WATER HEATER
SIZING GUIDE
FOR ENGINEERS
COMMERCIAL ▪ INSTITUTIONAL ▪ INDUSTRIAL
PVI Industries, LLC ▪ Fort Worth, Texas
SCALD WARNING
Because the danger of accidental scalding, the use of a thermostatically controlled
temperature regulator is mandatory in installations such as rest homes, homes for the
mentally handicapped, children’s homes, schools, churches and hospitals.
Such regulators should be set no higher than 110°F. Never should a water heater be
used to control a maximum outlet temperature suitable for body comfort.
SIZING
GUARANTEE
PVI sizing methods are guaranteed to be correct when used in
accordance with the instructions as printed, as long as PVI
equipment, with its unique performance characteristics, is used.
If an installation should not have an adequate amount of hot water
after proper use of the Guide, PVI will, at its cost, correct
the installation to the engineer’s satisfaction.
COMMON FACTORS
All calculated loads are converted to GPH (Gallons per Hour) 40°F to 140°F, or an 100°F rise.
Appropriate conversion factors will be found near each formula.
All BTU output calculations are based on RD (Recovery Demand) Requirement.
All SR (Storage Requirements) are a percentage of the RD.
CODES
Some city, municipal, state and/or federal regulations may require different sizing methods;
they take precedence.
WATER HEATER
SIZING GUIDE
FOR ENGINEERS
COMMERCIAL ▪ INSTITUTIONAL ▪ INDUSTRIAL
Contents
Section
Page
I
Apartment Houses, Hotels, Motels ……………………………….
2-4
II
Dormitories, Fraternity and Sorority Houses …………………….
5-6
III
Hospitals, Rest Homes, Nursing Homes, Orphanages, Convents ..
7-8
IV
Schools and Churches …………………………………………….
9
V
Laundries: Commercial & Institutional, Coin Operated …………
10-11
VI
Food Service ……………………………………………………..
12-14
VII
Showers: Schools, Correctional Facilities, Stadiums,
Industrial Plants, Foundries, Mines and Churches ……………….
15
VIII
Office Buildings ………………………………………………….
16
IX
Swimming Pools …………………………………………………
17
X Instantaneous Steam Sizing (Hunter’s Curves)
18-19
1
Section I. APARTMENT HOUSES, HOTELS AND MOTELS
Calculations in this section cover all hot water
demands for the individual living units.
Additional demands, for centralized food
service, coin-operated laundries, etc., may be
calculated by referring to other sections of this
Guide specified in the discussion below.
Diversity Factors “C” are a function of the
number of living units served, and are provided
in this section. As the number of units increases,
“C” decreases because the likelihood of all
living units using hot water at the same time
decreases.
The major hot water load in a living unit is
shower head consumption. If shower head
consumption is provided for, lavatories and
sinks will be well served. However, dishwashers
and clothes washers in the living units impose
large additional loads, and these are provided
for in the table of Adjustment Factors “AF” on
page 3.
HOTELS AND MOTELS: SPECIAL CONSIDERATIONS
If the hotel or motel has central food service,
calculate the additional load using Section VI,
Food Service. If it has central laundry facilities,
calculate the additional load using Section V,
Laundries. Add these to the basic load.
1.
Hotels designed primarily to accommodate
conventions and other regimented groups of
people tend to create peak demand periods. We
recommend NOT using the Diversity Factor.
2.
Some convention-type hotels are being designed
to accommodate three or four people per room,
using roll-away beds. In such cases, in addition
to eliminating the Diversity Factor, we
recommend increasing the Adjustment Factor by
multiplying the Recovery Demand by 1.25.
3.
Hotels designed primarily for commercial trade
rather than tourism will also see a regimented
hot water demand, especially at wake-up time.
We recommend NOT using the Diversity Factor.
The type of hotel or motel can have a strong
impact on real hot water demand.
Ask the architect about any of the following
considerations and include the basis of your
assumptions in your sizing proposal.
FORMULAS
Formula Legend:
RD
= Recovery Demand 40°F to 140°F
TU
= Total number of living units
FR
= Flow rate of shower heads in gallons per minute
AF
= Unit / Time Adjustment Factor
C
= Diversity Factor
SR
= Storage Requirement
Formula I (Apartments, Hotels and Motels designed for family or transient living)
RD = TU x FR x AF x C x 0.8
SR = RD x .25 (for minimum)
Formula II (Convention-type Hotels and Motels)
RD = TU x FR x AF x 0.8
SR = RD x .33 (for minimum)
NOTE: PVI strongly recommends insulating all hot water lines, and all calculations in this Guide are
based on insulated lines. For systems with non-insulated lines, multiply Recovery Demand “RD” by 1.5.
