HVAC Internal Loads for Load Calculation
HVAC Internal Loads for Load Calculation
(OP)
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.
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.





RE: HVAC Internal Loads for Load Calculation
RE: HVAC Internal Loads for Load Calculation
Short of buying any more software, any advice?
RE: HVAC Internal Loads for Load Calculation
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
RE: HVAC Internal Loads for Load Calculation
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!
RE: HVAC Internal Loads for Load Calculation
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.
RE: HVAC Internal Loads for Load Calculation
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.