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

[Floyd R Turbo]

When considering the Optional Calculations in Table 220-84 in NEC 2014/2017, the condition in 220.84 (A) (3) states "Each dwelling unit is equipped with either electric space heating or air conditioning, or both."

The "electric space heating" to me is pretty clear.

But is this statement meant to imply that in the case of air conditioning, it must be "equipped" with a dedicated air conditioning system for each dwelling unit, such as either a window air conditioner or a fan coil unit + a condenser/compressor?

What about a VRF (Variable Refrigerant Flow) System that utilizes a centralized unit for multiple dwelling units, with a FCU in each unit? So essentially, there would be (for sure) no electric heating coil, and no air conditioning unit that is connected to the panel within the unit (no condenser sitting outside) but there is still "air conditioning".

My gut tells me that the statement in 220.84 (A) (3) should really read "electric space heating or electric air conditioning" and that in such a situation, Table 220.84 could not be applied because the purpose behind that is knowing that not everyone's range and AC units are going to be running concurrently.

 

[jumper]

Where do the units get heat from?

 

[Floyd R Turbo]

A centralized VRF system - provides both heating and cooling modes to FCUs in each dwelling unit. To simplify it, you either pump hot or cold through the HVAC unit coil & blow a fan across it. So there would be one central heat pump unit (basically) that provides cooling flow to those units that need cooling, heating to those that need heating.

 

[Floyd R Turbo]

To me it's looking like 220.84 can't be used in such a situation because there is no electric heating/cooling load that is connected to the panel inside each individual dwelling unit.

It appears to me that 220.82 would instead be applicable. 220.82 (C) is where I start to scratch my head about that because technically, none of (C)(1) through (C)(6) actually exist in this scenario, except possibly (6) under the "and other heating systems" in which case one would just take the nameplate rating of the fan motor, which is not going to be anything significant (1/4 to 1/2 HP at the most).

220.82 (B) calls for 100% of first 10 kVA + 40% of the remainder of (1)-(4)

Meanwhile, Table 220.42 allows for 100% of the first 3 kVA + 35% of the remainder between 3001 VA -120 kVA. Now if I follow the path right, 220.14 (J) basically says all general use receptacles + bathroom 210.11(C)(3) can be included in the general lighting load calcs -> Table 220.42. Per 220.52 (A), small appliance loads as well. 220.55 would cover demand factors for electric cooking. But not garbage disposal, dishwahser, refrigerator or other fixed equipment, those would be at the nameplate rating - all of those fall under 200.82 (B)(3)a as part of the optional calc so I guess it depends on each case and how the numbers work out that determines which method one uses to calculate the feeder

 

[jumper]

Okay, you have a two pipe system. Hot or cold to each FCU.

Is each FCU fed by a circuit within the unit or are the units fed from a "house panel"?

 

[Floyd R Turbo]

Okay, you have a two pipe system. Hot or cold to each FCU.

Correct

Is each FCU fed by a circuit within the unit or are the units fed from a "house panel"?

Fed from the panel within the unit

Continuing from my previous post...

Actually, it looks like 220.82 only applies to "a dwelling unit" not a mutlifamily dwelling...

So if there's a building with 20 dwelling units, and I have a distribution panel for every 10 units, the feeder calcs for the individual units under 220.82 appears correct, but since each unit doesn't have it's own electric heating/air conditioning, then when I go to calculate the feeder size for each distribution panel, I can't use Table 220.84 and apply at 43% demand factor to that calculation.

Would one be able to use 220.82 instead for calculating the feeder size to the distribution panel?

All of the load for the centralized system would be a "house" load, so pretty much 100% on the MDP

 

[jumper]

Correct


Fed from the panel within the unit

There is your HVAC load for each unit. Size as continuous and calculate for unit feeder.

Use chart for number of units x percentage, add house loads with chiller plant load for service.

