A.O. Smith On Demand 305 Series 100, On Demand 705 Series 100, On Demand 505 Series 100, On Demand Series 100 186965-001 User Manual

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On-DemandWater Heater

System Design Manual

Design information for single and multiple unit installations for residential, commercial, recirculation and storage tank systems.

PRINTED 0209

186965-001

Table of Contents

Certifications..................................................................................

3

Installing Gas Water Heater...........................................................

4-7

Water Quality and Scale................................................................

8

Pump Sizing for Circulation..........................................................

9

Tank Water Heaters in a Circulation Loop...................................

10

Additional Guidelines....................................................................

10

Pump Sizing for Storage Tank Applications ...............................

11

Pressure Loss Curves ..................................................................

12-13

Domestic Hot Water - Standard Installation

 

1

Water Heater (H-1).......................................................................

14

2

Water Heaters (H-2) .....................................................................

15

3

Water Heaters (H-3) .....................................................................

16

4

Water Heaters (H-4) .....................................................................

17

5

Water Heaters (H-5) .....................................................................

18

6

Water Heaters (H-6) .....................................................................

19

Domestic Hot Water with Optional Freeze Protection

 

on Outdoor Models

 

1

Water Heater (H-1-E) ...................................................................

20

2

Water Heaters (H-2-E) .................................................................

21

3

Water Heaters (H-3-E) .................................................................

22

6

Water Heaters (H-6-E) .................................................................

23

Domestic Hot Water with Circulation Systems

 

1

Water Heater - Preferred (H-1-RP)...............................................

24

1

Water Heater - Optional (H-1-RO)................................................

25

2

Water Heaters - Preferred (H-2-RP) ............................................

26

2

Water Heaters - Optional (H- 2-RO)..............................................

27

3

Water Heaters - Preferred (H-3-RP) ............................................

28

6

Water Heaters - Preferred (H-6-RP).............................................

29

Domestic Hot Water with Backup Storage Tanks

 

1

Water Heater (H-1-T) ...................................................................

30

1

Water Heater with Circulation (H-1-TC) ........................................

31

2

Water Heaters (H-2-T) ..................................................................

32

2

Water Heaters with Circulation (H- 2-TC)......................................

33

3

Water Heaters (H-3-T) .................................................................

34

3

Water Heaters with Circulation (H- 3-TC) .....................................

35

6

Water Heaters (H-6-T) .................................................................

36

6

Water Heaters with Circulation (H- 6-TC) .....................................

37

Maintenance Procedure

 

Scale Flush Procedure (MP-01).......................................................

38

2

Approvals

ATI-305-NGTS-305-NIATI-305-PGTS-305-PIATO-305-NGTS-305-NEATO-305-PGTS-305-PEATI-505-NGTS-505-NIATI-505-PGTS-505-PIATO-505-NGTS-505-NEATO-505-PGTS-505-PEATI-705-NGTS-705-NIATI-705-PGTS-705-PIATO-705-NGTS-705-NEATO-705-PGTS-705-PE*ATI-705A-N*GTS-705-NIA*ATI-705A-P*GTS-705-PIA*ATO-705A-N*GTS-705-NEA

*ATO-705A-P*GTS-705-PEA

GT-305-NIGT-305-PIGT-305-NEGT-305-PEGT-505-NIGT-505-PIGT-505-NEGT-505-PEGT-705-NIGT-705-PIGT-705-NEGT-705-PE*AGT-705-NI*AGT-705-PI*AGT-705-NE

*AGT-705-PE

The models listed in this manual have received the following certifications except where noted:

Certified to applicable U.S. standards for appliances using gas or other petroleum fuel.

Certified to applicable Canadian standards for appliances using gas or other petroleum fuel.

UP

C

Certified by the Uniform

 

Plumbing Code (UPC)

 

 

Certified by National Sanitation Foundation (NSF), www.nsf.org

(indoor models must use the NSF approved top guard)

Air-Conditioning,Heating and

Refrigeration Institute

Met the California Energy Commission (CEC) standards

Approved by the Commonwealth of Massachusetts (G1-0208-249)

Received New York City’s Material

and Equipment Acceptance (MEA)

(MEA 327-02-EVol. 09)

(MEA 327-02-EVol. 10)

(MEA 327-02-EVol. 11)

R

*Water heaters are built in accordance with the requirements of the ASME Boiler and Pressure Vessel Code and received the Certificate of Authorization from the National Board. The heat exchanger has the NB and the HLW stamps.

