Skyjuice

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:-


Resun
Hailea
Arctica
model
CL150
HC 100a
DBI038
Range (hp)
1/20
1/20
1/20
Type

Electronic
R134a Freon
R134a Freon
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.

References
How to Service Resun CL650 Aquarium Chillers
Freon vs Peltier Chiller for Reef Keeping
DIY Bed Cooler

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