Friday, June 23, 2017

Comparison between lean burn and Rich Burn engines

Comparison between lean burn and Rich Burn engines:-
After certain emission calibration levels Lean‐burn gas engines are more economical  and these can even operate at higher loads,
But in rich‐burn engines have lower emission levels with a single after treatment these are more tolerant of broad fuel ranges and ambient conditions, and generally have better transient load capability.

Principle of operation of Rich Burn engines:-
Rich‐burn engines operate at principle of stoichiometric air/fuel ratio (AFR) according to this principle air in exact quantity is supplied to burn all of the fuel.  This will leads to reduction in nitrogen oxides (NOx), carbon monoxide (CO), hydrocarbons (HC), and HAPS (Hazardous Air Pollutants) after certain treatment for all in one i.e. by using catalytic converter used in cars.

Lean burn engines working principle:-
In these engines Lean‐burn engines use a lot of excess air. These engines take up to twice the amount needed in rich burn engines for complete fuel combustion. Excess air used in lean burn effectively cools down the peak combustion temperatures in the cylinder, this will reduces the NOx production and allows low engine‐out emissions without the need for an after treatment system in many applications.
In these engines there are advantages of reducing the detonation probability thus it will leads to higher Brake Mean Effective Pressure loads and an optimized combustion phasing. This results in higher power density and usually produces better fuel efficiency.

Emissions in Rich-burn engines:-
Rich‐burn engines have emissions of 12‐16 g/bhph‐hr NOx i.e. “5,000 ‐ 6,500 mg/Nm3@ 5 percent 02 in the exhaust gas “, in most stoichiometric/AFR exhaust gas composition and the increased exhaust gas temperatures allow the use of a three‐way catalyst.
These engines  have high NOx conversation rates i.e. above 99 percent that significantly reduce all three major types of engine‐out emissions ‐ NOx, CO and HC , Since there are low emissions that will destroy inferior but hazardous pollutants like formaldehyde (CH20).
Rich-burn engines emission are below 50 mg/Nm3 NOx and ultra‐low total hydrocarbon emissions, which will leads to decreased overall greenhouse gas footprint.

Emissions in Lean Burn Engines:-
If we have requirement of High power density and we required highest possible efficiency at moderate emission levels of 500 or 250 mg/Nm3 NOx (@ 5 percent 02 in the exhaust gas) lean burn engines have advantage. These engines at an adequate gas quality they deliver BMEP levels of up to 24 bar with electrical efficiencies up to 46.5 percent  without the need for a NOx or THC after treatment system.

To lower the NOx emissions that are reached by rich‐burn engines with a three‐way‐catalyst, lean-burn engines require selective catalytic converters with urea injection.
Oxidation catalysts perform most of the CO reduction in lean‐burn engines but  the fuel gas must be very pure. These catalysts also can reduce CH20 emissions ‐ again, if the gas is pure ‐ but their low exhaust temperature limits hydrocarbon conversion efficiency.

Operational flexibility
Rich burn engines can operate effectively only at clean fuels such as Natural gases. These will not operate at Biogas, Sewage gas or landfill gases as these will poison the three way catalyst. High combustion temperatures restrict specific output and the BMEP, so there is lower efficiency than with lean‐burn engines operating at higher air/fuel ratios. If lean burn engines are calibrated to operate at extremely low NOx levels (ultra‐lean), their efficiency begins to degrade so that the difference between rich‐burn and lean‐burn fuel consumption is minimized. Since lean‐burn engines have a much higher AFR ‐ with about 10 percent excess oxygen in the exhaust ‐ their engine‐out NOx emissions are only 5 percent to 10 percent of the amount discharged by a rich‐burn engine. Lean‐burn engines require selective catalytic reduction (SCR) treatment to obtain the lowest possible NOx emissions levels in the exhaust gas. SCR injects a controlled amount of urea into the catalyst to convert NOx to nitrogen. Being able to operate at a more optimal AFR with an SCR system makes the lean‐burn engine very efficient and allows high break mean effective pressures.

