LED Lighting Saves Energy?

28 November 2012

Updates:   This article is no longer applicable today.   LED technology has so many advances that it has overtook the events.  They can now produce LED lamps that are not only cheaper but also brighter and can save more energy than a conventional system

Introduction

Today, everyone is talking about  LED lighting. Many who used LED lightings before can  swear that such lights will save running bills. They also run cooler. This article will examine if it is true.

What is LED?

LED stands for Light Emitting Diodes. It was discovered in 1907. It is a semiconductor product. When a current passes through, it will emit lights as well as some heat. The earlier LED has only one colour, Red. Today, they are available in multi-colors. They match light spectrum of many other lightings. Some used LED lights for aquatic and reef tanks.

Are They Energy Efficient?

Lamp efficiency is often measured by lumens per watt (lm/W). Lumen is a measurement for lighting power emitted by the lamp. The earlier LED has a lm/W of around 65. This is about 4 times as efficient as incandescent lamp which is around 15 lm/W. It is still not as efficient as fluorescent lamp which is around 110 lm/W. Some manufacturers ever claimed that their LED can go as high as 160 lm/W but the United States Department of Energy (DOE)’s tests in 2009 showed that the LED lamps that were used to replace their existing lamp had only 17 to 79 lm/W.  Luxeon,  a well known US brand,  claimed their LEDs having the highest flux in the World;  they can only produce 30-40 lumens per watt.
 

Why Claimed to be Saving Energy?

Many who used LED lamps before always claimed so. They claimed to use lesser numbers of LED fittings for the same room.  Even the DIYs can tell one another to use only about 60% of LED in terms of wattage power. What could be wrong with DOE’s tests?

DOE’s Test Conditions

DOE’s explanation on the test conditions can be found here.

Its report clarified that the tests did not

a) Cover the measurement of luminaires;

b) Take account of the life maintenance

Luminaires Make a Difference?

Do a simple experiment. Use an incandescent bulb. Compare the lighting between one that has a reflector and one without. One will tell that the one having a reflector is much brighter. Similarly for LEDs.

The small LEDs of 5 mm usually have an in-built lens to concentrate the light source. 

The larger ones of 0.5 watts and above do not often have the lens as they are usually sold separately.  Many commercial LED also do not have the lens for each LED.  Different types of lens are available in the market and can be added to the LEDs to change their  beam angles so that lights can be focused in areas most needed for maximum efficiency.

Furthermore, efficient reflectors can also be designed for LEDs because of its smaller size and lesser heat emission.  Therefore, they can be much more efficient if the luminaires are also considered.

What Other Considerations?

One factor most users overlooked is the actual power consumed by LEDs. Actual power consumption will include KWs as well as KVARs. The latter is referred to as the reactive power that is not often charged in the electricity bill but will have to be accounted for when selecting the capacity of any generator.

Why?

The difference between fluorescent and LED fittings besides the lamps is the design of the ballasts.  The former uses magnetic ballast and the latter uses LED driver.  Both consume KVARs; inductive in former and capacitive in latter.

For a 30 watts T5 lamp, the fitting consumes only about 4 VAs or around 13%.

One LED driver with capacitor arrangement is shown below, the VAs consumed by this kind of driver could be as high as if not higher than the lamp itself.

Therefore,  when one measures the electric current consumed by LED lamps,  do not be alarmed as one is only charged for the KWs used.  The Power Generating Companies would not like this kind of LED drivers.  As for factories and large energy consumers where power factor is also charged,  it is not exactly a good idea to convert all fluorescent fittings to LED fittings as the power bills will not reduce by much.

What is the life of LED?

This DOE's chart showed that LED has longer life than some lightings and comparable to T5 fluorescent lamps.

 

Is it Worthwhile?

