0977000389 DEWALT HVACR Professional Reference Master Edition

7/29/2019 0977000389 DEWALT HVACR Professional Reference Master Edition

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CHAPTER 1Formulas and Design Data

1-1

HEAT TRANSFER

This equation is used to determine the amount of

heat required to heat or cool a given amount of any

specific substance.

BTU Specific heat lbs. T

BTU British Thermal Unit

T Temperature Difference (F)

The specific heat of a substance is the amount of

heat in BTU that it takes to change the temperature

of one pound of that substance by one degree

Fahrenheit.

For example, the specific heat of water is 1.0 BTU/

lb.F. Therefore, to raise the temperature of 1 pound

of water by 1 degree F takes 1 BTU. Specific heats

of other materials vary.

BTU/h 1.08 CFM T

BTU/h

BTU per hour, a quantity of heatCFM Cubic feet per minute of air flow

(for sensible heat only)

HEATING AND COOLING CAPACITY


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1-2

BTU/h 4.5 CFM H

H Difference between return & supply air, in

BTU/lb.

(all systems, including both sensible & latent heats)

Sensible heat 1.08 CFM T

Sensible heat 1.1 CFM T

Latent heat 0.68 CFM WGR.Latent heat 4840 CFM WLB.

Total heat 4.5 CFM H

Total heat HS HL

Total heat UA T

HS Sensible heat (BTU/h)

HL Latent heat (BTU/h)

HT Total heat (BTU/h)

T Temperature difference (F)

WGR. Humidity ratio difference (Gr.H2O/Lb.DA)

WLB. Humidity ratio difference (Lb.H2O/Lb.DA)

H Enthalpy difference (BTU/Lb.DA)

CFM Air flow rate (cubic feet per minute)

U U-value (BTU/h/sq. ft./F)A Area (sq. ft.)

SHR Sensible heat ratio

HFG Latent heat of vaporization at design pressure

SHR HS

HT

HS

HS HL

COOLING AND HEATING

TOTAL HEAT CAPACITY


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1-3

R-VALUES/U-VALUES

R R-value (hr. sq. ft. F/BTU)

U U-value (BTU/h sq. ft. F)

C Conductance (BTU/h sq. ft.F)

K Conductivity (BTU in./hr. sq. ft. F)aR Sum of the individual R-values

Blower RPM Motor pulley diameter RPM of motor

Diameter of blower pulley

TBTU/h

1.08 CFM

CFM Watts 3.42 (BTU/Watt)

1.08 T

CFM

BTU/h

1.08 T

U1

gR

R 1

C

1

K Thickness

OBTAINING CFM FROM CAPACITY

CFM OF AN ELECTRIC FURNACE

CHANGE IN TEMPERATURE

OBTAINING RPM OF EXISTING BLOWER


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1-4

C Distance, center to center, between pulleys

D Larger pulley diameter

d Smaller pulley diameter

Compression ratio Absolute head pressure in psiaAbsolute suction pressure in psia

Diameter of the driver Diameter of driven RPM

RPM of driver

Diameter of driven Diameter of driver RPM

RPM of driven

RPM of driver Diameter of driven

RPMDiameter of driver

RPM of driven Diameter of driver RPM

Diameter of driven

Belt length 2 C 1.57 D d(D d)2

(4 C)

CHANGE IN PULLEY, NEW BELT LENGTH

PULLEY LAWS

COMPRESSION RATIO


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1-5

GPM Gallons per minute of flow


H 500 GPM T

H Total heat (BTU/h)

GPM Water flow rate (gallons per minute)

T Temperature difference (F)

Tons Air conditioning load (tons)

GPMEVAP. Evaporator water flow rate(gallons per minute)

GPMCOND. Condenser water flow rate

(gallons per minute)

GPMCOND. Tons 30

T

GPMEVAP. Tons 24

T

Chiller tons GPM Tchiller water

30

CONDENSER TONNAGE

CHILLER TONNAGE

WATER SYSTEM

GPM Gallons per minute of flow


Condenser tons GPM 1.25 Tconditioned water

24


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COOLING TOWERS AND HEAT EXCHANGERS

EWT Entering water temperature (F)

LWT Leaving water temperature (F)

AWBAmbient wet bulb temperature (design WB,F)

CT Cooling Tower

HE Heat Exchange

HS Hot side

CS Cold side

RANGE EWT LWT

APPROACHHE EWTHS LWTCS

APPROACHCT LWT AWB

NPSHAVAIL Net positive suction available at pump (ft.)NPSHREQD Net positive suction required at pump (ft.)