The California Safe Drinking Water and Toxic Enforcement Act requires the Governor of California to publish a list of substances known to the State of California to cause cancer, birth defects, or other repoductive harm, and requires businesses to warn of potential exposure to such substances.

WARNING: This product contains a chemical known to the State of California to cause cancer, birth defects, or other reproductive harm.

This appliance can cause low-levelexposure to some of the substances included in the Act.

3

Installation

Consumer Information

The on-demandwater heaters must be installed according to all local and state codes or, in the absence of local and state codes, the “National Fuel Gas Code”, ANSI Z223.1 (NFPA 54) - current edition.

CSA American, Inc.

National Fire Protection Association

8501 East Pleasat Valley Road

1 Batterymarch Park

Cleveland, OH 44131

Quincy, MA 02269

Check your phone listings for the local authorities having jurisdiction over your installation.

Consumer Responsibilities

This manual has been prepared to acquaint you (trained service technician) with the installation, operation, and maintenance of the on-demandwater heater and provide important safety information in these areas.

Read all of the instructions thoroughly before attempting the installation or operation of the water heater. Service to the on-demandsystem should only be performed by a trained service technician.

Massachusetts code requires this water heater to be installed in accordance with Massachusetts Plumbing and Fuel Gas Code 248 CMR Section 2.00 and 5.00.

Water Temperature Regulation

For systems with storage tanks, the water temperature in certain situation may vary up to 30°F (16.7°C) higher or lower at the point of use such as, bathtubs,showers, sink, etc. HOTTER WATER CAN SCALD: Water heaters, are intended to produce hot water. Water heated to a temperature which will satisfy space heating, clothes washing, dish washing, and other sanitizing needs can scald and permanently injure you upon contact. Some people are more likely to be permanently injured by hot water than others. These include the elderly, children, the infirm, or physically/ mentally handicapped. If anyone using hot water in the home fits into one of these groups or if there is a local code or state law requiring a certain temperature water at the hot water tap, then you must take special precautions.

WARNING

Water temperature over 125°F can cause severe burns instantly or death from scalds.

Children, disabled and elderly are at highest risk of being scalded.

Feel water before bathing or showering. Temperature limiting valves are available.

4

Installation

In addition to using the lowest possible temperature setting that satisfies your hot water needs, a means such as a mixing valve, should be used at hot water taps used by these people or at the water heater.

Mixing valves are available at plumbing supply or hardware stores. Follow manufacturer’s instructions for installation of the valves. Before changing the factory setting on the thermostat see table below. Using the lowest hot water temperature that meets your needs will also provide the most energy efficient operation of the water heater.

Never allow small children to use a hot water tap, or to draw their own bath water. Never leave a child or handicapped person unattended in a bathtub or shower.

NOTE: A water temperature range of 120°F - 140°F(49°C-60°C)is recommended by most dishwasher manufacturers.

Temperature

Time to Produce 2nd & 3rd

Settings

Degree Burns on Adult Skin

160°F (71°C)

About 1/2 second

150°F (66°C)

About 1-1/2seconds

140°F (60°C)

Less than 5 seconds

130°F (54°C)

About 30 seconds

120°F (49°C)

More than 5 minutes

80°F (27°C)

- - - - - - - - - - - - - - - -

Table “A”

The thermostat of the water heater has been factory set at 120° F, to reduce the risk of scald injury. It is adjustable and can be reset to the desired temperature setting. Some states have a requirement for a lower setting. If you need hotter water, follow directions for temperature adjustment, but beware of the warnings in this section.

Site Location

Select a location near the center of the water piping system.

Consider the exhaust vent system piping and combustion air supply requirements when selecting the water heater location. The venting system must be able to run from the water heater to the termination with a minimal length and number of elbows.

Locate the water heater near the existing gas piping. If installing a new gas line, locate the water heater to minimize the pipe length and elbows.

NOTE: This water heater must be installed according to all local and state codes or, in the absence of local and state codes, the “National Fuel Gas Code”, ANSI Z223.1(NFPA 54)-currentedition.

