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Spring Wound Timers on Washroom Exhaust Fans |
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rev. 2008-12-07
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Spring Wound Timers on Washroom Exhaust Fans |
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rev. 2008-12-07
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Existing Conditions
Some washrooms have exhaust fans running continuously even when they are unoccupied. This uses unnecessary electricity at the fan motor, and also removes conditioned (heated or cooled) air from the space. Incoming makeup air must then be conditioned to replace the exhaust flow.
Retrofit Conditions
Wall mounted spring wound mechanical timers can be installed where occupants can activate smaller exhaust fans as needed. We recommend spring wound timers, with maximum operating time shown in brackets, on the following exhaust fans:
• Xxx (30 min)
• Xxx (60 min)
Further Benefits
Application Details
In spaces with irregular usage, install rundown timer switches to provide user control of air handling system operation.
Inexpensive and fairly foolproof. Somewhat less efficient than personnel sensors. Limited in application by inability to anticipate occupancy for warm-up and cool-down.
Issues and Concerns
Some users will not use the timers, while others will always wind the timers to the full extent every time. Make sure that the maximum timer period is suitable for the situation.
References
Analysis
This is a sample analysis, using temperature bin calculations. The tables can be copied to a spreadsheet. Note that most of the savings come from the volumes of conditioned air, not from the fan motors.
Assumed:
CFM |
mbh/gj |
kW Fan |
100 |
0.001055 |
0.100 |
A |
B |
C |
D |
E |
F |
G |
H |
I |
J |
K |
L |
M |
N |
O |
P |
Q |
R |
S |
T |
U |
V |
W |
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|
|
|
|
Natural Gas Consumption |
Electricity Consumption KWH |
|
Existing Conditions |
|
|
Retrofit Conditions |
Savings |
||||||||||
Start |
Stop |
Average F |
Average C |
Total Bin Hours |
Base |
Winter |
Total |
Base |
Summer |
Winter |
Total |
Fan Duty Cycle |
Heating cons. GJ |
Cooling cons. kWh |
Fan Cons. kWh |
Bin Hours 30% cycle |
Heating cons. GJ |
Cooling cons. kWh |
Fan Cons. kWh |
Heating cons. GJ |
Cooling cons. kWh |
Fan Cons. kWh |
10 |
15 |
13 |
-11 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
100% |
0.0 |
0.0 |
0.0 |
0 |
0.0 |
0.0 |
0 |
0.0 |
0.0 |
0.0 |
15 |
20 |
18 |
-8 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
100% |
0.0 |
0.0 |
0.0 |
0 |
0.0 |
0.0 |
0 |
0.0 |
0.0 |
0.0 |
20 |
25 |
23 |
-5 |
3 |
1 |
1 |
2 |
228 |
0 |
204 |
432 |
100% |
0.0 |
0.0 |
0.3 |
1 |
0.0 |
0.0 |
0 |
0.0 |
0.0 |
0.2 |
25 |
30 |
