PVI Industries, LLC ▪ Fort Worth, Texas

WATER HEATER SIZING GUIDE

FOR ENGINEERS

COMMERCIAL ▪ INSTITUTIONAL ▪ INDUSTRIAL

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.

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.

WATER HEATER SIZING GUIDE

FOR ENGINEERS

COMMERCIAL ▪ INSTITUTIONAL ▪ INDUSTRIAL

Contents

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

Section

1

2

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.

Section I. APARTMENT HOUSES, HOTELS AND MOTELS

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.

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.

HOTELS AND MOTELS: SPECIAL CONSIDERATIONS

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.

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.

3

ADJUSTMENT FACTORS

CLASSIFICATION

ADJUSTMENT FACTOR AF

APARTMENT HOUSES

1 Bath 4.5 1 Bath and Dishwasher 4.6 1 Bath and Clothes Washer 4.8 1 Bath, Dish and Clothes Washer 4.9 2 Baths 5.0 2 Baths and Dishwasher 5.1 2 Baths and Clothes Washer 5.3 2 Baths, Dish and Clothes Washer 5.4 1 Bath 5.0 2 Baths 5.5

HOTELS AND MOTELS

DIVERSITY FACTORS

NUMBER UNITS* TU

DIVERSITY FACTOR C

1-20 .98 21-40 .96 41-60 .94 61-80 .92 81-100 .89 101-120 .85 121-140 .84 141-160 .81 161-180 .79 181-200 .75 201-260 .70 261-310 .67 311-370 .64 371-440 .63 441-520 .60 521-600 .56 601-680 .54 681-760 .53 761-840 .52 841-920 .51 921-1000 .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.)

4

EXAMPLE

Select water heating equipment for a 200-room 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 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 Then add the loads: Total RD = 1600 Rooms RD + 540 Laundry RD 2140 gph 40°F to 140°F Total SR = 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.

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 (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.

RD Multiplier

(percent reduction in RD)

SR Multiplier

.75 2.4

.50 3.6

.25 4.8

Section I. APARTMENT HOUSES, HOTELS AND MOTELS continued

5

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

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.

Section II. DORMITORIES, FRATERNITY AND SORORITY HOUSES

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. Safety Requirement

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.

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 SR = RD x .4 SR = 593 x .4 SR = 237

EXAMPLE In this type of living, it is very important to separate the living unit hot water system from the kitchen system. Therefore, select a two-heater 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.

Also, select two heaters for the kitchen with a

combined minimum of 900 gallons 40°F to 140°F and 300 gallons storage.

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.

DIVERSITY FACTORS

NUMBER STUDENTS TS

DIVERSITY FACTOR C

NUMBER STUDENTS TS

DIVERSITY FACTOR C

1-9 1.00 50-74 .80 10-19 .97 75-99 .72 20-29 .94 100-199 .65 30-39 .91 200-299 .59 40-49 .88 300-399 .54

400-500 .50

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

(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.

RD Multiplier

(percent reduction in RD)

SR Multiplier

.75 2.5

.50 3.8

.25 5.0

6

7

Section III. HOSPITALS, REST HOMES, NURSING HOMES, CHILDREN´S HOMES and CONVENTS

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. Safety Requirement

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 central-ized 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

ADJUSTMENT FACTOR AF

HOSPITALS 3.7 REST HOMES 3.1 NURSING HOMES 3.1 ORPHANAGES 2.8

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.)

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.

8

DIVERSITY FACTORS

NUMBER UNITS TU

DIVERSITY FACTOR C

NUMBER UNITS TU

DIVERSITY FACTOR C

1-20 .96 261-310 .61 21-40 .92 311-370 .58 41-60 .88 371-440 .55 61-80 .86 441-520 .53

81-100 .82 521-600 .50 101-120 .80 601-680 .47 121-140 .77 681-760 .45 141-160 .75 761-840 .43 161-180 .72 841-920 .41 181-200 .70 921-1000 .39 201-260 .65

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 Then add the requirements together:

Total RD = 1083 Rooms RD 1620 Laundry RD + 900 Kitchen RD 3603 gph 40°F to 140°F Total SR = 433 Rooms SR 648 Laundry SR + 297 Kitchen SR 1378 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.

EXAMPLE 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

(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.

RD Multiplier

(percent reduction in RD)

SR Multiplier

.75 2.6

.50 3.9

.25 5.2

Section III. HOSPITALS, REST HOMES, NURSING HOMES, ORPHANAGES and CONVENTS continued

Section IV. SCHOOLS and CHURCHES

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. Safety Requirement

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 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.

COMMERCIAL, INSTITUTIONAL and INDUSTRIAL LAUNDRIES

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.

EXAMPLE

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

10

EXAMPLE

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.

11

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

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

COIN OPERATED LAUNDRY MACHINE

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.

Customer satisfaction depends on determin-ing the correct Diversity Factor. In the formulas that follow, this factor is built into the C2 and C3 factors.

12

Section VI. FOOD SERVICE ESTABLISHMENTS

Regardless of size, food service establish-ments 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 thermostatical-ly controlled mixing valve to reduce tempera-ture to 110°F.

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 high-temp 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 devel-oped.

