HVAC Chiller

  HVAC CHILLER

1. Vapor Compression Chillers:

(1.) Reciprocating  (2.)Centrifugal  (3.)Screw (4.) Scroll

2. Vapor Absorption Chillers:

(1.) Direct Fired (2.)Indirect Fired (3.)Lithium Bromide water (4.)Ammonia Water
(5.)Single Effects (6.) Double Effects (7.)Single Stage (8.)Double Stage

Condensation On HVAC Chiller:

1. Air-Cooled Condensation 2. Water Cooled Condensation 3. Evaporative Cooled Condensation

1.Vapor Compression Chiller:

Vapour compression chillers use an electrically driven mechanical compressor to force a refrigerant around the system. These are the most common types of chillers. There are two subcategories for vapor compression chillers which are Water Cooled or Air Cooled Chiller and we’ll look at these shortly.

How to decide between air-cooled and water-cooled – Chiller types and application guide:

Water Cooled Chiller:

• Water-cooled chillers are more efficient, especially for large cooling loads, they use the evaporation of water to dissipate heat which is less energy-intensive than blowing air across a hot surface like air-cooled chillers. Water also has a higher heat capacity than air so its inherently easier to remove the heat
• Water-cooled chillers can handle larger loads, for their floor space, compared to air-cooled.
• Water-cooled chillers generally last longer because they are inside the building so deteriorate much slower

Cons

• These use cooling towers and for this, you need access to a constant clean water supply. If the chiller is going to be installed in an area with water restrictions then you don’t want this type.
• Water-cooled chillers are located within the building and are very large machines, so depending on the compressor technology used, they can create a lot of noise and vibration inside the building which is why they are usually located in the basement.
• Water-cooled chillers cost more to install and maintain
• Water-cooled chillers take up space within the building, they need mechanical plant rooms, more risers, more pumps, cooling towers, and water treatment, this space therefore can’t be used for business purposes.

Air-cooled chillers.
Pros

• Air-cooled chillers cost less to install because they have less equipment.
• Air-cooled chillers require less space, they can sit on the roof and do not need a mechanical room. This means more space within the building for business purposes.
• Air-cooled chillers require less maintenance compared to water-cooled chillers, again because they have less equipment
• Air-cooled chiller systems are much simpler design and do not need another set of pumps for the condenser

Cons

• Air-cooled chillers sit outside the building, their fans and compressors will create noise which the surrounding areas might be able to hear, although some measures can be implemented to reduce this
• Air-cooled chillers typically do not have as long service life as water-cooled chillers because they are exposed to the sun, rain, frost, snow, and wind which deteriorate the materials.
• Air-cooled chillers can suffer from damage, blockages, and re-circulation issues.

Unfortunately, many building owners want the cheapest upfront option, but this is a bad idea because for a little extra they could have bought a more efficient chiller which will be cheaper to operate especially as chillers can last for around 15 – 25+ years in operation, so it will have paid for itself multiple times and would have resulted in reduced environmental emissions.

Reciprocating chillers:

• Air or water-cooled chillers – old technology, less common now
• Used in small to medium cooling loads – common in simple low-cost refrigerators
• Typically available in 50 – 500 TR, 170 – 1,700 kW
• COP of 4.2 to 5.5
• Use a piston and chamber to compress the refrigerant
• Capacity control through compressor staging or cylinder unloading and speed control

Centrifugal chillers

• Water-cooled chillers
• used in medium to large cooling loads
• Typically, available in 150 – 6,000 TR, 530 – 21,000 kW
• Water-cooled COP of between 5.8 to 7.1
• Typically use only one compressor sometimes two for exceptionally large capacity
• Work best at full loading, VFD can e fitted to improve part load
• Use one or two rotating impellers to compress the refrigerant and force it around the chiller
• Capacity control through speed control and vane guides

Screw chiller

• Air or water-cooled chillers
• Used in small to medium cooling loads
• Typically, 70 – 600 TR, 250 – 2,100 kW
• Air-cooled COP 2.9 – 4.15 Water-cooled COP: 4.7 – 6.07
• Typically, 1 compressor on water-cooled, 1 or 2 compressors on air-cooled
• Uses two interlocking rotating helical rotors to compress the refrigerant, capacity is controlled via speed control or slider

Scroll chiller:

• Air or water-cooled chillers
• Used in small to medium cooling loads
• Typically, available 40 – 400 TR, 140 – 1,400 kW
• Air-cooled COP 3.2 – 4.86 Water-cooled COP 4.45 – 6.2
• One or more compressors, fixed or variable speed, staged or speed controlled
• Use two spiral plates to compress the refrigerant, one fixed in place, one rotates.
• Capacity controlled via momentarily separating scrolls with solenoid valve and electronic modulation

Absorption chillers

Vapor absorption chillers will use a heat source to move the refrigerant around the system rather than using a mechanical compressor. The refrigerant in these chillers moves around between areas of different temperature and pressure.

• Use heat to drive the refrigeration process, usually steam or hot water
• Used in Medium to large buildings, Hospitals, Swimming centers, Heat Networks
• Typically, 70 – 1,400 TR, 250 – 4,900 kW
• COP of approx. 0.6 to 1.9
• No compressor, direct or indirect fired. Capacity controlled via the amount of heat entering
• The idea for using waste heat or cheap heat sometimes used to offset peak electricity costs
• Typically combined with mechanical chillers