Unlike incandescents that can be hot in operation and fluorescents,  big and bulky,   cheap plastic reflectors can be supplied as a standard for LED lightings;  also,  lens can be easily added to LEDs to focus lights in areas most needed.   These reflectors and lens can improve LED's efficiencies.   

LED lightings can be energy efficient when compared to others such as incandescent and fluorescent fittings if they are fitted with proper lens and reflectors.  They can be a worthwhile investment except today's good LED lightings come with a price.

Air Conditioning Filters

25 November 2012

Air conditioner is an essential thing to have in Singapore.  Maintenance of these air-conditioning equipment will involve regular cleaning of the air filters;  also,  the coils may  require chemical cleaning to restore the cooling efficiency from time to time.  This article will introduce a micro non-woven fabric material that will help to keep the cooling coils as clean as possible and to reduce maintenance requirement.

What is Micro non-Woven Fabric Material?

Non woven fabrics are sheet bonded together by entangling polyethylene(PE) or polyester fibers. They are porous sheets that are made from plastic film and not by weaving or knitting. Polyethylene or polyester is used everywhere;  in plastic bags,  plastic films etc.  Non woven fabric has many applications;  one of which is used in mops and brooms that we used to clean the floors. It has natural static charges making it suitable for air filtering work.

Their refills are cheap and a plenty in the market. The refills will cost only around SGD$ 1/= for 35 sheets of 200 x 300. There are 2 types in the market; the other one measured only 200 x 290 can be used for smaller air conditioners.

Application

The fiber sheet is placed just before the original air filter. To stick the sheet to the filter, just use the hook of the Velcro Fabric Fasteners stapled or glued onto the original filter. The hook will “catch” the fiber sheet and secure it in place.

The author has used the non woven fabric material for more than 4 years now without any ill effect on the occupants as well as the air conditioners.

This filter shown below was renewed about one month ago. Dust can be seen accumulating at the corners. When the fiber sheet is lifted up, one can see that there is no dust on the original filter at all except along the sides that was not fully covered by the filter.

Air Resistances

One of the concerns is that the additional sheet of filter will impede air flow. The author has no measuring equipment to measure such impedance. But the fiber sheet was so thin that one can even read the words “e-ion Air Purifying System” clearly written on the original filter as shown in the photo. The air conditioner can still work at its lowest speed without any degrading in performance.

Even if there is air resistance, it won’t be as high as when the fins of the air conditioner were clogged up with dirt; then only chemical cleaning work will restore the efficiency. By then, one would have wasted quite some energy without proper cooling for some period.

Application

This air conditioner shown below has been working every night for the past 4 years.  Non-woven fiber sheet was used since day one. The fins at the coil still looks very clean.  One can even see the reflected shine on the tube of the coil when a touch light was shined at it to take this picture. So far, no cleaning has ever been done on coil.   The gap of the fins is about 1mm which is slightly thinner than a 5 cts Singapore coin as shown.

US Long Term Mutual Fund Flow

24 November 2012

Introduction

The Investment Company Institution (ICI) is the national association of US. investment companies. It  tracks many business activities including those of mutual funds. Its members manage total assets of about $13.8 trillion all over the World and serve more than 90 million shareholders. It publishes Long Term Mutual Fund flow weekly. Its publications can be found here.

What’s the Use?

The data published by ICI on the money flow of the Mutual Fund (the Fund) has been used often by many to track the general market directions. A plot of the data is shown below:-

Chart Analysis

The chart shows the Fund’s money flow against S&P. It can be seen that the Fund are quite sensitive to the changes in the stock market. The fund curve exceeded stock market curve in 2007. As the market started its downward trending, the Fund discharged its holding sharply until mid 2008 where they dumped as much as they can. At one stage, the Fund dumped more than USD$180 billions per month in total. When market started picking up in March 2009, the Fund loaded heavily. Today, they are keeping bonds at reduced level but started selling equities averaging around $15 billions per month

What Can We Learn?

