HP and electric codes

[timjimbob]

I am installing Heat pumps to replace resistant heat furnaces to meet energy codes.

I am aware of the "non-consequential" electric loads addressed in the code book. How is this handled with old houses and heat pump installations. Any concern? Not seen a concern with inspectors?

[second opinion]

I am installing Heat pumps to replace resistant heat furnaces to meet energy codes.

I am aware of the "non-consequential" electric loads addressed in the code book. How is this handled with old houses and heat pump installations. Any concern? Not seen a concern with inspectors?

A little more detail in your question.

[timjimbob]

In 1980s,When you do calculations for residential service entrance cable and electric panels, you figure the higher of ac compressor load or electric furnace load and size with the higher number. You operate one or the other (hence non-consequencidental load), obviously not both.

Now with heat pump, both loads may draw current and overload your electric service.

[second opinion]

In 1980s,When you do calculations for residential service entrance cable and electric panels, you figure the higher of ac compressor load or electric furnace load and size with the higher number. You operate one or the other (hence non-consequencidental load), obviously not both.

Now with heat pump, both loads may draw current and overload your electric service.

Is this what you are looking for. I would be your responsibility to make sure the service can handle the compressor with auxiliary heat, but should yeild lower overall with heat pump and auxiliary if sized properly.
(C) Heating and Air-Conditioning Load. The largest of the following six selections (load in kVA) shall be included:

100 percent of the nameplate rating(s) of the air conditioning and cooling.
100 percent of the nameplate rating(s) of the heat pump when the heat pump is used without any supplemental electric heating.
100 percent of the nameplate rating(s) of the heat pump compressor and 65 percent of the supplemental electric heating for central electric space-heating systems. If the heat pump compressor is prevented from operating at 70-67 the same time as the supplementary heat, it does not need to be added to the supplementary heat for the total central space heating load.
65 percent of the nameplate rating(s) of electric space heating if less than four separately controlled units.
40 percent of the nameplate rating(s) of electric space heating if four or more separately controlled units.
100 percent of the nameplate ratings of electric thermal storage and other heating systems where the usual load is expected to be continuous at the full nameplate value. Systems qualifying under this selection shall not be calculated under any other selection in 220.82(C).

[timjimbob]

So the panel should be recalculated.

[timebuilder]

Remember, the code is a set of MINIMUM requirements.

As a prudent design consideration, you need to decide how much these units are going to run. Is there no insulation in the building? That electric heat could be supplementing the heat pumps all the time.

[timebuilder]

Remember, the code is a set of MINIMUM requirements.

As a prudent design consideration, you need to decide how much these units are going to run. Is there no insulation in the building? That electric heat could be supplementing the heat pumps all the time.

Here is why:

90.1 B (2008):

....Compliance therewith and proper maintenance results in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use.

[timjimbob]

Has anyonehad the mechanical inspector request an electrician certify that the electric service is adequate? I haven't.

[timebuilder]

Has anyonehad the mechanical inspector request an electrician certify that the electric service is adequate? I haven't.

First of all, electricians cannot issue any sort or "certification" that an electrical service is "adequate." That is not a purview of the trade. You might be able to get an engineer or architect to put a stamp on a plan, and that stamp serves as meeting the required standards for all legal purposes.

Second, mechanical inspectors do not require "certifications" other than a nod that the required standards have been met. They DO "sub out" inspections to private contractor agencies for some inspections, but that is because they have decided to accept their word that the required municipal standards have been met. Most AHJ's have a list of inspection contractors that they accept.

The key is understanding the words being used, such as "adequate." Adequate for what purpose?

Remember the code is a set of minimum standards, and it is NOT a set of "best practices."

[timjimbob]

What I'm saying is anyone been asked, by any inspectors or building department, to have the electric service re evaluated? Either applying for a mechechanical permit or the inspection.

[ga-hvac-tech]

I cannot answer the question in post $10... however my personal policy is I will not install a HP with strip heat without adequate elec service to run BOTH continuously, along with reasonable house load.