2
ADJUSTMENT FACTORS
ADJUSTMENT FACTOR
AF
CLASSIFICATION
APARTMENT HOUSES
1
1
1
1
2
2
2
2
Bath
Bath and Dishwasher
Bath and Clothes Washer
Bath, Dish and Clothes Washer
Baths
Baths and Dishwasher
Baths and Clothes Washer
Baths, Dish and Clothes Washer
4.5
4.6
4.8
4.9
5.0
5.1
5.3
5.4
HOTELS AND MOTELS
1
Bath
2
Baths
5.0
5.5
DIVERSITY FACTORS
NUMBER UNITS*
TU
DIVERSITY FACTOR
C
1-20
21-40
41-60
61-80
81-100
101-120
121-140
141-160
161-180
181-200
201-260
261-310
311-370
371-440
441-520
521-600
601-680
681-760
761-840
841-920
921-1000
.98
.96
.94
.92
.89
.85
.84
.81
.79
.75
.70
.67
.64
.63
.60
.56
.54
.53
.52
.51
.50
*If some units have one bath and some have two baths, use the Diversity Factor for the total number of units.
(Continues with examples on page 4.)
3
Section I. APARTMENT HOUSES, HOTELS AND MOTELS
continued
EXAMPLE
Select water heating equipment for a 200room convention-type motel. The flow rate of
each shower head will be 2 GPM. The laundry
will have three 50-lb washers. There will be no
food service. The owners request one central
system.
First, calculate the rooms load:
RD = TU x FR x AF x 0.8
RD = 200 x 2 x 5 x 0.8
RD = 1600
SR = RD x .33
SR = 528
The Trade-Off Between Recovery
Demand and Storage Requirements
Reducing recovery demand necessitates a
large increase in storage requirements and it is
occasionally desirable.
For example, if the energy source is gas, it
may be desirable to reduce the gas line size or
vent size. If the energy source is electricity , it
may be economical to reduce the building’s
transformer size to reduce the demand factor
applied by the utility. Or if steam or hot water
are used, it may be desirable to reduce control
and piping sizes and demands on the boilers.
In any case, the following factors must be
applied:
Then, calculate the laundry load (Section V):
RD = TW x PC x GC x 1.2
RD = 3 x 50 x 3 x 1.2
RD = 540
SR = RD x .4
SR = 216
RD
Multiplier
(percent reduction in RD)
SR
Multiplier
.75
2.4
.50
3.6
.25
4.8
Then add the loads:
Total RD =
Total SR =
1600 Rooms RD
+ 540 Laundry RD
2140 gph 40°F to 140°F
528 Rooms SR
+ 216 Laundry SR
744 Gallons Storage
Select two water heaters with a combined
minimum recovery of 2140 GPH of 40°F to
140°F, and a combined minimum storage of
744 gallons.
4
First multiply the original calculated RD
(recovery demand) by the factor in the above
chart to determine the new RD.
Then multiply the original calculated SR
(storage requirement) by the corresponding
factor to determine the new SR.
Use of these factors will ensure adequate
recovery and storage capacity to maintain
tenant satisfaction.
Section II. DORMITORIES, FRATERNITY AND SORORITY HOUSES
Safety Requirement
The danger of scalding is great in this type of installation. Design should include
thermostatically controlled water temperature regulators set no higher than 110°F.
Hot water demand for dormitory-type living is
based on total number of students and a diversity
factor for this number, which is directly related to
the flow rate of the shower heads installed.
When the total demand is calculated, there will be
sufficient hot water available for all general purpose
applications, such as lavatories, showers, tubs,
general cleanup and small hand laundering.
FORMULA
Formula Legend:
RD
= Recovery Demand 40°F to 140°F
TS
= Total number of students
FR
= Flow rate of shower heads in gallons per minute
AF
= 3.8 Student / Time Adjustment Factor
C
= Diversity Factor
SR
= Storage Requirement
Formula
RD = TS x FR x 3.8 x C x 0.8
SR = RD x .4
DIVERSITY FACTORS
NUMBER STUDENTS
TS
DIVERSITY FACTOR
C
1-9
10-19
20-29
30-39
40-49
1.00
.97
.94
.91
.88
NUMBER STUDENTS
TS
DIVERSITY FACTOR
C
50-74
.80
75-99
.72
100-199
.65
200-299
.59
300-399
.54
400-500
.50
Many of these installations also have centralized facilities with high demand. If there is central food service,
calculate the additional load using Section VI, Food Service. If there is a central laundry, calculate the additional
load using Section V, Laundries. Add these loads to the basic load.
EXAMPLE
Calculate the requirement for a dormitory to
house and feed 150 students. Shower head flow
rate is 2 gpm. Use the food service requirement
from example in Section VI, Food Service,
Solution 2.
In this type of living, it is very important to
separate the living unit hot water system from
the kitchen system. Therefore, select a twoheater system with a combined minimum of
593 gallons from 40°F to 140°F and 237
gallons storage. Water will be stored at 140°F.
RD = TS x FR x 3.8 x C x 0.8
RD = 150 x 2 x 3.8 x .65 x 0.8
RD = 593
Also, select two heaters for the kitchen with a
combined minimum of 900 gallons 40°F to
140°F and 300 gallons storage.
