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