HA Pressure at liquid surface (ft.34 ft. for water

at atmospheric pressure)

HS Height of liquid surface above () or below

() pump (ft.)

HF Friction loss between pump and source (ft.)

HVP Absolute pressure of water vapor at liquid

temperature

NPSHAVAIL HA; HS HF HVP

NPSHAVAIL NPSHREQD

PUMP NET POSITIVE SUCTION HEAD (NPSH)

1-6


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GPM Gallons per minute

RPM Revolutions per minute

HD Feet of water

BHP Break horsepower

Pump size Constant

Water density Constant

BHP2

BHP1 a GPM2

GPM1b 3 a RPM2

RPM1b 3 a HD2

HD1b1.5

HD2

HD1 c GPM2

GPM1d 2 c RPM2

RPM1d 2

GPM2

GPM1

RPM2

RPM1

PUMP LAWS

1-7


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1-8

PUMP LAWS (cont.)

SP.GR. Specific gravity of liquid withrespect to water

SP.GR. (water) 1.0

PUMPEFF 6080%

M/DEFF 8595%

M/D Motor/drive

MHP Motor horsepower

P Pressure in psi

VH Velocity head in ft.

V Velocity in ft./sec.

g Acceleration due to gravity

(32.16 ft./sec.2)

HD P 2.31

SP.GR.

VH V2

2g

MHP BHP

M/DEFF

BHP GPM HD SP.GR.

3960 PUMPEFF


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1-9

REFRIGERATIO

NFORMULAS

Enthalpyof

Entha

lpyof

Netrefr

igerating

vaporleaving

liquid

entering

effect(B

TU/lb.)

evaporator(BTU/lb.)

evapo

rator(BTU/lb.)

Compre

ssionwork

Heatofcompre

ssion

Refrigerantcirculated

(BTUm

in.)

(BTU/lb.)

(lb./m

in.)

Compre

ssionHP

Compressionw

ork(BTU/min.)/42

.4

Compre

ssionHP

Capacity(BTU/m

in.)/42.4

COP

Compre

ssionHP

4.715/COP

(perton

)


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1-10

Power(Watts)

CompressionHPperton

745.7

COP

Netrefrigeratingeffect(BTU/

lb.)

Heatofco

mpression(BTU/lb.)

REFRIGERATIONF

ORMULAS(cont.)

C

apacity(BTU/min.)

Refrigerantcirculated

N

etrefrigerating

(lb./min.)

e

ffect(BTU/lb.)

Compre

ssordisplacemen

t

(ft.3/min

.)

Enthalpyo

f

E

nthalpyof

Heatofcompression

vaporleaving

v

aporentering

(B

TU/lb.)

compresso

r(BTU/lb.)

c

ompressor(BTU/lb.)

(BTU/min.)

Netrefrigeratingeffect(BTU/lb.)

V

olumeofgasente

ring

c

ompressor(ft.3/lb.)

Capacity


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1-11

Volumetricefficien

cy

100

Compressionratio

R

efrigerantcirculat

ed,

lb.(min.)(ton)

42.4

heatflow,BTU/(min.)(hp);200

BTU/(min

.)(ton);COP

coefficientofperformance

200

Refrigeratingeffect

Headpressure,psia(absolute)

Suctionpressure,psia(abso

lute)

b

Actualweightofre

frigerant

Theoreticalweightofrefrigerant

a

REFRIGERATIONF

ORMULAS(cont.)


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1-12

AIR FLOW

CFM FPM area (ft.2)

FPM CFM/area (ft.2)

Area CFM/FPM

Q

A V

CFM

ft.2 FPM

AIR CHANGE RATE

AC/HR Air change rate per hour

CFM Air flow rate (cubic feet per minute)VOLUME Space volume (cubic feet)

SA RA OA RA EA RFA

If minimum OA (ventilation air) is greater than EA,OA EA RFA

If EA is greater than minimum OA (ventilation air),

OA EA RFA 0

For economizer cycle: OASAEARFA RA0

SA Supply air

RA Return airOA Outside air

EA Exhaust air

RFA Relief air

CFM AC/HR VOLUME

60

AC/HR

CFM 60

VOLUME

AIR BALANCE EQUATIONS


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1-13

CFM Cubic feet per minute


SP In. W.G.


Fan size Constant

Air density Constant

SP2 SP1 a RPM2RPM1

b 2

SP2

SP1 a CFM2

CFM1b 2 a RPM2

RPM1b 2

RPM2 RPM1 CFM

2CFM1

CFM2 CFM1 RPM2

RPM1

CFM2

CFM1

RPM2

RPM1

FAN LAWS


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1-14

CFM Cubic feet per minute


SP In. W.G.