 

[wwhitney]

chiller plant

Because the OP used the term Fan Coil Unit, I think you are envisioning a system where the "FCUs" in each unit are fed with hot or cold water. But VRF is "Variable Refrigerant Flow", so I think the set up is like a mini-split in each dwelling unit, but where several dwelling units share a single outdoor unit. The VRF system takes care of routing the refrigerant to the indoor units where it is needed.

I could be wrong, of course, and I'm not sure if the difference in technology makes any difference to your answers.

Cheers, Wayne

 

[Floyd R Turbo]

There is your HVAC load for each unit. Size as continuous and calculate for unit feeder.

Use chart for number of units x percentage, add house loads with chiller plant load for service.

Huh...I wouldn't have expected that would fly, seems like a situation that could be interpreted more than one way.

The only English class I ever got an "A" in was in college, and that was a technical writing class (one of the elective/requirement classes for engineering). Then I worked for Rockwell writing specs for flight management systems for 2.5 years, the result of those two is that I am very good at crafting a sentence such that it can only be interpreted one way.

So now I'm OCD about it...and when it comes to anything where I might have to deal with an AHJ, ambiguity is not desired!

 

[Floyd R Turbo]

Because the OP used the term Fan Coil Unit, I think you are envisioning a system where the "FCUs" in each unit are fed with hot or cold water. But VRF is "Variable Refrigerant Flow", so I think the set up is like a mini-split in each dwelling unit, but where several dwelling units share a single outdoor unit. The VRF system takes care of routing the refrigerant to the indoor units where it is needed.

I could be wrong, of course, and I'm not sure if the difference in technology makes any difference to your answers.

Cheers, Wayne

^^ this, precisely (emphasis added by me). Does this change things?

 

[jumper]

Huh...I wouldn't have expected that would fly, seems like a situation that could be interpreted more than one way.

The only English class I ever got an "A" in was in college, and that was a technical writing class (one of the elective/requirement classes for engineering). Then I worked for Rockwell writing specs for flight management systems for 2.5 years, the result of those two is that I am very good at crafting a sentence such that it can only be interpreted one way.

So now I'm OCD about it...and when it comes to anything where I might have to deal with an AHJ, ambiguity is not desired!

Only A- I got in college was in Engish. Hate it.

^^ this, precisely (emphasis added by me). Does this change things?

As long as each FCU or whatever is powered by the circuit in the unit, then my answer is the same.

The shared outside unit/ condenser pack or whatever units are on house power, correct?

 

[Floyd R Turbo]

As long as each FCU or whatever is powered by the circuit in the unit, then my answer is the same.

The shared outside unit/ condenser pack or whatever units are on house power, correct?

Yes, the "shared" unit is on house power, the air mover is on the dwelling unit panel.

As for the nomenclature, what it really comes down to is the unit has a fan blowing air over a coil & circulating air. The source that causes the coil to be cooler or hotter than the air in the dwelling unit is, IMO, irrelevant. You could be heating with steam or hot water from a boiler system and cooling with cold water from a ground source heat pump or refrigerant from a big chiller or swamp cooler...I don't think it makes a difference in this type of scenario.

 

[jumper]

Yes, the "shared" unit is on house power, the air mover is on the dwelling unit panel.

As for the nomenclature, what it really comes down to is the unit has a fan blowing air over a coil & circulating air. The source that causes the coil to be cooler or hotter than the air in the dwelling unit is, IMO, irrelevant. You could be heating with steam or hot water from a boiler system and cooling with cold water from a ground source heat pump or refrigerant from a big chiller or swamp cooler...I don't think it makes a difference in this type of scenario.

I know what the units are. Worked at a college for 10 years, lotsa dorms and offices.

More used to one central cooling/heating plant though.

I believe the conditions for 220.84 are met.

Where the heck is Charlie B at? This is right up his alley. Pretty sure he had a thread with a very similar scenario.

 

[charlie b]

OK, I had been ignoring this thread, because the title did not interest me. But at Derek’s request, I will chime in.