One can use the Fund’s money flow to chart market direction. Be the first to load when one sees the Fund are loading heavily and vice versa.  Note that this mutual fund money flow indicator tracks better than the Junk Bond ETFs indicator described here before.

Use Junk Bond ETF to Track Market Direction?

24 November 2010

Introduction

It was said that Junk Bond traders are knowledgeable, involved, and speculative investors. Junk bonds offer higher future return than corporate investment-grade bonds. Because of the higher volatility and risk, Junk Bond traders are often more sensitive to the market movements. Let’s examine if we can use their trading behaviour to track the general market direction.

Junk Bond ETFs

The market offers 2 junk bond ETFs; they are iShares iBoxx $ High-Yield Corporate Bond (HYG) and SPDR Barclays Capital High-Yield Bond (JNK). Their data can be downloaded from Yahoo Finance for analysis and tracking.

How Did Junk Bond Perform?

In order to filter out the noises, we will examine the monthly plot first as shown

HYG appears to be tracking DOW quite nicely during the period from 2007 to 2010. From then on, DOW took off and HYG was not doing well for some reasons. This chart does not tell much. It only tells that junk bond buyers were not as confident and as active as stock market players in the recent months.

Correlation with DOW

If we add a chart that shows direct correlation with DOW, the picture will be as shown:-

It is clear that though the Junk Bond traders were not as confident but they were not losing track. They hold-on to play the bonds during periods between 2009 to date except that they did not respond as fast to sell their bonds in 2008 until the stock market had almost bottomed. They also buy bonds when market is falling.

From the chart, one can tell that junk bond investors are always investing ahead of the stock market. So there is a time lag between the stock and the junk bond tradings.

Applying the Time Lag

When one projects HYG 6 days in the future and correlates back to DOW, one will find a completely different picture as shown in the attached.

 The new indicator tracks closely with DOW. It gives signals ahead as to where DOW will move next. The chart shows that the stock market is presently trending downwards but there is no immediate danger until the new indicator crosses below the zero line.

What about the Weekly and Daily Charts?

There are far too many noises to track the market using weekly or daily charts. However, one can still gauge if the junk bond investors are active although the signal will be confusing.

How to build the indicator

If one has metastock or similar software, one can build the new indicator using the following formula:-

Correl(Security("C:\MetaStock Data\sample\I\IDJI-1",C),Security("HYG-1",C),5,6);0

Conclusion

The Junk Bond ETFs can be used as an alternative indicator to track the direction. The monthly chart especially the correlation chart projected 6 days into the future has a much clearer picture;  however,  it does not track better than the US Long Term Mutual Fund flow indicator described here.

Bear Flag in the Making?

23 November 2012

Introduction

Bear flag is an interesting trading pattern. Many traders reaped profits by being able to identify a bear flag in advance. This article will help readers to identify the upcoming of this pattern and hope we all can also profit from the stock market.

What’s a Bear flag Pattern

Bear flag usually happens during a downturn when the price is below the 200-day MA. During this time, investors will lose interest and have sold away their stocks. Up to a point, market will stop “bleeding”. Some buyers will start coming back to do “bottom fishing”. Then the price would fluctuate within a range, which is often called “consolidation”. It may bounce above or drop below but generally, it will trace an ascending channel or triangular pattern as shown and price will go up slowly. The significant behaviour to watch out is the decrease in the trading volume as the price increases. The volume will suddenly jump at the end of the bear flag formation when the support is broken. The bear flag will end when price and volume again diverges as shows.  If the price breaks the support or resistance and the volume does not jump, it is likely the breakout is unreliable.

When bear flag is identified, the price will usually drop significantly below. The bear flag formation may be as short as 4 to 5 days and may take as long as 3-5 weeks. Other significant behaviours are

a) price never exceed Fibonacci 0.68 marked from the bottom of the “mast”;

b) MACD fails to pick up when recovered above 0

c) +DI of Directional Index never take off after crossing above –DI.

