Installation & Service Manual
7Domestic water heaters (continued)
Water Chemistry
The required temperature rise and the standard pump sizing are based on the heating of potable water with chemistry within the specified limits. Caution should be used when heating water softened to less than 5 grains per gallon. Many commercial water softeners reduce hardness to 0 grains which may result in long term problems in the system. Softened water will usually have a lower pH which can be aggressive and corrosive causing
Corrosion due to water chemistry generally shows up first in the hot water system because heated water increases the rate of corrosive chemical reactions. As water is heated it becomes less soluble. The dissolved minerals and solids will precipitate and collect as scale if water velocity is not properly controlled. Follow the temperature rise requirements for unsoftened water. Consult the manufacturer when heating potable water with hardness or total dissolved solids exceeding these specifications. Heating of high hardness and/or high total dissolved solids water may require a larger circulating pump, an optional
Softened Water Systems
Decreasing the flow rate will reduce the erosion process, however the heat exchanger should be monitored to ensure the scale/liming process is not made worse. The unit should be placed on a comprehensive inspection schedule until optimum flow rates can be established. Problematic water areas may require heat exchanger inspection every two weeks. The total scale accumulation should never exceed the thickness of a piece of paper. Should scale accumulation exceed this thickness the flow rate will need to be increased. The tubes should not have a bright shiny copper look. This would indicate that the erosion process has begun and the flow rate will need to be decreased. Once the proper flow rates have been established the inspection intervals can be increased to every 30 days, once a quarter, or to a
TABLE - 7B
COMMON WATER MANIFOLD SIZE FOR MULTIPLE HOT WATER SUPPLY BOILER INSTALLATIONS
Pipe sizing chart provides minimum pipe size for common manifold piping and tank tappings to ensure adequate flow.
| Number of Units | Common Manifold Size (Min.) |
|
|
|
|
|
| 1 | 2" |
|
|
|
|
|
| 2 | 2" |
|
|
|
|
|
| 3 | 2 1/2" |
|
|
|
|
|
| 4 | 3" |
|
|
|
|
|
| 5 | 3 1/2" |
|
|
|
|
|
| 6 | 3 1/2" |
|
|
|
|
|
Pump Operation
1.The water heater/hot water supply boiler must be connected to a properly sized pump that circulates water between the heater and storage tank.
2.A standard water heater is furnished with a 1/6 HP, 120 VAC, 3.6 AMP circulating pump to be mounted on the units inlet water connection. This pump is sized based on
installation of a single storage tank and heater in close
proximity. If the number of fittings and straight pipe exceeds the quantities shown in this section, a larger pump will be required.
3.The pump must run continuously when the burners are firing.
4.Lubricate the pump to the manufacturers recommendations. Pump damage due to inadequate lubrication is
5.Pump is sized to heater input and water hardness. Care should be taken to size the pump correctly. See “Water Chemistry”, this page.
The standard pump selection is based on the following pipe and fittings from the unit to the storage tank:
6 | - 90° elbows | 2 - ball valves |
2 | - unions | 1 - cold water tee |
Plus the following length of straight pipe based on the heater size:
90,000 through 360,000 Btu/hr Models Not more than 45 feet of straight pipe
399,999 through 500,000 Btu/hr Models Not more than 25 feet of straight pipe
For every elbow and tee in excess of those shown above, DEDUCT 5 FEET from maximum allowable straight pipe in heater to tank circulating loop.
47
