Heating and AC loads in the optional dwelling load method

[kyleapec]

I am trying to VE some apartment panels by downsizing them through the optional method. It has been awhile since I've done a dwelling load calculation bear with me. The apartment has a 2.4KVA condensing unit outside and a 7.5KW AHU inside. My question is when I get to 220.82(c) can I only use the AHU under (C)(2) or do I have to use them combined under (C)(1) since the AHU does have cooling capacity?

 

[brantmacga]

Use (C3). 100% of the 2.4kw and 65% of the 7.5kw; the 7.5kw rating should be the supplementary heat strips within the AHU.

So that would be 7.3kw.


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[Romel]

Use (C3). 100% of the 2.4kw and 65% of the 7.5kw; the 7.5kw rating should be the supplementary heat strips within the AHU.

So that would be 7.3kw.


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Isn't Article 220.82 (C)(2) to (C)(3) pertains to heating loads? Whenever I do AC Load Calcs using the optional method, I always go for (C)(1).

If you have a separate space heating/heat pumps, you use 220.82(C)(2) to (3), whichever has a higher demand between (C)(1) and (C)(2) to (6), use that.
The reason being with the option between the cooling demand and heating demand is that heating and cooling wont be used at the same time.

 

[brantmacga]

Isn't Article 220.82 (C)(2) to (C)(3) pertains to heating loads? Whenever I do AC Load Calcs using the optional method, I always go for (C)(1).

If you have a separate space heating/heat pumps, you use 220.82(C)(2) to (3), whichever has a higher demand between (C)(1) and (C)(2) to (6), use that.
The reason being with the option between the cooling demand and heating demand is that heating and cooling wont be used at the same time.

Setup described by OP is a split system with condensing unit and AHU.

The condensing unit is used for heating and cooling, as it pulls and dumps heat.

The 7.5kw rating they gave is for the auxiliary heat strips in the AHU, so if emergency heat is being used, both the condenser and heat strips are typically active unless the system is setup to lock out the condensing unit.


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[Romel]

Setup described by OP is a split system with condensing unit and AHU.

The condensing unit is used for heating and cooling, as it pulls and dumps heat.

The 7.5kw rating they gave is for the auxiliary heat strips in the AHU, so if emergency heat is being used, both the condenser and heat strips are typically active unless the system is setup to lock out the condensing unit.


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Oh I see, If that's the case the procedure would still be calculate the cooling load per (C)(2), then calculate the heating load using (C)(3) (100% of CU + 65% of the AHU Heat strips if both eqpt is meant to be operating simultaneuously)
Whichever higher should be used for the HVAC Demand

 

[brantmacga]

Oh I see, If that's the case the procedure would still be calculate the cooling load per (C)(2), then calculate the heating load using (C)(3) (100% of CU + 65% of the AHU Heat strips if both eqpt is meant to be operating simultaneuously)
Whichever higher should be used for the HVAC Demand

No, you would only use (C)(3). (C)(2) is if there is no supplemental heating and has nothing to do with cooling; with a split system, you do have supplemental heating. The compressor is the primary means of heat but you still have auxiliary strips within the AHU.

Maybe I can explain better;

(C)(1) is for air conditioning only
(C)(2) is for heating only without supplemental heat
(C)(3) is for heating with supplemental heat

pick the larger of those three, unless 4,5,6 would apply to your install. (C)(3) is the setup described by OP and is guaranteed to be the largest load of 1, 2, & 3.

 

[Romel]

Oh I see, If that's the case the procedure would still be calculate the cooling load per (C)(2), then calculate the heating load using (C)(3) (100% of CU + 65% of the AHU Heat strips if both eqpt is meant to be operating simultaneuously)
Whichever higher should be used for the HVAC Demand

"...still be calculate the cooling load per (C)(1)" (correction)

and yes I think we are on the same boat brantmacga.

 

[frofro19]

No, you would only use (C)(3). (C)(2) is if there is no supplemental heating and has nothing to do with cooling; with a split system, you do have supplemental heating. The compressor is the primary means of heat but you still have auxiliary strips within the AHU.

Maybe I can explain better;

(C)(1) is for air conditioning only
(C)(2) is for heating only without supplemental heat
(C)(3) is for heating with supplemental heat

pick the larger of those three, unless 4,5,6 would apply to your install. (C)(3) is the setup described by OP and is guaranteed to be the largest load of 1, 2, & 3.

Where does mini-split systems fit in?