CHILLER LEARNING CENTER
HOW TO CHOOSE BETWEEN A CHILLER AND A HEAT EXCHANGER?
HOW TO SIZE A CHILLER OR HEAT EXCHANGER, (MORE ACCURATELY, HOW MUCH HEAT DO I NEED TO REMOVE)?
WHAT FLUID OR COOLANT SHOULD I USE TO COOL MY PROCESS?
TERMINOLOGY
ê T = temperature difference
GPM = gallons per minute
Kw = kilowatts, one kilowatt is equal to 3400BTUH roughly
BTUH = British thermal unit/ per hour , (one BTU is equal to the amount of heat required to raise one pound of water one degree Fahrenheit at one atmosphere)
AMBIENT = surrounding air temperature
A chiller is a self contained machine with a refrigeration circuit that cools a fluid circuit.
Both circuits are separate but come together at the refrigeration evaporator. This is where the heat
from the fluid is cooled. Chillers can also contain heaters to rapidly heat up the fluid, these are usually
in the fluid reservoir. A chiller will also have a control circuit to control to the desired temperature and
a secondary control system to monitor the fluid and refrigeration systems for errors, based upon the
error, this secondary control system may shut down the chiller, signal the user via a remote signal,
led, audible alarm or in our case all three. Finally a chiller contains a pump in the fluid circuit to
re-circulate temperature controlled fluid between the chiller and the process.
A heat exchanger is much like a chiller in all aspects, except for one key difference.
Instead of removing heat via a refrigerated circuit, heat is removed though a heat exchanger
to your facility water supply. Essentially, the heat exchanger has all the same systems and
control circuits but uses water only to perform heat removal. For this reason heat exchangers
are only applicable when your desired process temperature will be above your facility water
supply temperature. For example, our catalog heat exchangers are based on a 5˚C ê T, or
5˚C temperature difference between your desired process temperature and your facility water
supply temperature. Say your desired process temperature is 23˚C and your facility water
temperature is 18˚C, and you need to remove 5 Kilowatts of heat at a flow rate of 4 GPM.
We would take this information and calculate the smallest model that would remove that heat
using the least amount of facility water for the 5˚C ê T.
HOW TO CHOOSE BETWEEN A CHILLER AND A HEAT EXCHANGER?
The easiest way to answer this question is to ask a few more; Do you have a facility water
supply available? If no, you need a chiller. If yes, then ask another question, will my process
temperature be above my facility water temperature? If no, you need a chiller. If yes, a heat
exchanger may suit your application. It is generally less expensive than a chiller and more
reliable overall as it has less mechanical components to fail. And if water consumption is not an
issue it is more energy efficient as well.
A chiller is always required for temperatures below the normal facility water temperature or any
time you need to 15˚C, or below.
HOW TO SIZE A CHILLER OR HEAT EXCHANGER, (MORE ACCURATELY, HOW MUCH HEAT DO I NEED TO REMOVE)?
Most often the equipment you need to cool will have a heat removal requirement or recommendation
from the manufacturer. Sometimes though you may have a used tool with no documentation, you may
be the manufacturer and need to figure out your heat load, etc. In this case the easiest way to determine
your heat load is run tap or facility water through the tool, with the tool at full power. Measure the flow rate
of the fluid in GPM or LPM, (liters per minute), then measure the incoming and outgoing water temperatures.
For water the formula works like this: BTUH = êT x GPM X 500, to convert BTUH to kilowatts divide it by
3.412. If your ambient or surrounding air temperature around the chiller is greater than 20˚C, add 1% to the
calculated wattage per degree C over 20˚C. Power is another factor that can add to the necessary size of a chiller.
If you are in a country with 50Hz power, add 20% to the calculated wattage. Other factors include high altitude
or low AC voltage, if your chiller will be faced with either condition, add 10% to the calculated wattage requirement.
WHAT FLUID OR COOLANT SHOULD I USE TO COOL MY PROCESS?
This may be answered by the process tool manufacturer, or if unavailable we can recommend the right fluid
for you. However some basic guidelines follow:
-When running your process between 10˚C and 90˚C water can suffice.
-When running below 10˚C the addition of an anti-freeze additive is essential. Our recommendation is industrial grade ethylene glycol and water if possible.
-When running above 90˚C the addition of glycol can also be beneficial as this helps to raise the boiling point of water.
-If conductivity or corrosion could be an issue you may want to use a non-conductive fluid like Galden or Fluorinert.
-When running below -25˚C use a mixture of at least 50/50 ethylene glycol and water.
-Most lasers and laboratory microscopes use simple de-ionized water.
Keep in mind there are numerous heat transfer fluids available for many different applications, we can advise you if you have any further questions.