HVAC Internal Loads for Load Calculation

[Casalli]

When performing load calculations on a room by room basis, what is customary for determining internal loads?

For instance, if the residence is a large 10,000 sq ft conditioned space with only two full-time occupants, are the occupants (230 btuh sensible per person, per room, FOR THE WHOLE HOUSE???) to be included in each of the room loads? If not, how should they be included?

I have the same question for the same example residence but regarding lighting and appliances? In a 10,000 sq ft residence are we interested to know every single light and appliance likely to be on during peak load time? If so, how does one come to determine the likely lights and appliances used by only two full-time occupants in such a large space? And further, how to design for situations that they may have guests?

I have read the Manual J procedure for internal loads but do not have a definitive concept of how this should be done.

If you have experience in a similar situation please let me know your thoughts. Thank you.

 

[SAK9]

The schedule function of your load calculation programme will address this.For eg the bed room schedule could be from 10PM to 6AM.Similarly different schedules for dining area and drawing areas.Therefore the coincident peak load can be as low as 50% of the sum of the individual peak loads.

 

[Casalli]

It seems that my residential load software does not offer that function (Wrightsoft), though it is available for a Wrightspft software addition having to do with commercial projects.

Short of buying any more software, any advice?

 

[cdxx139]

I dont do residential, but was told "from somebody" that you dont take into affect the people internal gains for residential cooling, like you do in commercial.

If you think about it, how much air are you really adding to a space because it has one person?

As for large dining rooms, you should discuss with the owner if they expect to have enough cooling for a 30 person dining event (in a 10k sf house that might not be uncommon). If so you provide the cooling for that type of event.



knowledge is power

 

[sspeare]

Buy Manual J Residential Loads from the ACCA, on their web site. I developed an easy-to-use spreadsheet from careful study of Manual J. Manual J covers ALL aspects of load estimation, including "internal loads." As far as determining the NUMBER of occupants, I use this: # Occupants = # bedrooms + 1. This is my own "rule", based on a lifetime of experience. Also, re: "internal loads", you need to add 1,200 BTU/hour for a kitchen load. You should buy that ACCA manual J Handbook - you'll get your money's worth!

 

[walkes]

I would also think that your system design would have some impact on the decisions. If you have decent zone control in this large house then account for the peak for each space. (This is almost small commercial). If the zones are individually thermostatically controlled and your system can tolerate fluctuating loads then you should be okay. Otherwise, you would overcondition spaces that are not in use.

 

[317069]

if you have only two persons living in this house then don't worry, and if you have two persons living in each room also don't worry.
for residential it is not that imporatant because cooiling load is peak load and rarly happen that you reach you design load, most time the actual load is less than calculated load.