Internal loads and lighting used in Manual J 1

[msb01]

Hi,
I am comparing load calculations using manual J and heat balance method for a small office building in Boston. Can anyone let me know what are the internal loads/lighting and minimum ventilation air requirements are considered in Manual J calculations. Also this is a code minimum building and Manual J calculations show 295 sf/ton - does it look reasonable?

Thanks,

MSB0

 

[AbbyNormal]

manual j will have some default values for kitchen and laundry heat, nothing for lights

Not many lights on when the sun is shining, lights at night will not be as much heat as sun during the day

If the place is big enough to have the lights on all the time, like large internal spaces, then run it as a commercial load

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[AbbyNormal]

I should of read your whole post, manual j is for houses not offices

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[Wareagl487]

Manual J calculations are intended for residential load estimation only - not commercial.

Andy W.

 

[msb01]

Thanks everyone..
When I look at the report sent by the designer - it says, "Calculations are based on 8th edition of ACCA manual J). Yes, this is a small office building not a residential. I am sure one needs take into account the equipment and lihting loads for colling load calculations and ignore these loads for heating load calc. i just wanted to know if anyone knows about the default values for lighting/equipment and ventilation in Manual J.

thanks
MSB01

 

[texanman]

For lighting load, you can refer to IECC com-check, this code has max values of Watt/sf for building types. A conservative assumtion is that all the watts are converted in to heat. This gives you a rough idea of heat load for the lights.

 

[AbbyNormal]

that 8th edition seems to minimize heat gains through glass

you want a commercial load calculation run, something set up for complete internal gains,factors in how long lights have been on, spreads out sensible load as solids heat up then release heat

Take the "V" out of HVAC and you are left with a HAC(k) job.

 

[mauricestoker]

If you are reviewing design, then why not use the actual lighting shown on the design?

As no concern is given over whether this is commercial or residential, I'd recommend using the watts/SF given by table in ASHRAE 90.1. For outside air, which will largely dictate SF/TN, I'd use the table from ASHRAE 62.1. If you want to consider lag factor and not overestimate cooling load, I'd recommend using the TETD method for spreadsheet given by ASHRAE. That will take fenestration and latent loading into account as well. You'll need to know how many people will be in the building to set OA in any case. It would also give you dry/wet bulb temp's, for whatever climate zone that is, for guessing if 295 SF/TN is correct.

If you don't like spreadsheet I'd recommend downloading EQUEST because, like my first wife, it is easy and free.

 

[msb01]

Thank you everyone for suggestions. I really appreciate it..