 

Have We Got the Pattern Before?

There are many such bear flags happened before. The biggest one just about 4-years ago in 2008. Then the author in Sept 2008 predicted that the market would fall about 30% or 800 points from 2,600 points to 1,800 point. The market eventually dropped below 1,600 points before recovering in March 2009.

The following is the chart for DOW during that period:-

Notice the divergence between the price and volume first occurring in Nov 2007.  When the first support was broken there was no jump in volume and the falls was not great.  It was not until Oct 2008 when that support was broken, the volume jumped 3 times with a hefty fall after that. The +DI was struggling to go above –DI but it never succeeded. Also the MACD never crossed above the 0 level convincingly. The target was set to around 770 points or about 30%.  There are altogether 4 bear flags from Nov 2007 to Jan 2009.

Is This Going to Repeat?

It is hard to tell right now because the bear flag has not even completed yet. However, the developing bear flag has all the ingredients; for example, the divergence in price and volume, the negative +DI and the MACD etc. One might have to wait for the price to touch the 200-day MA and plunge below the flag pole before confirming the bear flag.   Once the price rises above Fibonacci 0.618 marked from the bottom of the “mast”,  the bear flag pattern will be neutralised.  The last failed attempt to form a bear flag was around September 2011 when Operation Twist was announced.  Volume did not spike much. The one in June 2012 did not materialised because it was neutralised.  QE3 came in Sept 2012 as if investors were expecting it.

How To Trade?

It is definitely not the time to do bottom fishing. Intraday or short term trading is recommended.

Update 1 : 8 December 2012 -Bear Flag Forming

Last night, US index closed mixed.  Dow Jones closed up 81.09 points, or 0.6%, to 13,155.13.  The S&P advanced 4.13 points, or 0.3%, to close at 1,418.07.  Better unemployment reports was the reason.  However, Nasdaq went down 11.23 points, or 0.4%, to close at 2,978.04 due to poor Apple's stock performance.  The updated chart of DOW is as shown:-

The position still remain the same with volume divergence and negative MACD,  although there was a positive sign in +DI.  The RSI also gave hope of DOW crossing over the 61.8% Fibonacci resistance.  But the 50-day MA is still falling and had crossed under the 100 MA. The Stochastic chart showed overbought sign.  These are not quite in favour of DOW crossing the resistance.  DOW will have to show commitment going ahead with heavy trade volumes when crossing the line.

Update2:  19 December 2012- Bear Flag Neutralized

The quick exchanges between President Obama and Speaker John Boehner on fiscal cliff issue sent DOW back on track to higher ground this week.  The triple-digit rise, its first such two-day streak since July, seen DOW  finished at 13,350,  passing above the 61.8% Fibonacci resistance of 13,200 to neutralize the Bear Flag.

DOW made 2 attempts to neutralize the bear flag.  The first attempt on 10 December failed.  This second attempt showed considerable improvement with rising volume and a golden cross to support the cross over.  Barring any unforeseen circumstances,   DOW should rise to test the next resistance which is around 13,600.

Update 3 : 23 December 2012  Weakening Supports (revised on 25 December 2012)

The pulling out of the Tax Bill in the House by Speaker Boehner sent DOW falling on Friday to a level below the critical support of 13,200.  DOW made attempt and failed to cross the 70% Fibonnaci resistance level.

The issue posed some dangers ahead for DOW with the following signs showing up in the indicators

1.  Falling RSI ;- falling below the trend line
2.  Falling +DI and Rising -DI:- showing deteriorating performance
3.  Flattening MACD ;-  Showing diminishing hope for a recovery
4.  Breaking down rising Wedge :-  showing critical support being tested and broken with heavy volume support

The only consolation is the rising 20-day MA which now showing a Golden cross being formed after cutting up above the 50-day MA. 

