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Psychrometrics & Coil Load, Lecture notes of Refrigeration and Air Conditioning

AMET University Refrigeration and Air Conditioning

energy to/from the airstream in an airhandling system. Heat Transfer Media ???? Hydronic Fluid (Water) ???? Steam ???? Direct Expansion Important Coil Load Concepts ???? Apparatus Dew Point ???? Bypass Factor

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2019/2020

Uploaded on 07/09/2020

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ME 425 - Psychrometrics & Coil Load Calculation

ME 425

Psychrometrics & Coil Load

Keith E. Elder, P.E.

Coils

Coils are the main devices for transferring

energy to/from the airstream in an air-

handling system.

Heat Transfer Media

Hydronic Fluid (Water)

Steam

Direct Expansion

Important Coil Load Concepts

Apparatus Dew Point

Bypass Factor

Discover Lecture notes of Refrigeration and Air Conditioning AMET University

Partial preview of the text

Download Psychrometrics & Coil Load and more Lecture notes Refrigeration and Air Conditioning in PDF only on Docsity!

ME 425

Psychrometrics & Coil Load

Keith E. Elder, P.E.

Coils

Coils are the main devices for transferring

energy to/from the airstream in an air-

handling system.

Heat Transfer Media

Hydronic Fluid (Water)

Steam

Direct Expansion

Important Coil Load Concepts

Apparatus Dew Point

Bypass Factor

The Psychrometric Chart

Dry Bulb Temperature

Apparatus Dew Point

Relationship of ADP to Supply Air and

Chilled Water temperatures

Chilled water

Supply Air

t (^) ewb

t (^) lw

t (^) lew

Metal Surface Temp.

Surface Area

Temp

ADP

t (^) lwb

8-Row Coil

80 fpf /2 fps/44 EWT / WTR = 10

Coil Bypass

Apparatus Dew Point

An ADP is essential to any cooling/

dehumidifying process. The chart below

shows an impossible process because

there is no ADP

Coil Entering Air

Dry Bulb Temperature

Coil Leaving Air

Bypass Factor

Some of the air flowing through the coil

impinges on the water tubes or the fins and is

cooled to the ADP. Other air passes through

unchanged.

The percentage of air that passes through the

coil unchanged is called the bypass factor.

Coil

Entering

Air

Fin

Coil Selection

Determine Outside Air Requirements Using

ASHRAE Standard 62

Offices 20 CFM per person

Schools 15 CFM per person

Bars 30 CFM per person

Smoking Lounges 60 CFM per person

Corridors 0.05 CFM/ft

Plot Entering/Leaving Conditions

Coil

Entering

Air Apparatus

Dew Point

Dry Bulb Temperature

Outside Air

Room Air

Mixed Air

Coil

Leaving

Air

Define Process in Complete Cycle

Coil

Entering

Air Apparatus

Dew Point

Dry Bulb Temperature

Outside Air

Room Air

Mixed Air

Coil

Leaving

Air

SHR

Determine Required Coil Capacity

Coil Capacity Requirement

Q coil

= 4.5 x CFM x ∆h

Dry Bulb Temperature

Entering

Air Enthalpy

Leaving

Air Enthalpy

∆ h

Coil Load Example

Plot Space Conditions of 75°F/50% RH

Find the intersection of the SHR line

with space temperature and supply air

temperature

55°F

Dry Bulb Temperature

Room Air SHR=0.70 75°F / 50% RH

Supply Air Temperature

Coil Load Example

Plot Outdoor Conditions of 85°F/ 70°F WB

Locate Mixed Air Condition (25% OA)

Account for Fan ∆t

55°F

Dry Bulb Temperature

Room Air Design SHR=0.70 75°F / 50% RH

Supply Air Temperature

Outside Air 85°F / 70°F WB

53°F

∆t (^) fan

Mixed Air

Coil Load Example

Determine enthalpy for coil entering and

leaving conditions

Dry Bulb Temperature

Room Air Design SHR=0.70 75°F / 50% RH

Outside Air 85°F / 70°F WB

Mixed Air

h (^) LA = 20..5 Btu/lb

hEA = 29.8 Btu/lb

Coil Load Example

q

coil

= 4.5 x CFM x ∆h

= 4.5 x 1400 x (29.8 - 20.5)

= 58,590 Btu/hr

Dry Bulb Temperature

Room Air Design SHR=0.70 75°F / 50% RH

Outside Air 85°F / 70°F WB

Mixed Air

h (^) LA = 20..5 Btu/lb

hEA = 29.8 Btu/lb

Psychrometrics & Coil Load, Lecture notes of Refrigeration and Air Conditioning

Related documents

Partial preview of the text

Download Psychrometrics & Coil Load and more Lecture notes Refrigeration and Air Conditioning in PDF only on Docsity!

ME 425

Psychrometrics & Coil Load

Keith E. Elder, P.E.

Coils

Coils are the main devices for transferring

energy to/from the airstream in an air-

handling system.

Heat Transfer Media

 Hydronic Fluid (Water)

 Steam

 Direct Expansion

Important Coil Load Concepts

 Apparatus Dew Point

 Bypass Factor

The Psychrometric Chart

Apparatus Dew Point

Relationship of ADP to Supply Air and

Chilled Water temperatures

8-Row Coil

80 fpf /2 fps/44 EWT / WTR = 10

Coil Bypass

Apparatus Dew Point

An ADP is essential to any cooling/

dehumidifying process. The chart below

shows an impossible process because

there is no ADP

Bypass Factor

Some of the air flowing through the coil

impinges on the water tubes or the fins and is

cooled to the ADP. Other air passes through

unchanged.

The percentage of air that passes through the

coil unchanged is called the bypass factor.

Coil

Entering

Air

Fin

Coil Selection

Determine Outside Air Requirements Using

ASHRAE Standard 62

Offices 20 CFM per person

Schools 15 CFM per person

Bars 30 CFM per person

Smoking Lounges 60 CFM per person

Corridors 0.05 CFM/ft

Plot Entering/Leaving Conditions

SHR

Entering

Air Enthalpy

Leaving

Air Enthalpy

∆ h

Coil Load Example

Plot Space Conditions of 75°F/50% RH

Find the intersection of the SHR line

with space temperature and supply air

temperature

55°F

Coil Load Example

Plot Outdoor Conditions of 85°F/ 70°F WB

Locate Mixed Air Condition (25% OA)

Account for Fan ∆t

55°F

53°F

Coil Load Example

Determine enthalpy for coil entering and

leaving conditions

Coil Load Example

q

coil

= 4.5 x CFM x ∆h

= 4.5 x 1400 x (29.8 - 20.5)

= 58,590 Btu/hr

Unitary Equipment

Homework

Read 05F6.14-6.

Hydronic Fluid (Water)

Steam

Direct Expansion

Apparatus Dew Point

Bypass Factor

Indoor 76

Load (Btu/h) 100,000 Sensible - 40,000 Latent

Supply air 55

Fan Total Pressure = 3 in w.c.

Fan Efficiency = 60%

Outside air = 50% of total supply