Tag Archives: energy efficiency

Heat Transfer – Not Just Hot Air

Heat Transfer -Infrared

One of Grey Green’s areas of expertise is measurement of temperatures, calculation of heat loss and heat transfer analysis to quantify the potential for energy savings.

We have applied these skills in a variety of factories, including:

  • Furnaces in the foundry industry
  • Clay brick kilns
  • Rotary kilns in the lime industry
  • Flat presses used for cooking of wraps
  • Heat exchangers for drying of sawn timber
  • Barrels on extrusion machines for plastics.

Grey Green can apply the same expertise to the design of new equipment, and for process optimisation. We are familiar with all modes of heat transfer:

  • Conduction
  • Forced and natural (free) convection
  • Radiation

Earth, Wind, Fire, Water & Tyres


Grey Green recently completed a comprehensive energy audit at one of the largest tyre manufacturers in Africa. Our team investigated all energy and material flows. Excellent savings opportunities were found on:

  • Air compressors, plus compressed air distribution and use
  • Boiler, steam distribution and use
  • Effluent
  • Lighting
  • Materials handling
  • Solid waste
  • Water heating

The sixteen best savings opportunities gave payback periods between immediate (no Capex required, just improved control or maintenance) to ~3.9 years, with the average at less than 2 years. These were also quantified in terms of reduced carbon dioxide emissions and decreased carbon tax liability.

Annual financial savings were several millions of Rands.

The tyre company management shall also be able to use our Scenario Planning Tool to:

  • Graphically compare the savings produced by each savings opportunity
  • Decide when each opportunity should be implemented

Scenario Planning Tool

Grey Green also conducted pre-feasibility studies on various sources of renewable energy:

  • Earth – Biogas, from anaerobic digestion of locally sourced organic matter and biomass as a boiler fuel
  • Wind – Wind turbines opportunities in the region
  • Fire – Solar PV (i.e. photovoltaic) and solar water heating
  • Water – Hydro-electric options available.

As expected, the renewable energy opportunities have longer payback periods than energy efficiency opportunities, but once factory efficiency has been maximised, the only way of reducing energy costs further is by producing one’s own energy from renewable sources.

Fan of Energy Savings?

Grey Green has investigated the fans at numerous factories, including at several large grain mills. Often dampers are used to control flow rates and pressures. If so, removing the dampers or changing the fan speed produces good savings.

Case 1

A mineral processing works has six identical, belt driven fans. All operate against dampers which are approximately half closed.

Example of a Fan with Inefficient Control

Grey Green calculated that a simple change to the belt drive ratio with fully open dampers would:

  • Cost approximately R 7 500 to implement (equipment only – installation could be done by the factory’s own maintenance staff).
  • Produce annual savings of R 173 400 (No typos here the payback period is really only 0.04 years – i.e. less than 1 month).

Case 2

Another local grain mill has approximately 30 significant sized fans. None have damper control; whenever the mill is operating the fans run continuously at fixed speed.

Grey Green assessed 18 of the biggest fans. Our measurements and calculations showed that many of the fans were far from their optimum (maximum efficiency) operating points – i.e. when plotted on a fan curve like the typical one in the following diagram, their combination of flow rate and pressure rise was far from the best efficiency point.

Typical Fan Curve
Typical Fan Curve

Due to the age of the fans and their motors we recommended replacement of the worst performers.

  • For five fans replacement gave payback periods less than 1 year and total annual electricity savings of >R 2 million.
  • Six more fans could be replaced to produce payback periods between 1 and 2 years, with combined annual electricity savings of R 634 000.

Compressed Air Leaks – The Evil Hiss

Compressed air systems leak a bit, but not worth worrying about. Right? The shrug and ignore, business as usual approach is common. What a waste of an excellent opportunity to make big savings.

While assessing energy at factory, Grey Green’s engineers where able to measure compressed air leakage rate. Our client kindly agreed to leave all machines except their air compressor off for a few minutes. The photographs show the results.

The compressor is:
• An oil injected rotary screw machine
(by far the most common type used in SA factories).
• Relatively new, and fitted with a VSD (variable speed drive).

The photographs are of the display on the compressor when no other machines were running. The percentages show the speed of the compressor. Since it is a screw compressor, the percentages also indicate the proportion of rated flow rate which the compressor is delivering – an average of 41 %, when nothing else in the factory was on! 41 % of rated flow was feeding leaks!

• A 75 kW compressor supplying air to a system
with the same leakage rate
• Electricity cost of 65 c/kWh
• 2 shifts a day, 5 days a week, 48 weeks a year,
i.e. 3 840 hours operation a year.

• Wasted power = 0.41 x 75 = 31 kW
• Wasted energy = 118 080 kWh
• Wasted expenditure = R 76 750

Cost of locating and fixing leaks? Usually nothing more than time when a maintenance fitter is not busy with breakdowns.

Need help in getting started? Wondering what else could be improved on your compressed air system? Contact Grey Green now.

Come Wine with Grey Green

Grey Green have audited six wineries in the Western Cape during the harvest period over the past few months with another two winery energy audits in progress and a further three in the pipeline.

On average, the energy saving opportunities identified at each site could potentially save the wineries approximately R 370 000 per annum with a promising average pay-back period of 3 years. We also calculated an average of 400 tonnes of equivalent carbon dioxide emissions saved through our recommendations.

Highlights of the proposed interventions included: 

  • Effluent Treatment Optimizations
  • Feasibility Studies for Solar PV
  • Waste-Heat Recovery System design
  • Energy Efficient Extraction System design
  • Efficient Lighting Retro-fit proposals
  • Chiller System Optimizations including. insulation

Interestingly, chillers (cooling/refrigeration) accounted for approximately 40% of the total energy consumption, with the exception of those wineries with a distillery. The distillery accounted for 18% electrically and when converting the boiler fuel into equivalent kWh (using the calorific value of the fuel), the fuel accounted for 94% of the total energy consumption!

Lauren almost overshadowed by grape skins
Lauren almost overshadowed by grape skins


Share a Coca-Cola with us

Penbev Coca-Cola logoWe have successfully completed a major lighting upgrade program at Peninsula Beverage Company in Parow Industria consisting of 5 sub-projects over a period of more than 2 years and including some 3000 fittings. Every high-bay and fluorescent in the plants, warehouses and offices was replaced with a more efficient alternative. As a result, Penbev are now benefiting from more than R1.1m in annual energy savings and an additional estimate of R270k in demand charge reductions per annum. Grey Green also managed to secure ESKOM rebates for our client in excess of R1.1m to help subsidize the client’s investment in the program.

FAURECIA Energy Efficient Lighting Upgrade

Induction Lighting

Grey Green has been awarded a contract for a major lighting upgrade at Faurecia’s Cape Town operation. The scope of the project includes financing, supply and installation of the new lights, before and after lux level drawings, as well as a 3 year maintenance program. This project shall save our client approximately R 2.5 M over 3 years and is expected to be completed by end June 2014.