy efficient compared to incandescent bulbs. It has long rated life and gives good quality light and Lumens/W is very high. There are 2 types of fluorescent systems used in industry namely compact and tube fluorescents. Fluorescent tubes are available in a variety of lengths and diameters.

Advantages of fluorescent lighting are given below.

• Fluorescent lighting takes less energy to provide the desired level of light.
• Fluorescent tube lamps last 20000 h
• Conversion from incandescent to fluorescent will reduce energy usage by up to 75%.

Fluorescent typically has a payback time of less than 2 years.

Table 31.2 Power consumption and light output of incandescent light bulbs and compact fluorscent light bulbs

Light emitting diode (LED)

Light Emitting Diode or LED systems are not yet used in commercial factories. Research is required to ensure this technology for various applications. Energy efficiency of LED lamps can be very high (50 lumens/W) and life is much longer (up to 100,000 h) than other light systems. If the technology can be adapted for barn environments, it is expected that LED lighting systems will provide large on-farm energy savings in the future.

Advantages of LED are as under.

• Environmental friendly-energy efficient with 1/5th of the power consumption of incandescent lamps.
• Long life LEDs lasts up to 100,000 h compared to incandescent bulbs at 1,000 h or 20,000 h fluorescent lamps
• Low maintenance cost
• Miniaturization small size allows them to be used in areas not easily accessible
• High reliability LEDs are solid-state devices, without moving parts, glass or filament to break. They are robust and vibration proof.
• Fully dimmable
• Multicolour available in all colours
• High speed response immediate response, no preheat or starting time required.

31.4 Fly Control by Air Curtain

Air lock: It prevents contact of external air to internal air of cold store, it works as buffer. Its temperature is higher than the temperature of cold store and less than the temperature of external air. Air lock requires some space and at that space we cannot store the product.

Air curtain: Blowing of air at certain velocity with the blower producing air to prevent the entry of air from outside the door is called air curtain. Air lock system is not suitable if it is required to open the door frequently. Air curtain is a stream of air at usually certain velocity blown down it to prevent direct entry of external air. Its advantages are:

  • It controls the temperature
  • The door can be kept open
  • Control of dust and flying insects
Last modified: Thursday, 4 October 2012, 9:38 AM