FREE Certified Energy Manager Motors and HVAC Questions and Answers

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At a flow rate of 6750 cubic feet per minute, air with a relative humidity of 50% and a dry bulb temperature of 69°F is heated to 90°F. How much BTU per hour is needed for this process? Don't consider duct losses.

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There are roughly how many cooling degree days in a calendar year if the outside temperature stays constant at 75°F:

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" 65 Degrees F is the “target” outside temperature. If the average temperature is 75, then we are 10 degrees “off target”. For 365 days, the Cooling Degree Days would be:
(10)(365)
=3,650 CDD per year"

The COP of a 250-ton chiller is 4.2. What is the chiller's load (in kW) while it is operating at full capacity?

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Power input divided by Powermoved is the Coefficient of Performance. This machine can move 250 tons of cooling using a 250 ton chiller, hence the power input would be:

How much can you afford to spend for the waste heat exchanger (total installation cost) if your company's MARR is 30% and it saves $1,000,000 year and lasts for 7 years?

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In this problem, we are given A and must find P. Logically, for this project to have a positive NPV, we know the P (from the positive cash flows) must be at least equal to the Cost. Thus, let's find the P and then that is the maximum we can pay for the installed cost. The PV of the Annual Savings of $1,000,000 per year:
= $1,000,000/year (P/AIN Factor)
= $1,000,000/year (2.8021)
= $ 2,802,100
Thus, we can pay $2,802,100 for the Waste Heat Exchanger and still have a positive NPV.

The US industries and structures with the highest installation rates of electric motors are:

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Induction of Alternating Current The most common form of motor used in buildings is a motor.

Pick the most accurate estimate of electric motor efficiency (in percent) when motors are appropriately loaded in the absence of additional data:

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An appropriately loaded motor typically operates at 90% efficiency.

What are HP savings if a motor has a Variable Speed Drive (VSD) fitted that slows down a 200 HP motor by 20%?

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Use the “Fan Laws” HP2=HP1 (RPM2/RPM1)3. Therefore, if the new speed (RPM2) is 80% of the old speed (RPM1), the new power load (HP2) will be:
HP2=HP1 (.8)3
HP2=200HP (0.512)
HP2=102.4 HP

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