220.84 - what defines "heating" and/or "air conditioning"?

[Floyd R Turbo]

Thanks for pointing that out. Did you scan through the rest of this thread? The 1500 VA of "ghost" electric heat has actually been accepted by some AHJs.

 

[MyCleveland]

I did see that the 1500w was accepted....
Cannot write my opinion on that.

I would stand by that number IF my ME/MC told me it would heat the ENTIRE apartment.

 

[kwired]

Thanks for pointing that out. Did you scan through the rest of this thread? The 1500 VA of "ghost" electric heat has actually been accepted by some AHJs.

1500 VA of resistance heat in 20 different spaces is going to have a different load diversity then a single compressor unit that is intended to heat all of the same spaces I would think. Plus that compressor is also the cooling load, and on a VRF system with three pipes run - you can get heating and cooling at same time in different spaces served.

 

[Mgraw]

1500 VA of resistance heat in 20 different spaces is going to have a different load diversity then a single compressor unit that is intended to heat all of the same spaces I would think. Plus that compressor is also the cooling load, and on a VRF system with three pipes run - you can get heating and cooling at same time in different spaces served.

FYI There are 2 pipe systems that can heat and cool at the same time.

 

[Floyd R Turbo]

1500 VA of resistance heat in 20 different spaces is going to have a different load diversity then a single compressor unit that is intended to heat all of the same spaces I would think.

Maybe, but all that 220.84 section mandates is that you have either one, and...

I would stand by that number IF my ME/MC told me it would heat the ENTIRE apartment.

....while I can see the logic, 220.84 doesn't specify whether or not the presence of that AC/heat is required to actually perform....well....anything - it just says it has to be there. This vagueness might be why the AHJs let it slide, again, it's common sense vs strict adherence to the code.

Plus that compressor is also the cooling load, and on a VRF system with three pipes run - you can get heating and cooling at same time in different spaces served.

while this is true, I don't see how this changes anything

 

[Mgraw]

....while I can see the logic, 220.84 doesn't specify whether or not the presence of that AC/heat is required to actually perform....well....anything - it just says it has to be there. This vagueness might be why the AHJs let it slide, again, it's common sense vs strict adherence to the code.

While 220.84 does not Mechanical code does require some form of heat. It also requires enough heat to bring the space to 68 degrees. AC is not required.

 

[Floyd R Turbo]

Yup, and mechanical code can't take into account something that is not fixed in place, so in the instance where the AHJ signed off on the "ghost" 1500 VA electric heating circuit, there would have had to been a fully functional heating and cooling system in place that didn't need any additional boost from within the unit (such as a VRF system, or central chiller & boiler systems)

 

[kwired]

If you factor in a "ghost load" aren't you generally going to have higher load calculation then if you didn't have it?

20 units with a demand factor applied still yields more needed VA then zero units at 100%

 

[Floyd R Turbo]

If you factor in a "ghost load" aren't you generally going to have higher load calculation then if you didn't have it?

20 units with a demand factor applied still yields more needed VA then zero units at 100%

How do you figure that? Table 220.84 allows a 38% demand factor to be applied to a 20 units, which essentially means those 20 units act like 7.6. The demand factor applies to the total connected load, not just the heating and cooling load.

 

[kwired]

How do you figure that? Table 220.84 allows a 38% demand factor to be applied to a 20 units, which essentially means those 20 units act like 7.6. The demand factor applies to the total connected load, not just the heating and cooling load.

The items in (C)(1-4) are still there all you are doing is adding more load via (C)(5).

If dwelling units are all identical and you have 12.4 kVA of load other then non heating/cooling in each one, adding another 5kVA of heating/cooling to each one is going to increase the minimum needed service or feeder regardless.

Adding a load for a central heating/cooling unit vs. 20 individual units doesn't give you same kind of load diversity and therefore not allowed to apply same demand factor to that load. That individual unit is likely more efficient then 20 separate units for one thing.

 

[Floyd R Turbo]

The items in (C)(1-4) are still there all you are doing is adding more load via (C)(5).

If dwelling units are all identical and you have 12.4 kVA of load other then non heating/cooling in each one, adding another 5kVA of heating/cooling to each one is going to increase the minimum needed service or feeder regardless.

Adding a load for a central heating/cooling unit vs. 20 individual units doesn't give you same kind of load diversity and therefore not allowed to apply same demand factor to that load. That individual unit is likely more efficient then 20 separate units for one thing.

I have a feeling we are talking about the same thing, but I'm not sure so...

A) If you have 12.4 kVA/unit and 20 units with no diversity, that's 248 kVA at 100%. However, you can then use the diversity factors in Section III, but I haven't had the chance to run up an example of this yet to see how it would turn out.

B) If you have 17.4 kVA/unit with 20 units and 38% diversity factor, that's 348 * 0.38 = 132 kVA

So in A above, this would use a centralized system with has no load diversity that can be applied, since the full load may be used from time to time. However, this single load is likely to be much less than the sum of the connected loads for the individual unit based heating and/or cooling, and likely to be roughly equal to those loads actually once 220.84 diversity is applied, as in

C) 12.4 kVA/unit on 20 units at a randomly chosen actual effective diversity of 40% (it will likely actually be 3 kVA + 35% of remaining on the lighting load calc which includes most receptacles, plus the diversity on all ranges) = 99.2 kVA and then if the central cooling/heating is roughly 35 kVA, it's a wash.

This is what I'm getting at. I understand the purpose behind the 220.84 requirements, but the reality is that once you go through the long version of the exercise in section III, the result is probably going to be exactly the same as if you just said "lets throw in 1500 VA dedicated to electric heat and then never put it in there". Which is probably why the AHJ signed off on that.

That's where the common sense and experience over strict code adherence likely comes into play....

 

[kwired]

I have a feeling we are talking about the same thing, but I'm not sure so...

A) If you have 12.4 kVA/unit and 20 units with no diversity, that's 248 kVA at 100%. However, you can then use the diversity factors in Section III, but I haven't had the chance to run up an example of this yet to see how it would turn out.

B) If you have 17.4 kVA/unit with 20 units and 38% diversity factor, that's 348 * 0.38 = 132 kVA

So in A above, this would use a centralized system with has no load diversity that can be applied, since the full load may be used from time to time. However, this single load is likely to be much less than the sum of the connected loads for the individual unit based heating and/or cooling, and likely to be roughly equal to those loads actually once 220.84 diversity is applied, as in

C) 12.4 kVA/unit on 20 units at a randomly chosen actual effective diversity of 40% (it will likely actually be 3 kVA + 35% of remaining on the lighting load calc which includes most receptacles, plus the diversity on all ranges) = 99.2 kVA and then if the central cooling/heating is roughly 35 kVA, it's a wash.

This is what I'm getting at. I understand the purpose behind the 220.84 requirements, but the reality is that once you go through the long version of the exercise in section III, the result is probably going to be exactly the same as if you just said "lets throw in 1500 VA dedicated to electric heat and then never put it in there". Which is probably why the AHJ signed off on that.

That's where the common sense and experience over strict code adherence likely comes into play....

Or you could install the 1500VA of heat and never use it, or only use it when the VRF system goes down, can't supply demand, etc.

Air to air system that is in extreme cold doesn't draw much because it isn't moving much heat, it will have longer to nearly continuous run time at lower load level though. NEC doesn't exactly account for this - but is a reality.