ENERGY EFFICIENCY TECHNOLOGIES AND ENERGY SAVINGS POTENTIALS FOR COLD ROOMS

Tshwane University of TechnologyFaculty of Engineering and the Built Environment

Department of Mechanical Engineering

Master Student: Mr. Jean-Claude MULOBE (Presenter)Supervisor: Prof. Zhongjie Huan

INDUSTRIAL AND COMMERCIALUSE OF ENERGY

Cape Town, 14-16 August 2012

SOUTH AFRICA

I. INTRODUCTION

In foods manufacturing the energy is used through:

Refrigeration system; Cooling facilities (cold rooms); Air-conditioning

system; Cooling tower ; and Lighting system, ect.

More than 50% of energy demand is from refrigeration and cooling

facilities.

Since energy prices risen dramatically the attention of foods industries

is focusing on the development of the most efficient technologies

Energy efficiency is an effort reduces higher energy demand to provide

production and services

In South Africa foods industries, approximately 99% of energy usage is

electrical Energy efficiency technologies and energy saving potentials for cold rooms

The objective of this study is to develop the efficient technologies, thereby reduce as much as possible higher energy demand in cooling process for cold rooms

Then contribute to the success of the energy performance program

The food industry is among of the large users of energy and therefore it has a major role to play in reducing greenhouse emissions

II. OBJECTIVE AND MOTIVATION

Bulk

HE-Coils

Energy efficiency technologies and energy saving potentials for cold rooms

Click to add caption [10.5, italic]

III. REFRIGERATION SYSTEM (CHILLING SYSTEM) SCHEMATIC

Fig 1 Energy efficiency technologies and energy saving potentials for cold rooms

: Chilled Water

: Condenser Water

: Chilled Water

: Condenser Water

Energy efficiency technologies and energy saving potentials for cold rooms

Fig 2

Cooling facilities (cold rooms)

Energy efficiency technologies and energy saving potentials for cold rooms

III.1 COLD ROOM A cold room is the specific place which is maintained at low

temperature environment to provide safety, minimise deterioration, and pollution of products after harvest into the cold chain.

Energy efficiency technologies and energy saving potentials for cold rooms

Fig 3

Click to add caption [10.5, italic]

III. 2 COLD ROOM ENERGY CONSUMPTION

Table1

Figure 3 internal cold room

Room size (m3) Energy consumption (kWh/m3.Year)

10 000 100

1000 200

100 600

10 1500

Energy efficiency technologies and energy saving potentials for cold rooms

Fig 4

IV. CASE STUDY

Tshwane Market ripening banana section:66% of energy usage in this area is from refrigeration system + cooling facilities (Cold Rooms), and the average Energy consumption is in the range of 5 to 10.5 kWh/ Ton-Day during cooling process.

Energy efficiency technologies and energy saving potentials for cold rooms

Fig 6Fig 5

V. SAVINGS TECHONOLOGIES FOR COLD ROOMS 1.COULORING AND SHADING TECHNOLOGY ON THE EXTERNAL WALLS AND ROOF

• The use of extracting fan can be reduce:

(1) Shading by Convection + Conduction :

Energy efficiency technologies and energy saving potentials for cold rooms

totalR

TTq 21

T1 (⁰C)

T2(⁰C)

R total(m2.⁰C/W)

A wall (m2)

L wall (m)

Q rate (W)

40 14 0.01195 262.5 0.22 2176

38 14 0.01195 262.5 0.22 2008

36 14 0.01195 262.5 0.22 1841

34 14 0.01195 262.5 0.22 1674

32 14 0.01195 262.5 0.22 1506

30 14 0.01195 262.5 0.22 1339

Energy efficiency technologies and energy saving potentials for cold rooms

𝑞𝑟𝑎𝑑𝑖𝑎𝑡𝑖𝑜𝑛 = 𝜀𝜎(𝑇𝑠4 − 𝑇𝑜4)

Or : Radiation

𝑞𝑟𝑎𝑑 = (𝑇𝑠 − 𝑇𝑜)/ 1𝜀𝜎ሺ𝑇𝑠+𝑇𝑜ሻ൫𝑇𝑠2+𝑇𝑜2൯ Total Thermal resistance include: Convection + Conduction + Radiation Heat Transfer:

