Category Archives: Blogs

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

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.


SARS’s 12 i scheme allows companies to claim tax rebates for capital expenditure which produces energy savings. Several requirements apply. One is a baseline report which shows the energy intensity before installation of the energy savings equipment.

Grey Green compiled a baseline report for a large dairy in the Eastern Cape.

The baseline report met all the requirements and the diary is proceeding with installation of energy savings equipment.

Baseline reports have to conform to the procedures of the IPMVP [International Performance Measurement and Verification Protocol) and SANS 50010 – South Africa’s standard for Measurement and Verification.

Producing the baseline included correlating energy usage with production. The following graphic is an example.

Effect of Production on Steam Usage

Effect of Production on Steam Usage

Seasonal variations in production and therefore energy are common with agro-processing. For our dairy client these were investigated by first considering how output varies from month to month. The following graphic shows that there is considerable seasonal variation.

Seasonal Variation in Production

Seasonal Variation in Production

Next month to month electricity usage was investigated. The following graphic indicates that it does not change much.

Seasonal Variation in Electricty Usage

Seasonal Variation in Electricity Usage

In addition to using a baseline report for tax rebate applications, the data will often reveal opportunities for energy savings. For example, comparison of the previous two graphics seems to show a mismatch between production variations and monthly changes in energy consumed.


What is an ESCo?

ESCo Framework

This slide (Source: Jan W. Bleyl, 2009) summarizes what an Energy Service Company (ESCo) is by explaining what it does for its clients. The ESCo integrates the various Technology vendors and contractors offerings using its professional Know-How and design expertise to provide suitable energy Supply (Mega-Watt Hours) or Savings (Nega-Watt Hours) solutions for its clients based on their particular needs and contexts. These solutions are also based on available Energy Sources / Carriers, the current Legislative and regulatory frameworks in place and finally incorporating the best Finance options available, including incentives. The client need only be concerned about the energy Supply or Savings provided by the ESCo which comes with Functional, Performance and Price guarantees. The risk of dealing with the various other stakeholders and managing the energy solutions themselves are largely taken over by the ESCo being the specialists in this field.

Merger with Carbon & Energy Africa

Carbon & Energy Africa logo

Grey Green Sustainable Energy Engineering and Carbon & Energy Africa are pleased to announce that both companies have committed to merging their business operations. The combined operation shall function under one entity going forward viz. Grey Green. The shareholders of both companies believe that there is significant potential to unlock various synergies between these companies and in the process build more capacity, improve operational efficiencies and strengthen our current service offerings. The process has already been initiated and is expected to be completed over the next 2-3 months. Please feel free to contact us if you have any queries about this process.

Welcome New Interns!

Grey Green is pleased to welcome Yann Roynard, our French intern who is currently in his final year of studying Thermal Engineering & Energy and is completing his certificate of EICNAM. Yann shall be with us until mid-August 2014.

We are also pleased to welcome Matthew Kapp, our local student from Stellenbosch University who is currently in his second year studying Mechanical Engineering. Matthew shall be with us until end of June 2014.

Grey Green 24-Hour Tariff Clock

Grey Green 24 Hour Tariff Clock

We have developed our very own tariff clock based on ESKOM tariff structure for our time-of-use clients. This clock uses a 24-hour clock mechanism and simply shows people when they are in or close to peak, standard or off-peak zones during the day.  One is now able to schedule or avoid using high powered machinery and equipment by just timing these activities appropriately and thereby making substantial savings in electricity bills. The concentric rings also show the differences on weekdays, Saturdays and Sundays. Last but not least, it  can also help tell the time.