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Thread: HVAC Load

  1. #1

    HVAC Load

    Q:Can we assume the Killowatt converted from BTU/hr to be the electrical load of the HVAC Equipment? So that we may use it to calculate the electrical loads of a building.
    It is said that the killowatt calculated from btu/hr is actually mechanical(heAting/cooling) KW and not the electrical KW.

    If it is true, then we need to know the electrical load(consumption) of the HVAC Equipment from the manufacturer/catalog. Am I right?

    Pls. if somebody may clarify.

    gk

  2. #2
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    Hvac - Kw Load Calc

    If the HVAC tons are converted to Btu/Hr (tons x 12,000) and then divided by the unit's EER (typically 8-10 for commercial equipment), one will get a KW that is usually conservative. A seasoned mentor of mine taught me this trick and it has worked the majority of the time for capacity planning,

    Once the mechanical designers know there exact load and have selected equipment, one should confirm the actual load with the manufacturer's data sheets.

    DPW

  3. #3
    Quote Originally Posted by DPW
    If the HVAC tons are converted to Btu/Hr (tons x 12,000) and then divided by the unit's EER (typically 8-10 for commercial equipment), one will get a KW that is usually conservative. A seasoned mentor of mine taught me this trick and it has worked the majority of the time for capacity planning,

    Once the mechanical designers know there exact load and have selected equipment, one should confirm the actual load with the manufacturer's data sheets.

    DPW
    Dear DPW,

    Thanks. What does EER mean? My question is - can we consider the kw obtained by converting btu/Hr as the electrical load in kw?
    gk

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    Energy Efficiency Ratio.

    Acronym Finder

  5. #5
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    Quote Originally Posted by gulkhan123
    My question is - can we consider the kw obtained by converting btu/Hr as the electrical load in kw?
    gk
    Please clarify your equation. If you're saying a 4 TON AC, which is 48000 btu/hr, divided by btu per kw (48000/3412) is 14 KW, then you'll be oversized by a factor of 2 to 3. So yes you'd be plenty conservative using this conversion, but wasting quite a bit of service capacity.

    The EER is a rating from the manufacturer. It is basically the BTU/3.412/COP. The COP is Coefficient of Performance in heat pumps and is basically the factor you save by pumping heat rathing than converting it directly. It is easier to understand in heating mode -- a baseboard heater of 12K BTU uses 3 times the electricity of a 12K BTU COP=3 heat pump.

    Typical COP values range from 2 to 3 depending on ambient temperature and how hot or cold you want the interior of the building compared to what they designed it to.

    You could probably take the BTU rating and divide by 6800 and at least be closer.
    Mark
    Kent, WA

  6. #6

    Eelctrial load(KW) of HVAC

    Quote Originally Posted by suemarkp
    Please clarify your equation. If you're saying a 4 TON AC, which is 48000 btu/hr, divided by btu per kw (48000/3412) is 14 KW, then you'll be oversized by a factor of 2 to 3. So yes you'd be plenty conservative using this conversion, but wasting quite a bit of service capacity.

    The EER is a rating from the manufacturer. It is basically the BTU/3.412/COP. The COP is Coefficient of Performance in heat pumps and is basically the factor you save by pumping heat rathing than converting it directly. It is easier to understand in heating mode -- a baseboard heater of 12K BTU uses 3 times the electricity of a 12K BTU COP=3 heat pump.

    Typical COP values range from 2 to 3 depending on ambient temperature and how hot or cold you want the interior of the building compared to what they designed it to.

    You could probably take the BTU rating and divide by 6800 and at least be closer.
    Mark,

    Do you mean the electrical load of the HVAC equipt will be= (BTU/Hr)/3412/2 KW. Is this right?

    ghk

  7. #7
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    One horsepower per ton is the rule of thumb for comfort cooling temperatures with typical refrigerants (22, 134a or 410a).

  8. #8
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    Quote Originally Posted by gulkhan123
    Do you mean the electrical load of the HVAC equipt will be= (BTU/Hr)/3412/2 KW. Is this right?
    It would be if your COP is 2 and there is nothing unusual (like a giant fan, some fancy controls, or they use chilled water). Do you have nothing to go on -- no nameplate to look at (MCA or FLA/RLA), no manufacturers spec which lists EER or circuit ampacity?

    I'd try to find data for at least one unit as a sanity check.
    Mark
    Kent, WA

  9. #9
    Quote Originally Posted by suemarkp
    It would be if your COP is 2 and there is nothing unusual (like a giant fan, some fancy controls, or they use chilled water). Do you have nothing to go on -- no nameplate to look at (MCA or FLA/RLA), no manufacturers spec which lists EER or circuit ampacity?

    I'd try to find data for at least one unit as a sanity check.
    Mark,

    Thanks. Actually sometimes we need to estimate the electrical load of a building when we know the HVAC load in BTU/Hr,. At that time we need to estimate the electrical load of the HVAC in addition to other loads. We dont have any nameplate or say catlog etc. to determine the electrical load of the HVAC equipment. So I will use the above rule you mentioned.

    I will appreciate for the data you said will try to find.

    gk

  10. #10

    HVAC load

    Quote Originally Posted by mdshunk
    One horsepower per ton is the rule of thumb for comfort cooling temperatures with typical refrigerants (22, 134a or 410a).
    Marck,

    Thanks. That means the HP we get from the Tons can be onverted to KW (1 HP= .746 KW), and this KW obtained can be assumed as electrical load of the HVAC Equipment.

    Pls confirm if I am right.

    gk

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