We know energy costs run in cycles... I remember a few years back N/Gas was high and folks wanted to convert to elec heat (HP and strips). I had to tell lots of folks their home did not have enough electrical capacity to handle it... only to have a hack come behind me and install it. A few of them called me and asked if I could fix the dimming lights and breakers that kept popping... I said no; this was why I would not do the job. Call an electrician to upgrade your service.
I have literally seen a 3 ton HP and 10KW of strip heat in a 1000 ft house on 100A service... with an elec DWH and clothes dryer. We KNOW one cannot run all those at the same time...

Who's butt is on the line if an elec fire is started? Media LOVES to crawl all over this if children are hurt or killed... I do not want that on my conscious... much less my insurance.

[WyrTwister]

I am installing Heat pumps to replace resistant heat furnaces to meet energy codes.

I am aware of the "non-consequential" electric loads addressed in the code book. How is this handled with old houses and heat pump installations. Any concern? Not seen a concern with inspectors?

My biggest caution is to total the load when the heat pump goes into defrost and resistance hear comes on .

Many / most load calculations are basted at 80% capacity for continuous duty ( 3 hours or longer ) . I am not a HVAC guy , so I can not say how long the defrost cycle lasts or how often it goes into defrost ?

Now , if the temperature goes low enough that both the heat pump and the resistance heat run for an extended length of time , that is , perhaps , another issue ? Or , does the heat pump turn off when it goes into continuous resistance heat ?

And is the resistance heat in multiple stages ?

In my mind , it comes down to the ampacity of the electrical service and the ampacity of the circuit or circuits going to the HVAC equipment .

As a side note , I have seen many older houses with 60 amp services have to be upgraded when the change was made from evaperative coolers to central air .

God bless
Wyr

[timjimbob]

Wry,
HP can be configured to be run either both on or "one or the other" with regard to heat strips. Defrost may run 10 minutes every 60 or 90 minutes. I meant non coincidental, not "non-consequential" loads. As cited in the code book.

[WyrTwister]

Wry,
HP can be configured to be run either both on or "one or the other" with regard to heat strips. Defrost may run 10 minutes every 60 or 90 minutes. I meant non coincidental, not "non-consequential" loads. As cited in the code book.

I kind of thought they might be able to do either or ? I am correct , both run in defrost ?

Another issue , as far as stressing the service is heat . I have seen services fail much more often when temps approach 100 degrees or greater .

Obviously , in the winter , the stress on the service from ambient temps , would not be a factor .

Thanks ,
Wyr
God bless

[timebuilder]

Heating is a continuous load. Size the strip heat for 125%.

Since the strip heat is a separate feed from the outdoor unit, the outdoor feed is sized according to 440.

Questions?

[timjimbob]

My original post regarded installing a HP to replace a straight cool AC. Now required by energy code. Inspector never asks about panel upgrades.

[timebuilder]

My original post regarded installing a HP to replace a straight cool AC. Now required by energy code. Inspector never asks about panel upgrades.

Most inspectors use the International Residential Code which gets its electrical sections from the National Electrical Code. However, most inspectors are not familiar with the National Electrical Code and have no idea what its requirements are.

The onus is on you, the installer, to make yourself aware of the requirements of the Code.

[WyrTwister]

Heating is a continuous load. Size the strip heat for 125%.

Since the strip heat is a separate feed from the outdoor unit, the outdoor feed is sized according to 440.

Questions?

I size all my circuits for continuous load . Voltage drop , ambient temp , number of current carrying conductors , etc. .

Actually , that is only partially true . Much / most of what I bid , the engineer does all or part of that .

I have wired roof top package units / heat pump units that had one large circuit for the whole unit . They had circuit breakers or fuses to divvy out the load .

Thanks ,
Wyr
God bless

[timebuilder]

The key words there are "package units."

A package unit has a single number for MCA and MOD. It is a simple matter to follow those values, which include in those vales the factor of continuous load.

It's nice to have a set of stamped prints where all of the requirements have been met and approved by a plan review. Most HVAC contractors never see such a nicety.

[beenthere]

My original post regarded installing a HP to replace a straight cool AC. Now required by energy code. Inspector never asks about panel upgrades.

What size service is in these homes? Do you do a load calc to know if they really need as much aux heat as the straight A/C had in strip heaters?