How to find total Kw Usage of an A/C Unit PLEASE HELP

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  • #1
i am trying to find the total kw usage of a 10 ton rooftop unit. Its model # is TCD120C40AAB. Its EER value is 9.2. Nominal CFM is 4000. Gross Cooling Capacity is 125,000. System Power is 12.83 kw.

I am trying to figure out how much kw i will be saving by getting a "cool roof" instead of a typical black roof. The white roof will have R-20 insulation as the black roof only had R-6.

When i look at the Product Gross Cooling Capacity Performance Data Sheet, i can search what the MBH is going to be at different ambient temperatures. This way i can see what the kw usage is at 165 degree Fahrenheit and the kw usage at 115 degree Fahrenheit and determine how much i would save by implementing a white roof. I just cannot figure out how to calculate the kw usage of my unit at different temperatures as a projection.

  • #2
Welcome to PF!

First, we need to discuss units. You asked for "total kW". The total kW of this unit is 13.83 kW. What you probably really meant was total energy usage. Energy is measured in kWh, not kW.

Now, the question you are asking can't be answered with a simple thumb rule or equation. It needs to be calculated with a computer simulation of the annual air conditioning required by the building.

Also, the temperature vs output data for the AC unit isn't critical here. Even if the AC unit is on the roof, it won't experience a condenser inlet temperature of 165F now and 115 later. But what will happen is the black roof will make the building heat up less than it does now, making the AC unit run less often, and that's where most of the savings comes from.
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  • #3
So its better to have a black roof or white roof, and do you mean that the white roof will make the building heat up less?

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