The purpose of installing a Load Levelling Controller is to reduce your bill by monitoring and managing the maximum energy that will appear on your account. Most businesses are on a tariff rate which charges for the energy use (the kWh consumed) as well as a Demand charge (the maximum kVA used). The demand charge is about 40% of your account, so an energy saving project must address both energy used and maximum demand.Your demand charge is a charge for the maximum amount of energy that you used, measured over any ½ hour period during the month. That means that if you use a high amount of energy for only ½ hour during the month, you will be charged for that demand for the whole of the month. In Johannesburg, for example, they also take 80% of the average of your highest 3 months over the past 12 months and, if that is higher, than the current month, they take that average. So, one ½ hour mistake can result in a higher demand charge for the next year.If you could level your usage as much as possible, then the demand charge will be minimised. To determine the minimum that you can achieve, take your energy consumed (the kWh total for the 3 phases) on your bill and divide that by 720 hours (24 hours x 30 days). This will give you your average hourly kVA. Now compare that to your Demand (the KVA) which is charged.Unfortunately you will never achieve a ratio of one, but at least get it as low as possible. A dedicated controller that manages the load shifting can lower your maximum demand to its minimum. The process to implement a Load Levelling Controller according to your requirements is shown below.First, determine your daily consumption cycle. Then identify which energy can be shed or can be shifted to other periods. These shifting options can be arranged in categories. Categories are distinguished by:•Their contribution to the maximum demand.•Priority based on criticality to business operations.•Is the load shifted or shed? If you don’t heat water now, you have to heat it later, but if air condition settings are increased you don’t have to over cool later.•How long can you switch off the cool room, and how long does it have to be on, before you do it again.The schema is different for every business, so the business rules which you want to adopt and the levels at which they are applied have to be programmed into the Load Levelling Controller. A four level controller will take care of most applications. The most important success factor is to get the business rules right, so that you don’t experience discomfort in the business, but at the same time save on unnecessary maximum demand charges.Note that such a controller can save some energy, but mostly it reduces your account. It is however a win-win situation for you and the municipality. They charge maximum demand because they have to provide the capacity, and you pay for it, so if you reduce it, then both win.
If anything has the potential of saving you 20% or more on their energy bill, then it’s heat recovery. This is a wide topic and the solutions are mostly custom, so let’s focus on the more popular options to demonstrate the possibilities.Heat Exiting a Factory while Heating elsewhere (or cold exiting and cooling)Many definitions of heat recovery are limited to refrigeration systems, that is just one example. We include any situation where heat escapes from a factory or building, while at the same time you consume energy generating heat. A popular example is food or farming processes (e.g.: drying) which require the air volume to be replaced frequently while maintaining a set temperature.Blowing heated or cooled air into the room while simply letting hot or cold air out must be the biggest waste of energy imaginable. There are a number of ways to recover the heat from exit streams and use that to heat incoming streams. The choice of technology depends on many requirements ranging from the isolation between streams (often required by law) to temperature ranges, humidity, efficiency, effectiveness, existing configurations etc..There are five popular heat exchange options between incoming and outgoing streams:•Heat or Thermal wheel.•Fixed plate cross heat exchangers•Run-around heat recovery•Heat Pipe heat exchangers•Heat pumpThe choice of technology and design of the solution is a complex process which requires expert knowledge, but the savings are enormous.
Water has a very high specific heat and can be used effectively to store heat. The motivation can be twofold. You can use it to shift your electricity usage by heating water during lower use periods, to reduce you maximum demand charge. The 2nd option is where you are doing heat recovery and there is a time shift between the heat recovery and heat demand.An important example of load shifting is air conditioning with storage. Chillers supply water to air handling units (AHUs) at about 6 DegC and the water returns at 12 DegC. You may argue that you can only cool stored water to zero before it freezes leaving little storage margin. BUT, water has a specific heat of 4.186 KJ per litre and freezing water stores 334 KJ per litre. This means that by making ice, one can store the equivalent of 80 DegC energy. In practice it is mechanically more complex but must be considered if your peak consumption warrants it.
Next to heat recovery, insulation is the best return on investment that can be implemented in industrial environments. Given the current progress on new power stations, insulation in factories and buildings can achieve the same supply/demand shift much faster and cheaper, hence “Lets rather save a power station, than build one”. Simple insulation and heat recovery makes that possible.We know that heat is lost via conductance, convection and radiation. Of these, conductance offers by far the biggest potential. The applications are specific and each case has it’s own solution. Note however that wherever you have a surface, which you don’t want to touch, you probably have a potential energy saving opportunity.
The duty cycle of Industrial and Commercial lighting is generally between 12 and 24 hours per day, so the energy saving potential is high. Lighting design as an engineering discipline is a few years old, so the lighting in most premises have never even been designed.In the rush to save electricity, people simply replace old bulbs with newer technologies as recommended by some fool, and in the process destroy the little lighting quality that was there. The most important thing to know is that: the magical word LED can be used to describe lighting products ranging from superior to totally sub-standard.The design of lighting and LEDs have developed into a science which considers many human visual performance factors, photo-biological safety factors, the spectral distribution of the light, light delivery and a horde of other factors. If a LED project is going to deliver savings as well as visual performance in the workplace, it has to be preceded by a proper design process including computer aided design methods.This will mostly result in a totally new lighting layout. Most of the savings achievable in a lighting project result from design optimisation and intelligent controls integrated into the lighting system.LEDs are expensive, so if you embark on a project to switch to LEDs, we would recommend that you:•Implement a properly designed lighting schema.•Make sure lights have a long guarantee and design life. Is one or two years for an expensive light good enough?•Start with a pilot project to test the lights in your environment, all lights look good in showrooms.•Make sure the lighting units used and the design adheres to proper standards. Given the fast development of lighting engineering, we would recommend that you ensure EU standards were followed. They are simply more up to date, and exceed local standards.You can achieve super savings as well as excellent lighting if you get it right.