Whether DOW could pick up and resume its climb to test the resistance of 13,600 will be much depend on whether President Obama can resolve the "fiscal cliff" issue before year end which is less than 7 days to go.  Judging from the heavy volume,  the danger of remaking the bear flag could become real if DOW continues to drop and failed to recover the 0.618 Fibonnaci resistance level.

Update: 8 Jan 2013 Bear Flag Null

DOW jumped 2.5% or 331 after US averted the fiscal cliff issue.  The bear flag was null and now testing the resistance of the rising wedge after having broken down on 23 December 2012 with appreciable volume.   Unfortunately,  in the process, DOW formed last bullish engulfing on 4th Jan 2013 followed by a bearish engulfing candlestick as a confirmation.  It is likely that DOW will fail the test to break the wedge and instead,  head down to test the 200 day MA @ 13,000.

 

Declaration: The author has no short position.  Readers should verfiy the information before using any in this article for trading purposes.

Selecting Nano Aquarium Chillers

22 November 2012

Introduction

There is a choice when selecting chillers for nano aquarium tanks of  around 25 gallons or 100 litres or smaller. One can choose between a Peltier chiller or a Freon Chiller. This article will show the differences between the popular brands, using 1/20 hp range as examples.

What’re the Main Difference

Peltier chiller uses an electronic chip whereas Freon chiller uses mechanical compressor to generate the chilled water. The differences are discussed here in detail.

What're the Popular Brands?

In the 1/20 hp range, the popular brands in Singapore are

1. Resun CL150

2. Hailea HC100a

3. Arctica nano DBI-038

Their specifications from the manufacturers are tabulated as follows:-

Brands	Resun	Hailea	Arctica
model	CL150	HC 100a	DBI038
Range (hp)	1/20	1/20	1/20
Type	Electronic	R134a Freon	R134a Freon
Power Input (watts)	200	1101	1651
Power Output (Watts)	150	150 (from a website)	200 (600 BTU/hr)
Ampere (230V)		0.6	0.9 (1.8 @ 115V)
Tank size (litres)	120	50-200
Flow rate (LPH)	1000	200-1000	400 -600
Weight (kg)	8.5	9.2	12
Water Connection (mm)			12 (1/2”)
Dimension (mm)	260 x 310 x 205	338x18x25	195x320x358
Estimated cost (SGD$)	170	300	800

1. Estimated from running current

The Coefficient of Performance (COP)

This figure is never available for the manufacturers. Although COP can tell if one chiller is more efficient than the other,  it will depend on the operating conditions, the cooling as well as ambient temperatures.  Also, most tests in factories are carried out under laboratory conditions where good quality water are often used.

From the manufacturers’ data and some estimation of  input power, one can tabulate the following table:-

Brands	Resun	Hailea	Arctica
model	CL150	HC 100a	DBI-038
Range (hp)	1/20	1/20	1/20
Power Input (watts)	200	110	165
Power Output (Watts)	150	150	200
COP (output/Input)	0.75	1.36	1.21
Performance	100	180	160

Assuming that the chillers are operating under the same conditions and factory tests carried are identical, Hailea 100a appears to be more energy efficient.

Inside the chillers

Stripping out the case, the insides of the chillers are shown as follows:- (click to enlarge)

Comparing the pictures, one can straightaway tell that Resun CL150 has a different configuration. It has no compressor. A refrigerating chip was named to provide the cooling. Also, it uses a plastic heat exchanger for the cool side and an aluminium heat sink with forced air cooling for the hot side of the chip. It is hard to tell from the picture if the  refrigeration chip is actually a peltier chip.

Working out COP for Peltier Chillers

Ultrasonic2 has posted in his webpage a TEC calculator to workout the COP for Peltier chiller.
Enter the various measured data such as hot and cool side temperatures and also the power input etc, the TEC calculator will be able to work out the COP.   As for the freon chillers,  some calculations will be required to work out the cooling power.