Fan size Constant

Air density Constant

SP.GR. (air) 1.0

FANEFF 6585%

M/DEFF 8095%

M/D Motor/drive

MHP Motor horsepower

MHP BHP

M/DEFF

BHP CFM SP SP.GR.

6356 FANEFF

BHP2 BHP1 a RPM2RPM1

b 3BHP2

BHP1

aCFM2

CFM1 b

3

aRPM2

RPM1 b

3

aSP2

SP1 b

1.5

FAN LAWS (cont.)


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1-15

MIXED AIR TEMPERATURE

CFMSA Supply air (CFM)

CFMRA Return air (CFM)

CFMOA Outside air (CFM)

TMA Mixed air temperature (F)

TROOM Room design temperature (F)

TRA Return air temperature (F)

TOA Outside air temperature (F)

GPMAC COND Air conditioning condensate flow

(gallons/min.)

CFM Air flow rate (cu. ft./min.)

SpV Specific volume of air (cu. ft./lb.DA)

WLB. Specific humidity (lb.H2O/lb.DA)

WGR. Specific humidity (gr.H2O/lb.DA)

GPMACCOND CFM WGR.

SpV 8.33 7000

GPMACCOND CFM WLB.

SpV 8.33

TMA aTRA CFMRACFMSA

b aTOA CFMOACFMSA

b

TMA aTROOM CFMRACFM

SA

b aTOA CFMOACFM

SA

b

AIR CONDITIONING CONDENSATE


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1-16

condensation occurs)

T Temperature (F)

R R-value (hr. sq. ft. F/BTU)

U

U-value (BTUH sq. ft.F)

IA Inside airfilm

OA Design outside air temperature

DP Dew point

HS (0.244 Q T) (L 380)

HS Sensible heat gain (BTUH)

Q Steam flow (lb. steam/hr.)

T Steam temperature supply air temperature (F)

L Length of humidifier manifold (ft.)

(if TGLASS DPROOM

TGLASS TROOM cUGLASSUIA

(TROOM TOA) d

TGLASS TROOM c RIAR

GLASS

(TROOM TOA) dMOISTURE CONDENSATION ON GLASS

HUMIDIFIER SENSIBLE HEAT GAIN


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1-17

GRAINSREQD Grains of moisture required (gr.H2O/cu. ft.)

POUNDSREQD Pounds of moisture required (lb.H2O/ cu. ft.)

CFM Air flow rate (cu. ft./min.)

SpV Specific volume of air (cu. ft./lb.DA)

WGR. Specific humidity (gr.H2O/lb.DA)

WLB. Specific humidity (lb.H2O/lb.DA)

CFM POUNDSREQD 60

Lb. STM/hr. CFM GRAINSREQD 60

7000

POUNDSREQD aWGR.SpV

bROOM AIR

aWGR.SpV

bSUPPLY AIR

GRAINSREQD aWGR.SpV

bROOM AIR

aWGR.SpV

bSUPPLY AIR

HUMIDIFICATION


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1-18

VT Volume of expansion tank (gal.)

VS Volume of water in piping system (gal.)

T T2 T1 (F)

T1 Lower system temperature (F)

Heating water T1 4550F tempera-ture at fill condition

Chilled water T1 Supply water

temperature

Dual temperature T1 Chilled water supply

temperature

T2 Higher system temperature (F)

Heating water T2 Supply water

temperature

Chilled water T2 95F ambient

temperature (designweather data)

Dual temperature T2 Heating water

supply temperature

Diaphragm VT VS [(v2>v1) 1] 3T

1 (P1

>P2)

Open VT 2 5(VS [(v2>v1) 1]) 3T6

Closed VT VS [(v2>v1) 1 ] 3T

[(PA

>P1) (PA

>P2)]

EXPANSION TANKS


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1-19

PA Atmospheric pressure (14.7 psia)

P1 System fill pressure/minimum system pressure

(psia)

P2 System operating pressure/maximum operating

pressure (psia)

V1 SpV of H2O at T1 (cu. ft./lb.H2O)V2 SpV of H2O at T2 (cu. ft./lb.H2O)

Linear coefficient of expansion

6.5 106

9.5 106

System volume estimate:

12 gal./ton

35 gal./BHP

System fill pressure/minimum system pressureestimate:

To height of system add 5 to 10 psi

System operating pressure/maximum operating

pressure estimate:

150-lb. systems 45125 psi250-lb. systems 125225 psi

COPPER

STEEL

EXPANSION TANKS (cont.)


