3 ms·

> Their energy consumption is about half that of a condensation drier. Again, this is not necessarily a fair comparison, if what's being pumped actually costs

by mmt 8y ago

> Their energy consumption is about half that of a condensation drier. Again, this is not necessarily a fair comparison, if what's being pumped actually costs something that can't be measured at the dryer's plug. $500 would likely be worth it, even at $.12/kWh, but the market may not think so if they're not available for that price in places with cheap electricity (and/or cheap enough natural gas, which can be much cheaper, ranging between $.04/kWh and $.06/kWh, equivalent, on my last bill). > the heat pump is used to dehumidify the processing air. This seems a bit strange to me, but it makes sense, especially if there's recirculation going on. > The air is still heated using electricity. It just doesn't waste as much heat. This is pretty clear from the efficiency only being 2:1, which is much worse than what I'd expect from a heat pump being used for heating.

lorenzhs 8y ago
The only energy input is electricity. The heat pump is used to recover heat from the exhaust air. There is no other source of heat involved, so the comparison is entirely fair.
- mmt 8y ago
  I'm a bit confused, since, initially, you mentioned dehumidifying. However, I'm getting the impression that the heat pump in this case is entirely internal to the machine, which is not what I had in mind when mentioning heat pumps (thinking of their coefficient of performance of 3-4) [1]. Were I aware of these machines, I would have specified: It's not as if modern dryers are using a heat pump with an outdoor source to raise the temperature of the clothing instead of burning gas or "burning" electricity with resistive heating. That said, a 2x efficiency gain, by whatever method, is more than I expected, though still falling into what I would categorize as "not much room", especially if the gain comparison always assumes the oldest, least-efficient 5kW model only ever running at its highest setting. The other key assumption in all these comparisons is that all these dryers can finish the same sized load in the same amount of time, which can't possibly be true in the real world. If my $40-to-repair machine already has some efficiency tweaks such that its worst-case is only 4kW, the $500 machine's worst-case is 2.5kW, but my actual behavior averages out to running them at 70% power, I'm saving barely over a kilowatt per hour, and I'm back up to 3500 hours to break-even at $.12/kWh electric rates. $1800-for-1kW is nearly 14k hours, or nearly 18 hours a week over fifteen years, and I don't do that much laundry. [1] If this is so, it strikes me as odd to call it that, just as it would strike me as odd to call out a free-standing dehumidifier having a "heat pump", even though that's the crucial to the device functioning.

by mmt 8y ago

lorenzhs 8y ago

The only energy input is electricity. The heat pump is used to recover heat from the exhaust air. There is no other source of heat involved, so the comparison is entirely fair.

mmt 8y ago
I'm a bit confused, since, initially, you mentioned dehumidifying. However, I'm getting the impression that the heat pump in this case is entirely internal to the machine, which is not what I had in mind when mentioning heat pumps (thinking of their coefficient of performance of 3-4) [1]. Were I aware of these machines, I would have specified: It's not as if modern dryers are using a heat pump with an outdoor source to raise the temperature of the clothing instead of burning gas or "burning" electricity with resistive heating. That said, a 2x efficiency gain, by whatever method, is more than I expected, though still falling into what I would categorize as "not much room", especially if the gain comparison always assumes the oldest, least-efficient 5kW model only ever running at its highest setting. The other key assumption in all these comparisons is that all these dryers can finish the same sized load in the same amount of time, which can't possibly be true in the real world. If my $40-to-repair machine already has some efficiency tweaks such that its worst-case is only 4kW, the $500 machine's worst-case is 2.5kW, but my actual behavior averages out to running them at 70% power, I'm saving barely over a kilowatt per hour, and I'm back up to 3500 hours to break-even at $.12/kWh electric rates. $1800-for-1kW is nearly 14k hours, or nearly 18 hours a week over fifteen years, and I don't do that much laundry. [1] If this is so, it strikes me as odd to call it that, just as it would strike me as odd to call out a free-standing dehumidifier having a "heat pump", even though that's the crucial to the device functioning.