Heat Sink for Peltier Chillers

Someone in one of the forums pointed that the size of heat sink does not matter much in Peltier Chiller but this article about heat sink for Peltier will prove him wrong.

Ultrasonics2 and Shine7 have both provided TEC calculation results for their Peltier chips. Their webpages can be found here and here.   It is believed that Ultrasonics2 used the peltier for computer cooling whereas Shine7 used it for aquarium cooling.

As one can see from the following that the COP of peltier chip can vary a lot. In this case, Ultrasonic2’s 0.74 vs Shine7’s 0.54

Also noted that the Shine7’s peltier had a hot side temperature of 52C whereas the Ultrason2 had a temperature of 30C. Also,   the Delta T across the chip was lower in Ultrasonics’s case. The results  suggest that Ultrasonic2 has an extra efficient heat sink. But now, look at Shine7’s heat sink again and compare  to that of Resun CL150 chiller shown earlier (but the real one may be much larger though). 

How to Select the Right Size Chiller

Many aqua and reef enthusiasts pick up some knowledge here and there.  Some uses the one size larger rule and some just blatantly use figures provided by the manufacturers. Some suggested that chiller should be large enough so that it won’t run longer than half an hour on each start. Some preferred shorter operating time citing lesser wear on the compressor.

The correct chiller sizing should depend on heat loads transmitted into or out of the tank. There are basically the following heat losses/gains that can be found in an aquarium tank; 

1) The heat gain from the light fittings
2) The heat gain from the pump or in-line filter
3) The heat gain transmitted through the exposed glasses
4) The heat gain from the occupants
5) The heat gain through surface and the heat loss from evaporation
6) Others heat gain  such as those from internal circulating pumps, wave makers etc

As the calculation involves complicated thermodynamics and air conditioning engineering, it would not be discussed here. Those interested can read up this article.

Most enthusiasts just use rules of thumb. The thumb rule of using one size larger appear to be more appropriate because the manufacturer’s guideline often did not consider the extra heat load from the other equipment such as lights, pumps etc;  also,  the chiller will age and lost efficiencies. Then one might want to add more equipment such as more pumps in future.  Some manufacturers could also over-rate their chillers.

JBJ has a website that one can use to size various chillers.    Please note the following when using the website:-
a)  For metric to imperial conversion,  use the formula degree F= degree C * 9/5 +32 and 1 US gallon = 3.8 litres;
b)  Remember that actual water temperature refers to maximum water temperature which should be around 30C or 87F for Singapore; 
c)   A 40 watts flourescent fitting will give 50 watts of heat;  40 watts for the lamp and 10 watts for the ballast (25% for magnetic ballast, 20% for electronic ballast and 15% for LED driver);
d)  Assume full tank volume and not actual water volume to be safe. 
e)  It is still good to up one size larger after the calculation.
 
The term horsepower (hp) is often used for sizing a chiller.  One can take that 1 hp=2800 watts of cooling power.  Divide that by COP of the chiller (1.3 for freon and 0.55 for Peltier),  one should get roughly the power inputs in electricity watts.

The manufacturers appear to suggest the chiller should be sized such that the chiller should cycle on 15-20 minutes an hour for chiller to run about 6-8 hours per day. Depending on the setting of the temperature and the water flow rates, it may be normal for chiller to run for 1 hours and stay off for 2-3 hours before the next cycle.

Flow Through Vs Drop-in Coils

There was a misconception that drop-in coils are much more efficient than the normal flow through type of chiller.  However,  this is not quite true as the chiller efficiency depend much on the coil design of the evaporator and the condenser.  The manufacturers can further improve the condenser designs to make chiller more efficient;  such as providing more condenser tubes and fins with improved fan design.  However,  for evaporating coils,  the manufacturers will have to weigh between cost and efficient design as titanium which is often used in aquarium chiller comes with a price.  It is for this reason that the COP of aquarium chillers are never better than window airconditioners.  The following manufacturer's data will show that the amperage drawn for both flow through and drop-in chillers are identical.