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1-20

EFFICIENCIES

EER Energy efficiency ratio

COP = Coefficient of Performance

or

Turndown ratio Maximum firing rate: Minimum firing

rate (5:1, etc.)

Overall thermal efficiency range 75%90%

Combustion efficiency range 85%95%

Combustion eff. BTU input BTU stack loss

BTU input 100%

Overall thermal eff. Gross BTU output

Gross BTU input 100%

COP BTU output

Input watts 3.413 (BTU per watt)

COP BTU output

BTU input

EER

3.413

EER BTU output

Watts input


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1-21

Unitof

Measure

Multiply

By

ToObtain

Symbol

Ductwork

CFM

0.0004719

cubicmeters/sec.

m3/s

airflow

FPM

0.00508

meters/sec.

m/s

FPM

0.508

centimeters/sec.

cm/s

FPS

0.3048

meters/sec.

m/s

MPH

0.447

meters/sec.

m/s

Ductwork

In.H2O

0.25

kilopascals

kPa

pressure

In.H2O

249(use250)

pascals

Pa

In.H2O/100

8.176

pascals(N/m2)

Pa

In.Hg

3.386

kilopascals(kN/m

2)

kPa

Ductwork

In.

25.4

millimeters

mm

length&

In.

2.54

centimeters

cm

area

In.

0.0254

meters

m

D

UCTWORKHVAC

CONVERSIONS


22/24

1-22

Unitof

Measure

Multiply

By

ToObtain

Symbol

Ductwork

In.2

6.452

centimeterssquared

cm2

length&

Ft.

0.3048

meters

m

area

Ft.2

0.0929

meterssquared

m2

Ft.3

0.02832

meterscubed

m3

Fan

CFM

0.4719

liters/sec.

l/s

duty

In.H2O

249(use250)

pascals

Pa

HP

0.7460

kilowatts

kW

RPM

0.10472

radians/sec.

rad/s

RPM

60

revolutions/sec.

rev/s

Pump

Psf

47.88(use50)

pascals(N/m2)

Pa

duty

Psi

6895(use7000)

pascals(N/m2)

Pa

Psi

6.895

kilopascals(kN/m

2)

kPa

FANANDPUMPDUTY

HVACCONVERS

IONS


23/24

1-23

General

Total heat 300400 sq. ft./ton (range 230520)

Total heat 3040 BTU/h/sq. ft.(range 2352)

Room sens. heat 2528 BTU/h/sq. ft.(range 1937)

SHR 0.750.93

Perimeter spaces 1.03.0 CFM/sq. ft.

Interior spaces 0.51.5 CFM/sq. ft.

Building block CFM 1.01.5 CFM/sq. ft.

Air change rate 410 AC/hr.

Large, Perimeter

Total heat 225275 sq. ft./ton

Total heat 4353 BTU/h/sq. ft.

Large, Interior



Small



OFFICE DESIGN CRITERIA


24/24

GENERALDES

IGNVALUES

Roo

m

Air

TotalHeat

TotalHeat

Sens.Heat

Change

(Ton)

BTUh/sq.ft.

BTUh/s

q.ft.

SHR

S

paces

AirFlow

Rate

Banks,Court

200250

4

860

2838

0.750.90

410AC/hr.

Houses,

sq.ft./ton

B

TUh/sq.ft.

BTUh/s

q.ft.

Municipal

(range160340)

(range3575)

(range2148)

Buildings

PoliceStations

,

250350

3

448

2535

0.750.90

410AC/hr.

FireStations,

sq.ft./ton

B

TUh/sq.ft.

BTUh/s

q.ft.

PostOffices

(range200400)

(range3060)

(range2040)

Precision

50300

4

0240

32228

0.800.95

1050AC/hr.

Manufacturing

sq.ft./ton

B

TUh/sq.ft.

BTUh/s

q.ft.

Computer

50150

8

0240

64228

0.800.95

2.04.0

1520AC/hr.

Rooms

sq.ft./ton

B

TUh/sq.ft.

BTUh/s

q.ft.

CFM/sq.ft.

Restaurants

100250

4

8120

2162

0.650.80

1.54.0

812AC/hr.

sq.ft./ton

B

TUh/sq.ft.

BTUh/s

q.ft.

CFM/sq.ft.

(range75300)

(range40155)

(range2080)

Kitchens

150350

3

480

2056

0.600.70

1.52.5

1215AC/hr.

sq.ft./ton

B

TUh/sq.ft.

BTUh/s

q.ft.

CFM/sq.ft.

(at85Fspace)

(at85Fspace)

(at85F

space)

Documents

0977000389 DEWALT HVACR Professional Reference Master Edition