heat exchangers, general.pdf

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Heat exchangers (coils) are designed mainly for theheating and cooling of air and other gases.

Typical heating mediums used in coils include hotwater, oil, liquid from industrial processes or steam;typical cooling mediums are cold water, evaporativerefrigerant, oil or other types of liquids.

The coils are available in versions for e.g.

installation in the ducting or in air handling units,different materials and fin pitches, and in differenttightness classes on the air side.

In ordinary applications, design charts for thevarious types of coil are used for sizing. If demandsare made on high sizing accuracy, ABB Coiltech hasdeveloped a computer programme for this purpose.

The heat exchangers are produced as standard insizes up to 8 × 2.4 m and for air flows up to 96 m 3/s.They are designed for horizontal or vertical air flow.



Heat exchangers, generalPage 7

Sizing

Use the appropriate sizing chart for each type of coil. Thecharts enable the size to be determined quickly with suf-ficient accuracy for practical purposes. A computer pro-gramme is available for simple and optimum coil sizing.

If computer-aided sizing is required, get in touch withour nearest sales office.

Normal velocities for coils.

Coils for evaporative refrigerant – output stages

Coils used for evaporative refrigerants can be suppliedwith the total output broken down into two or morestages (depending on the height of the coil).

Coils with 2 output stages are normally connected sothat every other loop belongs to output stage 1, and theintervening loops belong to output stage 2. This is knownas interlace connection.

1.

1.

2.

2.

Air flow

Expansion valve (not included)

Coils with 3 or more output stages are normally split upvertically.

1.

1.

2.

3.

2.

3.

Airflow

Expansion valve (not included)

Cooling coil, m/s Heating coil, m/sAir velocity 2 – 31) 2 – 5Water velocity 0,22) – 23) 0,2 2) – 1,53)

1) A droplet eliminator should be fittedif the air velocity is above 3 m/s.

2) Min. water velocity for preventing

venting problems and laminar flow.

3) Max. water velocity due to therisk of erosion. For coils withsteel tube loops, the water vel-

ocity should not exceed 3 m/s.

Quality

Accuracy and precision are important ingredients in themanufacture of our coils.

To ensure the high quality and output of our coils, weemploy a documented quality system which conforms tothe provisions of SS-EN ISO 9001:1994.

COILS FOR EVAPORATIVE REFRIGERANT – SIZING – QUALITY



Heat exchangers, generalPage 9

FORMULAS

AIR

Heating coils

Output: P = q (m 3 /s) · ∆t (°C) · 1,2 (kW)

Air flow: q = P(kW) (m3 /s)∆t (°C) · 1,2

Temp. differential: ∆t = P(kW) (°C)q (m3 /s) · 1,2

Efficiency: η = tu – ti

tri – ti

Cooling coils

Output: P = q (m 3 /s) · ∆i (kJ/kg) · 1,2 (kW)

Air flow: q = P(kW) (m3 /s)∆i (kJ/kg) · 1,2

Enthalpy differential: ∆i = P(kW) (kJ/kg)q (m3 /s) · 1,2

Output required: P = q (m3 /s) · ∆p (Pa) (kW)∼0,65 ( η ) · 1000

Air mixture

Mixing temperature:

t =q1 (m3 /s) · t 1 (°C) + q 2 (m3 /s) · t 2 (°C)

°Cqtot

WATER

Output: P = q r (l/s) · ∆tr (°C) · 4,2 (kW)

Water flow: q r = P(kW) (l/s)∆tr (°C) · 4,2

Temp. differential: ∆tr = P(kW) (°C)qr (l/s) · 4,2

Power required, pump: P =qr (l/s) · ∆pr (kPa)

(kW)∼0,75 ( η ) · 1000

HEAT RECOVERY

Temperature efficiency: η t =t2 – t1t3 – t1

Optimum brine flow: q r ≈q1 (m3 /s) + q 2 (m3 /s)

(l/s)2 · 3

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