• The water heater should be located in an area not subject to freezing temperatures. Water heaters located in unconditioned spaces (i.e., attics, basements, etc.) may require insulation of the water piping and drain piping to protect against freezing. The drain and controls must be easily accessible for operation and service. Maintain proper clearances as specified on the data plate.

5

Main Water Supply

For Storage Tank System Installation

CAUTION - PROPERTY DAMAGE HAZARD

The storage tank should be located in an area where leakage of the tank or connections will not result in damage to the area adjacent to the storage tank or to lower floors of the structure. Due to the normal corrosive action of the water, the tank will eventually leak after an extended period of time. Also any external plumbing leak, including those from improper installation, may cause early failure of the tank due to corrosion if not repaired. If the owner/ operator is uncomfortable with making the repair a qualified technician should be contacted. A suitable metal drain pan should be installed under the storage tank as shown below, to help protect the property

from damage which may occur from condensate formation or leaks in the piping connections or tank. The pan must limit the water level to a maximum depth of 1-3/4”and be two inches wider than the tank and piped to an adequate drain. NOTE: The pan must

not restrict combustion air flow. Locate the storage tank near a suitable indoor drain. Outside drains are subject to freezing temperatures which can obstruct the drain line. The piping should be at least 3/4” ID and pitched for proper drainage.

Figure “1

A suitable metal drain pan should be installed under the storage tank.

1-3/4”max.

At least 2” greater than the storage tank.

Storage Tank

Pipe to an adequate drain

Closed System/Thermal Expansion

CAUTION - PROPERTY DAMAGE HAZARD

As water is heated, it expands (thermal expansion). In a closed system, the volume of water will grow. As the volume of water grows, there will be a corresponding increase in water pressure due to thermal expansion. Thermal expansion can cause premature tank failure (leakage). This type of failure is not covered under the limited warranty. Thermal expansion can also cause intermittent temperature-pressurerelief valve operation: water discharged from the valve due to excessive pressure build up. The temperature / pressure relief valve is not intended for the constant relief of thermal expansion. This condition is not covered under the limited warranty.

A properly-sizedthermal expansion tank should be installed on all closed systems to control the harmful effects of thermal expansion. Contact a local plumbing service agency to have a thermal expansion tank installed.

Figure “2

Hot Water

In a closed system use a

Typical water

Return Line

thermal expansion tank

 

 

piping installation

 

Cold Water

Pressure Reducing

 

 

Inlet Valve

Valve with Bypass

Hot Water

Outlet

Storage

Tank

Metal Drain

Pan 1-3/4”

Depth Max.

Cold Water Supply to Fixture

Temperature and

Pressure Relief Valve

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Discharge line

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

6” Max. above drain

 

 

 

 

 

 

1“ Min.

 

 

 

 

 

 

 

 

 

Drain line 3/4”

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

ID Min.

Massachusetts:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Drain

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Install a vacuum relief

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

in cold water line per

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

section 19 MGL 142

6

For Storage Tank System Installation

Temperature and Pressure Relief Valve

For protection against excessive pressures and temperatures, a temperature and pressure relief valve must be installed in the opening on the on-demandstorage tank. This valve must be design certified by a nationally recognized testing laboratory that maintains periodic inspection of the production of listed equipment or materials as meeting the requirements for Releif Valves for Hot Water Supply Systems, ANSI Z21.22. The function of the temperature and pressure relief valve is to discharge water in large quantities in the event of excessive temperature or pressure developing in the water heater. The valve’s relief pressure must not exceed the working pressure of the water heater as stated on the data plate.

IMPORTANT: Only a new temperature and pressure relief valve should be used with your water heater. Do not use an old or existing valve as it may be damaged or not adequate for the working pressure of the new water heater. Do not place any valve between the relief valve and the tank.

WARNING

Explosion Hazard

If the temperature and pressure relief valve is dripping or leaking, have a qualified service technician replace it.

Examples of a qualified service technician include: Licensed plumbers, authorized gas company personnel, and authorized service personnel.

Do not plug valve. Do not remove valve.

Failure to follow these instructions can result in death, or explosion.