SR = RD x .4
SR = 593 x .4
SR = 237
Good engineering practice dictates separate
systems for each major service. However, if
one central system must serve, recovery
demands may be combined and storage
requirements may be combined.
5
Section II. DORMITORIES, FRATERNITY AND SORORITY HOUSES
continued
The Trade-Off Between Recovery
Demand and Storage Requirements
Reducing recovery demand necessitates a
large increase in storage requirements and it is
occasionally desirable.
For example, if the energy source is gas, it
may be desirable to reduce the gas line size or
vent size. If the energy source is electricity , it
may be economical to reduce the building’s
transformer size to reduce the demand factor
applied by the utility. Or if steam or hot water
are used, it may be desirable to reduce control
and piping sizes and demands on the boilers.
In any case, the following factors must be
applied:
First multiply the original calculated RD
RD
Multiplier
(percent reduction in RD)
SR
Multiplier
.75
2.5
.50
3.8
.25
5.0
(recovery demand) by the factor in the above
chart to determine the new RD.
Then multiply the original calculated SR
(storage requirement) by the corresponding
factor to determine the new SR.
Use of these factors will ensure adequate
recovery and storage capacity.
6
Section III. HOSPITALS, REST HOMES, NURSING HOMES,
CHILDREN´S HOMES and CONVENTS
Safety Requirement
The danger of scalding is great in this type of installation. Design must include
thermostatically controlled water temperature regulators set no higher than 110°F.
These installations are similar in their hot
water demands. The calculations in this section
cover all hot water demands of the individual
rooms and living units.
Most of these installations also have centralized facilities with high demands. If there is
central food service, calculate the additional
load using Section VI, Food Service. If there is
central laundry, calculate the additional load
using Section V, Laundries. Add these loads to
the basic load.
FORMULAS
Formula Legend:
RD
= Recovery Demand 40°F to 140°F
TP
= Total number of persons
FR
= Flow rate of shower heads in gallons per minute
AF
= Person/Time Adjustment Factor
C
= Diversity Factor
SR
= Storage Requirement
Formula I (rooms with showers or tub/showers)
RD = FR x AF x TP x C x 0.8
SR = RD x .4
Formula II (rooms with tubs only)
RD = 12 x TP x C
SR = RD x .4
ADJUSTMENT FACTORS
TYPE OF INSTITUTION
HOSPITALS
REST HOMES
NURSING HOMES
ORPHANAGES
If the institution has showers or tub/showers
in the rooms use Formula I. If it has tubs only,
use Formula II. If it has both, apply both
formulas and add the results. (When using both
formulas, always use the diversity factor “C”
for the combined total of rooms or number of
beds.)
ADJUSTMENT FACTOR
AF
3.7
3.1
3.1
2.8
Good engineering practice dictates separate
systems for each major service. However, if
one central system must serve, recovery
demands may be combined and storage
requirements may be combined. In such cases,
remember to provide for line losses in
unusually long lines.
7
Section III. HOSPITALS, REST HOMES, NURSING HOMES,
ORPHANAGES and CONVENTS continued
DIVERSITY FACTORS
NUMBER UNITS
TU
DIVERSITY FACTOR
C
NUMBER UNITS
TU
DIVERSITY FACTOR
C
1-20
21-40
41-60
61-80
81-100
101-120
121-140
141-160
161-180
181-200
201-260
.96
.92
.88
.86
.82
.80
.77
.75
.72
.70
.65
261-310
311-370
371-440
441-520
521-600
601-680
681-760
761-840
841-920
921-1000
.61
.58
.55
.53
.50
.47
.45
.43
.41
.39
EXAMPLE
Calculate the requirement for a 300-room
hospital. Use the food service requirement
from the example in Section VI, Food Service.
Use the laundry requirement from example in
Section V, Laundries. Use flow rate of 2 gpm.
RD = TP x FR x AF x C x 0.8
RD = 300 x 2 x 3.7 x .61 x 0.8
RD = 1083
SR = RD x .4
SR = 1083 x .4
SR = 433
The Trade-Off Between Recovery
Demand and Storage Requirements
Reducing recovery demand necessitates a
large increase in storage requirements and it is
occasionally desirable.
For example, if the energy source is gas, it
may be desirable to reduce the gas line size or
vent size. If the energy source is electricity , it
may be economical to reduce the building’s
transformer size to reduce the demand factor
applied by the utility. Or if steam or hot water
are used, it may be desirable to reduce control
and piping sizes and demands on the boilers.
Then add the requirements together:
Total RD =
Total SR =
1083
1620
+ 900
3603
Rooms RD
Laundry RD
Kitchen RD
gph 40°F to 140°F
433
648
+ 297
1378
Rooms SR
Laundry SR
Kitchen SR
Gallons Storage
Select two water heaters with a combined
minimum recovery of 3603 GPH of 40°F to
140°F, and a combined minimum storage of
1378 gallons.