Oxidation catalysts are used to provide most of the CO and NMHC reduction in lean‐burn engines but, as with other catalytic systems, the fuel gas has to be very pure. These catalysts also can reduce CH20 emissions ‐ again, if the gas is pure ‐ but their low exhaust temperature limits hydrocarbon conversion efficiency

Saturday, April 22, 2017

Air conditioner Complete selection and installation guide

Why we need to Know Area of room before selection of air conditioner?

There is often confusion arises in customer mind that what size of air conditioner will be sufficient for their room. Most often everyone get some information from friends or from seller itself. Even other customers just try to explain their own experience and you buy according to their experience, and sellers always try to sell those products from where they get maximum profit.

So it will become very important to know what size of air conditioner should be selected for effective cooling of room, although friends experience gets to arrive at good product. But you should know how to select right capacity of Air conditioner as per requirements.

If you buy an air conditioner with higher capacity from requirements then this will leads to excessive power consumption and if lower capacity air conditioner selected then cooling will not be achieved which will defeat the purpose of air conditioner installation.

Air conditioners server two purposes:-
(i)                  For cooling
(ii)                For Dehumidification

If Air conditioner selected with higher capacity then requirement then it will cools the room and get auto-stop before removing the humidity from air, this will leads to uncomfortable inside room as room is cool and moist air will make you feel damp and clammy. 
Also higher capacity will ultimately leads to reduction in air conditioner efficiency.

Check your Room size appropriately:-

It is often practice to measure room size in Square feet’s.  For rooms are square and rectangular in shape than simply multiply the length into width. For Triangular rooms multiply Length and breadth and divide the area calculated by two to arrive at size of room. If room shapes are complex then you have to calculate room size accordingly or take help from sales executives to arrive at exact area.

Cooling capacity according to room size
Cooling capacity requirements will be calculated with help of BTU per hour i.e. British Thermal units. Now from BTU size of air conditioner can be calculated. For taking out heat of 12000 BTU/Hour size of air conditioner required is 1 ton so by using this air conditioner size can be chosen. Below table will help you out in selection of air conditioner according to BTU/Hour
Area To Be Cooled (square feet)
Capacity Needed (BTUs per hour)
Air conditioner size
100 up to 150
 0.5 ton
150 up to 250
0.5 ton
250 up to 300
0.75 ton
300 up to 350
0.75 ton
350 up to 400
0.75 ton or next higher size 1 ton
400 up to 450
1 ton
450 up to 550
1 ton
550 up to 700
1.25 ton or 1.5 ton if 1.25 not available
700 up to 1,000
1.5 ton
1,000 up to 1,200
1.75 ton or 2 ton of 1.75 ton not available
1,200 up to 1,400
2 ton
1,400 up to 1,500
2 ton
1,500 up to 2,000
2.5 ton
2,000 up to 2,500
3 ton

There are following parameters which will also be considered or taken care:-

(i)                  If room is considerably shaded than reduce your air conditioner requirement by 10%
(ii)                If room is front facing of sun then increase the capacity of air conditioner by 10%
(iii)           If there are persons more than 2 in a room then add 600 BTU per person in capacity addition i.e. increase of 5% capacity.
(iv)           If you are needed to add this unit into Kitchen then you should add heat generated during cooking i.e. add capacity of 4000-5000 BTUs in your capacity i.e. increase the capacity by at-least 30%
Location of Indoor and outdoor unit in room:-
(i)            Following points might be considered while installation of air conditioner in room
(ii)          Indoor Unit installation points:
(iii)         Air conditioner should be installed at location where air will be evenly distributed in whole room.
(iv)        Air conditioner should be installed at appropriate height. Usually height of air conditioner should not be more than 7-9 feet as if height is more than that than air conditioner mere serve the purpose of cooling your roof only. 
(v)          Try to install air conditioner above bed so that effective cooling can be obtained. Few don’t like air directly on body so you can install air conditioner on wall which is towards your feet or you can change direction of air using louvers

