HP and electric codes

[timjimbob]

Minisplits, I don't understand where the heat comes from to deice the coil. Conventionally, its sensible heat at the inside coil which means it gets cold and is warmed back up with resistance heat.

Only energy available would be compressor energy, and not the heat content of the air. I don't understand.

[ga-hvac-tech]

Minisplits, I don't understand where the heat comes from to deice the coil. Conventionally, its sensible heat at the inside coil which means it gets cold and is warmed back up with resistance heat.

Only energy available would be compressor energy, and not the heat content of the air. I don't understand.

I am not sure I can answer the question any more than they DO work.

I think since there are SOOOO many sensors all over the unit (inside and outside), perhaps they do not really get frosted up much before a mini-defrost may happen more often, smaller cycle time).

Someone that knows will be along soon to comment.

[second opinion]

Minisplits, I don't understand where the heat comes from to deice the coil. Conventionally, its sensible heat at the inside coil which means it gets cold and is warmed back up with resistance heat.

Only energy available would be compressor energy, and not the heat content of the air. I don't understand.

Both heat pumps use a reverse cycle strategy to defrost the outdoor coil. When operating in
defrost mode, the compressor pumps hot refrigerant vapor through th
e outdoor coil, melting ice
that has accumulated on the coil. During this time, the indoor fan is disabled and the heat pump
does not provide heating capacity. The defrost cycle reduces the integrated performance of the
heat pump since there are periods of
operation when the compressor is running but heat is not
being delivered from the unit. AHRI Standard 210/240 dictates that the second defrost cycle be
used to determine the defrost penalty to account for remaining moisture/frost not removed during
the fi
rst defrost cycle (AHRI 2008). Each unit implements slightly different defrost control
strategies as a function of outdoor temperature, run time, and refrigerant pressures

[beenthere]

As I said , I do not do very much residential . So I apologize for being rusty . :-(

Several times , I have been asked to bid a job where one or more A/C units were being retrofitted with heat pumps .

Naturally , no one wants to hear they have to up-size their electrical panel or service . Sometimes that is close to impossible , and certainly cost prohibitive .

I usually had to get with the mechanical contractor & find out exactly what he was proposing .

I usually had to make sure the resistance heat strip did not exceed the ampacity of the heat pump . And extract a promise the controls would be wired so that both did not run at the same time , even in defrost .

Even at that , I was careful to word my proposal with all those specifics .

It can be a dicey situation .

God bless
Wyr

Unless it would be fairly warm out. And the home owner decided to turn the stat up several degrees suddenly. The heat pump would never draw its rated amp while the aux heat was also on.

[timebuilder]

The only legal way to install a unit (NEC legal) is to wire according to the MCA and the MOD. You use article 440 to wire the OUTDOOR unit, and article 424 for fixed electric space heating equipment: strip heat.

[timjimbob]

HP needs to have heat added, at some point, to defrost outside coil.
Typically, it is the heat picked up by the inside coil. Cannot be the case if inside fan is stopped. Like a typicval system with a clogged AirFilter or broke evap motor, It does not generate much heat at the condenser and compressor is in danger of liquid slugging.

The way I see the minisplit in defrost mode is like an

Both heat pumps use a reverse cycle strategy to defrost the outdoor coil. When operating in
defrost mode, the compressor pumps hot refrigerant vapor through th
e outdoor coil, melting ice
that has accumulated on the coil. During this time, the indoor fan is disabled and the heat pump
does not provide heating capacity. The defrost cycle reduces the integrated performance of the
heat pump since there are periods of
operation when the compressor is running but heat is not
being delivered from the unit. AHRI Standard 210/240 dictates that the second defrost cycle be
used to determine the defrost penalty to account for remaining moisture/frost not removed during
the fi
rst defrost cycle (AHRI 2008). Each unit implements slightly different defrost control
strategies as a function of outdoor temperature, run time, and refrigerant pressures

[WyrTwister]

The only legal way to install a unit (NEC legal) is to wire according to the MCA and the MOD. You use article 440 to wire the OUTDOOR unit, and article 424 for fixed electric space heating equipment: strip heat.

Yep .

God bless
Wyr

[WyrTwister]

HP needs to have heat added, at some point, to defrost outside coil.
Typically, it is the heat picked up by the inside coil. Cannot be the case if inside fan is stopped. Like a typicval system with a clogged AirFilter or broke evap motor, It does not generate much heat at the condenser and compressor is in danger of liquid slugging.

The way I see the minisplit in defrost mode is like an

Do not know how the mini-split defrosts . As I said , have not switched it into heat , yet . That will be several months away .

Will probably use my gas fired central air furnace as primary heat & the HP for secondary heat

God bless
Wyr

[ga-hvac-tech]

Do not know how the mini-split defrosts . As I said , have not switched it into heat , yet . That will be several months away .

Will probably use my gas fired central air furnace as primary heat & the HP for secondary heat

God bless
Wyr

Might want to run that little mini and see how little elec it uses... you will be surprised.
Also; mini's tend to produce lots of heat down into the teens outside. Not sure where you live, but in my area we rarely see the teens... mostly the mid 20's, and those only a few nites a year. Having said that... we may have a cold winter this year after a cool summer.

[WyrTwister]

Might want to run that little mini and see how little elec it uses... you will be surprised.
Also; mini's tend to produce lots of heat down into the teens outside. Not sure where you live, but in my area we rarely see the teens... mostly the mid 20's, and those only a few nites a year. Having said that... we may have a cold winter this year after a cool summer.

It is a 12,000 btu unit . Currently pulling around 10 amps of 120 VAC .

Right now , I have the tstat of the central system set at 80 degrees F . This winter , I might set it at 65 - 70 degrees F ( on the heat side of the tstat ?

Wonder how much current the fan on the 125,000 btu ( gross ) gas fired condensing furnace pulls ? Maybe 1/3 to 1/5 of that the HP would pull ?

You may be correct , the HP may be cheaper to operate , down to the low 40's or even the high 30's ? I have no personal experience with a HP .

How does the equipment life of a straight A/C compare to the equipment life od a unit used for both heat and cool ?

Thanks ,
Wyr
God bless

[ga-hvac-tech]

Most split HP systems (conventional ducted equipment) tend to loose their heating capacity around freezing--give or take a few D. This is why they need elec strips backup heat.
Mini's tend to produce usable heat down into the teens. Has to do with all the electronics and controls... long explanation.

Might do a bit of testing (verify conditions are the same; low temp, humidity level, wind level--as these all affect heating needs). Probably better to do the test by reading the meters than waiting for the bill... weather is a component and is fickle...