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Diploma of HVAC & R EngineeringPresentation 2

How can we use psychrometrics?

Define dew point temperature.

Describe 3off process that can be shown on a psychrometric chart.

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Calculate the psychrometric performance of an air conditioning coil given operating HVACconditioning coil, given operating HVAC conditions.

Recommended reading, AIRAH Application Manual DA9 Air ConditioningLoad Estimating (Chapter 8)Load Estimating (Chapter 8) Honeywell - Automatic Control (SI Edition)

(Chapter 2)

After inspecting an operating Air Conditioner the following measurements have been takenfollowing measurements have been taken.

Coil Face Size - 980mm x 650mmVelocity of air over coil - 2.5m/sOutside Air - 200L/SOutside Air - 35°CDB 24°CWBOutside Air 35 CDB 24 CWBReturn Air - 23°CDB 50%RHSupply Air - 12°CDB 11°CWB

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1. Calculate the Volume Flow Rate of air through the coil.

2. Find the Mixed Air Dry Bulb temperature.3 d h3. Find the Apparatus Dew Point Temperature.4. Calculate the Bypass Factor.5. Measure / calculate the Total Heat, Sensible Heat &

Latent Heat removed by the coil.6. Calculate the Mass Flow Rate of air.7. Calculate the operating Refrigeration Capacity of

the coilthe coil.8. Calculate the Moisture Removal rate.9. How many litre’s of water would be removed from

the air in one hour if the machine operated with the same set of conditions?

Given:Coil Face Size 980mm x 650mmCoil Face Size - 980mm x 650mmVelocity of air over coil - 2.5m/s

Area = Length x WidthVolume = Area (A) x Velocity (U)

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When two or more air streams converge or mixed, the resultant temperature of the mixed air stream can be calculated.

MA = (T1 x Q1) + (T2 x Q2)Q3

T1 – Temperature 1st streamQ1 – Air quantity 1st streamT2 – Temperature 2nd streamQ2 - Air quantity 2nd streamQ3 - Air quantity 3rd stream

Extend a line from the Mixed Air through the Supply Air point t oug t e Supp y po tuntil it touches the saturation curve.

At the point the line touches the saturation curve is the ADPthe ADP

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The bypass factor represents the percentage of air the flows through the coil without being g gconditioned.

BF = Tleaving – TADPTentering – TADP

Coil Bypass factor Type of Application Example

0.30 - 0.50 High latent loads Residential

0.20 - 0.30 Typical comfort application with a low sensible heat factor

Retail shop or factory

0.10 - 0.20 Typical comfort condition Department Store or banks

0.05 - 0.10 Applications with high sensible loads

Office blocks, restaurants and factories

0.01 - 0.10 100% Outdoor air applications

Hospital operating rooms.

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Total heat absorbed is the amount of sensible and latent heat that is absorbed d hduring the process.

TH = hMA - hSA (kj/kg)

SH = hpoint - hSA (kj/kg)SH hpoint hSA (kj/kg)

LH = TH – SH (kj/kg)

Mass Flow Rate (kg/s)ass o ate ( g/s)

M = V (m3/s)v (kg/m3)

V = Volume Flow Rate (m3/s)v = Specific Volume (kg/m3)

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Q = M x THQ

Q = Capacity (kj/s or kW)M = Mass Flow Rate (kg/s)TH = Total Heat absorbed (kj/kg)

If we know the specific humidity of the air entering the coil and the specific humidity of the

l h l d h fl fair leaving the coil and the mass flow rate of air we can calculate the moisture the coil removes.

Mw = M (wEA – wLA)

Mw - Moisture Removal Rate (g/s)M M Fl R t (k / )M - Mass Flow Rate (kg/s)wEA - Specific Humidity (g/kg)wLA - Specific Humidity (g/kg)

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Item: Value:Volume Flow Rate (m3/s & L/s) 1.59m3/s & 1592.5L/sMixed Air Dry Bulb (°C) 24.51°CApparatus Dew Point (°C) 9 6°CApparatus Dew Point ( C) 9.6 CBypass Factor (%) 16.1%Total Heat (kJ) 16.97kJ/kgSensible Heat (kJ) 12.79kJ/kgLatent Heat (kJ) 4.18kJ/kgMass Flow Rate (kg/s) 1.85kg/sRefrigeration Capacity (kJ/s or kW) 31.42kWMoisture Removal rate (g/s & kg/s) 2.96g/s & 10.67kg/hr

Inspect and measure data of an operating air conditioner.

D t i th f ll iDetermine the following; Volume Flow Rate (m3/s & L/s) Mixed Air Dry Bulb (°C) Apparatus Dew Point (°C) Bypass Factor (%) Total Heat (kJ) Sensible Heat (kJ) Sensible Heat (kJ) Latent Heat (kJ) Mass Flow Rate (kg/s) Refrigeration Capacity (kJ/s or kW) Moisture Removal rate (g/s & kg/s)