# How can an electric dryer be so “efficient” compared to a dryer rack?

I wash my clothes, and when they get off the washer, its weight was increased by 3.35kg (amount of water to be evaporated to get dry clothes).

Now, I have two options:

• Use an electric dryer. It takes 2 hours to dry the clothes, it's a 2700W dryer, so I used 5.4kWh.

• Use a dryer rack. Then, water is evaporated by latent heat. I washed at 40°C, so the 3.35kg of water to be evaporated is probably at 35°C. Considering this formula, I need 2500-2,36*35+0,0016*35*35-0,00006*35*35*35, which is 2416kj/kg to evaporate the water, so, according to google converted, this is 0.617kWH/kg, so 2.07kWh.

I'm really surprised an electric dryer only consumes twice the energy needed to naturally evaporate the water. If my room heater works with fuel or gas, the 2.07kWh consumed to dry the clothes on the rack may end up emitting more carbon than the electric dryer would (if the electricity is produced cleanly).

This result really surprises me (I would have expected the electric dryer to consume at least 10 times more than natural evaporation). It makes me believe that I did something wrong in my computation...did I?

• How much energy is consumed at the power company to deliver the 5.4 kWh of electricity to your home? – Chet Miller May 9 '17 at 19:07
• @ChesterMiller: And to deliver the fuel I burn in my heater? ;-) – jpo38 May 9 '17 at 19:14
• Why would you think that your electric dryer needs so much input energy to dry the clothes? Using a dryer rack or simply hanging the clothes outside on a clothes line requires you to provide 0 watts of additional energy. Seems that you're assuming that the electric dryer has to actually elevate the temperature of all the water in the clothes to 100 C and also in addition supply the latent heat to transform all that liquid water into steam in order to dry clothes, but that's not what it does. – Samuel Weir May 9 '17 at 19:16
• @SamuelWeir: Why would you think that your electric dryer needs so much input energy to dry the clothes? 2 hours at 2700W is definitely 5.4kWh... – jpo38 May 9 '17 at 19:19
• Using the drying rack isn't really taking heat out of your home. The water vapor from the cloths may well condense somewhere else (cooler) and presto you get your heat back. – M. Enns May 9 '17 at 19:42