Heat Pump Dryers - Apply 5kVA Minimum?

[paullmullen]

220.54 sets the minimum of 5kVA for an electric dryer. Of course, this was written at the time that resistance heating was the only approach to electric drying. Is it reasonable to argue that the load calcs for a home with a heat pump dryer (1800 W) should not be subject to that rule? A strict reading of the book leads to "Yes, duh, it's electric, pal", but this doesn't match with a sensible approach.

Thoughts?

 

[LarryFine]

What size circuit does it require? Will a standard 30a circuit suffice?

What happens when someone replaces it with a conventional dryer?

If it plugs in, it's not really part of the house, it's a movable appliance.

 

[paullmullen]

Good point. 120V @ 15A with an ordinary receptacle plug on it. I had not thought of it in terms of whether it is fixed appliance or not, but that may be the key that unlocks the question. Thanks.

 

[LarryFine]

120V @ 15A with an ordinary receptacle plug on it.

Then it could use the standard 120v laundry receptacle. so nothing additional required.

However, I think it would be prudent, as well as required, to still provide a dryer circuit.

 

[don_resqcapt19]

How is a dryer a fixed appliance? It just sits on the floor and is plugged in. As it stands now, you need to comply with 220.54. There was a public input to make a change in the language for 220.54.

Public Input No. 4151-NFPA 70-2023 [ Section No. 220.54 ]
220.54 Electric Clothes Dryers — Dwelling Unit(s).
The load for household electric resistance or heat pump clothes dryers in a dwelling unit(s) shall be either 5000 watts (volt-amperes) or the nameplate rating, whichever is larger, for if available, for each dryer served. The use of the demand factors in Table 220.54 shall be permitted. Where two or more single-phase dryers are supplied by a 3-phase, 4-wire feeder or service, the total load shall be calculated on the basis of twice the maximum number connected between any two phases. Kilovolt-amperes (kVA) shall be considered equivalent to kilowatts (kW) for loads calculated in this section.

Not sure what was done with this public input. The first draft report will be published on July 10th.

 

[LarryFine]

How is a dryer a fixed appliance? It just sits on the floor and is plugged in.

I was suggesting that it is not fixed in place. but is effectively portable.

 

[kwired]

Then it could use the standard 120v laundry receptacle. so nothing additional required.

However, I think it would be prudent, as well as required, to still provide a dryer circuit.

It barely would be allowed by 210.23(A)(1) if it is rated 1800 VA @ 120 volts.

Like other heat pumps though, the question may be what is max rating vs what does it typically draw?

Something tells me they likely are 240 volt appliances though and intended to replace the traditional electric dryer, may even have 4 wire termination for supply conductors but have no neutral load within the appliance.

Seems smart for now to treat these like conventional electric dryers for install design and load calculation just in case the unit should be replaced with a conventional electric dryer when the heat pump fails someday. Whether that should be required by NEC however infringes upon NEC self stating it is not a design manual, like many other current sections already do.

 

[paullmullen]

Seems smart for now to treat these like conventional electric dryers

I've seen several comments like this one. I'm not sure, but I guess that the reason is that participants in the trade are not yet convinced that heat pump dryers are here to stay. What might be needed to be more confident of this?

[ ] More widespread use with good results?
[ ] More reliability data?
[ ] Larger appliance sizes?
[ ] Code changes?

The current project is an all electric PassiveHouse design so managing the electrical loads is a key design consideration. The owner is pushing to reduce the use of resistive loads except where absolutely necessary.

 

[LarryFine]

After thinking about it, I suggest installing a typical dryer circuit, but trimming it out as a 20a, 120v receptacle outlet, like we would if converting a 240v outlet to a 120v outlet.

 

[kwired]

I've seen several comments like this one. I'm not sure, but I guess that the reason is that participants in the trade are not yet convinced that heat pump dryers are here to stay. What might be needed to be more confident of this?

[ ] More widespread use with good results?
[ ] More reliability data?
[ ] Larger appliance sizes?
[ ] Code changes?

The current project is an all electric PassiveHouse design so managing the electrical loads is a key design consideration. The owner is pushing to reduce the use of resistive loads except where absolutely necessary.

Which is why I say NEC should not get involved with design decisions. Your project is designed for energy efficiency, hopefully the owners will still be considering that down the line should this unit need replaced. If you are in a place with high level of government influence/control then kind of no point of running a conventional 30 amp circuit either.

For many others when replacement time comes, they might not want to shell out the $$ for another heat pump, especially if they don't like some aspects about it. I have no idea if they require longer drying times or not than other methods but could see it being possible they do.

 

[winnie]

Dumb question: in this particular case, does this matter? Does it push the load calc above a threshold that means more costs?

I'd go with @LarryFine , install 10/3, trim out as 120/20, do the NEC load calc as 5000VA, and inform the owner that actual power use will be far lower.

The home probably needs a large service to handle things like EV charging and solar, so the oversized allocation for the dryer probably makes no difference .

Jon

 

[wwhitney]

For a single family dwelling unit on its own service, this apparent anachronism in 220.54 is likely to at worst require upsizing a feeder unnecessarily. Dwelling unit services are typically sized under the Optional Calculation, which ignores 220.54 and 220.55 and just uses the nameplate ratings of all appliances (and also excludes a heat pump dryer that is on the required 120V/15A laundry branch circuit). Similarly, as 220.14(B) uses the non-mandatory "shall be permitted," there is no need to apply 220.54 for the branch circuit supplying the heat pump dryer.

Cheers, Wayne