𝑅𝑖 = 1ℎ𝑜𝐴+ 𝐿𝑘𝐴+ 1ℎ𝑖𝐴+ 1𝜀𝜎ሺ𝑇𝑠 + 𝑇𝑜ሻ൫𝑇𝑠2 + 𝑇𝑜2൯4𝑖

(2): Colour; white colour on roof and Wall in place of dark one will be of great benefit in hot and sunny climates

2. AIRFLOW OPTIMISATION AND STACKING METHOD:

From many investigations in the literature, the flow resistance induced by:

• Container (Box)

• Product properties

• Bulk confinement ratio

• Affecting the cooling efficiency and effective box venting could enhance

the cooling efficiency

• Stacking arrangement with a low porosity will produce a higher pressure drop than a stacking arrangement with a high porosity

Energy efficiency technologies and energy saving potentials for cold rooms

Table 2- Key equations correlating resistance to airflow and pressure drop in fruit packages.

Equation SourceRamsin : (1) Chau et al., 1985Darcy–Forchheimer: (2)Forchheimer, 1901

∇𝑝= −𝑎𝑢𝑏 𝛁𝒑= − 𝒖− 𝜷�⃓� �⃓� 𝒖𝒌𝝁

The airflow resistance was mainly expressed by either Ramsin or Darcy-Forchheimer equation, used to estimate airflow resistance trough bulk fruit, vegetables and vented packages.

Energy efficiency technologies and energy saving potentials for cold rooms

Fig 7

Figure 8

Four different random stacking in Euro Pool System (EPS) were analyzed and the result gave different velocity according to the their stacking method.

Fig 8

Fig 9

Energy efficiency technologies and energy saving potentials for cold rooms

Fig 10 Pressure drop through vented EPS boxes loaded with 32 spheres of 75 mm diameter per box: C1 bulk without box; C2 box without bulk; C3 loaded box from sum of pressure drops; C4 loaded box from CFD simulation; C5.2 loaded boxes from sum of pressure drops; C6. 2 loaded box from CFD simulation.

The figure shows the pressure drop over the individual components of the boxes, the sum of those and pressure drop over the system as a whole, which can be simulated to the bulk case.

The result have shown that the total pressure drop was also expressed in the form of Darcy-Forchheimer and Ramsin power-law equations .

Energy efficiency technologies and energy saving potentials for cold rooms

3. The variable speed drives technology (VSD) on evaporator fans motor (EFMs).

From the ideal fan is law:

Airflow final = Airflow initial(𝑅𝑃𝑀𝑖𝑛𝑖𝑡𝑖𝑎𝑙𝑅𝑃𝑀𝑓𝑖𝑛𝑎𝑙 )

Pressure final = Pressure initial(𝑅𝑃𝑀 𝑖𝑛𝑖𝑡𝑖𝑎𝑙𝑅𝑃𝑀 𝑓𝑖𝑛𝑎𝑙 )2

Power final = Power initial(𝑅𝑃𝑀 𝑖𝑛𝑖𝑡𝑖𝑎𝑙𝑅𝑃𝑀 𝑓𝑖𝑛𝑎𝑙 )3

Evaporator Fan Motors

Energy efficiency technologies and energy saving potentials for cold rooms

3. The variable speed drives technology (VSD) on evaporator fans motor (EFMs).

The cooling load

• Varies during the cooling period with the maximum heat load at the beginning of the process.

• Once the food surface temperature reaches a temperature close to the air temperature it is possible to reduce the fan power and reduce energy to the fans without compromising the cooling times by the VSD.

Energy efficiency technologies and energy saving potentials for cold rooms

The VSD technology provide the opportunity to save 15-40% of the energy demand by electrical motors.

Extend equipment lifetime by allowing gentle start-up and shutdown.

Energy efficiency technologies and energy saving potentials for cold rooms

Energy efficiency technologies and energy saving potentials for cold rooms

VI. CONCLUSION

The improvement in energy efficiency are most often achieved by adopting a

more efficient technology or production process. The efficient technologies

studying will lead to save enough of the energy usage in foods

manufacturing, thereby increase the benefits and reduces higher energy

demand.

This study is also a contribution to the alleviation of South Africa is energy

problems.

THANK FOR YOUR ATTENTION