8
In any case, the following factors must be
applied:
First multiply the original calculated RD
RD
Multiplier
(percent reduction in RD)
SR
Multiplier
.75
2.6
.50
3.9
.25
5.2
(recovery demand) by the factor in the above
chart to determine the new RD.
Then multiply the original calculated SR
(storage requirement) by the corresponding
factor to determine the new SR.
Section IV. SCHOOLS and CHURCHES
Safety Requirement
The danger of scalding is great in this type of installation. Design must include
thermostatically controlled water temperature regulators set no higher than 110°F.
Hot water demands in schools and churches
are alike in that the two major loads are food
service and showers.
The kitchen demand should be calculated
using Section VI, Food Service. The shower
demand should be calculated using Section VII
Showers.
The trend is to use separate systems for each
bank of showers and the kitchen. However, if
one central system is required, sizing rules
differ.
SCHOOLS
The shower and kitchen loads should be
added together when sizing a central system.
CHURCHES
After calculating the shower and kitchen
loads separately, size the system to the heavier
load, since the two loads will rarely occur
during the same hour.
9
Section V. LAUNDRIES: COMMERCIAL, INSTITUTIONAL,
INDUSTRIAL and COIN-OPERATED
COMMERCIAL, INSTITUTIONAL and INDUSTRIAL LAUNDRIES
Commercial and institutional laundries
generally require 160°F. Industrial laundries
generally require 180°F.
Clothes washing machines vary in their use
of hot water per pound of capacity per cycle;
between 1 and 6 gallons. The only safe course
is to check the manufacturer for the particular
model of interest.
FORMULAS
Formula Legend:
RD
= Total gallons of 140°F water required
TW
= Total number of washers
PC
= Pounds Capacity, commercial or industrial
GC
= Gallons per pound per cycle (according to manufacturer)
1.4
= Conversion Factor, 180°F to 140°F
1.2
= Conversion Factor, 160°F to 140°F
SR
= Minimum Storage Requirement
Formula I (commercial and institutional laundries)
RD = TW x PC x GC x 1.2
SR = RD x .4
Formula II (industrial laundries)
RD = TW x PC x GC x 1.4
SR = RD x .4
EXAMPLE
Using Formula I, select equipment to supply
three 150 lb. washing machines that require
3 gals/pound/cycle.
RD = TW x PC x GC x 1.2
RD = 3 x 150 x 3 x 1.2
RD = 1620
SR = RD x .4
SR = 1620 x .4
SR = 648
Select a water heater with a minimum
recovery of 1620 GPH of 40°F to 140°F, and a
minimum storage of 648 gallons.
10
COIN-OPERATED LAUNDRIES
The number of machines and the length of
cycle are the basic factors. However, the most
critical factor is the Diversity Factor.
Customer satisfaction depends on determining the correct Diversity Factor. In the
formulas that follow, this factor is built into the
C2 and C3 factors.
FORMULAS
Formula Legend:
RD
= Total gallons of 120°F water required
TW
= Total number of washers
1.2
= Conversion Factor, 160°F to 140°F
C2
= Diversity Factor for 20-minute cycle
C3
= Diversity Factor for 30-minute cycle
SR
= Minimum Storage Requirement
Formula I (coin-operated, 20-minute cycle)
RD = TW x C2 x 1.2
SR = RD x .4
Formula II (coin-operated, 30-minute cycle)
RD = TW x C3 x 1.2
SR = RD x .4
DIVERSITY FACTORS
COIN OPERATED LAUNDRY MACHINE
Number of
Washing Machines
TW
Diversity Factor
20-Minute Cycle
C2
Diversity Factor
30-Minute Cycle
C3
2-4
38
33
5-8
35
30
9-12
33
28
13-16
31
26
17-24
30
25
25-36
29
24
37-52
28
23
53-60
27
22
EXAMPLE
A coin-operated laundry has twenty-six
20-minute cycle machines.
RD = TW x C2 x 1.2
RD = 26 x 29 x 1.2
RD = 905
SR = RD x .4
SR = 905 x .4
SR = 362
Select a water heater with a minimum
recovery of 905 GPH of 40°F to 140°F, and a
minimum storage of 362 gallons.
11
Section VI. FOOD SERVICE ESTABLISHMENTS
Regardless of size, food service establishments require two temperatures of hot water;
190°F and 140°F. Maximum demand typically
peaks for two hours. However, many fast-food
restaurants now have peak periods that last
three to five hours. These restaurants must be
given adequate storage capacity to cushion
such demands.
Traditionally, it seems, food service
installations are undersized and suffer a high
failure rate. Apparantly, their designers have
felt that the demand was so predictable that
they could safely ignore a cushion. PVI
recommended storage requirements factors are
set to ensure high peak capacity and long
equipment life.
