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SIZING - GENERAL

CONSTANTEMP HEATER SIZING

1. Determine inlet temperature, set po int, req uired

flow a nd s tea m press ure from the c usto mer. If flow

in G P M is not know n, use the AS HRAE fixture c ount

method in this sizing section to determine flow.

2. If steam pressure is greater than 15 P S I, use theReduc ing Va lve S election C hart.

3. To d etermine hea ter size, enter the left hand s ide

of the chart at the inlet temperature and corres-

ponding outlet temperature (set-point).

4. Read a cross to your steam pressure and then read

down till you see a flow equal to or greater than

the sys tem req uirements.

5. Then read ac ross to the right to the c orresponding

hea ter mod el number.

STEAM FLOW REQUIREMENTS

CONDENSATE FLOW

E 9 0 1 L H W

CONSTANTEMP HEATER CODE SELECTION CHART

1 2 3 4 5 6 7

M odel Flow Exchanger C oil D esign TubeG PM M aterial M aterial Pressure

* N om inal Flow in G PM based on

100°F rise

Model - Position 1

E - Single W all

F - D ouble W all

Flow GPM* - Position 2

15 = (15 G P M )

3 = (30 G P M )

45 = (45 G P M )6 = (60 G P M )

75 = (75 G P M )

9 = (90 G P M )

105 = (105 G P M )

12 = (120 G P M )

Exchanger Material -

Position 3

0 = D uctile iron, 75 psi

2 = C ast steel, 150 psi

4 = C ast steel, 150 psi,

ASM E ‘U’Stam p

5 = C ast steel, 150 psi,ASM E ‘UM ’Stam p

Coil Material - Position 4

0 = Copper

1 = Adm iralty

2 = C upro-N ickel

3 = Stainless steel

HR# = (GPH)(T2 - T1)

100

= GPM CONDENSATE500HR

#

EXAMPLE

Inlet 40°FOutlet 140°FSteam 15 PSIFlow 65 GPM

Selection E-7500L heater

VARIABLE PRESSURE HEATER SIZING

1. Determine inlet temperature, set point, required flow

and steam pressure from the customer. If flow in

GPM is not known use the ASHRAE fixture count

method in this sizing se ction to dete rmine flow.

2. Determine req uired stea m valve s ize from stea m

valve s election c hart.

3. To d etermine hea ter size enter the left hand s ide o f

the cha rt a t the inlet tempe rature and corresp onding

outlet te mpera ture (se t-point).

4. Read a cross to your inlet steam press ure and thenread down till you see a flow equal to or greater

than the system requirements.

5. Then read ac ross to the right to the c orresponding

heater model number.

Design - Position 5

B lank - H igh pressure

(up to 60 G PM only)

L - Low pressure (all sizes)

Tube Pressure -

Position 6 & 7

B lank - 150 psigH W - 250 psig

D W - D ouble W all



PRESSURE DROP VERSUS FLOWLESLIE-CONSTANTEMP HEATERS

Flow vs. Pressure Drop

10

8

6

4

2

0

0 20 40 60 80 100 120 140

1500 300 4500 6007500 900 10500 1200

Flow (GPM)

SIZING - GENERAL

Capacity tables for Leslie Constantemp Heaters

show various capacities for each model number,dep ending upon the temperature rise a nd inlet ste am

pressure.

The c urves s how n be low give the wa ter press ure

drop versus the flow in G P M for Les lie C onsta ntemp

Heaters. It is important to c a lculate the press ure d rop

for any pa rticular applica tion from thes e c urves to be

sure the pressure drop through our heater does not

exceed the customer requirements.



SIZING - GENERAL

DETERMINING LESLIE-CONSTANTEMPSTEAM-WATER HEATER LOAD REQUIREMENTS*

Apartment Hotels and IndustrialHouse Gymnasium Hospital Dormitories Plant Office Building School YMCA

B a s ins , priva te la va tory 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75

B a s ins , public la va tory ----- 1 1 1 1 1 1 1 1

B a thtubs 1.5 1.5 ----- 1.5 1.5 ----- ----- ----- -----

Dishw a shers 1.5 Five (5) Fixture Units per 250 S ea ting Ca pa city

Thera peutic ba th ----- ----- ----- 5 ----- ----- ----- ----- -----

Kitchen s ink 0.75 1.5 ----- 3 1.5 3 ----- 0.75 3

P a ntry s ink ----- 2.5 ----- 2.5 2.5 ----- ----- 2.5 2.5

S ervice s ink 1.5 2.5 ----- 2.5 2.5 2.5 2.5 2.5 2.5

S how ers 1.5 1.5 1.5 1.5 1.5 3.5 ----- 1.5 1.5

Circular wa sh founta in ----- 2.5 2.5 2.5 ----- 4 ----- 2.5 2.5

Semicircular wash fountain ----- 1.5 1.5 1.5 ----- 3 ----- 1.5 1.5

Fixture Units Fixture UnitsType of Building Unit Per Unit Type of Building Unit Per Unit

