How to Pipe Chillers in Parallel 

Two or more chillers may be installed in a parallel piping system to provide more capacity of a single chiller or redundancy and multi-staging of compressors. Normally the load on the chilled water system dictates the system capacity and the part load capacity of the process is the factor to determine the staging of the chillers on temperature. The thermostats can be set a few degrees apart. If one chiller cannot maintain the fluid temperature, the second chiller will stage on upon temperature rise and a third, etc.

The diagram below illustrates the concept of parallel piping of the chillers on a common header system. The main header must be sized for the total flow rate and good practices dictates a maximum flow rate of 7 Ft/sec.

When adding a chiller to an existing manifold system, also consider the ability of the pump to provide enough total flow and pressure to satisfy the process and the continuous flow through the chillers.  Nominal flow rate for commercial equipment of 2.5 GPM / on are normally a minimum with 70 to 100 ft. hd. (30 psi to 43 psi) capability. Contact American Chillers engineers for assistance.

Dry Cleaning Chiller Installation
Installing A Bypass Loop

Purpose:

1. To provide a continuously circulating water flow through the chiller coil, tank and piping system. This is necessary to maintain the reservoir at the cold temperature setting. The system should be balanced so that the flow through the bypass loop while maintaining sufficient flow to the process.
2. To establish the minimum operating pressure of the cooling water supply to the process machine. This is a result of setting the continuous flow at maximum. This also establishes a high-pressure supply to the process machine and a low pressure return to the chiller for good circulation through the process machine heat exchangers. The differential pressure between the supply and return should be a minimum of 20 psi.
3. To allow the chiller refrigeration to cycle on and off freely, and independently of external demands for flow and temperature.

Where To Put the Bypass:

The bypass valve must be located at the end of the line, with the process machine connections between the bypass and the pump.

The illustration below shows a modular chiller system with the process (dry cleaning) machine correctly connected to the piping between the pump and the bypass.

The pressure to the process machine (s) will be the same every inch in the line between the bypass and the pump. Two machines can be connected, and their supply pressure will be the same.

The picture shows the bypass before the process machine connections and the pressure will be lower to the machine when the bypass is open. The drop in pressure will increase as the bypass is opened and set for optimum flow to the chiller. The process machine heat exchangers very likely will starve for cooling as a result.

This photo clearly shows the wrong way to connect the bypass. The natural tendency of the operator when the process machine alarms due to lack of cold water is to close the bypass to force more pressure and flow to the process machine heat exchangers.

Starving the Chiller:

The process machine will get more pressure and flow as a result of closing the bypass – But what happens to the chiller?

The chiller will starve for flow causing the water temperature to be very cold coming out of the chiller but at a reduced flow that will cause the loop temperature to swing wildly between cold and hot! The purpose of the flowing loop has been defeated and the chiller cannot maintain the reservoir and loop temperature at an even temperature. The temperature fluctuations of the water supply can be 30 to 40 degrees or more.

Bypass Line Size:

The piping connections on the chiller are the correct size for the supply and return header lines based on sound engineering principles of flow, pressure drops, and fluid velocity. Reducing the line size from the recommended causes higher velocities, higher pressure drops, reduced supply pressure to the process machine, and fluctuations in the supply temperature.

WHY USE GLYCOL

A chiller will run without glycol as long as the fluid temperature in the system is above freezing. Glycol or other inhibitors are recommended for most process cooling applications even if the fluid temperature doesn’t reach temperatures near freezing to maintain fluid quality.

Which of glycol is best?
Inhibited Propylene Glycol is recommended. It works as an anti-freeze and contains rust inhibitors and other additives to keep your pump seals lubricated and fluids and chilled water system running in optimal condition. It is also deemed food and environmentally friendly.

NEVER USE AUTOMOTIVE OR RV ANIT-FREEZE IN CHILLERS. THEY BREAK DOWN AND WILL DAMAGE YOUR CHILLER AND DRY-CLEANING EQUIPMENT.

Glycol will reduce chiller capacity if the evaporator isn’t size for it. Our dry-cleaning chillers are sized for 40% PPG / 60% Water.

Questions about what glycol concentration and/or type to purchase? Contact and American Chillers sales engineer for assistance.

Glycol Correction Factors

All Heat exchangers experience a capacity loss when the fluid is a higher specific gravity than water. Glycols are heavy, syrup like fluids at full concentration, and become thinner when mixed with water. However, the mixed solution of water-glycol will be thicker, heavier, than the water alone was. Thus, to achieve the same heat exchange inside the heat exchanger , requires more surface area or a larger heat exchanger.

American Chillers heat exchangers are engineered for full rated capacity with the use of 30% glycol solutions. Our heat exchangers start out with 30% more surface area capacity than the heat exchangers used by other manufacturers so you still have full capacity with 30% water-glycol solutions. If you are using glycol concentrations above 30%, consult factory prior to purchasing your chiller for chiller selection assistance.

Propylene Glycol

Ethylene Glycol

Glycol Capacities and Correction Tables

* At standard ARI 590 conditions: 54°F entering fluid temperature, 44°F leaving fluid temperature, 95°F ambient temperature, 0.0005 fouling

The charts, above, illustrate the differences between propylene based and ethylene based glycol. Since we recommend propylene based glycols because of their non-hazardous nature, we must be aware of the effects on the standard refrigeration heat exchangers and pumps.

A 40% solution of propylene glycol will reduce the chiller heat exchanger’s ability to chill by at least 7.2%. We know from experience, that some heat exchangers chilling abilities is reduced by 20%. This means the chiller with a 10 ton capacity for chilling water will have a capacity between 8 tons and 9.3 tons with 40% PG.

Most American Chillers have heat exchangers large enough to handle 30% PG without loss of capacity due to our “value-added” engineering practices. We can easily provide a chiller heat exchanger for even 50% PG at the customer request at time of order.