Outdoor Unit location:
         i.        Outdoor unit should be installed in open space i.e. terrace of house or if terrace isn’t available than you can hand the same external wall of house. It should be always installed were free flow of air is available so that air can flow above compressor and condenser.
       ii.            Outdoor unit location should be easily accessible so that easy maintenance can be carried out.
      iii.            One very important point should be considered while installation of outdoor unit is that outdoor unit should always be installed above the position of indoor unit so that free flow of refrigerant can be achieved and compressor can function to full capacity. If outdoor unit location is below indoor unit then some of compressor capacity is utilized in pumping the refrigerant to indoor unit. This will leads to overall lower performance of compressor.
     iv.            Last but foremost important point of installation of outdoor unit is that distance between indoor and outdoor unit. In tubing refrigerant at very low temperature flows inside tubing between indoor and outdoor unit. There is always loss of some refrigerant to atmosphere from tubing so it is always advisable to install outdoor unit as closer to indoor unit as possible to reduce the loss of the cooling effect. The maximum distance between the indoor and the outdoor units can be about 15 meters.
           Difference between single Stage and Two Stage compressor Air conditioners:-   
          Difference between these two air conditioners are basically levels of operation in air conditioners
          Single Stage air conditioners compressors only works on single level of operation i.e. only for cooling the area, but two stage air conditioners compressors have two levels of operation i.e. they cool the room at full level as in case of single stage air conditioner compressors and provide mild cooling when temperature outside is not very high.
            So dual stage compressor technology provides comfortable cooling as per requirements.
           So there are following benefits of dual stage compressor technology in air conditioners
            As these air conditioners provided cooling as per requirements and don't always operate at full level as in case of single stage compressor air conditioners so these leads to energy savings , which will leads to lower down your electricity bill.
           Second most important advantage is that they provide comfortable cooling.


Wednesday, April 19, 2017

Air conditioners ISEER rating; Power consumption calculations from ISEER rating

ISEER Rating you often spotted on Commercial advertisements for air conditioners and every company is claiming that they are giving highest ISEER rating and rating is also mentioned for the same. They also even claim that their product consumes very low electricity. Now it becomes very important to know about what is ISEER rating? How it is very important parameter before buying a product. In this article we will study about ISEER rating.
With everyday new inventions in air conditioning it becomes important for BEE to introduce methodology for measuring efficiency of air conditioners. With invention of inverter air conditioners, it was thought that it may not be successful but inverter air conditioners become very successful. But they were introduced without any star label which becomes very important factor while buying any electrical/ electronic product. So people want star rating of inverter air conditioners. To overcome this problem ISEER was introduced. 
Earlier for measuring performance of Traditional air conditioners EER was introduced.
EER - Energy efficiency ratio also known as coefficient of performance
EER is measured as ratio of output wattage (i.e. cooling capacity) and Input power taken by air conditioner.
EER= Output Wattage (Cooling capacity)
         Input Power taken by Air conditioner

From formula Stated above Traditional air conditioners efficiency can be ascertained, this efficiency can be further divided into 5 groups named according to star rating of air conditioners. This star rating works very well for Traditional air conditioners.
For Inverter air conditioners this formula doesn’t work as both cooling capacity and Input power taken by air conditioner vary.
SEER was introduced known as Seasonal Energy efficiency ratio. In every season temperature will not be constant and keeps on varying. So working principle behind SEER is that temperature will not remain constant throughput the year. So as there are variations in temperature so are the cooling requirements vary e.g. cooling requirements will be different to cool a particular space at 40 degree , 45 degree and 35 degree so as operating hours of air conditioners.
SEER has taken care of all these factors i.e. temperature variations throughout year and air conditioners usage pattern. So SEER will different in different countries as temperature profile will be different. Now what BEE has done that they had defined ISEER i.e. Indian Seasonal energy efficiency ratio.
ISEER = Total annual amount of heat Air conditioner can remove from the indoor when operated at active mode
                                   Total annual amount of energy consumed by the Air conditioner

Thus ISEER is the ratio of heat removed to total energy consumed.

