Water-cooled shell-and-tube refrigerant condenser for chillers and refrigeration plants

01

105 °F condensing with 85 to 95 °F water: what an AHRI 450 rating fixes

AHRI Standard 450-2007 covers testing and rating of the total heat rejection and water pressure drop of remote water-cooled refrigerant condensers, with tests to ASHRAE Standard 22. A published Standard Rating must give at least one of four rating conditions and be based on initially clean tubes, with water-side and refrigerant-side fouling factors taken as zero. [1]

Editorial calculation: in condition 2 the water warms 10 °F (5.6 K) and leaves 10 °F (5.6 K) below the condensing temperature; in condition 1 it warms 20 °F (11.1 K) with the same 10 °F leaving approach. A rating quoted at one condition cannot be compared directly with one quoted at another.

Fouled ratings are calculated, not tested: the standard takes the clean-tube overall coefficient Uc from test and adds the specified fouling factor to 1/Uc, with separate equations for fouling inside or outside the tubes. To comply, measured heat rejection must be at least 95% of the published rating and measured water pressure drop no more than 110% of it. [1]

AHRI 450 also asks makers to publish maximum and minimum recommended clean-water flow rates, design pressures for both sides, connection sizes, operating weight with refrigerant and water, and maximum refrigerant storage capacity, defined as 80% of the refrigerant-side volume at saturated liquid density at 90 °F (32.2 °C). [1]

Give the supplier the refrigerant, total heat rejection (compressor duty plus refrigeration capacity), saturated condensing temperature, entering and leaving water temperatures or water flow, the water-side fouling allowance you want included, and the allowed water pressure drop.

02

Refrigerant shell at 30 or 45 barg, water tubes at 10 or 16 barg: two pressure ratings on one vessel

Bitzer's CXP condensers for HFC refrigerants list a maximum allowable pressure (PS) of 30 barg on the shell (refrigerant) side in the standard version and 45 barg in the high-pressure version, against 10 and 16 barg on the tube (water) side, all for −10 to 120 °C, with PED (CE) approval. [2]

Editorial calculation: Bitzer's test pressures are 1.45 times PS on the shell side (43.6 ÷ 30, 65.4 ÷ 45) and 1.54 times on the tube side (15.4 ÷ 10, 24.6 ÷ 16). [2]

Carrier's 90C02 seawater condensers are built on the refrigerant side to ASME Section VIII Division 1 and stamped, dual-rated for 450 psi at 150 °F or 305 psi at 250 °F, with the water side designed for 150 psi at 150 °F; the shell side is tested at 1.1 times and the tube side at 1.3 times design pressure. [3] Editorial calculation: 450 psi ≈ 31.0 bar, 305 psi ≈ 21.0 bar and 150 psi ≈ 10.3 bar.

Editorial note: the refrigerant-side rating has to cover the highest condensing pressure the plant can reach, including warm water or a fouled bundle, for the refrigerant actually charged; the water-side rating has to cover pump shut-off head plus static head of the tower or sea-water circuit. AHRI 450 requires both design pressures and the refrigerant designation on the nameplate. [1]

03

Fresh water or seawater: copper or CuNi 90-10 tubes, water passes and acting as the receiver

In Bitzer's CXP the refrigerant condenses on the outside of the tubes and water flows inside. For normal water it uses copper tubes in a carbon steel tube sheet; the seawater CXPM version uses CuNi 90-10 tubes in a 316L stainless steel tube sheet with carbon steel anodes, both with polymeric tube supports and a carbon steel shell. A modular front water box gives two or four water passes. [2]

Bitzer lists CXP condensing capacities of 15 to 150 kW in shell diameters of 114, 141 and 168 mm and total lengths of 973 to 1,906 mm, using enhanced-surface tubes and quoted for temperature approaches as low as 1.5 K, for refrigerants including R404A, R407C, R134a and R410A. [2]

Carrier's 90C02 marine condensers cover 18 to 1,160 nominal kW (5 to 330 nominal tons) with 90/10 cupro-nickel enhanced tubes roller-expanded into grooved 90/10 cupro-nickel tube sheets, cast bronze heads for seawater, and steel shells to ASME specification. They include dual liquid refrigerant outlets to keep a liquid seal under pitch and roll and can hold the refrigerant charge when the system is off, removing the need for a separate receiver. [3]

Editorial note: if the condenser is also to serve as the receiver, check its storage capacity on the AHRI 450 basis (80% of refrigerant-side volume) against the full system charge. [1]

State the water source (cooling tower, city, river or sea water), its quality and velocity limits, the number of water passes, tube and tube-sheet materials, whether anodes are needed, and whether the condenser must hold the pump-down charge.

04

Send the refrigerant duty, water circuit and pressure ratings together

Paste it into your enquiry below or into an email to a maker, then replace every bracket.

Refrigerant: [designation; total heat rejection kW; condensing temperature; entering vapour temperature; subcooling]
Water: [source; entering/leaving °C or flow; fouling allowance; max pressure drop; passes]
Pressure: [refrigerant-side PS; water-side PS; code PED or ASME VIII-1]
Materials: [tubes copper or CuNi 90-10; tube sheet; heads; anodes]
Receiver duty: [pump-down charge kg]
Rating: [AHRI 450 condition or application rating]
Dimensions: [length; shell diameter; connections]

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