Hospita l or nurs ing home B ed 2.50 Elementa ry school S tudent 0.30a

Hotel or motel Room 2.50 J r. a nd S r. high s chool S tudent 0.30a

Office building P erson 0.15 Apa rtment house Apa rtment 3.00

TABLE 1. Hot Water Demand in Fixture Units [1400F (600C) Water]

TABLE 2. Preliminary Hot Water Demand Estimate

a Plus shower load.

a- In applications where all showers can be used at one time the actual flow from each shower should be multiplied by the number of showers and added to flow obtained by the fixture unit method.

When sizing the Leslie-Constantemp heater it is necessary

to d etermine the ma ximum insta ntaneous flow in ga llons

per minute (GPM). If the customer cannot provide flow in

GP M, it is neces sa ry to perform a count of a ll fixtures that

the hea ter will serve.

Fixture units (Ta ble 1) a re se lecte d fo r ea ch fixture us ing

hot wa ter and are totalled. Maximum hot wa ter demand in

G P M is ob ta ined from Fig. 1 or 2 by matc hing total fixture

units to the curve for the type of building and read ing G P M.

Hot wa ter for fixtures a nd outlets tha t have c onsta nt flow s

should be a dded to dema nd.

Unusual hot water requirements in a building should be

analyzed to determine if additional capacity is required. An

example is a dormitory in a military school where all

showers and lavatories can be used simultaneously when

students return from a parade. In such a case, the heater

should be s ized for the full flow of the s ystem.

To ma ke preliminary estimate s of hot w ate r dem and whe n

the fixture count is no t know n, use Ta ble 2 w ith Fig. 1 or

2. The results w ill usua lly b e higher tha n the d ema nd

determined from the actual fixture count. Actual heater

size s hould be dete rmined from Ta ble 1.

Example: Determine the hot water flow rate for sizing a

heater for a 600-student elementary school with the fol-

lowing fixture count; 60 public lavatories, 6 slop sinks, 4

kitchen sinks, 6 show ers, and 1 d ishwa sher at 8 GP M.

Solution: For a p relimina ry, es tima te, us e Ta ble 2 to find

es tima ted flow. The ba sic flow is de termined from c urve D

of Fig. 2, at 600 students x 0.3 fixture units per student =

180 fixture units, plus 6 s how ers x 1.5 fixture units = 9, or

189 fixture units, for a total flow of 23 GPM.

To s ize the unit ba se d o n a ctua l fixture c ount a nd Tab le 1,

the ca lculation is as follow s:

60 public la va tories x 1 F.U. = 60 F.U.

6 service s inks x 2.5 F.U. = 15 F.U.

4 kitchen s inks x 0.75 F.U. = 3 F.U.

6 show ers x 1.5 F.U. = 9 F.U.

S ubtota l 87 F.U.

At 87 fixture units, curve D of Fig. 2 shows 16 GPM, to

which must be a dde d the dishwa sher req uirement of 8

G P M. Thus, the tota l flow is 24 GP M.

Co mpa ring the flow ba sed on a ctual fixture co unt to that

obtained from the preliminary estimate shows the prelim-

inary estimate to be slightly lower. It is possible that the

preliminary estimate co uld ha ve been a s much a s tw ice

the fina l fixture c ount res ult. To p revent oversizing th e

equipment, it is imperative to use the actual fixture count

method to s elect the unit.



SIZING - GENERAL

* Po rtions of text a nd ta bles “Rep rinted by permission from ASHRAE Handbo ok -- 1999 Sys tems”

Fig. 1 Modified Hunter Curve for Hot Water Flow Rate(Corrected for Type of Building Usage)

G A L L O N S P E R M I N U T E

FIXTURE UNITS

Fig. 2 Enlarged Section of Modified Hunter Curve for Hot WaterFlow Rate (Corrected for Type of Building Usage)

G A L L O N S P E R M I N U T E

FIXTURE UNITS

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