HVAC PRIME SOURCE, LLC

CHILLERS & DIRECT EXPANSION (DX) UNITS.

General
Chillers and DX units are the two main type of equipment used for air conditioning. Chillers provide cooling of the chilled
water which is then used in the air cooling coils for air conditioning, while DX units provide cooling by direct expansion of
the refrigerant in the air cooling coils. The air cooling coil in DX units and the chilled water heat exchanger in chillers are
also called an "Evaporator" since evaporations of the liquid refrigerant occurs in these components.

In general DX units are used for relatively small capacity systems and chillers are used for relatively large capacity system.
Typically a DX system is not used for systems larger than 100 ton capacity. Use the cooling load software given on the
"Hvac Software" link above to determine the required capacity. Further variations of applications are as follows.

Chillers are available in the following major categories, based on the type of compressor and size of the application.
Typically chillers are package units on one skid, with the water piping system being external to the unit. The package unit
includes the compressor, condenser, evaporator and associated components.

  • Centrifugal compressor chillers (used for medium to large capacity applications)
  • Screw compressor chillers (used for medium capacity applications)
  • Reciprocating compressor chillers (used for small to medium capacity applications)
  • Scroll compressor chillers (used for small to medium capacity applications)

DX Units are available in following major categories, based on the type of the compressor and packaged or split design:

  • Reciprocating or scroll compressor package units (condenser, compressor & evaporator are on the same skid).
  • Reciprocating or scroll compressor split systems (condenser, compressor, evaporator are located at separate
    locations - many systems have the condenser + compressor on the same skid as condensing unit, and the evaporator
    is located separately)

The condenser for both DX units and chillers can be air cooled or water cooled for relatively smaller sizes. For the larger
units the condenser is typically water cooled.

Diagrams (click on the links below)




Chiller & Dx Unit Sizing Rules –

  • Dx Unit Type – Reciprocating or Scroll
    Capacity range for package units – 0.5 to 150 Tons
    Capacity range for split units – 1 to 70 Tons
    Power – 0.9 to 1.3 KW / Ton
    Min Capacity Turndown capability – depends on number of cylinders

  • Chiller Type – Reciprocating
    Capacity range – 15 to 100 Tons
    Power – 0.9 to 1.3 KW / Ton
    Min Capacity Turndown capability – depends on number of cylinders
    Chiller Type – Scroll
    Capacity range – 10 to 150 Tons
    Power – 0.9 to 1.3 KW / Ton
    Min Capacity Turndown capability – depends on number of cylinders

  • Chiller Type – Rotary Screw
    Capacity range – 70 to 500 Ton
    Power – 1 to 1.5 KW / Ton
    Min Capacity Turndown capability – 25%

  • Chiller Type – Centrifugal
    Capacity range – 200 Ton to 2000 Ton
    Power – 0.5 to 0.85 KW / Ton
    Min Capacity Turndown capability – 10%

  • Chiller Type – Absorption
    Capacity range – 100 Ton to 2000 Ton
    Heat – 12000 Btuh/Ton (gas/oil), 12000 – 18000 Btuh/Ton (steam/hot water).
    Min Capacity Turndown capability – 10%