A complete guide for right rating selection and installation guide for air conditioners:-
This is best used when there are two air conditioners compared and also there usage will be same, but as usage may be different so electricity consumption may be different.

When you are going to compare Star ratings of different types of air conditioners, Window, Split and inverter,  it becomes quite difficult to compare air conditioners . Standards defined are even provide detailed information for the same. Although with introduction of EER for fixed speed air conditioners (Split and Window)  and ISEER for inverter air conditioners help in selection of air conditioners a lot and compare them also.
As per national weather records temperature distribution and operating hrs of air conditioner are as below, Data taken from BEESTARLABEL.COM:-

In above Temperature range is shown in 1st Row.
In Second row are Average Annual Hrs which indicates temperature remains for no. of Hrs.
In 3rd row is Fraction which is fraction of total no. of Hrs for which temperature remains
In 4th Row is No. of operating Hrs of Air conditioners- In 4th row total Hrs are also selected as 1600 hrs.  
Now BEE has made ISEER rating according to star rating of air conditioner but this is not mandatory and it was introduced in 29/06/2015 and will remains valid until 31/12/2017.  According to this star rating and corresponding ISEER rating is below:-
1 Star – Minimum ISEER rating should be 3.10 and Maximum ISEER rating should be 3.29.
2 Star- Minimum ISEER rating should be 3.30 and Maximum ISEER rating should be 3.49
3 Star - Minimum ISEER rating should be 3.50 and Maximum ISEER rating should be 3.99
4 Star- Minimum ISEER rating should be 4.00 and Maximum ISEER rating should be 4.49
5 Star- Above 4.50

BEE is making mandatory from year 2018 will be valid up-to Dec’19 onwards that for Star rating and corresponding ISEER rating, e.g. for
1 Star – Minimum ISEER rating should be 3.10 and Maximum ISEER rating should be 3.29.
2 Star- Minimum ISEER rating should be 3.30 and Maximum ISEER rating should be 3.49
3 Star - Minimum ISEER rating should be 3.50 and Maximum ISEER rating should be 3.99
4 Star- Minimum ISEER rating should be 4.00 and Maximum ISEER rating should be 4.49
5 Star- Above 4.50
Rating are same but BEE has made it mandatory from 2018.

Now days you have seen that Air conditioners are coming with ISEER rating of 5.8 even.
With recent launches in air conditioning it was found that dual inverter AC will save 834 units in-comparison to 5 star split air conditioner.
Air conditioners with having capacity of 1 ton will be capable for disposing off heat  of 12000 BTU (British Thermal Units)
Why Air conditioner’s capacity is measured in Ton:-
Air conditioners 1 Ton doesn’t indicates that it’s weight is 1 ton. Actually this indicates amount of heat that air conditioner is capable of removing from house in one hour. 1 ton of air conditioner will be capable of removing 12000 BTU/Hour heat from house. But still question remains why Ton is unit of measurement for air conditioner capacity.
Before invention of air conditioners people used ice for cooling purpose. They take that ice from frozen lakes or rivers. Now for melting 1 pound of ice 143 BTU are required at 32 degree Celsius, this means that if you have 1 ton equivalent to 2000 pounds of ice then 28600 BTU are required to melt the same. If this ice block is melted uniformly throughout the day than 11917 BTU/ Hour will be required which is rounded up to 12000 BTU/ Hour, which was the methodology adopted for arriving out at 1 ton AC capacity.

How Power consumption is related to ISEER rating of Air conditioners:-
12000 BTU/ Hour 3517 Watt/hour  power
Now for Assuming the ac to be a 3 star rated, its ISEER=3.5
For 2 ton AC ,power consumption of ac =cooling capacity/ISEER
=2.00 kWh.
In Split and Inverter air conditioners there are two units , Indoor unit is known as evaporator and outdoor unit is known as compressor. Most of power is consumed by outdoor unit only i.e. compressor only. Compressor get started only when indoor temperature is more than desired temperature. So you can assume that compressor will remains ON only for 60-70% of time so power consumed will be 60-70% of 2 KWH.
So from above you will see that more will be ISEER , lesser will be the power consumed by air conditioner per hour.

