Abstract—High quality cured tobacco is one of the most foreign

currency generators in Zimbabwe. Currently curing process within

the small to medium scale farmers is through curer’s experience. In

order to reduce this dependency and achieve high quality the curing

process requires a well-designed temperature control system. A

biomass fired flue curing tobacco barn design for small-medium scale

farmers in Zimbabwe with a clear objective to control temperature

and humidity is the focal point of this paper. The designed barn

accommodates capacity of small-medium tobacco farmers with a

provision to use firewood, coal or dung in as source of energy. To

reduce curer experience dependency a furnace with seized fuel trays,

which are charged into the furnace as per calculated frequency for

every curing stage basing on heat content and type of fuel was

incorporated. The designed barn system that, have an outside control

box contains a combination of heat extraction fans, cold air blowers

and humidifiers that regulate temperatures and humidity levels to

required levels for every curing stage under the instruction from

16F887 microcontroller. This has replaced the primitive way to check

thermometers inside the barn even at high temperatures of about

80°C. Commendable energy efficiency was realized in various system

performance simulations through different techniques.

Keywords—Humidity, Microcontroller, Stability, Temperature

Control System, Transient.

I. STATEMENT OF THE PROBLEM

OW quality tobacco with high curing costs is currently

produced by small-medium scale farmers in Zimbabwe.

A. Aim

To design a temperature-humidity control system of flue-

curing tobacco barns for small-medium scale farmers in

Zimbabwe.

B. Justification of the proposal

Cases of under and overheating tobacco are generally

tarnishing its quality and sale value at Auction floors, hence

they is need to find and commercialise innovative ideas of how

Portia Mupfumira is with the Harare Institute of Technology, Harare,

Zimbabwe BE 277 Belvedere (phone: +263 777 037 263; fax: +263 4

7414106; e-mail: mupfumirap@gmail.com, pmupfumira@hit.ac.zw ).

Webster. T. Rukweza, is an undergraduate student at Harare Institute of

Technology, Harare, (e-mail: websterukweza@gmail.com ).

best to control temperatures and humidity levels in a barn

with minimum use of fuel. Energy efficiency of the barn will

mean a significant reduction of the current alarming rates of

deforestation. Efforts to provide tobacco farmers with better

curing technology is needed as Zim-Asset identifies tobacco as

one of the major pillar of economic revival. [8]

C. Scope of the study

The main goal is to have temperature controllable system

hence, area of focus will be maintenance of the required

temperatures and humidity levels of the barn at different curing

stages with minimum fuel consumption.

D. Definitions of terms

Quality Function Deployment : the process of removing

lids from any container after the contents have been processed.

[7]

Semi Automated : When some processes in the production

or design of a product are done by machines but other

processes are still performed by humans. [1]

Finite Element Analysis : A type of computer program

that uses the finite element method to analyse a material or

object and find how applied stresses will

II. BACKGROUND

Successful tobacco production involves an energy intensive

curing process, which determines the final quality of the

tobacco leaf and ultimately the selling price of the leaf. The

sole objective of curing is to dry the green leaf in such a way

that the final leaf has required colour, texture and aroma. [2]

The golden leaf is passed through three stages of curing

requiring different temperatures, a range which varies between

32-80 degrees Celsius.

The process is usually done manually by controlling the

amount of firewood in the fireplace to suit the temperature

requirement of every stage. This requires high skilled labour to

produce a better quality. They are also reported cases of

accidents whereby the barn overheats and burn the produce.

According to the research done by Tobacco Research Board,

curing is one of the key determinants responsible for the

quality of tobacco which is being produced by small-medium

scale farmers.

The existing barns with temperature-humidity control

Design of a Microcontroller Based

Temperature-Humidity Control System of Bio-

mass Fired Tobacco Curing Barn for Small to

Medium Scale Farmers in Zimbabwe

Portia Mupfumira, and Webster. T. Rukweza

L

International Conference on Mechanical and Industrial Engineering (ICMIE'15) July 14-15, 2015 Harare (Zimbabwe)

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technology largely depend on electricity as the source of fuel.

This is beyond the reach of many small-medium scale farmers

since they do not afford this technology.

By using firewood an approximated value of 43m3 of fuel

wood (15 000kg)/ year produces an average of 1400kg of

cured tobacco. This translates to a Specific Fuel

Consumption(SFC) of 10.7kg/kg of tobacco which is

approximately a third of the farmers’ income [5].This indicates

a loss of 98.5% of energy during curing because of the current

system’s inefficiencies.