Sanitation Requirements
A National Sanitation Foundation regulation
requires that the temperature of a dish must
reach 170°F within ten seconds and that the
water pressure must be maintained between 15
psig and 25 psig (lower and higher water
pressure can cause slower dish heating). To
determine dish temperature accurately, a
“holding type” thermometer must be clipped to
a dish in the machine. Merely checking the
machine’s thermometer does not accurately
reflect dish temperature.
PVI’s field experience has proven that the
heating equipment must deliver water at 190°F
to allow for line loss and still deliver 180°F
water to a dish machine, to ensure 170°F at the
dish. All PVI equipment is certified by UL for
a maximum delivered outlet water temperature
of 194°F.
Safety Requirement
Most city and state codes require that 140°F
water must be supplied to the kitchen. Water at
that temperature is dangerous and can cause
scalding in as little as one second. If 140°F
water supplies a restroom, use a thermostatically controlled mixing valve to reduce temperature to 110°F.
12
Rule-of -Thumb Estimating
PVI does not recommend rule-of-thumb
estimating but sometimes there is no other
choice. The mechanical engineer may be
forced to size the central system based only
upon the number of people to be served. This is
an inexact method, but a number of 2.4 gallons
per hour per meal may be used based on PVI’s
140°F RD (recovery demand) sizing factor.
Once recovery demand is determined, multiply
by .33 to estimate the storage requirement.
Basic types of Food Service Systems
Single Water Heater Systems
A. Water is stored at 190°F for sanitizing
and a mixing valve reduces temperature
to 140°F for kitchen use. These hightemp systems are short-lived.
B. Water is stored at 140°F and delivered to
a dish machine designed to accept 140°F
with chemical sanitation.
Double Water Heater Systems
A. A primary water heater stores at 140°F
for kitchen use. It also supplies a booster
heater that delivers 190°F to the dish
machine for sanitizing.
B. Two heaters are used, each capable of
supplying the total demand. In normal
use, one heater supplies 140°F water for
general kitchen use and the other
supplies 190°F water for dish machine
sanitizing. PVI recommends this type of
system for kitchens that must not be shut
down.
NOTE: All general kitchen loads when added
together become the total RD (recovery
demand). When total RD is developed, only
then can SR (storage requirement) be developed.
SIZING PROCEDURE
1.
2.
3.
4.
5.
6.
9.
List all fixtures and equipment that require hot water
Make two columns, one for 140°F water and one for 190°F water
Enter the gallons required in the appropriate column
Total each column
Total columns to equal Recovery Demand (RD) at 120°F
Multiply each column total by the appropriate Conversion Factor:
1.5 = Conversion Factor for 190°F to 140°F = RD (Recovery Demand)
.40 = Conversion Factor for 140°F to 190°F = RD
Calculate SR: Multiply RD at 140°F by .33 for minimum SR (Storage Requirement)
EXAMPLES
The following table uses typical values presented later in this section:
Gallons at
140°F
KITCHEN EQUIPMENT
2 Vegetable Sinks
2 Double Pot Sinks
1 Pre-Rinse (Hand Type)
1 Mop Sink
2 Bar Sinks
6 Lavatories
1 Dish Machine (Single-Tank Conveyor)
1 Silver Washer
Gallons at
190°F
100
140
50
20
60
30
400 GPH
400
100
500 GPH
SOLUTION 1 (For single system A, storing water at 190°F)
GPH at 190°F = 500 x 1.5
GPH at 140°F = 400
Total RD
SR
SR
SR
=
=
=
=
=
=
750 GPH 40°F to 140°F
400 GPH 40°F to 140°F
1150 GPH 40°F to 140°F
RD x .33
1150 x .33
380
Select a heater with a minimum 1150 GPH 40°F to 140°F and 380 gallons storage. Water will be stored at 190°F.
SOLUTION 2 (For single system B, storing water at 140°F)
GPH at 190°
GPH at 140°
RD
SR
SR
SR
=
=
=
=
=
=
500
400
900 GPH at 140°F
RD x .33
900 x .33
297
(with chemical sanitation, the 140°F and 190°F loads are combined into the 140°F load)
Select a heater with a minimum 900 GPH 40°F to 140°F and 297 gallons storage. Water will be stored at 140°F.
Continues on page 14 with more SOLUTIONS and GPH requirements charts for kitchen equipment.
13
SOLUTION 3 (For double system A, storing water at 140°F for primary source and boosting to 190°F for sanitizing)
GPH at 190°F
GPH at 140°F
RD
SR (Primary)
SR (Primary)
SR (Primary)
SR (Booster)
SR (Booster)
SR (Booster)
=
=
=
=
=
=
=
=
=
500 x .4
400
900
RD x .33
900 x .33
297
RD x .33
200 x .33
66
=
200 GPH at 140°F
=
900 GPH at 140°F
Select a primary heater with a minimum 900 GPH 40°F to 140°F and 297 gallons storage. Select a booster heater
with a minimum of 200 GPH 40°F to 140°F and 66 gallons storage.
