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Mathematishan
Lv 5
Mathematishan asked in Science & MathematicsEngineering · 7 years ago

Electric Power to be paid required for running AHU?

An AHU (Air handling unit) removes an heat load of say 10000 BTU from an office over a period of 200 (25 x 8) hours office operation (this BTU is measured by BTU meter)

The chiller which supplies the cold water to AHU has an power consumption of 1.1 KW/ TR (air cooled condensor which is part of chiller package)

how much units of electric power (KWH) do we pay for.

Update:

For the momnet dont consider any power for running the AHU fan motor

Update 2:

I just gave that 11,000 BTU as an example - yes I meant removing that much Heat in 25 days, 8 hrs/day operation

I was also confused with the unit - but I am told a BTU meter measures heat removed (diff in enthalphy cumulative over 8hrs/day, 25 day)

Okay let me tell you the real number for the office. the AHU has a rated cap of 87 TR (I assume it is same as what you mention as ton) - does it not mean it remove at rated cap 87 x 120000 BTU

Update 3:

sorry 10000 not 11000

Update 4:

Yes that is why the question

this smaller office is part of a bigger office (Total aircooled chiller installed capacity = 350 Tr)

This small office is 10500 carpet sq ft in size, Human occupancy say 125 and say we run the AHU to achieve 24 deg C temp for working personnel, take a diversity of 0.8

An AHU with 87 TR cap is installed

was not sure why ??

Was trying to estimate how much the power bill would actually be. In India it is Rs.15/ KWH or about 0.3 USD per KWH

2 Answers

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  • Thomas C
    Lv 6
    7 years ago
    Favorite Answer

    I'm a bit confused by some of your units.

    Normally cooling equipment has units of 10,000 BTU/Hr.

    Are you saying the equipment is run for 8 hours a day for 25 days out of the month?

    What is the unit 'TR'?

    That being said, I will attempt to answer the question with my assumptions:

    Air conditioning units in the USA have cooling capacities represented in 'tons'. Where one ton is equal to 12,000 BTU/hr. A 'ton' is the cooling provided (heat absorbed) by melting one ton of ice (converting it from solid to liquid) over a 24 hour period.

    The electric power requirements of a relatively small air conditioning unit like this are around 1.1 kW per ton. (If there is an EER or SEER rating on the equipment, we can refine this estimate)

    I will assume operation for 8 hours per day, 25 days a month.

    10,000 BTU / 12,000 BTU/ton = 0.833 tons

    0.833 tons x 1.1 kW per ton = 0.916 kW

    0.916 kW x 8 hours per day x 25 days per month = 183 kWh for the month

    This assumes the cooling equipment is running at 100% rated capacity for the entire 8-hours every day of operation.

    Updates:

    Let's assume your 'TR' units represent "tons of refrigeration". 87 tons is equal to 87 x 12,000 BTU is over a million BTUs. An 87 ton cooling unit is pretty big -- how big is the office?

    If we use the 1.1 kW per ton estimate as the conversation factor to determine the electrical load per ton of cooling, the math is 87 x 1.1 = 95.7 kW. Now must apply the hours of operation.

  • Mathematishan
    Lv 5
    7 years ago

    Thanks, I have understood the concept,

    Don't want you to miss the BA as your effort is appreciated

    If you do want to comment on my latest update you can send me a mail

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