What type of chiller is ideal for your application?
The answer to this question is pretty obvious: it depends. Since we are always conscience of your time, we will assume that chilled water is required for your project. Chilled water could be required for a number of reasons: a chilled water system already exists, the project is a process application that requires chilled water, the owner is just a raving fan of H2O- the lists goes on. Okay, now that we are focused on chilled water only, we have a bunch of chiller options to choose from:
- Packaged air cooled chiller
- Split system chiller with an air-cooled condensing unit
- Split system chiller with an air-cooled condenser
- Indoor water cooled chiller with a cooling tower or ground loop
Packaged air cooled chiller
An outdoor, air cooled packaged chiller has all of its components located outside, in one package: the condenser, evaporator, compressors and pumps (Although the pumps can be, and often are, installed indoors). So why would you choose a packaged chiller?
- Lead time- Most manufactures have a packaged chiller stocking program. Which means you should be able to get a packaged air cooled chiller in just a few days (not weeks or months). Through our sources, we are able to get packaged chillers up to 275 tons in just 2-3 days!
- Space- A packaged chiller is typically installed on a roof or on the ground, where “real estate” is not typically at a premium. To a business owner, this means more indoor square footage to generate more revenue for their business.
- Maintenance friendly- Packaged chillers are generally the easiest to maintain compared to the other chiller options.
- Noise- Assuming the chiller is not installed directly over a noise sensitive area, getting the compressors and condenser fan motors out of the indoor space can be a huge benefit.
- Price- packaged chillers are generally the lowest upfront cost.
- Waterside Economizer Option- Since the chilled water loop is already outside, this gives an owner the option to add a waterside economizer. This option adds chilled water coils the condenser section of the chiller, and allows the chiller to run in “free cooling” mode when the ambient temperature starts to fall below the design leaving water temperature. It can be an expensive upfront option, but it typically pays for itself in 3-5 years. Most manufacturers will require a glycol solution for this option, so BE CAREFUL when designing your system to make sure you have enough capacity!
- Even though we just blasted you with a lot of good reasons to use a packaged chiller, there are a couple of downsides. Since the water leaves the comfort of the building, freeze protection must be considered. Which means adding glycol to the system, never shutting off pumps, or planning to drain the system every fall. The life expectancy is also shorter since the entire system is exposed to the elements.
Split system chiller with an air-cooled condensing unit
First a little industry lingo that gets some folks confused: A “condensing unit” is the high side of a split system that has compressors built-in to the unit. A “condenser” does NOT have compressors- it is just the condenser coil and condenser fans in a box. So, why would you choose this option?
- No freeze protection required: Since the evaporator is installed indoors, we don’t need to worry about freeze protection. This means NO glycol, NO draining of the system, NO freezes, NO need to run pumps all winter long.
- Noise- This is similar to a packaged unit. As long as you are careful about where the condensing unit is located, lower indoor noise could be experienced.
- Life expectancy- This gets a small boost, but it’s not as good as a water cooled chiller. Since the evaporator (and typically your controls) are located indoors, this section of the chiller should last a lot longer. However, the high side is still located outdoors, which might have a shorter life cycle.
- Disadvantages? The biggest one is the refrigerant piping component. On a packaged chiller, the unit comes pre-charged and ready to go. But on a split system, the contractor must install copper refrigerant lines (liquid and suction lines) from the evaporator to the condensing unit. This just adds another layer of complexity during startup and service. Also, careful consideration must be made for sizing the DX refrigerant piping before installation (luckily, cfm can help with this!). For a good mechanical contractor this is no problem. But it is still adds extra steps to the installation and the servicing of the chiller.
- Design Consideration- When you are designing a split system chiller, make sure your condensing unit has the correct capacity at the desired suction temperature. Some condensing units are designed to be connected to a chiller evaporator, and some are designed to be connected to a DX air coil. What is the difference? About 15% in the system capacity. For example, a 100 ton condensing that is rated for a DX coil, will have a 100 ton capacity at a suction temperature of about 45-50 degrees. But if you run it as a chiller, and you want 44 degree water, your suction temperature will need to be 35-38 degrees. Which will DE-RATE your condensing unit in the neighborhood of 15%. So, just BE CAREFUL when designing a split system chiller!
Split system chiller with an air-cooled condenser
Not nearly as common as the other three types is the split system chiller with an outdoor air condenser. Remember, this means the compressors are located INDOORS with the chiller evaporator, and the outside unit is just the condenser coil and fans. So, why would you pick this option?
- No freeze protection required: same as the split system chiller with a condensing unit, the water stays inside, so no freeze protection is required. Boom-shaka-lacka
- Noise- now that the compressors are inside, noise could be a problem if the compressors are located in the wrong place. If you are designing a new system, be careful where you decide to locate the indoor portion of the chiller.
Disadvantages? Just like the split system condensing unit option, we have to deal with DX refrigerant piping. Although, instead of a suction and liquid line, we have a liquid and hot gas line. But we still have to think about everything that goes into managing the refrigeration. Also, this option starts to take up a decent amount of precious indoor space and can introduce some “mechanical room smells” such as refrigerant oil, contactor and motor starter arcing, etc.
Indoor water cooled chiller
We end our journey today with the water-cooled chiller. This chiller type has all the components indoors with the exception of a cooling tower or ground loops. So, why would you pick a water cooled chiller?
- No freeze protection required: and for the third chiller type in a row, this option does not require freeze protection on the evaporator side, nor the expense of glycol. However, you still need to think about possible freeze protection on the cooling tower side, like an immersion heater.
- Non reversing heat pump: At least one manufacture that we know of has this option. On a 4 pipe system, when you might have some zones calling for both heating and cooling, you can change the chiller to “heat pump” mode and control the chiller based on condenser leaving water temp. This hot condenser water can be sent to the hot water side to assist the boiler for heating. Very cool!
- Life expectancy: Of all the chillers discussed today, this option has the longest life expectancy since all of the components (less the cooling tower) are installed indoors.
- Disadvantages? Water cooled chillers are generally the most expensive upfront option, however, since the life expectancy is typically longer than the other options, this can be a smart investment. The other disadvantage is maintenance. If the condenser is connected to an “open-loop” evaporative cooling tower, there will be an increased amount of service that will be required due to mineral build-up and other foreign materials that find their way into the system.
Well, there you have it. Now you are armed and ready to go sell some chillers! What is your favorite kind of chiller to design or to work on? What did we miss?
- Glycol Chiller & AHU Derates – January 5, 2021
- No Data Tag, No Problem – July 28, 2020
- Design Tips for Sound Sensitive Applications – July 6, 2020