single family dwelling calculation question?

[ch_0124]

I am preparing for the Colorado state exam for my journeyman's license and I have a question about load calculations. I have been working on industrial projects for about 7 years now and haven't had to deal with air conditioners and don't exactly understand all the components of a air conditioning and heating system in a house. I understand pretty much everything about the calculation except when i have electric heat, air handler(blower motor), air conditioner compressor, and a condenser fan motor. I know that the code allows you to omit the larger of the loads on heating and air but would the blower motor and condenser fan motor be factored into the heating and air load or would they just be appliances fastened in place? I have looked everywhere trying to find this answer and i really can't find much info on it.

 

[chris kennedy]

I know that the code allows you to omit the larger of the loads on heating and air

Backwards.

220.60 Noncoincident Loads.
Where it is unlikely that two or more noncoincident loads will be in use simultaneously, it shall be permissible to use only the largest load(s) that will be used at one time for calculating the total load of a feeder or service.

 

[Smart $]

In HVAC systems you can have heating loads and air-conditioning loads... but you can also have loads conincidental to both... and such loads have to be considered when using only heating or only air-conditioning loads to determine service ampacity.

 

[ch_0124]

i was just unsure about whether or not the two other loads were associated with both heating and air.

 

[LarryFine]

In case you didn't catch Chris' comment, you can omit the lesser of the heat and AC load calcs. Figure the 'worst-case' load of both heat and AC separately, and include whichever is greater.

One thing that can trip you up is that many heat pumps allow the compressor to run even when the backup, or auxillary, heat is called for, as long as it's still able to contribute some heat.

 

[Buck Parrish]

I am preparing for the Colorado state exam

about the calculation except when i have electric heat, air handler(blower motor), air conditioner compressor, and a condenser fan motor.

but would the blower motor and condenser fan motor be factored into the heating and air load or would they just be appliances fastened in place?

If it is a question on a test they may want you to figure the entire load for the furnace. Heat strips, fan , etc...

Where in the field that furnace will already be marked for the breaker and circuit size. In most cases:smile:

 

[Smart $]

i was just unsure about whether or not the two other loads were associated with both heating and air.

If it utilizes electrical energy for the heating and/or cooling of the occupancy, its load is calculated as heating and/or cooling equipment, and not as fixed-in-place utilization equipment.

As to which is used in both heating and cooling may depend on the configuration... such as a heat pump scenario Larry mentioned, where the compressor and [outside heat exchanger] fan may run to supplement the furnace. Typically, the blower is also used for both, in forced air systems.