SOLUTION 4 (For double system B, using two heaters; one storing water at 140°F, one storing water at 190°F )
GPH at 190°F = 500 x 1.5
=
750 GPH at 140°F
GPH at 140°F = 400
=
400 GPH at 120°F
RD = Larger of the two demands
SR = RD x .33
SR = 750 x .33
SR = 248
Select two heaters each of which meets the larger demand (a minimum of 750 GPH 40°F to 140°F ) and 248 gallons
storage each. One heater set at 140°F, the other set at 190°F. If either heater needs to be shut sown for an reason, the
other heater can carry the total demand by being set at 190°F, thus allowing for 100% backup.
GENERAL REQUIREMENTS OF COMMERCIAL AUTOMATIC DISH MACHINES
TYPE DISH MACHINE
Hood - Roll Type
Door
Single Tank Conveyor - Rack
Multiple Tank Conveyor - Rack
Flight
X Flight
Glass Washer
Silver Washer
Required GPH
190°F*
100
150
400
450
500
700
100
100
GENERAL REQUIREMENTS OF KITCHEN EQUIPMENT
TYPE EQUIPMENT
14
Required GPH
140°F*
Vegetable Sink
Single Pot Sink
Double Pot Sink
Triple Pot Sink
50
50
70
100
Pre-Rinse for Dishes (Shower Head Hand Held)
Pre-Scraper for Dishes (Salvajor Type)
Pre-Scraper for Dishes (Conveyor Type)
50
200
250
Mop Sink
Can Washer
Lavatory
Bar Sink
20
100
5
30
* The consumption rates are based on 20 psi flow pressure. These are maximum gph requirements for the dish
machine type listed. Refer to dish machine manufacturers’ literature for more accurate hot water requirements.
SECTION VII. SHOWERS: SCHOOLS, CORRECTION FACILITIES, SCHOOLS,
INDUSTRIAL PLANTS, FOUNDRIES, MINES, CHURCHES
The correct sizing of any multiple shower
head system is dependent on temperature,
quantity and time.
TEMPERATURE
Most people agree that 107 degrees is a hot
shower, so a factor or 100°F is most often used.
QUANTITY
It is vitally important to determine the flow
rate of the shower heads in GPM. Check the
manufacturer. PVI has found that only the best
shower heads flow at their rated gpm at varying
pressures. Most shower heads are rated at 40
psi and will deliver much higher flow rates at
higher pressures.
TIME
Time per shower is usually the most difficult
factor to predict. It should be discussed with all
officials who are in a position to criticize after
installation. It should be reduced to writing.
Correctional facilities are different than most
other types of gang shower loads in that there
are usually five to ten prisoners per installed
shower head. Man minutes per shower head
must be predetermined and accepted by prison
authorities.
Generally, in a regimented environment, three
minutes per man per shower is acceptable. This
theory can determine the number of shower
heads required. Most correctional facility loads
therefore are based on a maximum of a 45minute time for total shower load. This simply
states that all prisoners can complete their total
hygiene in one hour.
PVI has found the following acceptable:
Churches …………………………………………….
Junior High and Senior High School ……………..
Industrial ……………………………………………..
Foundries and Mines ……………………………….
High School Field Houses ………………………...
College and Professional Stadiums ………………
Correctional Facilities ………………………………
FORMULA
10 minutes
10 minutes
10 minutes
15 minutes
20 minutes
25 minutes
45 minutes
Formula Legend:
RD
= Recovery Demand
TS
= Total Shower Heads
FR
= Flow rate of shower heads in gallons per minute
T
= Time per Shower in Minutes
.7
= Conversion Factor, 110°F to 140°F
SR
= Storage Requirement = 1.2 x RD
Formula
RD = TS x FR x T x .7
SR = RD x 1.2
EXAMPLE
A high school gym has 20 shower heads reliably
rated at 3 gpm.
RD
=
TS x FR x T x .7
RD
=
20 x 3 x 10 x .7
RD
=
420
SR
SR
=
=
RD x 1.2
504
Select a heater with a minimum 420 GPH 40°F to
140°F and 504 gallons storage.
DERATING:
Formula assumes “hour-after-hour” shower use.
When “second-hour” operation is not required, RD
may be reduced by 50%
When “neither second- nor third-hour” operation is
required, RD may be reduced 66%.
Storage requirement, however, must always be
based on the original RD; it must NOT be reduced.
It is always advisable to use thermostatically
controlled mixing valves on shower installations.
15
Section VIII. OFFICE BUILDINGS
The formula below covers the basic hot water
load of office buildings - lavatories, mop sinks, and
bar sinks. Peaks in the load typically occur within
the half hour before lunch and the half hour before
quitting time.
FORMULA
If the building is to include restaurants, calculate
the load separately using Section VI, Food Service.
Laundry loads may be calculated using Section V,
Laundries.