SIZING PROCEDURE 1. List all fixtures and equipment that require hot water 2. Make two columns, one for 140°F water and one for 190°F water 3. Enter the gallons required in the appropriate column 4. Total each column 5. Total columns to equal Recovery Demand (RD) at 120°F 6. 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 9. 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:

KITCHEN EQUIPMENT

Gallons at 140°F

Gallons at 190°F

2 Vegetable Sinks 100 2 Double Pot Sinks 140

1 Pre-Rinse (Hand Type) 50

1 Mop Sink 20

2 Bar Sinks 60

6 Lavatories 30

1 Dish Machine (Single-Tank Conveyor) 400

1 Silver Washer 100

400 GPH 500 GPH

SOLUTION 1 (For single system A, storing water at 190°F)

GPH at 190°F = 500 x 1.5 = 750 GPH 40°F to 140°F GPH at 140°F = 400 = 400 GPH 40°F to 140°F

Total RD = 1150 GPH 40°F to 140°F SR = RD x .33 SR = 1150 x .33 SR = 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° = 500 GPH at 140° = 400

RD = 900 GPH at 140°F (with chemical sanitation, the 140°F and 190°F loads are combined into the 140°F load) SR = RD x .33 SR = 900 x .33 SR = 297

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

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.

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 = 500 x .4 = 200 GPH at 140°F GPH at 140°F = 400

RD = 900 = 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.

SR (Primary) = RD x .33 SR (Primary) = 900 x .33 SR (Primary) = 297 SR (Booster) = RD x .33 SR (Booster) = 200 x .33 SR (Booster) = 66

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

TYPE DISH MACHINE

Required GPH 190°F*

Hood - Roll Type 100

Door 150

Single Tank Conveyor - Rack 400

Multiple Tank Conveyor - Rack 450

Flight 500

X Flight 700

Glass Washer 100

Silver Washer 100

GENERAL REQUIREMENTS OF COMMERCIAL AUTOMATIC DISH MACHINES

TYPE EQUIPMENT

Required GPH 140°F*

Vegetable Sink 50

Single Pot Sink 50

Double Pot Sink 70

Triple Pot Sink 100

Pre-Rinse for Dishes (Shower Head Hand Held) 50

Pre-Scraper for Dishes (Salvajor Type) 200

Pre-Scraper for Dishes (Conveyor Type) 250

Mop Sink 20

GENERAL REQUIREMENTS OF KITCHEN EQUIPMENT

Can Washer 100

Lavatory 5

Bar Sink 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. 14

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 45-minute 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 ……………………………………………. 10 minutes Junior High and Senior High School …………….. 10 minutes Industrial …………………………………………….. 10 minutes Foundries and Mines ………………………………. 15 minutes High School Field Houses ………………………... 20 minutes College and Professional Stadiums ……………… 25 minutes Correctional Facilities ……………………………… 45 minutes

15

FORMULA 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 = RD x 1.2 SR = 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.

16

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.

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.

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 = RD x .33 SR = 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.

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

FORMULA

DIVERSITY FACTORS

TOTAL NUMBER OF FIXTURES

DIVERSITY FACTOR C

1-25 1.00 26-50 .97 51-100 .92 101-150 .87 151-200 .82 201-300 .75 301-400 .70 401-500 .63

17

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-pool-temperature” 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 Legend: FORMULA

L = Length in Feet W = Width in Feet AD = Average Depth in Feet E = Energy Factor : for atmospheric gas, use 89 : for TURBOPOWER®, use 78 : for electric, use 0.018

Formula

L x W x AD x E x (DT-40) +

L x W x HL Btu/h (Gas or Oil)

RH 2 KWH (Electric) =

Heat Loss = L x W x HL = Btu/h or KWH

HEAT LOSS FACTORS 75°F POOL TEMPERATURE

AIR TEMPERATURE

°F

WIND VELOCITY

MPH

HL GAS

INPUT BTUH

TURBOPOWER®

INPUT BTUH

ELECTRIC INPUT KWH

40 40 40 40 40

0 5 10 15 20

150 200 250 300 350

131 175 219 263 306

.031

.040

.051

.062

.072 50 50 50 50 50

0 5 10 15 20

107 143 179 215 250

94 125 156 188 219

.022

.029

.037

.044

.051 60 60 60 60 60

0 5 10 15 20

64 86

107 129 150

56 75 94

113 131

.013

.018

.022

.026

.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.

DT = Desired Temperature RH = Required Hours to Heat Pool HL = Heat Loss Factor

EXAMPLE 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) +

40 x 30 x 306 =

36 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.

Sizing Instantaneous and Semi-Instantaneous Water Heaters

The methods for sizing storage water-heating equipment should not be used for instantaneous and semi-instantaneous 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 involv-ing periodic use of shower banks, process equipment, laundry machines, etc., as may occur in field houses, gymna-siums, 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 modi-fied 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 sim-ple 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 simultaneous-ly when students return from a drill. In this case, the heater and piping should be sized for full system flow. Where-as 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 semi-instantaneous 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 fix-ture 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 fix-ture units is 23 gpm.

18 Reprinted from 2007 HVAC Applications with permission of ASHRAE

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

Subtotal 87 FU

b. To size the unit based on actual fixture count and Table 15, the calculation is as follows:

At 87 fixture units, curve D of Figure 26 shows 16 gpm, to which must be added the dishwasher require-ment 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)

Apartments Club

Gymnasi-um Hospitals

Hotels and Dormitories

Industrial Plant

Office Building School

YMCA

Basin, private lav 0.75 0.75 0.75 0.75 0.75 0.75 0.75 0.75 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 Five fixture units per 250 seating capacity

Therapeutic bath - - - 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

Circular wash fountain - 2.5 2.5 2.5 - 4 - 2.5 2.5

Semi-circular wash fountain - 1.5 1.5 1.5 - 3 - 1.5 1.5

Note: Data predate modem low-flow fixtures and appliances. *See Water-Heating Terminology section for definition of fixture unit.

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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 HOSPITALS, NURSING HOMES, NURSES’RESIDENCES, DORMITORIES, HOTELS AND MOTELS

Curve C APARTMENTS AND HOUSES

Curve D OFFICE BUILDINGS, ELEMENTARY AND HIGH SCHOOLS

Figure 26: MODIFIED HUNTERS CURVE

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