This very discussion came up about a year ago during a meeting of the “Electric League of the Pacific Northwest's monthly Code Committee.” http://electricleague.net/ Most of the attendees that day agreed that the very small load associated with the FCU is not going to qualify as an “air conditioning” unit under the context of this article. The air conditioning takes place in a common area, and its load goes on a house panel. No individual unit supplies power to the A/C compressor. So no individual unit can say that they have A/C, and if they don’t have heat you can’t use this article.

Then one of the engineers present told us about a solution that he proposed to the City of Seattle’sAHJ. He said he would include in the total load for each individual unit a fictitious amount to cover a non-existent space heater. He proposed that that could allow him to use the optional method. The city agreed. I have since used this same concept for a couple projects, and the AHJ allowed it. It has been a while, and I don’t recall the amount of load we assigned to this non-existent load. I think it was on the order of 1000 watts.

 

[kwired]

Okay, you have a two pipe system. Hot or cold to each FCU.

Is each FCU fed by a circuit within the unit or are the units fed from a "house panel"?

Because the OP used the term Fan Coil Unit, I think you are envisioning a system where the "FCUs" in each unit are fed with hot or cold water. But VRF is "Variable Refrigerant Flow", so I think the set up is like a mini-split in each dwelling unit, but where several dwelling units share a single outdoor unit. The VRF system takes care of routing the refrigerant to the indoor units where it is needed.

I could be wrong, of course, and I'm not sure if the difference in technology makes any difference to your answers.

Cheers, Wayne

I wired up a VRF system in a school a couple years ago. It is sort of like mini split system but more complex.

This school basically had three separate systems, though all the compressor units were located in same area. There were three compressor units for each system - nine for the entire facility. They are VFD driven compressors, they not only vary speed of compressor motor depending on system demands, but also can run just one compressor at low demand or run all of them at 100% for maximum output ability.

It is actually a three pipe system. A two pipe system needs the entire system changed over from heating to cooling mode or vice versa. With a three pipe system and additional mode change over valves spread throughout the system - you can heat one room and cool another room at same time. In fact the heat you remove from the room you are cooling circulates through the system and is given up in the room you are heating instead of just pumping it outside, increasing overall efficiency even more at those moderate outdoor temperature times of the year.

Even on a cold winter day, maybe you have a full gymnasium and instead of running exhaust fans in the gym to remove excess heat, you set the gym to cooling mode and pump that heat to other areas of the facility that are calling for heating.

The AHU's in classrooms on that system were only rated like 50 VA or so. High volume AHU's like the gym had bigger blowers, maybe 400 or 500 VA (can't recall for certain)

For a system like OP has the only load in each dwelling is AHU's and they are likely so little of a load you can just about ignore them if there is individual AHU's in each room. Maybe 30-50 VA each AHU.

The compressor(s) are centralized and likely on a "house panel" If it is a small system with only one compressor - you won't have any demand factor at all that can be applied. Reality is still that the thing will hardly ever draw full rating, but you still need capacity available if the demand is there.

 

[Floyd R Turbo]

Then one of the engineers present told us about a solution that he proposed to the City of Seattle’sAHJ. He said he would include in the total load for each individual unit a fictitious amount to cover a non-existent space heater. He proposed that that could allow him to use the optional method. The city agreed. I have since used this same concept for a couple projects, and the AHJ allowed it. It has been a while, and I don’t recall the amount of load we assigned to this non-existent load. I think it was on the order of 1000 watts.

This smilie about sums up my reaction to this
hmy:

I honestly can't believe this AHJ actually approved a non-existent load being used for purposes of allowing an optional calculation to be used. Just, wow...I would have never thought that argument would work at all!

I hope they got approval of that exception in writing!

I wired up a VRF system in a school a couple years ago. It is sort of like mini split system but more complex.