Formula Legend:
RD
= Recovery Demand 40°F to 140°F
L
= Number of Lavatories (allow 5 GPH)
B
= Number of Bar Sinks (allow 30 GPH)
M
= Number of Mop Sinks (allow 20 GPH)
C
= Diversity Factor
SR
= Storage Requirement
Formula
RD = ((L x 5) + (B x 30) + (M x 20)) x C x 0.8
SR = RD x .33
DIVERSITY FACTORS
TOTAL NUMBER
OF FIXTURES
DIVERSITY FACTOR
C
1-25
26-50
51-100
101-150
151-200
201-300
301-400
401-500
1.00
.97
.92
.87
.82
.75
.70
.63
EXAMPLE
Select water heating equipment for a 20-floor
office building. Each floor has 10 lavatories and
2 mop sinks. The first floor has 2 bar sinks.
RD
=
((L x 5) + (B x 30) + (M x 20)) x C x 0.8
RD
=
((200 x 5) + (2 x 30) + (40 x 20)) x .75 (there are 242 fixtures) x 0.8
RD
=
(1000 + 60 + 800) x .75 x 0.8
RD
=
1116 GPH 40°F to 140°F
SR
SR
=
=
RD x .33
1116 x .33
SR
=
368
If a single central system is required, select a
heater with a recovery rate of 1116 GPH 40°F to
140°F and 368 gallons storage.
16
Section IX. SWIMMING POOLS and BAPTISTRIES
The heating load for a swimming pool is
calculated in BTU/H. The desired pool temperature
must be established in discussion with the architect.
Most people prefer temperatures between 75°F and
80°F. The formula incorporates a “cold-pooltemperature” of 40°F to ensure a safety factor for
extreme conditions.
Required Hours “RH” to heat the pool must be
established. Typically, a value between 24 and 48
hours is chosen. Energy Factor “E” and Heat Loss
“HL” are determined from the table below.
FORMULA
L
W
AD
E
=
=
=
=
Formula Legend:
Length in Feet
Width in Feet
Average Depth in Feet
Energy Factor : for atmospheric gas, use 89
: for TURBOPOWER®, use 78
: for electric, use 0.018
DT
RH
HL
=
=
=
Desired Temperature
Required Hours to Heat Pool
Heat Loss Factor
Formula
L x W x AD x E x (DT-40)
RH
+
L x W x HL
2
=
Btu/h (Gas or Oil)
KWH (Electric)
Heat Loss = L x W x HL = Btu/h or KWH
HEAT LOSS FACTORS
75°F POOL TEMPERATURE
HL
GAS
TURBOPOWER®
ELECTRIC
INPUT
INPUT
INPUT
BTUH
KWH
BTUH
40
0
150
131
.031
40
5
200
175
.040
40
10
250
219
.051
40
15
300
263
.062
40
20
350
306
.072
50
0
107
94
.022
50
5
143
125
.029
50
10
179
156
.037
50
15
215
188
.044
50
20
250
219
.051
60
0
64
56
.013
60
5
86
75
.018
60
10
107
94
.022
60
15
129
113
.026
60
20
150
131
.031
Above factors are based on 75°F pool temperature. If temperatures desired are greater or less
than 75°F, add or subtract 7% per 5°F to energy calculated for 75°F.
AIR
TEMPERATURE
°F
EXAMPLE
WIND
VELOCITY
MPH
A swimming pool is 30' x 40' with an average depth of 6'. Energy source will be TURBOPOWER gas.
Desired temperature is 75°F. Required hours to heat pool: 36. Air temperature: 40°F. Wind speed 20 mph.
40 x 30 x 6 x 78 x (75-40)
36
+
40 x 30 x 306
2
=
729,600 Btu/h
Heat Loss = 40 x 30 x 306 = 367,200 Btu/h
NOTE: Total energy required to heat pool must always be greater than heat loss.
17
Sizing Instantaneous and Semi-Instantaneous Water Heaters
The methods for sizing storage water-heating equipment should not be used for instantaneous and semiinstantaneous heaters. The following is based on the Hunter (1941) method for sizing hot-and cold-water piping,
with diversity factors applied for hot water and various building types. Fixture units (Table 15) are assigned to each
fixture using hot water and totaled. Maximum hot-water demand is obtained from Figures 25 or 26 by matching
total fixture units to the curve for the type of building. Special consideration should be given to applications involving periodic use of shower banks, process equipment, laundry machines, etc., as may occur in field houses, gymnasiums, factories, hospitals, and other facilities. Because these applications could have all equipment on at the same
time, total hot water capacity should be determined and added to the maximum hot water demand from the modified Hunter curves. Often, the temperature of hot water arriving at fixtures is higher than is needed, and hot and
cold water are mixed together at the fixture to provide the desired temperature. Equation (24), derived from a simple energy balance on mixing hot and cold water, shows the ratio of hot-water flow to desired end-use flow for any
given hot, cold, and mixed end-use temperatures.
