All posts by Admin

SANEDI Tier 1 ESCo Accreditation

Grey Green have been accredited as a fully qualified Tier-1 Energy Services Company on the National ESCo register endorsed by SANEDI, DoE and GIZ. The ESCo register is meant to be an important tool to facilitate the market development and growth of ESCos in South Africa; and will be utilized by both the public and private sector to identify, plan, develop, finance or implement co-generation or energy efficiency and demand side management projects in buildings, public lighting or water infrastructure. See SANEDI ESCo Website for more information.

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.

Bonnievale 75MW Solar Farm

Grey Green was appointed to assist the project developers with the topographical modelling of the planned 75MW Solar PV plant layout onto the existing digital elevation model. This included high-level plant designs and 3D sketches of final appearance on the actual landscape near Bonnievale, which shall be used in the EIA process.

Our first export!

Close the Gap has commissioned Grey Green do a second DigiTruck. This time it will be sent, by sea (and road freight) to Kinshasa in the Democratic Republic of Congo.

The challenges faced once again were “How are we going to deliver a fully functioning off-grid IT lab to the DRC?” To keep logistics costs down, a revolutionary design was conceived by Grey Green that allows for no changes to the external dimensions or structural integrity of the container. To further reduce installation costs, the system was pre-engineered, mounted, wired and tested locally such that it was ready for a simple DIY installation in half a day once it reaches its destination by the recipient community members.

Grey Green has proven that it is now able to deliver containerized off-grid solar PV solutions to anywhere in the world.

Do you need electrical power in remote and isolated areas?
Do you need a self-sufficient mobile clinic, office or classroom?
We have a sustainable energy solution ready for you…

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.