This school basically had three separate systems, though all the compressor units were located in same area. There were three compressor units for each system - nine for the entire facility. They are VFD driven compressors, they not only vary speed of compressor motor depending on system demands, but also can run just one compressor at low demand or run all of them at 100% for maximum output ability.

It is actually a three pipe system. A two pipe system needs the entire system changed over from heating to cooling mode or vice versa. With a three pipe system and additional mode change over valves spread throughout the system - you can heat one room and cool another room at same time. In fact the heat you remove from the room you are cooling circulates through the system and is given up in the room you are heating instead of just pumping it outside, increasing overall efficiency even more at those moderate outdoor temperature times of the year.

Even on a cold winter day, maybe you have a full gymnasium and instead of running exhaust fans in the gym to remove excess heat, you set the gym to cooling mode and pump that heat to other areas of the facility that are calling for heating.

The AHU's in classrooms on that system were only rated like 50 VA or so. High volume AHU's like the gym had bigger blowers, maybe 400 or 500 VA (can't recall for certain)

For a system like OP has the only load in each dwelling is AHU's and they are likely so little of a load you can just about ignore them if there is individual AHU's in each room. Maybe 30-50 VA each AHU.

The compressor(s) are centralized and likely on a "house panel" If it is a small system with only one compressor - you won't have any demand factor at all that can be applied. Reality is still that the thing will hardly ever draw full rating, but you still need capacity available if the demand is there.

This is a better explanation of the system in use, not being a mechanical engineer I gloss over these details. But it can do exactly this - heat one space, cool another, simultaneously.

The bottom line is that when I ran the 220.82 optional calc alongside the 220.84 optional calc where the dwelling units were 18 to a panel, the 220.82 calc was about 10% higher than the 220.84 calc. Not a major difference, and not something that I believe would warrant trying to find a way to get the 220.84 optional calculation factored in through some kind of AHJ approval.

 

[MAC702]

This smilie about sums up my reaction to this
hmy:

I honestly can't believe this AHJ actually approved a non-existent load being used for purposes of allowing an optional calculation to be used...

If I understood it correctly, it's legitimate. The official heating for the space is an electric heater, and we factor in its electrical demand. But the owner never gets around to buying the heater and plugging it in because his fan-coil heat works just fine.

 

[charlie b]

If I understood it correctly, it's legitimate. The official heating for the space is an electric heater, and we factor in its electrical demand. But the owner never gets around to buying the heater and plugging it in because his fan-coil heat works just fine.

That was essentially the reasoning. That, and the owner does have the option of adding heat later - the load calculation has allowed for it.

 

[charlie b]

I hope they got approval of that exception in writing!

It wasn't an exception, but rather a code interpretation. And yes, the AHJ's approval came in writing.

 

[Floyd R Turbo]

That was essentially the reasoning. That, and the owner does have the option of adding heat later - the load calculation has allowed for it.

It wasn't an exception, but rather a code interpretation. And yes, the AHJ's approval came in writing.

What I find most interesting though is that when you have a MFD with, say, 40 or 60 units, you get to the point where the 220.84 calculation allows you to apply a smaller demand factor, resulting in a smaller distribution panel feeder & smaller service feeder (when compared to the 220.82 calculation)

So in essence, I have to add load (or allow for future load to potentially be added by accounting for it in the panel calculations) in order for the service feeder to be smaller. To me, that's reverse logic.

Also, if you flip this over to the mechanical side of things, the mechanical code doesn't allow you to account for cord & plug space heaters in the calculations for heat loading to determine the appropriate size HVAC unit for a given space. So this is a case, to me, where one hand (electrical) is taking something into account in order to be able to take advantage of the optional calculation, whereas the other hand (mechanical) can't allow that. Though I suppose if you just are making an allowance for it...when I have a unit that has a 100A panel but there's only something like 65-75A on it, adding a dedicated circuit for a 1 kW space heater won't affect that at all

Just seems like a "hole" to me....