Hot water flow rate =
(mixed temperature flow rate) * (T mixed – T cold)
(T hot – T cold)
Once the actual hot water flow rate is known, the heater can then be selected for the total demand and
total temperature rise required. For critical applications such as hospitals, multiple heaters with 100% standby are
recommended. Consider multiple heaters for buildings in which continuity of service is important. The minimum
recommended size for semi-instantaneous heaters is 10 gpm, except for restaurants, for which it is 15 gpm. When
system flow is not easily determined, the heater may be sized for full flow of the piping system at a maximum
speed of 600 fpm. Heaters with low flows must be sized carefully, and care should be taken in the estimation of
diversity factors. Unusual hot water requirements should be analyzed to determine whether additional capacity is
required. One example is a dormitory in a military school, where all showers and lavatories are used simultaneously when students return from a drill. In this case, the heater and piping should be sized for full system flow. Whereas the fixture count method bases heater size of the diversified system on hot-water flow, hot water piping should
be sized for full flow to the fixtures. Recirculating hot-water systems are adaptable to instantaneous heaters. To
make preliminary estimates of hot-water demand when the fixture count is not known, use Table 16 with Figure 25
or Figure 26. The result is usually higher than the demand determined from the actual fixture count. Actual heater
size should be determined from Table 15.
Example: A 600-student elementary school has the following fixture count: 60 public lavatories, 6 service sinks, 4
kitchen sinks, 6 showers and 1 dishwasher at 8 gpm. Determine the hot water flow rate for sizing a semiinstantaneous heater based on the following:
a. Estimated number of fixture units
b. Actual fixture count
Solution:
a. Use Table 16 to find the estimated fixture count: 600 students x 0.3 fixture units per student = 180 fixture units. As showers are not included, Table 15 shows 1.5 fixture units per shower x 6 showers = 9 additional
fixture units. The basic flow is determined from curve D of Figure 26, which shows that the total flow for 189 fixture units is 23 gpm.
18
Reprinted from 2007 HVAC Applications with permission of ASHRAE
b. To size the unit based on actual fixture count and Table 15, the calculation is as follows:
60
public lavatories
x
1.0
FU
=
60
FU
6
service sinks
x
2.5
FU
=
15
FU
4
kitchen sinks
x
0.75
FU
=
3
FU
6
showers
x
1.5
FU
=
9
FU
87
FU
Subtotal
At 87 fixture units, curve D of Figure 26 shows 16 gpm, to which must be added the dishwasher requirement of 8 gpm. Thus, the total flow is 24 gpm. Comparing the flow based on actual fixture count to that obtained
from the preliminary estimate shows the preliminary estimate to be slightly lower in this case. It is possible that the
preliminary estimate could have been as much as twice the final fixture count. To prevent oversizing of equipment,
use the actual fixture count method to select the unit.
Table 15:
Hot Water Demand in Fixture Units (140°F Water)
Basin, private lav
Apartments
0.75
Club
0.75
Gymnasium
0.75
Hospitals
0.75
Hotels and
Dormitories
0.75
Industrial
Plant
0.75
Office
Building
0.75
School
0.75
YMC
A
0.75
Basin, public lav
-
1
1
1
1
1
1
1
1
Bathtub
1.5
1.5
-
1.5
1.5
-
-
-
-
Dishwasher*
1.5
Therapeutic bath
Five fixture units per 250 seating capacity
-
-
-
5
-
-
-
-
-
Kitchen sink
0.75
1.5
-
3
1.5
3
-
0.75
3
Pantry sink
-
2.5
-
2.5
2.5
-
-
2.5
2.5
Service sink
1.5
2.5
2.5
2.5
2.5
2.5
2.5
2.5
Shower
1.5
1.5
1.5
1.5
1.5
3.5
1.5
1.5
-
2.5
2.5
2.5
-
4
2.5
2.5
Circular wash fountain
-
Semi-circular wash
1.5
1.5
1.5
3
1.5
fountain
Note: Data predate modem low-flow fixtures and appliances. *See Water-Heating Terminology section for definition of fixture unit.
1.5
19
Table 16:
Preliminary Hot Water Demand Estimate
Type of Building
Fixture Units
Hospital or nursing home
2.50 per bed
Hotel or motel
2.50 per room
Office building
0.15 per person
Elementary school
0.30 per student*
Junior or senior high school
0.30 per student
Apartment house
3.00 per apartment
* plus shower load (in fixture units)
Figure 25: Enlarged Section of Figure 26, MODIFIED HUNTERS CURVE
Curve A
RESTAURANTS
Curve B
Curve C
HOSPITALS, NURSING HOMES, NURSES’RESIDENCES, DORMITORIES, HOTELS
AND MOTELS
APARTMENTS AND HOUSES
Curve D
OFFICE BUILDINGS, ELEMENTARY AND HIGH SCHOOLS
Figure 26: MODIFIED HUNTERS CURVE
20
PV 592 11/2011
PVI Industries, LLC
Fort Worth, Texas
(817) 335-9531 ▪ (800) 784-8326 ▪ www.pvi.com