28 |
-3 |
97 |
18 |
34 |
52 |
7,761 |
0 |
5,774 |
13,535 |
100% |
0.5 |
0.0 |
9.7 |
29 |
0.1 |
0.0 |
3 |
0.3 |
0.0 |
6.8 |
30 |
35 |
33 |
0 |
551 |
101 |
165 |
266 |
44,178 |
0 |
26,103 |
70,282 |
100% |
2.4 |
0.0 |
55.1 |
165 |
0.7 |
0.0 |
17 |
1.6 |
0.0 |
38.6 |
35 |
40 |
38 |
3 |
1,034 |
189 |
258 |
447 |
82,818 |
0 |
36,257 |
119,075 |
100% |
3.8 |
0.0 |
103.4 |
310 |
1.1 |
0.0 |
31 |
2.7 |
0.0 |
72.3 |
40 |
45 |
43 |
6 |
1,503 |
275 |
300 |
575 |
120,449 |
0 |
34,294 |
154,743 |
100% |
4.7 |
0.0 |
150.3 |
451 |
1.4 |
0.0 |
45 |
3.3 |
0.0 |
105.2 |
45 |
50 |
48 |
9 |
1,539 |
282 |
231 |
513 |
123,328 |
0 |
16,235 |
139,564 |
100% |
3.9 |
0.0 |
153.9 |
462 |
1.2 |
0.0 |
46 |
2.8 |
0.0 |
107.7 |
50 |
55 |
53 |
11 |
1,503 |
275 |
151 |
426 |
120,433 |
0 |
0 |
120,433 |
100% |
3.0 |
0.0 |
150.3 |
451 |
0.9 |
0.0 |
45 |
2.1 |
0.0 |
105.2 |
55 |
60 |
58 |
14 |
1,202 |
220 |
61 |
281 |
96,353 |
0 |
0 |
96,353 |
100% |
1.7 |
0.0 |
120.2 |
361 |
0.5 |
0.0 |
36 |
1.2 |
0.0 |
84.2 |
60 |
65 |
63 |
17 |
752 |
138 |
1 |
138 |
60,268 |
0 |
0 |
60,268 |
100% |
0.6 |
0.0 |
75.2 |
226 |
0.2 |
0.0 |
23 |
0.4 |
0.0 |
52.6 |
65 |
70 |
68 |
20 |
381 |
70 |
0 |
70 |
30,491 |
2,473 |
0 |
32,964 |
100% |
0.1 |
0.0 |
38.1 |
114 |
0.0 |
0.0 |
11 |
0.1 |
0.0 |
26.6 |
70 |
75 |
73 |
23 |
148 |
27 |
0 |
27 |
11,837 |
2,509 |
0 |
14,346 |
100% |
0.0 |
17.5 |
14.8 |
44 |
0.0 |
5.3 |
4 |
0.0 |
12.3 |
10.3 |
75 |
80 |
78 |
25 |
32 |
6 |
0 |
6 |
2,536 |
869 |
0 |
3,406 |
100% |
0.0 |
11.3 |
3.2 |
9 |
0.0 |
3.4 |
1 |
0.0 |
7.9 |
2.2 |
80 |
85 |
83 |
28 |
15 |
3 |
0 |
3 |
1,203 |
570 |
0 |
1,772 |
100% |
0.0 |
8.9 |
1.5 |
5 |
0.0 |
2.7 |
0 |
0.0 |
6.2 |
1.1 |
85 |
90 |
88 |
31 |
1 |
0 |
0 |
0 |
77 |
46 |
0 |
123 |
100% |
0.0 |
0.8 |
0.1 |
0 |
0.0 |
0.2 |
0 |
0.0 |
0.6 |
0.1 |
90 |
95 |
93 |
34 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
100% |
0.0 |
0.0 |
0.0 |
0 |
0.0 |
0.0 |
0 |
0.0 |
0.0 |
0.0 |
95 |
100 |
98 |
36 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
100% |
0.0 |
0.0 |
0.0 |
0 |
0.0 |
0.0 |
0 |
0.0 |
0.0 |
0.0 |
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|
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8,760 |
1,604 |
1,201 |
2,806 |
701,961 |
6,468 |
118,867 |
827,296 |
|
21 |
38 |
876 |
2,628 |
6 |
12 |
263 |
15 |
27 |
613 |
Columns A to L are taken from the raw bin data, and HDD and CDD coefficients.
Column M is the existing fan duty cycle
Column N = IF(1.08 x CFM x (70-C)>0,1.08 x CFM x (70-C),0) x E/1000 x (MBh/GJ) ÷ M
Column O = IF(1.5 x 1.08 x CFM x (70-C)<0,1.5 x 1.08 x CFM x (70-C),0) x E ÷ 3414 x (-1)
Column P = (kW Fans) x E
Column Q = E x 0.3
Column R = N x 0.3
Column S = O x 0.3
Column T = P x 0.3
Column U = N - R
Column V = O - S
Column W = P - T
If there is no air conditioning, remove Column O and S.