Conclusion

Peltier chillers are less efficient but they cost much less. An economic will have to be worked out before choosing the right chiller. On the other hand, Freon chiller may cost more but on the longer term, it will cost less because of higher COP.

Other Reference Sites
tinyurl : https://tinyurl.com/y7p6tev3

Freon Vs Peltier Chillers

21 November 2012

Introduction

There were some interesting exchanges in one local forum about the use of Freon chillers and peltier chillers for aquatic and reef work. Many experienced aquatic enthusiasts in the forum argued that peltier chillers will not work. Those used peltier chillers before was of the view that such chiller is not suitable for reef tanks and cold-stored the chiller. This article will present the differences between the 2 types of chillers and their applications in aquatic and reef work.

What is a Peltier Chiller?

Peltier chiller is often referred to as an electronic chiller because it uses a semiconductor chip that has hot and cold plates.

When there is a current passes through, the chip will transfer heat between the plates for heat to be rejected or produced depending on the polarity of the plates. Peltier chip was discovered by a French Physicist Jean-Charles Peltier in 1834 when he passed a current through to product heat and cold energy from a junction composed of two different materials.   The largest Peltier chip from ebay has a power input around 500 watts.  This has about 300 watts or 1/10 hp cooling power,  good enough just  for a 300 litre tank.  Larger and more efficient ones are being developed.

What is a Freon Chiller?

Freon Chiller uses a compressor to compress gaseous freon into liquid state, then the freon is allowed to be cooled in a condenser for heat to be rejected to the atmosphere. After that, it is allowed to be expanded into an evaporator chamber either by means of an expansion valve or capillary tube. In the process of expanding from liquid to gaseous freon in the evaporator,  it absorbs heat from its surrounding. The cycle repeats when the gaseous freon is returned back to the compressor.

What’re the Differences?

As far as the quality of cooling is concerned, there is no difference between the two. This is because water from aqua or reef tank will cycle through heat exchangers of the chillers. For freon chillers, titanium tubes are often used as cooling coil inside the evaporator whereas for peltier chillers,  polypropylene or stainless steel sections are used for heat transfer. No copper or aluminium materials will be used in the water heat exchanger unit.

Apart from this, peltier chillers are often smaller in size except for the electricity consumption.  They are not  as efficient as the freon chillers. Also, there is no difference in the inlet and outlet connection because there is no cooling coil used in peltier chillers.

One aqua enthusiast built this peltier chiller for his 20-litre tank.

What're the Pros and Cons For Peltier Chiller?

Pros

1. Can be easily DIYed. Multiple units can be cascaded to give the desired cooling;

2. Light weight and smaller in size;

3. Can use for both cooling and heating by just reversing the polarity of the peltier chips;

4. Lower capital cost

5. Easier to maintain; no moving parts except the cooling fan; spares are a plenty;

6. Peltier chip claimed to have a life expectancy of 200,000 hrs

Cons

1. Higher running cost ; Freon chiller is 75% more efficient than Peltier chiller;

2. The fans for aluminium heat sinks can be noisy unless a bigger heat sink with less noisy fans or remote cooling can be used;

Design Pitfalls for Peltier Chillers

 

Pitfall No.1

Computer Heat Sink

They are a plenty in the market and often being used wrongly for Peltier chips. A wrong selection of a smaller size not only affects the cooling performance but also results premature failure of peltier chips. Too big a heat sink will cost money although the chiller will run more efficiently.  An economic will have to be worked out for the selection. Water cooling is a better alternative than forced air cooling because more heat can be transferred when properly designed;  and also, cooling devices can be remotely located to minimise fan noises.

The following is a good article to learn more about peltier and the heat sink selection. Read here.

