Heating water for coffee - efficiently.

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A bit of an engineering question. How to heat water quickly and efficiently?

Every morning I make a cup of coffee in a small french press. I use 350cc of water starting at 21C. I place the water in the microwave oven to bring it to a boil and this takes about 2 minutes.
The microwave is rated at 1.58kW (how much of that is actually radiated I don't know)

According to what I can calculate, the power needed to raise the water temp by 79 degrees in 2 minutes is 970 watts. That makes my microwave heating 60% efficient. Is that good, or can I do better?
 
I don't know about microwave ovens, but wouldn't a simple resistive heater be 100% efficient (neglecting losses through air cooling and evaporation)? Like one of those purpose made water boilers?

If you're looking to get higher efficiency, try thermoelectric coolers. The heat coming out on the hot side is the electrical energy put in plus the heat moved away from the cold side. For heating, better than 100% (I know, I know, doesn't make sense at first).
 
Many many years ago I used an electric immersion type of heater element that I put in the coffee mug and it boiled the water in no time. It looked like a soldering iron heating element. Since the electric heater was in the mug and the only heat loss was through the mug sides and a little bit from the water to air contact. I would say it was fairly efficient. I remember seeing a parabolic solar water heater, Im guessing it might be impractical when its raining or cloudy.
 
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Thanks. I was thinking of the little immersion heaters like I used to carry traveling. But typically those are 300W, and not very fast. But I have seen 1000W and 1500W models. Might be too big, tho.

Bill, thanks for looking at the kettle timing for me. The formula that seems most common is this:
volumeX4Xrise/3412 is the power (kW) need to raise the volume (liters) by degrees C in one hour. So in my case 0.35x4x79/3412=0.0324 for 1 hour.
 
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Mike something like this might work for you and would probably be an efficiency improvement over the microwave, it's probably slightly slower..

Amazon.com: Bonavita 0.5L Mini Kettle, Stainless Steel: Kitchen & Dining

I use something similar at work to boost the luke warm hot water from water filter to something actually suitable for brewing tea.

This one has the added benefit of no plastic in contact with the water.
 
The energy cost to manufacture an additional kettle is going to take years of use (if ever) to recoup. Your 60% isn't far off other efficiencies I'm seeing. Also, seeing as this is 2 minutes a day, not a lot of time per day to integrate these advantages.

Gotta think cradle to grave with these things. ;)
 
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Your 60% isn't far off other efficiencies I'm seeing. Also, seeing as this is 2 minutes a day, not a lot of time per day to integrate these advantages.
That's very true and I've given it a lot of thought. Electricity is not expensive were I now live, so how long would it take for a new kettle to pay for itself? I suppose I could figure that out. :)
 
Let's say $0.10/kWH: your total annual consumption is 2min/60min*1.58kW*365*$0.1/kWH = $1.92.

With a perfectly efficient heater, that's a $0.77 annual savings.

My objection is more philosophical, it's better the part is never made from a cradle-to-grave energy perspective, i.e the energy to manufacture, use, and dispose of an addition item with a very specific purpose.
 
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I know the big kettles well, having lived in London a few years. :) But I don't need anything that big.

DPH is on the right track. At my electricity costs, the microwave costs me $1.50 to heat heat 365 cups a year. A kettle would cost less, but damn, it would take a long time to pay for itself! Electricity is $0.076 per kWH here.
 
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My objection is more philosophical, it's better the part is never made from a cradle-to-grave energy perspective, i.e the energy to manufacture, use, and dispose of an addition item with a very specific purpose.
That's also an important consideration. :up:

Where I lived before (Hawaii) electricity costs 4.5X what it does here, so energy efficency was high priority. And solar paid for itself very quickly.
 
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