continuous load for heat pump w/ heat strips

[RustyShackleford]

The first step is to do a "Heat Load" study, so you know what size of unit you will need.

How can you determine the feeder size if you don't know what size unit you need ?

I mentioned above that there's already 6 AWG NM-B going to the location. I should've stressed that I'm working the problem from the other end. So I'm trying to spec which combination of compressors and heat strips can be supported (without pulling heavier wire). It still comes down to this: which of the many amperage figures quoted for heat pump compressors is the one that should be considered a continuous load; I'm coming to the conclusion that it's MCA (minimum circuit ampacity) with the 125% already baked in (so take 80% of MCA as continuous).

 

[augie47]

I mentioned above that there's already 6 AWG NM-B going to the location. I should've stressed that I'm working the problem from the other end. So I'm trying to spec which combination of compressors and heat strips can be supported (without pulling heavier wire). It still comes down to this: which of the many amperage figures quoted for heat pump compressors is the one that should be considered a continuous load; I'm coming to the conclusion that it's MCA (minimum circuit ampacity) with the 125% already baked in (so take 80% of MCA as continuous).

 

[RustyShackleford]

The thing that's giving me pause though, the NEC defines a continuous load as "A load where the maximum current is expected to continue for 3 hours or more." If one looks at the detailed performance charts for this unit (specifically the 3-ton version):

https://www.acwholesalers.com/manuals/c6532a38727cae1b80ee5f2517df363c.pdf

... indeed the MCA is 29.8 (page 3). But if one looks at the various performance charts on ages 6&7 and page 12, 16.9amps is the biggest number one will find, a far cry from 80% of 29.8. It's hard to imagine that any numbers besides those in the performance charts would be sustained for 3 hours.

 

[augie47]

Without entertaining the reasoning you might note Art 424 and 430 both require branch circuits to be considered continuous loads so your air handler and condenser are in line.

 

[RustyShackleford]

Without entertaining the reasoning you might note Art 424 and 430 both require branch circuits to be considered continuous loads so your air handler and condenser are in line.

Ah yes, 424.3(B).

 

[kwired]

In California we don't use the "Rule of Thumb" anymore. You can't take a 2,000 square foot home and divide 400 square feet to determine the size of unit. No more guessing, you have to do a "Heat Load" engineering study, like my attachment.

How can you determine the feeder size if you don't know what size unit you need ?

The HVAC designer maybe must do what you said.

The electrician installing the supply to it only needs to see nameplate of units to be installed regardless of how they were selected.

 

[RustyShackleford]

The electrician installing the supply to it only needs to see nameplate of units to be installed regardless of how they were selected.

There are different ways to skin a cat - different sorts of equipment to achieve the necessary HVAC performance. For example, a one- or two-state heat pump, with poor low-temperature performance, augmented by heat strips. Or by propane. Or, a cold-weather heatpump, with an inverter compressor, that can handle the entire load without any fossil-fuel or electric-resistance heat.

The HVAC designer wants to know, from the electrician, what the amperage budget is.

 

[kwired]

There are different ways to skin a cat - different sorts of equipment to achieve the necessary HVAC performance. For example, a one- or two-state heat pump, with poor low-temperature performance, augmented by heat strips. Or by propane. Or, a cold-weather heatpump, with an inverter compressor, that can handle the entire load without any fossil-fuel or electric-resistance heat.

The HVAC designer wants to know, from the electrician, what the amperage budget is.

That be nice if they would ask the electrician if the service can handle it, they don't always do that. You show up, they have a unit already installed and you have to tell them the service is really too small to run the backup heat. They might say just don't hook up that last 5 kW, we didn't really need it, if that will be ok.

 

[mtnelect]

The California Energy Commission requires a "HERS" (Home Energy Rating System) inspector. This is a "Special Inspector" that has the specialized training and experience, with the spiralized equipment that the AHJ does not have. Many other states have adopted this approach, because they have realized that they can't keep on building more fossil fuel generating plants. If the installation does not pass inspection the HVAC contractor has to make the required corrections to pass inspection on his own time and cost. This also applies to commercial lighting & mechanical systems; they also have there "Special Inspectors" beyond the AHJ.

 

[retirede]

The California Energy Commission requires a "HERS" (Home Energy Rating System) inspector. This is a "Special Inspector" that has the specialized training and experience, with the spiralized equipment that the AHJ does not have. Many other states have adopted this approach, because they have realized that they can't keep on building more fossil fuel generating plants. If the installation does not pass inspection the HVAC contractor has to make the required corrections to pass inspection on his own time and cost. This also applies to commercial lighting & mechanical systems; they also have there "Special Inspectors" beyond the AHJ.

What are some of those “many other states”? I’m skeptical.

 

[mtnelect]

This is an example of other states implementing their own energy policies.

 

[kwired]

This is an example of other states implementing their own energy policies.

how many are as strict as CA with rules and/or enforcement?

You maybe don't see it as much since you are in CA, but around here I see a lot of products that are labeled not for sale in CA.

 

[retirede]

This is an example of other states implementing their own energy policies.

I wasn’t questioning the fact that many states have energy efficiency policies.
I was questioning the claim that many other states have inspectors strictly for enforcement of energy codes.

 

[mtnelect]

how many are as strict as CA with rules and/or enforcement?

You maybe don't see it as much since you are in CA, but around here I see a lot of products that are labeled not for sale in CA.

I recently had a service call about a Whole House Fan, which needed to be replaced. The manufacturer was in Florida, so I checked with CEC website. It couldn't be sold in California because it does not meet the higher energy efficiency standards. So, instead of a change out "Same for Same" another manufacturer with different dimensions had to be purchased at a much higher price.

 

[mtnelect]

I wasn’t questioning the fact that many states have energy efficiency policies.
I was questioning the claim that many other states have inspectors strictly for enforcement of energy codes.

That is something you will have to research yourself. The scheme that California uses are private organizations that are approved by the California Energy Commission. The organizations like "CHEERS" and "CalCERTS" train and supervises the HERS special inspectors. They then set up their own company's and charge for their services, using the CEC Title 24 forms for inspection.

 

[RustyShackleford]

I recently had a service call about a Whole House Fan, which needed to be replaced. The manufacturer was in Florida, so I checked with CEC website. It couldn't be sold in California because it does not meet the higher energy efficiency standards. So, instead of a change out "Same for Same" another manufacturer with different dimensions had to be purchased at a much higher price.

Wow, most places I think would grandfather in a simple R&R like that.

 

[retirede]

That is something you will have to research yourself. The scheme that California uses are private organizations that are approved by the California Energy Commission. The organizations like "CHEERS" and "CalCERTS" train and supervises the HERS special inspectors. They then set up their own company's and charge for their services, using the CEC Title 24 forms for inspection.

I’m not doing research to prove or disprove a claim you made.

 

[kwired]

I recently had a service call about a Whole House Fan, which needed to be replaced. The manufacturer was in Florida, so I checked with CEC website. It couldn't be sold in California because it does not meet the higher energy efficiency standards. So, instead of a change out "Same for Same" another manufacturer with different dimensions had to be purchased at a much higher price.

So some bootlegger illegally imported the original? or was it legal when installed and rules changed later on?

 

[kwired]

Wow, most places I think would grandfather in a simple R&R like that.

I would think most places wouldn't even require any kind of inspection for such repair.

 

[mtnelect]

So some bootlegger illegally imported the original? or was it legal when installed and rules changed later on?

It was installed by the homeowner after the house was purchased in 1965 without a permit.

See attachments that explains when and how Title 24 was established in California.