Power Factor Correction
The power that you draw from Eskom consist of two components, one is real usable power and one is inductive power. Inductive power oscillates between you and Eskom and is essentially wasted but you still pay for it as part of the demand (kVA) power measurement through the meter.Capacitive power also oscillates between you and Eskom, but the phasing is opposite to inductive power and, as a result, you can cancel inductive power with capacitive power. To cancel the one with the other you have to add the correct amount of capacitive power and therefore a dedicated controller is need. The controller measures your inductive load and adds or removes capacitors to achieve zero reactive power -or- a power factor of close to one.That in a nutshell is power factor correction. To correct your power you have to measure your power factor with an intelligent meter. We like to have a look at the currents and voltages to determine harmonics as well.Note that as you get closer to a power factor of one, you get diminishing returns on the capacitive power added, so don’t necessarily go for a power factor of one. The trade-off must be done for each specific case, by comparing the investment with the power factor gain and picking the sweet spot.One can reason this is not really saving power, BUT, it will save you money, and will reduce the losses in Eskom’s distribution network, so it does save power.
Variable Speed Drives
This is another one of those high energy saving methods, complements of modern power electronics. Fans, pumps etc. mostly run at full speed. In many cases they were oversized for starters and more than often the system always run at partial load. Worst of all, partial loads are controlled with dampers. All and all it adds up to a huge waste of energy.Don’t blame that retired old engineer who designed it, he did not have variable speed drive technology available to him and had to design for worst case. The volumetric flow you get from a pump or fan in a system is equal to the cube of the energy input, so being able to slow down a motor and pumping slower reduces the power needed to the power of three (so 1/2 speed equal 1/8 power).
Many boiler systems currently running, were designed and built before coal became expensive and carbon became a swear word. Most of them were never optimised or improved since they were installed.Boilers lose energy in a many ways, but the two biggest sins are unburned fuel and wasted heat. To get the full picture, we normally also include downstream losses in the steam lines and in the use and waste of the actual steam, plus missed opportunities to do heat recovery and pre-heating.There are many books written on boilers and improving their efficiency, so we will only look at the main culprits.Combustion heat lossesThe following two graphs summarise the main factors which need to be controlled in a boiler system. The first graph shows the fuel to air ratio. Too little air means losses due to unburned fuel and too much air means you are blowing unnecessary air over the combustion system (See it as an optimum system, and then you cool it with additional air).To achieve the optimum, requires a control loop that determines the amount of oxygen in the flue gas and controls it to the optimum level.Heat in Flue GasOnce the amount of excess air is correct you need to extract all the energy from the flue gas and transfer that to the water, to generate steam. The efficiency will be evident in the temperature of the flue gasThe graph below shows the losses given different amounts of excess air. The important factor to note here is the trend, which shows less losses at lower temperatures.Finally, there are many ways to recover heat from stacks and many uses for the heat recovered. Each plant will have its own opportunities and challenges.This essentially summarises the main energy losing factors in a boiler, bar one universal enemy, heat loss. Heat losses start as soon as the water starts being heated and has to be minimised until we extracted as much energy as possible from the steam and water. We won’t go into the hundreds of options here.Note: These graphs originated from some UCT Mech Eng publication. I cannot remember which one, but thanks.
HVAC and Buildings
To say that everything has been published about HVAC will be an understatement. All of the methods covered above apply to HVAC, but one factor is always overlooked. A chiller and a heat pump is exactly the same thing. It is a compressor system which creates a cold and a hot side. Your impression of what it is, simply depends on which side you are standing.Both the cold and the hot side can be utilised, but for some reason, which we don’t understand, it is standard practice to use one side and waste the other side. Most facilities can use the hot side to heat (for example) water and the cold side for freezing or space cooling. The control system becomes more complicated and one has to make provision for dealing with the excess heating or cooling capacity at the given operating condition but, once you have the control system, you can achieve both heating and cooling with the same system (So you double the energy utilised).
Evaporative cooling is based on the fact that humans feel comfortable if the combination of temperature and humidity in ambient air is within a certain range. This is called the comfort zone and is a function of temperature and humidity. By cooling air, and increasing the humidity, we can move the ambient air conditions from feeling too warm to the comfort zone.Water has a latent energy of 4.2 kJ/kg.K (So it takes 4.2 kJ to heat 1 litre water one degree Celsius). To vaporise water takes 2260 kJ/kg, so vaporising an amount of water takes the same energy as heating it by 540°C.Evaporative coolers (or swamp coolers) use this energy absorption to cool air. Air is simply blown over a wet surface to evaporate the water. The evaporation energy is drawn from the air and the water, so both will cool down. In the process, the relative humidity of the air increases. The air is therefore cooler but contains more vapour.The advantage of this cooling is that it takes much less energy to run a fan than the compressor in a traditional air conditioner. The disadvantage is the increased humidity, which may move the conditions outside of the comfort zone again.