B) On/Off Conditions: Btu Requirements - A.O. Smith T-H3J-DV Service Manual

12-8. (B) ON/OFF conditions: BTU requirements

A. Calculating the ON/OFF conditions of the water heater
"Condition needed to turn the water heater ON"
( T – T ) × GPM × 500 > 14,880
set in
"Condition needed to turn the water heater OFF"
( T – T ) × GPM × 500 < 11,900 or T
set in
Where: T = Set temperature and T
set
B. Calculation example
Set temperature: T
set
"Condition needed to turn the water heater ON"
(120 – T ) × 2.5 × 500 > 14,880
in
"Condition needed to turn the water heater OFF"
(120 – T ) × 2.5 × 500 < 11,900
in
C. ON/OFF table
Set temperature
(˚F)
ON 40.5
100
OFF 52.4
ON 50.5
110
OFF 62.4
ON 60.5
120
OFF 72.4
ON 70.5
130
OFF 82.4
ON 80.5
140
OFF 92.4
ON 90.5
150
OFF 102.4
ON 100.5
160
OFF 112.4
ON 115.5
175
OFF 127.4
ON 125.5
185
OFF 137.4
240 (T-H3J), 340 (T-H3S) and 540 (T-H3) models Service Manial
= T
in set
= Inlet temperature
in
= 120˚F Flow rate = 2.5 GPM
T < 108.1 ˚F
in
T > 110.5 ˚F
in
The output temperature at that moment will be 120 ˚F
0.5 1.0 1.5
70.2 80.2
76.2 84.1
80.2 90.2
86.2 94.1
90.2 100.2
96.2 104.1
100.2 110.2
106.2 114.1
110.2 120.2
116.2 124.1
120.2 130.2
126.2 134.1
130.2 140.2
136.2 144.1
145.2 155.2
151.2 159.1
155.2 165.2
161.2 169.1
72
Flow rate (GPM)
2.0 2.5 3.0
85.1 88.1 90.1
88.1 90.5 92.1
95.1 98.1 100.1
98.1 100.5 102.1
105.1 108.1 110.1
108.1 110.5 112.1
115.1 118.1 120.1
118.1 120.5 122.1
125.1 128.1 130.1
128.1 130.5 132.1
135.1 138.1 140.1
138.1 140.5 142.1
145.1 148.1 150.1
148.1 150.5 152.1
160.1 163.1 165.1
163.1 165.5 167.1
170.1 173.1 175.1
173.1 175.5 177.1
Page
CONFIDENTIAL
Ver. 1.00
3.5 4.0
91.5 92.6
93.2 94.0
101.5 102.6
103.2 104.0
111.5 112.6
113.2 114.0
121.5 122.6
123.2 124.0
131.5 132.6
133.2 134.0
141.5 142.6
143.2 144.0
151.5 152.6
153.2 154.0
166.5 167.6
168.2 169.0
176.5 177.6
178.2 179.0