Fig. 1 Traditional Barn fuel feeding mechanism

III. METHODOLOGY

A. Introduction

Primary data were collected through informal interviews,

field observations and questionnaires. Microsoft Equation

Engineering tools such as Failure Mode Effect Analysis,

Quality Function deployment and Simulation packages were

used to analyse and design the system. The researchers

designed a comprehensive design of the barn control system.

Literature review was done on tobacco curing, electronic

design and software development on temperature and humidity

control systems. Raw data was retrieved from the native

farmers.

Interviews, questionnaires and direct observation provided

insight into the lid removal process and areas which could be

improved.

B. Instrumentation

The following instruments were used f or collecting data:

• Informal Interviews

• Field Observations

• Questionnaires

• Engineering Tools

C. Current scenario

Environmental impacts of Tobacco production

According to [3] by 2016 if the current trend shown in

Figure 4 do not change major tobacco areas will have no trees.

This is supported by high fuel usage of firewood shown in

Figure 3. An interview with a farmer in Mutare indicated that

deforestation is leading to major siltation of the rivers and long

term damage of soil, a scenario which is catastrophic. Besides

land degradation, tobacco farming has come under

international scrutiny as deforestation is causing global

warming. It is estimated that, on average, it takes about 20

cubic meters(approximately 6.6 tonnes of wood), cleared from

a hectare of wood to produce a tonne of flue cured tobacco[6].

High levels of deforestation have resulted in EMA imposing

barn of commercial firewood usage.

90%

8% 2%

Fuel usage

Firewood

Coal

Biomass

Fig. 2 Fuel usage distribution

0

20

40

60

80

100

2009

2010

2011

2012

2013

2014

TOBACCO PRODUCTION TREND(2009-2014)(in million kgs)

TOBACCO PRODUCTION TREND(2009-2014)(in million kgs)

Fig. 3 Tobacco production trend

The below graph shows that there is an exponential growth

of deforestation as new farmers enters the business every year

[4].

2009 2010 2011 2012 2013 2014

RATE OF DEFORESTATION

Fig. 4 Deforestation rate

IV. MODELING

A. System Model Design

This model has also been designed with the help of the

reviewed literature on the farmer requirements using QFD

basing on correlation between farmer requirements and

International Conference on Mechanical and Industrial Engineering (ICMIE'15) July 14-15, 2015 Harare (Zimbabwe)

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engineering characteristics. Product Design Specifications

(PDS) was used for conceptualisation.

Fig. 5 Quality Function Deployment (QFD)

Fig. 6 Humidification Mechanism

Fig. 7 Blower wind pipe and chimney

Fig. 8 Flue pipe arrangement

Fig. 9 Furnace tray for optimum fuel consumption

Use either SI (MKS) or CGS as primary units. (SI units are

strongly encouraged.) English units may be used as secondary

units (in parentheses). This applies to papers in data storage.

For example

V. RESULTS

The designed system operates under the instruction of a

computer program. It utilizes a microcontroller as the brain

with the cold-air fan, heat extraction fan furnace fan and

solenoid valve as the actuators. The program controls two

variables, humidity and temperature at required levels of

different curing stages. Figures below shows the system setup

and simulation using Proteus and temperature flow and control

in the barn.

Fig. 10 Designed system setup

Fig. 11 System simulation using Proteus

International Conference on Mechanical and Industrial Engineering (ICMIE'15) July 14-15, 2015 Harare (Zimbabwe)

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Fig. 12 Barn heat flow

Fig. 13 Barn temperature regulation

VI. RECOMMENDATIONS

It is recommended here that the following aspects be taken

into consideration for the improvement and full operational

performance of the tobacco barn.

• Maintenance of the fans as per the requirements of

the maintenance and reliability strategies outlined.

• Use of Eucalyptus grandis or some firewood

alternatives with almost similar heating value so as to

maintain stability of the system.

VII. CONCLUSION

The fire control system is cost effective , key in

environmental degradation reduction and seeks to

commercialise the technological idea in product quality

improvement that plays a critical role in the overall nation’s

revenue.

REFERENCES

[1] Angeles, J., 2007, Fundamentals of Robotic Mechanical Systems, Third

Edition Springer, New York

[2] Boyle P, Gray N, Henningfield J, Seffrin J, Zatonski W. A.(2010).

Tobacco: Science, Policy and Public Health, Second Edition. New

York: Oxford University Press

[3] Environmental Management Agency, (2016)

[4] Forest Commission of Zimbabwe, (2014)

[5] Scott P.( 2006). Development of Tobacco Rocket Barn for Small Holder

Farmers in Malawi

[6] Tobacco Research Board, (2012)

[7] www.wikipedia.com

[8] Zim-Asset Chapter 3 section12

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