 

Pitfall No 2

Cooling blocks

There are a plenty also from the market but most are designed for computer cpu cooling where clean water are often used. They are either of copper or aluminium type which is not suitable for use in aquatic or reef tanks. They could be corroded or choked up easily after sometime.

It may be more appropriate to use stainless steel channel cut to form a box with both ends sealed for plastic inlet and outlet.  Corrugated stainless steel sheets such as the following can be DIYed to stuff inside the box and stick lightly with non-toxic thermal conductive expoxy glue to help heat transfer.

Polypropylene plastic can also be used as alternative.  The heat transfer characteristic of polypropylene plastic is about as good as stainless steel.

As stainless steel may also corrode over time,  the other alternative is to use titanium tubes either embeded in the holes of solid aluminum block or high thermal heat transfer epoxy which has thermal conductivity comparable to titanium.  Multiple passes can be arranged for better heat transfer.

Confusion about Cooling Efficiency and Coefficient of Performance (COP)

Someone claimed that Peltier has only 8% efficiency as compared to Freon chiller which has 50% when he searched the net and might have tumbled into the following Wiki site. The paragraph in the Wiki site read as follows.  He argued strongly that no chillers will ever have cooling efficiency higher than 100%.

Thermoelectric junctions are generally only around 5–10% as efficient as the ideal refrigerator (Carnot cycle), compared with 40–60% achieved by conventional compression cycle systems (reverse Rankine systems using compression/expansion). Due to the relatively low efficiency, thermoelectric cooling is generally only used in environments where the solid state nature (no moving parts, maintenance-free, compact size) outweighs pure efficiency

For cooling and heating purposes, the efficiency of cooling or heating device is often measured in terms of Coefficient of Performance (COP) and not the Carnot cycle efficient. This is because freon, when allowed to be expanded in the evaporator, absorbs free energy from its surrounding and therefore, the efficiency can be more than 100%. Peltier chiller,  on the hand,  has no such advantage of getting free energy from the surrounding and therefore,  its COP is much lower. 

COP is often expressed as

COP cooling = Qc/W_in

Where Qc is the cooling output and Win is the power input

Normally, freon chiller has a COP around 1.3 whereas Peltier chiller will have a COP around 0.55. Air conditioner has much higher COP around 2 to 2.5 because it has larger and more efficient condenser and evaporator. Commercial chillers would have COP more than 5.0 because they have super large condensers with multiple water passes in the heat exchangers.

Why no Large Peltier Chillers?

Peltier chillers are limited to smaller sizes in the market. They usually have cooling power of less than 150 watts or 500 BTU/hr or 1/20 hp. It is not because larger one cannot be constructed or manufactured. It may be because the running cost may become more manageable for smaller sized chillers; moreover, Peltier chiller has a significant cost advantage in this range.

Why Peltier Failed to Work?

Some claimed that Peltier chillers not only failed to work but also tank temperature kept rising.  There are several reasons;  one of which may be there was not enough air cooling for the heat sink when it was placed in the cabinets.  The other could be due to over-rating by the manufacturers.  Some claimed Peltier chillers to have COP of around 0.75 with small heat sinks.

Economics

One can get a 1/20 hp Peltier chiller for about SGD$170/=  and will have to spend around SGD$300 for a similar size freon chiller.  Assuming the cooling power is around 140 watts, Peltier will need about 250 watts of electricity and Freon chiller around 110 watts. At current electricity tariff of 0.2727 per kwh and assuming 48 starts/stops per day with 10 minutes running and 20 minutes resting, the electricity cost will work out to be SGD16 per month for Peltier and SGD$8 for Freon chiller. With that difference in running cost, the straight payback for using Freon chiller will be around 14 months.

Conclusion

Peltier chillers are only good for those who have a smaller budget and not too worried about the higher running cost or for starters who just wanted to try nano reef keeping for a short period.  It is suitable for use as a backup chiller.


Other Reference Sites
tinyurl:  https://tinyurl.com/ybqva9ws