Chiller: A machine that removes heat from a liquid via a vapor-compression or absorption refrigeration cycle. They come in several different mechanical arrangements: reciprocating, rotary-screw, and centrifugal, and with unlimited combinations of features, capacities, and efficiencies.
Things to Consider: Cooling load size, Total required chiller capacity (ASHRAE HVAC Systems and Equipment – 2004 stated: “The practice of adding 10 to 20% to load estimates is unnecessary because of the availability of accurate load estimating methods…”), Equipment price should include starters, vibration mounts, condenser, water pump, tower, and piping; Installation cost (factory-packaged machines less expensive to install and are more compact than field assembled); Energy cost (use estimated load schedule and part-load power consumption curves from manufacturer to estimate annual energy cost); Water cost should include acquisition, treatment, tower blowdown, and overflow water; Maintenance cost (get competitive bids from contractors); Insurance and taxes, Life expectancy of equipment; Standby arrangement; Relationship of heating to cooling loads; Effect of package selection on sizing; Types of peripheral equipment; Type of chiller with choices of screw, reciprocating, scroll, centrifugal; Refrigerant type; Controls and sensors; Safety controls include High condenser pressure, Low refrigerant pressure or temperature, High lubricant temperature, High motor temperature, Motor overload, Low lubricant sump temperature, Low lubricant pressure, Chilled-liquid flow interlock, Condenser water flow interlock, Freeze protection, Relief valves (ASHRAE Standard 15); Warranty.
Cooling Towers. These towers remove low grade heat from cooling water. Hot water from heat exchangers is sent to the cooling tower. Cooling towers fall into two categories: natural draft and mechanical draft. Natural draft towers use large concrete chimneys and are generally used by utility power stations. Mechanical draft towers use large fans to force air through circulated water. The water falls downward over fill surfaces which increases contact time between the water and the air, maximizing heat transfer.
Things to Consider: Design conditions include: Thermal capability defined by entering and leaving water temperatures, Entering air wet-bulb or entering air wet-bulb and dry-bulb temperatures, Water flow rate; Types: Direct-contact or open cooling tower, Indirect-contact or closed circuit cooling tower; Materials of construction includes Wood, Metal, Plastics, Graphite Composites, Concrete/Masonry/Tile; Selection considerations are: height, length, width, airflow, fan/pump energy consumption, materials, water quality; Cost of interface with other subsystems needs consideration, taking into account: basin grillage and value of space occupied, pumps and prime movers, electrical wiring to pump and fan motors, electrical controls and switchgear, piping to and from the tower, tower basin, sump screens, overflow piping, makeup lines,shutoff and control valves, access ladders and walkways, fire protection sprinkler system; Safety features and codes; Building codes; Structural design and rigidity; Effects of corrosion, scale, and deterioration on service life; Availability of spare parts; Experience and reliability of manufacturers; Independent certification of thermal ratings; Operating flexibility for economical operation at varying loads or during seasonal changes; Equipment vibration; Sound levels; Acoustical attenuation; Compatibility with architectural design; Siting; Piping; Capacity control; Water-side economizer; Indirect free cooling, Direct free cooling; Winter operation; Drift of water droplets onto adjacent properties; Fogging; Maintenance schedule; Inspections; Water Treatment; Warranty.