In this article, we take a look at centrifugal chillers and the fundamentals of how they operate.
Since 1902, air conditioning has made life inside more comfortable. There are few modern commercial buildings lacking air conditioning in the U.S. The modern air conditioning system is what makes it possible to sit through a movie during the summer in comfort or produce chocolate truffles in 100F weather.
Comfort comes at a cost, though.
Commercial HVAC systems use 19% of the total U.S.energy. 39% of a commercial building’s energy consumption is dedicated to air conditioning and heating. Keeping air conditioning system components like your centrifugal chillers in tiptop shape for the highest efficiency, is the challenge for many businesses.
Read on to learn more.
Centrifugal Chiller Basics
A high-performance commercial HVAC system uses some sort of chiller to carry heat out of the interior circulating air. In some areas, water or air alone is sufficient to remove excess heat. Most HVAC systems depend on some sort of compressor system to move a heat-absorbing refrigerant around a coil.
A centrifugal chiller uses the vapor compression cycle to chill water. It throws off the heat collected from the chilled water plus the heat from the compressor to a water loop. The water loop is cooled by a cooling tower.
Centrifugal chillers are popular because they have relatively few moving parts. They are easy to maintain and long-lived. Centrifugal chillers provide high cooling capacity with a small footprint.
How Do Centrifugal Chillers Works?
There are four basic components of the refrigeration cycle.
An evaporator in a centrifugal water-cooled chiller is the heat exchanger that removes heat from the entering chilled water. A shell and tube heat exchanger is the most common configuration.
The heat changes the refrigerant from a liquid to a gas. A flooded evaporator is an energy-efficient choice. Chilled water circulates in the tubes and refrigerant completely submerges the tubes in the shell.
A centrifugal compressor converts rotational kinetic energy to the dynamic energy of fluid flow. Refrigerant enters the pump impeller and is accelerated, flowing radially outward, then exits. A frictionless centrifugal compressor uses magnetic bearing technology and a DC (direct current) motor drive.
The process raises the pressure of the refrigerant by converting kinetic energy into pressure and heat.
Similar to an evaporator, a condenser is also typically a shell and tube heat exchanger. The condenser removes heat from the refrigerant gas. The pressurized refrigerant condenses to a liquid.
Heat raises the temperature of circulating condenser water The condenser water then carries the heat away to the cooling tower where the excess heat is ejected to the atmosphere.
After the refrigerant condenses to a liquid, it passes through a device to reduce pressure. It can be a simple orifice plate or an electronic modulating valve.
Keep Your Chiller in Top Condition
A chiller is one of the key components of your HVAC system. A regular program of maintenance is the way to avoid system downtime.
Training workers in proper operations and maintenance is key. Enforcing routines is the most successful approach. Out of compliance operations are often unnoticed until it is too late. Regular safety and operations training is the best way to protect an HVAC system.
Optimize building loads by using more than one chiller. Use the most efficient chiller first. Increase the supplied chilled water temperature and establish a reset schedule to change the water temperature as the ambient air temperature changes. On a centrifugal chiller, increasing the temperature of chilled water supply by around 2°F will reduce chiller energy use by up to 5%.
Decrease the condenser water temperature. A temperature reduction of around 3°F in the cooling tower water returned to the condenser reduces energy consumption by nearly 3%.
The setpoint for water leaving the cooling tower should be as low as the manufacturer will allow for water entering the condenser.
Maintain a daily log to identify any concerns.
Air trapped in the refrigerant loop increases compressor exit pressure and increases the work required from the compressor. Modern chillers run-time meters and automatic air purgers. Regular tracking of run time shows if a leak permits air to enter the system.
If your system has a water-side economizer, use it during the cold season. Condenser water circulates through the cooling tower to push heat into the atmosphere. The water is cooled sufficiently to meet the cooling loads.
For peak chiller efficiency, check the refrigerant level and temperature readings. Compare them to the manufacturer’s operational recommendations. Correct anomalies promptly.
Perform Regular Maintenance
An annual inspection by a professional keeps your HVAC in its best condition. Look for a professional with expertise with your type of system. More frequent inspections by on-site personnel supplements professional service.
- Check chilled water reset settings and function
- Check and clean evaporator and condenser tubes for sediment or corrosion (at least annually)
- Verify motor load limit
- Conduct vibration analysis of compressor motor and assembly
- Check all alignments to specifications.
- Check all seals.
- Lubricate where necessary.
- Analyze compressor oil and filter.
- Check oil pump and seals
- Check oil heater and thermostat
- Check all strainers and valves, etc
- Check electrical connections
- Check refrigerant condition and add if needed
In areas where hard water is a problem, water treatment is a must. Without intervention, scale, and sediment build-up and reduce efficiency. At worst, the extra work can burn out your pumps and motors entirely.
Call a Professional You Can Trust
B.I.M.S., Inc. (BHA) is a Dallas-based company. It serves the greater Texas area. They specialize in HVAC, indoor air quality, and refrigeration for industrial, commercial, and residential customers.
Regular preventive maintenance helps maintain operational time. A combination of good operational practice and maintenance limits downtime. An annual or more often inspection prevents damage.
Need troubleshooting help with your centrifugal chiller? Can’t decide if it needs repairs or a full replacement? Give us a call today for a consultation. For urgent repair requests, telephone our 24-hour staffed emergency helpline.