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  1. #1
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    HP and electric codes

    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?

  2. #2
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    Quote Originally Posted by timjimbob View Post
    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.

  3. #3
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    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.

  4. #4
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    Quote Originally Posted by timjimbob View Post
    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).

  5. #5
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    So the panel should be recalculated.

  6. #6
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    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.
    [Avatar photo from a Florida training accident. Everyone walked away.]
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  7. #7
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    Quote Originally Posted by timebuilder View Post
    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.

    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

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  8. #8
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    Has anyonehad the mechanical inspector request an electrician certify that the electric service is adequate? I haven't.

  9. #9
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    Quote Originally Posted by timjimbob View Post
    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."
    [Avatar photo from a Florida training accident. Everyone walked away.]
    2 Tim 3:16-17

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  10. #10
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    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.

  11. #11
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    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.
    GA-HVAC-Tech

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  12. #12
    Quote Originally Posted by timjimbob View Post
    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

  13. #13
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    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.

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