A complete guide for right rating selection and installation guide for air conditioners:-

Friday, April 14, 2017

Transmission conductors are Aluminum instead of copper

Why Aluminum conductor is used in Transmission instead of copper conductors.
Material used in Transmission lines should have following properties:-
1.       Low cost of construction
2.       Resistivity should be lower
3.       Material should have high conductivity
4.       Material should have Low temperature coefficient
5.       Material should have High current carrying capacity
6.       Material should have High mechanical strength
7.       Weather resistance properties of material
8.      There should have good elasticity of material 

The metals which partially fulfill the above requirements are copper, aluminum and steel. These are used alone or in combination.
Aluminum conductors are having conductivity closer to conductivity of copper conductors. Aluminum conductors have conductivity 61% of copper conductors. For Same resistance of that of copper conductor, aluminum conductor weight will be half of that copper conductor. Although when we compare conductivity we should consider copper conductors for transmission instead of aluminum conductor. But Aluminum conductors have resistance 1.6 times as much resistance/foot of that equivalent gauge of copper conductor. This means for equivalent conductor size aluminum conductor will have more power losses (I²R). These losses will be 60% higher when compared to copper conductors. The above stated reason will justify that we should use copper conductor in transmission instead of copper conductors.
Aluminum conductors are used for transmission of electricity instead of copper conductors is due to below stated reasons:-
(i)                 Lower cost
(ii)               Lower density
Now let’s above two factors will be considered while designing Transmission system and why we use aluminum conductors instead of copper conductors:-
(i)                 Lower cost:-
Weight of Aluminum conductor is around 30% of Copper conductor for per meter length this means that we required more material which leads to very higher cost of Transmission , also copper is costlier about 5-6 times that of aluminum conductor. Higher weight means transmission towers to be strong enough to bear the load of conductor which means higher cost of designing the transmission towers. Since Transmission system is in multiple Kilometers so it is always beneficial to use aluminum conductors considering higher cost associated with copper conductors.
(ii)               Lower density.
Aluminum conductors have lower density of conductor. Density of conductor is about 1/3rd  the weight of copper conductor for same volume , so aluminum conductor will be lighter than copper conductor. So mechanically we can increase cross-section of aluminum conductor. With increase in cross-sectional area I²R loss will get reduced as Resistance is inversely proportional to cross-sectional area of conductor. By increasing cross-sectional area to double , this will increase diameter of conductor to 1.414 times. With increase in cross-sectional area I²R loss will get reduced to 0.8 times the I²R loss in copper conductor which earlier were 60%. Now increase in cross-sectional area weight of conductor will increase but still weight will be 2/3 times the total weight of copper conductor so constructing towers will become cheaper as they don’t need to be as strong by a factor of .66
Weight of Aluminum conductor is around 30% of Copper conductor. That means even though we used 2/3 the weight above we are still at a 10% cost (.66 x 1/6) for the wire itself, not to mention the tower costs savings as mentioned above.

So there are following advantages associated while using Aluminum conductor instead of copper conductors:-
1.       With increase in Conductor size by double resistance will get reduced by 20% and I²R power losses will be reduced from 6% to 5%.
2.       Very lower construction cost as due to lower weight and lower cost of aluminum conductor , cost of construction is 33% , tower strength required is less.
3.       Huge saving approx. 90% of the cost of the wire itself due to difference in material costs between aluminum and copper conductor.
4.       Aluminum conductors are easy to bend and easy to handle as aluminum has more elasticity then copper.

Although transmission losses are higher in aluminum conductors but while due consideration of above factors we must consider aluminum conductors for transmission.

There is another question arise why not we use Steel conductors for transmission as cost is very low for Steel conductors?

Steel conductors are not used for Transmission as these have very lower skin depth as they have large permeability at 50/60 HZ in comparison to copper and aluminum conductors, this will leads to very high huge power losses due to high resistance.