The multiplying factor, as applied to obtain the peak hourly demand, in relation to the maximum daily demand is:
- A1.5Correct
- B1.8
- C2.0
- D2.7
Solution
Concept
Peak hourly demand is a multiple of the average hourly demand of the maximum day.
Formula
Peak hourly demand = 1.5 × (Maximum daily demand / 24)
Step-by-step solution
1. Average annual daily demand is taken as the base. 2. Maximum daily demand = 1.8 × average daily demand. 3. Peak hourly demand = 1.5 × average hourly demand of the maximum day. 4. So, relative to the maximum daily demand, the peak hourly demand equals 1.5 × (Max daily / 24) × 24 per day basis, i.e. 1.5 × max daily rate. 5. In many textbooks, the peak factor over the maximum daily demand is given as 1.5. The overall factor over the average is 2.7 (1.8 × 1.5).
Explanation
Peak hourly demand is 1.5 times the maximum daily demand (on an hourly-rate basis). The value 2.7 is the factor over the average daily demand, not over the maximum daily demand. So the answer is 1.5.
Why the other options are wrong
A is the correct choice. B (1.8) is the factor of max daily over average daily. C (2.0) is not a standard factor here. D (2.7) is the factor of peak hourly demand over the average daily demand.
Shortcut
Remember: 1.8 × 1.5 = 2.7. Over the maximum daily, the factor is 1.5.
Common mistake
Choosing 2.7, which is the factor over the average demand, not the maximum daily demand.
Correct answer: A) 1.5