7

Water Quality and Scale

A complete water analysis and an understanding of system requirements are needed to protect the on-demandwater heaters and water heating systems from scale. Water analysis shows whether water is hard or soft. Hard water, unless treated, will cause scaling or liming of the heat exchanger. The rate of scaling increases with temperature and usage because calcium carbonate and other scaling compounds lose solubility (fall out of solution) at higher temperatures. For example, for every 20°F over 140°F, the rate of scale increases by a factor of 2 (See figure below). Reference target water quality levels found in the operation / installation manual and consider water treatment if these levels are exceeded. *

LIME DEPOSITED, lb/yr

210

180

150

120

90

60

30

0

BASED ON 10 grains/gal HARDNESS *

180°F

170°F

160°F

 

 

 

 

 

 

 

150°F

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

140°F

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

120°F

300 0

900

1500

2100

2700

3300

3900

WATER USAGE, gal/day

Figure “3

*Source 2003 ASHRAE Handbook HVAC Applications

8

Pump Sizing for Circulation

1.Use the chart below or one appropriate for your conditions to determine the heat loss in the length of the hot water supply and return piping. For example, 100 ft of 1-1/2in bare copper tubing results in a heat loss of 5300 Btu/h.

Approximate Heat Loss from Piping at 140 ºF Inlet, 70 ºF Ambient *

Nominal Size, in.

Bare Copper Tubing,

1/2 in. Glass Fiber Insulated

 

Btu/h-ft

Copper Tubing, Btu/h-ft

 

 

 

3/4

30

17.7

 

 

 

1

38

20.3

 

 

 

1-1/4

45

23.4

 

 

 

1-1/2

53

25.4

 

 

 

2

66

29.6

 

 

 

2-1/2

80

33.8

 

 

 

3

94

39.5

 

 

 

4

120

48.4

 

 

 

* Source: 2003 ASHRAE Handbook HVAC Applications

Table “B

2.Determine the acceptable temperature drop at the last fixture in the loop. For example, if the supply temperature from the water heater is 120 ºF (49 ºC) and an acceptable temperature at the last fixture is 100 ºF (38 ºC) then the acceptable temperature drop is 20 ºF (7 ºC).

3.Calculate the required pump flow rate using the following formula:

FLOW RATE (gpm) =

HEAT LOSS (BTU / h)

 

500 X ACCEPTABLE TEMPERATURE DROP (ºF )

4. Based on the above calculations select a pump for the type of circulation system you will be utilizing:

A). Preferred Method (reference drawing H-1-RP)- Reference pump manufacturers flow vs. pressure specifications to select a pump that can provide the flow rate calculated above while overcoming the pressure loss through:

Tank water heater (reference manufacturer’s information)

All building supply and return plumbing in the circulation loop (reference local plumbling codes, standards, or practices)

B). Optional Method (H-1-RO)- Reference pump manuf acturers flow vs. pressure specifications to select a pump that can provide 3 gpm of flow or the flow rate calculated above, whichever is greater, while overcoming the pressure loss through:

On demand water heater (reference flow vs. pressure curve of the model being used)

Optional storage tank (reference manufacturer’s information)

All building supply and return plumbing in the circulation loop (reference local plumbling codes, standards, or practices)

NOTE: Only use pumps of brass or stainless steel construction. Do not use pumps of iron construction as they will oxidize and clog the inlet filter on the appliance.

9

Tank Water Heaters in a Circulation Loop

The following applies when using a tank water heater (gas or electric) to provide heat for a circulation loop. Drawing H-1-RPis an example.

The heat output of the tank must be equal to or greater than the calculated circulation loop heat loss.

(Reference page 5, Step 1 on calculating heat loss).

Electric Tank Water Heater

Since the input and output are the same for an electric tank water heater, this can be expressed as:

Electric Tank Input (Kw) > Circulation loop heat loss (Btu/h) 3413

(1 Kilowatt = 3,413 BTU)

Gas Tank Water Heater

When using a gas style water heater, the efficiency of the tank must be taken into account.

Available Btu output = (Btu input of tank) x (efficiency) > Circulation loop heat loss (Btu/h)

Example:

30,000 Btu input gas tank

0.62 Efficiency

30,000 x .62 = 18,600 available Btu output

Additional Guidelines

On-demandwater heaters not recovering a storage tank:In applications involving a commercial dishwasher, a hot water circulation loop feeding the dishwasher is required.

On-demand water heater recovering a storage tank: In applications involving a commercial dishwasher, a hot water circulation loop feeding the dishwasher may be required depending on the distance between the dishwasher and the storage tank. Refer to local codes when determining the need for circulation

loops to dishwashers.

10